adhesive equaled the improvement obtained by the addition of an extra throw for most suture types.

Transcription

1 BSTRCT SMSON, GENEVIEVE. Reinforcing Effect of a Cyanoacrylate dhesive on Surgical Suture Knots. (Under the direction of Martin W. King and Bhupender S. Gupta). Despite the latest polymer materials and surgical suturing techniques, the knot will always be the weakest point of the tied suture loop. In theory, the knot must be as small as possible to prevent an excessive amount of tissue reaction and a delay in healing. There have been reports suggesting that topical cyanoacrylate adhesives could have a reinforcing effect on a surgeon s knot. Such an outcome could lead to the elimination of knot slippage and the unsatisfactory performance of some surgical knots. The main purpose of this study was to determine if the cyanoacrylate adhesive could have a significant reinforcing effect on typical suture types and sizes when tied as a surgeon s knot. The second aim was to evaluate if the cyanoacrylate adhesive could replace an additional throw in the surgeon s knot so as to achieve an equivalent mechanical performance. The topical cyanoacrylate adhesive LiquiBand was combined with six different suture materials (Ticron TM, Surgidac TM, Ethilon*, Nurolon*, Biosyn TM and PDS*II) in four different sizes (USP 5-, USP 3-, USP and USP 1). The surgeon s knot () with and without one () and two additional throws (=1) were tied in a reproducible way and mechanically tested. Six dependent variables were used to evaluate the performance of each knot with and without adhesive. The performance criteria were: the force at loop failure, the maximum loop holding force, the loop holding capacity, the knot efficiency, the knot elongation efficiency and the loop distraction. From the results and from scanning electron microscopic observations, the cyanoacrylate adhesive was found to significantly improve the knot performance. The improvement was superior with braided sutures and with absorbable polymer sutures. The reinforcement was more significant with thicker suture sizes and with the plain surgeon s knot. However, one cannot conclude that the improvement created by the

2 adhesive equaled the improvement obtained by the addition of an extra throw for most suture types.

3 Reinforcing Effect of a Cyanoacrylate dhesive on Surgical Suture Knots by Genevieve Samson thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Science Textile Engineering Raleigh, North Carolina 29 PPROVED BY: Tushar K. Ghosh Hechmi Hamouda Martin W. King Co-Chair of dvisory Committee Bhupender S. Gupta Co-Chair of dvisory Committee

4 Dedication What matters is not how much you know but what you do with it. ii

5 Biography Genevieve Samson was born in Vancouver, Canada, while still a young child her family moved to Quebec City, Canada where she earned her Bachelor of Engineering degree in Mechanical Engineering from Laval University in 26. s a young graduate, she was eager to learn more and to focus her attention on the textile industry, thus she found a project manager s position in a nonwoven company, located in Quebec, Canada. In pursuit of further studies, she challenged herself to research fiber and textile science abroad. She was accepted to North Carolina State University, the leading textile school in the United States, for a master s program in Textile Engineering in Fall 27. The focus of her research has been the mechanical properties of surgical sutures. She expects to graduate in May, 29 and return to the textile industry. iii

6 cknowledgments I would like to start by expressing my appreciation to my co-advisors, Dr. Martin W. King and Dr. B.S. Gupta. To Dr. King, a deep and sincere thank you for your guidance, but more importantly for providing me with two of the most valuable things in my life: education and travel experiences. Thank you for giving me these life changing opportunities. To Dr. Gupta, thank you for your wise counsel and the opportunity to work on the knot security project. I also wish to give my special thanks to other members of my committee: Dr. Tushar K. Ghosh and Dr. Hechmi Hamouda. In addition, I would like to thanks Dr. Stephen Michielsen for his instruction on fracture mechanics theory. This project would not be possible without the support of the College of Veterinary Medicine. I would like to thank in particular Dr. Simon Roe for the use of his laboratory and equipment; also to Dr. Kyle Mathews for his guidance and assistance in acquiring suture materials. I shall not forget John Hash for his time and availability. Special thanks to dvanced Medical Solutions Group plc. for their quick and enthusiastic support and for providing the Liquiband samples. Thanks to Ethicon, Inc., more specifically to Mr. Patrick Terry for providing the suture samples used in this study and Mr. Joe Hotter from Covidien for providing suture samples as well. Your participation was much appreciated. iv

7 From my heart, I would like to express my sincere appreciation to all the members of the Biomedical Textile Laboratory at the College of Textiles. Joshua, thank you for your good ear; Sarah, thank you for your strength and Nilesh, thank you for your help and continuous assistance. Finally, I would like to thank my love for his sacrifices, for his help and incessant support through this entire odyssey. Yoakim, thank you ten thousand times over for always believing in me and my craziest projects. v

8 Table of Contents List of Tables... x List of Figures... xiii 1. Introduction Problem Statement Goals and Objectives Limitations Review of Literature Surgical Sutures Knot Definition Types of Surgical Knots Knot Challenges and Limitations Knot Performance Knot Mechanics Type of Knot Failure Surgical Knot Evaluation Tissue dhesives Cyanoacrylate dhesive History of Cyanoacrylate dhesive Cyanoacrylate Chemistry vi

9 Utilization Cyanoacrylate Toxicity Fibrin Glue Other dhesives Prior rt Materials and Methods Independent Variables Dependent Variables Definitions Design of Experiment Materials Methods Specimen Preparation Linear Density and Suture Diameter Breaking Force and Elongation Tying Tension Loop Tying Knot Formation, Step by Step Procedure Loop Testing Loop Testing, Step by Step Procedure Specimen nalysis Data nalysis Statistical nalysis of Loop Performance vii

10 Normality Test Variance Test Mean Test Results and Discussion Results Results Obtained on Straight Suture Results Obtained on Suture Loop Examples of Force-Elongation Curves Plots of Mechanical Performance of Suture Loop SEM Pictures Discussion General Objective Specific Objectives Effect of Suture Material Effect of Suture Structure Effect of Suture Coating Effect of Suture Size Effect of the Number of Throws Knot Equivalence Standard Deviation of Ticron TM Suture Dependent Variables Evaluation Conclusion Conclusions... 8 viii

11 5.2 Recommendations and Future Work References ppendix Matlab Program No Matlab Program No Plot of Breaking Force and Elongation Mean and Standard Deviation of the Dependent Variables for Every Statistical nalysis of the Performance Criteria NOV results for the six specific objectives ix

12 List of Tables Table 2.1 Commercial suture coating [2]... 6 Table 2.2 Suture USP sizes and corresponding diameters [3]... 7 Table 2.3: Physical properties of alkyl 2-cyanoacrylates and cured properties [3] Table 3.1: Design of experiment Table 3.2: Suture material used in the study... 3 Table 3.3: Digital pictures of the monofilament and braided sutures Table 3.4: Physical measurements of suture materials (M: monofilament and B: braided) Table 3.5: Force at loop failure for a 6-throws square knot and the tying tension used (M: monofilament and B: braided) Table 4.1: Breaking force and elongation of suture material (M: monofilament and B: braided) Table 4.2: Two-way analysis of variance results for size USP knot with and without adhesive. (No: no adhesive, With: with adhesive, P: PDS*II, E: Ethilon*, T: Ticron TM and B: Biosyn TM ) Table 4.3: Two-way analysis of variance results for size USP 3- knot of Ethilon* (Mono) and Nurolon* (Braided) with and without adhesive. (No: no adhesive, With: with adhesive) Table 4.4: Two-way analysis of variance results for Biosyn TM, knot type (No: no adhesive, With: with adhesive) Table 4.5: Two-way analysis of variance results for Biosyn TM size USP 3- (No: No adhesive, With: With adhesive) x

13 Table 4.6: Two-way analysis of variance results comparing all suture material of size USP for knot with adhesive (w) and knot (B: Biosyn TM, E: Ethilon*, P: PDS*II and T: Ticron TM ) Table 7.1: Dependent variable results for all sutures for knot Table 7.2: Dependent variable results for all sutures for the knot with adhesive... 1 Table 7.3: Dependent variable results for all sutures for the knot Table 7.4: Dependent variable results for all sutures for the knot with adhesive Table 7.5: Dependent variables results for all sutures for =1 knot with and without adhesive Table 7.6: P-values of the Shapiro-Wilk W test for the dependent variables named Force at loop failure, Maximum loop-holding force and Loop holding capacity Table 7.7: P-values of the Shapiro-Wilk W test for the dependent variables named Knot efficiency, Knot elongation efficiency and Loop distraction Table 7.8: P-values of the Bartlett s Test, Welsh s T Test and One Way NOV test if applicable for the dependent variable named Force at loop failure, Maximum loopholding force and Loop holding capacity Table 7.9: P-values of the Bartlett s Test, Welsh s T Test and One Way NOV test if applicable for the dependent variable named Knot efficiency, Knot elongation efficiency and Loop distraction Table 7.1 P-values generated by NOV indicating the influence of adhesive and material on three suture sizes and five materials Table 7.11 P-values generated by NOV indicating the influence of coating and adhesive on knot type and xi

14 Table 7.12 P-values generated by NOV indicating the influence of suture size and adhesive on knot type and for Ethilon*, PDS*II, Ticron TM and Biosyn TM Table 7.13 P-values generated by NOV indicating the influence of the number of throws and the adhesive on Ethilon*, PDS*II, Ticron TM and Biosyn TM of size USP Table 7.14 P-values generated by NOV indicating the influence of the material and the knot type on Ethilon*, PDS*II, Ticron TM and Biosyn TM xii

15 List of Figures Figure 2.1 : High strength suture material [1]... 6 Figure 2.2: Different parts of a surgical knot [12]... 8 Figure 2.3: Three major types of surgical knots... 9 Figure 2.4: Square knot converted into a slip knot [12]... 1 Figure 2.5: Duncan loop used in arthroscopy [14]... 1 Figure 2.6: Knot configuration used to evaluate µ where T o is the tension inside the loop and T 1 the tension in the ears [18] Figure 2.7: Testing apparatus with knotted suture loop around 2 aluminum rods submerged in saline bath [21] Figure 2.8: Chemical structure of 2-cyanoacrylates where R is the alkyl group Figure 2.9: pplication of cyanoacrylate on a clean wound [26] Figure 2.1: Barbed suture used for wound closure [35] Figure 2.11: Knotless device to close a wound [36] Figure 2.12: Malleable collar with straight and double loop (a), Lapra-ty (b) with suture of size USP 3- [37] Figure 3.1: Force at loop failure Figure 3.2: Elongation at loop failure Figure 3.3: Maximum loop-holding force Figure 3.4: Elongation at maximum loop-holding force Figure 3.5: Loop holding capacity Figure 3.6: Loop distraction xiii

