bluuebunny/crossref_metadata_2025 huggingface dataset:
Toxic reactions evoked by glutaraldehyde‐fixed pericardium and cardiac valve tissue bioprosthesis
Authors: Gendler E. , Gendler S. , Nimni M. E.
Published: December 2004

Bovine pericardial tissue and tissue‐derived bioprosthesis fixed in glutaraldehyde and stored in either glutaraldehyde or formaldehyde can induce cytotoxic reactions even after prolonged washing due to the slow leaching of the chemicals used for crosslinking and sterilizing. Sequential rinsing for up to 60 min was still not sufficient to eliminate cytotoxic effects. On the other hand, satisfactory results were obtained when cardiac valves made from glutaraldehyde fixed pericardium were stored in a solution containing 0.02% of propyl‐hydroxy‐benzoate and 0.18% methyl‐hydroxy‐benzoate. The valves stored in this solution and rinsed three times for 1 min in normal saline showed few signs of residual cytotoxicity. Rinsing in a solution containing glycine was partially effective in neutralizing the cytotoxic effect, and this or similar approaches offer good possibilities. The use of Chang cells grown in culture provides an excellent quantitative assay for the assessment of residual cytotoxicity and for evaluating the host response to different methods of fixation, storage, and rinsing of tissue derived bioprosthesis.
Intraocular‐lens—endothelial interface: Adhesive force measurements
Authors: Reich S. , Levy M. , Meshorer A. , Blumental M. , Yalon M. , Sheets J. W. , Goldberg E. P.
Published: December 2004

An instrument for measuring the force of adhesion between intraocular lens materials and the endothelium of excised rabbit corneas was constructed. The adhesion force was measured for polymethylmethacrylate (PMMA), polyhydroxyethylmethacrylate (PHEMA), Duragel (amino‐polyamide hydrogel), PMMA surface grafted with polyvinylpyrolidone, and PMMA surface treated with sodium hyaluronate (Healon). The force of adhesion was reduced considerably when the PMMA surface was modified with a hydrophilic polymer coating. This is consistent with previous studies showing reduced endothelium cell damage for hydrophilic polymer coated intraocular lenses. Adhesive forces were also decreased by addition of polyvinyl alcohol or gelatin to the saline solution in which the corneas were immersed. Extension of this type of measurement to pericardium, vascular endothelium, and peritoneum surfaces may also be important to understand tissue damage problems in general surgery.
Significance of the inner‐surface structure of small‐caliber prosthetic blood vessels in relation to the development, presence, and fate of a neo‐intima. A morphological evaluation
Authors: Hess F. , Jerusalem C. , Grande P. , Braun B.
Published: December 2004

Microvascular prostheses with three different inner surface structures were examined morphologically 1–18 months after implantation to evaluate the presence and structure of the neo‐intima. Fibrous polyurethane tubes (length: 5–10 mm, inner diameter: 1.5 mm) were implanted in the rat abdominal aorta in group A with a fibrillar inner structure (pore sizes 20–50 m̈m), and in group B the inner fibrillar structure was coated with an impermeable continuous silicon sheet. Expanded polytetrafluorethylene vascular prostheses (length: 40 mm, inner diameter: 4 mm) were implanted in the dog carotid artery (group C). The specimens were examined by light microscopy and scanning electron microscopy. A continuous and permanent neointima was only found in the prostheses with the porous fibrillar inner structure (group A). The thin new lining sheet was well attached to the prosthetic wall by cellular protrusions. In the silicon‐coated prostheses (group B) also a continuous neo‐intima had developed which, however, was irregular, thicker, and not anchored to the prosthetic wall. The expanded polytetrafluorethylene prostheses (group C) showed also after 1 year only incomplete lining with a neo‐intima. Fresh blood cell deposits could be observed in the unlined prosthetic wall. It is concluded that a continuous lining of vascular grafts with a thin neo‐intima is only achieved if the cells invading the prostheses from the anastomotic areas can anchore their cytoplasmic protrusions onto an appropriately structured inner surface. If these anchoring facilities are not provided, the unattached neo‐intima will thicken, interfering with the patency of these microvascular prostheses, or fragments of the neo‐intima or alternatively mural thrombi may constantly strip off and embolize.
Development of topical BAPN delivery system for acute spinal cord injury in dogs
Authors: Chvapil Milos , Weinstein Philip R. , Misiorowski Ronald L. , Telles David , Rankin Lucinda , Stoy Vladimir
Published: December 2004

