Physiological osmolarities do not enhance long-term tissue synthesis in chondrocyte-laden degradable poly(ethylene...

Encapsulating chondrocytes in synthetic and degradable hydrogels for cartilage tissue engineering enables tuning of scaffold degradation, but provides no biological cues. Culture medium that recapitulates the physiological osmolarity of the interstitial fluid in cartilage can enhance matrix synthesis in the short term, but long-term benefits remain to be determined. This study investigates the long-term effect of culture medium osmolarity on tissue synthesis using chondrocytes isolated from three skeletally mature bovine donors encapsulated in degradable poly(ethylene glycol) hydrogels. The cell-laden hydrogels were cultured up to 4 weeks in standard chondrocyte-specific medium (330 mOsm) or medium adjusted by sucrose or salts (NaCl and KCl) to reach a physiological osmolarity (400 mOsm). Neocartilaginous matrix synthesis and matrix catabolism were evaluated by quantitative and immunofluorescence methods. Hydrogel degradation kinetics of acellular constructs were not affected by medium osmolarity or osmolyte. Matrix composition was predominantly aggrecan and collagen type II for all conditions. One day after encapsulation, total collagen accumulated in the constructs was increased by 80-90% in 400 mOsm medium, regardless of osmolyte. However, this effect did not persist, and at 4 weeks, total collagen synthesized and released to the medium was more than three times higher in 330 mOsm medium. Medium osmolarity had minimal effects on sulfated glycosaminoglycan content and did not affect catabolic activity. These findings suggest that culture medium at physiological osmolarities may not be beneficial for long-term chondrocyte culture in degradable hydrogels, but that initially culturing chondrocytes at a higher osmolarity may enhance early tissue deposition.