Anisotropic Nanofiber-Laden Hydrogel as Guidance to 3D Cell Orientation

Abstract

Along with continuous research in biotechnology, there is a growing demand for cell culture platforms that can provide a more biological microenvironment to induce complex cell behavior. The extracellular matrix (ECM) controls chemical signals and stores cytokines and nutrients beyond the structural support of tissue. It also serves to control the physical signals mediated by the integrins and has structural diversity. On the other hand, in conventional plastic substrates such as flasks and well plates, cells are attached to the surface and cultured so the behavior of cells can be explored only by the response to chemical signals such as growth factors. To mimic various biological tissues, an extracellular matrix environment suitable for each cell activity must be served. The three-dimensional hydrogel culture system can control mechanical properties within a physiological range by controlling crosslinking density of polymer. Hydrogel can also provide a microenvironment that mimics natural surroundings for cell growth. However, overall hydrogel structures were difficult to control the fine physical properties of the cell niche. The limitation of controlling the local environment around cells can be studied by introducing other nanomaterials within hydrogels. Electrospun nanofibers are widely used as scaffolds in tissue engineering that they are easy to fabricate and can simulate the structure of natural proteins derived from ECM. The other advantage of introducing nanofibers is that the porosity of the hydrogel can be maintained and the stiffness of the local area is controlled by the fiber density. Moreover, nanofibers can recreate the topographical heterogeneity of ECM architectures. In particular, aligned structures of connective tissue can be easily found across soft tissue, skeletal muscle, heart tissue, and cancer tumor. From a microscopic point of view, the aligned structure affects angiogenesis, ECM reconstruction, and, electrical signal propagation in neurons. From a macroscopic point of view, it supports tendon loading, transmits muscle force, and is used to determine the malignant prognosis of tumors. However, the traditional strategy to control the direction of cell migration is to give a chemical or physical cell adhesion gradient that would change cellular fates. Moreover, mimicking anisotropy in a three-dimensional structure still has been a challenge. Hence, this research demonstrates to regulate the orientation of cells along gelatin nanofibers aligned under an external magnetic field. This work establishes a new multifunctional scaffold strategy that mimics the aligned three-dimensional fiber structure of various nature tissues with independent control of physical and chemical properties.