16 Figure 3.7: Liquiband package and ampoules [23] Figure 3.8: Straight suture specimen mounted between pneumatics capstan clamps Figure 3.9: 1=1=1=1=1=1 knot on aluminum mandrel Figure 3.1: Tying equipment Figure 3.11: Surgeon s knot with additional throws, a. Two throws (), b. Three throws (), c. Four throws (=1), d. Five throws (=1=1) (6) Figure 3.12: Didactic pictures explaining two steps for the Surgeon s knot two-hand tie technique [12] Figure 3.13: Knot tying equipment showing the fixed ear and load cell moving in the direction of the white arrow... 4 Figure 3.14: Knotted loop specimen mounted between the pins on a tensile testing machine Figure 4.1: Force-elongation curve for Ethilon* size USP and knot Figure 4.2: Force-elongation curve for Biosyn TM size USP 5- and knot Figure 4.3: Performance plots for the Biosyn TM suture, size USP with (w) and without adhesive... 5 Figure 4.4: Performance plots for the Biosyn TM suture, size USP 3- with (w) and without adhesive Figure 4.5: Performance plots for the Biosyn TM suture, size USP 5- with (w) and without adhesive Figure 4.6: Performance plots for the Ethilon* suture, size USP with (w) and without adhesive Figure 4.7: Performance plots for the Ethilon* suture, size USP 3- with (w) and without adhesive xiv

17 Figure 4.8: Performance plots for the Ethilon* suture, size USP 5- with (w) and without adhesive Figure 4.9: Performance plots for the Nurolon* suture, size USP 3- with (w) and without adhesive Figure 4.1: Performance plots for the PDS*II suture, size USP with (w) and without adhesive Figure 4.11: Performance plots for the PDS*II suture, size USP 3- with (w) and without adhesive Figure 4.12: Performance plots for the PDS*II suture, size USP 5- with (w) and without adhesive Figure 4.13: Performance plots for the Surgidac TM suture, size USP 1 with (w) and without adhesive... 6 Figure 4.14: Performance plots for the Ticron TM suture, size USP with (w) and without adhesive Figure 4.15: Performance plots for the Ticron TM suture, size USP 3- with (w) and without adhesive Figure 4.16: Performance plots for the Ticron TM suture, size USP 5- with (w) and without adhesive Figure 4.17: SEM picture of Ethilon* size USP 5-, knot with adhesive (: dhesive and S: Suture) Figure 4.18: SEM picture of PDS*II size USP 5-, knot with adhesive (: dhesive and S: Suture) Figure 4.19: SEM picture of Ticron TM size USP 3-, knot with adhesive (: dhesive and S: Suture) xv

18 Figure 4.2: SEM picture of Ticron TM size USP 5-, knot with adhesive (: dhesive and S: Suture) Figure 4.21: SEM picture of Biosyn TM size USP 5-, knot with adhesive before (a) and after (b) mechanical test (: dhesive and S: Suture) Figure 4.22: SEM picture of Ethilon* size USP 5-, knot with adhesive before (a) and after (b) mechanical test (: dhesive and S: Suture) Figure 4.23: Contact angle θ formed by a drop of liquid on a solid surface Figure 4.24: The low bending rigidity of size USP 5- (a) allows a tight knot with not a lot of room for moisture but it is the opposite for size USP (b) (green: suture, blue: moisture Figure 7.1: Breaking force of every material used in the study including standard error bars Figure 7.2: Breaking elongation of every material used in the study including standard error bars xvi

19 1. Introduction Sutures have been used for thousands of years in the medical field, and they continue to be the technique of choice for wound closure, with about 35 million being used per year in the US alone [1]. By definition, surgical sutures are sterile yarns used to hold tissues together until they heal adequately for self-support or they are used to permanently join tissues with implanted prosthetic devices [2]. Currently, there is an abundance of different materials and methods available to close wounds, including staples, adhesives as well as permanent and absorbable sutures. Regardless of the latest materials and suturing techniques, physicians must keep in mind the safety and security of their knots. This is because the tied knot will always be the weakest point of the suture, with strength reductions varying from 35% to 95% [3]. Once constructed, the knot must be as small as possible to prevent an excessive amount of tissue reaction. On the other hand, surgeons will commonly correct for possible knot slippage and early knot breakage by using a thicker suture or tying a bulkier complex knot with additional throws. The potential negative effects of increasing the knot volume include increasing inflammation which results in delayed wound healing, extending the suturing time and the length of the operation, and/or the development of a suture reaction or fistula. ccordingly, it is important that an alternative way of improving knot security is found, while at the same time limiting or diminishing the knot volume. However, the concept of what knot security means is difficult to describe and the literature is full of definitions which differ with the author. In the past, some approaches have been studied that involve welding or fusing the structure of the knot which have relied on the thermoplastic nature of synthetic sutures [4, 5]. The approach, while successful in increasing knot security in laboratory experiments, 1

20 suffered difficulties of precision when applied in a clinical setting. More recently, a study has reported that the addition of cyanoacrylate adhesive to a surgeon s knot can increase the breaking strength of a looped suture significantly and reduce the amount of slippage [6]. This method could potentially be used successfully during orthopedic surgery where high tensile loads are involved, such as in tendon repair. 1.1 Problem Statement It is well known that the knot will always be the weakest point in the suture loop and this is why suture efficiency will invariably depend on the performance of the knot itself. dditional throws or thicker sutures can make the knot safer, more secure and have a reduced risk of slipping but to the detriment of other properties. recent study has demonstrated that combining conventional material of size USP 2 suture with a cyanoacrylate adhesive significantly reinforced the knot itself without the need for extra throws [6]. However, this investigation was limited to only one size of suture, and the heavy size reported is rarely used outside of orthopedic surgery. Therefore, based on these encouraging results, there is a demand among clinicians for research to be conducted on a broader range of suture types and sizes [7]. 1.2 Goals and Objectives The goal of this study is to determine if cyanoacrylate adhesive can have a significant reinforcing effect on the surgeon s knot when tied with typical suture types and sizes. The ultimate aim is to identify which factors contribute to knot reinforcement, and to establish a range of optimal reinforcing conditions. The materials to be studied include permanent sutures, namely polyester (Ticron TM and Surgidac TM ) and nylon (Ethilon* and Nurolon*), as well as absorbable materials 2

21 (Biosyn TM and PDS*II), combined with the topical cyanoacrylate adhesive LiquiBand. The specific objectives in completing these goals are to determine in detail the effect of reinforcement on the knot performance 1 of a looped suture, and more explicitly: 1) To determine the effect of different suture materials on the knot performance with and without reinforcement. 2) To determine the effect of the type of suture structure on the knot performance with and without reinforcement. 3) To determine the effect of suture coating on the knot performance with and without reinforcement. 4) To determine the effect of the size of the suture on the knot performance with and without reinforcement. 5) To determine the effect of the number of throws on the performance of the knot with and without reinforcement. 6) To determine if a small reinforced knot can be as safe and secure as a regular thicker knot. 1.3 Limitations The suture samples used in this study were supplied by manufacturers. These were not randomly selected from a population; rather we relied on the availability of the type of material chosen. In some cases, the recommended material had already expired or was soon to expire, according to the notation found on the package. Moreover, the experimental knots used for this research were tied by the investigator. This investigator does not have a surgeon s training and no tying 1 Knot performance is defined in the Definitions section of Chapter 3 with an explanation of how this multi-dimensional variable was measured during this study. 3

22 experiences other than the one gained during this study. The reliability of the investigator s knot tying ability has not been compared with that of an experienced surgeon. 4

23 2. Review of Literature 2.1 Surgical Sutures The surgical suture was one of the first biomaterial devices used by medicine. In fact, the use of linen by the Egyptians to create a suture thread was reported more than 4 years ago [3]. Over the years, new natural and synthetic biomaterials have been developed to produce sutures with enhanced mechanical properties and reduced inflammatory reaction. By definition, surgical sutures are sterile filaments used either to hold tissues together until they have healed adequately for selfsupport, or to join tissues with implanted prosthetic devices [2]. suture device is composed of a metal needle, usually made of stainless steel, and a thread. This second component is more important in terms of biocompatibility because it remains in the wound to hold the tissues together. The thread can be made of absorbable or nonabsorbable material. Nonabsorbable sutures will remain permanently in the body, and can be made of different synthetic polymers, including polyester, nylon, polypropylene and eptfe. On the other hand, absorbable suture materials lose a significant portion of their mechanical strength over a period of 2 to 3 months [3], or up to one year for new synthetic monofilaments. The first absorbable sutures were made of catgut. They have been progressively replaced by synthetic copolymer materials made by mixing flexible polymer segments with high-strength segments [8]. bsorbable sutures have received increasing interest over the last few decades and now represent about 42 % of the total suture market worldwide [8]. In terms of their physical structure, sutures can be classified as monofilament, multifilament, twisted and braided. The differences in structure affect the handling properties and the mechanical behavior of the suture. Recently, high strength performance sutures have emerged on the market (Figure 2.1) and these sutures combine different structures such as Supramid (S Jackson Inc., lexandria, V, US), which is a 5

24 twisted core of nylon enclosed in a smooth nylon 6 outer shell [9]. It is claimed to reach higher breaking strength while keeping good handling properties. Figure 2.1: High strength suture material [1] Since sutures must pass through various tissues with minimal friction, coatings are applied to multifilament braids and twisted structures to improve their surface lubricity. There are a variety of coatings available, some absorbable, some not, and they depend on the type of suture, the type of polymer and the suture s trade name (Table 2.1). Table 2.1 Commercial suture coatings [2] Coating Suture Trade Name Type of Polymer bsorbable Poloxamer 188 (Pluronic F-68) Dexon Polyglycolide Calcium stearate and copolymer of glycolide-lactide Vicryl Poly(glycolide-L-lactide) (polyglactin 91) Nonabsorbable Silicone silk Silk Ticron Polyester Surgilon Polyamide (nylon 66) Wax Nurolon Polyamide (nylon 66) Poly(tetramethylene adipate) Ethibond Polyester fluorocarbon Tevdek, Ethiflex Polyester 6

25 Finally, sutures can be classified according to their size or diameter. standard code was developed, agreed to and published in the United States Pharmacopoeia (USP) in order to define the sizing system of absorbable and nonabsorbable sutures (Table 2.2). However, because this national suture sizing standard is widely accepted, but not well policed, there is a tendency for manufacturers to produce commercial suture sizes near the upper size limits or even extend the sizing system illegally beyond that allowed by the USP [11]. In practice, the surgeon must use the smallest diameter suture that will hold the wound tissue safely and securely without breaking. Table 2.2 Suture USP sizes and corresponding diameters [3] Non synthetic absorbable suture USP Size Diameter limits (mm) Nonabsorbable and synthetic absorbable sutures Knot Definition surgical knot is composed of three components (Figure 2.2). First, the loop created by the knot maintains the approximation of the tissues and provides tension between the divided wound edges [12]. Secondly, the knot itself is composed of a certain number of throws that are made one after the other. single throw is 7

