bluuebunny/crossref_metadata_2025 huggingface dataset:
Durability of pyrolytic carbon‐containing heart valve prostheses
Authors: Schoen Frederick J. , Titus Jack L. , Lawrie Gerald M.
Published: December 2004

To assess abrasive wear of mechanical valve prostheses containing pyrolytic carbon components, we recovered at necropsy or surgery and analyzed by scanning electron microscopy and surface profilometry eight prostheses. Seven were implanted for 30–85 (mean 50 months). Valves included DeBakey aortic (2), DeBakey mitral (1), Beall mitral (2), Bjork–Shiley aortic (1), Cooley–Cutter mitral (1), and Lillehei–Kaster (L–K) tricuspid (1). All carbon occluders had undetectable wear. Carbon cage struts had a superficial burnish. Metallic struts had insignificant wear marks. In contrast, a Teflon Beall Model 104 valve implanted for 34 days and similarly analyzed had considerable material loss from the cage struts. This study suggests that clinically important abrasive wear will not be a late complication of cardiac valve replacement with pyrolytic carbon prostheses.
The effect of initial temperature on free radical decay in PMMA bone cement
Authors: Turner R. C. , White F. B. , Park J. B.
Published: December 2004

The effect of varying the initial temperature of the components of poly(methyl methacrylate) (PMMA) bone cement has been investigated. Electron paramagnetic resonance (EPR) spectroscopy was used to monitor free radical decay during the curing of the cement. Samples cured in saline at 37°C were found to exhibit first‐order decay kinetics for the polymerization radicals for approximately one week after mixing. This indicates that the decay did not take place by combination or disproportionation and was probably due to a transfer process. Decreasing the temperature of the bone cement components prior to mixing resulted in smaller decay rates, but still with first‐order kinetics. This decrease in decay rate with lower initial temperature may be due to decreased porosity of the cement, possibly due to decreased monomer evaporation. SEM micrographs of the samples were consistent with this change in porosity.
Dissolution of amalgam in saline solution
Authors: Kozono Yoshio , Moore B. K. , Phillips R. W. , Swartz M. L.
Published: December 2004

The experiment was designed to investigate the in vitro corrosion of several modern dental amalgams in saline solution over a six‐month period by measuring changes in the soluble corrosion products. Based on the change of the electrical conductivity of the solution, the dissolution rate seemed to decrease gradually for the first three to four months. Then a rapid increase was observed, indicating a reactivated corrosion process. Larger dissolutions of copper and mercury were observed, especially for the high copper alloys, in these later stages. Zinc and indium, if present, were preferentially released at the earlier stages. Silver and tin could not be detected. Evidence exists that the corrosion of tin results in insoluble deposits of corrosion products.
Corrosion of a new coppergold or copperplatinum intrauterine device
Authors: Gal‐Or L. , Gonen R. , Zilberman A. , Scharf M.
Published: December 2004

It has been shown previously that supplementing plastic intrauterine devices (IUDs) with copper wire enhances the antifertility effect of the device. The use of copper intrauterine contraceptive devices, however, is currently limited to two to three years, mainly because of wire fragmentation, which was observed as early as after eight months of use. In the resulting search for a long‐lasting device, two new systems of duplex wire, with gold and platinum cores electrolytically coated with copper, were devised and studied. Initially, duplex wires and controls were exposed to physiological solution. Copper dissolution rate and corrosion morphology were studied by weight‐loss measurements and optical metallography. Similar systems were then surgically implanted in rat uteri for varying periods of up to 26 weeks. Electron micro‐analysis of corrosion products, in addition to weight‐loss measurements and metallography, was performed. The results showed that a uniform and ductile copper coating is obtainable by electroplating on gold and platinum wires. Rate of copper dissolution is similar to that of solid copper wire. No dissolution of gold and platinum in the controls or coated wires was detected by weight loss, metallography, or atomic absorption measurements. Microanalysis of the deposits and corrosion products on the wires in the uteri environment showed sulfur, chlorine, and calcium, in addition to copper. The results of this study suggest that supplementing IUDs with copper‐coated gold or platinum wires may result in significant prolongation of the life span of the device by preventing uncontrolled loss of copper caused by wire fragmentation.
In vitro retinoid binding and release from a collagen sponge material in a simulated intravaginal environment
Authors: Dorr Robert T. , Surwit Earl A. , Droegemueller William , Alberts David S. , Meyskens Frank L. , Chvapil Milos
Published: December 2004

