Engineering osteochondral constructs through spatial regulation of endochondral ossification

Abstract

Chondrogenically primed bone marrow derived mesenchymal stem cells (MSCs) have been shown to become hypertrophic and undergo endochondral ossification when implanted in vivo. Modulating this endochondral phenotype may be an attractive approach to engineering the osseous phase of an osteochondral implant. The objective of this study was to engineer an osteochondral tissue by promoting endochondral ossification in one layer of a bi-layered construct and stable cartilage in the other. The top-half of bi-layered agarose hydrogels were seeded with culture expanded chondrocytes (termed chondral layer) and the bottom half of the bi-layered agarose hydrogels with MSCs (termed osseous layer). Constructs were cultured in a chondrogenic medium for 21 days and thereafter were either maintained in a chondrogenic medium, transferred to a hypertrophic medium, or implanted subcutaneously into nude mice. This structured chondrogenic bi-layered co-culture was found to enhance chondrogenesis in the chondral layer, appearing to help re-establish the chondrogenic phenotype that is lost in chondrocytes during monolayer expansion. Furthermore, the bilayered co-culture appeared to suppress hypertrophy and mineralisation in the osseous layer.The addition of hypertrophic factors to the media was found to induce mineralisation of the osseous layer in vitro. A similar result was observed in vivo where endochondral ossification was restricted to the osseous layer of the construct leading to the development of an osteochondral tissue. This novel approach represents a potential new treatment strategy for the repair of osteochondral defects.

Osteogenic Differentiation of Mesenchymal Stem Cells by Mimicking the Cellular Niche of the Endochondral Template

“…Another limitation of this study is the use of ascorbic acid and dexamethasone in the chondrogenic medium, which might be expected to cause MSCs to differentiate toward the osteogenic lineage. However, the use of dexamethasone and ascorbic acid in the chondrogenic medium is well documented 53,60,66,78,[91][92][93][94][95][96][97][98][99][100][101][102] and has not been shown to cause mineralization. Moreover, alizarin red staining of the aggregates before the coculture showed no positive staining and the control groups were all exposed to the same chondrogenic medium, so any differences seen between the groups were not because of exposure to these growth factors.…”

Engineering cartilage or endochondral bone: A comparison of different naturally derived hydrogels

“…Collagen types I, II and X were evaluated using a standard immunohistochemical technique as described previously [32].…”

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.…”