Modeling of Antibiotic Diffusion from Implanted Absorbable Beads in Localized Injured Tissue
Grant, Kara; Lawson, Olivia; Polins, Ben; Suen, Leslie
Prevention of infection during the healing process in tissue is a major concern and is especially crucial for the health of the patient. In order to combat infection due to bacteria, antibiotics must be deployed in the tissue at a high enough concentration for a long enough period of time in order to be deemed effective. Historically, systemic antibiotics have been administered to diminish the threat of infection, either through intravenous injection or oral ingestion. However, toxicity levels of the drug in the entire body must be taken account, lowering the efficacy of systemic antibiotics. Implanted antibiotic beads provide an attractive alternative by locally administering the antibiotics to the injured soft tissue, allowing higher concentrations of antibiotics to be delivered over a longer period of time, thus increasing the efficacy and safety of the drug. Although these beads must be physically placed into the injured soft tissue, a string of them can easily be implanted as the last step of surgery as a protective measure against future infections. The goal of this project is to model the delivery of vancomycin-impregnated biodegradable antibiotic beads as the vancomycin diffuses into the injured soft tissue. We constructed the model using 2D-axisymmetric geometry in COMSOL. Our bead was comprised of two separate layers, one made of Polylactic Acid containing the initial drug concentration of vancomycin of 12.9 mol/m3, and an outer layer of Polylactide-Polyglycolide Copolymer (PLA-PL:CG), containing no vancomycin. We successfully modeled the shrinking of the biodegradable bead and were able to get results that agreed with other experimental data. These results included collecting data for concentrations of vancomycin in the tissue over time and space. For vancomycin to be successful in fighting infection, the concentration needs to be above the minimum effective level while remaining below the toxic level. Using these requirements, we determined the optimal spacing between multiple beads to be 0.56cm. Our model can be used in place of experimentation to determine the optimal combination of parameters that meet a patient’s needs. This model allows estimation of concentration profiles in the tissue that would otherwise be difficult to gather in an experimental setting. Therefore, our model can be used as a tool for physicians to better prevent infection in traumatic injuries and surgeries.
antibiotic bead implants; vancomycin treatment; PLA bead; PLA-PL:CG polymer coating; antibiotic diffusion