Four in vitro preparations were constructed to simulate the intravaginal release of two retinoids, all‐trans‐retinoic acid (t‐RA) and 13‐cis‐retinoic acid (c‐RA), from a 0.7% collagen sponge diaphragm insert. Four t‐RA concentrations, 0.019, 0.05, 0.1, and 0.15% in methanol were added to the sponge. The release into an artificial vaginal fluid was monitored serially over 72 h by serial analysis for t‐RA and c‐RA using high‐pressure liquid chromatography. In each preparation, retinoid release was immediate and noncontinuous. At 37°C, the retinoids were stable for at least 48 h. Trans‐retinoic acid was the predominant retinoid recovered. Only trace amounts of the cis‐isomer were released. Peak t‐RA levels were 20 μM after 0.01%, 60–80 μM after 0.05%, 100–200 μM after 0.1%, and 320 μM after 0.15%. When the vaginal fluid bath was changed after 5 h, no further significant retinoid release occurred. There was significant loss of up to 70% of the applied t‐RA into the collagen sponge. The retinoid binding was concentration dependent (higher binding with higher concentrations) and was maximal only after 24 h of co‐incubation. The discontinuous release of t‐RA and the high degree of binding to collagen would seem to preclude use of the diaphragm insert as a vaginal drug delivery system, at least for retinoids.
Crystallinity, solubility, and dissolution rate behavior of fluoridated CO3 apatites
Authors: Okazaki Masayuki , Takahashi Junzo , Kimura Hiroshi , Aoba Takaaki
Published: December 2004

To study the effect of fluoride on the physicochemical properties of carbonate‐containing apatites, two series of fluoridated CO3 apatites with various fluoride contents were synthesized at 80°C and pH 7.4. The a‐axis dimensions of these apatites decreased with the increase of both fluoride and carbonate contents. The crystallinity of the apatites showed similar patterns of variation with the degree of fluoridation irrespective of carbonate content. These patterns appear analogous to the complex pattern of the fluoridated hydroxyapatites previously reported. In contrast to this unexpected crystallinity phenomena, the apparent solubility of fluoridated CO3 apatites in acetate buffer solutions at pH 4.0 and 6.0 and 37°C decreased monotonically with increasing degree of fluoridation and approached that of fluoridated hydroxyapatites at high fluoride content. Dissolution rate of fluoridated CO3 apatite pellets at pH 4.0 also showed a simple decrease with increasing degree of fluoridation and was extremely sensitive to acid at low fluoride content.
Mechanical properties of the fibrous tissue found at the bone‐cement interface following total joint replacement
Authors: Hori R. Y. , Lewis J. L.
Published: December 2004

A long‐term problem associated with total joint replacements is the formation of a fibrous tissue at the bone‐cement interface which may compromise the fixation of the prosthesis. In this study, harvestable amounts of interfacial fibrous tissue were generated using a prosthetic replacement of the canine stifle joint as an animal model. The collected tissues were examined histologically and by uniaxial, unconfined compression tests. The fibrous tissue had a matlike structure. The heavy collagen fibers were distributed at random in sheets and the sheets themselves were layered to form a mat. Such a structure may be able to resist compressive stresses normal to the plane of the mat but is probably not well suited to resist shearing stresses. The fibrous tissue proved to be a very compliant, deformable material and to undergo very large strains with load. The stress‐strain curve for the tissue was nonlinear and was characterized by large deformations at low loads. But with increasing loads, the material became stiffer, and at high loads, the stress‐strain curve became linear with a short‐term tangent modulus of 1.9 MPa at a stress level of 0.5 MPa and a compressive strain level of 50%. With regard to total joint replacement systems which consist of an outer bone shell followed by a thin layer of fibrous tissue, a mantle of PMMA cement and a central core of metal or UHMW polyethylene, the fibrous tissue is substantially more yielding and deformable than the other elements of the structure and may have a significant effect on the structural behavior of the system.
Effect of a cement‐bone composite layer and prosthesis geometry on stresses in a prosthetically resurfaced tibia
Authors: Shrivastava S. C. , Ahmed A. M. , Shirazi‐Adl A. , Burke D. L.
Published: December 2004

A comparative study of stress distributions in the component materials of a number of models of a prosthetically resurfaced tibia is presented. Although the geometry is idealized to be axisymmetric, the loadings for which the finite element analyses are performed are considered to be nonaxisymmetric, simulating more realistically the loading conditions in vivo. The different models are chosen with the view of determining the influence of changes in the prosthesis design on the induced stress distribution in the component materials. The changes considered are in the thickness of the cement and the cement‐bone composite layers, and in the shape of the prosthesis. Experimentally measured values of strains are compared with the analytically predicted values to check the validity of the assumptions used in the finite element modeling. The comparison of induced stresses in the different materials reveals the desirability, from a mechanical behavior point of view, of introducing a cement‐bone composite layer and using a prosthesis with domed subsurface in the fixation system. It is shown that for a model incorporating these features, considerable reduction of stresses in the cement, in its bulk and at its interface with the prosthesis plate, is achieved. The reduced stresses can be expected to have beneficial effects on the long‐term behavior of the cement and its interfaces in the fixation system.
Detecting margin leakage of dental composite restorations
Authors: Wu W. , Cobb E. , Dermann K. , Rupp N. W.
Published: December 2004

The degree of microleakage between a restoration and the cavity wall is difficult to quantify objectively. A silver‐staining method is used and compared to the radioisotope method with results that indicate a superior definition and more accurate evaluation of microleakage. In addition to the accuracy, two advantages are presented: (1) scoring of the leakage can be refined and divided into more precise numbers, and (2) teeth can be observed directly in a microscope without resorting to the indirect interpretation of film or photograph.
Preliminary report on the osteogenic potential of a biodegradable copolymer of polyactide (PLA) and polyglycolide (PGA)
Authors: Hollinger Jeffrey O.
Published: December 2004

