Research On Preparation Of Porous Titanium With Biomechanical Compatibility And Bioactivity

Ideal bone substitute materials should satisfy some requirements such as biocompatibility, bioactivity and compatibility in biomechanics. Up to date, all developed bone substitute materials (including ceramics, polymers, metals and composites) have their own advantages and disadvantages. Hydroxyapatite, which represents calcium phosphate ceramics family, is similar in composition with natural bone. It is biocompatible, osteointegrative and osteoinductive in some situation. However, the biomechanical property of calcium phosphate ceramics is not ideal, it is limited to be used in non-load-bearing situation due to its brittleness and shortages in anti-fatigue property. On the other hand, titanium, which represents metals and alloy family, has been widely used in clinic as bone substitute in load-bearing situations because of their mechanical properties. After some kinds of surface bioactive treated, titanium also can be biocompatible, bioactive, even osteoinductive. However, Mismatch of the mechanical property between titanium and natural bone can cause severe stress concentration, deteriorate the implant-bone interface, cause the failure of the implants finally. The particular porous structure of porous titanium enhances the biocompatibility and biomechanical compatibility of the porous titanium. As a new bone substitute, porous titanium may be the ideal bone substitute material in the load-bearing situation.In this paper, traditional slurry foaming has been used to prepare the porous titanium with different mechanical porosities. The composition analysis (XRD)found that the porous titanium is pure titanium, which will ensure the porous titanium have good biocompatibility, there are no other phases appeared. The compressive strength, bending strength and Young's modulus of porous titanium with the porosity of 58vol% are 190.7Mpa, 159Mpa and 4.15Gpa, respectively, similar to that of the nature bone. This kind of porous titanium with good bio-mechanical compatibility may be potential to alleviate the problems caused by the mismatch of the strength and Young's modulus between implant (105 GPa for Ti) and bone (3.5-20 GPa), enhances the life of the implants. Moreover, the scanning electron micrograph found that there are two kinds of pores in the porous titanium, one is the spherical and interconnected macrospores with homogeneously distributing, which are mainly in 100-700μm and the average pore size is 460μm measured by quantitative image analyses system; the other is microspores (about 10μm) in the wall of the macrospores. This porous structure would be beneficial to the osteoinduction of the porous titanium.Research on the bioactivity of the biomechanical compatible porous titanium found that the bone-like apatite appeared on surface of the porous titanium with the surface modification of alkali-heat treatment or acid-alkali treatment; this shows that the porous titanium after surface modification is bioactive. The cellular porous structure was formed on the surface of the porous titanium with acid-alkali treatment; however, the surface of the porous titanium with alkali-heat treatment is spiculate. The surface structure of the acid-alkali treated porous titanium will endow the porous titanium higher surface energy than alkali-heat treatment, accelerate the crystal of bone-like apatite formation, control the growth of the crystal consequently, thereby, form a flat of uniform distribution and small crystal bone-like apatite on the surface of the acid-alkali treated porous titanium. The bone-like apatite formed more quickly on the surface of the porous titanium with acid-alkali treatment than alkali-heat treatment. So, the acid-alkali treatment will endow the porous titanium better bioactivity than alkali-heat treatment.At the same time, we research on the characteristic of the BSA adsorption on the porous titanium. Results show that the amount of BSA adsorbed on the differentsurface treatment is different. The amount of the BSA adsorbed on the different surface treatment are SPT>JPT>PT and ST>JT>T. the cellular porous structure on the um level of the acid-alkali treated titanium provide the surface higher surface energy than alkali-heat treatment, and more OH" group formed on the acid-alkali treated titanium, this will benefit for the BSA adsorb on the titanium. So, the acid-alkali treatment is an efficient surface bioactivity technology for the porous titanium.Finally, the biocompatibility of the porous titanium was studied by cell culture. Results show that the acid-alkali and alkali-heat treated porous titanium will accelerate the proliferation and differentiation of the osteoblasts on the early time of the culture. After 6 days culture, the results of SEM showed osteoblasts grow overlaply on the surfaces of the samples (PT, SPT, JPT) and the pseudopod of cells spread outside obviously. The morphology of osteoblasts were integrated and the osteoblasts proliferate very well. These showed that the acid-alkali and alkali-heat treated porous titanium have good biocompatability.