The Modified Poly (DL-lactic Acids) And Their In-vitro Degradation And Cell Compatibility

Poly(DL-lactic acid) (PDLLA) with ultra-high molecular weight was prepared and a series of bulk modifications (non-surface modifications) of PDLLA were carried out with maleic anhydride(MAH), ethylenediamine and collagen type Ⅰ, aiming to develop an ideal PDLLA-based tissue engineering biomaterial with controlled degrading rate, excellent cell compatibility and biospecificty and whole physiological functions, whose degrading products are not of acidity. Their chemical structures were characterized by means of chemical analysis, FTIR (Fourier Transform Infred), 1H-NMR (Nuclear Magnetic Resonance), 13C-NMR and fluorescence labeling, their thermal properties done by DSC (Differential Scanning Calorimeter) and the mechanical properties by Instron 1011. Thereafter, the hydrophilicity, degradation and cell compatibility of PDLLA and those modified PDLLAs were investigated. The main works and conclusions are included as follows: (1) PDLLA was prepared from DL-lactide by melt ring-opening polymerization. The effects of DL-lactide purity, polymerization time, temperature and the percent of initiator in lactide were investigated in detail, resulting in an optimum condition to synthesize PDLLA with 2200000 of viscosity-average molecular weight (Mv). The obtained results show that:① The DL-lactide purity has significant influence on PDLLA's Mv. Ultrahigh molecular weight PDLLA with 2200000 of Mv could be obtained from lactide with purity of more than 99.8% and melting point of 126.3~126.4℃ at 160℃ for 36h.② The stretching (compressing) strength and module, tenacity and elongation of ultrahigh PDLLA are significantly improved compared to PDLLA with 800000 of Mv, suggesting its potentially wide applications in medical areas as bone screw, surgical suture and tissue scaffolds and in general plastics as full degradable plastics.(2) MAH modified PDLLA (MPLA) was synthesized by solution blending and subsequent free radical polymerization, attempting to introduce highly reactive anhydride into PDLLA backbone and providing chemical basis for further chemical modification.FTIR, 13C-NMR and DSC analysis showed the successful covalent grafting of MAH into PDLLA. Furthermore, the unique Tg of 41.7℃ for MPLA and the greater Tg of 56.5℃ for PDLLA indicated in DSC proved that the purification method in this① study was efficient enough to produce pure MPLA.② The results of chemical titration showed that MAH grafting ratio in MPLA was 1.86% and 2.36% respectively when the percentage of fed MAH in PDLLA was 5% and 10% in weight.(3) Diamine modified PDLLA (DMPLA) from ethylenediamine and MPLA was synthesized and its preparing technique well established. The modification of PDLLA with diamine is to eliminate or weaken acidity of degraded products from PDLLA and MPLA with the help of basic diamines and change the acid catalyzed auto-accelerating degradation, developing a new family of biomaterials with no acidic degrading products. Furthermore, DMPLA could provide reactive groups -COOH and -NH2 for further bulk modification with collagen, peptides or growth factors to obtain biospecific biomaterial with whole physiological functions.① The chemical titration indicated the bonds in anhydride had thoroughly reacted with diamine.② FTIR, 1H-NMR, 13C-NMR and DSC analysis exhibited the successful covalent introduction of daimine into MPLA. Furthermore, the unique Tg of 59.5℃ for DMPLA proved the efficiency of the purification method for DMPLA. The Tg of DMPLA is much greater than those of both PDLLA and MPLA. It maybe lie in the formation of inner salt between -NH2 and -COOH in DMPLA. (4) The bulk-modification of PDLLA (CPLA) was carried out from collagen type Ⅰ and DMPLA with dicyclohexylcarbodiimide (DCC) as condensating agent, and a solution reaction technique suitable to the reaction between collagen or peptide or protein and DMPLA was well established. The purpose of bulk modification of DMPLA with collagen, peptides or proteins are to obtain a biomaterial with no acidic degrading products but exce...