Investigation On Preparation Of Shape Memory Polymeric Porous Scaffold And Its Application In Bone Tissue Engineering

In recent years, bone tissue engineering scaffolds have achieved great developments, but there are still many problems. For example, it is difficult to tailor and match the irregular shape of bone defect for inorganic porous scaffold; the method of drug-loading is single, and the drug-loading efficiency is not high. So a new type of bone tissue engineering having the following characteristics becomes critical:easy to load medicine, facility to change pore size and porosity, good biocompatibility, and an ability of matching the irregular bone defect in the shape of scaffolds. In this thesis, we take BMP-2 loaded calcium alginate hydrogel microspheres as pore-forming agent, and prepare a series of porous scaffolds with shape memory function by the method of freeze drying, and investigate its osteogenesis ability in maxillary sinus of the dog animal model.Firstly, we successful prepared a biodegradable shape memory polymer material based on block copolymer PEG-PCL, which was prepared through ring-opening polymerization of caprolactone with polyethylene glycol (PEG), as the soft segments, MDI and chain extender DMPA as hard segment. It was found that the transition temperature of the polyurethane(PU) with soft and hard segment ratio of 3:1 is close to body temperature, and the material has a good shape memory performance. Meantime BMP-2 loaded calcium alginate hydrogel microspheres were prepared by micro flow pump with high voltage direct current technology. The microspheres were measured by a stereoscopic microscope. The microspheres with an average diameter of 334 μm are very uniform and have spherical shapes. And the size of the microspheres can be regulated by adjusting the concentration of sodium alginate.Secondly, the polyurethane solution was poured into a accumulational calcium alginate hydrogel microspheres and oscillated in the ultrasonic oscillator for 30min in order to keep the solution penetration into the space among these microspheres. After that, the sample was processed with vacuum freeze-drying technique for 24h and a porous scaffold could be obtained. The surface morphologies and the average diameter of the scaffolds were measured by a scanning electron microscope (SEM). The result showed that the scaffolds had an average pore size of 345μm, and the porosity was approximately 82%. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) results indicated that the polyurethane scaffold possessed good shape memory effect(SME). And the pore size of scaffold can be adjusted by changing the size of calcium alginate hydrogel microspheres.Finally, the results of cell toxicity and in vivo osteogenesis ability proved that the porous scaffolds had good cell compatibility and osteogenetic capability in the maxillary sinus area of the dog.In this paper, the method of preparing porous scaffolds has several advantages, such as easy to process and convenient for regulating the pore size. Moreover, it can synchronize carrying multiple drugs and forming pores at the same time. In conclusion, the porous scaffolds have good memory properties, biocompatibility and biodegradability, and have great potential applications in the biomedical field.