Preparation And Bioactivity Of Skull Implants Based On Stereolithography

At present,the appearance of defect part can be realized by the implantation of stents,which can provide support and protection and achieve the basic functions of the moving parts.However,the repair of metabolic function is still a big problem.The premise of metabolic function repair is that the bone scaffold with good osteogenic performance can quickly complete the bone reconstruction after the implantation.In addition,the features of pores are also one of the important factors affecting the osteogenesis performance of bone repair scaffolds.Therefore,it is of great significance to explore the porous structure with good osteogenesis for the repair of bone defects.In this paper,hydroxyapatite,which is the most abundant inorganic substance in bone tissue,is taken as the research object and prepared by the stereolithography technology,and the internal pore structure of natural loofah spong is selected to carry out the research on the preparation of skull implants and their biological activity and bionic structure.In the preparation of hydroxyapatite bone scaffolds by stereolithography technology,hydroxyapatite powder was mixed into photosensitive resin to form the complex shape by UV light,and then the final entity was obtained successively by debinding and sintering.It is crucial to confirm whether the prepared hydroxyapatite scaffold have the toxic effects after our designed printing,debinding and sintering processes because the photosensitive resin in the starting printing paste is poisonous to cells.To investigate these issues in details,thermogravimetric analysis,in vitro cytotoxicity test and implantation pre-experiment in the rabbit parietal were performed,aiming to verify the biosafety of SL-3D prepared hydroxyapatite scaffold.Through the thermal analysis,it was proved that photosensitive resin would be completely pyrolyzed at temperature ranging from 350? to 580? during debinding,corresponding to a secondary chemical reaction mechanism.The cytotoxic grade was reduced from Grade 4 to the Grade 1 as a result of debinding process.After sintering,the cytotoxicity level of the sample changed to Grade 0.The honeycomb-like implant was implanted into the defect of the New Zealand rabbit skull.After implantation,there was no inflammatory reaction in the implant site,and the bone scaffold formed a good bone bonding with the defect edgePorous structure with high porosity and high connectivity is often adopted in designing bone scaffold.The porous structure will facilitate the attachment and growth of bone cells,while the porosity of loofah in nature can be more than 90%.Its high specific surface area and multi-level pore structure provided favorable structural conditions for cell growth.In addition,the middle part of the outer wall of loofah spong is similar to the structure of cancellous bone in bone tissue.Based on the principle of structural bionics,the three-dimensional structure of loofah was reconstructed by micro-CT data,and then modified to form porous scaffolds.Finally,six different porous three-dimensional models(?-?)were obtained.After printing,debinding and sintering,the porosity of the scaffolds was about 50%,the distance between wires was 146-839?m,and the wire diameter was 230-450?m.In order to test the osteogenesis of bionic porous bone scaffold,four kinds of bionic loofah-like porous bone scaffolds(Types ? to ?)were selected for in vivo implantation test.Loofah-like bone scaffolds,which were debinded and sintered,were implanted into the defect site of the rabbit parietal bone.The samples were scanned by micro-CT at the 8th and 12th weeks,and then three-dimensional modeling was builded to analyze the bone volume fraction,bone volume and other parameters of different bone scaffolds.The results showed that the bone volume fraction of Type ? and Type IV(dense type,the filament distribution is dense,the filament diameter is small)was higher than that of Type V and Type VI(loose type,the filament distribution is loose,the filament diameter is large),which indicated that the new bone production of the dense bionic loofah-like bone scaffold became more.The bone volume fraction of Type IV can reach 33%at 12th week.It can be seen that the bionic bone repair scaffolds designed and prepared by stereolithography has a good osteogenic performance,the edge of bone defect formed the good bone integration with bone scaffolds,and bone tissue grew along the bone repair scaffolds.