Surface chemistry, substrate, and topography guide the behavior of human articular chondrocytes cultured in vitro

Understanding the behavior of chondrocytes in contact with artificial culture surfaces is becoming increasingly important in attaining appropriate ex vivo culture conditions of chondrocytes in cartilage regeneration. Chondrocyte transplantation‐based cartilage repair requires efficiently expanded chondrocytes and the culture surface plays an important role in guiding the behavior of the cell. Micro‐ and nanoengineered surfaces make it possible to modulate cell behavior. We hypothesized that the combined influence of topography, substrate, and surface chemistry may affect the chondrocyte culturing in terms of proliferation and phenotypic means. Human chondrocytes were cultured on polystyrene fabricated microstructures, flat polydimethylsiloxane (PDMS) or polystyrene treated with fibronectin or oxygen plasma, and cultured for 1, 4, 7, and 10 days. The behavior of chondrocytes was evaluated by proliferation, viability, chondrogenic gene expression, and cell morphology. Contrary to our hypothesis, microstructures in polystyrene did not significantly influence the behavior of chondrocytes neither under normoxic‐ nor hypoxic conditions. However, changes in the substrate stiffness and surface chemistry were found to influence cell viability, gene expression and morphology of human chondrocytes. Oxygen plasma treatment was the most important parameter followed by the softer substrate type PDMS. The findings indicate the culture of human chondrocytes on softer substratum and surface activation by oxygen plasma may prevent dedifferentiation and may improve chondrocyte transplantation‐based cartilage repair

Intermittent Hypoxic Therapy Inhibits Allogenic Bone-Graft Resorption by Inhibition of Osteoclastogenesis in a Mouse Model

Systemic Intermittent Hypoxic Therapy (IHT) relies on the adaptive response to hypoxic stress. We investigated allogenic bone-graft resorption in the lumbar spine in 48 mice. The mice were exposed to IHT for 1 week before surgery or 1 week after surgery and compared with controls after 1 and 4 weeks. Complete graft resorption was observed in 33–36% of the animals in the control group, but none in the preoperative IHT group. Increased bone-graft volume was demonstrated by micro-computed tomography in the preoperative IHT group after 1 week (p = 0.03) while a non-significant difference was observed after 4 weeks (p = 0.12). There were no significant differences in the postoperative IHT group. Increased concentration of immune cells was localized in the graft area, and more positive tartrate-resistant acid phosphatase (TRAP) staining was found in controls compared with IHT allogenic bone grafts. Systemic IHT resulted in a significant increase of the major osteoclast inhibitor osteoprotegerin as well as osteogenic and angiogenic regulators Tgfbr3, Fst3l, Wisp1, and Vegfd. Inflammatory cytokines and receptor activator of nuclear factor kappa-B ligand (RANKL) stimulators IL-6, IL-17a, IL-17f, and IL-23r increased after 1 and 4 weeks, and serum RANKL expression remained constant while Ccl3 and Ccl5 decreased. We conclude that the adaptive response to IHT activates numerous pathways leading to inhibition of osteoclastic activity and inhibition of allogenic bone-graft resorption