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A multilayer injectable hydrogel system sequentially delivers bioactive substances for each wound healing stage.

Wound healing is a dynamic and complex process that contains several sequential phases. However, most of the current drug delivery systems were designed to treat only one certain phase of wound repair, ignoring the facts that every stage plays critical roles in wound healing process and those critical stages coordinately work to ensure an optimal tissue regeneration. Therefore, a delivery system that can precisely meet the requirements of each wound healing stage is desired to enhance tissue regeneration. In this study, an injectable sodium alginate/bioglass (SA/BG) composite hydrogel was used to carry SA microparticles containing conditioned medium (CM) of cells (SACM). Inside the SACM microparticles, poly(lactic-co-glycolic acid) (PLGA) microspheres containing pirfenidone (PFD) were encapsulated (PLGAPFD). This multilayer injectable hydrogel system (SA/BG-SACM-PLGAPFD) was designed to sequentially deliver bioactive molecules for meeting bioactivity requirement and timeline of each wound healing stage. Firstly, SA/BG hydrogels could rapidly release BG ionic products in first 1-3 days to regulate the inflammatory response of the host and initiate the subsequent tissue regeneration. Then, SACM hydrogel microparticles could release conditioned medium of RAW 264.7 cells stimulated with BG ionic products in 2-7 days to facilitate the formation of vascularized granulation tissue. Finally, PLGAPFD microspheres released PFD in 8-20 days to prevent the fibrosis and scar formation in the regenerated skin. Thus, this SA/BG-SACM-PLGAPFD delivery system could restrain host inflammation, accelerate wound healing and inhibit the fibrosis formation in a diabetic mouse skin damage model, enhancing skin regeneration. As the bioactive components in each layer of the system can be adjusted according to the requirements of different tissue regeneration, this three-layered injectable biomaterial system has a wide application potential in regenerative medicine field.