Biological and mechanical compatibility of biomedical titanium alloy materials

doi:10.3969/j.issn.2095-4344.2013.25.020

Abstract

Abstract:

BACKGROUND: Biomechanical compatibility is the key factor for the research and development of surgical implants and orthopedic devices. But the present research lacks systematic and common knowledge.
OBJECTIVE: To preliminarily analyze the concept and intension of biomechanical compatibility of biomedical titanium alloys in order to direct the designing and applying of medical devices.
METHODS: A computer-based search was performed for articles related to biomechanical compatibility in PubMed, Elsiver, SpringerLink, CNKI and VIP databases (1995-2012) to investigate the effects of alloy elements, microstructure and its phase transformation, and surface modification on the biomechanical compatibility of titanium alloys.
RESULTS AND CONCLUSION: It is a comprehensive evaluation for biomechanical compatibility. To design biomedical titanium alloys, first, there should be no toxic alloy elements to ensure the safety in the reaction with the tissue, blood, immune system and whole body; second, it is also required that added elements should have the minimum adverse effects on the mechanical properties and other performance of titanium alloys. Common alloy elements in titanium alloys include α-phase stable element, β-phase stable element, and neutral element. It is important for better biomechanical compatibility of biomedical titanium alloys to control microstructure and phase transitions and even carry out surface modification. But we cannot simply pursue the low modulus and high strength of a titanium alloy that is close or matching the human bone tissue, by which, we adjust the pros and cons of the biomechanical compatibility.

Key words: biomaterials, biomaterial review, titanium alloy materials, biomedical metal materials, orthopedic implants and devices, biocompatibility, mechanical compatibility, National “863&rdquo, Project of China

CLC Number:

R318

Yu Zhen-tao, Han Jian-ye, Ma Xi-qun, Yu Sen, Zhang Ming-hua, Zhang Yu-sheng. Biological and mechanical compatibility of biomedical titanium alloy materials [J]. Chinese Journal of Tissue Engineering Research, 2013, 17(25): 4707-4714.

Figures/Tables 3

2.1 生物医用钛合金材料的生物相容性生物相容性是指材料与生物体之间相互作用后产生的各种生物、物理、化学等反应或耐受能力，即材料植入人体后与人体的相容程度，也就是说是否会对人体组织造成毒害作用。因为任何医疗器械与人体接触、介入或植入体内后都存在一定的潜在风险性。天然或合成的生物材料无论是与人体组织接触或取代、修复病变组织，还是采用模拟人体器官功能的人工装置暂时或永久替代已基本丧失功能的病变器官，它们除少数作为诊断和康复用途外，其中大部分是以治疗疾病为目的。由于它们间接或直接与人体组织和血液相接触，而人工关节、人工心脏瓣膜等要在体内植入几十年直至失效为止，因此，生物医用材料质量的优劣直接关系到患者的生命安危，在临床应用前必须确保其生物相容性和安全性。进行医用钛合金材料选型设计时，首先要求合金中的组成元素无不良反应，同时要求所添加元素对钛合金的机械性能等其他性能不良影响最小。钛合金中常见的合金化元素主要包括α相稳定元素(Al及O、N等气体元素)、β相稳定元素(Mo、Nb、Ta、V等)和中性元素(Zr、Sn)3类，其中Al、V是钛合金中最常用的添加元素，Ti6A14V钛合金已成为目前国内外通用的传统医用材料，也在国防及民用中获得大量应用。但20世纪80年代中期临床应用发现V是对生物体有潜在不良反应的元素，特别是V的生物毒性要超过Ni、Cr[3]，而且此类合金的耐蚀性相对较差。20世纪90年代中期瑞士和德国先后开发出以Nb、Fe替代V的第2代医用钛合金Ti6Al7Nb和Ti5Al2.5Fe并纳入国际生物材料标准，但这两种合金仍含有对人体有不良反应的Al和Fe元素[4]，而Ti5Al2.5Fe钛合金已被弃用。近年来，世界各国先后研究和开发了近百种第3代新型型医用钛合金材料，其涵盖了二元到六元的各个合金系列，见表1[5]。"

2.2 生物医用钛合金材料的力学相容性对于外科植入物用医用金属材料来讲，其力学相容性一般是指植入材料(施体)要有足够的强度和塑韧性，能够将载荷均匀、连续、持久地传递到体内待治疗骨等生物组织(受体)上，并使施体与受体之间在界面处匹配、共存、协调的能力。因此，生物医用钛合金材料的生物力学相容性评价涉及的材料力学参数应包括强度、塑性、弹性模量、耐磨性、疲劳性能、超弹性等方面[7]，它是一个综合评价的概念，单纯追求材料的低模量、高强度等某一单项力学指标与人体骨组织接近或匹配都不能简单判定生物材料生物力学相容性的优劣。而“生物力学相容性”自然也包括和涉及植入材料和周围骨组织弹性形变相匹配的性质，当钛合金植入物产生超过弹性允许应变而发生塑性变形时，即意味着植入材料失效，因此，对于弹性模量的研究和评价自然就成为了生物医用钛合金材料研究的重点。对于人工关节和牙种植体等人体骨硬组织长期替代类产品，医用钛合金材料应同时满足高强度、低弹性模量和优良的抗疲劳性能、耐磨和耐蚀性能，以及良好加工塑韧性等综合力学性能，但要完全满足上述条件又是一个技术难题。通常条件下，提高材料强度，其材料硬度/耐磨性、疲劳强度和弹性模量将增加，而材料的塑韧性将降低。上述矛盾规律使得工程应用中有时必须牺牲材料的部分力学强度来保证其他力学性能的匹配。例如，Al、V元素对钛合金的强化非常有效，但降低了材料的塑韧性，又提高了弹性模量，因此医用钛合金应避免采用或少量加入。但Zr、Nb、Ta、Mo、Hf、Sn等元素能够使钛强化而对塑韧性不利影响较小，同时有利于降低钛合金的弹性模量，可以优选加入。有关合金添加元素对钛合金生物力学性能影响的基本规律见表2。"

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