An in vivo study was conducted to assess the sensitivity of fibrous capsule thickness and macrophage density to polymer fiber diameter. Single polypropylene fibers of diameters ranging from 2.1 to 26.7 microm were implanted in the subcutaneous dorsum of Sprague-Dawley rats. Results at 5 weeks demonstrated reduced fibrous capsule thickness for small fibers. Capsule thickness was 0.6 (+/-1.8) microm, 11.7 (+/-12.0) microm, 20.3 (+/-11.6) microm, and 25.5 (+/-10.0) microm for fibers in the ranges of 2.1 to 5.9, 6.5 to 10.6, 11.1 to 15.8, and 16.7 to 26.7 microm, respectively. Fibers very near to blood vessels had smaller capsules than did those with local vasculature further away. The macrophage density in tissue with fiber diameters 2.1 to 5.9 microm (23.03 +/- 8.67%) was comparable to that of unoperated contralateral control skin (18.72+/-10.06%). For fibers with diameters in the ranges of 6.5 to 10.6, 11.1 to 15.8, and 16.7 to 26.7 microm, macrophage densities were 33.90+/-13.08%, 34.40+/-15.77%, and 41.68+/-13.98%, respectively, all of which were significantly larger (p<0.002) than that for the control. The reduced fibrous capsule thickness and macrophage density for small fibers (<6 microm) compared with large fibers could be due to the reduced cell-material contact surface area or to a curvature threshold effect that triggers cell signaling. A next step will be to extend the analysis to meshes to evaluate fiber-spacing effects on small-fiber biomaterials.

The matricellular protein thrombospondin 2 (TSP2) regulates a variety of cell-matrix interactions. A prominent feature of TSP2-null mice is increased microvascular density, particularly in connective tissues synthesized after injury. We investigated the cellular basis for the regulation of angiogenesis by TSP2 in cultures of murine and human fibroblasts and endothelial cells. Fibroblasts isolated from murine and human dermis synthesize TSP2 mRNA and secrete significant amounts of immunoreactive TSP2, whereas endothelial cells from mouse lung and human dermis did not synthesize TSP2 mRNA or protein. Recombinant mouse TSP2 inhibited growth of human microvascular endothelial cells (HMVECs) mediated by basic fibroblast growth factor, insulin-like growth factor-1, epidermal growth factor, and vascular endothelial growth factor (VEGF). HMVECs exposed to TSP2 in the presence of these growth factors had a decreased proportion of cells in S and G 2 /M phases. HMVECs cultured with a combination of basic fibroblast growth factor, insulin-like growth factor-1, and epidermal growth factor displayed an increased proportion of nonviable cells in the presence of TSP2, but the addition of VEGF blocked this TSP2-mediated impairment of cell viability. TSP2-mediated inhibition of DNA synthesis by HMVECs in the presence of VEGF was not affected by the broadspectrum caspase inhibitor zVAD-fmk. Similar findings were obtained with TSP1. Taken together, these observations indicate that either TSP2 or TSP1 can inhibit HMVEC proliferation by inhibition of cell cycle progression and induction of cell death, but the mechanisms responsible for TSP2-mediated inhibition of cell cycle progression are independent from those leading to cell death. INTRODUCTIONThe process of wound healing is highly dependent on angiogenesis to provide a vascular network for the regenerating tissue. The study of mechanisms governing vascularization of healing connective tissues has primarily focused on proangiogenic factors occurring early in the wound-healing process. Degranulating platelets and a fibrin clot provide growth and chemotactic factors and an adhesive substrate for initial influx of endothelial cells (ECs) (Singer and Clark, 1999;Tonnesen et al., 2000). Infiltrating inflammatory cells, such as macrophages, appear at the wound site shortly after the wounding event and are also potent sources of proangiogenic factors such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) (Sunderkö tter et al., 1994). A number of these factors also induce migration of fibroblasts into the wound area and stimulate fibroblasts to deposit extracellular matrix (Kalluri and Sukhatme, 2000). The direct influence of fibroblasts on ECs in determining the vascularity of the healing wound is less clear. Regression of blood vessels seen in the resolution phase of a wound, in which fibroblasts become the predominant cell type, suggests an inhibitory role for fibroblasts in the angiogenic process (Kyriakides et al., 1999b).A large number of factors...

A technique from the paper manufacturing industry was used to manufacture fibroporous meshes for potential biomaterial implant applications. Meshes were made from small diameter (10 μm) bombyx mori cocoon silk (fibroin). Meshes with a range of fiber lengths were created, though at long fiber lengths flocculation (clumping of fibers) tended to occur. Load-deformation curves were nonlinear with lower slopes at high loads than at low loads, contrary to natural soft-tissue biomaterials. Single fiber in vivo studies to evaluate tissue response sensitivity to biomaterial architectural features demonstrated reduced fibrous encapsulation for smaller diameter fibers (2.6 μm) than larger ones (10 μm). Thus the use of small diameter fibers in biomaterial fibrous implants is a viable concept, and it should be pursued. However, alternative methods to the paper manufacturing process will need to be used for mesh fabrication.