| Due to the obvious limitations and shortcomings,bone graft substitutes with biocompatibility and osteogenesis ability were found to simulate the composition and structure of natural bone matrix.Nano-hydroxyapatite(n-HA)and chitosan/hydroxyapatite(CS/n-HA)composite microsphere were prepared by ultrasound-assisted precipitation and inverse crosslinking-emulsion method,respectively.Owing to obtain the scaffold with excellent properties,porous calcium sulfate hemihydrate/chitosan/hydroxyapatite composite scaffolds(CSH/CS/n-HA).The preparation technology and properties of composite scaffold were explored in subsequent experiments.The main contents and conclusions of research are as follows.(1)In this paper,nano-hydroxyapatite and chitosan/hydroxyapatite composite microspheres were prepared by ultrasonic-assisted chemical precipitation method and reverse crosslinking-emulsion method,respectively.Then the samples were characterized and analyzed by infrared spectroscopy,X-ray diffraction and field-emission scanning electron microscopy.The experimental results are given as follows: nano-hydroxyapatite were synthesized by ultrasonic-assisted chemical precipitation method with high crystallinity,without impurities.And the sample with uniform showing rod-like morphology.CS/n-HA composite microspheres were prepared by inverse crosslinking-emulsion method.The results of single factor experiment showed that composite microspheres with regular morphology and good dispersibility in appropriate circumstances.(2)Porous CSH/CS/n-HA composite scaffold was constructed with calcium sulfate hemihydrate and CS/n-HA,while citric acid was used as the cement liquid.Then the scaffolds were characterized and analyzed by infrared spectroscopy,X-ray diffraction and tungsten filament scanning electron microscopy.The results showed that porous CSH/CS/n-HA composite scaffolds were successfully prepared by this method.The results of mechanical test showed the maximum compressive strength of porous composite scaffolds can be effectively improved with appropriate amount of CS/n-HA composite microspheres.While the content of CS/n-HA was 6%,the compressive strength of composite scaffolds was 17.46±1.29 MPa which was the highest level among the five groups of samples.In the simulated body fluid immersion test experiment,the residual weight of all the composite scaffolds was reduced to 1%~4% of the initial weight on the 15 th day,with white sediments formed at the bottom of beaker.The experimental results are given as follows: the composite scaffold was biodegradable,and hydroxyapatite was produced with the dynamic equilibrium of calcium and phosphorus.(3)Levofloxacin was used as model drug to investigate the drug loading and entrapment efficiency of CS/n-HA microspheres and CSH/CS/n-HA scaffolds.Origin software was used to fit the test data.The results showed that drug loading and entrapment efficiency of CS/n-HA were 5.65±0.08% and 28.25±0.4% respectively,while efficiency of CSH/CS/n-HA were 4.49±0.31% and 22.42±1.56% respectively.Compared with the encapsulation method of drug-loading of CS/n-HA composite microspheres,the oscillating adsorption method of porous CSH/CS/n-HA composite scaffold is easier to operate,and no significant difference in drug-loading rate and encapsulation rate.Moreover,the sustained-release ability of CS/n-HA drug-loaded microspheres was poor,reaching the plateau stage at 8 h,while CSH/CS/n-HA composite scaffold was at 18 h with drug-release time up to 48 h.Compared with CS/n-HA microspheres,the sustained-release effect of drug of porous CSH/CS/n-HA was better.The modeling results showed that the release model of CS/n-HA microspheres can be described with first-order release kinetics equation,while the release curve of CSH/CS/n-HA scaffold was fitted to Higuchi equation.(4)The in-vitro erythrocyte hemolysis test was adopted to study the hemocompatibility of the materials.The results showed that the hemolysis rate of the suspensions of n-HA,CS/n-HA and CSH/CS/n-HA which in the range of 0.025 to 0.8 mg/mL was within 5%,meeting the requirements of materials and national standards. |
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