26 defined as two threads wrapped around each other so that the angle of wrap equals 36 degrees [13]. sliding throw is one in which the thread enters and leaves the throw on the same side [14]. Finally, the ears are the cut ends of the suture. They provide the insurance that the last throw will not unravel if the loop expands or if the knot slips. The doctor s side of the knot is defined as the side of the knot with ears, or the side where tension is applied during tying [12]. The patient s side is defined as the side of the knot with the loop. Figure 2.2: Different parts of a surgical knot [12] In 1976, a standardized nomenclature was created to describe a knot s configuration. The number of wraps in each throw is indicated by an rabic number, and the relationship between each throw, being either crossed or parallel, is signified by the symbols X or =, respectively [12]. The presence of a slip knot is indicated by the letter S instead of an rabic numeral and the configuration is detailed by using symbols // and #. 2.3 Types of Surgical Knots Various types of knots are used to tie sutures, but the principal ones are the square knot, the granny knot and the surgeon s knot. The square knot (1=1) has been investigated and is reported to be the easiest and most reliable for tying the majority of suture materials [15]. The reason is that its geometry allows high tension points 8

27 to be located within the strand where it passes around another strand [13]. It is a single throw followed by a single throw. The right ear and loop both come out on either the anterior or posterior side of the knot. The left ear and loop come out opposite to the right ear and loop (Figure 2.3) [13]. The granny knot (1x1) is not recommended because of its tendency to slip. However, it may be inadvertently tied by a considerable proportion of surgeons by incorrectly crossing the strands of a square knot (Figure 2.3) [3]. The surgeon's knot or friction knot is recommended for tying a lot of materials such as braided synthetic absorbable sutures, coated Vicryl, polyester, nylon and polypropylene sutures. It is composed of a double throw followed by a single throw; with the right ear and loop coming out on the same side of the knot (Figure 2.3). Further single throws can be added on top of the surgeon s knot to improve security. Figure 2.3: Three major types of surgical knots With the new less invasive surgical techniques, such as laparoscopic surgery, new types of knots have had to be created (e.g. half-hitch or sliding knots). They are called sliding knots because they can be slid for a certain distance, and then be locked at the desired position. The square knot (1=1) can easily become a slip knot (S=S) if the surgeon does not reverse the position of his hands after each throw, or, if a greater tension is apply to one ear (Figure 2.4) [12]. Finally, some sliding knots have been developed for specific surgical operations like the Duncan loop or the 9

28 Overhand loop. They are used extensively in the field of arthroscopy (Figure 2.5) [14]. Figure 2.4: Square knot converted into a slip knot [12] Figure 2.5: Duncan loop used in arthroscopy [14] 2.4 Knot Challenges and Limitations The significant advances in materials science and engineering over the past decades have provided surgeons with a wide and complex range of choices and approaches to wound closure [3]. series of research studies has been motivated by the fact that tying a knot in a suture is associated with considerable challenges and limitations. First, knot tying requires time and extensive training, especially for less-invasive surgeries. For some surgical operations, tying knots can take as much as 5% of the surgeon time [16]. Irrespective of the knot configuration and the suture material, the inherent weakest link in the surgical suture is the knot, and the second weakest point is the portion immediately adjacent to the knot. The strength reduction due to knotting can be as large as 35% to 95% [3]. This decline is attributable to knot slippage, the mechanical crushing of the suture by surgical instruments and stress concentrations in the knot itself. The applied tension on the suture strand is transformed into tensile, bending, compression and shear stresses on the filaments in the knot. These forces and the shearing action break the filament at a load lower than the simple tensile breaking load [13]. When a knotted suture 1

29 fails, the consequences may be disastrous, including wound dehiscence, massive bleeding, and/or incisional hernia [12]. In order to avoid such complications, the general surgical practice is to either introduce additional throws or to use a thicker suture. Once formed inside the body, the larger knot can produce a delay in wound healing, constrict the blood flow and cause a distortion in the tissue which can lead to necrosis and/or scar formation [17]. Sutures provoke a significant inflammatory response, particularly if the knot is larger. For example, an increase in size from USP 4- to USP 2- increases the volume of subsequent reaction by 137% to 255% [3]. 2.5 Knot Performance In 1937, Taylor was the first person in modern times to become interested in the security of surgical knots [13]. Even now, seven decades later, clinicians and scientists still debate the most accurate way to evaluate the knot performance of a suture Knot Mechanics It is the friction between suture filaments that allows the knot to stay tied. In order to take advantage of this phenomenon, the number of crossing points inside the knot and the contact angle can be increased. The surface of the suture or the filaments can also be altered (e.g. braided filament or coating). Each time two suture threads are in contact, the frictional forces created will oppose the tension applied to the loop. If the knot is in equilibrium, the frictional forces will equal the tension applied at the loop ends [13]. It has been shown that the coefficient of friction of a suture (µ) can be established using the following equation, where n is the number of turns and β is the angle between the two suture strands (Figure 2.6) [18]: 11

30 T 1 = T o e µπnβ Figure 2.6: Knot configuration used to evaluate µ where T o is the tension inside the loop and T 1 the tension in the ears [18] Types of Knot Failure ccording to Thacker, there are three types of knot failure modes. 1) The suture material can yield, fracture or break (called knot breakage), 2) the knot can slip (called knot slippage), and 3) the knot can untie from the doctor s side (called knot untying) [13]. The first mode is the preferred mode of all three. It will happen when the knot has been tied under the correct tension and locked properly. The ideal surgical knot is one that requires the least number of throws to achieve knot breakage behavior. The tissue in which the suture is implanted can also influence the knot strength or knot security. In the case of absorbable sutures, a progressive decline in knot breaking strength is expected after tissue implantation [12]. Knot slippage is required up to a certain level. Ideally, the suture should elongate under low loads to accommodate any developing wound edema, but return to its original length after healing and resolution of the edema [12]. However, too much slippage will cause a separation of the wound edges. If the internal geometry has not reached equilibrium when tied by the surgeon, further tension will make the knot 12

31 tighten or snug down. Secondly, if the tension applied to the loop is higher than the frictional forces in the knot, then slippage will occur. Multifilament sutures tend to slip less than monofilament sutures [3]. The degree of knot slippage can also be influenced by the coefficient of friction, the suture diameter, the type of knot and the level of moisture in the wound [12]. Finally, there is a small chance that the knot will untie on the doctor s side. When using a stiff material, such as a monofilament, and a thicker suture, the last unrestrained throw has a tendency to open up and untie. This is the reason why it is important to leave about 3 mm of suture material to form the ears [12] Surgical Knot Evaluation s mentioned earlier, evaluating and rating the performance of surgical knots has been done in the past using different criteria. However, there are certain concepts that have been broadly accepted. Chu et al has defined the loop holding capacity (LHC) as either the force required to break a tied suture loop or alternatively to provoke slippage of at least 2 mm within the knotted loop [3]. The concepts of knot failure and knot holding capacity (KHC) are only variants of the same LHC. second definition often used in the literature is the knot efficiency. Depending on the source, the exact meaning of this concept changes slightly. Chu et al has defined it as half of the loop holding capacity expressed as a percentage of the breaking strength of the unknotted suture thread [3]. Others have defined it as the tensile strength of a knotted suture divided by the tensile strength of the unknotted suture expressed as a percentage [12]. third and last important concept is the handling characteristics of the suture. Surgeons evaluate the handling characteristics of sutures by constructing knots using manual and instrumental tying techniques. They will then select that suture which permits a two-throw knot to be easily advanced or 13

32 snugged down [12]. nother way of evaluating the handling properties is to record the time [14] or the number of steps [19, 2] required to complete the tying of a particular knot. Knot security is not a concept that has a clear and straight forward definition. Some studies have attempted to define knot security as a collection of characteristics and they have created new test methods and equipment to evaluate the knots performance. Ilahi et al have used a cyclic loading protocol in saline solution to test knotted loops and record the applied load required to generate a 3 mm separation as well as the ultimate failure load (Figure 2.7) [21]. Hong et al evaluated the knot performance of new suture materials by testing the knot pull strength, the knot rundown and the knot security. Here, the knot pull strength was the breaking force applied between the ears of a knotted suture, and the knot security was the breaking force applied to a knotted suture inside the loop [22]. Figure 2.7: Testing apparatus with knotted suture loop around 2 aluminum rods submerged in a saline bath [21] 14

33 Finally, it is important to note that the only way to identify the type of failure is by visual observation during testing. No other tests or concepts have been found in the literature to accurately differentiate knot slippage from knot breakage. 2.6 Tissue dhesives Unlike sutures that close wound mechanically, tissue adhesives use chemical bonds. The ideal adhesive should be safe, biodegradable, effective and easy to use even in moist tissues. Nowadays, there are different categories of adhesives available. ccording to some estimates it is predicted that as much as 4% of the global suture/staple market could eventually be accounted for by tissue adhesives and sealants [23] Cyanoacrylate dhesive History of Cyanoacrylate dhesives Work with cyanoacrylate adhesives started with rdis in 1949 followed by clinical uses in 1965 by Watson and Maguda for tympanic membrane repair [24]. t about the same time, Krazy Glue was being used in the medical field, although it was found to have severe histotoxicity. survey conducted in 1984 on the medical applications of Krazy Glue in US demonstrated that 34% of the institutions contacted had a working knowledge of this adhesive [25]. While the FD prohibited its usage, more research was being done to develop fast setting and strong n-butyl cyanoacrylates that were less toxic (e.g. Histocryl (B Braun), Indermil (Vygon), or LiquiBand (Medlogic)). Then, Closure Medical Inc. developed DermaBond, that was a slower setting octyl-cyanoacrylate adhesive with more flexibility. It was approved for external clinical use by the FD in More recently, we have seen overseas development of blended butyl and octyl cyanoacrylates (e.g. LiquiBand 15

