Molecular Design of Synthetic Biodegradable Polymersas Cell Scaffold Materials

Poly(lactic acid) and its copolymers are regarded as the most useful biomaterials. The good biocompatibility, biodegradability and mechanical properties of them make the synthetic biodegradable polymers have primary application to tissue engineering. The advantages and disadvantages of the synthetic biodegradable polymers as cell scaffold materials are evaluated. This article reviews the modification of polylactide-family aliphatic polymers to improve the cell affinity when the polymers are used as cell scaffolds. We have developed four main approaches: to modify polyester cell scaffolds in combination of plasma treating and collagen coating; to introduce hydrophilic segments into aliphatic polyester backbones; to introduce pendant functional groups into polyester chains; to modify polyester with dextran. The results of the cell cultures prove that the approaches mentioned above have improved the cell affinity of the polyesters and have modulated cell function such as adhesion, proliferation and migration.

Synthesis and Characterization of Novel Biodegradable Poly (butylene succinate-co-triethylene glycol succinate)Copolymers

Novel biodegradable aliphatic polyesters,poly（butylene succinate-co-triethylene glycol succinate）（P（BS-co-TEGS））and poly（butylene succinate）（PBS）,were synthesized through a two-step procedure of esterification and polycondensation with succinic acid and1,4-butanediol/triethylene glycol as raw materials as well as tetrabutyl titanate and diphenylphosphinic acid as the co-catalysts.The chemical structure and molecular weight of the copolymers were characterized by 1^H nuclear magnetic resonance（1^H NMR）and gel permeation chromatography（GPC）,respectively.In addition,thermal properties,crystal structure and mechanical properties were also analyzed with various techniques.P（BS-co-TEGS）exhibited more excellent mechanical properties than PBS,especially in elongation at break.Meanwhile,the crystal structure and thermal stability of the P（BS-co-TEGS）have hardly changed.The crystallinity of P（BS-co-TEGS）was lower than that of PBS and decreased with the increase of mole ratio of triethylene glycol.With the increase of TEGS unit molar composition,the melting point（Tm）,crystallization temperatures（Tc）and heat of fusion（ΔHm）of P（BS-co-TEGS）decreased,while glass transition temperature（Tg）increased.

The effect of mechanical loads on the degradation of aliphatic biodegradable polyesters

Aliphatic biodegradable polyesters have been the most widely used synthetic polymers for developing biodegradable devices as alternatives for the currently used permanent medical devices.The performances during biodegradation process play crucial roles for final realization of their functions.Because physiological and biochemical environment in vivo significantly affects biodegradation process,large numbers of studies on effects of mechanical loads on the degradation of aliphatic biodegradable polyesters have been launched during last decades.In this review article,we discussed the mechanism of biodegradation and several different mechanical loads that have been reported to affect the biodegradation process.Other physiological and biochemical factors related to mechanical loads were also discussed.The mechanical load could change the conformational strain energy and morphology to weaken the stability of the polymer.Besides,the load and pattern could accelerate the loss of intrinsic mechanical properties of polymers.This indicated that investigations into effects of mechanical loads on the degradation should be indispensable.More combination condition of mechanical loads and multiple factors should be considered in order to keep the degradation rate controllable and evaluate the degradation process in vivo accurately.Only then can the degradable devise achieve the desired effects and further expand the special applications of aliphatic biodegradable polyesters.

Synthesis of Cyclic Oligo(ethylene adipate)s and Their Melt Polymerization to Poly(ethylene adipate)

We present here the first synthesis of cyclic oligo（ethylene adipate）s （COEAs） via pseudo-high dilution condensation reaction of adipoyl chloride with ethylene glycol, and the synthesis of corresponding poly（ethylene adipate） （PEA） via the melt polymerization of COEAs. The structure of COEAs was characterized and proved by 1H-NMR and MALDI-TOF mass measurements. The effects of organic base, reaction temperature and the ratio of adipoyl chloride to ethylene glycol on the yield of COEAs were studied, and the optimum reaction condition was revealed. PEA, a diacid and diol based semi-crystalline green aliphatic polyester, was synthesized by the melt polymerization of COEAs using Ti（n-C4H90）4 as catalyst and 1,10-decanediol as initiator at 200 ℃, which follows the polycondensation-coupling ring- opening polymerization method. Our strategy should be applicable to the synthesis of versatile aliphatic polyesters based on diacid and diol monomers, which have potential applications as biocompatible and biodegradable materials.

Homo-and Copolymerization of ε-Caprolactone and 2,2-Dimethyltrimethylene Carbonate by Rare Earth Initiators

Rare earth tris(2,6-di-tert-butyl-4-methylphenolate) [Ln-(OAr)3, Ln = La, Nd, Dy, Y] alone has been developed to initiate polymerization of e-caprolactone (CL) and random copolymerization of CL with 2, 2-dimethyltrimethylene carbonate (DTC). The structures of polymers were analyzed by GPC, ER and NMR methods. Their crystal and thermal properties were discussed in terms of DSC. The initiating efficiencies were mainly affected by the size of rare earth metal in the sequence of La(OAr)3 > Nd(OAr)3 ～ Y(OAr)3 > Dy(OAr)3. La-(OAr)3 exhibited rather high activity to prepare PCL with a molecular weight of 2.15 × 105 and Ma/Ma of 2.27. The composition of random copolymer can be quantitatively controlled either by reaction time or by feed ratio of monomer.