High Aspect Ratio and Light-Sensitive Micropillars Based on a Semiconducting Polymer Optically Regulate Neuronal Growth

Many nano- and microstructured devices capable of promoting neuronal growth and network formation have been previously investigated. In certain cases, topographical cues have been successfully complemented with external bias, by employing electrically conducting scaffolds. However, the use of optical stimulation with topographical cues was rarely addressed in this context, and the development of light-addressable platforms for modulating and guiding cellular growth and proliferation remains almost completely unexplored. Here, we develop high aspect ratio micropillars based on a prototype semiconducting polymer, regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT), as an optically active, three-dimensional platform for embryonic cortical neurons. P3HT micropillars provide a mechanically compliant environment and allow a close contact with neuronal cells. The combined action of nano/microtopography and visible light excitation leads to effective optical modulation of neuronal growth and orientation. Embryonic neurons cultured on polymer pillars show a clear polarization effect and, upon exposure to optical excitation, a significant increase in both neurite and axon length. The biocompatible, microstructured, and light-sensitive platform developed here opens up the opportunity to optically regulate neuronal growth in a wireless, repeatable, and spatio-temporally controlled manner without genetic modification. This approach may be extended to other cell models, thus uncovering interesting applications of photonic devices in regenerative medicine.

Surface Patterning and Innate Physicochemical Attributes of Silk Films Concomitantly Govern Vascular Cell Dynamics

Functional impairment of vascular cells is associated with cardiovascular pathologies. Recent literature clearly presents evidence relating cell microenvironment and their function. It is crucial to understand the cell-material interaction while designing a functional tissue engineered vascular graft. Natural silk biopolymer has shown potential for various tissue-engineering applications. In the present work, we aimed to explore the combinatorial effect of variable innate physicochemical properties and topographies of silk films on functional behavior of vascular cells. Silk proteins from different varieties (mulberry Bombyx mori, BM; and non-mulberry Antheraea assama, AA) possess unique inherent amino acid composition that leads to variable surface properties (roughness, wettability, chemistry, and mechanical stiffness). In addition, we engineered the silk film surfaces and printed a microgrooved pattern to induce unidirectional cell orientation mimicking their native form. Patterned silk films induced unidirectional alignment of porcine vascular cells. Regardless of alignment, endothelial cells (ECs) proliferated favorably on AA films; however, it suppressed production of nitric oxide (NO), an endogenous vasodilator. Unidirectional alignment of smooth muscle cells (SMCs) encouraged contractile phenotype as indicated by minimal cell proliferation, increment of quiescent (G0) phase cells, and upregulation of contractile genes. Moderately hydrophilic flat BM films induced cell aggregation and augmented the expression of contractile genes (for SMCs) and endothelial nitric oxide synthase, eNOS (for ECs). Functional studies further confirmed SMCs' alignment improving collagen production, remodeling ability (matrix metalloproteinase, MMP-2 and MMP-9 production) and physical contraction. Altogether, this study confirms vascular cells' functional behavior is crucially regulated by synergistic effect of their alignment and cell-substrate interfacial properties.