Degradable hydrogels for spatiotemporal control of mesenchymal stem cells localized at decellularized bone allografts

Abstract

Transplantation of cells, such as mesenchymal stem cells (MSCs), has numerous applications in the field of regenerative medicine. For cell transplantation strategies to be successful therapeutically, cellular localization and persistence must be controlled to maximize cell-mediated contributions to healing. Herein, we demonstrate that hydrolytic degradation of poly(ethylene glycol) (PEG) hydrogels can be used to spatiotemporally control encapsulated MSC localization to decellularized bone allografts both in vitro and in vivo. By altering the number of hydrolytically degradable lactide repeat units within PEG-d,l-lactide-methacrylate macromers, a series of hydrogels were synthesized that degraded over ~ 1, 2, and 3 weeks. MSCs were encapsulated within these hydrogels formed around decellularized bone allografts, and non-invasive, longitudinal fluorescence imaging was used to track cell persistence both in vitro and in vivo. Spatiotemporal localization of MSCs to the exterior of bone allograft surfaces was similar to in vitro hydrogel degradation kinetics despite hydrogel mesh sizes being ~ 2–3 orders of magnitude smaller than MSC size throughout the degradation process. Thus, localized, cell-mediated degradation and MSC migration from the hydrogels is suspected particularly as ~ 10 % of the total transplanted MSC population was shown to persist in close proximity (within ~ 650 μm) to grafts 7 weeks after complete hydrogel degradation. This work demonstrates the therapeutic utility of PEG-based hydrogels for controlling spatiotemporal cell transplantation for a myriad of regenerative medicine strategies.

Development of Poly(Ethylene Glycol) Hydrogels for Salivary Gland Tissue Engineering Applications

“…6 In addition, in previous transplantation studies using MSCs, hydrogels with an in vivo degradation time of 2 weeks were employed to improve femoral allograft healing. 43 Together, these studies supported our choice of 14 days as a therapeutic timeframe over which to maintain viability in vitro. SMG cells were isolated, encapsulated in thiolene hydrogels and cell viability was measured using LIVE/ DEAD staining (Fig.…”

“…Previous work using a PEG hydrogel periosteum mimetic to deliver MSCs significantly improved bone healing in a segmental defect model. 31,42 Critical to this approach was the localization and temporal release of MSCs provided by the PEG hydrogel, 43 as MSCs seeded directly on an allograft have little effect on healing. [107][108][109] In previous studies, transplantation of primary SMG cells into irradiated glands was performed using intraglandular *5-10 mL injections.…”

“…40,41 In addition, recent work has demonstrated the ability of PEG hydrogels to provide spatiotemporal control of MSC delivery in vivo to promote bone regeneration. 31,42,43 In this work, methods have been explored to encapsulate, culture, and characterize primary SMG cells within PEG hydrogels, with the long-term goal of developing a tissue engineering approach for the salivary gland. Due to the sensitivity of salivary gland cells to reactive oxygen species (ROS), [44][45][46][47][48] we examined the effects of two forms of radical-mediated hydrogel polymerization: chain addition methacrylate-based polymerizations and step-growth thiol-ene polymerizations on primary SMG cells.…”

Encapsulation of primary salivary gland cells in enzymatically degradable poly(ethylene glycol) hydrogels promotes acinar cell characteristics

“…Hydrogels provide highly controllable platforms to study the mechanistic effects of extracellular matrix (ECM) and soluble factors on encapsulated cell populations. Furthermore, hydrogels can be used to control cell localization and persistence simply through modulation of hydrogel degradation [18]. SMG cells have been cultured in several types of hydrogels derived from natural (e.g., Matrigel, fibrin, hyaluronic acid, and laminin) and synthetic (e.g., poly(ethylene glycol) (PEG)) materials [23–30].…”

Retroductal Nanoparticle Injection to the Murine Submandibular Gland

“…This approach enables the confirmation without euthanizing the mouse and can be continued longitudinally until signal is no longer detectable 26,27 .…”