34 Laparoscopic (Medlogic)) providing both a fast setting adhesive with a good degree of flexibility [26]. Recent research has demonstrated that the new family of cyanoacrylate hemostatic agents (OMNEX, Ethicon), which had previously proven their safety and efficacy in topical use, are now safe and effective absorbable surgical sealants for internal use Cyanoacrylate Chemistry Cyanoacrylate tissue adhesives are liquid monomers that polymerize in the presence of moisture on contact with tissue surfaces in an exothermic reaction creating a strong yet flexible film that bonds the apposed wound edges [27]. The following chemical structure represents the family of 2-cyanoacrylate monomers (Figure 2.8) and the various properties of the cured adhesive are listed in Table 2.3. CN CH 2 = C O = C- O - R Figure 2.8: Chemical structure of 2-cyanoacrylates where R is alkyl group Table 2.3: Physical properties of alkyl 2-cyanoacrylates and cured properties [3] Cranoacrylate Structure of lkyl (R) Viscosity (cp) Cured bonding to Stainless Steel Set time (min) Strength (kg/cm 2 ) Methyl 2-cyaboacrylate CH < Ethyl 2-cyanoacrylate (Krazy CH 3 CH < 1 14 Glue) n-propyl 2-cyanoacrylate CH 3 (CH 2 ) n-butyl 2-cyanoacrylate CH 3 (CH 2 ) Isobutyl 2-cyanoacrylate CH 3 CH-CH CH 3 n-hexyl 2-cyanoacrylate CH 3 (CH 2 ) n-octyl 2-cyanoacrylate CH 3 (CH 2 ) Ethoxyethyl 2-cyanoacrylate CH 3 CH 2 O CH 2 CH

35 The glue is metabolized by hydrolysis to yield formaldehyde and alkylcyanoacetate that can be further metabolized and excreted in urine and feces [24] Utilization dhesives have several advantages over traditional sutures. First, they are easy to use compared to suturing procedures that often require highly skilled and experienced surgeons. They also reduce patient trauma because the procedure is faster, sometimes eliminating the need for anesthesia, and no needles are required [23]. Postoperative removal procedures are required with nonabsorbable suture materials but not with adhesives. When compared to fibrin glue, cyanoacrylate can be stored at room temperature. It serves as a sealant mechanically and therefore does not depend on the body s clotting mechanism to function [28]. Optimal results are obtained when the wound incision is clean and dry with absolute haemostasis prior to application of the skin adhesive. Otherwise the cyanoacrylate will polymerize with fluids in the wound rather than bonding to the skin (Figure 2.9) [26]. During use, the glue should not get between the skin edges because it may prevent healing and lead to a foreign body inflammatory reaction. Figure 2.9: pplication of cyanoacrylate to a clean wound [26] 17

36 Cyanoacrylate products can be used to close most laparoscopic port site incisions [26], and seal and reinforce suture lines [3]. Finally, they can be used effectively and successfully in emergency and pediatric departments. Cyanoacrylate adhesives also have antimicrobial activity. lthough its exact mechanism is unclear, it probably relies on the strong electronegative charge on the polymer. recent study demonstrated that contaminated wounds closed with sutures had higher infection rates compared with those repaired with topical tissue adhesive [29]. Some criticize the high cost of adhesives compared to sutures. Still, some studies have shown that when equipment utilization, pharmaceutical use, health care worker time and parental loss of income for follow-up visits are all included in the calculation of the total repair cost for pediatric facial lacerations, there is a significant saving by using adhesive [19]. Lastly, in most cases, cyanoacrylate adhesive provides equivalent or more attractive cosmetic outcome with less visible scarring than sutures. However, these results can be contradictory depending on the skill and experience of the plastic surgeon in handling sutures compared to adhesive agents, as well as the method of cosmesitic evaluation selected. Having said that, the cosmetic outcome of closing cutaneous excisional surgical wounds with standard suturing has been found to be superior to that of wounds closed with octyl cyanoacrylate [3], even after one year [31]. nd, Handschel et al have found that sutured wounds give better cosmetic results in younger patients [32] Cyanoacrylate Toxicity topic that has generated a lot of concern is the toxicity level of cyanoacrylate adhesives since the by-product of degradation is formaldehyde. The released formaldehyde is histotoxic and can cause acute and chronic inflammation unless the 18

37 level accumulated in the treated area is below a certain threshold [3]. Research has shown that longer-chain cyanoacrylate derivatives degrade at a slower rate, thereby permitting the degradation products to be more safely metabolized with the generation of a less intense inflammatory response [25]. This is the same reason why n-butyl-cyanoacrylate has a less intense inflammatory response than methyland ethyl-cyanoacrylates (Krazy Glue). The cytotoxicity of cyanoacrylates is also directly proportional to the dose applied. This explains the superior tolerance reported in ocular surgery since they only use from half a microliter to several microliters per application [3] Fibrin Glue Fibrin is another type of adhesive that has been used to replace the traditional suture. It was first used as a hemostatic agent by Bergel et al in 199 and then used as sheets to rapidly stabilize hemorrhage during WW1 [24]. Fibrin glue mimics the final stage of the coagulation cascade and takes advantage of its adhesive properties. It is a mixture of fibrinogen and thrombin manufactured from human or bovine blood, and for this reason, safety issues had until recently delayed commercial approval by the FD. Cross-contamination and xenogeneic reactions remain a major concern. Unlike cyanoacrylate adhesives, fibrin adhesive is biodegradable through the regular fibrinolysis process. The mechanical strength is limited compared to synthetic adhesives but can be tailored by adjusting the concentration of fibrinogen and thrombin. The highly concentrated solutions, however, are excessively viscous and expensive [3]. This fairly new product has found interesting applications. It has served as a drug carrier and has replaced sutures for skin grafting. s an adhesive, fibrin glue has found several urologic applications. It has excellent potential in laparoscopic surgery, where conventional tissue approximation techniques are cumbersome and time-consuming [33]. It has 19

38 also been used to seal air leaks from pulmonary staple lines, seal gastrointestinal anastomoses and reduce cerebrospinal fluid leaks after neurosurgical procedures [33] Other dhesives The use of other adhesives to replace sutures have been explored. Gelatinresorcinol-formalin (GRF) glue is formed from gelatin, resorcinol, and distilled water in the presence of formaldehyde, glutaraldehyde and heat [24]. It requires dry conditions to perform as an adhesive. Lastly, other adhesives are derived from collagenous material produced by mussels. This interesting gel is composed of 17 amino acids. It claims to have a rapid curing time and promotes vigorous adhesion [24]. 2.7 Prior rt In order to improve knot security and to overcome the flaws of knots and adhesives, some other suggestions have been made regarding alternative approaches to wound closure. First, some clinicians and engineers have tried to eliminate the use of knot by conceiving of a barbed suture [35]. The barbs along the outer surface of the suture are designed to anchor themselves in the surrounding tissues without the need for a suture knot. Barbed sutures can be used in multiple layers at the same time (Figure 2.1) [34]. No knots are needed as the sutures interact mechanically with the surrounding tissues all along the length of the suture. The same concept applies to US Patent (Figure 2.11). 2

39 Figure 2.1: Barbed suture used for wound closure [35] Figure 2.11: Knotless device to close a wound [36] Others have attempted to replace the suture knot by devices that claimed to be faster and stronger than a comparable knot. Titanium clips, locking polydioxanone clips and malleable collars have all been assessed and compared to a 3-throws square knot. It was found that sutures secured with malleable collars and polydioxanone Lapra-ty clips (Ethicon) were as strong as the 3-throws square knot and have the potential for use as knot substitutes in laparoscopic surgery (Figure 2.12) [37]. a. b. Figure 2.12: Malleable collars with straight and double loops (a) and Lapra-ty (b) with suture of size USP 3- [37] The idea of reinforcing a knot has also been explored in the past. carbon dioxide laser was used to heat, soften and weld a two square throw knot (1=1) made from synthetic thermoplastic polymers. The average increase in knot strength was found to be about 16% and knot slippage was observed to have been completely eliminated [4]. However, this technique required a lot of precision and was difficult to use reliably in a clinical setting. More recently, Komastu et al have applied 21

40 cyanoacrylate adhesive to knots in order to improve their tensile strength with a view to eventually using them in tendon repair. Five different suture materials of size USP 2 were tested and four of them showed significant improvements in suture knot security. The monofilament made from PDS*II (Ethicon) produced knots that were the most significantly reinforced with improvement of 128% in tensile strength [6]. No other studies have been found that have demonstrated the reinforcing effect of adding tissue adhesives to suture knots. 22

41 3. Materials and Methods In this design of experiment, the ultimate goal was to evaluate whether or not a cyanoacylate topical adhesive could have a significant reinforcing effect on a surgeon s knot when tied with common sutures. In order to do so, a list of independent variables was identified to determine their effect on relevant dependent variables. Mathematical programs have been further used to analyze the forceelongation curves generated and to obtain comparative factors. 3.1 Independent Variables 1) Type of suture polymer: Four materials were used in the experiment; 1. polyester under the trade names Surgidac TM and Ticron TM, 2. nylon with Ethilon* and Nurolon*, 3. polydioxanone under the name of PDS*II, 4. poly(glycolidetrimethylene-carbonate-co-dioxanone) with Biosyn TM. 2) Size of suture: Four sizes of suture have been tested; USP 5-, USP 3-, USP and USP 1. 3) Type of knot: The surgeon s knot has been evaluated in three different configurations; 1. the regular surgeon s knot (), 2. the surgeon s knot with one extra throw (), 3. the surgeon s knot with two extra throws (=1). 4) Type of reinforcement: The topical adhesive named Liquiband has been used as the reinforcement. 23

42 5) Type of suture coating: Two types of coating have been compared on braided polyester sutures. These are chemically described as a silicone coating and polybutylene adipate coating on Ticron TM and Surgidac TM respectively. 6) Type of suture structure: Both braided sutures (Surgidac TM, Nurolon* and Ticron TM ) and monofilament sutures (PDS*II, Ethilon* and Biosyn TM ) have been studied. 3.2 Dependent Variables The following list comprises those dependent variables that are considered relevant to understanding the behavior of suture knots when under mechanical loading. 1) Breaking force 2) Breaking elongation 3) Force at loop failure 4) Elongation at loop failure 5) Maximum loop-holding force 6) Elongation at maximum loop-holding force 7) Loop holding capacity 8) Knot efficiency 9) Knot elongation efficiency 1) Loop distraction 3.3 Definitions s stated previously, the concept of knot security for a suture is often interpreted differently depending on the author. For this reason, the term has been avoided and the ten dependent variables listed above were used instead. In this case, some of the stated terms have been taken directly from standards and publications while 24

43 others has been created or adapted specifically for the purpose of this research project. 1) Breaking force: The breaking force of the suture is the tensile force in Newtons required to break the unknotted suture thread [38]. 2) Breaking elongation: The breaking elongation of the suture is the tensile elongation in millimeters at which the unknotted suture thread breaks [38]. 3) Force at loop failure: Force in Newtons at which either the loop fails due to suture breakage and the knot remains intact, or the force causing the knot to slip completely off the ears when a force is applied inside the loop (Figure 3.1). This definition has been adapted from the definition of knot security from Li [14]. 4) Elongation at loop failure: Elongation in millimeters at which either the loop fails due to suture breakage and the knot remains intact, or the elongation causing the knot to slip completely off the ears when a force is applied from inside the loop (Figure 3.2). This definition has been adapted from the definition of knot security from Li [14]. Figure 3.1: Force at loop failure Figure 3.2: Elongation at loop failure 5) Maximum loop-holding force: The maximum force in Newtons that the knotted loop has supported before failure (Figure 3.3). This definition has been inspired by Batra et al [39]. 25

