bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of aggregation state of hard segment in segmented poly(urethaneureas) on their fatigue behavior after interaction with blood components
Authors: Takahara Atsushi , Tashita Jun‐ichi , Kajiyama Tisato , Takayanagi Motowo 
Published: December 2004

AbstractCharacterization of microphase separated structure, interaction with blood components such as lipids, and fatigue behavior after immersion in blood components were carried out for segmented poly(urethaneureas). The materials studied were Biomer and segmented poly(urethaneurea) (TU‐Mn) composed of hard segment with 4,4′‐diphenylmethane diisocyanate (MDI)‐ethylenediamine (EDA) or 4,4′‐diaminodiphenylmethane (DAM) and soft segment with MDI‐polytetramethylene glycol (PTMG) [Mn of 856, 1350, and 2000]. Small‐angle x‐ray scattering, wide‐angle x‐ray diffraction, and dynamic viscoelastic measurements revealed that these materials showed the state of microphase separation. TU‐Mn with PTMG of Mn = 856 shows the partial phase mixing between hard and soft segments, and phase separation was improved with an increase of Mn of PTMG. Biomer has the characteristics of stronger aggregation of hard segment than that of TU‐Mn. All the specimen showed lipid absorption, but the amount of absorption decreased remarkably after precoating on the specimen surface with serum albumin. Lipid absorption of the specimen was confirmed by dynamic viscoelastic and IR measurements. In the case of segmented poly(urethaneurea) which did not immersed in lipids solution, their fatigue strength are sufficient for application to artificial heart systems. However, fatigue strength of the TU‐Mn series was decreased drastically after absorption of lipids. On the other hand, Biomer did not show a decrease of fatigue strength after lipid absorption. The reduction of fatigue strength in the TU‐Mn series after lipid absorption will be attributed to the weak aggregation of hard segment domain. This reduction of fatigue strength in the TU‐Mn series is characterized by formation of microcrack and mirror zone in fatigue fractured specimen. As the precoating of the specimen surface with serum albumin inhibits the absorption of lipids, the reduction of fatigue strength was not observed for the specimen precoated with serum albumin even after immersing the TU‐Mn series in lipids solution for 96 days.
Material test system for the evaluation of mechanical properties of biomaterials
Authors: Hayashi Kozaburo , Nakamura Takao 
Published: December 2004

AbstractA new material test system has been designed to evaluate the mechanical properties of biomaterials which are very often subject to complicated dynamic and repetitive force and deformation inside the body. The test system has high versatility, being incorporated with a miniature servohydraulic testing machine which can smoothly apply various modes of load and deformation to materials, and a vidicon displacement analyzer for the accurate, non‐contact measurement of specimen length. A minicomputer system is used for the data acquisition and processing. Performance tests of the system and preliminary experiments on elastomeric polymers have indicated that the test system is very useful for the detailed studies of the mechanical properties of various kinds of biomaterials.
Parallel flow arteriovenous shunt for the ex vivo evaluation of heparinized materials
Authors: Ip Wan Fong , Zingg Walter , Sefton Michael V. 
Published: December 2004

AbstractThe patency of heparin‐polyvinyl alcohol (hep‐PVA) coated polyethylene tubing was found to be significantly longer than control tubes coated with polyvinyl alcohol (PVA) but without heparin at low flow rates in dogs using a novel parallel flow arteriovenous shunt designed to avoid surgical artifacts. A standard Silastic chronic shunt (3.18 mm i.d.) was inserted between the iliac artery and vein of a dog. After a 2‐week recovery period, a small diameter coated polyethylene tube (1.14 mm i.d.) was connected in parallel with the exteriorized portion of the chronic shunt through a pair of Silastic Y‐connectors, so that <3% of the shunt flow was diverted into the test tube. The chronic shunt was reused many times over a >6 month patency period, eliminating the need for frequent surgery and reducing interanimal variability in the results. The difference in patency between heparinized and control tubes was greater at higher mainshunt flow rates indicating the presence of a significant effect of the Y‐connectors on platelet adhesion or aggregation. This effect was manifested in a time‐dependent reduction in circulating platelet count. Scanning electron microscopy (SEM) examination of the midportion of the heparinized tubes after occlusion demonstrated the absence of platelet and fibrin deposits, unlike the control tubes without heparin. Although the Y‐connectors played a significant role, they did not dominate the thrombotic processes occurring in this shunt and consequently the biological effectiveness of the immobilized heparin could be demonstrated.
Bone modelling in the implantation bed
Authors: Boyde Alan , Jones Sheila J. 
Published: December 2004