A biodegradable copolymer of 50 polylactide:50 polyglycolide was prepared for implantation into experimentally created osseous defects in the tibias of 25 rats. Similarly prepared defects were made in the humeri of the same rats and these defects did not receive copolymer implants. Upon sacrifice, both the implant treated and untreated sites of the experimentally produced osseous defects were evaluated by gross appearance and by histomorphometric examination using a Zeiss Videoplan Image Analysis System with Osteoplan (version 4.1). The animals were evaluated in groups of five at 7, 14, 21, 28, and 42 days. When compared with bony defects that were not treated with the biocompatible, biodegradable copolymer implant, the implant sites displayed an accelerated rate of healing at 7, 14, 21, and 28 days (p < 0.001). A similar healing response rate, however, was observed at 42 days (p < 0.25–0.1). No adverse host tissue responses were observed histologically.
The incidence and significance of rub marks on the stem of removed total hip replacements
Authors: Dobbs H. S. , Robertson J. L. M.
Published: December 2004

This article presents data on the incidence of rub marks (burnishing) on the stems of 180 removed total hip replacement femoral components most of which were McKees and Stanmores. The incidence varied with the reason for removal. It was low for assorted removals excluding fractured stem removals, higher for “loose stem” removals, and highest for fractured stem removals. For “loose stem” removals, it appeared to increase with implantation time. For fractured stem removals it appeared to increase with the time elapsed between fracture and removal. On not‐fractured removal, rub marks appeared to indicate that the component had been loose, but on fractured stem removals they appeared to indicate only that the component had been loose after fracture.
Surface modification and evaluation of some commonly used catheter materials. I. Surface properties
Authors: Triolo Philip M. , Andrade Joseph D.
Published: December 2004

Double catheter systems consisting of a stiff outer catheter and a flexible, buoyant, flow‐directed, inner catheter which is often balloon‐tipped have been employed with increasing frequency recently in both therapeutic and diagnostic procedures. Their use, however, has been restricted because of the excessive friction generated between the two catheters. In an attempt to decrease friction between polymers commonly used as catheter materials, oxidation of polyethylene, fluorinated ethylene‐propylene copolymer, poly(vinyl chloride), silicone rubber, and polystyrene surfaces was induced by exposing the polymers to radio frequency glow discharge (RFGD) in a helium environment. All polymers were surface characterized utilizing x‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and contact angle measurements before and after oxidation. This article describes the materials and methods used to fabricate and characterize the polymer surfaces and the results of the characterization. The results indicate that increases in oxygen concentration at the surface of the polymers and decreases in air‐water contact angles occur with increased RFGD exposure time. Plateau values were usually obtained after 5–30 s exposure time, yet no apparent changes in surface topography were noted by scanning electron microscopy. The hydrophilic surfaces produced were stable for up to three months storage time in air.
Surface modification and characterization of some commonly used catheter materials. II. Friction characterization
Authors: Triolo Philip M. , Andrade Joseph D.
Published: December 2004

The effects of the modification of polystyrene (PS), polyethylene (PE), poly(vinyl chloride) (PVC), silicone rubber (SR), and fluorinated ethylene propylene (FEP) copolymer by radio frequency glow discharge in a helium environment were presented in part I. The hydrated polymer surfaces were characterized by XPS, SEM, visual microscopy, and by contact angle measurements. In general, exposure of the polymers to RFGD produced an oxidized hydrophilic surface, yet the roughness of the surface was unaltered by the relatively mild plasma conditions used. In this article, the frictional behavior of oxidized and unoxidized SR, PE, and FEP in distilled water, isotonic saline, and blood plasma environments is examined experimentally. The results are discussed in relation to the properties generally believed to affect frictional phenomena and to the surface properties as determined in part I. Results indicate that RFGD‐treated SR generates less friction than untreated SR when dragged across all untreated and treated polymer surfaces, whether the medium is distilled water or an isotonic saline solution. Friction is consistently lower in a blood plasma medium between all surfaces investigated, most probably because of the presence of adsorbed proteins at the polymer interfaces.
Isobutyl 2‐cyanoacrylate as an osseous adhesive in the repair of osteochondral fractures
Authors: Harper Marion C. , Ralston Michael
Published: December 2004

An in vivo evaluation of isobuty 2‐cyanoacrylate as an osseous adhesive was done in an effort to answer two questions: Used in limited amounts, can this monomer maintain the reduction of an unstable intra‐articular osteochondral fracture while allowing for fracture healing around the sites of adhesive placement? Used in limited amounts, in this monomer toxic to adjacent viable bone? Osteochondral fractures were created in 32 dog knees. In 16 knees, the fracture reduction was secured with three small drops of adhesive placed around the periphery of the fracture surface. In 16 control knees no adhesive was used. Eighty‐one percent of the fractures in the adhesive‐treated group united compared to 56% of the control group. Although the difference in number of fractures that healed in the two groups is not definitely statistically significant and no conclusion was drawn as to effectiveness of the adhesive, osseous healing was noted to proceed around the sites of adhesive placement and the monomer appeared nontoxic to adjacent bone.
Ultrastructural observations of cells at the interface of a biodegradable polymer: Polyglactin 910
Authors: Matlaga Barbara F. , Salthouse Thomas N.
Published: December 2004

