Study Of Calcium Phosphate Coated Porous Zinc Alloy Scaffold Material In Repairing Craniomaxillofacial Bone Defect

Nowadays,biological materials for bone defect repair mainly include non-degradable metal materials such as titanium(Ti)alloys,absorbable organic polymer materials and bioceramic materials.Metal materials such as Ti alloy require secondary surgery to remove the material,which brings much more unenjoyable suffering and cost burden to the patient.The biodegradable biomaterials have poor mechanical properties and cannot meet the loading requirement of bone reconstruction.In recent years,biodegradable metal materials have gradually developed.They utilize advantages of metal and biodegradable materials to avoid their shortcomings,which makes them promising in applications in bone reconstruction.This subject mainly studies the toxicity,biocompatibility and degradability of new coated zinc(Zn)alloy in vivo and in vitro,and provides a new choice for craniomaxillofacial bone defect repair.Objective: To explore new biodegradable coated Zn alloy to repair craniomaxillofacial bone defect.Surface activity can be enhanced by coating to obtain ideal surface structure and biological properties.Furthermore,biological characteristics such as cell proliferation,osteogenic differentiation,degradability and toxicity of this novel material were studied.Materials and Methods: 1.Surface morphologies of porous Ti alloy,porous Zn,Zn alloy and coated porous Zn alloy were observed by scanning electron microscopy(SEM).The components of the surface were detected using X-ray photoelectron spectroscopy(XPS).The degradability of porous Zn alloy and novel coated porous Zn alloy was evaluated by ion concentrations of Zn,cuprum(Cu),magnesium(Mg)and calcium(Ca),PH value and osmotic pressure via immersion tests.2.Bone marrow mesenchymal stem cells(BMSCs)extracted from rabbit ilium were cultured in mediums supplemented with different sample extracts in vitro.Cell proliferation was evaluated by CCK-8 test to assess cell viability.The expression of osteogenic-related genes was tested by real-time PCR.Immunofluorescence staining was utilized to evaluate the expression of vascular endothelial growth factor(VEGF)and osteocalcin(OCN).Osteogenic differentiation of BMSCs in different groups was assessed by alkaline phosphatase(ALP)staining and alizarin red staining(ARS).3.Rabbit cranial defect model was constructed to evaluate toxicity,degradation products and osteogenic ability in vivo.Ion concentrations of Zn,Cu,Mg and Ca in serum were measured by atomic absorption spectrometry(AAS)3 months after surgery.Degradation products of materials in vivo were detected by X-ray diffraction(XRD)6 months after surgery.Osteogenesis of new bone around different samples was examined by sequential fluorescent labeling and Van Gieson’s picrofuchsin 3 months after surgery.Results: 1.New surface structure of porous Zn alloy was obtained by chemical deposition method.Micron dot-shaped depressions were observed on the surface of coated Zn alloy composition.The result of XRD indicated that the coating component is dicalcium phosphate dihydrate.The results of immersion tests showed that ion concentration of Zn increased in both Zn alloy and coated Zn alloy groups,and that of Zn alloy group was higher.Ion concentration of Ca significantly increased in coated Zn alloy group,while there was no significant difference in that of Mg between two groups.PH value and osmotic pressure of medium increased in both groups.2.Cell proliferation was measured by the CCK-8 assay.The proliferation of BMSCs was in a time-dependent manner in Zn alloy and coated Zn alloy group,and there was no significant difference in proliferation of BMSCs compared with Ti group,which suggested that both materials had ideal biocompatibility.3.ALP activity and deposition of calcium nodule were enhanced in coated Zn alloy group evaluated by ALP staining and ARS.The expression of osteogenic-related genes including RUNX2,osteocalcin(OCN),ALP and osteopontin(OPN)was significantly promoted in coated Zn alloy group examined by real-time PCR,which indicated that coated Zn alloy might have promising potential in promoting osteogenic differentiation of BMSCs.4.The results of quantitative immunofluorescent staining indicated that there is no difference in the expression levels of OCN and VEGF between Zn alloy,coated Zn alloy group and Ti alloy group,which indicated that Zn alloy and Zinc alloy and coated zinc alloy and titanium alloy have no significant difference in promoting bone differentiation and vessels.5.The results of sequential fluorescent labeling and Van Gieson’s picrofuchsin showed more new bone formation and accelerated mineralization rate in porous coated Zn alloy group.There was no significant difference in metal ion concentration between metal ion-contained material groups and the blank control group,which suggested that metal ion-contained materials had no blood toxicity.Furthermore,all results of tests showed ideal bio-absorbability of metal ion-contained materials.Conclusions: 1.Zn alloy based porous Zn alloy scaffold was manufactured,and then surface of Zn alloy scaffold was modified by coating via chemical deposition method to obtain ideal surface structure.Zn alloy and coated Zn alloy material both possessed bioabsorbability.2.Coated Zn alloy had ability to promote osteogenic differentiation.Compared with Ti alloy group,coated Zn alloy showed better ability in enhancing mineralization in vitro.The coated Zn alloy had good biocompatibility.3.Zn alloy and coated Zn alloy showed good biodegradability in vivo,and coated Zn alloy showed optimal ability in promoting new bone reconstruction.