44 6) Elongation at maximum loop-holding force: The elongation in millimeters at which the maximum loop-holding force occurs (Figure 3.4). Figure 3.3: Maximum loop-holding force Figure 3.4: Elongation at maximum loopholding force 7) Loop holding capacity: The definition of loop holding capacity given by Chu et al is the force required either to break a tied suture loop, or to provoke slippage of over 2 mm within the loop [3]. This corresponds to the criteria for clinical failure. In this set of experiments, the suture loops were 1 cm in circumference. ccording to the surgeon Dr. Geoffrey P. Kohn, the circumference of a typical suture loop used during surgery is approximately 2 cm [4]. Therefore, in order to follow Chu s definition, the term loop holding capacity used in this study was defined as either the force required to sustain loop elongation over 1 mm, or the force required to break the suture loop if the elongation does not reach 1 mm (Figure 3.5). Figure 3.5: Loop holding capacity 8) Knot efficiency: Knot efficiency is defined as the loop holding capacity divided by 2, expressed as a percent of the breaking force of the unknotted suture thread [3]. 26

45 9) Knot elongation efficiency: Knot elongation efficiency is defined as the mathematical ratio expressed as a percentage of half of the breaking elongation of the unknotted suture divided by the elongation at loop failure. The length of the unknotted suture must be equal to the circumference of the loop (1 cm in this case). perfect loop would have a knot elongation efficiency of 1%. By considering the knot as a defect inserted in the loop, the knot elongation efficiency evaluates the impact of this defect on the elongation of the loop. If the knot elongation is greater than 1%, this is because considerable knot slippage occurred during the test. This is a new concept developed by the author. 1) Loop distraction: This is a new concept which has never been applied to a suture. Initially, the author was looking for a way to distinguish knot slippage from loop breaking behavior without involving visual observation of the failed specimen. gain, the knot is considered as a defect. Therefore, this criterion compares the force-elongation curve of the knotted loop to a perfect loop. In this case, the perfect loop is in fact a thread having the same length as the knotted loop circumference (1 cm). Because it is impossible to join the suture in a loop without adding a knot or a fastening system, this straight thread is considered as perfect. When a knot is inserted in a loop, the force-elongation curve will demonstrate several slip-stick peaks and valleys because the knot is reforming and/or slipping. Those peaks and valleys will cause the curve to deviate from the perfect forceelongation curve. This last variable is measuring the deviation in force of the knotted loop from the perfect curve. The loop distraction value is determined as the elongation in millimeters at which the force of the knotted loop differs by more than 1% from the force of the perfect thread suture curve (Figure 3.6). The 1% is obtained by the ratio of the force deviation over the mean value of the force at loop failure defined earlier in point 4. If the loop fails before the 1% criteria is reached, then the value of the loop distraction is equal to the elongation at loop failure. It is suspected that a stronger and safer knot will experience less slip-stick behavior and 27

46 therefore less deviation, and reach a higher loop distraction value. From a clinical point of view, it becomes interesting to see if the loop distraction value is greater than the clinical failure criterion (in this case 1 mm elongation in a 1 cm loop). If this is the case, this would mean that the knotted loop has behaved perfectly up to the point of clinical failure. Figure 3.6: Loop distraction 3.4 Design of Experiment The number in Table 3.1 represents the number of specimens that were actually tested for each type and size of suture. In almost all cases, ten or more specimens were tested. Due to preliminary test failures, a shortage of sutures and limitations on accessing the equipments, a few samples were tested less than ten times. This specific limit of ten specimens was originally planned based on the literature. Except for ndrews et al [37] and Ilahi et al [21] who used fifteen and five specimens respectively, most of the literature concerned with the knot evaluation of suture has used ten replicates [6, 14, 22, 39]. 28

47 Table 3.1: Design of experiment Type of knot (N = No adhesive W = With adhesive) =1 Suture Material N W N W N W Biosyn TM USP USP USP USP Ethilon* USP USP USP PDS*II USP USP Surgidac TM USP Nurolon* USP Ticron TM USP USP USP Materials Six suture materials were included for investigation in this study. The suture materials employed are listed in Table 3.2 with the additional information provided on the packages, and illustrated in Table 3.3. The polydioxanone suture called PDS*II was chosen because in a previous study it was reported to be the material that demonstrated the most knot strength improvement when reinforced with a cyanoacrylate adhesive [6]. Biosyn TM was the second absorbable material chosen for this study so as to evaluate if the same trend applied to other polymer compositions different than 1% polydioxanone. Ethilon* and Nurolon* were selected to assess the performance of nylon material in two different structure types. nd, Surgidac TM and Ticron TM were chosen to represent polyester material, which was also included in Komatsu s previous study. These last two sutures were also picked to evaluate the impact of different coatings on knot performance. 29

48 Suture Trade Name Manuf. Table 3.2: Suture material used in the study Polymer Type Exp. Date Suture Structure Coating Information bsorbable (5% strength retention) Suggested usage Surgidac TM Covidien Polyester 23-9 Braided polybutylene adipate General soft tissue surgery Ticron TM Covidien Polyester Braided Silicone Cardiovascular Ethilon* Ethicon Nylon 6 and Nylon 6, Monofilament General soft tissue surgery Nurolon* Ethicon Nylon 6 or Nylon 6,6. It is dyed black to enhance visibility. Unknown Braided General soft tissue surgery, including use in cardiovascular, ophthalmic and neurological procedures. PDS*II Ethicon polydioxanone Monofilament 8 weeks Pediatric cardiovascular tissue and ophthalmic surgery. Biosyn TM Coviden poly(glycolide trimethylenecarbonate-codioxanone) Monofilament 1 to 2 weeks Size USP : Gastrointestinal surgery Size USP 5-: Urology Four different sizes of sutures were included in the study. They were: USP 5-, USP 3-, USP and USP 1. These sizes were chosen because they represented a typical range used in most surgical interventions [7, 4]. These sizes were much finer than the USP 2 size used in the previously reported study on knot reinforcement [6]. ll these sutures were obtained in sterile packages directly from the suppliers. The sampling of the various specimens was neither controlled nor randomized. 3

49 Table 3.3: Digital pictures of the monofilament and braided sutures Suture Material Suture Size USP 5- USP 3- USP USP 1 Biosyn TM Ethilon* PDS*II Ticron TM Surgidac TM 1 mm Scale Nurolon* Liquiband was used in this study to reinforce the knotted sutures. This product is a sterile, single use, tissue adhesive designed for the closure of both trauma tie and minor surgical wounds [23]. The two major compounds that compose this adhesive 31

50 are 2-octyl cyanoacrylate and n-butyl cyanoacrylate (also called Enbucrylate). The exact weight ratio constitutes a trade secret. It was supplied in sterile polyethylene ampoules, each containing.5 g of adhesive (Figure 3.7). It needed to be kept at a temperature between 2 o C and 5 o C in order to maintain its shelf life for one year. The applicator, which was made in the shape of a syringe, provided precise control over the placement and volume delivered. This adhesive is indicated for low tension wounds to the scalp, face, trunk and limbs where the wound edges are easily approximated and where the tissue is not under tension [23]. In the instructions for use, it is advised that after application, the tissue edges should be held together for approximately 3 seconds until Liquiband has fully cured. pplying excessive amounts should be avoid as this can lead to reducing flexibility at the wound edges and reduce the strength of the closure. This product is manufactured by the company MedLogic Global Limited located in Plymouth, UK. Figure 3.7: Liquiband package and ampoules [23] This adhesive is from the same chemical family as the ron lpha cyanoacrylate adhesive used by the previous study conducted by Komatsu et al [6]. 32

51 3.6 Methods Specimen Preparation sample of each type and size of suture was taken from the package and the needle was removed using a pair of scissors. ny section of the suture that appeared to have been affected by the swaged needle during manufacture was also removed [41] Linear Density and Suture Diameter fter specimen preparation, the length of the suture was measured to the nearest millimeter and then weighed on a G242 Mettler Toledo balance with a precision of.1mg. The linear density was calculated in units of denier with the following formula: Linear density (denier) = Weight (g)/ length (mm) * 1mm/m * 9 The linear density was converted to tex simply by dividing the denier value by 9. The same specimens were used to measure the suture diameter. n optical microscope (Model Nikon Labophot2-POL) with a 1x objective lens and graduated eyepiece scale were used to measure the thickness at several points along the suture. While measuring the diameter, a limited amount of tension was applied to the suture to make it straight but not enough to alter its diameter. The eyepiece was calibrated using a standard calibration slide with a 1 mm long scale divided into 1 µm divisions (represented in the last column of Table 3.3). The linear density and the diameter values are located in Table

52 Table 3.4: Physical measurements of suture materials (M: monofilament and B: braided) Linear density ± SD Diameter ± SD Suture Material (tex) (mm) USP ± ±.13 Biosyn TM (M) USP ± ±.5 USP ± ±.4 USP 14.9 ±.7.46 ±.5 Ethilon* (M) USP ± ±.5 USP ± ±.5 USP ± ±.8 PDS*II (M) USP ±.9.31 ±. USP ± ±.5 Nurolon* (B) USP ± ±.6 Surgidac TM (B) USP ±.4.61 ±.15 USP ±.2.4 ±.13 Ticron TM (B) USP ±..278 ±.13 USP ± ± Breaking Force and Elongation The breaking force has been defined as the force in Newtons required to break a straight unknotted suture. The breaking elongation is the elongation in millimeters when the break occurs. In order to complete the measurements, the suture sample was cut in 25 cm long sections. The packages of sutures were selected at random from the boxes supplied by the manufacturer. In most cases, at least ten specimens per suture material and size were tested. The specimen was first immersed in a ph 7.4,.1 M phosphate buffered saline solution for 5 min at 21 o C, in order to ensure that the suture material would be tested in a wet state, similar to in vivo conditions. Each specimen was handled carefully with gloves in a manner to avoid any change in twist or damage due to any stretching [38]. The two ends were mounted and secured on a tensile testing machine MTS Model # 1122 (Figure 3.8). Pneumatic capstan clamps were used to prevent any slippage or damage to the specimen. The gauge length of the straight suture was set at 1. cm which corresponded exactly to the circumference of the lopped specimens. pretension load was set at 5 ± 1 34

