摘要:

AbstractHuman von Willebrand Factor (vWF) was studied by atomic force microscopy under physiologic buffer on a hydrophobic octadecyltrichlorosilane self‐assembled monolayer. The self‐assembled monolayer deposited on glass was sufficiently smooth (root mean square roughness = 0.25 ± 0.12 nm) to permit identification of adsorbed vWF. Adhesion of the protein to the hydrophobic substrate was sufficient to allow repeated scanning by the atomic force microscope probe, and images of vWF on a submolecular scale were obtained. The frictional force between the surface and the protein was sufficient to withstand an applied lateral force of 19 nN. This result shows that vWF experiences strong interaction with a hydrophobic surface in aqueous media. Statistical analysis of adsorbed vWF shows that the protein is composed of large globular domains with elliptical cross sections of average dimensions 56 ± 24 nm (major axis) 26 ± 19 nm (minor axis), and 2.8 ± 1.0 nm (height). Further analysis of the major axis dimension shows that the molecular chain of vWF contains two statistically different populations of domain size. However, no sequence order of the different population of domains within the individual molecule was found. On the basis of our analysis of the globular domains, we present a model describing the three‐dimensional structure of vWF protomer adsorbed on a hydrophobic surface in a physiologic solution. © 1994 John Wiley

ISSN:0021-9304    

DOI:10.1002/jbm.820280902

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractWith the identification of the exacerbating effect of glutaraldehyde on calcification of heart valve materials, there exists a renewed interest in both alternative reagents and the effects of crosslinking on connective tissues. One potentially useful class of reagents are poly(glycidyl ether) compounds. We have examined 5 of these reagents with different molecular sizes and functionalities for their effects on mechanical properties and collagen denaturation (shrinkage) temperature. Samples of bovine pericardium were tested fresh or after 48 h fixation in one of the five compounds for denaturation temperature, stress‐strain response, stress relaxation, plastic deformation, and fracture properties. Of the compounds tested, those with intermediate length backbones and 4 or 5 epoxide groups were most effective in producing intrahelical crosslinking and increased denaturation temperature over 48 h. However, in samples examined after 17 months of fixation, all reagents had equivalently increased the denaturation temperature. Examination of mechanical results revealed two distinct mechanisms for mechanical change. Observed shifting of the stress‐strain curve to the right (due to shrinkage), increased plastic deformation, and some reduction of stress relaxation are all unrelated to denaturation temperature (and hence to changes in intrahelical crosslinking). An alternate mechanism, perhaps formation of intermolecular crosslinks may be responsible. Intrahelical crosslinking produces only lesser reductions in stress relaxation. Cross‐comparison of reagents of differing molecular structure provides a useful tool toward increased understanding of the mechanical consequences of tissue crosslinking. © 1994 John Wiley&Son

ISSN:0021-9304    

DOI:10.1002/jbm.820280903

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractFour Ca,P particle containing surface reactive glass composites and two glasses(in the SiO2‐aO‐P2O5‐Na2O‐Al2O3system) were implanted in the diaphyseal area of goat femora up to 24 weeks. Scanning electron microscopic, energy dispersive x‐ray, and histological analysis were performed to evaluate the material‐tissue interactions. A new type of integration mechanism was observed. Instead of the bone growing to the material surface, a gel‐like silica formation appeared between the cortex bone and the material surface. In time the gel‐like formation was replaced by a Ca,P layer. The results provided indirect evidence that pure silica gel formed in the tissues could also achieve an apatite layer formation and bone bonding on its surface. © 1994 John

