Preparation And Study Of Cystine Dimethyl Ester Cross-Linked Polyurethane/Nano-Hydroxyapatite Composited Scaffold For Bone Repair

Objective:Polyurethane was synthesized with glycerol ethoxylate as raw material and cystine dimethyl ester as cross-linker.polyurethane and nano hydroxyapatite are composited to prepare a new bone repair scaffold with high mechanical properties,degradability,pore connectivity,perfect biocompatibility and osteogenic activity.Methods:Firstly,glycerol ethoxylate,isophorone diisocyanate and dibutyltin dilaurate were added to the glass reactor,and the mixture was further stirred under vacuum at 70? for 1 hour to obtain the prepolymer.Then,the prepolymer was dissolved in N,N-dimethylformamide,and then salt particles,nano-hydroxyapatite and cystine dimethyl ester were added successively.The obtained products were soaked in water to remove solvent and salt.Finally,the scaffolds were dried to constant weight in vacuum.The synthesis process was monitored by NMR and FTIR.TGA was used to determine the thermal stability of the scaffolds.Elemental composition of scaffolds was measured by EDS.X-ray diffractometer was used to analyze the composition of the scaffolds.The tensile strength of the scaffolds was measured by the universal testing machine.SEM was used to observe the microstructure of the scaffolds.The hydrophilic properties of the scaffolds were measured by contact angle meter.The degradation performance and porosity of the materials were measured by weighing and calculating.Fetal bone marrow mesenchymal stem cells were used to detect the cell proliferation,adhesion and osteogenic differentiation of scaffolds.Cells were cultured with extracts from three scaffolds,and cell viability was measured by CCK-8 at 1,3,5,and 7 days,respectively.The cells were seeded on the surface of the scaffold,and measured with CCK-8.Cells were stained with phalloidin and 4,6-diamidino-2-phenylindole to observe the cell morphology by laser confocal microscopy.The cells on the material were cultured with osteogenic differentiation medium,and stained with alizarin red at 14 and 21 days.Results:The structure of dimethyl cystine was confirmed by NMR.Fourier transform infrared spectrometer proved that the synthesis of polyurethane was carried out according to the design route.TGA indicate thermal stability of the scaffolds.The decrease at 220?-260 ? is mainly caused by the thermal cleavage of disulfide bond.The decrease between 300? and 400? may be due to thermal cleavage of isocyanate bond and ether bond.XRD show that nano-hydroxyapatite is added to polyurethane accurately.EDS show that compared with PU scaffolds,composite scaffolds with nHA have calcium and phosphorus elements.With the increase of nHA,the maximum strain of PU,10%nHA/PU and 20%nHA/PU scaffolds decreased from 315.87±8.70%to 147.33±3.72%,while the tensile strength of PU,10%nHA/PU and 20%nHA/PU scaffolds first increased and then decreased,and the tensile strength of PU,10%nHA/PU and 20%nHA/PU scaffolds were 10.49 ± 2.29 MPa,20.30±0.98 MPa and 15.72 ± 1.55 MPa,respectively.SEM pictures show that the scaffolds have about 200 ?m of interconnected pores and nano size of hydroxyapatite,and the salt leaching-phase inverse technique can be proved to prepare porous scaffolds successfully.The contact angles of PU,10%nHA/PU and 20%nHA/PU scaffolds were 87.67±2.52°,81.25 ± 1.52 ° and 72.83± 2.36 ° respectively.With the increase of nHA,the hydrophilic properties improved gradually.The degradation showed that the scaffold had degradation performance.By calculating the weight and volume of the scaffold before and after immersion in water,the porosity of the scaffold is about 35%.There was no significant difference between the different scaffolds,and the number of cells increased with the increase of culture time.Cell adhesion experiments showed that compared with PU scaffolds,the scaffolds with nHA were easier to promote cell adhesion.Osteogenesis experiments show that the scaffolds with nHA were easier to make cells grow.Conclusion:The cystine dimethyl ester crosslinked PU/nHA composite biomimetic scaffolds have porous structure,excellent mechanical properties,biodegradability,perfect cell compatibility and osteogenic ability.Therefore,the composited scaffolds have great potential in the field of bone defect repair.