CLINICAL SIGNIFICANCE: All implanted materials elicit an immune response that leads to the foreign body reaction. This foreign body reaction often causes fibrosis around the implant. For implants such as glucose sensors, the fibrosis is one of the primary causes for limiting current FDA-approved implanted glucose sensors to 5 to 7 days for clinical decisions (e.g., to inject insulin or to consume carbohydrate). Macrophages are believed to provide the complex bioactive molecular cues that direct the foreign body reaction leading to fibrosis of the implant. Our hypothesis is that directing the polarization of macrophages to a wound healing M2c phenotype will promote healing and tissue integration without excessive fibrosis or inflammation. Completion of this work will provide significant in vivo bioactive agent pathway information to create and rapidly assess new and improved bioengineering approaches to reduce or eliminate the fibrosis associated with the foreign body reaction. Additionally, these studies will provide important quantitative molecular information with respect to cytokine pathways altered during efficacious methods that alter macrophage phenotype. EXPERIMENTAL APPROACH. Microdialysis sampling probes will be used as glucose sensor mimics that can concomitantly deliver mediators aimed to alter macrophage phenotype while sampling the bioactive cytokines produced at the implant/tissue interface in rats. This approach will allow rapid testing of different drugs or cytokines with the aim of directing macrophages to the wound healing M2c phenotype. The compounds that will be used in this study to direct macrophage polarization include interleukin-10 (IL-10), an anti-inflammatory cytokine;dexamethasone, an anti-inflammatory corticosteroid;iloprost (PGI2), a promising anti-fibrotic agent;and PGE2, an endogenous prostaglandin known to reduce fibrosis. The microdialysis probe will be used to collect the cytokines produced during polarization alteration to predict successful conversion to the M2c polarization state. The microdialysis probe will also be used to assess how device calibration and longevity is altered during the different treatments. Real- time whole animal cellular imaging will be employed to image cellular movement to the implanted device. The combination of these approaches will provide rapid translation of in vitro studies to animal models with efficacy verification.
Many implanted medical devices including glucose sensors generate an immune response that ultimately leads to the formation of a collagen capsule (fibrosis) that limits their longevity. Direct delivery of compounds to the tissue/device interface to direct immune cells to a wound healing state would increase device longevity. Measuring the complex chemical signals produced during wound healing will provide important information for reducing the immune response to any implant.
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