This thesis investigates whether the testing method proposed by the International Standards Organisation (ISO) for determining the fatigue performance of total knee tibial trays is clinically relevant, and if so what would be the appropriate load for testing. Fracture of tibial trays occurs for a number of reasons. These include poor design, insufficient support beneath the tray, inadequate manufacturing and material properties, malalignment, incomplete coverage of the tibial plateau, and overloading due to patient weight and/or activity level. The literature identified a number of trays that had a propensity for fracture. These tray designs are now no longer used. A survey was conducted of current designs from manufacturers' data. Examples of trays that had a history of clinical failure and those that are regarded as clinically successful were analysed using finite element analysis (FEA) and mechanical testing under the ISO test conditions for a range of load values. The results showed that using a physiological value of 2000N (peak force during the normal walking cycle) all trays that had some history of failure and some of the clinically successful trays failed. Further analysis revealed that a load level of 900N distinguished between clinically successful and unsuccessful trays. The ISO test also showed that trays always failed with a crack propagating in the anteroposterior direction (across the length of the tray). Examination of retrieved trays using light microscopy and scanning electron microscopy revealed that crack propagation occurred in a number of other ways as well as across the length of the tray. FEA of a tibial tray placed in a realistic bone model showed that support conditions play a large part in the way in which crack propagation occurs and the likelihood of fatigue fracture. Further fatigue testing with a variety of support conditions validated this result. Hence an alternative testing method was developed based on clinical findings. This showed that multiple crack formation occurred for a tray that had some history of clinical failure due to fatigue. Using this method, a load of 2000N can be used to distinguish between clinically successful and unsuccessful trays. The test was also repeatable. However the results of this testing method always revealed the same design faults as those predicted by the ISO test protocol. Based on these factors, it is the final conclusion of this study that the ISO test protocol is clinically relevant when using a load level of 900N.

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Debris created during the wear of prosthetic joints is known to have an effect on the success of the implant. As such the factors affecting wear and lubrication need to be understood in order to reduce wear as much as possible in vivo. In this thesis a number of orthopaedic biomaterials were tested in vitro, and various factors affecting their tribology were investigated. Load was found to affect wear for stainless steel on UHMWPE contacts, but not the wear factor which has a load term incorporated into it. Increasing nominal contact stress, however, was found to cause a decrease in wear factor particularly at low values of contact stress. The wear factor was less affected at higher values of contact stress. Clearance and roughness were both seen to affect the lubrication mode under which ceramic-on-ceramic joints operated, as noted by extensive friction testing. Lower clearances and lower roughnesses respectively promoted fluid film lubrication. The wear remained very low in both cases and was undetectable gravimetrically. However, changes in the surface morphology throughout testing supported the fact that some wear did occur, but that this was so small as to be beyond the detection limits of the experiment. This is encouraging for the longevity of these joints in vivo. The "running-in" phenomenon seen in metal-on-metal combinations was investigated using large diameter metal-on-metal resurfacing prostheses. During the course of wear testing the initially higher wear rate dropped to a much lower steady state wear. Friction testing indicated that the joints were operating closer to fluid film lubrication and the topography of the joint surfaces became more negatively skewed as the test progressed.

Implantable devices such as urethral catheters are the most commonly used urological devices. The most common problem affecting these devices is infection, leading to significant morbidity and eventual mortality. The challenge is to alleviate the long-term issue of device related infection. This study involved the development of light-responsive biomaterials, which demonstrated the controlled release of model therapeutic agents from within the polymer matrix, when irradiated with a specific wavelength of light. The use of light as a trigger for the release of a therapeutic agent from a polymeric matrix is attractive, as wavelength, intensity, site and duration of application of light can be coupled to release of the therapeutic agent. The pphotolabile ester of3,5-dimethoxybenzoin with a model acidic drug (ibuprofen) attached was synthesised and loaded into the polymer scaffold, which comprised of2-(hydroxyethyl) methacrylate crosslinked with ethyleneglycol dimethacrylate, once irradiated, the porous hydrogel allowed the diffusion of the model drug from the polymer matrix once liberated, and the retention of the photolytic by-product within the polymer structure. A second 3,5-dimethoxybenzoin ester was synthesised with ciprofloxacin attached, achieving controlled release of an antimicrobial in situ, thus preventing bacterial adherence and subsequent biofilm formation. The idea of chromatic orthogonality was explored and the 3,5-dimethoxybenzoin and nitrobenzyl derivatives were synthesised and utilised due to their differential reactivities at specific wavelengths, allowing multi-drug release, stimulated using monochromic light of different wavelengths. Light triggered transdermal drug delivery was examined,. novel pHEMA microneedles with the light reactive conjugate incorporated into the matrix were successfully synthesised. Drug release studies demonstrated the ability of the pHEMA microneedles to penetrate the synthetic skin and deliver the model drug ibuprofen. Modification of the surface ofa silicone biomaterial to allow the incorporation of two different porphyrins Meso- Tetraphenylporphyrin and Protoporphyrin IX was carried out, in order to develop an anti-adherent surface, preventing attachment of microorganisms and subsequent biofilm formation. An anti-infective surface has been developed which is successful at preventing bacterial colonisation of Gram-positive microorganism. The concept of light-triggered drug release of a model therapeutic agent from a hydrogel biomaterial has been demonstrated, it offers an exciting new prospect within drug delivery.

The MITCH PCRTM Cup is an evolution of the anatomic, flexible Cambridge Cup. The Cambridge Cup two layer mechanical interlock design has been converted to a mono-block structure, where the bearing articulation is formed of the same material as the bulk of the cup. The cup has an outer surface that should enhance long term bony fixation. The Cambridge Cup metal on polyethylene bearing has been changed to a ceramic on polyetheretherketone bearing. Prior to seeking Ethical Committee approval for the first MITCH PCRTM Cup clinical study, validation that the acetabulum could be prepared in a manner which would allow the MITCH PCRTM Cup to be implanted safely, was undertaken. This study describes the four phases of the validation process and the modification made to the cup design in order to ensure safe acetabular preparation. The first study investigated the effect of interference fit on cup deflection. An interference fit of O.5mm or less was required to ensure polar contact necessary for safe tribological performance. The second study examined the variability of socket dimensions achieved in foam blocks, using reamers provided by five different commercial manufacturers. Excessive socket undersizing was a common finding with all but the EPM reamers. These reamers were validated for accuracy and precision. In the third study, EPM reamers were used to ream cadaveric bone. The socket dimensions obtained were variable with an interference fit of up to 1.8mm obtained. Bony protrusions were observed which could also increase cup deflection and compromise proper cup seating. As a consequence, the cup internal geometry was modified to accommodate the spectrum of findings observed. The fourth study used the modified cups and a new reaming strategy comprising both conventional and custom MITCH PCRTM finishing reamers to achieve safe acetabular preparation. The results showed satisfactory clearance was achieved at the cup side arms in all cases. The reaming solution was appropriate for progression to the first clinical implantation. The surgical technique manual was completed and the cup was CE marked.

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