TRIBOLOGICAL SYSTEMS FOR THE EVALUATION OF SUPERCRITICAL CARBON DIOXIDE STERILIZED ULTRA-HIGH MOLECULAR WEIGHT POLYETHYLENE

Polymeric biomaterials are especially susceptible to changes in mechanical and surface material properties as a result of sterilization processes that involve heat, moisture and/or irradiation. This is problematic for polymeric materials used in total joint replacement bearings, as these constructs must retain their superior mechanical and tribological properties over their expected 10-20 years of implantation. A younger more active patient population has now exacerbated this longevity issue with service lifetimes of 20+ years now being expected. Supercritical phase carbon dioxide (SC-CO2) is an industrial solvent that has shown great promise as a sterilizing agent in the food industry. Recently, SC-CO2 has adapted for the sterilization of medical grade total joint replacement ultra-high molecular weight polyethylene (UHMWPE), reducing the exposure of the polymer to the detrimental effects of heat, moisture and/or radiation. Further research is needed however to evaluate the effect of SC-CO2 sterilization on the mechanical, surface and tribological properties of UHMWPE over time. This dissertation explores the use of SC- CO2 sterilization for UHMWPE for total joint applications from a tribological perspective. It seeks to investigate and quantify fundamental tribological measures that occur at the bearing contact of total joint replacements, and it formulates and develops new experimental techniques and testing systems to investigate these tribological phenomena. This dissertation explores the hypothesis that SC-CO2 sterilization does not significantly affect the mechanical and/or tribological properties of UHMWPE, making it a \u27material safe\u27 sterilization treatment for this sensitive polymer. To answer this hypothesis, this dissertation develops and employs a series of clinically relevant wear testing methodologies in conjunction with industry standard material and surface characterization techniques to evaluate the efficacy of SC-CO2 for UHMWPE sterilization

Alien Registration- Desjardins, John (Old Town, Penobscot County)

https://digitalmaine.com/alien_docs/5883/thumbnail.jp

Service Induced Byproducts for Localized Drug Delivery in Orthopaedic Implants

A composite material including ultra-high molecular weight polyethylene in conjunction with a biologically active agent is described. The biologically active agent can be, for example, an anti-osteolytic agent such as a bisphosphonate. The composite material can be utilized in forming implants such as total joint replacement implants. The biologically active agent can be released from the composite material either from the bulk or from wear particles released from the surface of the implant component during use. Upon release, the biologically active agent can carry out the intended function of the agent

Lockable Implants

Total joint replacements for implants include a first member configured to attach to a first bone, a second member configured to reside in an adjacent second bone and a locking mechanism. The locking mechanism is configured to (i) lock the first and second members in alignment for full extension or other defined stabilized configuration and (ii) unlock to allow the first and second members to pivot relative to each other for flexion or bending

Lockable Knee Implants and Related Methods

Total knee replacements for hinged knee implants include a tibial member, a femoral member, a hinge assembly having a laterally extending axle configured to hingedly attach the femoral member to the tibial member, and a lock mechanism in communication with the hinge assembly. The lock mechanism is configured to (i) lock the femoral member in alignment with the tibial member for a full extension or other defined stabile walking configuration to thereby allow an arthrodesis or stiff knee gait and (ii) unlock to allow the femoral and tibial members to pivot relative to each other for flexion or bending when not ambulating

Lockable Knee Implants and Related Methods

Total knee replacements for hinged knee implants include a tibial member, a femoral member, a hinge assembly having a laterally extending axle configured to hingedly attach the femoral member to the tibial member, and a lock mechanism in communication with the hinge assembly. The lock mechanism is configured to (i) lock the femoral member in alignment with the tibial member for a full extension or other defined stabile walking configuration to thereby allow an arthrodesis or stiff knee gait and (ii) unlock to allow the femoral and tibial members to pivot relative to each other for flexion or bending when not ambulating

Some Like It Hot: Linking Diffuse X-ray Luminosity, Baryonic Mass, and Star Formation Rate in Compact Groups of Galaxies

We present an analysis of the diffuse X-ray emission in 19 compact groups of galaxies (CGs) observed with Chandra. The hottest, most X-ray luminous CGs agree well with the galaxy cluster X-ray scaling relations in $L_X-T$ and $L_X-\sigma$, even in CGs where the hot gas is associated with only the brightest galaxy. Using Spitzer photometry, we compute stellar masses and classify HCGs 19, 22, 40, and 42 and RSCGs 32, 44, and 86 as fossil groups using a new definition for fossil systems that includes a broader range of masses. We find that CGs with total stellar and HI masses $\gtrsim10^{11.3}$ M$_\odot$ are often X-ray luminous, while lower-mass CGs only sometimes exhibit faint, localized X-ray emission. Additionally, we compare the diffuse X-ray luminosity against both the total UV and 24 $\mu$m star formation rates of each CG and optical colors of the most massive galaxy in each of the CGs. The most X-ray luminous CGs have the lowest star formation rates, likely because there is no cold gas available for star formation, either because the majority of the baryons in these CGs are in stars or the X-ray halo, or due to gas stripping from the galaxies in CGs with hot halos. Finally, the optical colors that trace recent star formation histories of the most massive group galaxies do not correlate with the X-ray luminosities of the CGs, indicating that perhaps the current state of the X-ray halos is independent of the recent history of stellar mass assembly in the most massive galaxies.Comment: 20 pages, 7 figures, accepted for publication in Ap

Evaluation of Isokinetic Single-Leg Cycling as a Rehabilitation Exercise Following Anterior Cruciate Ligament Reconstruction Surgery

The anterior cruciate ligament (ACL) is one of the most commonly injured ligaments, with over 250,000 injuries per year in the United States. Previous studies have found that ACL-deficient individuals avoid use of the quadriceps in the injured limb as a means of limiting anterior movement of the tibia in the absence of a functioning ACL. From these results, a study was designed to investigate the effectiveness of isokinetic single-leg cycling in increasing quadriceps muscle recruitment and activation. Ten control and seven ACL-reconstructed subjects completed a series of 15 s cycling trials in isokinetic mode at 75 rpm, while kinematic, kinetic, and electromyographic data of the lower limbs were collected, with the trials including both double-leg and single-leg cycling. It was hypothesized that there would be an increase in quadriceps muscle activity, peak knee extensor moment, and knee joint power in single-leg cycling when compared to double-leg cycling. The results of the study suggest that single-leg cycling may be an effective exercise in increasing the strength of the quadriceps following anterior cruciate ligament reconstruction surgery. Although no significant changes occurred, the results indicate that, given a specific limb power, more muscle force will be generated from the quadriceps muscle group in single-leg cycling than double-leg cycling