In vivo biocompatibility and biostability of modified polyurethanes Anshu B. Mathur, 1 Terry O. Collier, 2 W. John Kao, 1 Michael Wiggins, 1 Mark A. Schubert, 1 Anne Hiltner, 1 and James M. Anderson 1,2,3, * Departments of 1 Macromolecular Science, 2 Biomedical Engineering, 3 Institute of Pathology, Case Western Reserve University, 2085 Adelbert Road, Cleveland, Ohio 44106 Modified segmented polyurethanes were examined for bio- stability and biocompatibility using an in vivo cage implant system for time intervals of 1, 2, 3, 5, and 10 weeks. Two types of materials were used: polyether polyurethanes and polycarbonate polyurethanes. Two unmodified polyether polyurethanes (PEUU A' and SPU-PRM), one PDMS end- capped polyether polyurethane (SPU-S), and two polycar- bonate polyurethanes (SPU-PCU and SPU-C) were investi- gated in this study. Techniques used to characterize untreated materials were dynamic water contact angle, stress–strain analysis, and gel permeation chromatography. Cellular response was measured by exudate analysis and by macrophage and foreign body giant cell (FBGC) densities. Material characterization, postimplantation, was done by at- tenuated total reflectance-Fourier transform infrared spec- troscopy (ATR-FTIR) in order to quantify biodegradation and scanning electron microscopy (SEM) to qualitatively de- scribe the cellular response and biodegradation. The exudate analysis showed that the acute and chronic inflammatory responses for all materials were similar. Lower FBGC den- sities and cell coverage on SPU-S were attributed to the hy- drophobic surface provided by the PDMS endgroups. The polycarbonate polyurethanes did not show any significant differences in cell coverage or FBGC densities even though the macrophage densities were slightly lower compared to polyether polyurethanes. By 10 weeks, biodegradation in the case of PEUU A' and SPU-PRM was extensive as compared to SPU-S because the PDMS endcaps of SPU-S provided a shield against the oxygen radicals secreted by macrophages and FBGCs and lowered the rate of biodegradation. In the case of polycarbonate polyurethanes, the oxidative stability of the carbonate linkage lowered the rate of biodegradation tremendously as compared to the polyether polyurethanes (including SPU-S). The minor amount of biodegradation seen in polycarbonate polyurethanes at 10 weeks was attrib- uted to hydrolysis of the carbonate linkage. © 1997 John Wiley & Sons, Inc. INTRODUCTION Segmented polyurethanes (SPUs) have been used extensively as biomaterials because of their biocom- patibility as well as for their desirable physical prop- erties, such as strength and flexibility. 1 Polyester poly- urethanes have been used as catheters, gastric bal- loons, and Meme prostheses, but they were found to be unstable in acidic environments. 2 The acid-cata- lyzed hydrolysis of the ester linkage promotes further degradation of the polyester polyurethane by cleaving the urethane linkage. Polyether polyurethanes were introduced as pacemaker lead insulators due to their hydrolytic stability 2 ; however, polyether polyure- thanes containing polyether soft segments are suscep- tible to oxidative cleavage in vivo. In order to reduce the oxidation of the soft segment, antioxidant addi- tives, 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 seg- ment chemistries have been varied by substituting the polyether segment with a polybutadiene, polydimeth- ylsiloxane (PDMS), 5 polycarbonate, 6–11 and aliphatic hydrocarbon segment. 11 Hergenrother et al. 12 and Lim et al. 13 were motivated to incorporate PDMS as the soft segment in the polyurethanes due to attractive PDMS properties, such as good blood compatibility, low toxicity, good thermal and oxidative stability, low modulus, and their anti-adhesive nature. It has been shown that the polycarbonate soft segment is less likely to be cleaved via oxidation although hydrolysis of the carbonate linkage is possible. 6–9 Ward et al. 14 conducted in vitro experiments to test the hydrolytic stability of a polycarbonate polyurethane, and in vivo *To whom correspondence should be addressed. Journal of Biomedical Materials Research, Vol. 36, 246–257 (1997) © 1997 John Wiley & Sons, Inc. CCC 0021-9304/97/020246-12