Topical sustained release of various medications by a subdurally implantable device at the site of spinal cord injury is considered advantageous in the treatment of early symptoms of tissue damage. A typical case is the interference with collagenous scar by β‐aminopropionitrile, inhibiting collagen polymerization. Four materials, silicone, polyethylene, polytetrafluoroethylene (PTFE), and polyacrylonitrile‐based hydrogel were evaluated for biocompatibility in subcutaneous implantations. The hydrogel, the least reactive, was then compared with silicone sheets as subcural implants. The histology favored the hydrogel as the most inert material, which was then used for the construction of soft, pliable pouches, releasing the drug through the hydrated wall at a rate controlled by an osmotic pump.
Bond strength and hardness of light‐activated composite resins
Authors: Schulein Thomas M. , Boyer Daniel B. , Chalkley Yvonne
Published: December 2004

The bond strength of visible light‐activated composites to etched enamel was measured as a function of exposure time. Studies have shown that the bottom surface may not be as hard as the top after customary cure times. Therefore this study also measured hardness and related it to enamel bonding. Plexiglas molds were used to simulate extracoronal applications where light is not attenuated by enamel. Bond strength and hardness of the bottom surfaces reached maximum values after the same exposure times with two of the three composites. More exposure time than normally recommended by manufacturers was needed to obtain maximum bond strength to enamel.
Inhibition of thrombus formation on intravascular sensors by electrical polarization
Authors: Schmitt J. M. , Baer M. , Meindl J. D. , Anderson M. F. , Mihm F. G.
Published: December 2004

Implantable biomedical sensors built on a silicon substrate capped with glass are currently being developed for intravascular applications. Electrical techniques for inhibiting thrombus formation on the surface of a proposed optical sensor in direct contact with blood have been investigated. Glass‐on‐silicon specimens (4 × 1.2 × 0.4 mm3) were coated with indium–tin oxide, a transparent conductor, and implanted in the vena cava and iliac veins of three dogs for 10, 20, or 33 days. The equilibrium surface—blood interface potentials of the specimens were modified by implanted current sources which supplied either direct current (8–15 m̈A) or 100 KHz alternating current (5 m̈A, root mean square). Light‐microscopic and scanning electron‐microscopic analyses showed each of the DC‐polarized specimens to be free of thrombus, in contrast to nonpolarized (control) specimens on which varying amounts of adsorbed protein and thrombus deposits were found. Like the control specimens, the AC‐polarized specimens formed thrombus, but the appearance of the deposits differed. These findings support the view that the polarity, magnitude and time dependence of the potential across conducting surface—blood interface significantly influence thrombogenicity. Further work is necessary to determine the roles of electrochemical and electrostatic factors in preventing thrombus formation on foreign materials.
Marginal leakage of class V cavity preparations
Authors: Dumsha Thomas C. , Biron George
Published: December 2004

Dentin‐bonding materials, ferric oxylate (FO), addition reaction between N‐phenylglycine and glycidyl methacrylate (NPG—GMA), and addition reaction product of pyromellitic acid dianhydride and 2‐hydroxyethyl methacrylate (PMDM), were tested together for their ability to inhibit marginal leakage in Class V composite restorations in vitro. Sixteen experimental teeth were pretreated with FO, NPG—GMA, PMDM, and restored with composite. Sixteen control teeth were treated conventionally with composite. The teeth were then thermally cycled (5 and 55°C) for 7 days, silver stained, and evaluated blindly for degree of marginal leakage on a scale of 0 (no leakage) to 7 (leakage into the pulp). The experimental group displayed significantly greater leakage values (p ≤ 0.01) than controls. The results of this study support the hypothesis that FO, NPG—GMA, and PMDM, together with composite inhibit marginal leakage.
An in vivo method for the biological evaluation of metal implants
Authors: Keller J. C. , Marshall G. W. , Kaminski E. J.
Published: December 2004

The peritoneal cavity of the rat was used as an implantation site in order to study the quantitative, cellular response and the qualitative, histopathological response to three metals (Ag, Sn, Cu). The effects of the metals on the cells were correlated with the cellular concentrations of the metal as determined by chemical analysis. Small variations in the cell population and a minimal foreign body reaction was observed with an implanted control material (silicone polymer). Large increases in the number of cells and an intense foreign body reaction was observed with Cu implants. Decreases in the number of cells were seen with Sn and Ag implants, but only Sn elicited a foreign body reaction. Implantation of Ag failed to elicit a foreign body reaction. Significant concentrations of all three metals were detected in the retrieved cells.
Demineralization and ion binding action of polycarboxylate cement liquid on human dental enamel
Authors: Vaidyanathan J. , Vaidyanathan T. K. , Schulman A.
Published: December 2004

