PubMed Health⌕ Search

Biomedical subjects

F H Silver

Publications and source records attributed to F H Silver.

At least 55 records · Page 3Linked to original sources
PubMed1989

Achilles tendon replacement by a collagen fiber prosthesis: morphological evaluation of neotendon formation.

Reconstituted type I collagen was processed into fibers which were subsequently severely dehydrated and cyanamide cross-linked. Fibers prepared by this method were stronger and more resistant to degradation than uncrosslinked fibers. When used as a tendon replacement prosthesis, morphological events occurred which were observed by light, scanning, transmission electron microscopy and electron histochemistry. Resorption was the initial host response to the prosthesis and involved gradual biodegradation. Formation of a host-replacement tendon was the second response. Increased collagen fibril diameters and a transition in the proteoglycan/collagen fibril interactions occurred in the newly developing connective tissue between 3 and 10 weeks postimplantation. These extracellular matrix transitions were major events occurring during wound healing and led to the assembly of a mature connective tissue. When used as a tendon prosthesis, these collagen fibers rapidly resorb while allowing simultaneous formation of aligned connective tissue. The fibers may have other applications in the fields of Orthopaedic Surgery, Neurosurgery and Biomaterials Research.

Achilles Tendon↗
PubMed1989

Mechanical properties of the aorta: a review.

Measurement and calculation of the mechanical properties of the aorta depend on a number of factors, including the degree of surgical invasion, vasomotor tone, tissue hydration, physical contact (i.e., the presence of a strain gauge), and the use of inside or outside diameter. Measurements on the aorta using angiography, transit-time determination, and echocardiographic techniques yield the most consistent values for parameters, including PVD, Ep, and Eo. Values of these parameters are listed in Table 7 and range from about 8 to 12.0% (PVD), 337 to 741 g/cm2 (Ep), and 0.33 to 3.6 x 10(6) dyn/cm2 (Eo) for human ascending aorta. Measurements made with invasive techniques tend to result in lower values of PVD and higher values of elastic moduli. Modeling studies focus on predicting the mechanical properties of a viscoelastic, anisotropic tube. Difficulty arises in modeling aorta because of hysteresis and the large deformations that are associated with physiologic loading patterns. Various forms of the strain-energy density function have been used to model relationships between stress and strain in three dimensions; however, they have limited value in understanding the mechanism of time-dependent stress transfer between fibrous and nonfibrous components found in aortic tissue. The ultimate utility of these models will include improved understanding of the physical basis of deformation of this important tissue and the mechanisms of premature failure associated with different disease processes.

Animals↗
PubMed1988

Wound healing using a collagen matrix: effect of DC electrical stimulation.

Rapid fibroblast ingrowth and collagen deposition occurs in a reconstituted type I collagen matrix that is implanted on full-thickness excised animal dermal wounds. The purpose of this study is to evaluate the effects of direct current stimulation on dermal fibroblast ingrowth using carbon fiber electrodes incorporated into a collagen sponge matrix. Preliminary results suggest that fibroblast ingrowth and collagen fiber alignment are increased in collagen sponges stimulated with direct currents between 20 and 100 microA. Maximum fibroblast ingrowth into the collagen sponge is observed near the cathode at a current of 100 microA. These results suggest that electrical stimulation combined with a collagen matrix may be a method to enhance the healing of chronic dermal wounds.

Animals↗
PubMed1988

Material properties of living soft tissue composites.

Collagen sponges seeded with fibroblasts have been used as a soft tissue substitute in wound healing applications. This biomaterial is a good in vitro analog of a connective tissue. Therefore, analysis of the properties of this material may be useful for theoretically modeling soft tissues. Stress-strain curves for such cell-seeded collagen sponges were measured to determine composite stiffness and ultimate tensile strength. Theoretical modeling was done by defining a particle-reinforced matrix using the composite sphere model. A system of uniaxially oriented fibers was then introduced to this equivalent homogeneous media and material properties were determined using the composite cylinder model. Geometric averaging was performed to yield the stiffness and Poissons' ratio for a composite with randomly oriented fibers. Inputs to the model were constituent material properties, cell volume fraction, and fiber volume fraction. From theoretical results, material properties of soft tissues and their substitutes depend on fiber mechanical properties and volume fraction and not cellular mechanical properties and volume fraction. Therefore, the increase in experimentally observed composite stiffness with increased cell number was due to deposition of newly synthesized stiffer collagen fibers, and not due to the physical presence of cells themselves.

Collagen↗
PubMed1988

Behaviour of fibroblasts and epidermal cells cultivated on analogues of extracellular matrix.

A porous collagen sponge can be used for supporting epidermal cells and fibroblasts in order to manufacture an artificial skin. Fibroblasts were grown on analogues of extracellular matrix containing collagen and glycosaminoglycans and/or glycoproteins. Cell replication, and also infiltration of fibroblasts, were enhanced by the presence of hyaluronic acid and/or fibronectin. Epidermal cells grown on a collagen sponge have been characterized by microscopic observations. Epidermal cells on the surface of the sponge showed an incomplete differentiation in comparison to normal skin; clumps of epidermal cells were found in the interior of the sponge. Epidermal cell replication was enhanced in the presence of collagen sponge seeded with fibroblasts.

