Poly copolymers with different PLLA

Various copolymers with a high PDO content have been synthesized and studied to improve the mechanical performance and increase the rate of resorption [40]. A copolymer with 80 % PDO and up to 20 % PGA has a resorption profile similar to Dexon and Vicryl and yet maintains a compliance similar to PDS . The copolymer with 85 % PDO and up to 15 % PLLA exhibits higher compliance and a lower modulus than the PDO homopolymer, yet its resorption profile is similar to PDS [41]. Copolymers with three or more different monomer units have also been explored. One such example is poly(GA-co-PDO-co-LA), which has been proposed as a possible suture material with suitable crystallinity, good flexibility, better strength retention, and a reasonably rapid resorption rate [42]. Until recently, there was not much interest in developing PDO as a biomaterial, mainly because of the lack of commercial availability and difficulties in its synthesis. However, with the development of new alternative synthesis procedures and the availability of the PDO monomer, there has been more commercial interest in developing PDO as a bioresorbable polymer in recent years (Table 4.6). 

The commercial forms of PLA are the homopolymer poly(L-Lactide) (L-PLA or PLLA) and the copolymer poly(D,L-Lactide) (D,L-PLA or PDLLA), which are produced from L-lactide and D,L-lactide, respectively. The L-isomer constitutes the main fraction of PLA derived from renewable sources, since the majority of lactic acid from biological sources exists in this form [43]. Polylactides (PLAs) exhibit different properties depending on the D/L unit radio and sequence distribution. Generally, the crystallinity of PLLA and PDLA decreases with increasing racemic content. PLA polymers with an L-content >90% tend to be semicrystalline, while those with a lower optical purity are generally amorphous [43-45]. 

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