AbstractWe consider results from tissue culture studies and the comparative histology of mineralized tissues and other natural tissue interfaces which may have some relevance in understanding the abnormal biology of the immediate environment of an implant in bone. We discuss factors influencing settling, colonization, and migration on natural and artificial substrates by various cell types which may make or remove matrix near the implant. A knowledge of mechanisms of mineral and organic matrix destruction by osteoclasts and other cells must be important in addition to an understanding of the interaction of local and systemic hormones with bone cells. More studies of the role of the immune system in implant failure are urgently required.
Implant‐stimulated interface reactions during collagenous bone matrix‐induced bone formation
Authors: Reddi A. H. 
Published: December 2004

AbstractThe sequential cellular reactions in the interface of collagenous bone matrix implants are described. The multistep cascade in response to bone matrix implantation include: binding of fibrin and fibronectin to the implanted matrix, chemotaxis of cells, proliferation of fibroblasts, differentiation into chondroblasts, cartilage formation, vascular invasion, bone formation, remodeling, and bone marrow differentiation. The mechanism of action is not known. However, several properties governing the implantcell interface are described. It is possible that bone matrix is a suitable biomaterial with potential applications in periodontal and orthopedic practice.
Interface reactions between machinable bioactive glass‐ceramics and bone
Authors: Höland W. , Vogel W. , Naumann K. , Gummel J. 
Published: December 2004

AbstractA new biomaterial for bone substitution, a “machinable bioactive glass‐ceramic” has been developed. The material contains two main crystal phases, mica and apatite, and is therefore machinable and bioactive. It has the advantage to be workable by the surgeon, if necessary, during operation. The preparation method of this glass‐ceramic is described. Different types of the material can be produced in dependence of the composition, nucleation, and crystallization of the basic glass.In vivoandin vitroinvestigations showed a characteristic solubility of the material. A Caphosphate‐rich interface layer with apatite crystals (from the basic glass‐ceramic) and a thickness of about 5–10 μm grows as solid‐state reaction between glass‐ceramic and bone. This interface reaction is interpreted as a chemical process which includes a slight solubility of the glass‐ceramic and a solid state reaction between the stable apatite crystals in the glass‐ceramic and the bone.
Protein adsorption and desorption phenomena on clean metal surfaces
Authors: Williams D. F. , Askill I. N. , Smith R. 
Published: December 2004

AbstractThe noncompetitive adsorption of the proteins albumin and fibrinogen onto 17 different metal surfaces has been studied in vitro using 125I‐labeled proteins. Although many of the metals showed very similar adsorption characteristics to polymers, several of them adsorbed considerably greater amounts. Copper, gold, and silver were the most significant in this respect, all three being face‐centered cubic, group 1B metals known to bind to many types of protein in vitro and in vivo. The desorption of the proteins was studied in an in vivo model in which preproteinized metals were implanted in rats. There was considerable variation in the amounts of the proteins removed from the various metal surfaces. Generally those metals onto which protein is most readily adsorbed tend to lose the protein quickly, whereas others, such as iron, with only moderate adsorbed amounts, may retain a large part of the adsorbed layer for a long time.
Surface charge on polymeric implants and calcified tissues: Interfacial implications
Authors: Stupp S. I. , Kusleika R. 
Published: December 2004

