A Paradigm for Functional Tissue Engineering of Articular Cartilage via Applied Physiologic Deformational Loading

Abstract

Deformational loading represents a primary component of the chondrocyte physical environment in vivo. This review summarizes our experience with physiologic deformational loading of chondrocyte-seeded agarose hydrogels to promote development of cartilage constructs having mechanical properties matching that of the parent calf tissue, which has a Young's modulus E(Y) = 277 kPa and unconfined dynamic modulus at 1 Hz G* = 7 MPa. Over an 8-week culture period, cartilage-like properties have been achieved for 60 x 10(6) cells/ml seeding density agarose constructs, with E(Y) = 186 kPa, G* = 1.64 MPa. For these constructs, the GAG content reached 1.74% ww and collagen content 2.64% ww compared to 2.4% ww and 21.5% ww for the parent tissue, respectively. Issues regarding the deformational loading protocol, cell-seeding density, nutrient supply, growth factor addition, and construct mechanical characterization are discussed. In anticipation of cartilage repair studies, we also describe early efforts to engineer cylindrical and anatomically shaped bilayered constructs of agarose hydrogel and bone (i.e., osteochondral constructs). The presence of a bony substrate may facilitate integration upon implantation. These efforts will provide an underlying framework from which a functional tissue-engineering approach, as described by Butler and coworkers (2000), may be applied to general cell-scaffold systems adopted for cartilage tissue engineering.

Computational Study of Culture Conditions and Nutrient Supply in Cartilage Tissue Engineering

“…In this study the best nutrient supply was found for the mixed tube configuration. However, to achieve optimal functionality, mechanical stimulation could prove essential (63). A further design criterion will therefore be to incorporate dynamic compression and to perform efficient mixing and oxygenation, while avoiding possibly excessive shear stress (3,5,55).…”

Engineering custom-designed osteochondral tissue grafts

“…For cartilage, tissue engineering can involve cell seeding into a scaffold and cultivation of the resulting construct under conditions that promote cartilage formation (reviewed in Ref. [7]). …”

“…Additionally, the development of functional, load-bearing characteristics of the graft would be enhanced by the application of biophysical stimulation to attain mechanical competence in both the cartilage and bone regions. For cartilage, dynamic compression can be applied to stimulate increased matrix organization by the cells [7]. For bone, medium perfusion can be applied to enable local control of mass transport and provide shear-stress-enhancing in vitro bone formation [54].…”

“…Mature chondrocytes were loaded into the cartilage layer but the bony substrate (also milled into the exact anatomical shape) remained acellular. Using this method, it was also possible to produce anatomically shaped loading platens for dynamic compression of the cartilage region during cultivation [7]. Dynamic compression has been shown to improve the mechanical properties of tissue-engineered cartilage grafts [56] and, for the anatomically-shaped patella, it also effectively increased nutrient transfer to regions within the constructs via compression-induced fluid flow.…”

Mechanobiology of Human Pluripotent Stem Cells

“…[10][11][12][13][14][15][16] Cells sense and react to changes in the mechanical properties of their microenvironments by assembling and reassembling focal adhesions, and up-and down-regulating cell adhesion molecules that are associated with cell-cell and cell-extracellular matrix (ECM) interactions. These physicochemical factors have significant implications for stem cell self-renewal, proliferation, and differentiation in vitro.…”