Transmission electron microscopy was used to study the ultrastructure of cells at the interface with an implanted biodegradable polymer, Polyglactin 910. Various stages of implantation were observed from 1 day to 63 days, when absorption of the polymer was essentially complete. Events occurring at the interface include initial adhesion of macrophages on the implant surface; phagocytosis of wound debris; and subsequent erosion, invasion, and phagocytosis of the polymer by macrophages and giant cells. A vascular perfusion technique for fixation of the polymer sites implanted in soft tissue is also described.
A novel process for the manufacturing of porous grafts: Process description and product evaluation
Authors: Leidner Jacob , Wong Edward W. C. , MacGregor David C. , Wilson Gregory J.
Published: December 2004

A novel process has been developed for the manufacture of porous vascular grafts from solutions or melts of polymers. It allows the manufacture of grafts with controllable porosity, pore size, and mechanical properties. In this process, the polymer melt or polymer solution is extruded through fine orifices; the fibers are then fibers are then stretched and wound on a rotating mandril. Fiber‐fiber bonding takes place, resulting in the formation of stable porous tubes. The effects of the process variables on the physical properties of the resulting graft have been studied and preliminary in vivo evaluation in dogs has demonstrated graft patency with a thin, stable neointima in both small (4 mm) and large (10 mm) caliber configurations.
Structural evidences of the microfilled composites
Authors: Lambrechts Paul , Vanherle Guido
Published: December 2004

The new composite concept of microfilled composites has certain advantages, such as polishability, permanent smoothness, and high abrasion resistance. In the mouth, however, these new materials are not perfect and they often fail in stress‐bearing restorations. In the present study, the weak links and imperfections of these materials are determined by means of direct and indirect SEM techniques. The chemical adhesion between polymer blocks and polymer matrix is questionable; fractures occur most often at the filler‐matrix interface. In vivo, there is still a certain preferential wear of the resin matrix. In Estic Microfill, rear weak zones with starlike condensations are observed, which could be related to a certain incompatibility of its composing resins and/or to incomplete and inhomogeneous polymerization. In a fractured Isopast restoration, the polymer blocks are clearly revealed, scattered in a three‐dimensional polymerized matrix network.
Analysis of deposits on high water content contact lenses
Authors: Hosaka S. , Ozawa H. , Tanzawa H. , Ishida H. , Yoshimura K. , Momose T. , Magatani H. , Nakajima A.
Published: December 2004

Deposits on soft contact lenses of high water content were investigated morphologically and chemically and compared with those on conventional soft contact lenses of poly(2‐hydroxyethyl methacrylate). The material of the lenses examined in this investigation was the crosslinked copolymer of methyl methacrylate and N‐vinylpyrrolidone with a water content higher than 70%. Morphologically, the deposits on the lenses with high water content were found to have no characteristics distinguishable from those on conventional lenses. By the electron microscopic observation of the cross section of a lens that had become opaque, it was confirmed that the deposit was on the lens surface and that no deposit was within the lens. Some spots on the lenses were recognized as colonies of microorganisms, but the majority of the spots had no involvement by microorganisms. Surface analysis with Fourier transform infrared spectrometer (FT‐IR) confirmed that the main component of the filmy deposit was protein. Protein was detected in most of the deposits. The amino acid compositions of the proteins were found to be close to that of lysozyme. From the elemental analysis of several spots, silicon, aluminum, iron, and some other elements were detected. The structural analysis of some spots by a laser Raman microprobe (MOLE) revealed the existence of lipids. In several cases, the deposits were found to have grown around a defect of the lens surface. A mechanism for the formation of deposits is suggested.
Polymerization kinetics of resin‐based restorative materials
Authors: Cook Wayne D. , Standish Paul M.
Published: December 2004

The kinetics and mechanism of cure of resin‐based restorative materials have been investigated by incorporating into commercial materials additional amounts of inhibitor, initiator, and accelerator. The polymerization was monitored by IR spectroscopy, viscosity measurements, and an oscillating rheometer. The rate of initiation of the polymerization was found to be first order with respect to the initiator and accelerator concentration. The inhibitor was found to be responsible for the induction period during which no polymerization occurred. The duration of this period was proportional to the inhibitor concentration. It was also found that the efficiency of the inhibitor affected the difference between the initial and final set times so that with one particularly effective inhibitor a “snap‐set” behavior could be obtained.
Setting of dental polyelectrolyte cements–viscosity studies of model systems
Authors: Cook Wayne D.
Published: December 2004

