Effect of strain and strain rate on fatigue‐accelerated biodegradation of polyurethane

Abstract

A diaphragm-type film specimen was used to study in vitro degradation of poly(etherurethane urea) (PEUU) under conditions of dynamic loading. This geometry allowed both uniaxial and biaxial loading in a single experiment. During testing, the film was exposed to a H(2)O(2)/CoCl(2) solution that simulated in vivo oxidation of PEUU. The combination of dynamic loading and biaxial tensile strain accelerated oxidative degradation. The effects of biaxial strain magnitude and strain rate were examined separately by increasing the frequency of fatigue loading from 0 to 1 Hz with constant maximum biaxial strain and by changing the maximum biaxial strain while maintaining constant strain rate. In the ranges of biaxial strain energy (0.17 to 0.55 MPa) and strain rate (0 to 46% s(-1)) tested, the rate of degradation increased with increasing strain rate whereas strain magnitude had essentially no effect on degradation rate. Although loading conditions affected the rate of oxidative degradation, ATR-FTIR analysis suggested that in all cases the mechanism of degradation did not change. Chemical degradation produced a brittle crosslinked surface layer marked by dimpling and pitting, as observed with scanning electron microscopy. Pits served as stress concentrators and initiated environmental stress cracks under dynamic loading but not under static (creep) loading. Small pits were sufficient to initiate cracks at higher strain rates whereas only large pits initiated cracks at lower strain rates. Consequently, a higher strain rate produced more profuse cracking.

Deformation-induced hydrolysis of a degradable polymeric cylindrical annulus

“…Furthermore, the applied strain itself, in the absence of a chemically reactive environment, did not change the mechanical properties of the suture. With polyurethane (on which the degradation mechanism is oxidation), Wiggins et al (Wiggins et al 2003) found that the degradation rate of polyurethane increased with increasing cyclic strain rate, while the magnitude of the strain magnitude had essentially no effect. Their experiments employed a circular membrane device in which pressure was applied to one side of the membrane, causing it to deflect into a well.…”

Mechanical characterisation of polyurethane elastomer for biomedical applications

“…This is 303 adequately covered in literature (Stokes et al, 1995;Wiggins et al, 2003;Thoma, 1987;Schmidt et 304 al., 1998;Zhao et al, 1990Zhao et al, , 1991Wu et al, 1992;Schubert et al, 1995Schubert et al, , 1997 …”

“…Their superior mechanical properties and 10 blood compatibility has favored their use and development as biomaterials, particularly as 11 components of implanted devices (Lamba et al, 1997). Polyurethane elastomers offer superior 12 mechanical properties over silicone elastomers, particularly in relation to tear and abrasion, and flex-13 fatigue life (Wiggins et al, 2003). The chemical composition of these elastomers offers substantial 14 opportunities to synthetic polymer chemists to tailor the structures to meet specific requirements.…”

“…Much research and developments have 21 been done in achieving polyurethanes with excellent biostability with a combination of good 22 mechanical properties and biocompatibility. Polyurethanes used in chronic implants are subject to 23 hostile in vivo conditions which can lead to their failure (Stokes et al, 1995;Wiggins et al, 2003;24 1997).…”

Biodegradable Stents: Biomechanical Modeling Challenges and Opportunities

“…Wiggins et al 78 found that the degradation rate of polyurethane increased with increasing cyclic strain rate, whereas strain magnitude had essentially no effect. Their experiments employed a circular membrane device in which vacuum was applied to one side of the membrane, causing it to deflect into a well.…”