Material Stiffness Directs Valvular Interstitial Cell Extracellular Matrix Production – A Study Using a Novel Material Platform

More than 100,000 Americans each year undergo aortic valve (AV) replacement due to valve failure. An AV can become diseased, impairing the proper function of the valve. Common treatments for a defective valve are either replacement with a decellularized biologic or a synthetic valve. These treatments options are limited by short functional lifetime and thrombogenic surfaces. Tissue engineered heart valve will have the ability to integrate with the surrounding tissue as well as to repair and remodel. However, a greater understanding of valve cell biology is required to induce analogous tissue formation. A diseased valve is associated with stiffening of the tissue. Researchers have probed the impact of stiffness on cell function but have had results complicated by the limitations of the in vitro models used. 

The synthetic materials commonly used to fabricate cell culture platforms with varied moduli are limited in applicability due to a restricted range of achievable moduli and/or surface instabilities. The copolymer network n-octyl methacrylate (nOM) and diethylene glycol dimethacrylate (DEGDMA) offers attractive material properties that overcome these limitations. We have fabricated co-polymer networks with 3 to 33 wt% DEGDMA with bulk compressive modulus ranging from 25±2 to 4700±300 kPa. Nanoindentation determined cellular level mechanics of the nOM / DEGDMA ranged from 6.5 ± 0.00 to 1,562.5 ± 192 MPa.  The networks demonstrated consistent surface properties of wettability/hydrophobicity, chemical composition, and topography. The nOM/DEGDMA substrates vary in modulus over three orders of magnitude while maintaining comparable chemical and topographical surface features.

The primary cells of the AV, valvular interstitial cells (VICs), were cultured on the nOM/DEGDMA substrates. It was found that the rate of proliferation was not impacted by the stiffness of the culture platform. Additionally, expression levels of the markers of the active and osteoblastic-like cellular phenotypes were not affected by the stiffness of the substrates. Production of collagen-I and sulfated glycosaminoglycans did not change between the different substrate moduli. However, elastin production was significantly upregulated on the softest materials. We have fabricated a cell culture platform that is capable of varying modulus over a three orders of magnitude of a physiologically relevant range and used it to study the changes of VIC functions.