In order to gain information on the setting of dental cements, the influence of Ca2+, Mg2+, Zn2+, and Al3+ ions on the viscosity of concentrated solutions of partly neutralized poly(carboxylic acids) has been measured. The increase in viscosity with increasing cation concentration was semi‐quantitatively interpreted in terms of chain growth and branching due to intermolecular bridging of the carboxylate groups by the metal ions. The concentration of cation required to produce gelation was considerably greater than expected and may be due to the wastage of cations by the formation of intramolecular links. The incorporation of tartrate ion into the polyacid solution retarded the reaction between Al3+ and the polyacid and may explain some features of the setting of glass ionomer cements.
Strength testing of dental stone: A comparison of compressive, tensile, transverse, and shear strength tests
Authors: von Fraunhofer J. A. , Spiers R. R.
Published: December 2004

The strength of two dental stones under three standard test regimens and two novel testing modes is reported. It was found under all test regimens that the water/powder ratio significantly affected the strength of the two gypsum products in a similar manner. It was established that the new central fulcrum loading mode gave strength data directly relatable to that determined in the conventional transverse strength test which requires larger test specimens.
Properties of a heparin‐poly(vinyl alcohol) hydrogel coating
Authors: Goosen Mattheus F. A. , Sefton Michael V.
Published: December 2004

Some physical, chemical, and biological characteristics of a heparin‐PVA hydrogel potentially useful as a thromboresistant coating for the preparation of small‐diameter vascular prostheses and blood‐sampling catheters have been determined. The molecular weight between crosslinks in the acetal crosslinked gel was approximately 8000, permitting proteins the size of albumin to enter the interior of the gel. The release rate of heparin from a gel containing 7 mg/g gel was 10−2 μg/g min which was significantly lower than the reported minimum required for thromboresistance of ionically heparinized materials. Nevertheless, in vitro biological activity was observed in both thrombin time and plasma recalcification time assays, which could not be attributed to the release of heparin into the incubated plasma. Correlation of final heparin contents with the amount of terminal amino acid residues in three samples of heparin suggests that the heparin is bound to the PVA in the gel through the amino acid terminus; this provides a plausible explanation for the retention of biological activity by the immobilized heparin.
Creep rupture behavior of polypropylene suture material and its applications as a time‐release mechanism
Authors: Kusy R. P. , Whitely J. Q.
Published: December 2004

The controlled failure of polypropylene (PP) sutures is studied via creep rupture tests. From plots of log time (tB) vs. stress (σ), linear relationships are generated over the failure times of 1–1000 h. Results show that as a function of stress, the time dependence varies with irradiation dose (15, 20, 25, and 50 Mrad), irradiation atmosphere (air and vacuum), suture diameter (7–0, 6–0, 5–0, and 4–0), and test temperature (26 and 37°C). For a given stress, the time to failure is least for the greatest dose in the presence of air and at the highest temperature. When suture loops are wrapped around a small wire sheave, however, failure occurs in the largest suture as much as two decades sooner than the smallest suture studied. Within the limitations stated herein, they are independent of test method, loop diameter, aging, and humidity. Consequently, after irradiation in vacuum and postirradiation heat treatment, the processed material may be stored at room temperature for at least 1 month. Such materials are advocated when the time release of a dental or medical device is required, for example, in the self‐activating cleft palate appliance.
A new approach to the design of internal fixation plates
Authors: Woo Savio L‐Y. , Simon Bruce R. , Akeson Wayne H. , Gomez Mark A. , Seguchi Yasuyuki
Published: December 2004

Mathematical analysis by finite element modeling methods was used in conjunction with laboratory bench experiments in selecting appropriate stiffness parameters for internal fixation plate designs. Bench experiments performed included tests of an idealized plated magnesium tube and of a plated canine femur. Finite element modeling of the plate‐tube and plate‐bone structures was also performed, and the computed results were compared with those obtained experimentally. Three types of internal fixation plates–one “rigid” control plate and two less rigid experimental plates–were examined using both the finite element and experimental models. These plates were further examined by finite element modeling of a plated human femur during single stance loading. In all cases, the “rigid” control plate was found to shield the underlying bone from stress, while both experimental plates were found to have significantly less bone stress shielding. Our findings suggest that an improved plate design should have a low axial stiffness but moderate bending and torsional stiffnesses to facilitate fracture healing and bone remodeling without causing osteopenia.
Mechanical strength of poly(methyl methacrylate) cement‐human bone interfaces
Authors: Kusleika R. , Stupp S. I.
Published: December 2004

A device was constructed to test the inter‐facial strength of PMMA‐based bone cement and human cancellous bone under pure tension. Two types of tissue were used in the investigation: (1) formalin‐fixed vertebral bone as an in vitro model for weak cancellous bone, and (2) freshly removed metatarsal bone. Tissue‐cement joints were allowed to solidify under two different pressures (0.11 and 0.47 MPa), and cement placement time on tissue surfaces was also controlled as a variable. The higher curing pressure only seemed to enhance the strength of interfaces formed with mechanically weak fixed bone but had no significant effect for joints formed with the stronger, freshly extracted tissue. Cement placement time did not have a discernible effect on interfacial strength regardless of the tissue used or the pressure applied during setting. An analysis of fracture morphology by optical microscopy revealed largely cement cohesive failure in some cases and bone or mixed fractures in others. Joints exhibiting mainly cement fracture had the highest interfacial tensile strengths (in the order of 7.5 MPa). Once measured values of tissue porosity were taken into account, the observed joint strength correlated well with cement tensile strength. Based on experimental findings, better stress‐dissipating qualities and higher tensile strength are suggested as two important necessary improvements of bone cements based on poly(methyl methacrylate).
Quantitative histologic evaluation of LTI carbon, carbon‐coated aluminum oxide and uncoated aluminum oxide dental implants
Authors: Cook Stephen D. , Weinstein Allan M. , Klawitter Jerome J. , Kent John N.
Published: December 2004

