Three-dimensional culture of human nucleus pulposus cells in fibrin clot: comparisons on cellular proliferation and matrix synthesis with cells in alginate.

Regeneration of nucleus pulposus (NP) tissue may stop or reverse early intervertebral disk (IVD) degeneration. Cellular proliferation and matrix synthesis can be promoted by incorporation of cells and bioscaffolds. However, insertion of preshaped solid bioscaffolds may damage remaining IVD integrity. Fibrin clots can be introduced in a minimally invasive manner with polymerization in desired three-dimensional shape and retention of cells. In this study, we investigated the cellular proliferation and matrix synthesis of human NP cells in the fibrin clots in vitro. Monolayer-expanded cells were embedded in fibrin clot or alginate and were cultivated in vitro for 2 weeks. Increased DNA content and decreased expression of apoptosis stimulating fragment (Fas)-associated death-domain protein in fibrin scaffolds suggested higher cellular proliferation and reduced apoptosis. Superior proteoglycan synthesis was found in fibrin scaffolds. As expression of collagens I and X increased and SOX9 expression decreased, fibrin scaffolds tended to promote fibrotic transformation and inhibit chondrogenesis. Adjustments of fibrin preparations are needed to make it more suitable for IVD regeneration.