AUTHOR=Hixon Katherine R. , Katz Dakota B. , McKenzie Jennifer A. , Miller Anna N. , Guilak Farshid , Silva Matthew J. 

TITLE=Cryogel Scaffold-Mediated Delivery of Adipose-Derived Stem Cells Promotes Healing in Murine Model of Atrophic Non-Union

JOURNAL=Frontiers in Bioengineering and Biotechnology

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2022.851904

DOI=10.3389/fbioe.2022.851904

ISSN=2296-4185

ABSTRACT=Nonunion is defined as the permanent failure of a bone to heal and occurs clinically in 5% of fractures. Atrophic nonunions, characterized by absent/minimal callus formation, are poorly understood and difficult to treat. We recently demonstrated a novel murine model of atrophic nonunion in the 3.6Col1A1-tk (Col1-tk) mouse wherein dosing with the nucleoside analog ganciclovir (GCV) was used to deplete proliferating osteoprogenitor cells, leading to a radiographic and biomechanical nonunion after mid-shaft femur fracture. Using this Col1-tk atrophic nonunion model, we hypothesized that scaffold-mediated lentiviral delivery of doxycycline-inducible BMP-2 transgenes would induce osteogenesis at the fracture site. Cryogel scaffolds were used as a vehicle for GFP+ and BMP-2+ cell delivery to the site of nonunion. Cryogel scaffolds were biofabricated through the crosslinking of a chitosan-gelatin polymer solution at subzero temperatures which results in a macroporous, spongy structure that may be advantageous for a bone regeneration application. Murine adipose-derived stem cells were seeded onto the cryogel scaffolds where they underwent lentiviral transduction. Following the establishment of atrophic nonunions in the femurs of Col1-tk mice (4 weeks post fracture), transduced, seeded scaffolds were surgically placed around the site of nonunion, and animals were given doxycycline water to induce BMP-2 production. Controls included GFP+ cells on cryogel scaffolds, acellular scaffolds, and sham (no scaffold). Weekly radiographs were taken and endpoint analysis included microCT and histological staining. After 2 weeks of implantation, the BMP-2+ scaffolds were infiltrated with cartilage and woven bone at the nonunion site, while GFP+ scaffolds had woven bone formation. Later timepoints of 8 weeks had woven bone and vessel formation within the BMP-2+ and GFP+ scaffolds with cortical bridging of the original fracture site in both groups. Overall, cell-seeded cryogels promoted osseous healing; however, while the addition of BMP-2 promoted endochondral ossification, it may provide a slower route to healing. This proof-of-concept study demonstrates the potential for cellularized, cryogel scaffolds to enhance healing of nonunions.