Bio-sample testing on an adaptation to a tensile testing machine Design Team Collin Creegan, Sarah Chamberland Kristine Murphy, Christine Sniezek Design Advisor Prof. Kai-Tak Wan Abstract The purpose of the Synergetic Bio-system project is to streamline the tensile testing process for a bio-material in a liquid environment. The goal is to develop mechanical grips, an environmental chamber, and a transporting mechanism that will fit the specifications of the TA.XT tensile testing machine available in the lab. The whole system must be easily sterilized and emptied to be available for later testing and it is imperative that the sample not be contaminated, dehydrated, or damaged during testing. The grips must be delicate enough to not damage the sample but strong enough to prevent slippage. They must also survive in a liquid environment. The chamber must be small enough to fit the limits of the TA.XT machine, but big enough to hold the grips. The transporting mechanism must transfer the sample from a Petri dish to the grips in under two minutes. Additionally, the sample must be accessible to photographic documentation while it is within the chamber during testing. A laser will also pass through the sample to measure light deflection. The proposed product will be used by students to conduct research on the response of bio-materials to tensile tests in specific liquid environments. The proposed product consists of different components shown below. Not shown below are the liquid loading system, a temperature control system, and an electromagnet which are also included with the system. Cradle and Arm Top Grip Enclosure Parallel Brackets Bottom Grip Electromagnet Holder Base Plate
The Need for Project Mechanical testing of materials Tensile testing is an important analytical tool to characterize under tensile load, specifically natural and prosthetic biomaterials. By performing tensile tests, the bio-materials, is important to viscoelastic properties such as strain, elastic modulus and deformation extract viscoelastic properties of of various tissues can be quantified and subsequently utilized to better the sample. understand the materials being used, fixed, or designed. The results from testing bio-materials will assist in solving problems in the biomaterial field by providing the characteristics of bio-materials and how they react in a biological environment and with varying biological liquid reagents. This testing can be used in research of prosthesis development and modes of failure in human and animal tissues. Currently, there is a need for an adaptation to the existing tensile testing machine. The machine cannot perform testing on bio-materials in a liquid environment, nor does it have the capability of performing tensile tests on soft and malleable bio-materials like corneas. The new design will overcome such shortcomings. The Design Project Objectives and Requirements The objective is to construct a Design Objectives system that will allow for the The objective of this project is to construct a system that will allow loading and subsequent testing of for the loading and subsequent testing of the viscoelastic properties of a the viscoelastic properties of a soft bio-material on the universal testing machine known as TA.XT soft bio-material. texture analyzer (Figure 1). The machine measures the applied load as a function of actuator displacement. Design Requirements The design requirements of this project include preventing contamination and dehydration of the sample. Also, there are requirements for the different components of the system. To begin, both the top and bottom grips must hold the sample within a liquid environment and must not damage the sample or grips. The system must also work within the constraints of a Petri dish. The top grip will be used to remove the sample from the Petri dish to place the sample in Figure 1 TA.XT Texture the enclosure. The sample must also be removed from the system in a Analyzer way that will allow the sample to be used for future testing. The system must also be easy to use with little to no prior experience. Also, the system must have a liquid loading and unloading system as well temperature control. The sample must be immersed in a liquid environment throughout the griping, transferring, and testing processes.
