This invention relates generally to water-insoluble but water-swellable and deformable crosslinked PEGylated microgel particles of proteins and protein-based macromolecules that are pseudoplastic (shear thinning) and flow in aqueous media under shear and which can be injected or made to flow, wherein said microgel particles can reform as a cluster of microgel particles when shearing forces are removed. The microgel particles function as a matrix to support cell growth, viability, and proliferation.