Magnetic Microgels for Composite Musculoskeletal Tissue Regeneration

PROJECT SUMMARY Humans have limited regenerative potential after extensive musculoskeletal injuries, particularly following limb loss. As such, the ability to biologically restore the missing limb will significantly improve the quality of life for millions of amputees. To this end, the murine digit has emerged as a powerful pre-clinical model to investigate potential mechanisms for mammalian limb regeneration. Previous studies showed that combined delivery of bone morphogenetic protein 2 (BMP2) and BMP9 to amputated digits stimulated skeletal elongation and cartilage/synovial joint regeneration, respectively. This suggests that presenting appropriate soluble cues to endogenous cells at the amputation site can restore key signaling pathways involved in limb morphogenesis. However, these studies relied on multiple surgeries to deliver proteins in a time- and location-dependent manner, which would be clinically challenging. Therefore, the overarching goal of this Trailblazer Award proposal is to develop a translational strategy to sequentially deliver BMP2 and BMP9 and assess its potential to spatiotemporally control bone and joint formation after digit amputation. To direct protein release towards specific regional compartments, we will engineer BMP2- and BMP9-releasing micron-sized hydrogels (‘microgels’) that can be co-delivered as a single injection and then separated in vivo using an externally applied magnetic field. We will test the central hypothesis that spatiotemporally delivering BMP2 and BMP9 using magnetic microgels will promote progenitor cell-mediated regeneration of bone followed by articular cartilage after digit amputation. To test this hypothesis, in Aim 1 we will fabricate and evaluate bioactive magnetic field-responsive microgels in vitro. In Aim 2, we will probe the in vivo therapeutic effect of microgel-mediated growth factor delivery to non- regenerative amputated digits in adult mice. By developing a novel biomaterial delivery platform to release multiple growth factors in a localized and tunable fashion, this Trailblazer Award proposal will open new avenues to therapies that will help restore the biological composition and structure of complex musculoskeletal tissues. More broadly, this innovative technology may find widespread application for treating commonly injured tissues that regenerate via outgrowth, including spinal cord, peripheral nerves, vasculature, as well as engineering composite tissue interfaces that require modular and user-controlled chemokine gradients, such as the tendon enthesis.