Viscoplasticity of parylene-C film at body temperature

As parylene-C, a thermal plastic, has been extensively used as an implant material, its viscoplastic behavior at body temperature has never been systematically studied. Presented here is the first extensive in vitro study of the viscoplastic behaviors of 20-μm-thick parylene-C film at 37°C. The viscoplastic behaviors are investigated by uniaxial tensile tests at different strain rates (Figure 2), cyclic loading/unloading test (Figure 3) abrupt strain rate changing (Figure 4), creep-recovery (Figure 5), and stress-relaxation (Figure 6). There are three major conclusions here. First, below a stress of 2.5MPa, no observable viscoplastic behavior of 20-μm-thick parylene-C is found. Secondly, parylene-C film is a strain (or stress) and strain-rate dependent viscoplastic material. Thirdly, Burger's model is adequate to describe both creep and stress relaxation behaviors. In addition, the rate of the creep recovery (modeled with a single time constant) and stress relaxation (modeled with two time constants) decreases with increasing applied stress and/or strain.