Fiber distribution is an important factor affecting the workability and mechanical properties of fiber reinforced concrete. It reviews the characterization methods,theoretical derivation and control methods of fiber distribution in fiber reinforced concrete. First,experimental characterization methods of fiber distribution are described in details through indirect test and direct test; the advantages and disadvantages,the applicable scope of each method are analyzed. Second,theoretical derivation and prediction methods of fiber in random state and real situation are reviewed. Last,influence and control methods of fiber distribution are described,and the existed problems to be solved in the further study of fiber distribution are proposed.
Type IV collagen promotes integrin-mediated cell adhesion, spreading, and motility. Several regions within the triple-helical domain of type IV collagen have been identified as tumor cellular recognition sites. Among these regions, the α1(IV)531−543 sequence, designated l-Hep-III, promotes integrin-mediated tumor cell adhesion and directly binds to the α3β1 integrin [Miles, A. J., et al. (1994) J. Biol. Chem. 269, 30939−30945; Miles, A. J., et al. (1995) J. Biol. Chem. 270, 29047−29050]. We have presently compared the activities of the all-d enantiomeric peptide model of α1(IV)531−543, designated d-Hep-III, with l-Hep-III, for promoting the adhesion, spreading, and motility of metastatic melanoma and breast carcinoma cells. d-Hep-III was found to support melanoma and breast carcinoma cell adhesion, spreading, and motility in a dose-dependent fashion similar to that of l-Hep-III. The adhesions of melanoma and breast carcinoma cells to both type IV collagen and fibronectin were effectively inhibited by l-Hep-III and d-Hep-III. Melanoma cell invasion of the basement membrane was also inhibited by d-Hep-III. Characterization of the cell surface receptor for d-Hep-III was acheived via cell adhesion assays and affinity chromatography using monoclonal antibodies against integrin subunits. Immunoprecipitation analysis following EDTA elution from a d-Hep-III affinity column indicated that d-Hep-III binds to the α3β1 integrin but not to the α2 or α6 integrin subunits. In summary, these studies demonstrate that an all-d model of the α1(IV)531−543 sequence mimics the biological activities of the all-l peptide. d-Hep-III is the first all-d peptide that has been shown to promote tumor cell adhesion, spreading, and migration, inhibit tumor cell adhesion and migration on type IV collagen and invasion of the basement membrane, and bind directly to an integrin. Due to the resistance to proteolysis, all-d receptor-binding peptides such as d-Hep-III have great potential for in vivo studies and as therapeutic agents.
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