Differential Morphology and Homogeneity of Tissue-Engineered Cartilage in Hydrodynamic Cultivation with Transient Exposure to Insulin-Like Growth Factor-1 and Transforming Growth Factor-β1

Abstract

Successful tissue-engineering strategies for cartilage repair must maximize the efficacy of chondrocytes within their limited life span. To that end, the combination of exogenous growth factors with mechanical stimuli holds promise for development of clinically relevant cartilage tissue substitutes. The current study aimed to determine whether incorporation of transient exposure to growth factors into a hydrodynamic bioreactor system can improve the functional maturation of tissue-engineered cartilage. Chondrocyte-seeded polyglycolic acid scaffolds were cultivated within a wavy-walled bioreactor that imparts fluid flow-induced shear stress for 4 weeks. Constructs were nourished with 100 ng/mL insulin-like growth factor-1 (IGF-1) or 10 ng/mL transforming growth factor-b1 (TGF-b1) either for the first 15 days of the culture (transient) or throughout the entire cultivation (continuous). Transiently treated constructs were found to exhibit better functional properties than continuously nourished constructs. The limited development of engineered tissues continuously stimulated by IGF-1 or TGF-b1 was related to massive growth factor leftovers in the environments that downregulated the expression of the associated receptors. Treatment with TGF-b1 eliminated the formation of a fibrous capsule at the construct periphery possibly through suppression of Smad3 phosphorylation, yielding constructs with greater homogeneity. Furthermore, TGF-b1 reversely regulated Smad2 and Smad3 pathways in articular chondrocytes under hydrodynamic stimuli partially via Smad7. Collectively, transient exposure to growth factors is likely to maintain chondrocyte homeostasis, and thus promotes their anabolic activities under hydrodynamic stimuli. The present work suggests that robust hydrodynamically engineered neocartilage with a reduced fibrotic response and enhanced tissue homogeneity can be achieved through optimization of growth factor supplementation protocols and potentially through manipulation of intracellular signals such as Smad.

Tissue-Engineered Cartilage: The Crossroads of Biomaterials, Cells and Stimulating Factors

“…TGF‐β1 stimulates in vitro chondrogenesis of chondrocytes, synovial lining and bone marrow‐derived MSCs activity . Diao et al, have demonstrated the promising role of TGF‐β1 in rabbits and showed enhanced repair of cartilage defects.…”

“…This highlights the importance of IGF for growth and development. The role of IGF‐1 has been extensively studied with respect to cartilage repair and considered as an essential mediator for cartilage homeostasis and metabolism due to its capability to promote the chondrocyte survival and proliferation, induce chondrogenic differentiation and stimulate proteoglycan synthesis . IGF‐1 have shown induction of a number of anabolic effects and decreases catabolic responses, when added to monolayer or explant cultures of normal articular cartilage from a variety of species .…”

Effects of Glucosamine and Nucleotide Association on Fibroblast: Extracellular Matrix Gene Expression

“…IGF-I presents structural and functional analogies to insulin and is ineolved in growth and development. IGF-I is successfully used in tissue-engineering for cartilage repair and its homeostatic control was demonstrated; in fact, in cell cultures continuously stimulated by IGF-I or TGF-~l the massive growth factor leftovers in the environment down regulates the expression of the associated receptors (8).…”

“…IGF-I and -II are known to stimulate proliferation and proteoglycan synthesis in cultured chondrocytes (8).…”

Bone marrow extract as a growth supplement for human iliac apophyseal chondrocyte culture

“…Bone marrow aspirate has many essential growth factors needed for chondrocyte growth, and its constituents have been evaluated earlier7. Human chondrocytes proliferate at a faster rate without dedifferentiation in the presence of such individual growth factors than FBS9.…”