AbstractSamples of human bone, dentin, and enamel were analyzed through the technique known as thermally stimulated discharge (TSD). It is possible through this technique to detect current flow resulting from appearance or loss of net polarization in a material. Samples of freshly extracted tissue give rise to well‐defined TSD current maxima without having been exposed to external electrical potentials. Calculation of activation energies for these currents and their thermal range suggests the involvement of collagen denaturation in the loss or appearance of a net surface charge on bone and dentin surfaces. In the cse of enamel samples, TSD current maxima are possibly the result of dipolar alignment in water or biopolymers by surface charges in the mineral phase. Interfacial implications of surface charge were studied through the measurement of adhesive strength in dentin/acrylic polymer joints. Enhancement of joint strength by a factor of two or higher was observed when powder particles of the experimental adhesive carried externally induced surface charge. It is hypothesized that electrostatic coupling between polarization domains on the tissue surface and the setting implant improves wetting and produces stronger interfaces.
A cartilagenous graft as an adjunct to finger joint implant arthroplasty
Authors: Powers Dennis L. , Worthy Fred L. , von Recum Andreas F. 
Published: December 2004

AbstractA method is described which is proposed to prolong the functional life of a Silastic finger joint endoprosthesis which has been shown to fail because of abrasion and cutting by the recipient bones. Swanson design Silastic finger joints prostheses were implanted into the knee joints of rabbits. The technique of simultaneously transplanting ear cartilage to the prosthetic implant bed was tested for the purpose of protecting the prostheses from wear and eventual failure. The clinical, radiographic, gross, and histologic results of the animals implanted for 1, 3, and 6 months show that the cartilage graft remains viable and it proliferates. The cartilage provides a smooth, gliding surface with normal appearing joint fluid surrounding the Silastic implant. Control limbs, with no cartilage grafts, had thinner, fibrous tissue encapsulating the implants. The presence of the cartilage reduced the amount of prosthetic wear particles observed in the tissue sections, thus indicating a protective function. The rabbit model developed an osteoarthritis that was caused by the prostheses in its knee joints and was unaffected by our cartilage grafting procedure. The success of our cartilage grafts, in the presence of such an arthritis, provides the impetus for its clinical use in arthritic human finger joints. Further studies are necessary to determine the clinical feasibility of a cartilage grafting technique and its efficacy in reducing implant failure in human finger joints.
The biocompatibility of a dental Ag‐Pd‐Cu‐Au‐based casting alloy and its structural components
Authors: Niemi L. , Syrjänen S. , Hensten‐Pettersen A. 
Published: December 2004

AbstractThe biocompatibility of a type III casting gold alloy, an Ag‐Pd‐Cu‐Au‐based dental casting alloy and its two main structural components, a CuPd‐rich and an Ag‐rich phase, was studied after subcutaneous implantation for 7 weeks in 20 guinea pigs. The Ag‐Pd‐Cu‐Au alloy was surrounded by a capsule of immature collagen with fibroblasts and an increased vascular supply. The CuPd‐rich component induced and maintained an acute inflammation with highly vascularized granulation tissue. The tissue reaction to the Ag‐rich component and the Au‐based alloy was slight. Ten of the guinea pigs were sensitized to PdCl2 prior to the implantation period, but this caused no enhanced tissue reaction, except for an increase in the number of mast cells around three of the alloys.
In vitro cytotoxicity of Ag‐Pd‐Cu‐based casting alloys
Authors: Niemi L. , Hensten‐Pettersen A. 
Published: December 2004

AbstractThe cytoxicity and its correlation to alloy composition, structure, corrosion, as well as galvanic coupling was studied with 12 Ag‐Pd‐Cu‐type alloys, one conventional type III gold alloy and pure Ag, Cu, and Pd. The agar overlay cell culture technique was used. Single phase binary CuPd alloys were only slightly cytotoxic below a Cu content of 30 wt%. The tested multiphase alloys were all toxic, but no correlation between toxicity and Cu content could be observed. Solid solution annealing increased the cytotoxicity of a multiphase alloy. Exposure of a single phase alloy to an artificial saliva for 1 week prior to the test decreased its cytotoxicity significantly. Galvanic coupling of the alloys through an outer copper wire decreased their cytotoxicity.
Effect of silicone oil on the cornea
Authors: Refojo Miguel F. , Roldan Manuela , Leong Fee‐Lai , Henriquez Antonio S. 
Published: December 2004

