Hannah M. Zlotnick (1,2,3), Ryan C. Locke (2,3), Sanjana Hemdev (2,4), Brendan D. Stoeckl (1,2,3), Sachin Gupta (2,3), Ana P. Peredo (1,2,3), David R. Steinberg (2,3), James L. Carey (2,3), Daeyeon Lee (5), George R. Dodge (2,3), Robert L. Mauck (1,2,3)
bioRxiv,September 2021. DOI: 10.1101/2021.09.24.461696

Keywords

osteochondral interface; bone; articular cartilage; controlled release; animal model; microcapsule

Abstract

Chondral and osteochondral repair strategies are limited by adverse bony changes that occur after injury. Bone resorption can cause entire scaffolds, engineered tissues, or even endogenous repair tissues to subside below the cartilage surface. To address this translational issue, we fabricated poly(D,L-lactide-co-glycolide) (PLGA) microcapsules containing the pro-osteogenic agents triiodothyronine and ß-glycerophosphate, and delivered these microcapsules in a large animal model of osteochondral injury to preserve bone structure. We demonstrate that developed microcapsules ruptured in vitro under increasing mechanical loads, and readily sink within a liquid solution, allowing for gravity-based positioning onto the osteochondral surface. In a large animal, these mechano-active microcapsules (MAMCs) were assessed through two different delivery strategies. Intra-articular injection of control MAMCs enabled fluorescent quantification of MAMC rupture and cargo release in a synovial joint setting over time in vivo. This joint-wide injection also confirmed that the MAMCs do not elicit an inflammatory response. In the contralateral hindlimbs, chondral defects were created, MAMCs were locally administered, and nanofracture (Nfx), a clinically utilized method to promote cartilage repair, was performed. The NFx holes enabled marrow-derived stromal cells to enter the defect area and served as repeatable bone injury sites to monitor over time. Animals were evaluated 1 and 2 weeks after injection and surgery. Analysis of injected MAMCs showed that bioactive cargo was released in a controlled fashion over 2 weeks. A bone fluorochrome label injected at the time of surgery displayed maintenance of mineral labeling in the therapeutic group, but resorption in both control groups. Alkaline phosphatase (AP) staining at the osteochondral interface revealed higher AP activity in defects treated with therapeutic MAMCs. Overall, this study establishes a new micro-fluidically generated delivery platform that releases therapeutic factors in an articulating joint, and reduces this to practice in the delivery of therapeutics that preserve bone structure after osteochondral injury.

How Our Software Was Used

Dragonfly was used to calculate bone volume/total volume within cylindrical (5 mm diameter x 0.5 mm thickness) regions of interest. It was also used to acquire snapshots at the mid-plane of defects contained in osteochondral units.

Author Affiliation

(1) Department of Bioengineering, School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, PA, USA.
(2) McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
(3) Translational Musculoskeletal Research Center, Corporal Michael J Crescenz VA Medical Center, Philadelphia, PA, USA.
(4) Department of Biotechnology, School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, PA, USA.
(5)Department of Chemical and Biomolecular Engineering, School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, PA, USA.