| Poly(D, L-lactic acid)(PDLLA) is a biodegradable and biocompatible polymer. Due to its low immunogenicity, excellent biocompatibility and mechanical properties, it can be widely used in the pharmaceutics and other medical applications. The degradable cycle of poly(D, L-lactic acid)(PDLLA) is generally several months, so it is used in areas of required short period of degradation, and pure PDLLA material has the following disadvantages:(1) the lack of active groups;(2) poor hydrophilicity, low biological activity;(3) local inflammation caused by acidic degradation products. In order to overcome the above defects, researchers have done a lot of modified work. Maleic anhydride(MAH) has high active anhydride groups that can open to form carboxyl groups; arginine-glycine-aspartic acid(RGD) peptide sequence is an amino acid sequence, which can promote cellular adhesion through binding to integrin receptors; hydroxyapatite(HAP) has good biocompatibility and biodegradability, which can neutralize some acidic degradation products. In this paper, MAH and RGD were used to modify PDLLA matrix material, then the polymer materials with HAP were blend, and a series of tests and analyses were performed.PDLLA of high molecular weight was used as raw material, dibenzoyl peroxide(BPO) as an initiator, and maleic anhydride(MAH) grafted to the side chain of PDLLA(PLA-MA) was synthesized via free radical polymerization. PLA-MA reacted with pentapeptide(GRGDY) in the condensing agent 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride(EDC) and 1-hydroxybenzotriazole(HOBt) to synthetize polymer PRGD. The nano-hydroxyapatite(n-HAP) was modified by silane coupling agent(KH-550). Then proportional PRGD and n-HAP were added to the matrix material PDLLA using the solvent evaporation method to get three kinds of composite films.The molecular structure of PLA-MA was characterized with IR, 13 C NMR and pyrolysis/gas chromatography-mass spectrometry(Py/GC-MS), the results show that MAH has successfully grafted to the side chain of PDLLA; the molecular weight and molecular weight distribution of PLA-MA were tested by GPC, the results indicate that the more of the amount of MAH, the smaller of the molecular weight of PLA-MA. The content of GRGDY in polymer was measured by automatic amino acid analyzer(AAA), the results show that the molar content of amino acids is 6.02~ 12.27?mol/g. The modified nano-hydroxyapatite was characterized with XRD, SEM and TG, and the results show that the modification is successful.The composite materials have good hydrophilicity, thermal stability and mechanical properties. PDLLA films were used as control group, three kinds of composite membranes were used to take 3 months' degradation, in the process of degradation, the pH, the rate of weight loss and changes of the surface morphology were tracked. The results show that the pH value of four kinds of materials are downward trend as a whole, and the pH values of pure PDLLA and PRGD/PDLLA are gradually declining to about 6.4 at 12 th week, but composite materials that were added n-HAP are staying at around 6.9 at 6th week. The weight loss rate of the materials is fast at first and then slows down. The n-HAP will dissolve and come off from the film, which can neutralize some acidic degradation products, but also to a certain extent affect the rate of degradation of the polymer, so before 6 weeks the degradation rate of n-HAP/PRGD/PDLLA composite films is faster than the PDLLA. Due to the acidic environment will accelerate the degradation of PDLLA, so after six weeks, the weight loss rate of PDLLA is higher than composite materials.Cytotoxicity test and adhesion experiment both illustrate that the biocompatibility of composite materials is better than pure PDLLA. The datas of statistical analysis show that the RGD peptide and n-HAP have important roles in promoting cell adhesion, from the incubation time analysis, RGD peptide is slightly stronger role in the short term, n- HAP is slightly stronger role in the long term. |
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