UC Santa Barbara

Surgical repair of some connective tissues, such as tendon, has a high failure rate. Exploration of surgical adjuvants, including platelet-rich plasma, bioactive scaffolds, and cell delivery, are being explored in an effort to enhance tissue healing. The purpose of this study is to quantify the capture and concentration of platelets (PLTs) during fibrin clot (FC) formation and to evaluate how the immunoreactivity and secretion of growth factors VEGF, PDGF and bFGF from FCs is modulated by the addition of allogeneic adipose stem cells (ASCs). Platelet concentration during fibrin clot formation was determined by quantifying pre-clot and post-clot serum samples. Fibrin clot formation concentrated 92% (p<0.01) of the available PLTs in whole blood. Two experimental conditions and one control condition were evaluated over two weeks in vitro. FCs made from human whole blood without ASCs, FC(-)ASC, were compared with FCs with ASCs incorporated, FC(+)ASC, and a control group of synthetic polyethylene glycol gels with ASCs incorporated, PEG(+)ASCs. All conditions were examined for secretion and retention of VEGF, PDGF, and bFGF. Analysis of platelet retention for FCs made with this device was performed. ELISA analysis showed significantly higher (p<0.01) secretion of VEGF in FC(+)ASC compared to FC(-)ASC or PEG(+)ASC. In contrast, FC(-)ASC produced soluble PDGF, and the addition of ASCs results in decreased soluble PDGF with concomitant increases in PDGF immunoreactivity of ASCs. Soluble bFGF levels were low in FC(-)ASC, and were found to increase at early time-points in FC(+)ASC. Furthermore, bFGF immunoreactivity could be detected in FC(+)ASC while no bFGF immunoreactivity is present in FC(-)ASC or PEG(+)ASC. These findings provide evidence that FCs made through this described method concentrate a high proportion of available platelets that are known to secrete growth factors over time. The incorporation of ASCs to this system results in increased growth factor production, particularly of VEGF. Enhanced growth factor production localized to a surgical repair site may enhance the healing response and strengthen connective tissue to lower the incidence of re-tear.