Preparation Of Poly(Amino Acid)s And Regulation Of Their Thermo-sensitivity

Now, the temperature-sensitive polymer materials have been applied in the biomedical field such as issue engineering, drug controlled release, bio-separation and enzyme immobilization and so on. The studies about thermo-sensitive polymers have become a current research focus. Because of the specificity in the application, the non-toxicity or good biocompatibility is an inevitable requirement for thermo-sensitive polymers, and also a safeguard to human body. In this paper, several attempts have been made to prepare the polymeric materials with good thermo-sensitivity and biocompatibility by combination of natural amino-acid and adjustability of thermo-sensitivity. Three main parts in this paper are included:First, the literature review section, it includes the introduction of thermo-sensitive polymer materials including their type, synthesis, characterization and applications in the biomedical field.Second, non-cytotoxicity or good biocompatibility is an essential requisite for the thermo-sensitive polymeric materials used in the biomedical fields. In this part, a new poly(morpholine-2,5-dione-co-L-lactide) with excellent thermo-sensitivity and biocompatibility was synthesized from natural L-glycine and L-lactide by Ring-opening polymerization at higher temperature. The chemical structures of the monomers and polymers are characterized by 1H NMR, FTIR spectrum and GPC. Poly(morpholine-2,5-dione-coL-lactide) solution shows a reversible upper critical solution temperature(UCST) of 18-35 ℃, and the thermo-sensitivity is affected by its structure and concentration. The viability of He La cells in 0.01-50 μg/m L poly(morpholine-2,5-dione-co-L-lactide) solution is found to be in a range of 70-85% after 48 h incubation. To sum up, this new thermo-sensitive poly(morpholine-2,5-dione-co-L-lactide) has excellent biocompatibility that makes it a promising material in the biomedical fields.Third, in order to prepare the thermo-sensitive polymer with biocompatibility, the attempts have been made to change or break the interactions of poly(amino-acid) chains, to regulate the hydrophilic and hydrophobic balance by alteration side-groups and co-polymerization. For this purpose, several L-amino-acid N-carboxyanhydrides(NCA) such as L-alanine-N-carboxyanhydride, L-phenylalanine-N-carboxyanhydride, O-tert-butyl-Lserine-N-carboxyanhydride have been synthesized. And also, the copolymer including poly(L-alanine-co-L-phenylalanine), poly(O-tert-butyl-L-serine-co-L- phenylalanine), poly(Lserine-co-L-phenylalanine) and poly(L-alanine-co-epoxypropane) were prepared. The preliminary results showed that the attempts failed to change the hydrophilic and hydrophobic balance in order to regulate the thermo-sensitivity of polymers. Consequently, the relevant adjustments should be made to this study in future.