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Title: Tribology of bio-implants
Author: Sharifi, Shayan
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2013
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The service life of bio-materials used as implants depends on many factors. One of the factors which may significantly reduce the implant's service life duration is wear. Many tribologists have attempted to propose a model to predict wear behaviours involving a wide range of material properties and operating conditions, but it is still believed that there is no way of predicting tribological performances of surfaces with absolute certainty. As a result, laboratory tests on wear of different bio-implants are the most trusted method to evaluate the wear performance of such components in this era. Bio-tribological techniques are developing constantly as long-term clinical results from various designs and materials are needed and wear testing is a critical gating item for preclinical evaluation. Recently, for abrasive wear tests, sphere-on-disc technique in microscale has been used to study the performance of different materials under abrasive wear. However, the possibility of occurrence of different wear mechanisms simultaneously in a tribological environment is high. Therefore, methods have been developed to combine different types of wear mechanisms with a variety of sliding conditions such as tribocorrosion testing. Wear processes which occur in the oral cavity can lead to dental defects which may require a restoration or replacement of damaged tissues. In the first part of this work the tribological behaviour of Y-TZP, as a dental restoration material, in popular caffeine based soft drinks, tea and coffee, under micro-abrasion conditions is investigated. The results suggested that the tea environment is less detrimental to Y-TZP implants than that of coffee. It was also suggested that Y-TZP implants will last up to twice as long when drinking coffee with milk compared to plain coffee, and up to four times as long compared to coffee with sugar. Evidence from the experiments showed that viscosity and acidity exacerbate the effects of load and exposure time. The work continues with investigating the tribocorrosion and wear performance of 316L grade stainless steel as an orthodontic material in artificial saliva using a micro-abrasioncorrosion apparatus. The results showed that linearity in the relationship between load and wear volume is limited to certain ranges. Also, the observed differences between the corrosion potentials at the various loads with and without particles indicated that the stability of tribo-films is critically dependent on the tribological conditions in such environments. Wear is also one of the main limiting factors on the life of total hip joint replacements. As bio-implants in the human body can be exposed to simultaneous chemical/electrochemical and mechanical stresses such as tribocorrosion, the evaluation of such surface degradation were carried out as a combined mechanism of corrosion and mechanical wear. The later part of this work considers and compares the tribological behaviour of a titanium alloy (Ti- 6Al -4V) with a CoCr alloy (CoCrMo) as common bearing materials in artificial hip joints, coated with DLC coating under micro-abrasion-corrosion conditions. The results analysis suggested that the combination of DLC coating and CoCrMo can exhibit a better performance for hip replacement applications. Also, the role of adhesion between the coating and substrate on material removal was pointed out. In order to understand the wear mechanisms involved in each set of experiments, wear mechanism maps were developed to describe the influences of different parameters.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available