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F H Silver

Publications and source records attributed to F H Silver.

84 records · Page 5Linked to original sources
PubMed1982

Collagen fibrillogenesis in tissues, in a solution and from modeling: a synthesis.

Collagen fibril formation has been studied in tissues by light and electron microscopy; in solution by light scattering and microscopy; and from modeling based on the amino acid sequence of type I collagen. Taken together these studies indicate that collagen fibril assembly involves a stepwise formation of intermediate aggregates in which each intermediate is formed from earlier aggregates. In this sequence, monomeric collagen contributes only to the formation of early aggregates; and fibrils grow in length by the addition of intermediate aggregates to the end of a subfibril and in width by lateral wrapping of subfibrils. Modeling based on amino acid sequence data of possible intermolecular charge-charge interactions indicate 2 different kinds, one which promotes linear aggregation and the other which promotes linear aggregation. The effects of different collagens and coprecipitants such as glycoproteins and proteoglycans can begin to be explained by their influence on the character of intermediate subassemblies. Ultrastructural data from 2 tissues, embryonic cornea and tendon, indicate that the site of fibril growth and assembly is at the cell surface.

Animals↗
PubMed1981

The molecular structure of lubricating glycoprotein-I, the boundary lubricant for articular cartilage.

Lubricating glycoprotein-I (LGP-I) was prepared from bovine synovial fluid by density gradient sedimentation and gel-permeation chromatography. The LGP-I sample obtained was able to lubricate articular cartilage in a manner equivalent to that of whole synovial fluid. Chemical, physical, and electron microscope measurements were carried out to determine the structure of the LGP-I molecules. The molecular weight calculated from sedimentation equilibrium measurements was 2 X 10(5), and the solute distribution obtained indicated that LGP-I was relatively monodisperse. The s(0)20,w value was 4.84, and the intrinsic viscosity was 92 ml/g. The molecular weight and diffusion coefficient calculated from later light-scattering measurements was 2.06 x 10(5) and 1.10 x 10(-7) cm2/s, respectively. The electron microscope measurements showed that the LGP-I molecules had a number average length of 204 nm, a weight average length of 222 nm (with a standard deviation of 54 nm), and a width of 1-2 nm. These data and the kinked appearance of the molecules indicate that LGP-I is a partially extended flexible rod. The hydrodynamic measurements also indicate that LGP-I has the same structure in solution, although the apparently high s(0)20,w value, compared to other rod-like molecules, suggests that due to its flexibility LGP-I can occupy a more compact domain than would be expected based on its extended dimensions. The name of "lubricin" is suggested for this lubricating glycoprotein.

Amino Acids↗
PubMed1981

Type I collagen fibrillogenesis in vitro. Additional evidence for the assembly mechanism.

The intensity of scattered light at angles between 30 degrees and 120 degrees has been measured during the heat gelation lag phase of rat tail tendon collagen. As previously reported, the intensity at a scattering angle of 90 degrees does not change during the lag phase of gelation, whereas during this period, the intensity extrapolated to zero degrees more than doubles. Based on measurement of the Rayleigh factor at low angles, it is concluded that the lag phase terminates when the molecular weight is greater than 930,000 which is consistent with the formation of a linear 4D staggered trimer as previously proposed. Once lateral growth begins, the molecular weight continues to increase approximately linearly with time until a molecular weight of 4 X 10(6) (5 +/- 1 trimers) is reached, at which time the rate of increase of molecular weight increases significantly. It is concluded that a trimer with about 5 strands forms during the early phases of lateral growth and appears similar to the microfibrillar unit proposed based on x-ray diffraction modeling. Further growth occurs by linear and lateral addition of the trimeric units in a manner still under investigation.

Animals↗
PubMed1981

Type V collagen from the chick embryo: biochemical, physicochemical and ultrastructural characteristics.

Two collagen alpha chains have been isolated from whole 17 day chick embryos which are similar to the B chain or alpha 1(V) and the A chain or alpha 2(V) recently described in mammalian and avian tissues. A non-collagenous acidic protein was co-purified with the Type V collagen which was resistant to pepsin digestion. The molecular weight, circular dichroism spectrum, melting temperature and diffusion coefficient of the native Type V collagen and isolated alpha chains were similar to values obtained for other chick collagen types. The SLS crystallite of Type V collagen had a distinct pattern of banding as identified by electron microscopy. We consistently observed more alpha 2(V) than alpha 1(V) following both CM-cellulose and QAE-Sephadex ion exchange chromatography of denatured Type V collagen, but unusual solubility properties and recoveries of the alpha 1(V) chain may have diminished its relative amount. In addition we have found that the alpha 1(V) chains are chemically heterogeneous and one component electrophoreses as an alpha 2(V) chain on SDS gels.

Animals↗
PubMed1980

Type I collagen in solution. Structure and properties of fibril fragments.

