Encapsulation and recovery of murine hematopoietic stem and progenitor cells in a thiol-crosslinked maleimide-functionalized gelatin hydrogel

Biomaterial platforms are an integral part of stem cell biomanufacturing protocols. The collective biophysical, biochemical, and cellular cues of the stem cell niche microenvironment play an important role in regulating stem cell fate decisions. Three-dimensional (3D) culture of stem cells within biomaterials provides a route to present biophysical and biochemical stimuli such as cell-matrix interactions and cell-cell interactions via secreted biomolecules. Herein, we describe a maleimide-functionalized gelatin (GelMAL) hydrogel that can be crosslinked via thiol-Michael addition click reaction for the encapsulation of sensitive stem cell populations. The maleimide functional units along the gelatin backbone enables gelation via the addition of a dithiol crosslinker without requiring external stimuli ( e.g ., UV light, photoinitiator), reducing reactive oxide species generation. Additionally, the versatility of crosslinker selection enables easy insertion of thiol-containing bioactive or bioinert motifs. Hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs) were encapsulated in GelMAL, with mechanical properties tuned to mimic the in vivo bone marrow niche. We report insertion of a cleavable peptide crosslinker that can be degraded by the proteolytic action of SortaseA, a mammalian-inert enzyme. Notably, SortaseA exposure preserves stem cell surface markers, an essential metric of hematopoietic activity used in immunophenotyping. This novel GelMAL system enables a route to producing artificial stem cell niches with tunable biophysical properties with intrinsic cell-interaction motifs and orthogonal addition of bioactive crosslinks. ### Competing Interest Statement The authors have declared no competing interest.