Nutrient channels and stirring enhanced the composition and stiffness of large cartilage constructs

A significant challenge in cartilage tissue engineering is to successfully culture functional tissues that are sufficiently large to treat osteoarthritic joints. Transport limitations due to nutrient consumption by peripheral cells produce heterogeneous constructs with matrix-deficient centers. Incorporation of nutrient channels into large constructs is a promising technique for alleviating transport limitations, in conjunction with simple yet effective methods for enhancing media flow through channels. Cultivation of cylindrical channeled constructs flat in culture dishes, with or without orbital shaking, produced asymmetric constructs with poor tissue properties. We therefore explored a method for exposing the entire construct surface to the culture media, while promoting flow through the channels. To this end, chondrocyte-seeded agarose constructs (θ10mm, 2.34mm thick), with zero or three nutrient channels (θ1mm), were suspended on their sides in custom culture racks and subjected to three media stirring modes for 56 days: uniaxial rocking, orbital shaking, or static control. Orbital shaking led to the highest construct E_Y, sulfated glycosaminoglycan (sGAG), and collagen contents, whereas rocking had detrimental effects on sGAG and collagen versus static control. Nutrient channels increased E_Y as well as sGAG homogeneity, and the beneficial effects of channels were most marked in orbitally shaken samples. Under these conditions, the constructs developed symmetrically and reached or exceeded native levels of E_Y (~400kPa) and sGAG (~9%/ww). These results suggest that the cultivation of channeled constructs in culture racks with orbital shaking is a promising method for engineering mechanically competent large cartilage constructs.