Acquired and innate immunomodulatory effects in vitro of electrospun polydioxanone, collagen, and soluble elastin

Immune response testing of biomaterials is an essential component of biocompatibility assessment, particularly when the materials of interest are used to design bioresorbable scaffolds that promote in situ regeneration, using the host as both the bioreactor and the cell source for remodeling of scaffolds into native tissue. Typical studies evaluating effects on the immune system are frequently incomplete and only evaluate small fragments of the immune responses. In particular, effects on acquired (i.e. cell-mediated and humoral) immune responses are largely ignored in favor of inflammatory responses and macrophage cytokine production. This research presents the first comprehensive in vitro evaluation of biomaterial-induced modulation of acquired and innate immune responses following exposure to electrospun blends of polydioxanone (PDO) with elastin (ELAS) or type I bovine collagen (CI). Results indicated that in vitro exposure of murine spleen cells to both PDO-ELAS and PDO-CI blends results in significant immunomodulation in multiple cell-mediated (T-cell proliferation, mixed leukocyte response, and cytotoxic T-cell response), humoral (B-cell proliferation and Mishell-Dutton antibody-forming cell response), and innate assays (natural killer cell activity). No effects were seen in multiple macrophage functional assays (phagocytosis, chemotaxis, and production of reactive oxygen and nitrogen species). PDO-ELAS and PDO-CI blends each promoted decreases in LPS-stimulated macrophage release of IL-1, IL-6, and IFN-gamma. In addition to these assessments of in vitro immune responses, electrospun PDO scaffolds incorporated with Monocyte Chemotactic Protein-1 (MCP-1) were fabricated and examined for their potential to influence macrophage infiltration/adherence, and to allow extended chemokine release. Over the course of 120 hours, MCP-1 released into supernatant peaked at 24 hours and was detectable by enzyme-linked immunosorbent assay (ELISA) only when added to PDO solutions at 3000 ng/ml prior to electrospinning. The biological activity of PDO/MCP-1 hybrids was characterized for their influence on macrophage adherence/infiltration of scaffolds. Results demonstrated an increasing dose-responsive trend with increasing MCP-1 concentration. These studies represent the first comprehensive immunotoxicological evaluations of bioresorbable materials that have significant potential uses in vascular replacement applications to meet the cardiovascular health crisis facing today's aging population.