Mesenchymal stromal cell spheroids in sulfated alginate enhance muscle regeneration

The therapeutic efficacy of mesenchymal stromal cells (MSCs) for tissue regeneration is critically linked to the potency of the complex mixture of growth factors, cytokines, exosomes, and other biological cues that they secrete. The duration of cell-based approaches is limited by rapid loss of cells upon implanta-tion, motivating the need to prolong cell viability and extend the therapeutic influence of the secretome. We and others demonstrated that the secretome is upregulated when MSCs are formed into spheroids. Although the efficacy of the MSC secretome has been characterized in the literature, no studies have re-ported the therapeutic benefit of in situ sequestration of the secretome within a wound site using engi-neered biomaterials. We previously demonstrated the capacity of sulfated alginate hydrogels to sequester components of the MSC secretome for prolonged presentation in vitro , yet the efficacy of this platform has not been evaluated in vivo . In this study, we used sulfated alginate hydrogels loaded with MSC spheroids to aid in the regeneration of a rat muscle crush injury. We hypothesized that the use of sulfated algi-nate to bind therapeutically relevant growth factors from the MSC spheroid secretome would enhance muscle regeneration by recruiting host cells into the tissue site. The combination of sulfated alginate and MSC spheroids resulted in decreased collagen deposition, improved myogenic marker expression, and in-creased neuromuscular junctions 2 weeks after injury. These data indicate that MSC spheroids delivered in sulfated alginate represent a promising approach for decreased fibrosis and increased functional re-generation of muscle.Statement of significanceThe therapeutic efficacy of mesenchymal stromal cells (MSCs) for tissue regeneration is attributed to the complex diversity of the secretome. Cell-based approaches are limited by rapid cell death, motivating the need to extend the availability of the secretome. We previously demonstrated that sulfated algi-nate hydrogels sequester components of the MSC secretome for prolonged presentation in vitro , yet no studies have reported the in situ sequestration of the secretome. Herein, we transplanted MSC spheroids in sulfated alginate hydrogels to promote muscle regeneration. MSC spheroids in sulfated alginate de-creased collagen deposition, improved myogenic marker expression, and increased neuromuscular junc-tions. These data indicate that MSC spheroids delivered in sulfated alginate represent a promising ap-proach for decreasing fibrosis and increasing functional muscle regeneration.(c) 2022 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc.This is an open access article under the CC BY-NC-ND license( http://creativecommons.org/licenses/by-nc-nd/4.0/ )