Abstract:Recently, rapid development of medical application of shape memory alloys,mainly NiTi alloys has been made with its unique shape memory effect and superelasticity,Some important achievements and focusing issues related to medical basic research. modeling of mechanical behaviour,new porous alloy,surface modification,medical instrumentation and clinical applications of Nitinol have been briefly introduced in the present paper.

Abstract:In order to describe the shape memory effect and pseudoelasticity due to the martensitic transformation and the R-phase transformation of TiNi shape memory alloy,a thermomechanical constitutive equation considering the volume fractions of induced phases associated with both transformations is developed.The proposed constitutive equation expresses well the properties of the shape memory effect, pseudoelasticity and recovery stress.

Abstract:Widespread methods of ventral stabilization of spine have some insufficiencies,particularty in patients with reurological deficit.From our point of view, Biocompatible Osteoconductive Polymer Block (BOP-B)is a good plastic material.It allows to reduce the operation time and to decrease intraoperative trauma.Experimental studies(18 dogs)and clinical experience(24 patients)have shown a high degree of biointegration of this material which can be compared with original bone.Partial loss of deformity correction during the first, months of bone block formation is an insufficiency of this material.Since 1988, 29 patients have been treated with porous TiNi implants,developed in our clinic.Biomechanical characteristics of this material are comparable to those of bone tissue.Loss of deformity correction was minimal, even without external immobilization.In 1993,6 patients have been operated on with the use of a new combined implant,which consists of porous TiNi and BOP-B, and has properties of both these materials.Porous TiNi supports BOP-B during the period of bony block formation.BOP-B,being a bony conductor, at the same time plays the role of a combined implant fixator. The combind implant allows to mobilize a patient immediately after operation,and to conduct all control examinations, including MRI without artifacts.This implant has been successfully used for the stabilization of cervical and thoracolumbar spine.

Abstract:For the development of Nickel Titanium NiTi)biomaterial devices,the study and improvement of cytocompatibility and biomechanical performances are of prime importance. Following the guidelines of the American Society for Testing Materials (ASTM), our study established that the cytotoxicity of NiTi was worse than that of pure Ti, Ti6A14V and 316L stainless steel. The deposition of plasma polymerized tetrafluoroethylene (PPTFE) thin film on NiTi surface improved cytotoxicity and corrosion resistance of NiTi alloys. The fatigue propertics were improved by various heat treatments and the degradation of the superelastic properties were tested by cyclic tension-tension tests.

Abstract:Constitutive relations describing thermomechanical behaviour of shape memory alloys(SMA)are discussed based on Tanaka's model. Special attention has been paid to the isothermal tensile process and the constrained recovery process.The material parameters in the constitutive equations,namely the elastic modulus D,the transformation tensor Ω,and the thermoelastic tensor Θ.are assessed by using experimental date of TiNi alloys.Strong temperature dependencies of D and are found from different experimental stress-strain-temperature relations.

Abstract:The stress distribution and concentrated forcein the longitudinal and lateral directions produced by Nitinol Patellar Concentrator (NT-PC) in the Two-dunensional patella model were analyzedusing by using the method of photoelasticity.The results showed that the memory compression mainly comes frorri the longitudinal direction (30￣40Kg)and partially from the lateral direction (5￣7.5Kg).NT-PC was employed in 4, 000 cases.It turns out that the time needed for the affected knee to bendstretch like the opposite healthy knee is 2.5￣20 weeks,with a mean of 7.14 weeks. There were no complications of postoperative infection, refracture,necrosis,non-union or functional impediment in the injured knee jonts.It is noteworthy that NT-PC not only adaptable to various kinds of patellar fracture but also advantageous to avoiding"partial or total patellectomy".It is a simple and effective new-method for treatment of patellar fracture.

Abstract:Transverse osteotomy was performed at the middle of each of 52 dog femur.and then fixed pespectively with shape memory sawteeth-arm embracing internal fixator,bone plate and intramedullary nail.The stress shielding rate,bending strength of different directions and torsion strength of the three different fixation methods were measured and compared.The embracing force of the embracing fixtor was found to be high enough,so that the bending force between the embracing fixatorgroup and bone plate group showed no significant difference.But thestress shielding rate of the embracing fixation group was much lower than that of the bone plate group(p<0.01).While the torsion strength of the embracing fixator group was significantly higher than that of intramedullary nail group(p<0.01),The results showed that the embracing fixtor to provide reliable fracture fixation, and prevent osteoporosis caused by stress shielding of bone plate.The embracing fixator also has a good property in the resistance to torsion which is less than that in case of intramedullary nailing fixation, and does not induce further damage to the intramedullary circulation.

Abstract:The therma l oxidation of Ti-50at% Ni alloy between 300℃-400℃ offers a compact thin oxide film. This oxide film on the TiNi specimens of 0.26mm thick affects little on shape recovery ratio and shape recovery temperature. The Ni concentration in oxide film is decreased with increasing oxidation temperature. The existence of this oxide film on TiNi alloy reduces effectively both passive current density of anodic polarization and release of Ni ions in saline solution.in addition.the cell culture experiment further comfirms the advantageous influence of thermal oxidation on the biocompatibility of TiNi alloy.

Abstract:The configuration and characteristics of a newly developed comprehensive characteristic instrument for shape memory materials (SMM), Model SMT-1,have been introduced briefly in this paper.By using several advanced technologies and methods,this instrument can carry out the combination measurements of force(tensile, compression or bending),displacement and electrical resistivity in a wide range of temperature from -150℃ to 400℃ for sheet,strip,wire or spring of SMM,according to different requirements.A computer system autocontrols the experimental process,proceeds data and draws curves.It is possiblo to investigate and estimate the characteristic properties and the phase transformation of shape memory materials, and carry out some research work, which can be hardly studied by using mechanical or physical testing method independently.Some of the essential experimental methods and the significant results,as examples,have also been listed in this paper

Abstract:In this study,an Auto-Even-Load connecting components has been developed by means of self-adapting property of superelasticity of NiTi shape memory alloy.The component can adjust automatically any uneven loads at the conjunction of structures.So the rapture accident due to uneven loads of structures can be avoided. 自动均载; 连接件 auto-even-load connecting component; shape memory alloys