Medical News Observer

Researchers from Moscow Institute of Physics and Technology (MIPT) have researched nanofibrous scaffold structure and its interaction with rat heart muscle cells.  This study revealed that cardiac muscle cells envelop nanofibers as they grow, but fibroblasts tend to spread out on fibers forming several focal adhesion sites.

Nanofibers enveloped by Heart muscle cells. The 3-D model was reconstructed using scanning probe nanotomography. Credit: Moscow Institute of Physics and Technology.

The study was conducted at MIPT’s Laboratory of Biophysics of Excitable Systems in collaboration with the researchers from the Shumakov Federal Research Center of Transplantology and Artificial Organs and the Institute of Theoretical and Experimental Biophysics of the Russian Academy of Sciences. The article is published in the journal Acta Biomaterialia.

“Using three independent methods, we discovered that during their development on a nanofibrous scaffold, cardiomyocytes wrap the fibers on all sides creating a ‘sheath’ structure in the majority of cases,” explains Professor Konstantin Agladze, head of the Laboratory of Biophysics of Excitable Systems. “Fibroblasts, by contrast, have a more rigid structure and a much smaller area of interaction with the substrate, touching it only on one side.”

The scaffolds used for cardiac tissue engineering are based on a matrix of polymer nanofibers. Nanofibers may vary regarding elasticity and electrical conductivity, or they may have additional “smart” functions allowing them to release biologically active molecules at a certain stage. Nanofibers are designed to mimic the extracellular matrix, which surrounds the cells, providing structural support. Also, nanofibers can be used as a medium for delivering substances into the surrounding cells to induce biochemical changes in them.

The team conducted a three-stage study. First, the researchers examined the structure of cardiomyocytes (heart muscle cells) and fibroblasts (connective tissue cells) grown on a substrate of nanofibers using confocal laser scanning microscopy. Cell samples were then sectioned into ultrathin slices in a plane perpendicular to the direction of the fibers and “photographed” using transmission electron microscopy (TEM). The researchers discovered that heart muscle cells envelop nanofibers on all sides so that the fiber ends up being in the middle of the cell. Nevertheless, it remains separated from the cytoplasm by the cell membrane.

Connective tissue cells, on the other hand, do not “swallow” the fiber; they only touch it on one side. Moreover, transmission electron microscopy images demonstrate that the nucleus of the fibroblast is relatively rigid compared to other cell components. This makes fibroblasts less flexible, reducing their ability to stretch along the fiber. Transmission electron microscopy made it possible to study the cross sections. Then, using scanning probe nanotomography, a comprehensive 3-D model was created.

Researchers observed some crucial aspects of the cell-fiber interaction. First of all, since stronger mechanical adhesion, i.e., the cell-scaffold attachment means cells are more stable growing on the substrate, heart muscle cells will be firmly attached to the scaffold, while fibroblasts will be less stable.

Secondly, additional “smart” scaffold functions, such as the release of growth factors will also differ depending on the cell type. In the case of heart muscle cells, which tend to envelop the nanofiber, the released substances will diffuse directly from the fiber through the cell membrane and into the cytoplasm. In the case of fibroblasts, on the other hand, a certain amount of these substances will leak out.

Thirdly, heart muscle cells isolate the polymer fibers from the surrounding solution. Since heart muscle cells are responsible for the transfer of electromagnetic waves within the heart immersing the fibers of the scaffold entirely in heart muscle cells will enable researchers to test the electrical conductivity of the cells.

Researchers feel that this study will enable the creation of nanofibers that would provide cells with the properties needed to form regenerative tissues.

Citation: Balashov, Victor, Anton Efimov, Olga Agapova, Alexander Pogorelov, Igor Agapov, and Konstantin Agladze. “High resolution 3D microscopy study of cardiomyocytes on polymer scaffold nanofibers reveals formation of unusual sheathed structure.” Acta Biomaterialia 68 (2018): 214-22. doi:10.1016/j.actbio.2017.12.031.

Research funding: Ministry of Education and Science of the Russian Federation

Adapted from press release by Moscow Institute of Physics and Technology  (MIPT)