An Experimental Study On Biocompatibility And Ni～(2+) Separation Of Nitinol Modified On Its Surfaces By Titanium Or Titanium-Niobium Alloy

The metal or the alloys are playing the role in that its intensity is not substituted by other nonmetallic kinds of materials. The characteristic of Nickel Titanium Shape Memory Alloy (NiTi) includes anti-corrosion, anti-wearability , good biocompatibility, unique super-elasticity and shape memory property. However, controversies exist in that this alloy has its toxicity,carcinogenesis and others. In the international medical fields, the titanium is the metal material that was widely accepted, however, its resistance to wearability is worse. The metal niobium then is at present thought to be the best material in biocompatibility. The titanium-niobium alloy made by the titanium and the niobium, may obviously enhance its physical performance, and both have non-toxic effects. Using the Plasma Spray (PS) technique, we took NiTi as a substrate and coated on its surfaces by the titanium-niobium alloy to observe the followings: whether the unique super-elasticity and the shape memory property exist or not;the biocompatibility;the biology security.Materials and methodsMaterial:NiTi was provided by the Jing Hang Company. NiTi group: implants were Cut from its casting plate and was polished by SiC sandpaper, the superficial impurity and the pollutant was removed, the 10mm×10mm×10mm cubic implants and diameter 4mm, length 12mm column implants was made,implants contains Ni (atomic ratio), 48.4%, Ti,51.6%;Ti group: Taking NiTi as substrate, the surfaces were coated by the metal titanium by the Plasma Spray (PS) technique, coating thickness was 3.25 urn;TiNb group: Taking NiTi as substrate, too, the surfaces were coated by the titanium-niobium alloy by the homogeneous technique, Coating thickness was the same, the craft was completed in German. Method:1 Preparation before experiments (to clear about correlation parameter and to increase experiment commeasurability)NiTi ingredient by MMAs and Af of the three groups by mercury thermometer change of MRF by MTS 858 MiniBiox II machinesuperficial ingredient of implants by XPS, coating thickness and the shape by XFAMsurface roughness by roughness template meter2 Ni2+ separating experimentsIn vitro ,we used the physiological immersing experiment after l-7d experiment to incinerate in low temperature, to take Mg (NO3) 2 as the substrate improver, and to determine the Ni2+ concentration in each group of physiological saline by GFAAS.In vivo, we took 18 grown-up dogs as the experimental object, randomly divided into 3 groups, to implant the cube about the musculu spinalis and the column into the thighbone in the surgical operation way separately, each 10, after 12 months, to execute dogs to select materials, used the GFAAS to examine Ni2+ concentration of the heart, the liver, the spleen, the lung, the kidney, the brain, the bone, the nasopharyngeal mucous membrane, the blood, bone tissue and muscular tissues around the implant separately.3 Biocompatibility experiments Muscular tissuesWe watched roughly by histological observation to detect the FCAl thickness and the structure and to analyze quantitatively separately Bone tissueWe watched no decalcify slice ,push-out test and OR test4 Corrosion experimentsTo determine year corrosion rate of each group by determining the Ni2+ content in physiological saline immersing testTo watch surface luster (tarnishing), to analyze and appraise the anti-corrosive performance of three groups materials by XPSTo use the fracture technique , to observe coating thickness and the structural change with XFAM in vivoTo determine coating attrition and corrosion situationResults1 Preparation before experimentsNiTi ingredient is stable, Ni/Ti atom percentage is 48.46/51.65TT has slightly elevated after coated ,but does not have the remarkable differenceTo partial implants, after the coating, although MRF has reduced , but still retained its original above 80%, still could satisfy deformation to need.Coating indicated that, two kinds of coating have succeeded, have shielded the Ni element, the coating was smooth, thickness is approximately 3.25umRoughness of NiTi, Ti and TiNb is 6, 8 and 9" respectively2 Ni2+ separating experimentsIn vitro, separating in physiological saline immersing experiment was 12.5 u g/L, 2.35 H g/L, 1.21 u. g/L and 0.32 Mg/L respectively before 4 day, after 5th day did not have obvious Ni2+ separation. The control had noIn vivo ,the Ni2+ concentration is higher in the bone tissues and in the muscular tissues around the implants (P < 0.05) compared to control and blank group . 3 Biocompitibility Muscle tissuesThe histology observation did not have the obvious macrophage and the inflammation cell infiltrate;capillary formation could be seen in the fiber capsule around the TiNb coating, but others did no. The thickness (um)of FCAI of the NiTi group, the Ti group and TiNb group was 38.8, 25.8 and 26.1 respectively, the difference is remarkable( p< 0.01) Bone tissuesThe MPS (MPa) of NiTi group, Ti group and TiNb group was 71.6, 95.1 and 91.2 respectively, the difference is remarkable (< 0.01);OR (%) of three groups above were 21.3, 32.5 and 38.6 respectively, between each other ,the difference is remarkable (P< 0.01).4 Corrosion experimentsIn vitro, the corrosion rate (^m/a) of NiTi, Ti and the TiNb group was 0.0691, 0.0324 and 0.0713 respectively;In vivo, the obvious corrosion phenomenon can be seen in all NiTi groups, possibly was corroded by the ammonium salt, but the difference between Ti group and TiNb group was not obvious, roughness changed from 6, 8 and 9'before experiment to 9, 9+ and 9 after.Conclusions1 The ingredient of NiTi is stable;the TT of NiTi after coated by Ti and the TiNb had slightly elevated, but was not remarkable. To the partial implants, MRF have reduced, but can still meet the medical needs. The Ni element have been shielded by the coating , the coating was smooth. The thickness was approximately 3.25um.2 Physiological saline immersing experiments indicated that the coating of Ti or TiNb had prevented Ni2+ from separating out. The difference of Ni2+ concentration of bone tissues and muscular tissues around implants of NiTi was remarkable compared to the same tissues (P < 0.01)3 Biocompatibility of each group was good histologically, biocompatibility of Ti groups and TiNb groups were better then NiTi groups by FCAI, MPS and OR, but the difference was not remarkable between Ti groups and TiNb groups4 In vitro, the experiment indicated three groups of implants had good anti- corrosion , but NiTi groups in vivo had the obvious corrosion phenomenon, mainly for tarnishing and ingredient change, but Ti groups and TiNb groups had not obviously corrosion.