Polymers, biodegradable degradation mechanisms

Liebmann-Vinson A, Timmins M (2003), Biodegradable polymers Degradation mechanisms, part 2, in PBM Series, vol. 2, Citus Books, 329-372. 

The mechanical properties that are most often measured during biodegradable polymer degradation experiments are stiffness, strength, and elongation-at-break. These mechanical properties are influenced by a large number of factors, the most important... 

Some other degradation mechanisms other than simple hydrolysis are presented for biodegradable polymers. Such mechanisms include oxidative cleavage by a radical mechanism. Oxidative degradation is the main mechanism for non-hydrolyzable polymers, such as polyolefins, natural rubber, lignins, and polyurethanes. For many polymers, hydrolysis and oxidation occur simultaneously in the environment. 

Fig. 3. Mechanisms for polymer degradation. The illustration is a schematic representation of three degradation mechanisms I, cleavage of cross-links II, hydrolysis, ionisa tion, or protonation of pendent groups III, backbone cleavage. Actual biodegradation may be a combination of these mechanisms.

Aliphatic polyesters are the most economically competitive of the biodegradable polymers moreover, synthetic polyesters are expected to be degraded nonspecifi-cally by lipases. Although these polyesters are biodegradable, they often lack good thermal and mechanical properties. On the other hand, aromatic polyesters - such as... 

Poly(esters) (Table 11.2) are the first class of polymers discussed, as they are the most widely investigated of all of the polymer families for oral protein delivery. Poly(esters) used for oral drug delivery have primarily been biodegradable polymers (Figure 11.1). Biodegradation is the primary delivery mechanism for poly(ester) polymers used for protein and peptide delivery. The degradation properties of poly(esters) are dependent on the monomers used to produce the poly(ester). Several poly(esters) are discussed in detail in the following sections. 

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