Marked differences in local bone remodelling in response to different marrow stimulation techniques in a large animal

Regeneration: Bone-Marrow Stimulation of the Talus-Limits and Goals

Bone Marrow Stimulation of osteochondral lesions of the talus has been shown to be a successful way to treat cartilage injuries. Newer data suggest that Bone Marrow Stimulation is best reserved for osteochondral lesions of the talus Sizes Less Than 107.4 mm2 in area. Additionally, newer smaller and deeper techniques to perform bone marrow stimulation have resulted in less subchondral bone damage, less cancellous compaction, and superior bone marrow access with multiple trabecular access channels. Biologic adjuvants such as platelet-rich plasma (PRP), hyaluronic acid (HA), and bone marrow aspirate concentrate (BMAC) may lead to better functional outcomes when used concomitant to bone marrow stimulation.

Effect of autologous lyophilized platelet‑rich fibrin on the reconstruction of osteochondral defects in rabbits

Osteochondral defects caused by degenerative diseases of joints, traumas and inflammation are important issues in clinical practice. Different types of autologous platelet concentrate (PCs) are used in bone and cartilage regeneration. The present study aimed to investigate the effect of lyophilized platelet-rich fibrin (L-PRF) on the repair of osteochondral defects in rabbits. L-PRF was first prepared from fresh PRF (F-PRF) through freeze-drying, and histological and microstructural observations were performed to compare the characteristics of L-PRF and F-PRF. Thereafter, these bioactive scaffolds were implanted into osteochondral defects surgically created in rabbits to assess their effects on tissue repair using micro-CT scanning, histological observations and the evaluation scoring method for cartilage repair established by the International Cartilage Repair Society (ICRS). L-PRF had a histological structure similar to F-PRF. At 16 weeks after implantation surgery, full-thickness osteochondral defects with a diameter of 5 mm and a depth of 4 mm were well-filled with newly regenerated tissues, exhibiting the simultaneous regeneration of avascular articular cartilage and well-vascularized subchondral bone, as proven through macroscopic and microscopic observations in PRF-treated groups compared with that in the untreated group. The application of L-PRF and F-PRF for osteochondral defects in rabbits contributed to massive host remodeling and reconstruction of osteochondral tissues, thus offering a prospective bioactive scaffold for the simultaneous reconstruction of articular cartilage and subchondral bone tissue.

Evaluation of surgical fixation methods for the implantation of melt electrowriting-reinforced hyaluronic acid hydrogel composites in porcine cartilage defects

The surgical repair of articular cartilage remains an ongoing challenge in orthopedics. Tissue engineering is a promising approach to treat cartilage defects; however, scaffolds must (i) possess the requisite material properties to support neocartilage formation, (ii) exhibit sufficient mechanical integrity for handling during implantation, and (iii) be reliably fixed within cartilage defects during surgery. In this study, we demonstrate the reinforcement of soft norbornene-modified hyaluronic acid (NorHA) hydrogels via the melt electrowriting (MEW) of polycaprolactone to fabricate composite scaffolds that support encapsulated porcine mesenchymal stromal cell (pMSC, three donors) chondrogenesis and cartilage formation and exhibit mechanical properties suitable for handling during implantation. Thereafter, acellular MEW-NorHA composites or MEW-NorHA composites with encapsulated pMSCs and precultured for 28 days were implanted in full-thickness cartilage defects in porcine knees using either bioresorbable pins or fibrin glue to assess surgical fixation methods. Fixation of composites with either biodegradable pins or fibrin glue ensured implant retention in most cases (80%); however, defects treated with pinned composites exhibited more subchondral bone remodeling and inferior cartilage repair, as evidenced by micro-computed tomography (micro-CT) and safranin O/fast green staining, respectively, when compared to defects treated with glued composites. Interestingly, no differences in repair tissue were observed between acellular and cellularized implants. Additional work is required to assess the full potential of these scaffolds for cartilage repair. However, these results suggest that future approaches for cartilage repair with MEW-reinforced hydrogels should be carefully evaluated with regard to their fixation approach for construct retention and surrounding cartilage tissue damage.

Promoting endogenous articular cartilage regeneration using extracellular matrix scaffolds

Articular cartilage defects fail to heal spontaneously, typically progressing to osteoarthritis. Bone marrow stimulation techniques such as microfracture (MFX) are the current surgical standard of care; however MFX typically produces an inferior fibro-cartilaginous tissue which provides only temporary symptomatic relief. Here we implanted solubilised articular cartilage extracellular matrix (ECM) derived scaffolds into critically sized chondral defects in goats, securely anchoring these implants to the joint surface using a 3D-printed fixation device that overcame the need for sutures or glues. In vitro these ECM scaffolds were found to be inherently chondro-inductive, while in vivo they promoted superior articular cartilage regeneration compared to microfracture. In an attempt to further improve the quality of repair, we loaded these scaffolds with a known chemotactic factor, transforming growth factor (TGF)-β3. In vivo such TGF-β3 loaded scaffolds promoted superior articular cartilage regeneration. This study demonstrates that ECM derived biomaterials, either alone and particularly when combined with exogenous growth factors, can successfully treat articular cartilage defects in a clinically relevant large animal model.

Gravity-based patterning of osteogenic factors to preserve bone structure after osteochondral injury in a large animal model

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 thick-shelled 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 the developed microcapsules ruptured in vitro under increasing mechanical loads, and readily sink within a liquid solution, enabling gravity-based patterning along the osteochondral surface. In a large animal, these mechanically-actived 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 patterned in situ, 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 develops a gravity-based approach to pattern bioactive factors along the osteochondral interface, and applies this novel biofabrication strategy to preserve bone structure after osteochondral injury.