Development of in situ assembling microgel-in-hydrogel matrices for directed spinal cord regeneration

Rose, Jonas C.; Möller, Martin (Thesis advisor); De Laporte, Laura (Thesis advisor)

Aachen (2019)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2019

Abstract

The assembly of soft filamentous structures is nature’s way to create the extracellular matrices (ECMs) which surround the cells in tissues. These ECMs are oftentimes anisotropic and enable dynamic interaction with living units. With the aim to template the natural ECM and assemble structures bottom-up, an injectable biomaterial has been developed that forms an anisotropic matrix with high assembly precision. Microscale gel rods were doped with small quantities of superparamagnetic iron oxide nanoparticles (SPIONs) to induce an ultrahigh magnetic response. The magnetic responsiveness of the microgels has been investigated in-depth to develop and verify a model that allows for describing their degree of alignment based on the specific system parameters (aspect ratio, volume, SPION-content, viscosity of surrounding fluid, magnetic field strength and direction). As a result, a broad spectrum of microgel parameters can be varied,while assembling them magnetically with a high degree of control. After alignment, the microgel orientation and position are maintained by a surrounding enzymatically crosslinked hydrogel. The resulting “Anisogel” is a very suitable biomaterial that can be injected for regeneration of sensitive tissues which have a specific directionality, such as the spinal cord, cardiac, or brain tissue. In vitro experiments revealed that cells strongly sense the microgel guiding structures of 5 · 5 · 50 μm3 and grow aligned, despite the very low contents of anisometric microgels of 3 vol%. Moreover,long small diameter microgels of 2.5 · 2.5 · 50 μm3 were sufficient to align neuronal axons at contents as low as 0.6 vol% - a concentration, at which the geometrical constrain for orientation is minimum. These findings indicate a highly efficient cellular sensing mechanism of the 3D guiding structures over multiple micrometer distances. Translocation of the mechanotransducer YAP (Yes-associated protein) into the cell nucleus which scales with the content of microgels is a first evidence of the mechanism by which cells sense the bulk material anisotropy. The material is envisioned as a new, minimally invasive route for therapy after spinal cord injury and may find applicability as a regenerative construct in a number of hierarchically organized tissues with anisotropy or as a platform to study fundamental biological questions related to 3D adhesion, migration and mechanotransduction.