High resolution 3D microscopy study of cardiomyocytes on polymer scaffold nanofibers reveals formation of unusual sheathed structure.

Building functional and robust scaffolds for engineered biological tissue requires a nanoscale mechanistic understanding of how cells use the scaffold for their growth and development. A vast majority of the scaffolds used for cardiac tissue engineering are based on polymer materials, the matrices of nanofibers. Attempts to load the polymer fibers of the scaffold with additional sophisticated features, such as electrical conductivity and controlled release of the growth factors or other biologically active molecules, as well as trying to match the mechanical features of the scaffold to those of the extracellular matrix, cannot be efficient without a detailed knowledge of how the cells are attached and strategically positioned with respect to the scaffold nanofibers at micro and nanolevel. Studying single cell - single fiber interactions with the aid of confocal laser scanning microscopy (CLSM), scanning probe nanotomography (SPNT), and transmission electron microscopy (TEM), we found that cardiac cells actively interact with substrate nanofibers, but in different ways. While cardiomyocytes often create a remarkable "sheath" structure, enveloping fiber and, thus, substantially increasing contact zone, fibroblasts interact with nanofibers in the locations of focal adhesion clusters mainly without wrapping the fiber.

STATEMENTS OF SIGNIFICANCE: We found that cardiomyocytes grown on electrospun polymer nanofibers often create a striking "sheath" structure, enveloping fiber with the formation of a very narrow (∼22 nm) membrane gap leading from the fiber to the extracellular space. This wrapping makes the entire fiber surface available for cell attachment. This finding gives a new prospective view on how scaffold nanofibers may interact with growing cells. It may play a significant role in effective design of novel nanofiber scaffolds for tissue engineering concerning mechanical and electrical properties of scaffolds as well as controlled drug release from "smart" biomaterials.