The Research Of A Biodegradable Polyurethane Material For Cartilage Repair

Articular cartilage is a tissue that lacks of blood vessels, nerves, and lymphatic system.In the intra-articular synovial fluid provides nutrition alone, and the metabolism ability ofarticular cartilage is poor. Articular cartilage is not a simple structure tissue, it can be dividedinto superficial zone, transitional zone, radial zone and calcified cartilage zone along with thechanges in depth. It has a totally different structure and function between each layer. Theproliferative capacity of chondrocyte is low as well. These characteristics of articular cartilagemake it very hard to regenerate itself when damage happens. Avariety of approaches in clinic,such as consultation, HA injection, arthroscopic treatment, osteochondral allografting andjoint replacement are motivated by the clinical need for articular repair. However, currentclinical therapies are facing some challenges more or less. Consultation and HAinjection onlyplay a role in mitigation, arthroscopic treatment only works in a period of time, autologousosteochondral transplantation has a problem of insufficient donors and allogeneic cartilagetransplantation has a rejection problem, joint replacement is now the most effective treatment,but the cost is high and the replacement will come loose after a period of time. Therefore, itremains to be solved urgently to seek a new method of cartilage repair. Fortunately, cartilagetissue engineering is considered to be one of the most promising alternative therapies forarticular cartilage defects.Tissue engineering scaffold materials include natural materials and synthetic polymermaterials. Nowadays, synthetic polymer materials is the most widely used scaffold material.Polylactic acid is mainly used as the traditional tissue scaffolding materials, however, itscharacteristics of being highly elastic modulus limits its appliance in the cartilage tissueengineering, specifically the regeneration of superficial zone and transitional zone. Thedifferent modulus and degradation rate biodegradable polyurethane can be easily achieved bymolecular structure design which received a wide attention in cartilage repair. In this study,PCL-2000as a soft segment HMDI as a hard segment PMG-250as a chain extender wereused for the synthesis of biodegradable polyurethane.5groups of biodegradable polyurethanematerial having different characteristics were synthesized by adjusting the proportion ofdiisocyanate, soft-segment and chain-extender. The molecular weight and mechanicalproperties of all groups were studied. FTIR and1H-NMR results revealed the structure of PU.The molecular weight decreases, but the Young’s modulus and crystallinity increases with theincreasing content of diisocyanate. The comprehensive performance of PU-1.7and PU-1.8was the best of all. A multilayer scaffold for cartilage tissue engineering was fabricated by the synthesized PU. The transition between each layers was good through the stereo microscopeand SEM. The scaffolds showed uniformed pore size and good connectivity. The preparedscaffold also owned a rough surface which possessed potentially significance for theproliferation and adhesion of cells.Although biodegradable polyurethane has excellent mechanical properties, thebioactivity need further improvement. In this study,2,2-propargyl-1,3-propanediol(DPPD)was synthesized and used as the chain extender for getting a biodegradable polyurethanecontaining alkynyl. The structure of the PU containing alkynyl was confirmed by thecharacteristic1H-NMR chemical shift at2.03ppm and IR spectrum absorption band at2138cm-1. When the DPPD chain extender and PU prepolymer were polymerized with themolar ratio of1,0.7and1(70%DPPD+30%1,3-propanediol), the obtained alkynyl graftingratio were0.396,0.235and0.197mmol/g, respectively. The “click” coupling of the PUalkynyl group with RGD-azide was proved by the chemical shift at7.91ppm of the1H-NMRtest result. Cell viability experiments revealed that alkynyl grafted on the PU has no influenceon the cell viability. Some surface modification was also done by using surface exposedalkynyl group. The TGF-β1affinity peptide HSNGLPL was grafted onto the polyurethanesurface. The XPS results showed that the N elements significantly increased in peptide graftedpolyurethane. QCM detected the growth factor adsorption process, trough software fitting thegrowth factor adsorption quantity of grafted surface was2.11mg/m2.In order to realize the further functionalization and avoid serious infection complications,the ofoxacine microsphere was made and combined with polyurethane scaffold in this study.PLGA microsphere contained ofoxacine were made using double-emulsion(water-in-oil-in-water) solvent evaporation method. The influence of mesoporous silicon,hyaluronic acid, polylysine in internal aqueous solution on the microparticle size distribution,surface morphology, ofoxacine loading efficiency and release behavior were investigated. TheSEM pictures indicated the microparticles with the microcavities inside were fabricated. Theaverage particle size of HA internal phase group was the largest and span index smallest.Loading efficiency was increased in both MS and HA internal phase groups but decreased inpolylysine group. The bust realease of all groups was higher than the control group observedin this research. Releasing frofiles presented the fatest release rates of polylysine internalphase microparticles, while HA internal phase microparticles presented the slowest releaserates. The fit curve of drug release pattern of the microparticles with different internal phaseall presented the slogistic mathematic mode.