Packed Hydrogel Microfibers as Scaffolds Supporting Dynamic Cellular Behavior and Biomaterial Inks in 3D Printing.

Particle-based hydrogels have been used as injectable scaffolds, biomaterial inks for extrusion bioprinting, and permissive systems for 3D cell culture owing to their unique physical properties, including bulk yielding and porosity. These properties are in part governed by interparticle interactions and spatial organization, with limited potential to design these properties in systems based on spherical hydrogel microparticles. Here, we engineer particle-based hydrogels where each particle is a discrete electrospun hydrogel microfiber that has been segmented to a length of 93 ± 51 µm, with a diameter of 1.6 ± 0.3 µm, presenting unique viscoelastic properties allowing stability without interparticle crosslinking (annealing). The fibers' flexibility and high aspect ratios enable interactions among fibers that give packed hydrogel microfiber (PHM) materials that are mechanically robust, can stretch without breaking when strained, and exhibit tissue-mimetic stress relaxation under constant strain. As cell culture scaffolds, shear-induced alignment of the individual fibers within 3D printed PHM filaments provide topographical cues to cells that promote alignment. Cells embedded in 3D within PHMs spread due to the permissive microenvironment presented by the microfibers. This work highlights strengths of fiber-based particle systems as dynamic and permissive scaffolds and printable biomaterials for tissue engineering and regenerative medicine.