Burdick, J. | Search bioRxiv

bioRxiv2021

Anisotropic Rod-Shaped Particles Influence Injectable Granular Hydrogel Properties and Cell Invasion

Granular hydrogels have emerged as a new class of injectable and porous biomaterials that improve integration with host tissue when compared to solid hydrogels. Granular hydrogels are typically prepared using spherical particles and this study considers whether particle shape (i.e., isotropic spheres versus anisotropic rods) influences granular hydrogel properties and cellular invasion. Simulations predict that anisotropic rods influence pore shape and interconnectivity, as well as bead transport through granular assemblies. Photocrosslinkable norbornene-modified hyaluronic acid is used to produce spherical and rod-shaped particles using microfluidic droplet generators and formed into shear-thinning and self-healing granular hydrogels at low and high particle packing. Rod-shaped particles form granular hydrogels that have anisotropic and interconnected pores, with pore number and size, storage moduli, and extrusion forces influenced by particle shape and packing. Robust in vitro sprouting of endothelial cells from embedded cellular spheroids is observed with rod-shaped particles, including higher sprouting densities and sprout lengths when compared to hydrogels with spherical particles. Cellular invasion into granular hydrogels when injected subcutaneously in vivo is significantly greater with rod-shaped particles, whereas a gradient of cellularity is observed with spherical particles. Overall, this work demonstrates potentially superior functional properties of granular hydrogels with rod-shaped particles for tissue repair.

bioengineering↗

bioRxiv2021

Microstructured hydrogels to guide self-assembly and function of lung alveolospheres

Epithelial cell organoids have increased opportunities to probe questions on tissue development and disease in vitro and for therapeutic cell transplantation. Despite their potential, current protocols to grow these organoids almost exclusively depend on culture within three-dimensional (3D) Matrigel, which limits defined culture conditions, introduces animal components, and results in heterogenous organoids (i.e., shape, size, composition). Here, we describe a method that relies on polymeric hydrogel substrates for the generation and expansion of lung alveolar organoids (alveolospheres). Using synthetic hydrogels with defined chemical and physical properties, human induced pluripotent stem cell (iPSC)-derived alveolar type 2 cells (iAT2s) self-assemble into alveolospheres and propagate in Matrigel-free conditions. By engineering pre-defined microcavities within these hydrogels, the heterogeneity of alveolosphere size and structure was reduced when compared to 3D culture while maintaining alveolar type 2 cell fate of human iAT2 and primary mouse tissue-derived progenitor cells. This hydrogel system is a facile and accessible culture system for the culture of primary and iPSC-derived lung progenitors and the method could be expanded to the culture of other epithelial progenitor and stem cell aggregates.

bioengineering↗