AbstractSilicone oil can dissolve about seven times more oxygen that can water. Placed in a depot between a rigid scleral lens and the corneal surface, silicone oil might thus be useful for treating severe dry‐eye patients and for preventing exposure keratitis. To explore this possibility, generic (300, 500, 1000, and 12,500 cs) and medical‐grade (1000 cs) silicone oils were tested on rabbit eyes. When oxygenated silicone oil was placed in a cup formed by the lids and hanging sutures and allowed to remain for 3 h on the eyes of anesthetized rabbits, the immediate reaction was mild epithelial edema. By 3 to 6 days later, the thickness of the epithelium and of the entire cornea had increased irregularly. The most common histologic finding was intracellular epithelial edema, particularly in the basal cell layer. The reaction was most intense for the generic oils of the lowest viscosities. The medical‐grade oil was the best tolerated, but it too affected epithelial and corneal thickness. Ultrastructural studies of treated eyes showed abnormal epithelial surfaces but no major changes within the epithelial cells. Biochemical analysis showed some decrease of glycogen in the corneal epithelium of eyes kept under oxygenated medical‐grade silicone oil. A smaller decrease of glycogen level persisted after 2 days exposure of the treated eye to air, suggesting that the corneal epithelium was injured by a mechanism other than hypoxia.
Fracture properties of composite and glass ionomer dental restorative materials
Authors: Goldman M. 
Published: December 2004

AbstractThe double‐torsion technique has been used to determine critical stress intensity factor (K1c) values for a range of composites and glass ionomer cements used in restorative dentistry. From these values and determined elastic modulus (E) and tensile strength (σT) values, two other fracture properties: G1c, the critical strain energy release rate and a0, the inherent flaw size, have been evaluated. Glass ionomers have low K1c and high a0 values, coarse particle composites high K1c and high a0 values, microfine materials low K1c and low a0 values and fine particle composites medium to high K1c values and medium to low a0 values. Light curing materials have K1c values according to their group but tend to have lower a0 values than their chemically curing analogues. Glass ionomers have very low G1c values; however, there is no significant difference between the G1c values of the composite groups. The K1c and a0 values have been used to predict relative performance of the materials in highly stressed restorations and wear.
Immunochemical detection by specific antibody to thrombin of prothrombin conformational changes upon adsorption to artificial surfaces
Authors: Chuang Hanson Y. K. , Andrade Joseph D. 
Published: December 2004

AbstractPolyclonal antihuman α‐thrombin antibodies produced in rabbits reacted minimally (<0.05%) in solution with human prothrombin. However, when prothrombin was adsorbed to artificial surfaces such as polyvinyl chloride (PVC), the crossreactivity of surface‐bound prothrombin with antibody IgG to thrombin (>95% purity) was shown to be significantly enhanced. On PVC, the molar ratios of antibody IgG to thrombin/prothrombin approached the same level as that of antibody IgG to thrombin/thrombin when thrombin was adsorbed to the same material. The analyses of antigen–antibodies interaction, in solution with a direct binding assay by immune precipitation at high‐speed centrifugation (160,000 g, 30 min), and on solid‐phase PVC, were accomplished by use of double‐labeling technique, i.e., 131I‐thrombin (or 131I‐prothrombin) and 125I‐antibody IgG to thrombin. The results appear to suggest that prothrombin adsorption to PVC has resulted in some molecular conformational changes so that immunologically the adsorbed prothrombin resembles that of adsorbed thrombin on the same PVC surface.
An evaluation of variables influencing implant fixation by direct bone apposition
Authors: Thomas Kevin A. , Cook Stephen D. 
Published: December 2004

