| Poly(β-L-malic acid)(PMLA) is a natural aliphatic polyester, and it was proved to be biodegradable, non-toxic and non-immunogenic. Furthmore, it could provide multiple suspend carboxyl to form polymer pro-drugs. However, Its strong hydrophilicity and fast degradation time limits its application. Poly(β-hydroxybutyrate)(PHB) is a thermoplastic polyester produced by a bacterial fermentation, and it has good biocompatibility. But it is strongly hydrophobic and shows long degradation time. In this study, PHB was used to modify PMLA, realizing complementary advantages.The copolymer was synthesized by ring-opening polymerization of benzyl β-malolactone(MLABe) and β-butyrolactone(BL), using tetraethylammonium benzoicacid as initiator. Ratio of the two monomers, reaction times, temperaturesand adding orders were studied to examine the impact of these factors on the copolymerization.Two monomerswere added simultaneously or successively,and two different hydrophobic polymers were obtained: random copolymers P(MLABe-co-BL) and block copolymers PMLABe-co-PHB. Amphiphilic copolymers P(MLA-co-BL) and PMLA-co-PHB were obtained by hydrogenation.The synthetic process of benzyl β-malolactone monomers was optimized before the copolymerization.In our previous study,the initiator tetraethylammonium benzoate was used to trigger the ring-opening polymerization to form PMLA. However, this study still needed to confirm if the initiator can also trigger the polymerization of β-butyrolactone. 1H-NMR, 13C-NMR and FT-IR were used to characterize the polymer poly(β-hydroxybutyrate)(PHB). The results showed that the initiator could be used to initiate the polymerization of β-butyrolactone, which laid the foundation for copolymerization reaction.Research on polymerization process of the random copolymer P(MLABe-co-BL) showed that there was a significant differences in the composition of the copolymerswhen different ratio of monomers added. Scale of micro polymerization mechanism indicated that the ratioof MLABe and BL is 50/50(mol/mol), which resulted in severetransesterification in the polymerization process, tended to random copolymerization.When the ratio was 75/25(mol/mol), copolymerization productsobtained in short time which have moderate molecular weight and narrow distribution width.Therefore, all of the subsequent polymerization experiments used this ration.The hydrophilicity, degradability and solubility of P(MLA-co-BL) and PMLA-co-PHB were between that of P(MLABe-co-BL) and PMLA, which could overcome the shortcomings of PMLA, such as fast degradation and stongly negative charge. In vitro cytotoxicity study found that P(MLABe-co-BL) showed certain cytotoxicity.The resultof hemolysis assay suggested that P(MLABe-co-BL) possess good biocompatibility. P(MLA-co-BL) did not inhibit cell growth at low concentrations(0.4 mg/m L or less). A slight inhibition would happen with increasing concentration to 0.8 mg/m L.Accordingly, the block copolymers PMLA-co-PHB with increasing concentration did not exhibit cytotoxicity.In hemolysis test, the concentration of material at 0.2 mg/m L, hemolysis rate of random copolymer is 0.5543 ± 0.05 %, less than that of block copolymer, 3.249 ± 0.04 %. This suggested that random copolymer may be easier to form micelles in aqueous solution compared to block copolymer. With the increasing of concentration of material, cells turned into brown and settled onto the bottom.The research of nanomicelles formed by PMLA-co-PHB block copolymer used as drug carriers was further studied in this subject. Tryptanthrin severed as a drug model, drug loaded nanosphere was prepared by dialysis method. Entrapment efficiency is 8.35 ± 0.29 %, drug-loaded rate is 2.67 ± 0.2 %, and particle size is 242 nm. The results provided a preliminary experimental basis that PMLA-co-PHB used as Polymer nano drug delivery system. The next step in this work is to develop PMLA-co-PHB as drug carriers, and exploit the application of P(MLA-co-BL) in tissue engineering scaffolds. |
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