Strategies for cartilage regeneration : use of human mesenchymal stem cells, alginate microcapsules and bioreactor technology

Alginate/chitosan polysaccharide capsules were encapsulated with human bone marrow cells (HBMC), articular chondrocytes (AC) or a co-culture of both cell types at varying ratios, and placed in a rotating (Synthecon) bioreactor, a perfused bioreactor system or held in static 2D culture conditions for 28 days. Additionally collagen, RGD-peptide, BMP-2 or Sox-9 transfected cells were added to promote chondrogenic differentiation and extracellular matrix synthesis. Constructs were also examined using the sub-cutaneous implant model in SCID mice. Rotating bioreactor samples demonstrated the presence of metabolically active type II collagen positive cells within lacunae and rotating conditions were superior to static and perfused culture conditions in the promotion of cartilaginous constructs. Co-culture studies indicated an optimum encapsulation ratio of 2:1 (HBMC:AC) with the generation of large regions of osteoid tissue within static culture and in vivo constructs. Additions of collagen, RGD-peptide, BMP-2 and Sox-9 transfected cells all resulted in the generation of large regions of extracellular matrix, and within type 1 collagen constructs there was the development of extracellular matrix with a mature chondrogenic phenotype and areas of new bone-like tissue formation. These studies outline a tissue engineering approach utilising individual and mixed human mesenchymal progenitors coupled with innovative polysaccharide templates in the synthesis of in vitro and in vivo chondrogenic and osteogenic constructs. Under the conditions examined rotating bioreactor systems alongside alginate templates encapsulated with HBM cells with the addition of type I collagen are optimum for chondrogenesis, whereas osteogenesis was promoted in 2:1 co-culture static constructs. These studies demonstrate the pivotal role of 3D biomimetic microenvironments and the ability to harness the interactions between different types to create specific tissues.