(84h) Phenotypic Control of Valvular Interstitial Cells Using Self-Assembled Monolayers

Current research in heart valve tissue engineering focuses on the use of valvular interstitial cells (VICs) for repair and regeneration of healthy, living valve tissue, with the goal of synthesizing replacement tissue for diseased valves. As myofibroblasts, VICs exhibit phenotypic plasticity in response to their micro-environment.  However, the specific cues that regulate phenotypic expression and ECM production are not well understood.  This work aims to isolate the effects of material surface chemistry on VIC behavior in vitro using well-defined, homogeneous self-assembled monolayers (SAMs).  Due to the large quantities of negatively charged molecules present during valvogenesis, it was hypothesized that a negatively charged environment would induce VICs to an active, ECM producing phenotype. To examine the influence of physiologically relevant functional groups on attachment, proliferation, and differentiation of VICs, SAMs presenting CH₃ (hydrophobic), OH (hydrophilic), COO^- (negative at physiological pH), and NH₂⁺ (positive at physiological pH) end groups were fabricated. Surfaces were consistent with previous literature as determined by static sessile drop contact angle and x-ray photoelectron spectroscopy (XPS). Initial seeding of VICs showed uniform attachment on all surfaces except CH₃, which exhibited a 50% reduction in cellular binding. Over seven days in culture, VICs on the negatively charged COO^- surfaces exhibited the greatest rate of proliferation (MTT assay) and alpha-smooth muscle actin expression (immunocytochemical staining, qPCR) among the treatment groups indicating a healthy, activated phenotypic state. Amine (NH₂⁺) surfaces also showed increased proliferation and aSMA expression but exhibited indications of differentiation to an osteobastic-like, diseased state with changes in morphology, formation of calcified nodules, and production of osteocalcin. These results support our hypothesis that the negatively charged surface of the carboxyl terminated SAMs leads to an environment that induces the healthy, active VIC phenotype most suited for use in tissue engineering applications.  Further studies are currently being conducted to examine integrin expression as well as tissue production.