Stable, long-acting mesenchymal stromal cell secretome delivery via injectable starPEG-heparin hydrogels for sustained immunomodulation.

The secretome of mesenchymal stromal cells (MSCs) has emerged as a promising cell-free therapeutic strategy for regenerative medicine and immune modulation. However, its clinical translation remains limited by restricted stability and the short in vivo half-life of its bioactive factors, often requiring repeated administrations. Here, we describe an injectable star-shaped poly(ethylene glycol)-heparin (starPEG-heparin) hydrogel that enables the stable loading and sustained release (up to 14 days) of a lyophilized immunomodulatory MSC secretome (LS). Controlled delivery resulted from the interplay between LS-derived protease-driven hydrogel degradation and bioactive factor affinity to the heparin building block. Release studies showed sustained liberation of regenerative, immunomodulatory, and matrix-modulating factors, including VEGF, PDGF-AA/BB, IL-1Ra, IL-4, IL-10, Gal-9, and TIMP-1, yielding a compositionally balanced release profile over time. Importantly, hydrogel-released LS preserved robust bioactivity for 14 days, inhibiting ConA-induced PBMC proliferation and partially repolarizing M1 macrophages toward an anti-inflammatory phenotype (reduced CD86 and increased CD209/CD163). These results demonstrate that starPEG-heparin hydrogels maintain LS stability and immunomodulatory bioactivity in vitro for up to two weeks, supporting their use as controlled-release matrices for MSC-derived secretome-based approaches.