Louise M. Jennings

Decellularised heart valves are a promising option for right ventricular outflow tract reconstruction, such as during the Ross procedure. A terminal sterilisation method is required to enhance the clinical translation of these biological scaffolds and ensure patient safety. This study therefore evaluated the feasibility of using supercritical carbon dioxide (scCO ₂ ) supplemented with oxidising agents, as a potential sterilisation approach for low-concentration sodium dodecyl sulfate-decellularised porcine pulmonary heart valve (dPHV) roots. The findings demonstrated that scCO ₂ sterilisation preserved the histoarchitecture and microscopic structure of the dPHV roots, with no observable reduction in collagen or glycosaminoglycan content, and no cytotoxic effects, confirming biocompatibility. A reduction in collagen thermal stability was observed, although matrix composition remained largely unchanged. Several significant differences in biomechanical properties were observed post-scCO ₂ treatment, mainly within elastin-phase behaviour, whereas collagen-phase parameters were largely preserved. Overall, structural integrity was maintained, supporting scCO ₂ as a feasible sterilisation strategy for dPHV roots.

Hemiarthroplasty is a partial joint replacement where one half of the joint is replaced, resulting in a cartilage-on-artificial-material articulation. With the development of novel joint replacement materials and coatings, there is a need to develop and standardise test methods to assess materials tribologically for use in hemiarthroplasty applications prior to implantation. Several different protocols and approaches with differing levels of complexity have been developed to study materials for use in hemiarthroplasty applications, but to date, no consensus has been reached as to the most appropriate method, or suite of methods, to use. The aim of this review article was to assimilate and critique published methods for tribologically evaluating hemiarthroplasty materials, to discuss advantages and limitations of the methods used, to highlight the variables that should be considered when developing new test methods and to identify gaps in the current literature. There is clearly a need to study materials and implants specifically for use in hemiarthroplasty applications and much research has been carried out in the field. However, for protocols to be standardised, there is a need for experts to converge on the most appropriate methodologies.

Hip resurfacing is a bone-conserving alternative to total hip replacement particularly suited to younger or more active patients with good bone stock. Historical issues with metal-on-metal hip resurfacing devices have led to investigations of new materials. In this study, the wear of a BIOLOX delta ceramic-on-ceramic hip resurfacing under a range of activities of daily function was investigated in an experimental simulation model. Under a standard walking gait, increased frequency, and stop–dwell–start conditions, the wear of the ceramic head and cup was low and at the limit of the sensitivity of the measurement technique used (3/million cycles). Only when tested under a jogging-like protocol with higher loading (maximum 4.5 kN) coupled with higher frequency (1.25 Hz), under both continuous running and stop–dwell–start conditions, was wear measurable but still low, with a mean 3/million cycles. At the conclusion of the study, no wear scar was visible on any components and no changes in the surface roughness of the implants was measured. This short-term, pre-clinical study showed low wear of BIOLOX delta ceramic-on-ceramic hip resurfacings when evaluated under a range of activities of daily living and that this material combination has potential for the next generation of large-diameter hip bearings.

Experimental wear simulation of a PEEK-OPTIMA™ polymer-on-UHMWPE total knee replacement has shown equivalent UHMWPE wear to conventional knee replacement materials (cobalt chrome-on-UHMWPE) when tested in a clean environment. The aim of this study was to experimentally investigate the wear of this all-polymer total knee replacement under third body wear conditions. Three PEEK-OPTIMA™ and three cobalt chrome femoral components articulating against all-polyethylene tibial components were tested in a knee simulator. One million cycles of wear simulation was carried out in clean lubricant under conditions replicating walking followed by one million cycles with the lubricant contaminated with porcine bone particles, then one million cycles with PMMA cement particles. UHMWPE wear was determined gravimetrically. Statistical analysis compared UHMWPE wear against PEEK femoral components to cobalt chrome. In clean lubricant and with bone particles in the lubricant, there was no significant difference (p > 0.05) in UHMWPE wear against the different femoral component materials, and wear rates were similar under both conditions. With PMMA particles, there was a dramatic increase in UHMWPE wear for both knee replacement systems but no significant difference (p > 0.05) in UHMWPE wear between the femoral component materials. This is the first study to investigate wear of an all-polymer knee under third body wear conditions.

