Micro Topography Patterning of General Elastomer Surfaces as Endothelial Substrate

Endothelialization of cardiovascular implants, such as ventricular assist devices, is a promising approach to counter the adverse events associated with foreign body reactions. However, this approach has its own set of challenges, including issues with endothelium retention under non-physiological flow conditions. Although surface topography modification has been demonstrated to be effective in protecting endothelial cells under flow, the technology is primarily based on silicon-wafer micromanufacturing and thus difficult to apply on curved surfaces. This thesis introduces a novel approach for the engineering of surface topography, which involves utilizing spontaneous polymer curing and droplet condensation to pattern free surfaces, instead of relying on a fixed template. This method, known as "breath figures" (BF), has been demonstrated to work effectively on a wide variety of surfaces. By adjusting curing temperature and droplet nucleation time, a broad range of topography sizes can be achieved. With a specific protocol, the resulting topography is compatible with endothelialization and can protect endothelium under dynamic flow changes. Comprehensive characterization was conducted to assess the endothelium's response to the topography and anticipate any potential adverse reactions. Importantly, the new topography was shown to be immediately conductive on free form surfaces coated with a thin elastomer layer. The topography that protect endothelial cells under flow was applied on a tubular surface, conductive wires and the inflow cannula of a ventricular assist device. To determine whether the protective effect was caused by the conditioned flow or by the topography, we pursued two approaches comparing the response of an endothelium on a flat surface (flat group) with an endothelium on a BF treated surface (topography group). First, we subjected the endothelium to a different mechanical signal, cyclic stretch, in the presence of the topography. The results demonstrated that the endothelial morphology under cyclic stretch was very similar between the flat group and the topography group, indicating that the topography did not significantly alter the response to cyclic stretch. Secondly, we investigated the molecular changes that occur within endothelial cells, such as protein phosphorylation, protein localization, and gene expression. Our findings showed that the endothelial cells behaved similarly on a molecular level between the flat group and the topography group. These findings indicate that the protective effect is likely due to the flow diversion that occurs in the near field of the BF topography. Additionally, we identified a mechanotrasduction pathway that is triggered by the adherens junction and that regulates the endothelial barrier function under different conditions. This discovery contributes to shed new light on the long-standing debate regarding whether junctional $\beta$-catenin participates in the well-known $\beta$-catenin signaling pathway. The results demonstrate that physical cues, such as topography, flow shear and substrate deformation can influence the integrity of the endothelium, with implication for the endothelialization of cardiovascular devices as well as for mechanobiological investigation of the pathophysiology of cardiovascular diseases