Polyurethanes degradation characteristics

It is believed that most of PUR biodegradation occurs by the action of esterases, however polyester-polyurethane degrading enzymes have been purified and their characteristics have been reported. These enzymes have a hydrophobic binding domain at the surface of the PUR, and a catalytic domain [22]. But there is no evidence that the urethane linkage has been broken. 

S. Davaran, M.R. Rashidi, J. Hanaee, A. Khani, M. Mahkam, M. Hashemi, Synthesis and degradation characteristics of polyurethanes containing azo derivatives of 5-amino salicylic acid, J. Bioact. Compat. Polym. 21 (2006) 315-326. 

In dentistry, silicones are primarily used as dental-impression materials where chemical- and bioinertness are critical, and, thus, thoroughly evaluated.546 The development of a method for the detection of antibodies to silicones has been reviewed,547 as the search for novel silicone biomaterials continues. Thus, aromatic polyamide-silicone resins have been reviewed as a new class of biomaterials.548 In a short review, the comparison of silicones with their major competitor in biomaterials, polyurethanes, has been conducted.549 But silicones are also used in the modification of polyurethanes and other polymers via co-polymerization, formation of IPNs, blending, or functionalization by grafting, affecting both bulk and surface characteristics of the materials, as discussed in the recent reviews.550-552 A number of papers deal specifically with surface modification of silicones for medical applications, as described in a recent reference.555 The role of silicones in biodegradable polyurethane co-polymers,554 and in other hydrolytically degradable co-polymers,555 was recently studied. 

FIGURE 2. The absorbance at 508 nm vs. time for four thin films of the polyurethane synthesized by equation 3. Only the sample exposed to both light and air degraded. The absorbance at 508 nm is characteristic of the metal-metal bond. The differences in absorbance at time = 0 are due to different thicknesses of the various samples. 

Polymers can be classified in various ways. The most obvious is to think of them as either being natural or synthetic. This is the classification used in this book. Alternative ways of classification are based on their use (structural and non-stmctural polymers) and their characteristics (degradable and non-degradable polymers). These aspects are discussed in the first chapter. This chapter will give an overview of the synthetic and natural degradable polymers. However, overall, the book focuses on the synthetic polymers used for biomedical appfications. Amongst the class of synthetic polymers, this chapter will discuss polyesters, polycarbonates, and polyurethanes, the most commonly used synthetics polymers for biomedical appfications. 

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