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We have developed biodegradable fibrin-derived microbeads as potent cell carriers. The fibrin-derived microbeads, 50-200 microm in diameter, were tested for their attachment to a wide range of cell types. Fibrin-derived microbeads were shown to be greatly haptotactic to cells (such as endothelial cells, smooth muscle cells and fibroblasts), which respond to fibrinogen in contrast to keratinocytes and different cell lines derived from leukocytic lineage. The cells on fibrin-derived microbeads could be maintained for more than 10 d and achieved a high density. 31P-nuclear magnetic resonance was employed to monitor phosphate metabolism in cells, with densities on the order of 100 million cells per g of fibrin-derived microbeads. The 31P-nuclear magnetic resonance adenosine triphosphate and phosphocreatine signals, equivalent to the signal obtained with perfused normal skin, indicated that metabolism of cells on fibrin-derived microbeads was responsive to oxygenation and nutrients. Light, fluorescent, and confocal laser microscopy revealed that the porous fibrin-derived microbeads accommodate up to 200-300 cells due to their high surface area which minimized contact inhibition. Cells could degrade the fibrin-derived microbeads and be transferred to seed culture flasks without trypsinization. In a pig skin wound healing model, fibrin-derived microbeads + fibroblasts were transplanted into full thickness punch wounds. This procedure was compared with other treatment modalities, such as the addition of human platelet-derived growth factor BB or fibrin-derived microbeads alone. By the third day after wounding, only the wounds in which fibroblasts on fibrin-derived microbeads were added showed significant formation of granulation tissue. Based on the above, we project many uses of our novel fibrin-derived microbead technology for cell culturing, wound healing and tissue engineering.

Fibroblast migration from the peri‐wound collagenous stroma into the fibrin‐laden wound is critical for granulation tissue formation and subsequent healing. Previously we found that fibroblast transmigration from a collagen matrix into a fibrin matrix required the presence of fibronectin (FN). Several cell surface receptors, namely integrins α4β1, α5β1 and αvβ3 were also required for this invasive migration. Here we demonstrated that syndecan‐4, a transmembrane heparan sulfate proteoglycan, known to bind FN at the highly cationic HepII domain is also required for fibroblast invasive migration of a fibrin/FN gel. This conclusion was based on fibroblast migration using two independent means of disrupting syndecan‐4: heparinase degradation of heparan sulfate glycosaminoglycans or suppression of syndecan‐4 core protein with antisense oligodeoxynucleotides. Isolated syndecan‐4 from these fibroblasts bound the Hep II recombinant constructs FN III12–15v > FN III12–15 > FN III12–14 but did not bind the alternatively spliced IIICs (V) domain. Furthermore, we found that platelet‐derived growth factor (PDGF), which is required to stimulate fibroblast migration, markedly increased cell levels of syndecan‐4 core protein in a time and dose dependent fashion. PDGF also induced up‐regulation of syndecan‐4 at transcriptional level as determined by RT‐PCR. These results demonstrate that syndecan‐4 is essential for fibroblast invasive migration into fibrin clot and that PDGF, the stimulus for migration, induces increased syndecan‐4 core protein expression.