The demineralization and ion binding effects on dental tissues due to poly(acrylic) acid attack under different dilution conditions of the latter are studied by scanning electron microscope (SEM) and infrared (IR) spectroscopy. The results indicate that in addition to the general demineralization effects such as preferential prism core attack, prism periphery attack, and protruding prism rods, competing ion binding effects also occur. Using optimum dilution conditions, the microstructural effects of demineralization and ion binding are shown and the effects are related to IR spectral observations.
Effects of immersion in cholesterol‐lipid solution on the tensile and fatigue properties of elastomeric polymers for blood pump applications
Authors: Hayashi K. , Matsuda T. , Takano H. , Umezu M.
Published: December 2004

Tensile and fatigue properties were studied on three kinds of segmented polyether polyurethanes developed for blood pump applications. To study the effects of plasma constituents, specimens were immersed in a cholesterol‐lipid solution whose composition is similar to that of plasma. The results obtained were compared with those observed in a saline solution which had been reported previously. Immersion in the cholesterol‐lipid solution has influence on the mechanical properties of Toyobo TM5 polyurethane and Avcothane 51: Its effect is enhanced by cyclic deformation. Cholesterol‐lipids change the mechanical characteristics of Avcothane 51 more remarkably than those of Toyobo TM5 polyurethane possibly because the former contains about 10% silicone. On the other hand, there is little effect of the constituents of the cholesterollipid solution on the static and dynamic mechanical properties of Biomer, although moisture and cyclic deformation have some influence on the mechanical characteristics.
Covalent coupling of polysaccharides to silicon and silicon rubber surfaces
Authors: Elam Jan H. , Nygren Håken , Stenberg Manne
Published: December 2004

A method to produce a hydrogel by covalently coupling dextran polysaccharide to silicon and silicon rubber surfaces is described. A bifunctional epoxysilane was used as coupling mediator and the conditions for the reaction were optimized. Coupling of the silane to silicon rubber was possible only after oxidation of the surface by plasma etching. The reaction between the epoxy‐group and dextran was concentration dependent and required high concentrations of dextran. The turnover rate of fibrinogen in solution at the hydrophilic surface was found to be high when measured by ellipsometry.
Determination of extractable methylene dianiline in thermoplastic polyurethanes by HPLC
Authors: Mazzu A. L. , Smith C. P.
Published: December 2004

Polyurethanes are finding increasing utilization in biomedical applications. Recently, the reported finding of methylene dianiline (4,4′‐diaminodiphenylmethane, MDA) in the aqueous extracts of autoclaved 4,4′‐diphenylmethane diisocyanatebased polyurethanes promoted our investigation of the origin and extent of extractable methylene dianiline in polyurethanes. A high‐pressure liquid chromatography procedure using precolumn derivatization is utilized to selectively monitor the appearance of this diamine in the aqueous extracts of polyurethanes subjected to water immersion, heat aging, and various sterilization techniques. No MDA was found in the aqueous extracts of the treated polyurethane except for the case of prolonged steam autoclaving. The appearance of 3–5 ppb MDA in the extract under these conditions is attributed to hydrolysis of the polymer. The stability of the polyurethanes under most conditions renders these materials useful in biomedical applications.
Improved photochemical bonding of composites to dentin using 4‐methacryloxyethyl trimellitate anhydride
Authors: Nagata K. , Lundeen T. F. , Turner D. T.
Published: December 2004

The main objective was to evaluate the use of 4‐methacryloxyethyl trimellitate anhydride (4‐META) to improve bonding of composite materials to dentin. Bowen's resin, containing camphoroquinone, was polymerized by exposure to visible light. In composites, made with a silanated silicate, inclusion of 4‐META (3%) had little effect in increasing mechanical strength or adhesion to bovine teeth. However, direct application of 4‐META via acetone solution was found to be an effective way of increasing tensile adhesive strength; by 240% to dentin (to 7.2 MPa) and by 160% to enamel (to 10.8 MPa). Applying the experience mentioned above, 4‐META was used to bond a proprietary photocuring microfilled composite material to Class V cavities in freshly extracted human teeth. After thermal cycling between water baths held at 5°C and 60°C, all dentin restorations without 4‐META failed, as judged by marginal leakage of a dyestuff. In contrast, using 4‐META there was no leakage in 9 out of 10 cases. In restorations involving enamel, 4‐META failed to prevent marginal leakage at the enamel margins but did prevent penetration along the dentin/composite interface. It is concluded that 4‐META shows great promise for preventing marginal leakage at dentin/composite interfaces.
Property changes of UHMW polyethylene hip cup endoprostheses during implantation
Authors: Eyerer Peter , Ke Yu Cai
Published: December 2004

