Abstract:

Objective To prepare the polypropylene carbonate（PPC）/polybutylene succinate（PBS） biofilm that mimics the structure of human bone periosteum，and to evaluate its physicochemical properties and biological characteristics. Methods The PPC/PBS biofilm was prepared by salting-out method. ¹H nuclear magnetic resonance spectra（¹HNMR） was used to observe the spectral absorption peak of PPC， PBS， and PPC/PBS，and the chemical structure changes of PPC， PBS， and PPC/PBS were analyzed； the ultramorphology of the PPC/PBS biofilm was observed by scanning electron microscope （SEM）； and the physicochemical properties， including porosity， Young’s modulus， fracture strength， fracture elongation， and static contact angle of the PPC/PBS biofilm were measured by GPC membrane permeation chromatography. The osteoblasts of the primary SD rat were isolated， cultured， and purified， and divided into control group （without biofilm）， BME-10X collagen membrane group， and PPC/PBS biofilm group. SEM was used to observe the adhesion and growth of the osteoblasts in various groups； cell counting was performed to detect the number of osteoblasts；alkaline phosphatase （ALP） assay kit was used to the differentiation of the osteoblasts； rabbit muscle degradation experiment was used to evaluate the degradation performance of the PPC/PBS biofilm in vivo. Results The PPC/PBS biofilm had a dual-layer structure consisting of a smooth surface layer and a rough surface layer， with a total thickness of approximately 0.5 mm and an average pore size of about 120 μm；the porosity was approximately 77.4%， the Young’s modulus was approximately 38.1 MPa， the fracture strength was approximately 1.22 MPa， the fracture elongation was approximately 7.4%， and the contact angle on the rough surface was 85°， while the contact angle on the smooth surface was 57°. The SEM observation results showed that fewer cells adhered to the surface of the PPC/PBS biofilm 1 d after culture； 3， 7， and 14 d after culture， a large number of osteoblasts were observed to adhere and grow on the surface of the biofilm， with cell protrusions attached to the film and cell bodies distributed in the pores. Compared with control group， the numbers of osteoblasts attached to the surface of the materials in BME-10X collagen membrane group and PPC/PBS biofim group were decreased after cultured for 1， 3， 7， and 14 d （P<0.05）. Compared with BME-10X collagen membrane group， the number of the osteoblasts attached to the surface of the materials in PPC/PBS biofilm group was increased after cultured for 1， 3， 7， and 14 d （P<0.05）. Compared with control group， the ALP levels in the osteoblasts attached to the surface of the materials in BME-10X collagen membrane group and PPC/PBS biofilm group were significantly decreased after cultured for 1， 3， 7， and 14 d （P<0.01）. Compared with BME-10X collagen membrane group， the ALP level in the osteoblasts attached to the surface of the materials in PPC/PBS biofilm group was significantly increased after cultured for 1 and 3 d （P<0.01）. The degradation experiment results showed that compared with 0 week after degradation， the weight loss rate and weight loss rate of number-avarage molecular of the PPC/PBS biofilm were increased 4 weeks after degradation （P<0.05）， while the fracture strength and fracture elongation were significantly decreased（P<0.05 or P<0.01）. From the 2nd week after degradation，the number of microstructures on rough surface of the PPC/PBS biofilm was gradually increased， and the pore sizes was ranged from 0 to 10 μm； by 26 weeks after degradation，the number of micro-porous structures was evenly distributed on rough surface of the PPC/PBS biofilm； by 4 weeks after degradation， the smooth surface of the biofilm showed exfoliation changes， but no micro-porous structures were observed； by 12 weeks after degradation， a small number of micro-porous changes were observed on the smooth surface， and the pore diameters were less than 5 μm； by 26 weeks after degradation， the number of micro-porous structures on the smooth surface was increased，and the pore diameters were less than 10 μm. Conclusion The structure of PPC/PBS biofilm is similar to that of human bone outer membrane，with a double-layer structure，good hydrophilicity，dense smooth surface，high porosity of rough surface，good biocompatibility，and slow degradation；it is an ideal guided regeneration biofilm.

Key words: Guided bone regeneration, Biofilm, Poly propylene carbonate, Poly butylene succinate, Bone defect