bluuebunny/crossref_metadata_2025_split huggingface dataset:
Susceptibility of surgical cobalt‐base alloy to pitting corrosion
Authors: Lucas L. C. , Buchanan R. A. , Lemons J. E. , Griffin C. D. 
Published: December 2004

AbstractThe objective of this investigation was to evaluate thein vitroandin vivosusceptibilities of a surgical cobalt‐chromium‐molybdenum alloy to localized corrosion.In vitrocyclic anodic polarization curves were generated for the cobalt alloy under various surface and electrolyte conditions. Surfaces of the test specimens were examined before and after each polarization experiment.In vivoanalyses involved macroscopic and microscopic examinations of cobalt alloy surfaces on retrieved total hip prostheses. The electrolyte selected for thein vitropolarization study was 0.9% saline at a pH of 7.00 ± 0.05 and temperature of 37 ± 1°C in both aerated and deaerated conditions. Surface conditions for the cobalt alloys included nonpassivated and passivated treatments. Hysteresis behavior was exhibited by the passivated alloy but not by the nonpassivated alloy. According to the protection potential theory, hysteresis behavior indicates a material should be susceptible to pitting corrosion. Therefore, based on polarization curves and theory, the results of the present study indicated the cobalt alloy was susceptible to pitting corrosion when in the passivated condition but not when in the nonpassivated condition. Examination of the surfaces before and after each polarization curve revealed no evidence of pitting corrosion. Also, the examination of nonwear cobalt surfaces of total hip prostheses with implantation times up to 6 years revealed no features uniquely identified as the result of pitting corrosion. Therefore, it was hypothesized that certain conditions inherent in the electrochemical phase of this study had caused the development of hysteresis behavior for the passivated alloy, and this hysteresis behavior should not be associated with pitting corrosion as is normally taken to be the case by application of the protection potential theory. Instead, it is postulated that the hysteresis behavior exhibited by the passivated alloy is due to processes involving a breakdown of the pre‐established passive film followed by a repassivation characteristic of the saline electrolyte.
Stress analysis of porcine bioprosthetic heart valves in vivo
Authors: Thubrikar M. J. , Skinner J. R. , Eppink R. T. , Nolan S. P. 
Published: December 2004

AbstractDuring the normal functioning of aortic porcine bioprosthetic valves, the leaflets undergo complex configurational changes which can produce stresses large enough to damage the leaflets. Stress analyses of these valves in vivo have not been performed before. We investigated the behavior of aortic bioprostheses in vivo in calves by placing radiopaque markers on the valves and observing them under x‐ray. Based upon the behavior of the leaflets, a method of stress analysis is proposed. Membrane stresses were associated with a pressure gradient across the leaflet and bending stresses with a change in the leaflet curvature. Total stresses were obtained by summation of the two stresses. A model of leaflet deformation at its attachment is proposed and the stresses determined. In diastole, the total stresses in the leaflet were tensile. In systole, the total stresses at the leaflet attachment were large and compressive on the aortic surface. Since the leaflet is unable to sustain compressive stresses, it is concluded that large compressive stresses cause structural damage at the leaflet attachment. This may explain the clinical observation that bioprosthetic leaflets detach or calcify in this region.
A study of the interface between a fibrous polyurethane arterial prosthesis and natural tissue
Authors: Beahan P. , Hull D. 
Published: December 2004

AbstractFibrous polyurethane samples were implanted in subcutaneous tissue, muscle, and as an arterial prosthesis for periods up to six months. The interface between the polymer and living tissue was studied using optical, scanning, and transmission electron microscopy. A good correlation was found between the micromorphology of the polymer–tissue interface observed in three experimental methods used. Ingrowth of tissue occurs by cell penetration into the fibrous network of the polymer implant and eventual encapsulation by connective tissue. Full details of the distribution of collagen and the cell components around the individual polymer fibers and the structure of the connective tissue are given.
Electrically enhanced osteogenesis at various metal cathodes
Authors: Spadaro J. A. 
Published: December 2004

