Density of Micropillar Array Influences Shear Traction of Individual Pillars on Soft Substrates

Micropatterned surfaces have the potential to greatly enhance anchoring, or traction, performance between medical devices such as stents or catheters and tissue. There are numerous geometric parameters (e.g., cross-sectional shape, diameter, height, array density), loading conditions (e.g., pressure or indentation depth), and material properties that influence micropattern contact properties, thereby creating a vast design space. Previously, our group identified that contact between the lateral surface of an individual pillar in a micropillar array and a soft hydrogel substrate acts as the governing mechanism for enhanced shear traction under a given shear displacement. Here, we explore the influence of the array density on the global shear traction via changes in lateral contact. The experimental and simulation results provide evidence that the array density directly influences the amount of substrate deformation between neighboring pillars for a given indentation depth. Ultimately, the substrate deformation, or deflection, leads to sufficient lateral contact that is required for an increased shear response. Finally, the simulation results show that the total shear traction of a pillar is dominated by the lateral contact pressure when sufficient lateral contact is engaged and by interfacial friction otherwise.