Studies On Synthesis And Property Of Biodegradable Polyurethanes Containing Amino Acid

Biodegradable polymeric materials mean a kind of macromoleculars which could be degradedby the action of enzyme or chemicals created by living beings. The biodegradation is acomplicated biophysics and biochemist process. Among all kinds of biodegradation mechanism,the degradation of peptide bond or disulfide bond by the action of protease or peptide is effectiveand selective. These advantages attract more and more interests. The action towards polymerscontaining peptide bonds or disulfide bonds still remains in force. These polymers provided activesites for biodegradation when they get into the body of living beings. As a result, thebiodegradation could be precisely controlled by adjusting the sorts and numbers of peptidebonds/disulfide bonds, the molecular structures and the protease or peptide.Polyurethane is a kind of polymer with unique microphase separation structure. As a result, thesurface of the polyurethanes may mimetic the biological membranes and show fine qualities ofbiocompatibility and hemocompatibility. In this work, we plan to introduce the protease or peptidesensitive active sites, like disulfide bonds, peptide bonds and pseudo peptide bonds intopolyurethane to develop peptide mimetic biodegradable polyurethanes. The details about thestudies were shown as following:1. Synthesized and characterized of reduction-sensitive rapid biodegradablepoly(urethane-urea)sCystine dimethyl ester (CDE) contained disulfide bond was synthesized. Then CDE wasintroduced into the main chain of polyurethane to fabricate two series of reduction-sensitive rapidbiodegradable poly(urethane-urea)s. The poly(urethane-urea)s were characterized by means ofFIR spectra, HMR spectra, GPC, DSC and TG. In vitro degradation study was carried out underphysiological conditions mediated by glutathione and dithiothreitol respectively, and was assessed by1H NMR, GPC and SEM. The results indicated that the disulfide bonds in poly(urethane-urea)swere effectively cleaved. the rate and degree of reductive biodegradation could be controlled bythe structures of the polymers and the reduction environment. The results of cell viabilityexperiments indicated that the polymers sustained much higher cell viability than the controls.2. Synthesized and characterized of pepsin-inspired peptide mimetic polyurethanes derivedfrom pseudo tripeptideA kind of novel tyrosine-fumaric acid-tyrosine pseudo tripeptide (TFT) was synthesized. Basedon TFT, two kinds of peptide mimetic pepsin-inspired degradable polyurethanes were synthesizedand characterized. Broken strain of PEG600PU sample was11.8MPa while PCL1000PU was19.1MPa. In vitro degradation behavior was investigated in simulated gastric fluid containingpepsin for32days, the results indicated that the pseudo peptide bonds in polyurethanes wereeffectively digested by the action of pepsin. The rate and degree of pepsin degradation could becontrolled by alteration of the soft segments and activity of pepsin. The results of cell viabilityexperiments indicated that the polymers sustained pretty good cell viability.3. Synthesized and characterized of trypsin-inspired rapid degradable poly(urethane-urea)sPeptide mimetic degradable poly(urethane-urea)s were prepared based on polylysine and PCL.The structure of the poly(urethane-urea)s was characterized by FIR and NMR. The thermalstability and hydrophilic property of the poly(urethane-urea)s increased with increasing content ofpolylysine. The results of in vitro degradation experiments indicated that samples were rapidlydegraded by the action of trypsin. For the samples, the mass loss was about35%after24daysincubation while less than10%for the controls.4. Synthesized and characterized of trypsin-inspired poly(urethane-urea)s/GOnanocompositesThe poly(urethane-urea)s containing polylysine was grafted to the surface of the GO based onthe "graft to" method and the variation before and after functionalization of GO was investigated.The results of in vitro degradation experiments indicated that PU/GO nanocomposites maintainedthe trypsin-inspired rapid degradable behavior. The results of AC impedence method revealed that the load resistance of the PU/GO nanocomposites decreased obviously in comparison with thecontrol PU. It proved that2%GO was able to improve the electronic property of PU.