The response of mandibular bone to identical geometry LTI carbon, carbon‐coated aluminum oxide, and uncoated aluminum oxide blade‐type dental implants in baboons for 2 years was evaluated using histologic, microradiographic, and scanning electron microscopic methods. In addition, a quantitative histologic analysis was performed identifying the type, amount, and distribution of tissue surrounding the dental implant systems. This is the final phase of a study investigating the effect of implant elastic modulus and implant surface chemical composition on the performance of dental implants. Previous studies have utilized clinical and radiographic evaluations, postretrieval mechanical testing, and finite element stress analysis to evaluate the dental implant performance. The results of the histologic study revealed a direct implant‐bone interface with no intervening soft tissue in 16 of the 21 implants (76%). A fibrous tissue interface was observed in 5 of 21 implants (24%). Quantitative histologic results for the implants with a direct implant‐bone interface showed statistically larger crestal cortical plates (p < 0.05) and greater area fraction crestal cancellous bone (p < 0.05) in the LTI carbon implant compared to the carbon‐coated and uncoated aluminum oxide implants. The carbon‐coated and uncoated aluminum oxide implants demonstrated statistically greater area fraction cancellous bone at the inferior region of the implant (p < 0.05) and thinned and reduced crestal cortical plates when compared to the LTI carbon implants. The results indicate that significant stress shielding of the crestal bone had occurred with the rigid carbon‐coated and uncoated aluminum oxide implants when compared to the LTI carbon implants which had a material elastic modulus similar to cortical bone. Based upon the histologic results, it appears that the LTI carbon implants with the direct implant‐bone interface exhibited a greater potential for long‐term successful performance compared to the aluminum oxide substrate implants.
Mass transfer rates in hemodialyzers–An empirical correlation
Authors: Okazaki Masayuki , Yoshida Fumitake
Published: December 2004

From the experimental data on the rates of urea transfer from blood to dialysate in a test hemodialyzer, a practical equation for the effect of the hematocrit on the blood‐phase urea transfer coefficient is proposed. With this equation, the overall mass transfer coefficient that takes into account the properties of the blood can be estimated for the commercially available disposable flat membrane‐type and hollow fiber‐type hemodialyzers from the data for a relatively simple dialysate‐dialysate system.
Some characteristics of collagen‐heparin complex
Authors: Raghunath K. , Biswas G. , Rao K. Panduranga , Joseph K. T. , Chvapil M.
Published: December 2004

In various forms of purified collagen (powder of insoluble collagen from bovine skin, fibers from rat tail tendons, membrane from bovine gut), carboxyl groups were activated by carbodiimide to allow covalent binding of heparin. Collagen powder and collagen fibers from rat tail tendons were also incubated in a haparin solution under the same reaction conditions but without carbodimide present to account for other forms of collagen‐heparin interaction. It was found that the linkage of heparin to collagen formed in the presence of carbodiimide is stable, as heparin was minimally extractable by 0.2M buffers with a pH ranging from 5 to 9. Collagen powder incubated with heparin in the absence of carbodiimide released heparin almost completely into Tris buffer of pH 9.0. As a consequence of covalent binding of heparin to collagen, the collagen fibers became more stable as shown by their significantly reduced swelling capacity and significantly increased shrinkage temperature. Collagen fibers interacted with heparin in the absence of carbodiimide also showed some stabilization of their structure, which was, however, significantly less than with carbodiimide reaction. By two independent methods it was shown that heparin linked to collagen by a stable bond retains its anticoagulant activity. It is concluded that, in the presence of carbodiimide, heparin covalently binds to collagen thus forming an antithrombogenic surface. At the same time, collagen is crosslinked. Incubation of collagen in the solution of heparin without carbodiimide also stabilizes collagen structure, but to a significantly lesser degree. Such a linkage is unstable as heparin dissociates and is readily extractable into 0.2M Tris buffers with pH 7–9.
Dispersion and polar surface free energies of human enamel
Authors: van Pelt A. W. J. , de Jong H. P. , Busscher H. J. , Arends J.
Published: December 2004

In this study, the dispersion (γ) and polar (γ) surface free energies of human enamel with and without an acquired enamel pellicle and of crystalline hydroxyapatite were determined from contact angle measurements. The results show that γ is strongly influenced by the presence of a pellicle; the total surface free energy (γs) is considerably smaller for enamel with an acquired pellicle than for enamel without an acquired pellicle. Enamel without an acquired enamel pellicle shows surface free energies comparable with those of crystalline hydroxyapatite.
Total surface hip arthroplasty in dogs using a fiber metal composite as a fixation method
Authors: Ronningen Helge , Lereim Paul , Galante Jorge , Rostoker William , Turner Thomas , Urban Robert
Published: December 2004

