Poly tensile strength changes

Poly((3-PL) has been hydrolytically degraded in a buffered salt solution (pH 7.2) at 37 °C [125,175], Oriented fibers and unoriented fibers showed different mechanical properties on degradation. The changes in tensile strength were slower for the oriented material. The molecular weight decreases rapidly during the first 50 days while the crystalline phase increases, probably due to an anneal-ing-like effect caused by the temperature at which the degradation was performed and rapid water absorption [175]. 

Implanted polymeric materials can also adsorb and absorb from the body various chemicals that could also effect the properties of the polymer. Lipids (triglycerides, fatty acids, cholesterol, etc.) could act as plasticizers for some polymers and change their physical properties. Lipid absorption has been suggested to increase the degradation of silicone rubbers in heart valves (13). but this does not appear to be a factor in nonvascular Implants. Poly(dimethylsiloxane) shows very little tensile strength loss after 17 months of implantation (16). Adsorbed proteins, or other materials, can modify the interactions of the body with the polymer this effect has been observed with various plasma proteins and with heparin in connection with blood compatibility. 

Figure 4.11 Changes of the tensile strength of poly-L-lactide (PLLA), PTLA, and PTLGA...

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