53 mn/tex, as directed by STM Method The testing speed was set at 4 mm/min, which was two times faster than the one used to test the looped specimens. This was to make sure that the straight sutures experienced the same strain rate as the looped specimens [14]. ll tests were performed under standard textile testing conditions of 21 ± 1 o C and 65 ± 2% relative humidity. The results of the tension test were recorded on a microprocessor attached to the tensile testing machine. Data analysis was subsequently performed using the program No.1 (ppendix 7.1). Figure 3.8: Straight suture specimen mounted between pneumatic capstan clamps Tying Tension The amount of tension applied to close a wound should ideally be established according to the type of wound and its location. However, the range of tensions is extremely broad and hard to evaluate. In the past, many researchers have encountered difficulties in tying reproducible knots. This is why recent studies have 35

54 proposed that the tension during tying be controlled in order to obtain a more reliable knot [5, 39, 42]. The approach used to determine the tying tension for this study has been proven to provide a good knot security [3]. The appropriate level of tension for each throw of each size and type of suture polymer was ascertained by measuring the force at loop failure for a 6-throws square knot (1=1=1=1=1=1) [39]. The knot was hand tied on an aluminum mandrel (1.25 inch in diameter) by the principal investigator to form a loop of 1. cm in circumference (Figure 3.9). Figure 3.9: 1=1=1=1=1=1 knot on aluminum mandrel In each case, five specimens were prepared and tested until failure at a speed of 2 mm/min. Each suture loop failed by breaking and no slippage was observed. The results were recorded by a microprocessor attached to the mechanical tester and analyzed subsequently by the program No. 1 (ppendix 7.1). Twenty percent of the mean force at loop failure was later used to tie the knots under investigation for that size and type of suture. The value obtained was then rounded up to the closest whole integer because the digital indicator on the tying equipment was accurate to the nearest integer. However, due to the very small amount of material available for the Nurolon* suture, this test was omitted. The tying tension has been established at 8 N because it was similar to the other nylon sutures of the same size (Ethilon* at 7 36

55 N) and to the other braided sutures of the same size (Ticron TM at 8 N). Table 3.5 represents the results of the loop test with the corresponding tying tension used for the specimens studied. Table 3.5: Force at loop failure for a 6-throws square knot and the tying tension used (M: monofilament and B: braided) Force at loop failure ± SD Tying tension Suture Material N N USP ± Biosyn TM (M) USP ± USP ± USP 81.5 ± Ethilon* (M) USP ± USP ±.6 3 USP 18.5 ± PDS*II (M) USP ± USP ±.4 4 Nurolon* (M) USP 3-8 Surgidac TM (M) USP ± USP 7.1 ± Ticron TM (M) USP ± USP ± Loop Tying The principal investigator wrapped each suture specimen around an aluminum rod measuring 1.25 inches in diameter. Each knot was constructed with the help of a tying device designed to provide uniform knot tying tension to each throw (Figure 3.1). The apparatus was designed to produce knotted suture loops each measuring 1. cm in circumference. 37

56 Mandrel Moving load cell Figure 3.1: Tying equipment Three different knots were used in this study. First, the surgeon s knot, also called friction s knot, was used (Figure 3.11). This knot is recommended by Ethicon on various types of suture materials and is commonly used by surgeons in a clinical situation as well as by researchers [5, 6, 22, 41]. The second knot used was the surgeon s knot with an extra throw () (Figure 3.11). This knot configuration has also been used by Komatsu et al to evaluate the reinforcing effect of a cyanoacrylate adhesive agent [6]. Finally, the surgeon s knot with two extra throws (=1) (Figure 3.11) was added to the design of the experiment following discussion with veterinary surgeons [7]. This knot configuration is often used clinically, which justifies its inclusion. Figure 3.11: Surgeon s knot with additional throws: a. Two throws (), b. Three throws (), c. Four throws (=1), d. Five throws (=1=1) [6] 38

57 The investigator followed the two-hand tie technique explained by Covidien on how to tie a suture knot (Figure 3.12) [12]. Practice sessions involving the tying of more than 5 knots were conducted for each of the three knot types, prior to starting the knot tying procedure for the experimental specimens. Figure 3.12: Didactic pictures explaining two steps for the Surgeon s knot two-hand tie technique [12] There was no randomization of knots, and all the specimens for each knot type were tied and tested before moving on to the next type of knot. ll tying was performed under standard textile testing atmospheric conditions of 21 ± 1 o C and 65 ± 2% relative humidity Knot Formation, Step by Step Procedure 1. The suture specimen was passed around the aluminum mandrel and the loop was secured with a two throw knot following the two-hand tie technique. t this stage, the tension was applied by hand only. The investigator was pulling directly on each ear in opposite directions that were in the horizontal plane and perpendicular to the mandrel. 2. The subsequent throw was tied and tensioned by holding one ear fixed with a surgical clamp and the second ear was attached to a movable load cell on the tying equipment (IMD load cell Model ZPS-DPU-22). This load cell was mounted on a sliding platform and the load was displayed digitally (IMD 39

58 Digital indicator Model ZPS). The load cell was moved away from the knot until the numerical screen indicated the pre-determined tying tension of 2% of the force at loop failure of a 1=1=1=1=1=1 knot (Figure 3.13). Once the desired tying tension was reached, it was held constant for 3 seconds. Figure 3.13: Knot tying equipment showing the fixed ear and load cell moving in the direction of the white arrow 3. In the cases of the and =1 knots, additional throws were tied using the same tension as described in the previous step. 4. Following the last throw, the suture ears were then cut to 5 mm in length and the loop was removed from the rod without additional tension. 5. In the following step, the looped suture specimens were placed in a.1 M phosphate buffered saline solution for a period of 5 minutes. This period of aqueous immersion was sufficient to wet out the specimens thoroughly [22]. Surgical gloves were worn during this process so as to protect the specimens from direct hand contact during manipulation and testing. 6. fter five minutes in the wetting bath, the looped specimens that had no adhesive applied (controls) were allowed to dry for one minute before being mechanically tested on the MTS equipment. If reinforcement was to be applied, then a small drop of adhesive was placed directly after the bath on the knot and allowed to dry for 1 minute under controlled conditions. No tension was applied to the loop or 4

59 the ears during this time. The exact quantity of liquid applied to each knot was estimated to be about.1 g/knot. This approach differed from that used by Komatsu et al who applied the adhesive to the knot during tying. In their procedure, after applying the drop of agent, the last throw was made on top of the adhesive [6] Loop Testing The mechanical tests were performed on a tensile testing machine MTS Model 1122 in order to obtain a force-elongation curve. The load cell selected was a 25 N for every loop test because the expected maximum force fell within 1 to 9% of the load cell s capacity. Output from the load cell was recorded on a personal computer and later analyze using program No. 2 (ppendix 7.2) Loop Testing, Step by Step Procedure 1. First, the loop was mounted around the two pins on the tensionmeter (Figure 3.14). The diameter of the pins was 6 mm so as to make them similar to the study conducted by Komatsu et al [6]. Figure 3.14: Knotted loop specimen mounted between the pins on a tensile testing machine 41

60 2. The pretension load of the specimen was set at 1 ± 1 mn/tex. This was twice the value suggested in STM Method 2256 because we were testing loops instead of straight yarns. This provided a zero elongation reference point for the knotted loop. 3. The loop was subjected to a slow strain rate of 2 mm/min. This speed was chosen because it has been used previously in other suture knot studies [6, 41]. The 2 pins were forced apart until the suture knot failed Specimen nalysis Following the mechanical testing, scanning electron microscope (SEM) images were taken of the knotted specimens before and after failure. The SEM specimens were prepared by mounting the suture residues on an aluminum stub with carbon tape and sputter coating with u/pd under.5 to 1 mbar and 18 m conditions for 45 seconds. The equipment used was the EMITECH SC762 Sputter Coater and the coating obtained was 1 nm thick. These SEM photomicrographs were taken to facilitate the study of the failure behavior of the reinforced knots compared to the normal knots Data nalysis fter being recorded and saved on a microprocessor connected to the tensile testing machine, the data was processed and analyzed with the help of Matlab 27 software. Programs were written to evaluate each of the dependent variables discussed earlier. First, the values for breaking force and breaking elongation were generated with the help of program No.1 (ppendix 7.1). In this program, all the data were first imported and then transformed into SI units. Finally, the breaking point was taken as the fourth point recorded before the end. This was because the very 42

61 last few points recorded by the system were either noise or zeros. program was also used for the analysis of the six throw square knot. The same second program was created to analyze the dependent variables related to loop testing (ppendix 7.2). In Part 1 of this program, the data were transformed into SI units. In Part 2, the mean breaking force and breaking elongation of the unknotted suture were calculated from the fourth last point that was recorded. In Part 3 of the program, an interpolated curve was generated for each specimen at every.1 mm. This incremental value was chosen because it corresponded to the mean increment in the original data generated by the tensile testing machine. In Part 4 of the script, a mean force-elongation curve was generated from the interpolated curves obtained in Part 3. Parts 5, 6 and 7 performed similar functions to Parts 1, 2 and 3 but this time analyzing the results of the looped specimens. In Part 8, the loop holding capacity was evaluated by recording the force when the elongation of the interpolated curve was equal to 1 mm. In Part 9, the knot efficiency of the loop was calculated from the mean breaking force of the suture obtained in Part 2 of the program. Part 1 performed a similar operation but with the elongation value so as to obtain the knot elongation efficiency. Finally, Part 11 generated the loop distraction value by comparing the curves for the straight suture and the loop. The force values of the loop were divided by two to make them equivalent to a straight suture. For the same reason, the elongation values of the straight suture were divided by two while keeping the force values constant. 43

62 3.6.9 Statistical nalysis of Loop Performance Since the objective of the research was to evaluate the effect of the adhesive on the knot performance, the means of all the dependent variables were compared by statistical analysis with the help of the software program JMP 7 SS Normality Test The first step of the statistical analysis was to evaluate the normality of the test results. normal curve was fitted within the results distribution and the Shapiro-Wilk test was used to evaluate the goodness-of-fit of this normal curve assuming a 95% confidence interval. The Shapiro-Wilk test calculates a W statistic (or p-value) that tests whether a random sample comes from a normal distribution. The null hypothesis for this test was that the data was from a normal distribution. For p- values smaller than.5, the null hypothesis was rejected Variance Test Secondly, the equivalence of the variances among each group was verified. In order to do so, the Bartlett s Test was used. The null hypothesis of the test was that all variances of each group were equal. If the p-value was smaller than.5, then the hypothesis was rejected, which indicated that at least one variance was unequal Mean Test If at least one variance was unequal, a Welsh s T test was performed to evaluate the means. This test uses the following formulae, where, and N i are the i th sample mean, sample variance and sample size respectively. This test is adapted for unequal sample sizes and variances. The null hypothesis of the Welsh s T Test was that all the means were equal. 44

63 If the variances were equal, a One Way NOV test was performed to evaluate the means. If the p-values obtained by the NOV were smaller than.5, at least one mean was significantly different from the others. Finally, if the conclusion was that at least one mean was different for a specific material, an additional step was taken. Each knot type was statistically tested against each other, with the Welsh s or NOV Test depending on whether the variances were equal or not. Every mean that was not significantly different was marked by the same letter. 45