Osteochondral grafts are used for repair of focal osteochondral lesions. Autologous grafts are the gold standard treatment; however, limited graft availability and donor site morbidity restrict use. Therefore, there is a clinical need for different graft sources/materials which replicate natural cartilage function. Chitosan has been proposed for this application. The aim of this study was to assess the biomechanics and biotribology of a bioresorbable chitosan/chitosan-nano-hydroxyapatite osteochondral construct (OCC), implanted in an in vitro porcine knee experimental simulation model. The OCC implanted in different surgical positions (flush, proud and inverted) was compared to predicate grafts in current clinical use and a positive control consisting of a stainless steel graft implanted proud of the cartilage surface. After 3 h (10 800 cycles) wear simulation under a walking gait, subsidence occurred in all OCC samples irrespective of surgical positioning, but with no apparent loss of material and low meniscus wear. Half the predicate grafts exhibited delamination and scratching of the cartilage surfaces. No graft subsidence occurred in the positive controls but wear and deformation of the meniscus were apparent. Implanting a new chitosan-based OCC either optimally (flush), inverted or proud of the cartilage surface resulted in minimal wear, damage and deformation of the meniscus.

Experimental in vitro simulation can be used to predict the wear performance of total knee replacements. The in vitro simulation should aim to replicate the in vivo loading, motion and environment experienced by the joint, predicting wear and potential failure whilst minimising test artefacts. Experimental wear simulation can be sensitive to environmental conditions; the environment temperature is one variable which should be controlled and was the focus of this investigation. In this study, the wear of an all‐polymer (PEEK‐OPTIMA™ polymer‐on‐UHMWPE) total knee replacement and a conventional cobalt chrome‐on‐UHMWPE implant of similar initial surface topography and geometry were investigated under elevated temperature conditions. The wear was compared to a previous study of the same implants under simulator running temperature (i.e. without heating the test environment). Under elevated temperature conditions, the wear rate of the UHMWPE tibial inserts was low against both femoral component materials (mean 3 /million cycles) and significantly lower ( p < 0.05) than for investigations at simulator running temperature. Protein precipitation from the lubricant onto the component articulating surfaces is a possible explanation for the lower wear. This study highlights the need to understand the influence of different variables including environmental temperature to minimise the test artefacts during wear simulation which may affect the wear rates.

Decellularised heart valve roots offer a promising option for heart valve replacement in young patients, having the potential to remodel and repair. Replacement heart valves have to undergo billions of opening and closing cycles throughout the patient’s lifetime. Therefore, understanding the effect of cyclic loading on decellularised heart valve roots is important prior to human implantation. The aim of this preliminary study was to investigate the influence of low concentration sodium dodecyl sulphate (SDS) decellularisation treatment on the in vitro real time mechanical fatigue of porcine aortic heart valve roots under physiological real time cyclic loading conditions. This required a specific real time in vitro method to be developed, since previous methods relied on accelerated testing, which is non-physiological, and not appropriate for valve replacement materials that exhibit time dependent characteristics. The effects of the real time fatigue on hydrodynamic function and mechanical properties of the heart valve roots were assessed. The mechanical fatigue of decellularised porcine aortic heart valve roots (n = 6) was assessed and compared to cellular porcine aortic heart valve roots (n = 6) in a modified Real time Wear Tester (RWT) at a physiological frequency and under cyclic pressure conditions for a maximum of 1.2 million cycles. Periodically, the heart valve roots were removed from the RWT to assess the influence of cyclic loading on valve competency (static leaflet closure). At the end of testing further hydrodynamic performance parameters were ascertained, along with determination of leaflet material properties. A real time mechanical fatigue assessment method was developed and applied; with two cellular and two decellularised porcine aortic leaflets in different heart valve roots showing tears in the belly region. The decellularised aortic heart valve roots exhibited comparative functionality to the cellular heart valve roots under in vitro static and pulsatile hydrodynamic conditions. However, the material properties of the decellularised aortic leaflets were significantly altered following cyclic fatigue assessment and showed increases in elastin and collagen phase slopes and ultimate tensile strength compared to the cellular porcine aortic leaflets in the circumferential direction. This preliminary study demonstrated that low concentration SDS decellularised porcine aortic heart valve roots can withstand physiological cyclic deformations up to 1.2 million cycles in a RWT whilst maintaining their overall hydrodynamic function and leaflet mechanical properties. This is the first full report of preclinical mechanical fatigue assessment of decellularised porcine aortic heart valve roots under physiological real time conditions.