W. M. Keck Biomedical Materials Research Laboratory, School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164-2920, United States.
W. M. Keck Biomedical Materials Research Laboratory, School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164-2920, United States.
Acta Biomater. 2018 Jan 15;66:118-128. doi: 10.1016/j.actbio.2017.11.022. Epub 2017 Nov 8.
To mitigate shortcomings in current biomedical CoCrMo alloy, composites of CoCrMo with calcium phosphate (CaP) were envisioned. CoCrMo alloy was reinforced with CaP to enhance the wear resistance of the alloy. A powder based direct energy additive manufacturing technique of Laser Engineered Net Shaping (LENS™) was used for processing of CoCrMo alloy with 1% and 3% (by weight) of CaP in the form of hydroxyapaptite. Addition of CaP was found to stabilize the ε (hcp) phase along with the more common γ (fcc) phase of the CoCrMo alloy, and the microstructure showed discontinuous chromium carbide phase. The resultant composite showed hardness similar to the base material, however, there was significant increase in the wear resistance of the alloy due to the addition of CaP. During wear testing, a tribo-layer or a tribofilm was found to develop on the surface. This led to the reduction in the leaching of Co and Cr ions during wear testing. The tribofilm was found to be dependent on the wear distance, and made the CoCrMo-CaP composites an in situ self-protecting system. The overall coefficient of friction of the CoCrMo-CaP composite was found to increase but was more stable with the wear distance as compared to the CoCrMo alloy with no CaP addition.
Co-based alloys, an ideal choice for biomedical load-bearing implants, show low wear rates along with low coefficient of friction (COF) and good resistance to corrosive media. However, significant material loss can occur in vivo due to wear and/or corrosion of CoCrMo over long periods of time. Release of metal ions in the human body over time leads to medical complications such as metallosis, which can often require a revision surgery that can adversely affect the quality of life for the patient. We hypothesize that metal ion release from CoCrMo alloys can be reduced during articulation using an in situ formed inorganic tribofilm, and our results validate our hypothesis in calcium phosphate reinforced CoCrMo composites.
为了弥补当前生物医学 CoCrMo 合金的不足，设想了将 CoCrMo 与磷酸钙（CaP）复合。在 CoCrMo 合金中加入 CaP 以提高其耐磨性。采用粉末床直接能量添加制造技术激光工程净成形（LENS™），以制造添加 1%和 3%（重量）羟磷灰石形式的 CaP 的 CoCrMo 合金。研究发现，添加 CaP 可以稳定 CoCrMo 合金中的 ε（hcp）相以及更常见的 γ（fcc）相，并且微观结构显示出不连续的碳化铬相。复合材料的硬度与基体材料相似，但由于添加了 CaP，合金的耐磨性显著提高。在磨损试验过程中，发现表面形成了一层摩擦层或摩擦膜。这导致在磨损试验过程中 Co 和 Cr 离子的浸出减少。摩擦膜的形成依赖于磨损距离，使 CoCrMo-CaP 复合材料成为原位自保护系统。与未添加 CaP 的 CoCrMo 合金相比，CoCrMo-CaP 复合材料的整体摩擦系数增加，但随着磨损距离的增加更加稳定。