In this study it is demonstrated that the combined chemical and mechanical influences of the implant situation cause property changes of ultra‐high‐molecular‐weight polyethylene (UHMW PE) hip joint cups. Nearly 30 out of 48 loosened cups, retrieved 3 weeks to 11 years after implantation, were investigated. Density measurements show a density increase with implantation time and a dependence of these changes from implant position and loading conditions. The rate of extractable constituents also increases with course of time. An increased in vivo conditioned oxidation of the UHMW PE can be demonstrated by infrared (IR) spectrometry. The density increase can be explained by post‐crystallization, which is the result of oxidative chain scission. This leads to a reduction of the average molecular weight of the PE and to an increased extractability of constituents. Since these changes have been recognized as the reasons for aging and failing of UHMW PE, the methods of material characterization used in this study for retrieved implants will help to develop suitable in vitro testing and simulating methods. They are the prerequisite for the necessary improvements of the material properties of UHMW PE.
Immunogenicity of glutaraldehyde‐treated bovine pericardial tissue xenografts in rabbits
Authors: Salgaller M. L. , Bajpai P. K.
Published: December 2004

Xenograft valves of glutaraldehyde‐treated bovine pericardial tissue have been claimed to be an excellent choice for the replacement of malfunctioning human heart valves. These valves exhibit low thrombogenicity, hemodynamic function, and transvalvular gradients superior to their mechanical and tissue counterparts. However, there are differences of opinion concerning the immunogenic properties of these valvular devices. This study was conducted to evaluate the immune reactivity of such implants. Data obtained indicated that whole xenograft sections of both untreated and treated valvular tissue remain immunogenic following initial and secondary subcutaneous implantations in rabbits. Homologous and cross‐reacting antibodies were detected by means of indirect hemagglutination test 30 days after initial implantation of the grafts. Presence of cellular immune response as judged by skin reaction and leukocyte migration inhibition tests indicated that glutaraldehyde treatment of tissues does not destroy cellular immunity. Data obtained also suggest that chemical modification of such implants by glutaraldehyde probably alters, but does not abolish some antigenic determinant sites on the tissue surface. Glutaraldehyde treatment of bovine pericardial tissue does not render the tissue immunologically inert.
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

Characterization 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

A 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

The 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

We 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

The 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

A 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

The 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

Samples 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

A 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

The 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

The 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

Silicone 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

The 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

Polyclonal 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

A 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

A 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

In 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

Circular 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.
Degradation of adsorbed fibrinogen by surface‐generated plasmin
Authors: Brash J. L. , Chan B. M. C. , Szota P. , Thibodeau J. A.
Published: December 2004

An investigation of the physical status of fibrinogen that has been adsorbed to glass and then eluted has been conducted. Exposure of Kabi fibrinogen to glass was carried out using a glass bead column experiment. The fibrinogen was eluted sequentially, first by 1 M Tris and then by SDS. The initially eluted fibrinogen showed considerable degradation (SDS polyacrylamide gel electrophoresis) while the later fractions were less degraded. Fibrinogen purified by chromatography on either DEAE‐cellulose or Sepharose‐lysine to remove plasminogen was less degraded. When purfied plasminogen was added to fibrinogen, degradation of column eluates was very extensive in all eluted fractions. These results are interpreted in terms of a surface‐mediated activation of plasminogen to plasmin followed by fibrinogenolysis. Although such an effect remains to be demonstrated as a general property of surfaces, it is speculated that surfaces may vary in their activation of fibrinolysis as well as their activation of clotting, and that maximization of fibrinolysis is a worthwhile goal in the development of blood‐compatible surfaces.
Evaluation of in vivo adsorption of blood elements onto hydrogel‐coated silicone rubber by scanning electron microscopy and fourier transform infrared spectroscopy
Authors: Seifert Linda M. , Greer Raymond T.
Published: December 2004

