ABSTRACT
The metal/ceramic interface that constitutes an important part of the plasma-sprayed HA-coated Ti-6A1-4V system may, in fact, represent the "weak link" in the implant design. A post-plasma-spray heat treatment to enhance chemical bonding at the metal/ceramic interface and, hence, improve the mechanical properties (interface fracture toughness and tensile coating adhesion strength) of the plasma-sprayed implant system does show promise. In preliminary heat treatment studies, however, any improvements realized were lost due to the chemical instability of the coating in a moisture-laden environment, with a concomitant loss in bonding properties. This deterioration in properties appears to be related to environmentally assisted crack growth as influenced by processing conditions. Still, an ability to improve HA/Ti-6A1-4V bonding through enhanced diffusion bonding was demonstrated, warranting further heat treatment studies involving atmosphere control during processing.
Subject(s)
Metal Ceramic Alloys , Prostheses and Implants , Titanium , Alloys , Hot Temperature , Metal Ceramic Alloys/chemistry , Microscopy, Electron, Scanning , Porosity , Prosthesis Failure , Surface Properties , Titanium/chemistry , X-Ray DiffractionABSTRACT
The successful use of plasma-sprayed hydroxyapatite (HA) coatings on Ti-alloy implants for implant-to-bone fixation requires strong adherence of the ceramic coating to the underlying metal substrate. In this study, the metal-ceramic interface was evaluated using mechanical, chemical, and structural characterization methods. Evaluations of an HA-coated Ti-6Al-4V implant system using a modified short bar technique for interfacial fracture toughness determination revealed relatively low fracture toughness values. Additionally, conventional tensile bond strength testing indicated much lower values than previously reported. Using high resolution electron spectroscopic imaging, evidence of chemical bonding was revealed at the plasma-sprayed HA/Ti-6Al-4V interface, though bonding was primarily due to mechanical interlock at the interface. This study illustrates the benefits of, and the need for, a multilevel approach to evaluate and improve these plasma-sprayed ceramic-metal substrate interfaces.
Subject(s)
Biocompatible Materials , Fracture Fixation , Hydroxyapatites , Titanium , Alloys , Analysis of Variance , Ceramics , Durapatite , Microscopy, Electron, Scanning , Stress, Mechanical , Surface Properties , Tensile Strength , X-Ray DiffractionABSTRACT
Syrian hamster embryo cells have been grown in culture on thin (10-50 nm), evaporated substrates of chromium, and examined by analytical transmission electron microscopy. After 10 d exposure, significant metal uptake was observed and numerous cell colonies showed the physical characteristics of carcinogenic transformation. The majority of the ingested chromium appeared to be associated with nucleic acid complexes. As a control, cells grown on titanium showed no signs of metal uptake and had morphologies very similar to cells grown on conventional carbon substrates.
