a biomaterial, a sham- rgical proc ale for the edure group is often included inv
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a biomaterial, a sham- rgical proc ale for the edure group is often included involving the comple out implanting the biomaterial. What is the rationauults? (5 points) experiments to evaluate the tissue response to In ex but with inclusion of th s control group, and how to interpret the Please rank the following three materials on glass transition temperature lowest to highest, and rationalize your answer: (5 points) a) Poly(styrene) b) Poly(acrylonitrile) H CN CN H CN H HHH H CNHHH c) Poly(tetrafluoroethylene)Explanation / Answer
3. When tissue response to a biomaterial is analyzed, the biomaterial will be implanted in the tissue and effects will be analyzed. However, it is difficult to assess whether the responses observed in the tissue is due to the biomaterial or the surgical procedure. Every experimental design has to have a control group. The sham surgeries are the control group in the experimental design. A sham surgery determines the placebo effect in the experiment. The sham surgery group will involve performing the surgery without implanting the biomaterial in tissue. In this sham group, false positive results are excluded. All tissue responses due to surgery wounds in the experimental group would be negated when compared to the sham group. Hence, only specific responses to the biomaterial can be deciphered. It also accounts for mental responses to the surgery in the experimental group. If there are inflammatory responses detected in the experimental group, a sham surgery would indicate whether these inflammatory responses are due to the biomaterial or the surgery itself. Sham surgeries remove all bias from the experimental results.
When a biomaterial is implanted in a tissue, host reactions will be initiated, which includes injury, blood-material interactions, matrix formation, acute and chronic inflammation, development of granulation tissue development, etc. Injury to the tissue will activate coagulation and complement system, the fibrinolytic system, the kinin-generating system, and platelets. Surgical wounds will also activate these responses. Hence, responses need to be quantified in both experimental and sham treated groups. Only if there is a significant increase in the proteins involved in these processes as compared to the sham surgery group, the responses are attributed to the biomaterial. Further, any response not exhibited by the sham group will be a genuine response in the tissue to the biomaterial.
4. Glass transition is specific to polymers wherein polymer hardens below the specific glass transition temperature (Tg). At Tg, they convert to the glassy state. The polymer molecules can move easily and hence, the polymer can be bent in any structure. At temperature below Tg, the polymer will harden and the molecules cannot move. Hence, the stress laid on them is released. It indicates the brittleness of the polymer.
Polystyrene is a thermoplastic hard polymer that is solid at room temperature. Its glass transition temperature is 1000C. (approx 1070C), where it forms glass. Due to this Tg it has medium to high tensile strength, but low impact strength. It Tg allows it to be converted into products like foams, films and sheets. PS is a an electrical insulator, and its lack of crystallinity give it optical clarity. The Tg depends on the thickness of film. They have linear polymers without crosslinks. Tg decreases as the water absorption of the network increases i.e. if more water molecules are associated with the polymers.
Polyacrylonitrile (PAN) has a Tg of approximately 87-960C while polytetrafluoroethylene (PTFE) has a Tg of 1300C. PAN is a linear homopolymer that is highly crystalline. It has high number of nitrile groups and is insoluble. It produces yield to form a thermally stable, highly oriented, graphite like molecular structure. It has linear side chains.
PTFE, a semi-crystalline polymer, is insoluble in all solvents and resistant to acids and caustic materials. high melt viscosity makes it ideal for industrial and engineering use. Extensive chain lengths of the polymers make it impossible for the polymers to crystallize. The unique structure of PTFE gives it considerable strength at melting point of around 400°C.
Polyacrylonitrile has the lowest Tg of 87-960C, followed by polystyrene with Tg of 1000C and then PTFE with a Tg of 1300c. Tg are determined by chain stiffness that is dependent on bulky side groups. PAN are linear with CH groups while polystyrene are linear polymers with ring side chains and no crosslinks. PTFE are polymers with bulky side chains. Hence, PTFE has the largest Tg due to Fluoride side chains, making them more stiff.
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