Biocompatibility Of Activated Low Modulus Ti-29Nb-13Ta-4.6Zr And Ti-Nb-Zr-Sn Alloy

ObjectivePure titanium and Ti - 6A1 - 4V alloys are currently widely used as structural biomaterials for the replacement of hard tissues in devices such as dental implants, because they have excellent specific strength and corrosion resistance, and the best biocompatibility characteristics among metallic biomaterials. The rigidity of titanium alloys is still considerably greater than that of the cortical bone although the rigidity of titanium alloys is less than that of Co - Cr type alloys and stainless steels used for biomedical applications. However, β type titanium alloys Ti -29Nb - 13Ta —4. 6Zr have been developed in order to obtain low rigidity, which is considered effective for promoting bone healing and remodeling. The recent trend in research and development of titanium alloys for biomedical applications is to develop low rigidity β type titanium alloys composed of non - toxic and non - allergic elements with excellent mechanical properties. According to this concept, a newer alloy, Ti - Nb - Zr - Sn alloy which has lower elastic modulus and high strength has been developed by Institute of Metal Research, Chinese Academy of Sciences.Titanium reacts strongly with atmospheric oxygen to create titanium oxides (TiO, TiO2, Ti2O3). Moreover, titanium and its alloys are generally recognized among the most biocompatible metallic materials, such a high degree of biocompatibility also being intimately connected with the oxide layer formed on the metallic surface. However, none of these alloys can form a chemical bond with living bone. A common method to resolve this problem is physically forming a thin film of the highly biocompatible calcium phosphate ( Ca - P) coating on the surface of the alloys. Processes for this purpose include dip coating, electron- beam deposition, hot isostatic pressing, pulsed laser deposition and plasma spraying. Of these methods, plasma spraying is most often used. Recently, new treatments that create a biocompatible layer mainly by chemical reactions after improvement of the bioconductivity of implant surfaces (without physically making a Ca - P thin film on the surface of the alloy) were developed. Compared with previous physical methods, the chemical treatments are simpler, more economical and capable of producing uniform coating on complex shape implant.Similar to other biomedical titanium alloys, Ti -29Nb - 13Ta -4. 6Zr and Ti - Nb - Zr - Sn alloy also cannot form a chemical bond with bone directly. Our previous study shows that oxidation treatment of the alloy led to the formation of a hard layer on its surface which greatly improves its wear resistance. If the surface after the oxidation treatment is bioconductive, a Ca - P layer will form therein after immersion in a biomimetic solution, and the wear resistance may be improved simultaneously.The biological performance of a biomaterial has to take into account the material's mechanical, physical, and chemical properties, as well as the host response. Biological evaluation plays a crucial role when these materials are intended for human use. The selection of materials for medical applications is usually based on considerations of biocompatibility. The biocompatibility of a material can be evaluated by in vitro and in vivo tests. In vitro testing is usually accepted as a first - choice method for testing toxicity of a material. Among many in vivo evaluation tests, the osteointegration methods are used to measure the biocompatibility of intraosseous implants. The inflammatory response to the implant is also examined. Many in vivo implants studies have attempted to provide an understanding of the implant bone interface by measuring the mechanical performance of this interface in various ways. Others have attempted to describe the structural nature of the bone implant interface, of various biomaterials, by means of qualitative and/or quantitative estimates.In this work, biocompatibility of Ti -29Nb - 13Ta -4. 6Zr and Ti - Nb -Zr - Sn alloy, the surface characteristics after alkali treatment of preoxidized Ti -29Nb - 13Ta -4.6Zr and Ti - Nb - Zr - Sn alloy, as well as the bioconductivity of the resultant surface, have been investigated. And finite element analy-sis ( FEA) is performed to investigate stress distribution of mandible and implant with different moduli and different face loads.Methods1. FEA is performed to investigate stress distribution of mandible and implant with different moduli and different face loads.2. Biocompatibility testing 2. 1 Materials and treatmentA Ti -29Nb - 13Ta -4. 6Zr (the alloy is abbreviated as TNTZ below) ingot with a diameter of 60 mm was fabricated by induction skull melting using pure Ti, Nb, Ta and Zr as raw materials and then hot forged to rods of 20mm in diameter. The composition of the experimental alloy obtained by wet chemical and gas analysis is 30.2 Nb, 12.4 Ta, 4. 