Tailoring polylactide degradation: Copolymerization of a carbohydrate lactone and s,s-lactide
Tang M., Dong Y., Stevens MM., Williams CK.
A series of copolymers are reported, synthesized via the random copolymerization of acetic acid 5-acetoxy-6-oxotetrahydropyran-2-yl methyl ester (1), and S,S-lactide. The copolymers are characterized by 1H NMR spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and static water contact angle measurements. Four different copolymer compositions are obtained with 1 (RP1), 6 (RP2), 11 (RP3), and 25 wt % (RP4) of ring-opened monomer 1 incorporated with ring-opened S,S-lactide, and these are compared with a sample of poly- (S,S-lactide) (P-S,S-LA) of related number-averaged molecular weight. As the loading of ring-opened monomer 1 increases, the glass transition temperatures of the copolymers decrease, in line with the values calculated using the Fox equation. The glass transition temperatures can, therefore, be controlled within the range 55 °C(RP1)-46 °C(RP4). The copolymers are spin-coated onto glass or electrospun into fibers and the static water contact angles determined. The static water contact angles, measured for either the fibers or the films, depend on the loading of ring-opened monomer 1 in the copolymers. The contact angle for RP4 is ̃7° lower than that of P-S,S-LA. The degradation of the copolymers is studied using size exclusion chromatography (SEC) conducted using samples in phosphate buffered chloroform solutions, enabling determination of the degradation rate constant. The degradation experiments show that as the loading of ring-opened monomer 1 in the copolymers increases, the degradation rate constants increase; thus, RP4 degrades̃4 times faster than P-S,S-LA or RP1. Electrospun fibers of the copolymers are used to assess cell viability and growth. The viability of human osteogenic sarcoma Saos-2 cells on RP4 electrospun fibers is significantly higher than that on RP1, RP2, and P-S,S-LA fibers (p < 0.05). © 2010 American Chemical Society.