ISSN:0021-9304    

DOI:10.1002/jbm.820280904

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractA bioartificial pancreas, that is, transplantation of islets of Langerhans (islets) which are enclosed in a semipermeable membrane, has been proposed as a treatment for type I diabetes. The islets are immuno‐isolated from the host by the semipermeable membrane preventing rejection while maintaining control of glucose metabolism for an extended period. The purpose of the current research is to evaluate the feasibility of preparing agarose microbeads with xenogeneic hamster islets as a bioartificial pancreas in streptozotocin induced diabetic mice. In the recipients with a low level of anti‐hamster antibodies, the combination of encapsulation of hamster islets in 5% agarose microbeads andin vitroculture of them prolonged xenograft survivals. Four of 6 recipients were still normoglycemic at 100 days after implantation. However, the same procedure was not effective in the recipients which were sensitized in advance by transplantation of free hamster islets and thus had high levels of anti‐hamster antibodies. The average normoglycemic period was 32 days. Antibodies permeated through the microbeads and activated complement on the cell surfaces. The network of agarose microbeads was rendered dense by increasing the concentration of agarose to restrict the diffusion of antibodies. Graft survivals were prolonged with increasing concentrations of agarose. As an analysis using diffusion equations predicted, the survivals were inversely proportional to the diffusion coefficient of IgG in each agarose gel. Islet xenotransplantation was enabled by the combination of the microbeads with a concentration of agarose higher than 7.5% andin vitroculture even in recipients having a high level of preformed antibodies. © 1994 John Wiley&Son

ISSN:0021-9304    

DOI:10.1002/jbm.820280905

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractPorcine collagen membranes having a rough and a smooth side were used for subcutaneous implantation studies in rats. Two tanning protocols were used for the membranes, a new one involving microwaving and glutaraldehyde treatment (NEWGA), and the other, a conventional method using glutaraldehyde treatment at room temperature (OLDGA). Untreated membranes (NONGA) were also implanted. Sections of the implants were examined by light microscopy and with the confocal laser scanning microscope focusing on neovascularization and incorporation of the implant. At 64 days, the smooth sides of NEWGA and OLDGA implants were not well incorporated, with scarring subjacent to the surface and dystrophic calcification of that side of the membrane. At the same time, the rough sides of the NEWGA and OLDGA were not calcified with a giant cell reaction around the porcine collagen. The best incorporation was found in the NONGA membranes with no dystrophic calcification, excellent neovascularization of all layers, and complete remodeling at day 64. After 5 months, the completely remodeled NONGA membrane still could be identified, and the NEWGA and OLDGA membranes were calcified with a giant cell reaction having a dense fibrous capsule. It is concluded that if cross‐linking is deemed necessary, the microwave cross‐linking method is advisable because in the early stages there is less reactive inflammation around it, and the implant surfaces should be rough with an open structure, making calcification of crosslinked collagen unlikely. © 1994 John Wiley&Sons,

ISSN:0021-9304    

DOI:10.1002/jbm.820280906

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe objective of the investigation was to study the basic problems related to the firing of dental porcelain to commercially pure titanium. The firing of a low‐fusing porcelain to sandblasted or electrolytically polished titanium was carried out in an ordinary dental furnace. The interfacial regions between the ceramic coatings and titanium were analyzed using scanning acoustic microscopy (C‐SAM) and scanning electron microscopy (SEM) techniques. Thermal stresses in the joints were evaluated by means of a finite element model based on multilayer elastic strain analysis. The chemical reactions and their formation sequence at 750°C was predicted thermodynamically and observed experimentally both at 750 and 800°C. The C‐SAM results gave evidence that the integrity of the porcelain‐titanium joints are better in the sandblasted samples than in the elecropolished ones, where defects were larger. SEM analyses of the same samples confirmed the C‐SAM findings. Because the reaction layers are more continuous in the electropolished samples, cracks propagated more readily in these samples during the cooling procedure. Both thermodynamic calculations and experimental chemical analyses strongly indicate that the cause for the cracking of the reaction zone is thin layer of Ti (oxo) silicide and/or a relatively thick solid solution layer of Ti and oxygen. © 1994 John Wil

ISSN:0021-9304    

DOI:10.1002/jbm.820280907

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe biocompatibility of a new semisolid, hydrophobic poly‐(ortho ester) (POE) intended for controlled drug delivery to the eye was evaluated. The polymer was injected subconjunctivally in rabbits, and clinical and histologic examinations were performed 3, 10, 15, and 21 days after injection. Polymers injected as controls were an aqueous gel of sodium hyaluronate (SH), 1% in phosphate buffer, and medical grade silicone oil. After injection, the POE emulsified into small droplets and a focal eosinophilic reaction was noted at 3 days' implantation. At 10 days' implantation, the inflammatory reaction had resolved, with fibroblasts being the predominant cell type. At 15 and 21 days, no POE was identified and normal appearing tissue was present in the injection site. Sodium hyaluronate was not inflammatory over the period of the implantations. Silicone oil induced a slight inflammation at 3 days, with the presence of eosinophils and limited necrosis with cellular debris. Silicone oil was present in the implantation site at 3, 10, 15, and 21 days. The inflammatory response to the respective polymers was evaluated in the subconjunctival tissue. The inflammatory reaction was quantified at the implant site, adjacent subconjunctival tissues, and scleral and corneal stroma. The inflammatory cell densities in these respective tissue zones were determined, and the ratio of eosinophils over total inflammatory cells was calculated. POE did not become encapsulated with fibrous tissue, but biodegraded in a short time, indicating its potential for use after glaucoma filtration surgery. © 1994 John Wiley&Sons, I