A total hip surface replacement was performed on 13 adult mongrel dogs using a porous fiber metal composite for fixation to bone. Titanium fiber composite rings were molded onto cylindrical acetabular prostheses, and cobalt‐chrome fiber inserts were sintered onto the cast cobalt‐chrome femoral components. The animals were allowed unrestricted walking. Four dogs were sacrificed between 3 and 5 weeks, five at 7 weeks, one with a femoral neck fracture at 12 weeks, and three at 26 weeks. Bone ingrowth was accomplished in 20 of the 26 prosthetic components. This included 12 femoral components and eight acetabular. The main reason for failure appeared to be inadequate primary fixation, secondary to either poor design or technical difficulties experienced during the surgical procedure.
Release of cobalt and nickel from a new total finger joint prosthesis made of vitallium
Authors: Woodman J. L. , Black J. , Nunamaker D. M.
Published: December 2004

An in vivo study of a new total finger joint prosthesis was performed to evaluate a biological ingrowth system of attachment of the device to bone. The prosthesis consisted of two conical ribbed ultrahigh molecular weight polyethylene plugs that were fixed by impaction into the medullary cavity after reaming. A cobalt‐chromium alloy metal stemmed hinge slides inside the plugs with the joint articulation at the end of the stem. The focus of this study was to measure the concentration of cobalt and nickel in the serum, erythrocytes, and periarticular tissue (muscle from the sartorius and vastus medialis) resulting from the implantation of this device in the knee of the cat for periods of up to 1 year. The results indicate significant elevation in serum cobalt concentrations only after 5 months and increased concentrations in serum nickel which, were more pronounced after two months. Column chromatographic separations on cross‐linked Dextran (G‐200) shows a different distribution across the three principal protein peaks for each metal.
Reduction in complement activation from biomaterials by removal of air nuclei from the surface roughness
Authors: Ward C. A. , Koheil A. , Johnson W. R. , Madras P. N.
Published: December 2004

The activation of the rabbit complement system by each of three different synthetic materials is reported. Samples of each type of material were subjected to one of two different priming procedures. One priming procedure was intended to remove the air nuclei from the surface roughness of the materials; the other procedure was just the normal one. It was found that the removal of the air nuclei during priming reduced the complement activation by each of the two materials of lower surface tension, but not by a statistically significant amount for the material of highest surface tension, cellophane. For the denucleated samples of the three materials, the amount of complement activation was found to correlate with the critical surface tension of the materials; if the samples of the materials were normally primed, there was no correlation of the amount of complement activation with the critical surface tension of the material.
In vivo metal‐ion release from porous titanium‐fiber material
Authors: Ducheyne P. , Willems G. , Martens M. , Helsen J.
Published: December 2004

Dense and porous Ti, Ti‐alloy, and stainless steel specimens were implanted in canine trabecular bone. After 6 and 12 months the specimens were retrieved together with bone tissue immediately adjacent. The trace metal content in the tissue samples was determined using neutron activation analysis, differential pulse polarography, graphite furnace atomic‐absorption spectrophotometry, electron microprobe analysis, and laser microprobe analysis. The results are discussed in view of (i) the release of Ti ions, which is larger for porous than for bulk specimens, (ii) the various artifacts arising in electron microprobe (EMP) and laser microprobe mass analysis (LAMMA) determination of compositional gradients of trace metal‐ion content in bone tissue, (iii) the absence of measurable quantities of V in bone tissue, and (iv) the difference in local tissue accumulation between Ti, released from Ti specimens, and Ni, released from stainless steel specimens.
Some factors that influence prolonged interfacial continuity
Authors: Hall C. William , Cox P. A. , McFarland Samuel R. , Ghidoni John J.
Published: December 2004

Bringing a percutaneous implant through the integument with the intentions of leaving it as a functional device for prolonged periods of time has not yet become a reality. If we are ever to achieve prolonged uninfected implants, attention must be directed toward a variety of failure mechanisms. Some of these mechanisms have defined our scrutiny, and our awareness of others are poorly understood. Some of the causes for failure of a percutaneous implant are the forces, either extrinsic or intrinsic, that cause shearing and tearing at the skin‐implant interface. Extrinsic forces are defined as those forces applied either to the skin or the implant by the external environment. Intrinsic forces are those that have to do directly or indirectly with the body's growth and cell maturation, such as the retraction of maturing scar tissue and the surface migration of squamous epithelium. An intact skin‐implant interface is important to attain in order to close the portal which might allow microbial invasion. The integument must remain intact, since a suppurative wound makes the implant's removal mandatory.
Infection of percutaneous devices: Prevention, monitoring, and treatment
Authors: Dasse Kurt A.
Published: December 2004

