Oxidative biodegradation mechanisms of biaxially strained poly(etherurethane urea) elastomers

Abstract

As part of ongoing studies in polyurethane biostability and biodegradation, we have investigated an in vitro system to test strained poly(etherurethane urea) (PEUU). Recently, we utilized this system to reproduce in vivo stress cracking in strained Pellethane. In this study, strained PEUU was tested to determine whether it degrades through a common mechanism with Pellethane and to further examine the steps involved in this degradation. Biaxially strained PEUU elastomers were treated with an alpha 2-macroglobulin (alpha 2-Mac) protein solution followed by an oxidative H2O2/CoCl2 treatment. Characterization of the strained PEUU specimens was performed with attenuated total reflectance-Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), electron spectroscopy for chemical analysis, and contact angle analysis. The results from these characterization techniques provide conclusive evidence that biodegradation of PEUU and Pellethane occurs through a common mechanism. Chemical changes to the PEUU include cleavage of the polyether soft segments and urethane linkages, leaving the hard segment domains unaffected. SEM analysis shows that this chain cleavage leads to the development of severe pitting and cracking of the PEUU surface. In addition, the in vitro degradation accurately reproduces the in vivo degradation chemically and physically. This result verifies that the primary species responsible for biodegradation of PEUUs, in vivo, are hydroxyl and/or hydroperoxide radicals. alpha 2-Mac pretreatment increases the rate of degradation compared to direct treatment in H2O2/CoCl2. As the PEUU soft segment chains are cleaved, the degradation products are extracted into the treatment solution or environment. Finally, a new biodegradation mechanism of PEUUs is presented that involves crosslinking of the polyether soft segments.

The use of CD47-modified biomaterials to mitigate the immune response

“…81,82 This normal host response causes soft segment chain scission and aberrant crosslinking of the polyether or polycarbonate soft segments, which is then grossly observed as surface cracking of the poly(ether urethane) components of the cardiovascular device. [83][84][85] Microscopic evidence of surface degradation has been observed by others and us to be present as early as 90 days post implantation. [83][84][85][86] With respect to pacemaker leads, which commonly use polyurethane insulation, the duration from implantation to device failure has been shown to be as short as $2.5 years.…”

In vivo biocompatibility and biostability of modified polyurethanes

“…It has been shown that biodegradation can be monitored in polyether polyurethanes by peak height analysis of the peaks associated with ether, methylene, and urethane linkages. 3 Other bands that show changes due to biodegradation are: 1367 cm −1 , (CH 2 ) from the ␣-carbon of the PTMG; 1709 cm −1 , hydrogen-bonded urethane carbonyl; and 1730 cm −1 , nonhydrogen-bonded urethane carbonyl. The 1174 cm −1 band is attributed to degradation products in the polyether polyurethanes, and this band has been assigned to a branched ether created by crosslinking of the soft segment.…”

“…The 1174 cm −1 band is attributed to degradation products in the polyether polyurethanes, and this band has been assigned to a branched ether created by crosslinking of the soft segment. 3 Since SPU-S is a polyether polyurethane with polydimethylsiloxane endcaps, the 1260 cm −1 (C−H of Si−CH 3 ) and 800 cm −1 (Si−C) also were examined for any changes. 19 Peak height analysis on SPU-C and SPU-PCU, with the polycarbonate soft segment, was done on the 1740 cm −1 (C=O) band associated with the carbonate linkage.…”

“…In order to reduce the oxidation of the soft segment, antioxidant additives, such as Santowhite and others, have been used. 3,4 Modifications or substitutions of the soft segment have been made to enhance biostability. The soft segment chemistries have been varied by substituting the polyether segment with a polybutadiene, polydimethylsiloxane (PDMS), 5 polycarbonate, [6][7][8][9][10][11] and aliphatic hydrocarbon segment.…”

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 …”