64 4. Results and Discussion 4.1 Results Results Obtained on Straight Suture s explained in Chapter 3, the breaking force and elongation values were obtained when a straight suture was tested in tension up to the breaking point. Table 4.1 illustrates the collected results. The same information is also located in ppendix 7.3 in the form of bar charts. Surgidac TM size USP 1 has the highest breaking force followed closely by the Biosyn TM size USP. Ethilon* size USP 5- has the smallest breaking force value. lso, it was observed that the monofilament sutures have significantly higher breaking elongation values than the braided sutures. The monofilament suture Ethilon* size USP has the highest breaking elongation value. The braided sutures Nurolon* size USP 3- and Ticron TM size USP 5- and USP have the lowest mean values of breaking elongation. These results were compared and were found to be similar to other values obtained in previous studies (Table 4.1). Table 4.1: Breaking force and elongation of suture materials (M: monofilament and B: braided) Breaking force ± SD Breaking elongation ± SD Suture Material N Literature (N) mm USP ± [17] 59.3 ± 2.7 Biosyn TM (M) USP ± ± 1.7 USP ± ± 2.5 USP 47.8 ± ± 3.9 Ethilon* (M) USP ± [15] 58.9 ± 3.6 USP ± ± 2.3 USP 74. ± [17] 74.4 ± 5.6 PDS*II (M) USP ± ± 4.1 USP ± ± 1.3 Nurolon* (B) USP ± ± 1. Surgidac TM (B) USP ± ± 2.9 USP 74.5 ± ±.8 Ticron TM (B) USP ± ±.9 USP ± ±.9 46

65 4.1.2 Results Obtained on Suture Loop fter the knots were tied, they were tested as explained in the method section and a force-elongation curve was generated for each specimen. From these curves, the mean and standard deviation of the dependent variables described in Section 3.3 were calculated. The detailed results are explicitly presented in Tables 7.1 to 7.5 of ppendix 7.4. These values were compared with those in the literature. For example, the knot with an Ethilon* suture of size USP 3- had an equivalent value. Tera et al obtained a knot efficiency of 16% with a hand tying knot technique [15]. This value is comparable to the 12.9% knot efficiency obtained in this study. The elongation at loop failure and the elongation at maximum loop-holding force criteria were not retained for further investigation due to the high level of variation among specimens Examples of Force-Elongation Curves Figures 4.1 and 4.2 represent examples of four typical interpolated curves obtained by program No. 2. In Figure 4.1, monofilament nylon loops were tested with and without adhesive for the size USP and the knot. The lower curve represents the typical behavior of a knot that fails through slippage. s explained by Komatsu et al, the tensile strength suddenly decreased and the plateau at the end corresponds to slippage at the ears [6]. In this case, the loop failed and the suture had not ruptured during testing. It can also be observed on the second curve that the addition of adhesive had a reinforcing effect. The loop had reached a higher maximal force value and the failure of the knot happened by the suture breaking with little sign of slippage. 47

66 Force (N) Force (N) No adhesive with adhesive Elongation (mm) Figure 4.1: Force-elongation curve for Ethilon* size USP and knot Figure 4.2 also depicts two typical force-elongation curves of Biosyn TM, size USP 5-, with knot. t the beginning the two loops behaved similarly and both failed suddenly. Suture ruptures occurred near the knot or at the knot depending on the specimen. In this case, the reinforcing effect of the adhesive was less significant. However, the curve with adhesive had reached a higher force before breaking no adhesive with adhesive Elongation (mm) Figure 4.2: Force-elongation curve for Biosyn TM size USP 5- and knot 48

67 Plots of Mechanical Performance of Suture Loop The mean values and the standard error bars of the six remaining dependent variables have been plotted in Figure 4.3 to 4.16 and grouped according to the suture size and knot type. The p-values obtained from the statistical analysis described in Section are located in ppendix 7.5, Tables 7.6 to 7.9. Most of the distributions were normal or close enough to assume normality. However, a few distributions had equal variances. From the results of the mean test (Section ), every mean that was not significantly different was marked by the same letter (, B and C) on Figure 4.3 through

68 2 2 Force at loop failure (N) Maximum loopholding force (N) w w w w Loop holding capacity (N) Knot efficiency (%) w w w w Knot elongation efficiency (%) Loop distraction (mm) w w w w Figure 4.3: Performance plots for the Biosyn TM suture, size USP with (w) and without adhesive 5

69 Force at loop failure (N) B B B Maximum loopholding force (N) B B B 1 1 w w =1 =1 w w w =1 =1 w Knot type Knot type Loop holding capacity (N) Knot efficiency (%) w w =1 =1 w w w =1 =1 w Knot elongation efficiency (%) C Knot type B C B C B Loop distraction (mm) Knot type w w =1 =1 w w w =1 =1 w Knot type Knot type Figure 4.4: Performance plots for the Biosyn TM suture, size USP 3- with (w) and without adhesive 51

70 Force at loop failure (N) C B C B Maximum loopholding force (N) C B C B 5 5 w w w w 35 9 Loop holding capacity (N) B B Knot efficiency (%) B B w w w w Knot elongation efficiency (%) Loop distraction (mm) w w w w Figure 4.5: Performance plots for the Biosyn TM suture, size USP 5- with (w) and without adhesive 52

71 Force at loop failure (N) Maximum loopholding force (N) w w w w Loop holding capacity (N) Knot efficiency (%) w w w w Knot elongation efficiency (%) (Loop distraction (mm) w w w w Figure 4.6: Performance plots for the Ethilon* suture, size USP with (w) and without adhesive 53

72 Force at loop failure (N) B B Maximum loopholding force (N) B B C C 5 5 w w =1 =1 w w w =1 =1 w Loop holding capacity (N) B B Knot efficiency (%) B B 5 1 w w =1 =1 w w w =1 =1 w Knot elongation efficiency (%) Loop distraction (mm) B B B B w w =1 =1 w w w =1 =1 w Figure 4.7: Performance plots for the Ethilon* suture, size USP 3- with (w) and without adhesive 54

73 2 2 Force at loop failure (N) Maximum loopholding force (N) w w w w Loop holding capacity (N) Knot efficiency (%) w w w w Knot elongation efficiency (%) Loop distraction (mm) w w w w Figure 4.8: Performance plots for the Ethilon* suture, size USP 5- with (w) and without adhesive 55

74 Force at loop failure (N) w Maximum loopholding force (N) w Loop holding capacity (N) w Knot efficiency (%) w Knot elongation efficiency (%) w Loop distraction (mm) w Figure 4.9: Performance plots for the Nurolon* suture, size USP 3- with (w) and without adhesive 56

75 Force at loop failure (N) Maximum loopholding force (N) w w w w Loop holding capacity (N) B w B w Knot efficiency (%) B w B w Knot elongation efficiency (%) w w Loop distraction (mm) w w Figure 4.1: Performance plots for the PDS*II suture, size USP with (w) and without adhesive 57

76 Force at loop failure (N) Maximum loopholding force (N) w w =1 =1 w w w =1 =1 w Loop holding capacity (N) C B C B Knot efficiency (%) C B C B w w =1 =1 w w w =1 =1 w Knot elongation efficiency (%) Loop distraction (mm) B C C B C w w =1 =1 w w w =1 =1 w Figure 4.11: Performance plots for the PDS*II suture, size USP 3- with (w) and without adhesive 58

77 2 2 Force at loop failure (N) Maximum loopholding force (N) w w w w Loop holding capacity (N) Knot efficiency (%) w w w w 6 6 Knot elongation efficiency (%) B B Loop distraction (mm) w w w w Figure 4.12: Performance plots for the PDS*II suture, size USP 5- with (w) and without adhesive 59

78 2 2 Force at loop failure (N) Maximum loopholding force (N) w w w w Loop holding capacity (N) Knot efficiency (%) w w w w Knot elongation efficiency (%) w w Loop distraction (mm) w w Figure 4.13: Performance plots for the Surgidac TM suture, size USP 1 with (w) and without adhesive 6

79 Force at loop failure (N) Maximum loopholding force (N) w w w w Loop holding capacity (N) Knot efficiency (%) w w w w Knot elongation efficiency (%) B B B Loop distraction (mm) B B B w w w w Figure 4.14: Performance plots for the Ticron TM suture, size USP with (w) and without adhesive 61

80 Force at loop failure (N) Maximum loopholding force (N) w w =1 =1 w w w =1 =1 w Loop holding capacity (N) Knot efficiency (%) w w =1 =1 w w w =1 =1 w Knot elongation efficiency (%) B C B C B C Loop distraction (mm) B B w w =1 =1 w. w w =1 =1 w Figure 4.15: Performance plots for the Ticron TM suture, size USP 3- with (w) and without adhesive 62

81 Force at loop failure (N) Maximum loopholding force (N) w w w w Loop holding capacity (N) Knot efficiency (%) w w w w 8 4. Knot elongation efficiency (%) Loop distraction (mm) w w. w w Figure 4.16: Performance plots for the Ticron TM suture, size USP 5- with (w) and without adhesive 63

82 SEM Pictures The first observation that can be stated from viewing the SEM photomicrographs is that the adhesive significantly increased the knot volume. Once polymerized, the adhesive swelled around the knot and between the ears. This was true for all types of suture materials, as seen on Ethilon* and PDS*II material (Figures 4.17 and 4.18). It should be noted that originally, one of the potential advantages of using the adhesive to reinforce a knot was to decrease its volume. s revealed by the SEM images, an additional throw on a size USP 5- suture could be smaller than the simple knot plus the polymerized adhesive. S S Figure 4.17 SEM picture of Ethilon* size USP 5-, knot with adhesive (: dhesive and S: Suture) Figure 4.18 SEM picture of PDS*II size USP 5-, knot with adhesive (: dhesive and S: Suture) Secondly, it was noticed that the adhesive coated and penetrated in between the yarns of the braided suture independently of the suture size (Figures 4.19 and 4.2). In the case of the monofilament suture, the adhesive stayed on the surface and spread around the knot (Figures 4.17 and 4.18). This could explain why the adhesive was more effective in reinforcing the braided sutures. 64

83 + S + S Figure 4.19: SEM picture of Ticron TM size USP 3-, knot with adhesive (: dhesive and S: Suture) Figure 4.2: SEM picture of Ticron TM size USP 5-, knot with adhesive (: dhesive and S: Suture) Finally, when the mechanically tested samples were compared to the initial samples, it can be observed that the absorbable suture materials still had adhesive around the knot after failure (Figure 4.21). This is not the case for the sutures made of nylon where after failure the adhesive is almost totally absent (Figure 4.22). Moreover, in Figure 4.21 b), it can be observed that the type of fracture, according to Hearle et al, was brittle fracture, since it showed an angular displacement along the new fracture surface at the edge of the fibers [42]. S S a. b. Figure 4.21 SEM picture of Biosyn TM size USP 5-, knot with adhesive before (a) and after (b) mechanical test (: dhesive and S: Suture) 65