Design Concepts Considered Five candidate design concepts The first iteration of the TA.XT adaptation consisted of a platform were developed of which two that would lift the container around the grip faces, submerging the fully meet the requirements. sample once it was fully raised. The design was created prior to receiving more specific design constraints and had a volume of approximately 1liter. The idea was to have an actuator lift the entire platform up and along a rod that housed the bottom grip and would stay lifted throughout testing (Figure 2). The grips would be pressed together using a calibrated screw and a series of pins would guide the grip faces towards each other along a straight line. The second iteration involved a change in grip styles. In order to streamline the process, the focus design was grips that functioned as a tool to pick up the sample in the liquid as well as the functional grip component used during testing. To accomplish this, a design of a Figure 2 Design 1 forcep-like grip with a block on the top was developed. The block fit into a component that was affixed to the arm of the TA.XT for easy loading. The main problem with this design was that by simply slipping the block into the adapter on the arm, it would be difficult to ensure that there was no vertical movement of the block within its cradle during testing. This vertical movement would falsify the results of the test so different grip styles were investigated. The third iteration came about after the constraints were further defined to include a desired chamber volume of 3.5mL. In order to conform to this requirement an adaptation to the original actuating platform design was developed. The container would be 70mm tall, Figure 3 Design 3 10mm wide and 5mm thick (Figure 3). The grip faces would be on the top of the actuating rod and the 3.5mL container would rise up to submerge the sample throughout testing. It was determined that by using an actuator, the design was much more complicated than it needed to be, so the design was completely changed for the fourth iteration. The fourth iteration is composed of a metal enclosure, with a rectangular hole cut out of the middle to be the liquid chamber. The chamber would be sealed with plates of glass, through which scattered light could be observed. The grips were similar to the first iteration in that they were closed with screws (Figure 4). Unfortunately the grips Figure 4 Design 4 could not be designed small enough to fit in the new constraints, and
Recommended Design Concept the grip design was changed once more to the current iteration. The recommended system design Design Description components consist of a cradle The recommended system design components consist of a cradle and arm, an enclosure, top and and arm, an enclosure, top and bottom grips, parallel brackets, an bottom grips, parallel brackets, electromagnet holder, a base plate to attach to the bottom of the electromagnet holder, a base TA.XT, and a project box to house all the electronic components. plate, and a project box. The purpose of the cradle and arm is to attach the top grip to the TA.XT. The top of the cradle contains a space for a screw to attach to the arm of the TA.XT. The cradle and arm consists of a box-like structure with a swinging arm that will hold the block of the top grip as seen in Figure 5 without the top grip. The arm will swing down and secure the block of the top grip to the back of the cradle with a screw, which will make sure the top grip is immobile within the cradle. The next component is the enclosure shown in Figure 6. The Figure 5 Cradle and Arm enclosure holds the sample in both the top and bottom grip as well as holds the liquid in which the sample will be tested. The enclosure will be sealed with a layer of rubber on one side and glass plates covering both sides. One of the glass plates will be fixed and one will be removable, for easy placement of the sample in the bottom grip once the top grip lowers the sample into the enclosure. The enclosure will be attached to the base of the TA.XT by the base plate using screws. The enclosure also holds the thermocouple and heating pads for the temperature control. The enclosure contains channels milled into it to allow for the liquid loading system. Figure 6 Enclosure The top grip is made of stainless steel and is shown in Figure 7. The top is connected to a block to be placed in the cradle. The bottom part of the top grip closes together and holds the sample between a gripping material of blown PVC. The top grip is held together by the forces of magnets placed in the slots directly under the block of the top grip. The first part of the bottom grip is made of a rectangular piece of magnetic steel and placed in the enclosure to meet the second part of the bottom grip, which has been machined out of the enclosure. The first part of the bottom grip swings up to meet the second part and holds the material between the gripping material with Figure 7 Top Grip the use of an electromagnet. The parallel brackets hold the glass plates in place and compress
the rubber in order to seal the enclosure to make sure no leaking occurs. The brackets slip over the top of the enclosure and hold the glass securely in place. The electromagnet holder (Figure 8) holds the electromagnet to the surface of the glass plate so the second part of the bottom grip will securely hold the sample to the first part of the bottom grip. The power needed by the electromagnet is found in the project box. The base plate fixes the enclosure to the base of the TA.XT and also holds magnet holder steady next to the enclosure (Figure 9). Figure 8 Electromagnet The project box holds all of the electronic components for power Holder for the electromagnet and the temperature control. Analytical Investigations One of the analytical investigations performed includes the measurement of force applied to a sample with different forces of magnets. Experimental Investigations Figure 9 Base Plate One of the experimental investigations performed includes the testing of different gripping materials for usability and how the material would react to testing in a liquid. Key Advantages of Recommended Concept One of the key advantages of the recommended concept include that because the system is broken up into different components, the different components can be adapted and modified separately and not all of the components would need to be affected. Financial Issues The price of this prototype totals The main components which would need upkeep include gripping approximately $900. material after numerous tests, glass covering the enclosure if the glass Maintenance and upkeep of this were to break, rubber sealing the container from spilling the liquid, prototype will be approximately magnets if they should break, and syringes. $100 every two years. Recommended Improvements An improvement on the liquid Along with the improvement of the liquid loading, the loading loading system would be an and unloading of the magnets into the top grip can be improved. automated loading system. Another improvement includes a better gripping material that does not allow for dehydration but also does not need to be switched out of experimentation right after testing.