Antibiotic-Loaded Ultrahigh Molecular Weight Polyethylenes

Local Antimicrobial Potential of Bupivacaine and Tolfenamic Acid-Loaded Ultra-High Molecular Weight Polyethylene (UHMWPE) for Orthopedic Infection

Peri-prosthetic joint infection (PJI) is a major post-arthroplasty complication that warrants alternative antibacterial approaches to improve prophylaxis and treatment outcomes. Local administration of analgesics post-surgery is common. Recent studies have demonstrated the antimicrobial potential of analgesics and the feasibility of dual drug-eluting ultra-high molecular weight polyethylene (UHMWPE) for local antibacterial applications. However, the antibacterial mechanism of action is poorly understood, and the translational value of antimicrobial dual drug-loaded UHMWPE has not been evaluated. In this study, we utilized the Laurdan assay and gene expression analysis to demonstrate the antibacterial action of bupivacaine hydrochloride (BP) and tolfenamic acid (TA) against Staphylococcus aureus. Furthermore, we incorporated BP and TA into UHMWPE at different weight concentrations and studied their longitudinal drug release and real-time antibacterial properties. The analgesics showed a significant effect on the bacterial membrane properties comparable to known antibiotics and regulated bacterial gene expression. For the dual drug-loaded UHMWPE, the drug release rate from BP/TA combinations was interestingly not a direct function of the loaded drug weight percent, potentially due to the hydrophobicity of TA and the interactions between the two drugs. Combinations of BP and TA at the higher total drug concentration (10 and 20%) showed a prolonged antibacterial effect against S. aureus, with great potential for prophylactic use.

Synergistic antibacterial drug elution from UHMWPE for load-bearing implants

Total joint replacement is a successful procedure for restoring the patient's musculoskeletal mobility and quality of life, but it carries the risk of severe peri-prosthetic joint infections (PJI) and is accompanied by post-operative pain. Cocktails of multiple drugs are often used for prevention/treatment of PJI and for addressing pain. Local drug delivery systems are promising for improving the outcome of the treatment and decreasing the side effects of systemic drugs. To this end, the ultra-high molecular weight polyethylene (UHMWPE) bearing surface of the joint implant is here proposed as a platform for simultaneous release of multiple therapeutics. The combined use of non-antibiotic drugs and antibiotics, and their incorporation into UHMWPE allows to obtain novel antibacterial implant materials. The combined elution of analgesics and antibiotics from UHMWPE is found to be synergistically effective in eradicating Staphylococcus aureus, as the non-antibiotic compound significantly enhances the antibacterial activity of the antibiotic. The drug properties and the employed method for their incorporation into UHMWPE are found to dictate the morphology, thus the mechanical properties of the resulting material. By adopting various fabrication methods, novel formulations showing an enhanced antibacterial activity and outstanding mechanical properties are here proposed to amplify the functionality of polymeric implant materials.

Enhanced Antibiotic Release and Mechanical Strength in UHMWPE Antibiotic Blends: The Role of Submicron Gentamicin Sulfate Particles

BACKGROUND

Periprosthetic joint infections (PJIs) are a major complication of total joint replacement surgeries. This study investigated the enhancement of mechanical properties and antibiotic release in ultra-high molecular weight polyethylene (UHMWPE) through the encapsulation of submicron gentamicin sulfate (GS) particles, addressing the critical need for improved implant materials in orthopaedic surgery, particularly in managing PJIs.

METHODS

The present study involved embedding submicron GS particles into UHMWPE flakes at concentrations of 2% to 10% by weight. These particles were prepared and blended with UHMWPE flakes using a dual asymmetric centrifugal mixer, and the blends were consolidated. The present study compared the mechanical properties and antibiotic release rate of UHMWPE containing submicron, medium (as-received), and large (resolidified) GS particles.

RESULTS

UHMWPE samples with submicron GS particles exhibited superior mechanical properties, including higher ultimate tensile and Izod impact strengths, compared with samples with larger particles. Additionally, the submicron GS UHMWPE blends demonstrated a markedly higher and more sustained antibiotic release rate.

CONCLUSIONS

This study highlights the potential of incorporating submicron GS particles into UHMWPE to drastically improve the feasibility of using these therapeutic and functional spacer implants in expanded indications.