84 S S a. b. Figure 4.22 SEM picture of Ethilon* size USP 5-, knot with adhesive before (a) and after (b) mechanical test (: dhesive and S: Suture) 4.2 Discussion General Objective s indicated in Chapter 1, the objective of the study was to compare the knot performance of different types of sutures when cyanoacrylate adhesive was used as a reinforcement. The knot security or knot performance was evaluated in terms of six different criteria (force at loop failure, maximum loop-holding force, loop holding capacity, knot efficiency, knot elongation efficiency and loop distraction). fter studying Figures 4.3 to 4.16, an overall improving trend is observed for all six dependent variables when the adhesive was applied to the knotted loops Specific Objectives To go over these results in more detail, and in order to answer the six specific objectives listed in Chapter 1, more statistical analysis was undertaken. lthough most of the variances have been recognized as unequal, according to Yandell [14] the unequal variances do not cause appreciable problems when comparing means. 66

85 Therefore, a two-way analysis of variance was performed to identify the significant influence of the adhesive on the knot performance for each dependent variable Effect of Suture Material The first specific objective was to determine the effect of the suture material on the knot performance when Liquiband TM was applied. In order to do so, two-way analyses of variance were calculated for each type of knot to compare the behavior with and without adhesive on the different materials. The generated p-values will determine whether the material, or the adhesive and/or their interaction significantly influenced the dependent variables. The results are gathered in Table 7.1 in ppendix 7.6. fter an analysis of the p-values obtained and the interaction profiles, it was concluded that the suture material has a significant effect on the knot performance. In general, all materials tested improved their performance with the use of Liquiband TM. However, Nurolon* and Ethilon* were the two materials that showed the least improvement when adhesive was applied, disregarding the size of the suture or the number of throws. These two sutures were both made of nylon polymer. This result agrees with that of Komatsu et al where Surgilon* (nylon multifilament) showed a decrease in the mean tensile strength after the application of the cyanoacrylate adhesive [6]. lternatively, PDS*II and Biosyn TM showed the most significant improvement, more specifically with the force at loop failure, maximum holding force and loop distraction values. This was also the case in the previous study where the adhesive had improved the tensile strength of a PDS*II three throw knot by more than four times [6]. s far as Ticron TM was concerned, this polymer showed improvement in some cases and decline in others, depending on the suture size and knot type. Due to this variation, it is hard to conclude the effect of the adhesive on the braided polyester suture. It is important to remember that this 67

86 Loop distraction Knot elongation efficiency Knot efficiency Loop holding capacity Maximum loopholding force Force at loop failure material demonstrated a significantly larger standard deviation. Table 4.2 represents an example of the results obtained with size USP and knot. Table 4.2: Two-way analysis of variance results for size USP knot with and without adhesive. (No : no adhesive, With : with adhesive, P: PDS*II, E: Ethilon*, T: Ticron TM and B: Biosyn TM ) 2 Material p-value dhesive p-value Material* adhesive p-value Force at loop failure (N) LS Means Maximum loop-holding force (N) LS Means Least Squares Mean Plot P E T B Material P E T B Material No With No With Force at loop failure (N) M ho Maximum loopholding force (N) Interaction Profiles No No With With B P E T B P ET Loop holding capacity (N) LS Means P E T B Material No With Loop holding capacity (N) No BP ET With Knot efficiency (%) LS Means P E T B Material No With Knot efficiency (%) No With P E TB Knot elongation efficiency (%) LS Mean Loop distraction (mm) LS Means P E T B Material P E T B Material No With No With Knot elongation efficiency (%) Loop distraction (mm) Loop distraction (mm) dhesive No No With With B P E T PTB E 2 Points in Least Squares Mean Plot and Interaction Profiles of Tables 4.2 to 4.6 have been linked by different color lines to enhanced the understanding of the trend observed. 68

87 These results could be explained by two different concepts. First, each suture material tested had a different value for surface energetic. Several parameters determine the interaction between a solid (in this case the suture thread) and a fluid (the adhesive). The contact angle of water (θ in Figure 4.23) when tested on nylon and polyester film materials is 68º and 71º respectively [43]. However, once converted into a suture thread, these values could change. Therefore, it is possible to assume that the absorbable sutures, such as PDS*II and Biosyn TM, are likely to have a final contact angle lower than the nonabsorbable sutures such as Ethilon *, Nurolon*, Ticron TM and Surgidac TM, made of nylon and polyester. lower contact angle will allow the liquid adhesive to spread on the suture whereas a higher value will indicate that the fluid will bead up on the surface, creating a weaker bond and hence having a lower reinforcing effect on the knot. Figure 4.23 Contact angle θ formed by a drop of liquid on a solid surface The second theory that could explain the variations of the reinforcing behavior of the adhesive on different suture materials is the moisture content. It should be remembered that Liquiband needs moisture to polymerize and cure. Synthetic absorbable sutures, such as Biosyn TM and PDS*II, undergo hydrolytic degradation when exposed to water in tissues. For this reason, it can be assumed that the moisture content of the absorbable sutures was higher than for the nonabsorbable ones after immersion in the saline bath, and the degree of polymerization of the adhesive would have been enhanced, providing a stronger reinforcement to the knot. This theory is supported by the SEM photomicrographs taken before and after mechanical testing, which showed that adhesive residue remained on the surface of 69

88 the absorbable material after testing (Figure 4.21), but not on the permanent ones (Figure 4.22) Effect of Suture Structure The second specific objective was to determine the effect of the difference in suture structure (monofilament and braided) on the performance of the knot when adhesive was applied. In another words, this objective was interested to evaluate if the adhesive was more active on braided or monofilament sutures. Ethilon* and Nurolon* were both nylon polymer sutures but the former was a monofilament and the latter a braided suture. Their USP and actual diameters were the same (Table 3.4) and the knot used to compare them was. The two-way analysis of variance showed that the braided suture was significantly more reinforced by Liquiband TM than the monofilament. This difference was accentuated with the loop holding capacity and knot efficiency values because the monofilament suture showed a significant fall in mean value when the adhesive was added. The braided suture offers more surface area to the adhesive to penetrate within the structure of the knot and bind the different throws together. Moreover, the effect of capillarity permits braided sutures to hold moisture and provide a better medium for the polymerization of the adhesive compared to monofilament sutures. This can explain why Nurolon* was reinforced more effectively by the adhesive agent. This theory is confirmed by the SEM photomicrographs which are discussed earlier (Figures 4.19 and 4.2). The results of the two-way analysis of variance are located in Table

89 Loop distraction Knot elongation efficiency Knot efficiency Loop holding capacity Maximum loopholding force Force at loop failure Table 4.3: Two-way analysis of variance results for size USP 3- knot of Ethilon* (Mono) and Nurolon* (Braided) with and without adhesive. (No : no adhesive, With : with adhesive) Structure p-value dhesive p-value Structure* adhesive p-value Force at loop failure (N) LS Means Least Squares Mean Plot No Knot With Mono Braided Force at loop failure (N) M Interaction Profiles Mono With No Braided Maximum loop-holding force (N) LS Means Mono Braided h Maximum loopholding force (N) With No No Knot With Mono Braided Loop holding capacity (N) LS Means Mono Braided Loop holding capacity (N) With No Knot efficiency (%) LS Means No No With Knot With Knot Mono Braided Knot efficiency (%) Mono Mono Braided With No Braided Knot elongation efficiency (%) LS Means No Knot With Mono Braided Kn e Knot elongation efficiency (%) Mono No With Braided Loop distraction (mm) LS Means No Knot With Mono Braided d Loop distraction (mm) With No Mono Braided Effect of Suture Coating Two braided polyester sutures were evaluated in this study but with distinctly different coating materials in order to determine the effect of suture coating on the knot performance with and without adhesive. Ticron TM had a silicone based coating 71

90 whereas Surgidac TM had a polybutylene adipate coating. Since the suture materials were not of the same size, it was not possible to compare them directly. This is why the mean value obtained for each dependent variable was divided by the area of the suture (m 2 ), using the diameter obtained in Table 3.4. The obtained values of sizes USP, USP 3- and USP 5- of Ticron TM have been averaged and compared with values of size USP 1 of Surgidac TM in a two-way analysis of variance for knot and knot separately. Overall, the difference in coating did not produce a significant difference in the reinforcing effect of the adhesive on either type of knot. There could be two exceptions with silicone coating which performed better than the polybutylene adipate coating in terms of knot efficiency (knot ) and maximum loop holding force (knot ). The p-values are illustrated in Table 7.11 of ppendix 7.6. It is suggested to try to analyze the same criterion again but with sutures of the same size to avoid the data conversion process. For this reason, it is difficult to conclude about the significance of the impact of the different coating on the reinforcing effect of Liquiband Effect of Suture Size The fourth objective was to determine if the size of the suture could change significantly the reinforcing effect of the adhesive on the knot. To ensure this point, the results from Ethilon*, PDS*II, Ticron TM and Biosyn TM were evaluated separately and two-way analyses of variances were performed for the and knot types (Table 7.12 in ppendix 7.6). In the light of these results, thicker sutures are clearly more positively affected by the adhesive. For every dependent variable, whatever knot size or polymer type, the size USP was more reinforced by Liquiband TM and size USP 5- was the least 72

91 reinforced. Table 4.4 is giving an example of the results obtained for Biosyn TM with knot. The Least Squares Mean plots showed a strong improvement when the adhesive is added. The gradient of the line for size USP climbs steeply whereas the line of size USP 5- is almost horizontal. The only exception is for Ticron TM size USP 3-, which was more affected than size USP. However, it should be remember that Ticron TM generated high standard deviations. The reason that could explain this phenomenon probably lies in the bending rigidity of the suture. The bending rigidity of a round fiber is defined as its resistance to bend and can be calculated with the following formula [43]: where E is the tensile modulus, d the linear density, ρ the density and β a unit constant. Based on this formula, a suture with a thicker diameter has a higher bending rigidity than a finer suture. knotted suture material with a high bending rigidity would be inclined to resist lying in a sharp bending angle and have the tendency to straighten out within the knot. In this case there would have been more room for water and moisture to be trapped within the knot volume after the saline bath immersion, providing a potentially higher degree of polymerization of the adhesive for thicker sutures (Figure 4.24). a) b) Figure 4.24: Low bending rigidity of size USP 5- (a) allows a tight knot with limited room for moisture; the opposite applies to size UPS (b) (green: suture, blue: moisture) 73