AbstractElectode‐induced bone formation was studied at six different metallic cathode materials in the rabbit medullary canal. Direct cathodic currents of 0.02 and 0.2 μA/mm2 were applied for 21 days. Quantitative differences in new bone growth were found. Platinum, cobalt‐chrome (F‐90) and silver had more bone relative to controls at the lower geometric current density, while stainless steel (316L) and titanium cathodes were more effective at the higher current. On average, there was a significant increase (46–48%) in new bone formation at active versus control implants for either current level. No corresponding difference in the number of vascular channels were observed in the 21 day specimens. Metal‐specific differences in bone formation at control implants were also found, with platinum being most stimulatory. These observations are consistent with an interfacial electrochemical mechanism for electrode stimulated osteogenesis, which perhaps acts in concert with purely electrical and mechanical forces.
Parameters affecting the stress distribution around LTI carbon and aluminum oxide dental implants
Authors: Cook S. D. , Weinstein A. M. , Klawitter J. J. 
Published: December 2004

AbstractThree‐dimensional finite element stress analysis was used to study the effects that implant neck geometry and the tissue properties at the implant‐bone interface have on the stress distribution around freestanding blade‐ and post‐type LTI carbon and aluminum oxide dental implants. Implants having neck flares of 13° and 26° were studied. In addition, to simulate fibrous encapsulation of the implant as opposed to a direct bone apposition retention mechanism, a soft tissue interposing layer between implant and bone was also modeled. The results of the study indicate that a reduction in neck flare from 26° to 13° was a positive design change for blade‐ and post‐type LTI carbon implants and blade‐type aluminum oxide implant but not for post‐type aluminum oxide implant. The results of the study indicate the presence of fibrous tissue surrounding the implants may be indicative of a failing system and may be the result of either hypophysiological stress (aluminum oxide implants) or hyperphysiological stress (LTI carbon implants).
A clinical comparison of LTI carbon, alumina, and carbon‐coated alumina blade‐type implants in baboons
Authors: Kent J. N. , Cook S. D. , Weinstein A. M. , Klawitter J. J. 
Published: December 2004

AbstractThe clinical performance of LTI carbon, carbon‐coated aluminum oxide, and uncoated aluminum oxide blade‐type dental implants was studied in baboons. The objective of the study was to determine the effect that implant material elastic modulus and surface composition have on implant performance. Clinical parameters of mobility, sulcus depth, soft tissue characteristics, and radiographic appearance were used in the evaluation. The implants were placed in healed extraction sites in adult female baboons and were used as a distal abutment for a three‐unit fixed gold prosthesis. The restorations were allowed to assume normal occlusal function and were left in situ for a period of two years. The radiographic and sulcus depth measurements appeared inferior for the LTI carbon implants and best for the carbon‐coated aluminum oxide implants. No differences in mobility or soft tissue characteristics were noted for the three implant systems. Two implants both in the same animal—one LTI carbon and one uncoated aluminum oxide—were definite clinical failures. The results of the study indicate that an elastic modulus mismatch between implant and bone is not an a priori cause of implant failure and that the implant surface composition had little apparent effect on the clinical and radiographic performance of these implant materials.
Microleakage of conventional and microfilled composite restorative resins
Authors: Retief D. H. , Rutland J. R. , Jamison H. C. 
Published: December 2004