AbstractA systematic mechanical and histologic evaluation of design variables affecting bone apposition to various biocompatible materials was undertaken. The variables investigated included material elastic modulus, material surface texture, as well as material surface composition. The implant materials included polymethylmethacrylate (PMMA), low‐temperature isotropic (LTI) pyrolytic carbon, commercially pure (C.P.) titanium, and aluminum oxide (Al2O3). Implant surface texture was varied by either polishing or grit‐blasting the various materials. Implant surface composition was varied by applying a coating of ultra‐low temperature isotropic (ULTI) pyrolytic carbon to the various implants. A total of 12 types of implants were evaluated in vivo by placement transcortically in the femora of adult mongrel dogs for a period of 32 weeks. Following sacrifice, mechanical push‐out testing was performed to determine interface shear strength and interface shear stiffness. The results obtained from mechanical testing indicate that for implants fixed by direct bone apposition, interface stiffness and interface shear strength are not significantly affected by either implant elastic modulus or implant surface composition. Varying surface texture, however, significantly affected the interface response to the implants. For each elastic modulus group the roughened surfaced implants exhibited greater strengths than the corresponding smooth surfaced implants. Undecalcified histologic evaluation of the implants demonstrated that the roughened implants exhibited direct bone apposition, whereas the smooth implants exhibited various degrees of fibrous tissue encasement. Thus, for implants utilizing direct bone apposition fixation, it appears that of the parameters investigated, implant surface texture is the most significant.
Compressive properties of polymer coated synthetic hydroxyapatite for bone grafting
Authors: Tencer A. F. , Mooney V. , Brown K. L. , Silva P. A. 
Published: December 2004

AbstractA porous hydroxyapatite material hydrothermally converted from the calcium carbonate exoskeleton of the coral, genus Goniopora (CHAG) was either microcoated using polymethylmethacrylate (PMMA) or polylactic acid (PLA) to cover all internal surfaces, or externally coated to produce a shell, with the objective of reducing the brittleness of the material. Compressive testing showed that while CHAG, externally coated with PMMA, showed the largest increases in strength, stiffness, and energy absorption, the uncoated hydroxyapatite core cracked at low loads although the shell remained intact. CHAG internally microcoated with PMMA showed a 3.84 increase in compressive strength while specimens with internal PLA coatings had 1.81 times the compressive strength of uncoated CHAG specimens. Compared to the mechanical properties of cancellous graft material, specimens internally microcoated with either polymer could be produced having properties equivalent to or greater than those of cancellous graft.
Determination of residual stresses in denture base polymers using the layer removal technique
Authors: Murphy K. M. , Carter J. M. , Johnson R. R. , Sorensen S. E. 
Published: December 2004

AbstractIn order to study the influence of residual stresses on dimensional accuracy and mechanical properties of denture bases, an experimental model was devised for measurement of residual stresses in acrylic denture base polymers. Rectangular bar coupons were cut from resin plates heat processed by conventional dental methods. They included samples which had been slow and fast cooled after polymerization and had been stored in dry and wet environments. Uniaxial residual stress distributions for each coupon were disclosed by removing layers of known thicknesses and measuring the ensuing deflection of the specimens. Coupons of a commercial acrylic resin were annealed and used as controls. ANOVA and Scheffe's test were used to compare experimental conditions at the 95% confidence level. Dry specimens exhibited residual surface compressive stresses from 0.43–0.83 MPa (62–120 psi). Water‐stored specimens showed higher stress levels, 2.86–3.24 MPa (414–470 psi). Slow cooled pigmented acrylic coupons which were dry showed higher residual stresses compared with other dry but nonpigmented specimens. No significant differences were found between pigmented or clear coupons which contained moisture.
The measurement of contact angles on circular tubing surfaces using the captive bubble technique
Authors: Lelah Michael D. , Grasel Timothy G. , Pierce Jeffrey A. , Cooper Stuart L. 
Published: December 2004

AbstractCircular tubings are used extensively in biomedical implants and devices. It is desirable to determine contact angles on the inner or outer surfaces of such tubing in its final fabricated form. In this study, a technique for the measurement of contact angles on tubing surfaces in an aqueous environment is reported. This has particular applications to biomaterials research, where polymer tubings contact the biologic environment. In this technique, air or octane captive bubble dimensions can be measured, and an underwater contact angle calculated from these dimensions. The validity of the technique was experimentally confirmed using Solution Grade Biomer and NIH standard polyethylene surfaces.