8 Zr, 0. 16 0, 0.01N(mass% ) and balanced by Ti.The cleaned samples were dried in air and used for the oxidation treatment and alkali treatment.The melting and treatment methods of Ti - Nb - Zr - Sn (TNZS) alloy is abbreviated.2. 2 Formation and growth of calcium phosphate on the surface of activated TNTZ alloyThe bioconductivity of a new titanium alloy TNTZ achieved by a combination of surface oxidation and alkali treatment is reported in this paper. Surface treatment and immersion in a protein - free simulated body fluid and fast calcification solution were perform. Characterization of TNTZ surface after treatment was investigated in detail by JSM -6301F scanning electron microscope (SEM) and Ca - P precipitation on the treated TNTZ was investigated by the XPS.2. 3 In vitro SampleTwelve 1.0 - mm - thick disk - shaped pure Ti, TNTZ, Ti - 6A1 -4V, TNZS alloy samples were cut from a 10 - mm diameter rod supplied by Institute of Metal Research, Chinese Academy of Sciences.2.4 In Vivo SamplesFor the in vivo tests 20 pure Ti, Ti -6A1 -4V, TNTZ, TNZS alloy implants were machined from the above rod as cylinder - shaped screws. They were about 6 mm long and 3. 3 mm in diameter. Ten of these implants remained uncoated; the other ten were oxidation treated and alkali treated.2. 5 Sterilization of SamplesAll samples, both the disk - shaped ones used for the in vitro tests and the cylinder - shaped screw implants used in vivo, were ultrasonically degreased in acetone plus ethyl alcohol solution for 10 min each. They were then air dried and sterilized by routine method.2. 6 In Vitro testRat gingival fibroblasts were used for in vitro tests. These cells were sub-cultivated over the material samples in order to evaluate their behavior. To cultivate rat gingival fibroblast with the TNTZ and TNZS alloy extraction and examine the cell growth ratio by MTT test. Rat gingival fibroblasts were seeded on the surface of TNTZ,TNZS, Ti -6A1 -4V alloy and pure titanium plate. The cells attached to the mental surface were counted respectively and morphology of them was observed after acridine orange stain by fluorescence microscope. And morphology of them was observed by scanning electron microscopy. Then we can learn effects of low modulus TNTZ and TNZS alloy for implantation on the biological behavior of gingival fibroblast.2. 7 In vivo testRabbit's left high bone was drilled transcortically. Three insertion beds were created on left side of the high bone for implantation under saline irrigation, according to a routinely used surgical protocol. The implants were inserted. After a healing period of 12 weeks the animals were sacrificed and the bone block containing plants were immediately fixed in 10% buffered formalin solution, Firstly the interfaces of the implant bone were checked with the radiograph , then undecalcified sections were made and observed by light microscope.Results1. The FEA results show that with the decrease of Young's modulus of theimplant, the stress in the spongy bone area will decrease and the stress in the cortical bone region will increase slightly, which is quite benefit for the vulnerable spongy bone from injuring.2. After alkali treatment, the oxidized surface became more porous and many cracks were found in the oxidation layer. After immersion in SBF and FCS, respectively, some spherical and platy precipitations formed on oxidized and alkali - treated TNTZ surface, respectively. The XPS results shown that bone - like apatite layer formed on FCS and SBF - soaked TNTZ, but the apatite layer on SBF - soaked TNTZ is thin.3. The results of MTT test indicate that TNTZ and TNZS alloy has no harmful effect on rat gingival fibroblast. The study of the cell adherence and proliferation suggests that there was no significant difference between TNTZ, TNZS alloy and pure titanium.4. In vivo test indicated that the implant surfaces of pure Ti, TNTZ and TNZS alloy samples which were oxidation treated and alkali treated integrate with the bone more closely than the ones without treatment.Conclusion1. It is concluded that reducing elastic modulus of implant is a valid way to improve biomechanic compatibility of dental implant.2. Alkali treatment induced bioactivity of oxidized TNTZ alloy. Bone - like apatite layer formed on the surface of the treated substrate after soaked in two kinds of biomimetic solution for proper times.3. The histocompatibilities of two new biomedical titanium alloy TNTZ and TNZS are excellent.4. The biocompatibilities of two new biomedical titanium alloy TNTZ and TNZS achieved by a combination of surface oxidation and alkali treatment are excellent.