Mesenchymal Stem Cell Spheroids Embedded in an Injectable Thermosensitive Hydrogel: An In Situ Drug Formation Platform for Accelerated Wound Healing

The ability of mesenchymal stem cells (MSCs) to enhance cutaneous wound healing has been well established. Extensive expansion of cells to reach sufficient cell numbers for regenerating tissues has always limited cell-based therapies. An ingenious solution to address this challenge is to develop a strategy to increase the immunomodulatory effects of MSCs without expanding them. In this study, we employed a simple characteristic of cells. It was observed that an optimized three-dimensional (3D) MSC culture in spheroid forms significantly improved their paracrine effects. An electrospray (ES) encapsulation apparatus was used to encapsulate individual or 3D spheroid MSCs into microscale alginate beads (microbeads). Furthermore, alginate microbeads were embedded in an injectable thermosensitive hydrogel matrix, which gels at skin temperature. The hydrogel fills and seals the wounds cavities, maintains high humidity at the wound area, absorbs exudate, and fixes microbeads, protecting them from direct contact with the harsh wound environment. In vitro investigations revealed that secretion of interleukin 10 (IL-0) and transforming growth factor beta 1 (TGF-beta 1) gene was gradually enhanced, providing a delivery platform for prolonged release of bioactive molecules. In vivo study on full-thickness wounds showed granulation and re-epithelialization, only after 7 days. Moreover, increased expression of alpha-smooth muscle actin (alpha-SMA) in the first 14 days after treatment ensured wound contraction. Besides, a gradual decrease in alpha-SMA secretion resulted in reduced scar formation. Well-organized collagen fibrils and high expression of the angiogenesis biomarker CD31 confirmed the promoting effect of the hydrogel on the wound-healing process. The proposed wound-dressing system would potentially be used in scalable and effective cell-based wound therapies.