We have measured the diffusion coefficient and weight average molecular weight of type I collagen fibril fragments obtained by acid extraction of rat tail tendons and neutral extraction of lathyritic chick skin, using laser light scatttering techniques. The molecular weight and translational diffusion coefficient were found to be 8.05 +/- 0.40 x 10(5) and 0.450 +/- 0.04 x 10 (-7) cm2/s, respectively, for preparations which contain aggregates in 0.01 M HCl, and 2.82 +/- 0.20 x 10 (5) and 0.780 +/- 0.04 x 10 (-7) cm(2)/s for collagen single molecules. Using these data, as well as the theoretical diffusion coefficient for a single collagen molecule, models for various staggering modes and aggregate mixtures were developed in an attempt to understand the structure of the fibril components present in solution. It was found that several models with 1 to 4 D (D = 67 nm) staggers fit the experimental data for the aggregated preparations. Analysis of the end-to-end distance of negatively stained segment long spacing crystallites prepared from solutions containing fibril fragments and the banding pattern of positively stained segment long spacing crystallites suggest that collagen solutions contain linear aggregates with 4 D and possibly 4.4 D staggers in agreement with light scattering data. Thermal denaturation studies demonstrate that the apparent melting point of cross-linked linear aggregates, 33.5 +/- 0.5 degrees C, is identical with that of single molecules at pH 2.0. We conclude that a linear filament with predominant 4 D stagger is a basic unit of type I collagen fibrillar structure.

Animals↗
PubMed1979

In vitro blood compatibility of glycosaminoglycan-precipitated collagens.

Precipitation of bovine hide collagen by chondroitin 6-sulfate at low pH and subsequent crosslinking enhances the blood compatibility of native collagen. Both dehydrothermal crosslinking and complexation with chrondroitin 6-sulfate separately decrease the platelet-aggregating activity of collagen. Crosslinking also decreases the number of free acidic and free basic residues on collagen, which suggests that crosslinking involves these residues in condensation reactions with formation of intrachain and interchain synthetic peptide bonds. Clotting times for collagen precipitated with chondroitin 6-sulfate indicate that this surface does not activate or interfere with coagulation via either the intrinsic or extrinsic pathway. These findings support further consideration of collagen modified by chondroitin 6-sulfate as a blood compatible material.

Animals↗
PubMedDate not supplied

Anterior cruciate ligament reconstruction using a composite collagenous prosthesis. A biomechanical and histologic study in rabbits.

We evaluated a prototype composite collagenous anterior cruciate ligament replacement device designed to possess the advantages of biological grafts and synthetic materials. Collagenous anterior cruciate ligament prostheses were made by embedding 225 reconstituted type I collagen fibers in a type I collagen matrix, and placing polymethylmethacrylate bone fixation plugs on the ends. The collagenous prosthesis was used to replace the anterior cruciate ligament of 31 mature rabbits. At 4 and 20 weeks postimplantation, histologic and mechanical studies were performed on the developing neoligament tissue, and compared to values for the contralateral sham-operated control. At 4 weeks, neoligament tissue infiltrated the collagen fibers of the prostheses. The tibial bone tunnel attachment site contained new bone approaching the fibrous neoligament. The glutaraldehyde-treated prosthetic fibers appeared intact, while the carbodiimide-treated prosthetic fibers began to resorb. The ultimate load and ultimate tensile strength of femur-neoligament-tibia complexes had decreased. At 20 weeks, glutaraldehyde-treated fibers appeared partially intact; in contrast, the carbodiimide-treated prostheses appeared to be completely degraded, and were replaced by organized, crimped neoligament tissue. The ultimate tensile strength and ultimate load increased substantially due to deposition and remodeling of neoligament tissue. The neoligament ultimate load was 2 to 4 times the initial load value of the prosthesis. Implantation of a resorbable, composite collagenous anterior cruciate ligament prosthesis encourages the development of functional neoligament tissue. Studies are underway to optimize the mechanical and biological properties of the prostheses.

Animals↗
PubMedDate not supplied

Evaluation of collagen crosslinking techniques.

The properties of collagen films crosslinked by physical and chemical techniques were compared to the properties of films crosslinked with glutaraldehyde (GTA). Physical techniques studied include exposure to short wave (254 nm) u.v. irradiation and severe dehydration. Chemical techniques studied include immersion of collagen films in aqueous solutions of cyanamide or GTA. Collagen films exposed to combinations of aqueous solutions of cyanamide and severe dehydration had moduli of elasticity, swelling ratios and resistance to bacterial collagenase similar to films crosslinked with GTA. Theoretical calculations based on amino acid composition indicate that approximately seven times as many amino acid residues are capable of forming crosslinks using cyanamide or severe dehydration procedures as compared to GTA crosslinking. In addition, using severe dehydration or cyanamide forms crosslinks involving both amino and carboxyl residues which may allow these procedures to act synergistically. Based on our studies this two-step procedure effectively crosslinks collagen-based biomaterials while the only by-product of this reaction is water-soluble urea. Preliminary biocompatibility studies suggest that this crosslinking procedure may allow for pronounced tissue ingrowth.

Amino Acids↗