Enhancement Of The Entangled Porous Materials And Investigation Of Their Structures,Properties And Biological Evaluation

Due to the interconnected porous structure and the 100% open porosity(which can be beneficial for the transportation of the body fluids,osteoinduction and osseointegration),and the easily adjusted mechanical properties and excellent toughness(which are good for the long-term implantation)the entangled porous material has drawn widespread attentions in the field of orthopedic implants.However,the entangled porous material is limited for load-bearing biomedical applications because of their rather low strength and elastic modulus.To expand their applications,three kinds of methods are proposed to enhance the entangled porous materials.This paper mainly discusses the advantages and disadvantages of different enhancement methods in the view of fabrication process,structure,mechanical property and biological evaluation,and these results would provide the important experimental and theoretical basis for their medical clinical applications.The main conclusions are listed as follows:PMMA is selected as the bonding agent to enhance the porous Ti.The results show that PMMA-enhanced porous Ti still keeps their porous structure,the free nodes become to the fixed nodes.The elastic modulus of the entangled porous Ti with 55% porosity is 0.03 GPa,the elastic modulus of the PMMA-enhanced porous Ti is 1.02 GPa,and the amplification reaches to 3300%,this enhancement method is more effective than the sintering.The pure Mg is used as the enhancement phase to improve the entangled porous material.(1)A kind of solid p-Ti/Mg composite is prepared by infiltration casting.For p-Ti/Mg composite,the continuous Ti wire is embedded in the matrix of Mg and the distribution of the Ti is dependent on the spatial structure of initial entangled porous Ti.For the porous Ti with 46.4%-62.9% porosity,the strength is in the range of 11.5 MPa-58.4 MPa,the elastic modulus is in the range of 0.26 GPa-2.15 GPa.The strength of p-Ti/Mg composite is in the range of 175 MPa-246 MPa,the elastic modulus is in the range of 22 GPa-47 GPa.The mechanical properties of as-prepared p-Ti/Mg composite are comparable to that of the cortical bone,suggesting considerable potential for the load-bearing orthopedic applications.(2)A kind of graded porous Ti-Mg composite(Gp-Ti/Mg),consisting of outer porous Ti layer and the internal dense Ti-Mg composite,is fabricated by infiltration casting and acid etching.Gp-Ti/Mg composite provides good osteoconduction ability compared with p-Ti/Mg composite.(3)The Ti-Mg composite(including p-Ti/Mg composite and Gp-Ti/Mg composite)is mainly dependent on the biodegradability of Mg,which could provide enough strength at early implant stage,but the porous structure would occur at late implant stage.However,the high corrosion rate of Ti-Mg composite,which is due to the galvanic corrosion and exterior surface of the Mg phase in Ti-Mg composite,could limit their biomedical applications.The pure Mg is used as the enhancement phase.A kind of graded porous Ti-Ta(Gp-Ta/Ti)composite is fabricated by infiltration casting and acid etching.The structure of Gp-Ta/Ti consists of outer porous Ta layer and internal dense Ti-Ta composite.The outer porous layer is beneficial for the transportation of the body fluids,osteoinduction and osseointegration,and the dense core could provide suitable properties,being comparable to that of natural bone.The Ta phase and Ti phase in the Gp-Ta/Ti material are mutually independent of each other and Gp-Ta/Ti material inherits the advantages of the entangled porous Ta and has excellent biocompatibility.The structure of Gp-Ta/Ti is rather reasonable and the volume fractions of porous layer and dense core could accurately control,when the outer porous Ta layer accounts for 41.2-83..4% of the total volume of the samples,the compressive properties is improved greatly compared with porous Ta,coming to 160-412 MPa compressive strength and 5.9-31.2 GP elastic modulus,respectively,suggesting their potentials for the load-bearing orthopedic applications.The in vitro evaluations including cell adhesion,activity and alkaline phosphatase(ALP)reveal that the Gp-Ta/Ti material can promote great osteoblasts adhesion,spread and proliferation,which in return further accelerate the maturation and mineralization of osteoblasts.More importantly,in vivo evaluations including push-out test,sequential fluorescent labeling and histological observations verify that the Gp-Ta/Ti material could efficiently promote new bone formation.These promising results including structure,mechanical properties and the biological evaluations suggest that the Gp-Ta/Ti material has the potential for future application in orthopedic field.