Our investigation into the oxidative environments of implantable medical devices has led to the understanding that implants can oxidize through free radical-mediated oxidation, biological fluid-mediated oxidation and stress-induced oxidation. Clinically relevant material development relies on in vitro testing of oxidative stability, which is supported by the characterization of retrieved implants.
Our further work focuses on incorporating the effect of synovial fluid lipid absorption and cyclic loading in accelerated aging methods to explain oxidation observed in vivo and to evaluate the clinically relevant oxidative stability of newly developed antioxidant stabilized implant materials.
In vitro accelerated aging of implant material in the presence of synovial fluid lipids absorbed from an laboratory emulsion resemble oxidation of retrieved highly cross-linked UHMWPE.
The incorporation of drugs using different methods such as radiation grafting or high temperature diffusion can result in a wide variety in the macroscopic properties of polymers as well as different limitations in terms of the type and concentration of drugs that can be incorporated into polymeric matrices. Our focus in this area is to explore drug-polymer interactions during manufacturing processes and use them to our benefit in obtaining clinically optimized mechanical properties.
Exploitation of specific drug-polymer interactions result in highly eccentric drug clusters and a percolated porous morphology.
Medical-device and medical procedure-related infections are one of the major factors that can independently determine the success or failure of medical implants. To make a clinically important difference in reducing infection rates associated with orthopaedic devices and procedures, we are interested in exploring multimodal material strategies in preventing, detecting and treating microbial infections. Our approach in this area is to combine our expertise in the structure-property relationships of polymeric matrices to develop anti-infective treatments and medical devices which can be functional in orthopaedic applications and can be versatile at different stages of treatment.
There is a need for soft, load-bearing materials with cartilage-like elasticity and lubricity as early stage treatments in the repair of cartilage defects. Fixation and load-sharing properties are crucial in protecting surrounding and affecting cartilaginous tissue from further damage with the intent of delaying end-stage treatments such as joint replacement.
Implantable polymers used in medical devices can function many decades in vivo in contact with diverse but challenging environment of bodily tissues and fluids. Antioxidants can be incorporated into these polymers to prevent oxidative reactions but there is a higher burden of proof on the efficacy and safety of the incorporation of such additives into medical polymers. The goal of our work in this area is to investigate the benefits and risks of using antioxidant stabilization in medical polymers, especially UHMWPE and to develop associated methods of incorporation and testing.
The antioxidant vitamin E is diffused into UHMWPE to combat radiation-induced and biological fluid-induced free radicals. Vitamin E (alpha-tocopherol) donates a hydrogen to active free radicals and breaks the oxidation cascade.
The structure-property relationships of this unique, high molecular weight polymer, specialized for use in total joint implants, has long been a focus of our lab. The central goal is to modify the crystalline and amorphous structure of this semi-crystalline polymer improving clinically relevant macro properties such as multidirectional wear resistance, resistance against fatigue damage and impact. We work on incorporating structural changes such as extended chain crystal formation (see picture below), controlled chain cross-linking and scissioning or porosification to further the application of this polymer in orthopaedic and other applications.
The Harris Orthopaedics Laboratory comprises preclinical biomechanical research and biomaterials testing along with clinical research involving in vivo follow-up of implant performance.