Infection continues to pose the major obstacle to long‐term percutaneous access. Development of methods to prevent infection or techniques to determine early onset of infection at a time when antibiotic therapy may prove successful would be of enormous value. Our laboratory has been working toward developing and testing a noninvasive semiquantitative swab culture technique (SQ) to monitor percutaneous leads for infection. This technique was found to have a 76% sensitivity having identified 47 of 62 organisms detected by a quantitative tissue culture technique (Q) at the time of system explant. Furthermore, 47 of 61 organisms identified by the SQ technique accurately detected those isolated by the Q techniques. Accordingly, the SQ technique has a 77% specificity. This technique was capable of detecting organisms a median of 14 days prior to overt clinical infection. Prompt initiation of oral antibiotic treatment based on SQ results has doubled system survival compared with untreated systems. Clearly, the SQ technique has proven useful to monitoring percutaneous devices.
Casting properties of Ni–Ti shape memory alloy
Authors: Takahashi Junzo , Okazaki Masayuki , Kimura Hiroshi , Furuta Yasuhiro
Published: December 2004

A Ni–45 wt % Ti (Ni–50 at % Ti) alloy was cast into molds of magnesia and silica investments by use of a dental argon‐arc pressure casting machine with a copper crucible. The castings exhibited shape memory properties. The shape recovery process was sharper in the specimens cast in magnesia investment molds than in those cast in silica (phosphate‐bonded) investment molds. The latter casting had a hard region of the periphery, suggesting that shape recovery process may be affected by reaction of molten metal with silica. Furthermore, the alloy possessed the adequate mechanical properties for consideration as crown‐and‐bridge prostheses.
Free radical decay kinetics in PMMA bone cement
Authors: Turner R. C.
Published: December 2004

Electron‐spin resonance has been used to measure the decay of the concentration of polymerization radicals in polymethyl methacrylate (PMMA) bone cement and the kinetics of the decay determined. Thermal annealing at various temperatures has shown that the logarithm of the concentration of radicals varies linearly with time, but with a nonzero intercept. These results have been analyzed by including both first‐ and second‐order decay processes. The first‐order process has an activation energy of 39 ± 2 kcal/mol and is probably due to a diffusion‐limited termination. The second‐order process has an activation energy of 36 ± 5 kcal/mol and is probably due to bimolecular termination.
The healing of hamster skin ulcers treated with n‐butyl‐2‐cyanoacrylate (Histoacryl blue)
Authors: Galil K. A. , Wright G. Z. , Schofield I. D.
Published: December 2004

This study was undertaken to examine the effectiveness of a commercially available n‐butyl‐2‐cyanoacrylate (Histoacryl blue

Tri‐Hawk International, 1570 Barré, Montréal, H4L 4M6 Quebec.

) as a local treatment for cutaneous ulcers. Two ulcers, approximately 0.5 cm2 each, were made on the backs of 30 hamsters. The right side was covered with a thin film of tissue adhesive, while the left side was left untreated as a control. Animals were sacrificed at various times post‐operatively, the tissue excised, processed, and examined with the light microscope. Results showed that cyanoacrylate decreased the inflammatory exudate early in the experiment, and epithelial migration occurred slightly earlier in experimental tissue. Scab formation was absent in experimental sites until the layer of adhesive was lost. After 2 days, healing was comparable in both experimental and control, and the sites were indistinguishable histologically at day 5.
Convex‐lens‐on‐slide: A simple system for the study of human plasma and blood in narrow spaces
Authors: Adams A. L. , Fischer G. C. , Munoz P. C. , Vroman L.
Published: December 2004

On clot‐promoting surfaces, intact normal blood or plasma deposits fibrinogen and then supplants it with high molecular weight kininogen (HMWK). On glass, plasma layers of less than about 25 μm thick, while still containing enough fibrinogen to coat the surrounding surfaces, lack sufficient HMWK per surface area to remove this fibrinogen deposit. Thus normal intact citrated plasma allowed to enter the space between a glass slide and a convex lens resting belly‐down on the slide will leave a disc of fibrinogen where the thickness of plasma layer was below this “critical height” H. The discs of fibrinogen left by plasma that lacks HMWK pathologically or by activation or dilution, are larger—the required H being greater. The present study shows that plasma dilution (final volume divided by original plasma volume) plotted against H yields a straight line. In preliminary series, the slope of this line increases with the atomic weight of five metals whose oxidized surfaces were used as substrates. In whole blood collected in either heparin or ACD, a circle of platelets adheres to oxidized silicon, anodized tantalum, or glass; this circle is similar in size to the one of fibrinogen left by plasma.
Equilibrium adsorption of human serum albumin and human fibrinogen on hydrophobic and hydrophilic surfaces
Authors: Brynda E. , Cepalova N. A. , Štol M.
Published: December 2004

The adsorption of human serum albumin and human fibrinogen on flat surfaces was quantitatively determined by measuring the decrease in UV absorption in the adsorption solution. The applicability of the method is discussed for hydrophilic and hydrophobic materials. The values of equilibrium adsorption are presented—albumin on polyethylene, and fibrinogen on polyethylene, carbon, poly(2‐hydroxyethyl methacrylate), and cellophane.