Bone Formation on Tissue-Engineered Cartilage Constructsin Vivo: Effects of Chondrocyte Viability and Mechanical Loading

Abstract

Interactions between bone and cartilage formation are critical during growth and fracture healing and may influence the functional integration of osteochondral repair constructs. In this study, the ability of tissue-engineered cartilage constructs to support bone formation under controlled mechanical loading conditions was evaluated using a lapine hydraulic bone chamber model. Articular chondrocytes were seeded onto polymer disks, cultured for 4 weeks in vitro, and then transferred to empty bone chambers previously implanted into rabbit femoral metaphyses. The effects of chondrocyte viability within the implanted constructs and in vivo mechanical loading on bone formation were tested in separate experiments. After 4 weeks in vivo, biopsies from the chambers consisted of a complex composite of bone, cartilage, and fibrous tissue, with bone forming in direct apposition to the cartilage constructs. Microcomputed tomography imaging of the chamber biopsies revealed that the implantation of viable constructs nearly doubled the bone volume fraction of the chamber tissue from 0.9 to 1.6% as compared with the implantation of devitalized constructs in contralateral control chambers. The application of an intermittent cyclic mechanical load was found to increase the bone volume fraction of the chamber tissue from 0.4 to 3.6% as compared with no-load control biopsies. The results of these experiments demonstrate that tissue-engineered cartilage constructs implanted into a well-vascularized bone defect will support direct appositional bone formation and that bone formation is significantly influenced by the viability of chondrocytes within the constructs and the local mechanical environment in vivo.

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

“…[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]…”

“…These recent publications (Tables 2-4) have demonstrated the capacity of cartilage tissue constructs to promote EC ossification in vivo after in vitro priming with seeded BMSCs, 60,63,64,66,67,[72][73][74][75][76][103][104][105][106][107] ESCs, 27,62,67,76 ADSCs, 108 iPSCs, 109 and articular chondrocytes (ACs). 61,67,70,71,75 Most of these studies utilized a heterotopic bone formation model in immunocompromised animals to provide evidence of osteo-and chondro-conductivity and inductivity. However, more recent studies by Bahney et al, 110 van der Stok et al, 106 Harada et al, 105 and Shoji et al 108 (Table 2) showed critical-size defect regeneration in rat femurs and mice tibias via EC ossification.…”

“…67,75,76 Most of these comparative studies concluded that only certain cell sources, most often ESCs or BMSCs, were capable of inducing EC ossification in animal models 67,[75][76][77]111 ; however, other studies clearly showed significant EC ossification with ADSCs, 108 iPSCs, 109 and even ACs in vivo. 61,70,71 The only stem cell population that did not exhibit EC ossification were SDSCs, which instead went through fibrous degradation and resorption in vivo. 75,77 This contradicting evidence highlights the fact that the spatiotemporal control of cell culture priming conditions is essential in determining implant fate in vivo.…”

Simulation of bone tissue formation within a porous scaffold under dynamic compression

“…The model was implemented under dynamic compression considering the same ranges of level and rate of compression as the ones applied cyclically in experimental studies (Duty et al 2007;Case et al 2003). Various cases of strain-controlled dynamic compression were simulated.…”

“…The model was based on the architecture and the material properties of a PLA-Glass scaffold developed by Navarro et al (2006) and characterized by Charles-Harris et al (2008) and Charles-Harris et al (2007). Reconstructed from micro-computed tomography (micro-CT) scans, the porous scaffold was here considered filled by a biological material containing fluid, cells, and matrix and was submitted, via finite element (FE) analysis, to loading conditions reproducing cyclic compression tests performed in vivo within bone chambers (Duty et al 2007;Case et al 2003). In this study, the influence of environmental factors other than load for determining cell differentiation is ignored, and it was hypothesized that the formation of tissue with a given phenotype such as mature bone or cartilage within a porous scaffold may be controlled by a given mechanical loading condition.…”