A FoxA2+ long-term stem cell population is necessary for growth plate cartilage regeneration after injury.

Longitudinal bone growth, achieved through endochondral ossification, is accomplished by a cartilaginous structure, the physis or growth plate, comprised of morphologically distinct zones related to chondrocyte function: resting, proliferating and hypertrophic zones. The resting zone is a stem cell-rich region that gives rise to the growth plate, and exhibits regenerative capabilities in response to injury. We discovered a FoxA2+group of long-term skeletal stem cells, situated at the top of resting zone, adjacent the secondary ossification center, distinct from the previously characterized PTHrP+ stem cells. Compared to PTHrP+ cells, FoxA2+ cells exhibit higher clonogenicity and longevity. FoxA2+ cells exhibit dual osteo-chondro-progenitor activity during early postnatal development (P0-P28) and chondrogenic potential beyond P28. When the growth plate is injured, FoxA2+ cells expand in response to trauma, and produce physeal cartilage for growth plate tissue regeneration.

In situ gelling and dissolvable hydrogels for use as on-demand wound dressings for burns.

Currently, no dressings utilized in burn clinics provide adhesion, hydration or mechanical strength on the same order as human skin as well as the ability to be atraumatically removed. We report the synthesis, characterization, and in vivo evaluation of in situ polymerized and subsequent dissolvable hydrogels as burn wound dressings. Hydrogel dressings, from a small library of synthesized materials form in situ, exhibit storage moduli between 100-40 000 Pa, dissolve on-demand within 10 minutes to 90 minutes, swell up to 350%, and adhere to both burned and healthy human skin at 0.2-0.3 N cm-2. Further, results from an in vivo porcine second degree burn model demonstrate functional performance with healing equivalent to conventional treatments with the added benefit of facile, in situ application and subsequent removal via dissolution.

Temporary In Situ Hydrogel Dressings for Colon Polypectomies.

Currently, no dressings are utilized after removal of polyps during a colonoscopy rendering these tissue sites susceptible to bleeding, sepsis, and perfusion. We report the design specifications, synthesis, and ex vivo evaluation of in situ polymerized hydrogels as colon wound dressings post polypectomy. The hydrogels exhibited varied properties to include moduli between 100 and 16 000 Pa, dissolution times between 4 h to 7 days or longer, swelling up to 200%, and adhesion to colon tissue from 0.1 to 0.4 N/cm2. The hydrogels displayed minimal cytotoxicity, prevented the migration/spread of bacteria, and exhibited rapid gelation, a requirement for application to the lumen of the colon via an endoscope. This work highlights the structure-property relationship of hydrogels prepared from N-hydroxysuccinimide functionalized PEG cross-linkers and hyperbranched polyethylenimines or 4-arm PEG-NH2 star polymers, and their potential as colon wound dressings.