Neocartilage Formation in 1 g, Simulated, and Microgravity Environments: Implications for Tissue Engineering

Aim: The aim of this study was to analyze and compare the deposition of cartilage-specific extracellular matrix components and cellular organization in scaffold-free neocartilage produced in microgravity and simulated microgravity. Methods: Porcine chondrocytes were seeded (100 x 10(6)/mL) into cylindrical culture chambers (n = 8) and cultured in the following environments: (i) microgravity during the Flight 7S (Cervantes mission) on the International Space Station (ISS), (ii) simulated microgravity in a random positioning machine (RPM), and (iii) normal gravity (1 g, control). After 16 days, each neocartilage tissue was processed for histology, immunohistochemistry, quantitative real-time reverse transcriptase-polymerase chain reaction, and histomorphometric analysis. Results: Weaker extracellular matrix staining of ISS neocartilage tissue was noted compared with both Earth-cultivated tissues. Higher collagen II/I expression ratios were observed in ISS samples compared with control tissue. Conversely, higher aggrecan/versican gene expression profiles were seen in control 1 g samples compared with microgravity samples. Cell density produced in microgravity was significantly reduced compared with the normal gravity neocartilage tissues. Conclusion: Tissue cultivated on the RPM showed intermediate characteristics compared with ISS and 1 g conditions. These data indicate that the RPM system does not sustain microgravity. Although microgravity impacts the development of in vitro generated cartilage, simulated microgravity using the RPM may be a useful tool to produce cartilaginous tissue grafts with fewer cells.