Three hydrogel formulations consisting of 2‐hydroxyethyl methacrylate (HEMA) copolymerized with N‐vinyl pyrrolidone (NVP) were incorporated into silicone rubber by irradiation‐induced polymerization. These coatings were chosen to represent different degrees of hydrophilicity, and they changed the hydrophobic character of the silicone rubber surface to that of hydrophilic. These composite materials and the silicone rubber comparison material were used as femoral artery‐to‐vein (A‐V) shunts and were removed at 15 min, an approximate time representative of an initial buildup stage of blood elements on test surfaces. Data obtained by scanning electron microscopy (SEM) were used to determine the type and amount of adhering blood cells and fibrin at the time interval described. One‐half of each specimen was used for Fourier Transform Infrared (FT‐IR) analysis to provide a direct comparison of the relative amounts of protein present on the silicone rubber and the three hydrogel composite samples. The combined SEM and FT‐IR analyses were performed on A‐V samples from three dogs. Differences in the response of blood to the surfaces were found by the combined SEM and FT‐IR analyses. The more hydrophilic a hydrogel grafted surface, the less fibrin and cellular elements were seen deposited on it. This is not interpreted as an indication of less reactivity, but is more likely due to thrombus buildup and a degree of subsequent embolization (a tearing of sections of the platelet matting away from a surface, revealing an area that again can be covered).
Modification of polyetherurethane for biomedical application by radiation‐induced grafting. I. Grafting procedure, determination of mechanical properties, and chemical modification of grafted films
Authors: Jansen B. , Ellinghorst G.
Published: December 2004

Radiation grafting of monomers onto suitable trunk polymers is a useful tool for tailoring new polymers for special purposes. This technique has been used in the past for the development of biocompatible materials, e.g., by grafting hydrogels onto mechanically stable polymers. In this first part of our work, the radiation grafting of hydrophilic or reactive monomers onto a polyetherurethane film using the preswelling technique is described. Following this technique the trunk polymer was swollen in the monomer before irradiation. As monomers 2‐hydroxyethyl methacrylate (HEMA), 2,3‐epoxypropyl methacrylate (GMA), 2,3‐dihydroxypropyl methacrylate (GOMA), and acrylamide (AAm) were used. The kinetics of the grafting reactions were examined, and the distribution of the graft component inside the trunk polymer was investigated by means of infrared (IR) spectroscopy. Surface‐grafted as well as bulk‐ and surface‐grafted products could be obtained. The mechanical behavior of the grafted films—especially in the water‐swollen state—was examined and compared with that of the pure trunk polymer. In nearly all cases it was found that the tensile strength σB and the elongation at break εR decreases as the grafting yield increases. Modification of GMA‐ and AAm‐grafted films via chemical reactions was performed to create new functional groups of biomedical interest. In this manner a diol structure, a carboxylic acid structure, and a sulfonic acid group could be introduced in the grafted polymer. The water uptake of such modified films is increased markedly when compared with that of the unmodified samples.
Rat peritoneal macrophage adhesion to hydroxyethyl methacrylate–ethyl methacrylate copolymers and hydroxystyrene–styrene copolymers
Authors: Lentz Anthony J. , Horbett Thomas A. , Hsu Lawrence , Ratner Buddy D.
Published: December 2004

Macrophage adhesion to a wide variety of substrates has been measured, but no systematic study of the influence of specific substrate chemical properties on adhesion is available. These studies were conducted using two series of materials, copolymers of hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA) and copolymers of hydroxystyrene and styrene, to determine the effect of a single chemical property, polar character, on adhesion. Rat periotoneal macrophages were allowed to contact polymer substrates for periods ranging from 1 to 240 min before being subjected to a shear stress of 60–120 dynes/cm2 in a thin‐channel flow cell. Percentage adhesion was calculated from the number of cells that remained adherent to the substrate after 30 s of applied shear stress. Macrophages remained adherent to 100% EMA and all hydroxystyrene–styrene copolymer surfaces after only 1 min of contact. In copolymers of the HEMA‐EMA series, the time required to attain peak adhesion levels increased with increasing substrate hydrophilicity (increasing HEMA content). Cells did not attach to the 20% EMA/80% HEMA copolymer and the 100% HEMA polymer. The results demonstrate that there is a time delay between contact and adhesion of the cells to surfaces of increasing hydrophilicity within the HEMA‐EMA series and no time delay with the hydroxystyrene–styrene series. The time delay is thought to be a function of the excluded volume provided by polymers that are able to undergo significant chain rotation and or swelling in the solvent, water. Small excluded volumes present in copolymers of high EMA content and all hydroxystyrene–styrene copolymers offer little or no resistance to formation of adhesive bonds by macrophages, whereas copolymers with large excluded volumes (high HEMA content) prevent contact and/or adhesion. A mechanism based on the net excluded volumes of both the cell and substrate surface macromolecule is proposed to explain this phenomenon.