No abstract

No abstract

Summary: Cartilaginous constructs have been grown in v i f m with use of isolated cells, biodegradable polymer scaffolds, and bioreactors. In the present work, the relationships between the composition and mechanical properties of engineered cartilage constructs were studied by culturing bovine calf articular chondrocytes on fibrous polyglycolic acid scaffolds ( 5 mm in diameter, 2-mm thick; and 97% porous) in three different environments: static flasks, mixed flasks. and rotating vessels. After 6 weeks of cultivation, the composition, morphology, and mechanical function of the constructs in radially confined static and dynamic compression all depended on the conditions of in vitro cultivation. Static culture yielded small and fragile constructs, while turbulent flow in mixed flasks yielded constructs with fibrous outer capsules: both environments resulted in constructs with poor mechanical properties. The constructs that were cultured freely suspended in a dynamic laminar flow field in rotating vessels were the largest, contained continuous cartilage-like extracellular matrices with the highest fractions of glycosarninoglycan and collagen, and had the best mechanical properties. The equilibrium modulus, hydraulic permeability, dynamic stiffness, and streaming potential correlated with the wet-weight fractions of glycosaminoglycan, collagen, and water. These findings suggest that the hydrodynamic conditions in tissue-culture bioreactors can modulate the composition. morphology, mechanical properties, and electromechanical function of engineered cartilage.Articular cartilage derives its form and mechanical function from its matrix. which consists of tissue fluid and a framework of structural macromolecules (collagens, proteoglycans, and noncollagenous proteins and glycoproteins). During the development, maintenance, and remodeling of cartilage, chondrocytes synthesize appropriate types and amounts of macromolecules and assemble thcm into a highly organized matrix (4). Adult articular cartilage has a limited capacity to repair damage resulting from injury or disease, and there have been many different approaches to restore tissue composition, structure, and function. including the development of engineered cartilage for potential implantation (5.27). Cartilaginous constructs have been grown in vitro with use of isolated chondrocytes. biodegradable polymer scaffolds, and bioreactors and implanted in vivo to form subcutaneous cartilage or to promote joint repair (16). Fibrous polyglycolic acid scaffolds permitted chondrocytes to Received April 3,1998; accepted September 30. lYY8. Address correspondence and reprint requests to G. VunjakNovakovic at Massachusetts Institute of Technology E25-342. 45 Carleton Street, Carnbridgc, MA 02139, U.S.A. E-mail: gordana@ rnit.edu maintain their differentiated phenotype and provided a three-dimensional framework for tissue regeneration (14), and bioreactors provided control over the conditions of cell seeding and tissuc cultivation and affectcd construct structures and compositio...

Mesenchymal stem/stromal cells (MSC) are typically used to generate bone tissue by a process resembling intramembranous ossification, i.e., by direct osteoblastic differentiation. However, most bones develop by endochondral ossification, i.e., via remodeling of hypertrophic cartilaginous templates. To date, endochondral bone formation has not been reproduced using human, clinically compliant cell sources. Here, we aimed at engineering tissues from bone marrow-derived, adult human MSC with an intrinsic capacity to undergo endochondral ossification. By analogy to embryonic limb development, we hypothesized that successful execution of the endochondral program depends on the initial formation of hypertrophic cartilaginous templates. Human MSC, subcutaneously implanted into nude mice at various stages of chondrogenic differentiation, formed bone trabeculae only when they had developed in vitro hypertrophic tissue structures. Advanced maturation in vitro resulted in accelerated formation of larger bony tissues. The underlying morphogenetic process was structurally and molecularly similar to the temporal and spatial progression of limb bone development in embryos. In particular, Indian hedgehog signaling was activated at early stages and required for the in vitro formation of hypertrophic cartilage. Subsequent development of a bony collar in vivo was followed by vascularization, osteoclastic resorption of the cartilage template, and appearance of hematopoietic foci. This study reveals the capacity of human MSC to generate bone tissue via an endochondral program and provides a valid model to study mechanisms governing bone development. Most importantly, this process could generate advanced grafts for bone regeneration by invoking a "developmental engineering" paradigm.bone repair | endochondral ossification | hypertrophic chondrocytes | regenerative medicine | tissue engineering

No abstract