Animals↗
PubMed1988

Relationship between mechanical properties and collagen structure of closed and open wounds.

Mechanical properties and collagen structure of excisional wounds left open are compared with wounds closed by clips. In both wound models, collagen fiber diameter increases with time post-wounding and is related to tensile strength. Clipped wounds show a higher ultimate tensile strength and tangent modulus compared with open wounds. In clipped wounds, newly deposited collagen appears as a biaxially oriented network as observed in normal skin. In open wounds a delay in the organization of the collagen network is observed and parallel wavy-shaped ribbons of collagen fibers are deposited. At long term, the high extensibility observed in open wounds may be due to the sliding of ribbons of collagen fibers past each other.

Animals↗
PubMed1988

Mechanical properties of septal cartilage homografts.

The compressive mechanical properties of untreated and chemically and physically treated nasal septum homografts were determined. Mechanical properties of control, saline-, thimerosal (Merthiolate)- and Alcide-treated specimens were similar. At high strains, the stiffness of treated cartilage ranged from 12.8 to 22.5 MPa and was unaffected by storage time. In comparison, irradiated and freeze-dried nasal septum exhibited stiffnesses of 35 and 37.5 MPa, respectively, after approximately 1 month of storage. These values of stiffness were significantly different from controls at a 0.95 confidence level. On the basis of these results, it was concluded that Alcide and Merthiolate treatment did not alter the compressive mechanical properties of cartilage and that a combination of these treatments may adequately sterilize and preserve nasal septum homografts.

Adolescent↗
PubMed1988

Clinical applications of electron microscopy in the analysis of collagenous biomaterials.

Scanning and transmission electron microscopy are of clinical value in assessing the interaction between biomaterials and ingrowing tissues. Ultrastructural information allows the clinician and biomaterials specialist to determine events occurring during wound healing and the biocompatibility of prosthetic devices. This paper reviews some of the experimental and clinical studies done in our laboratory on the use of natural and reconstituted collagen as replacements for connective tissues. Consideration is given to collagen flakes used for the treatment of dermal ulcers, a collagen fiber prosthesis used for tendon and ligament replacement, the effects of chemical preservatives on cartilage used for replacement of tissues during plastic surgery and the growth and orientation of nerve cells on reconstituted collagen fibers. Our results show that reconstituted collagen can be prepared into prosthetic devices which encourage cell attachment and orientation thereby facilitating healing of injured tissues. Furthermore chemical preservation of cartilagenous tissues kills chondrocytes resulting in eventual resorption by inflammatory cells.

Biocompatible Materials↗
PubMed1988

Fibroblast and epidermal cell-type I collagen interactions: cell culture and human studies.

Fibroblast and epidermal cell-type I collagen sponge interactions were studied in cell culture as well as in humans. In cell culture, fibroblasts were observed to migrate and proliferate throughout a type I collagen sponge containing either hyaluronic acid (HA) or fibronectin (FN). Fibroblasts accumulated in the center of the pores in sponges containing HA and appeared to surround themselves with newly synthesized extracellular matrix. In sponges containing FN, fibroblasts attached to and elongated along the collagen fibers of the sponge. In the absence of FN or HA protein synthesis of fibroblasts appeared to be inhibited by the presence of the type I collagen sponge. Epidermal cells grown on plastic or on type I collagen, formed sheets. Epidermal cells grown on a collagen sponge morphologically appeared different than cells grown on plastic. The type I collagen matrix studied in cell culture was applied to dermal wounds of patients with pressure ulcers in order to evaluate its effect on dermal wound healing. The areas of ulcers treated for 6 weeks with a type I collagen sponge decreased by about 40% compared with no change in the areas of untreated controls. Preliminary results suggest that a type I collagen sponge is a biocompatible substrate with fibroblasts and epidermal cells and may be effective in enhancing healing of chronic skin ulcers.

Animals↗
PubMed1987

Increased aortic root stiffness associated with osteogenesis imperfecta.

M-mode echocardiograms obtained from 31 patients with types I and IV osteogenesis imperfecta (OI) were evaluated for increased aortic root dilatation and wall stiffness. Four patients were observed to have dilated aortic roots. The pressure-strain elastic moduli (Ep) of the majority of OI patients studied were significantly different from those of age-matched controls; the observed values of Ep were both greater and less than that of controls. At high strain in the circumferential direction, nine of 31 OI patients had aortic roots that were significantly stiffer than those of controls. Increased stiffness in the circumferential direction was associated with decreased aortic pumping efficiency. The increased stiffness observed in the circumferential direction is consistent with increased accumulation and crosslinking of collagen within the aortic wall and may reflect premature aging of OI patients.

