Using Cartilage to Repair Bone: An Alternative Approach in Tissue Engineering

Abstract

Materials and techniques currently used for bone replacement/repair conform to the current paradigm, relying on bone or bone products to produce bone or induce bone formation. Yet, nature forms and heals most of the skeleton by ossification of a cartilaginous model. In this study, we cultured aggregates of E10.5 or E12 mouse embryonic limb cells in the bioreactor for 3 weeks, determined the stages of cartilage differentiation attained, and assessed the ossification and bone healing potential of the spheroids by implantation adjacent to, or directly in, a skull defect. Cultured spheroids had large cartilaginous areas, sometimes with cellular arrangements characteristic of growth plate zones. Aggregates implanted for 2 weeks adjacent to a defect mineralized and ossified (histology, micro-CT). Defects with implants had a central mass of differentiated and differentiating bone, with osteoclast activity, filling the defect. Controls had considerable remodeling on the bone edges demarcating the still present defect. This study shows that cartilage, grown in the bioreactor for 3 weeks, ossified when implanted adjacent to a bone defect, and when implanted directly in a defect, contributed to its healing. Our ability to grow differentiated bone-forming cartilage for implantation is an alternative approach in the field of bone repair.

Endochondral Ossification for Enhancing Bone Regeneration: Converging Native Extracellular Matrix Biomaterials and Developmental Engineering In Vivo

“…Coupling these results with the previously discussed evidence regarding DBM's influence on EC ossification [26][27][28][29][30][31][32] provides a potent array of strategies for future bone regeneration designs. Furthermore, it is evident that the selection of appropriate native ECM components is essential for exploiting the advantages of EC ossification.…”

“…Inspiration for in vivo developmental designs already exists with native ECM biomaterials, specifically acellular DBM grafts, which have already been shown to elicit some EC ossification in addition to the IM pathway. [26][27][28][29][30][31][32] However, as previously mentioned, DBM composition reflects the physicochemical properties of the late bone reparative stage ECM (Fig. 1) 6,9,33,34 and suggests that designs aimed at mimicking the composition of bone ECM may insufficiently elicit an EC ossification response inside healing fractures.…”

“…Inspiration for in vivo developmental designs already exists in the form of native ECM biomaterials. There is significant evidence that EC ossification occurs in acellular DBM grafts, [26][27][28][29] which inherently resemble the composition of late reparative stage bone-healing ECM. [1][2][3][4][5][6][7][8]15 In a critical-sized rat femoral defect model, Oakes et al 26 observed histological evidence of increased EC ossification foci in human DBM implants suspended in a hyaluronic acid carrier fluid compared with similar DBM implants suspended in a glycerol solution.…”

“…[1][2][3][4][5][6][7][8][9] Insights into the conductive and inductive biomolecules that control EC ossification have been essential to tissue engineering strategies focusing on cartilage formation, 57,58 osteochondral defects, 59,60 and, more recently, bone regeneration (Tables 2-4). 27,43,57,58,[61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76] While cartilage tissue engineering strategies have focused on inducing and maintaining chondrogenic phenotypes, the induction and modulation of cartilage hypertrophy is critical to the progression of EC ossification in bone regeneration designs. 9,33,34,[37][38][39][40][41][42][43]72,[77][78][79]…”

“…91 Step-wise designs from both allogeneic and xenogeneic tissue sources have been utilized clinically for cartilage and bone tissue engineering along with dermal, vascular, nerve, and urogenital tissue. 15,17,18,20,93 Furthermore, previous evidence was presented as linking step-wise-derived DBM to extensive bone regeneration via IM and EC ossification, [26][27][28][29][30][31][32] an attribute that likely contributes to its role as a key protagonist in the bone graft substitute market. 15 If alternative ECM biomaterials are to be used to enhance bone regeneration as proposed in the current review, then key technical, regulatory, and commercial features surrounding the use and approval of DBM should be utilized as a guiding template for potential success.…”