CLINICAL RELEVANCE

By offering improved mechanical strength and effective, prolonged antibiotic release, this innovative material could be used as a spacer implant to reduce the considerably high morbidity and mortality associated with PJIs. This material has the potential to prevent PJIs not only in high-risk revision cases but also in primary total joint arthroplasty procedures.

Investigating the Translational Value of Periprosthetic Joint Infection Models to Determine the Risk and Severity of Staphylococcal Biofilms

With the advent of antibiotic-eluting polymeric materials for targeting recalcitrant infections, using preclinical models to study biofilms are crucial for improving the treatment efficacy in periprosthetic joint infections. The stratification of risk and severity of infections is needed to develop an effective clinical dosing framework with better treatment outcomes. We use in vivo and in vitro implant-associated infection models to demonstrate that methicillin-sensitive and resistant Staphylococcus aureus (MSSA and MRSA) have model-dependent distinct implant and peri-implant tissue colonization patterns. The maturity of biofilms and the location (implant vs tissue) were found to influence the antibiotic susceptibility evolution profiles of MSSA and MRSA, and the models could capture the differing host-microbe interactions in vivo. Gene expression studies revealed the molecular heterogeneity of colonizing bacterial populations. The comparison and stratification of the risk and severity of infection across different preclinical models provided in this study can guide clinical dosing to prevent or treat PJI effectively.

Diffusion doping of analgesics into UHMWPE for prophylactic pain management

Pain management after total joint arthroplasty is often addressed by systemic delivery of opioids. Local delivery of non-opioid analgesic drugs directly in the joint space from the UHMWPE component of the prosthesis would be highly beneficial to increase the efficacy of the drugs, decreasing the overall side effects and the risk of opioid addiction. It has been shown that effective concentrations of local analgesics can be achieved by eluting from analgesic-blended UHMWPE; however, this approach is limited by the decrease in mechanical properties resulting from the extent of phase separation of the blended drugs from the polymeric matrix. Here we hypothesized that mechanical properties could be maintained by incorporating analgesics into solid form UHMWPE by diffusion as an alternative method. Lidocaine or bupivacaine were diffused in solid form UHMWPE with or without radiation crosslinking. The loaded drug content, the spatial distribution of the drugs and their chemical stability after doping were characterized by FTIR and NMR spectroscopy, respectively. Drug release kinetics, tensile mechanical properties and wear rates were assessed. The results showed that diffusion doping could be used as a promising method to obtain a therapeutic implant material without compromising its mechanical and structural integrity.

Investigating the translational value of Periprosthetic Joint Infection (PJI) models to determine the risk and severity of Staphylococcal biofilms

With the advent of antibiotic-eluting polymeric materials for targeting recalcitrant infections, using preclinical models to study biofilm is crucial for improving the treatment efficacy in periprosthetic joint infections. The stratification of risk and severity of infections is needed to develop an effective clinical dosing framework with better outcomes. Here, using in-vivo and in-vitro implant-associated infection models, we demonstrate that methicillin-sensitive and resistant Staphylococcus aureus (MSSA and MRSA) have model-dependent distinct implant and peri-implant tissue colonization patterns. The maturity of biofilms and the location (implant vs tissue) were found to influence the antibiotic susceptibility evolution profiles of MSSA and MRSA and the models could capture the differing host-microbe interactions in vivo. Gene expression studies revealed the molecular heterogeneity of colonizing bacterial populations. The comparison and stratification of the risk and severity of infection across different preclinical models provided in this study can guide clinical dosing to effectively prevent or treat PJI.

Irradiation Behavior of Analgesic and Nonsteroidal Anti-Inflammatory Drug-Loaded UHMWPE for Joint Replacement

Local delivery of pain medication can be a beneficial strategy to address pain management after joint replacement, as it can decrease systemic opioid usage, leading to less side and long-term effects. In this study, we used ultrahigh molecular weight polyethylene (UHMWPE), commonly employed as a bearing material for joint implants, to deliver a wide set of analgesics and the nonsteroidal anti-inflammatory drug tolfenamic acid. We blended the drugs with UHMWPE and processed the blend by compression molding and sterilization by low-dose gamma irradiation. We studied the chemical stability of the eluted drugs, drug elution, tensile properties, and wear resistance of the polymer blends before and after sterilization. The incorporation of bupivacaine hydrochloride and tolfenamic acid in UHMWPE resulted in either single- or dual-drug loaded materials that can be sterilized by gamma irradiation. These compositions were found to be promising for the development of clinically relevant drug-eluting implants for joint replacement.