AbstractMicrofilled composite resins have been introduced in clinical dentistry because of the difficulty in finishing conventional composite resins satisfactorily. Owing to the difference in coefficients of thermal expansion of the two resin systems, the objective of this in vitro study was to evaluate microleakage of a conventional and a microfilled composite resin. Class V cavities with butt cavosurface margins were prepared in the middle third of the facial surfaces of the crowns of 80 noncarious human premolar teeth; they were acid etched within the preparations only. Forty preparations were restored with Concise composite and forty with Silar microfilled resin. Ten teeth from each group were subjected to cyclic temperature changes between 5 and 55°C for 1000, 2500, or 5000 cycles, respectively, and ten teeth from each group were not cycled (controls). After suitable preparation, the teeth were immersed in 45Ca solution for 18 h and contact radiographs were prepared. Microleakage was scored 0–3 at both the cervical and occulusal margins of the restorations. Microleakage was significantly greater at the cervical margins than at the occlusal margins. Differences within occlusal and cervical microleakages among the two resins were not significant.
Physicochemical characterization and in vivo blood tolerability of cast and extruded biomer
Authors: Lelah Michael D. , Lambrecht Linda K. , Young Brian R. , Cooper Stuart L. 
Published: December 2004

AbstractSolution grade and extruded grade Biomer (SB and EB, respectively) are polyurethanes that have been suggested for use in biomedical applications. The bulk materials were examined by elemental analysis, differential scanning calorimetry, thermomechanical testing, and stress‐strain testing. The extruded grade material has a lower soft segment molecular weight (650 g/mol) than the solution grade material (2000 g/mol). As a result of its higher molecular weight, the soft segment phase of SB is semicrystalline in the solid state. The hard segments of the extruded grade material are chain extended with water yielding a lower urea concentration than in the solution grade material in which the hard segments are chain extended with diamines. Chemical structures for the two materials consistent with elemental analysis, urea/urethane ratios and thermal and mechanical data, are proposed. X‐ray photoelectron spectroscopy (ESCA) was used to analyze the surfaces of extruded grade Biomer, solution grade Biomer cast on the inner surface of polyethylene tubing, and extruded grade Biomer dissolved in DMA and similarly cast on polyethylene (CB). Soft segment concentrations were highest on the EB surface and lowest on the SB surface. Soft segment concentrations on the EB surface were higher than on the CB surface, indicating that the method of fabrication affected the composition of the surface layer. The three materials were tested for blood tolerance in a canine femoral arteriovenous shunt configuration. Blood compatibility was correlated with increasing concentration of polyether soft segments on the surface.
Fatigue properties of implant materials in hip prosthesis form: A standardized test
Authors: Ducheyne P. , Wevers M. , De Meester P. 
Published: December 2004

AbstractThe determination of the fatigue properties on small specimens is not accurate. It does not take into account the considerable scatter in fatigue properties which may arise in the implants. Therefore, testing of the properties on the actual implant is needed. The working hypothesis of the present article is that four‐point bending fatigue tests allow determination of the fatigue limit of the femoral component material in total hip prostheses. It eliminates the disadvantages of the previously proposed load on head test because (1) the reproducibility of the stress pattern is easy; (2) the fatigue testing is over the whole critical part of the stem; and (3) the stresses do not change during the test. Testing of a series of hip prostheses shows that (1) the measured fatigue limit is typical for the material tested; (2) the location of the fatigue fractures is over the critical medial third of the stem; and (3) the fractographic aspects correspond to those of in vivo failed prostheses. The four‐point bending procedure is proposed as a standard method.
Fracture of porous polyethylene‐bone composite
Authors: Mayer R. D. , Moyle D. D. , Sauer B. W. 
Published: December 2004

