骨科植入金属材料表面电化学制备磷酸钙涂层方法及机理研究

Investigation on method and mechanism of electrochemical deposition ofcalcium phosphate coating on metallic orthopaedic implants

目的 探讨骨科植入金属材料表面化学制备磷酸钙涂层方法及机理。方法 首先在控制钙/磷摩尔比条件下采用滴定法建立磷酸钙的沉淀边界pH曲线,然后根据曲线确定4种涂层工作溶液浓度和pH。接着利用线性扫描伏安法确定4种溶液中在不同电极电位下所发生的界面阴极反应,并明确合适的工作电位。结果 滴定测得磷酸钙溶液的沉淀边界曲线显示,当溶液pH低于边界0.7~1.2时溶液可保持3天以上不发生沉淀且可以稳定形成涂层。电化学沉积电位的合理区间为-1.0~-1.2 V。将pH控制在沉淀边界以下(~1.0),选择-1.15 V为电化学沉积的工作电位,在4种工作溶液中均成功制备了磷酸八钙为主要相的涂层。通过电极反应动力学研究了电流-时间关系,发现涂层形成初期氢离子还原为涂层沉积提供了初始过饱和度,水分子还原为涂层生长提供持续的驱动力。结论 成功确定了电化学沉积磷酸钙的关键条件并阐述了涂层生成机理,且该涂层方法也已成功应用于钽金属,具有广泛适用性。

Objective Electrochemical deposition is a new technique for preparation of calcium phosphate coatings on metallic orthopaedic implants.However,existing studies on this technique are primarily empirical and systemic studies are lacking.The present study attempted to address these limitations by rational establishment of coating conditions and investigation of mechanisms.Methods First,a calcium phosphate precipitation boundary curve was established by titration under a constant Ca/P molar ratio,and then four working solutions were selected based on this curve.Subsequently,cathodic reactions in the four solutions were determined by linear sweep voltammetry,and optimal potential range was selected based on the voltammograms.Results The precipitation boundary curve of calcium phosphate solution was obtained by titration and found that when the solution pH was below the boundary of 0.7-1.2,the solution remained stable for more than 3 days and the coating could be formed.The range of the electrochemical deposition potential is approximately 1.0 to 1.2 V.When the pH was controlled~1.0 below the precipitation boundary,1.15 V was selected as the working potential,uniform coatings consisting predominantly of octacalcium phosphate were prepared on titanium from all four working solutions.Current-time curves were fitted to the Cottrel equation,indicating a two-phase pattern:initial driving force provided by reduction of H+,and sustained calcium phosphate crystals formation driven by reduction-splitting of water molecules.Conclusion The key factors affecting electrochemical deposition of calcium phosphate coatings are successfully determined and the coating formation mechanism is elaborated.Moreover,coating conditions are similarly established for tantalum,indicating this mechanism-based approach to be a robust and for designing coating techniques for various metallic implants.