Adult↗
PubMed1987

Fibroblast growth on a porous collagen sponge containing hyaluronic acid and fibronectin.

We have previously shown that the presence of fibronectin (FN) and/or hyaluronic acid (HA) in a 3-dimensional type I collagen sponge enhances wound healing in vivo. In the present study the same material was used as a support for growth of fibroblasts in vitro. Using radiochemical techniques, scanning electron and light microscopy, the properties of fibroblasts cultured on the collagen sponge or on the sponge containing HA or FN have been compared with cultures grown on plastic dishes. Fibroblast replication and collagen synthesis were higher on plastic than on the collagen sponge. In the presence of HA or FN the entire thickness of the sponge was infiltrated by fibroblasts which rapidly replicated. The presence of HA or FN increased synthesis of collagen which was largely deposited around cells.

Animals↗
PubMed1987

Diffusivity of 125I-labelled macromolecules through collagen: mechanism of diffusion and effect of adsorption.

Diffusion of angiotensin II, albumin and aldolase was studied through collagen membranes with swelling ratios between 4 and 15. The diffusion coefficient was measured from the time-lag for the onset of steady-state flux through the membrane. Binding of macromolecules to collagen was evaluated from the results of sorption studies conducted as a function of macromolecular concentration. Results presented indicate that the diffusion of macromolecules through collagen membrane is slowed by electrostatic and hydrogen bonding between individual macromolecular chains and collagen. The extent of adsorption is increased as the molecular weight of the diffusant increases. Diffusion of water soluble macromolecules through collagen occurs rapidly, suggesting that diffusion occurs through water filled channels as opposed to between collagen molecules. The results of these studies are useful in understanding diffusion through connective tissues and in the design of drug delivery systems based on collagen.

Adsorption↗
PubMed1986

Collagen-based wound dressings: control of the pore structure and morphology.

Collagen-based sponges have been used as both temporary and permanent coverings for dermal defects in animals and humans. Cellular ingrowth within such a sponge has been shown to depend on the porosity and the presence of fibrous structure. Collagen sponges were made by freezing and freeze-drying dispersions under acidic conditions. These studies involved the effects of dispersion pH and viscosity as well as freezing temperature on the surface and bulk morphology of collagen-based sponges. Using scanning electron and light microscopy, the results of these studies indicated that large surface pores that form connections (channels) with the interior of the sponge were formed using low-viscosity collagen dispersions. At high dispersion pH (3.2) and at a moderate freezing temperature (-30 degrees C), fibrous structure and a large number of channels were present. When a lower dispersion pH (2.0) and freezing temperature (-80 degrees C) were used, pores sizes were smaller with channels and fibrous structure, whereas a higher freezing temperature (-20 degrees C) resulted in a sheet-like structure and increased pore sizes. Differences in pore size and surface morphology were explained on the basis of ice crystal growth. In the case of abundant free water (high pH) and high freezing temperature, the pore size was greatest because of enhanced ice crystal growth.

Bandages↗
PubMed1986

Non-invasive assessment of aortic mechanical properties.

Echocardiography and sphygmomanometry were used to noninvasively assess the changes in aortic mechanical properties associated with aging. Fifty normal individuals were examined and were divided into three groups: young (less than 35 years of age), middle-aged (35-55), and old (greater than 55). Experimental measurements indicated that elastic aortic stiffness in the circumferential direction increased with increased age. It was concluded that this was consistent with increased deposition of circumferentially oriented collagen within the media. Associated with increased elastic aortic stiffness in the circumferential direction was a decrease in the ability of the aorta to act as an auxiliary pump. The average work per unit length recovered from aortas of older individuals was only 44% of that recovered from the aortas of individuals in the young group. These studies suggest that increased elastic aortic stiffness results in decreased aortic pumping efficiency and may lead to a compensating increase in blood pressure.

Adult↗
PubMed1986

Diffusivity of 125I-calmodulin through collagen membranes: effect of source concentration and membrane swelling ratio.

Diffusivity of 125I-calmodulin (MW congruent to 17,000) through collagen membranes was studied as a model for the release of macromolecules from collagen matrices. The diffusion coefficient of calmodulin through collagen membranes was determined from time-lag experiments conducted in a dialysis cell at 24 degrees C. Based on time-lag experiments, the diffusion coefficient was observed to be a function of source concentration and membrane swelling ratio after denaturation. The dependence of the diffusion coefficient on source concentration was consistent with a model involving calmodulin immobilization by the collagen membrane. At high source concentrations the diffusion coefficient of calmodulin through collagen membranes was observed to vary from about 10(-8) for uncrosslinked membranes to 10(-9) cm2/s for highly crosslinked membranes. Based on theoretical calculations, the release rate from collagen matrices may be altered by a factor of three. It was concluded that the release rate of biologically active molecules from collagen matrices can be controlled by varying the extent of crosslinking and the macromolecular concentration. Further studies are necessary to characterize the release of other macromolecules from collagen matrices.

Animals↗