In Vitro and in Vivo Cytokine-Associated Immune Response to Biomaterials
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The success of implanted medical devices, such as biosensors, is dependent on the immune reaction to the surface of the implanted material. This immune reaction, termed the foreign body reaction, is potentially affected by the physical and chemical properties of the implanted material. Macrophages interact with the surface of the implanted material and secrete intercellular signals, including cytokines and growth factors, which direct the actions of immune cells in the surrounding tissue. The type and quantity of cytokines and growth factors produced by macrophages at an implant surface could be an indicator of the outcome of the foreign body reaction.
This study investigated the effect of the surface chemistry of an implanted device on the production of cytokines and growth factors. First, microdialysis sampling was characterized as a technique for collecting cytokines and growth factors from the tissue surrounding an implant. Based on this characterization, it was determined that a direct sampling method would be more suitable than microdialysis sampling for determining accurate tissue concentrations of cytokines and growth factors. Second, an in vitro model was developed and utilized to assess cytokine and growth factor production from monocyte/macrophage cultures seeded onto commonly implanted polymeric biomaterials with varying surface chemistries. The materials included in this study were polyethylene (PE), polyurethane (PU), polymethyl methacrylate (PMMA), expanded polytetrafluoroethylene (ePTFE), and a cytotoxic organo-tin polyvinyl chloride (ot-PVC) as a positive control. From this in vitro model, it was determined that the varying surface chemistries of these non-toxic materials, excluding ot-PVC, did not significantly affect the types and quantities of cytokines and growth factors produced. Finally, an in vivo model for evaluating the cytokine and growth factor response to an implanted biomaterial was utilized for comparison with the in vitro findings. In this model, biomaterials were implanted subcutaneously within the lumen of a stainless steel mesh cage. The mesh cage served to create a "pocket" where wound exudate fluid collected within the cage, surrounding the implanted biomaterial. The materials included in this study were PE, PU, and ot-PVC. Cytokines and growth factors produced at the material surface were sampled directly from the exudate fluid. The results from this in vivo study indicate that cytokine and growth factor production were not significantly impacted by the varying surface chemistries of the implanted biomaterials. The in vivo data support the findings from the in vitro model, suggesting that the foreign body reaction proceeds in a similar fashion for each of these non-cytotoxic, polymeric biomaterials with varying surface chemistries.
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