ISSN:0021-9304    

DOI:10.1002/jbm.820280908

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThis study reports on the soft‐tissue response to titanium fiber mesh percutaneous implants. The implants were inserted in the backs of 15 rabbits. The surgical procedure was performed in two steps: implantation of the subcutaneous part of the implants and, after 3 months, fixation of the percutaneous part into the subcutaneous part. Two and 6 months after insertion the animals were sacrificed and the implants, with their surrounding tissues, were processed histologically. Light microscopic analysis demonstrated that only one implant showed considerable skin retraction in the percutaneous area. Around the rest of the implants no downgrowth or only a very limited epidermal downgrowth was observed. Furthermore, the fiber mesh material showed good biocompatible behavior. These results confirm the previous finding that sintered titanium fiberweb structures are effective for the stabilization of percutaneous devices located in soft tissues and can improve their performance. © 1994 John Wiley&Sons, I

ISSN:0021-9304    

DOI:10.1002/jbm.820280909

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractWith the resurgence of the use of bone cement in total hip arthroplasty, a renewed interest in techniques or designs that may reduce cement fixation failure has arisen. Analysis of the stresses at the tip of the prosthesis may suggest strategies to reduce loosening. This study analyzed stresses in the cement near the tip of a femoral component as a function of cement thickness, using a three‐dimensional finite element model. A section of an idealized circular femoral shaft with implanted prosthesis and cement was modeled with loading conditions representing the stance phase of gait. Increasing cement thickness from 2 to 5 mm by reducing the prosthesis diameter from 15 to 9 mm is predicted to reduce stress significantly in the cement mantle of a femoral implant. Peak tensile stresses are reduced 45%, whereas peak von Mises and shear stresses are reduced 40%. Such a reduction in stress can increase fatigue life by an order of magnitude. Peak interface tensile stresses occur on the medial side at the tip of the prosthesis in a transverse direction, indicating likelihood of failure due to debonding. The shear and tensile stresses predicted by our model greatly exceed the fatigue endurance limit values for both bulk cement and the cement‐prosthesis interface, indicating the likelihood of premature fatigue failure, even allowing for considerable uncertainty. These analytical results suggest that the surgeon should adopt a strategy of selecting a prosthesis that permits a 5‐mm cement mantle near the tip of the prosthesis. © 1994 John Wiley&Son

ISSN:0021-9304    

DOI:10.1002/jbm.820280910

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractAside from the considerable number of reports on the physical and chemical properties of dental bonding agents, information concerning their biologic effects is sparse. Three dentin bonding agents (Prisma Universal Bond, Pertac Universal Bond, and Syntac) and the ingredients methylmethacrylate, 2‐hydroxyethyl‐methacrylate, and glutaraldehyde were investigated in theSalmonella typhimuriummutagenicity test system using five different bacterial strains (TA97a, TA98, TA100, TA102, and TA104). The materials as well as the ingredients were eluted in both dimethyl sulfoxide and physiologic saline, and serially diluted eluates were used in the plate incorporation test. Pertac Universal Bond and Prisma Universal Bond did not elicit any mutagenic effects in any of the bacterial strains. In contrast, Syntac adhesive showed clear mutagenicity inS. typhimuriumstrain TA102. Dimethyl sulfoxide eluates, as well as physiologic saline eluates of the Syntac bonding agent, caused numbers of revertants that were about 6 times higher than control values. Reversion rates with other strains were moderately enhanced. Glutaraldehyde, an ingredient of Syntac adhesives, caused mutagenicity in a manner similar to Syntac adhesive eluates. Neither 2‐hydroxyethyl‐methacrylate nor methylmethacrylate monomer was found to be mutagenic over a broad concentration range. © 1994 John Wiley&S

ISSN:0021-9304    

DOI:10.1002/jbm.820280911

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY