| Objective Injectable hydrogels have high degree of flexibility to adapt to complex and irregular bone defect as well as excellent biocompatibility due to high water content.Therefore,Recently the study of application of injectable hydrogels in the field of bone repair has been paid wide attention.However,limited by low viscosity and low mechanical strength,it is still a challenge for normally designed injectable hydrogels to repair some defect situations that requires restoration of the defect contour immediately and later load bearing.In this study,hydrogels composed of GelMA,Laponite and nHAP were specially designed.The hydrogels can be easily extruded,stacked,and kneaded into desired shapes based on the thixotropic property and transformed into a load-bearing elastomer scaffold in situ after photocrosslinking.Therefore,GLH hydrogels provide a new idea for the design of bone defect repair materials in some special cases.Methods The GelMA-L and GLH hydrogels were prepared by changing the proportion of nHAP,the weight ratio of GelMA,Laponite,and nHAP was 3:2:0,3:2:2,3:2:3,3:2:4.The stress strain of the GelMA-L and GLH hydrogels were tested by mechanical universal testing machine.The rheological and compressive properties of the hydrogels were tested.The microstructure of the GelMA-L and GLH hydrogels was observed by SEM.XRD and FTIR were used to characterize the ingredients of the material.Rabbit bone marrow mesenchymal stem cells（MSCs）were used for biocompatibility test in vitro,alkaline phosphatase staining and alizarin red staining were used to verify the osteogenesis of the MSCs.The in vivo evaluation of the hydrogels for bone formation was proceeded by using a rabbit calvarial bone critical-sized defect model.Results SEM showed that nHAP nanoparticles were uniformly distributed in the GelMA-L matrix,XRD and FTIR showed that nHAP existed in the GLH hydrogels.Rheological analysis testified the injectable and plastical deformable properties and determined the curing time of the GLH hydrogels.Mechanical test result showed that the compressive strength of the hydrogels increased first and then decreased with the nHAP ratio,and the number reached the maximum when the ratio of GelMA,Laponite and nHAP was 3:2:3.In vitro experiments showed that GLH hydrogels had good biocompatibility and provided a suitable environment for cell adhesion,proliferation and differentiation.ALP and alizarin red staining showed that the presence of GLH hydrogels enhanced the differentiation rate and mineral deposition of osteoblasts.In vivo studies showed that at 12 weeks,new bone was found in both the edge and the center of the defect area in the GLH group,which was more than that in the GelMA-L and blank control group,and the difference was statistically significant（P<0.05）.Conclusion In this study,the GLH hydrogels composed of GelMA,Laponite and nHAP was synthesized and optimized to obtain a photocrosslinkable material with injectable and plastical abilities.Based on the thixotropic property of Laponite,the GLH hydrogels can be stackable after injected and kneaded into desired shapes afterwards to restore the outline of the irregular bone defect area.Besides,the GLH hydrogels were able to crosslink under UV light thanks to the exist of GelMA and maintained the excellent biocompatibility of GelMA.nHAP was homogeneously distributed into system and further stabilized the rheological properties and enhanced the mechanical strength of the hydrogels after UV curing.The GLH hydrogels showed suitable injectability,plastical deformability,mechanical properties and high bioactivity and biocompatibility.In vitro cell culture studies showed enhanced rabbit bone marrow derived MSC growth and matrix mineralization.In vivo evaluation in a rabbit calvarial critical-sized bone defect model showed significantly bone regeneration in the GLH hydrogels-filled defect site.To sum up,GLH hydrogels are bone repair biomaterial with promising clinical application for some irregular bone defects that require contour restoring and load bearing. |
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