AbstractPorous high‐density polyethylene specimens were implanted in the femurs of mongrel canines. At the end of the residency period (3 or 6 months), the animals were sacrificed and the implants were retrieved. The work‐of‐fracture of the implant specimens was then determined using the technique of Tattersall and Tappin. The work required to fracture a specimen in three‐point bending by controlled crack propagation through a triangular cross section was obtained directly from the load‐deflection curve. The area of the resulting fracture surface was measured by macro‐photographic techniques, and the work‐of‐fracture was calculated as work per unit area. The implants were subsequently sectioned and examined microradiographically to determine the extent of bone ingrowth. Bone specimens adjacent to the implants and porous high‐density polyethylene controls (no ingrowth) were also tested to determine their work‐of‐fracture. The results showed that bone adjacent to the implant specimens had a higher work‐of‐fracture than normal medial, canine femoral bone and was not appreciably different from the composite. The work‐of‐fracture of porous high‐density polyethylene was not significantly increased by an increase in bone infiltration, and this anomalous behavior was attributed to a degradation of the polyethylene during implant residence. Control studies supported this hypothesis.
Biomaterials for drug delivery systems
Authors: Buckles Richard G. 
Published: December 2004

AbstractDrug delivery systems have unusual materials requirements which derive mainly from their therapeutic role: to administer drugs over prolonged periods of time at rates that are independent of patient‐to‐patient variables. The chemical nature of the surfaces of such devices may stimulate biorejection processes which can be enhanced or suppressed by the simultaneous presence of the drug that is being administered. Selection of materials for such systems is further complicated by the need for compatibility with the drug contained within the system. A review of selected drug delivery systems is presented. This leads to a definition of the technologies required to develop successfully such systems as well as to categorize the classes of drug delivery systems available to the therapist. A summary of the applications of drug delivery systems will also be presented. There are five major challenges to the biomaterials scientist: (1) how to minimize the influence on delivery rate of the transient biological response that accompanies implantation of any object; (2) how to select a composition, size, shape, and flexibility that optimizes biocompatibility; (3) how to make an intravascular delivery system that will retain long‐term functionality; (4) how to make a percutaneous lead for those delivery systems that cannot be implanted but which must retain functionality for extended periods; and (5) how to make biosensors of adequate compatibility and stability to use with the ultimate drug delivery system—a system that operates with feedback control.
In vivo biocompatibility studies. I. The cage implant system and a biodegradable hydrogel
Authors: Marchant Roger , Hiltner Anne , Hamlin Clive , Rabinovitch Albert , Slobodkin Rimma , Anderson James M. 
Published: December 2004

AbstractA cage implant system has been utilized to examine the in vivo biocompatibility of a biodegradable hydrogel, poly(2‐hydroxy‐ethyl‐L‐glutamine) (PHEG). This system permits the quantitative determination of the components of the inflammatory exudate which surrounds the implanted polymer within the cage system. This system permits the serial examination of exudate components without sacrificing the animal. In addition, this system allows the subsequent removal of the polymer for surface and mechanical studies. Following implantation of the biodegradable hydrogel, quantitative and differential white cell counts of the exudates were determined over a 21‐day period. In addition, concomitant extracellular enzyme analyses for alkaline phosphatase, acid phosphatase, prostatic acid phosphatase, leucine aminopeptidase, and Cathepsin B1 were determined. Corresponding control samples from exudates of the cage implant without the polymer were also determined. The two‐tailed Student's t‐test for unpaired samples was used to statistically compare the control and implanted polymer values for these respective analyses at the various time periods. A comparison of the cellular response for the control system and the PHEG system did not show statistically significant differences during the first 7 days following implantation. The acute inflammatory response, polymorphonuclear leukocyte predominant, was followed by a mild chronic inflammatory response, macrophage and lymphocyte predominant, and during this time period, 8–14 days, macrophages were present in significantly larger numbers for the PHEG system when compared to the control values. Enzymic analysis of the exudates revealed statistically significant differences between control and PHEG values at time intervals where no differences were noted in cell density or population. These results are discussed in terms of cell‐polymer interactions leading to cellular activation and enhanced enzyme exocytosis by the inflammatory cells. Stress‐strain measurements on implanted PHEG samples showed that significant in vivo degradation had occurred during the acute inflammatory phase of the response, i.e., the first 7 days.
Preparation of etched tantalum semimicro capacitor stimulation electrodes
Authors: Robblee L. S. , Kelliher E. M. , Langmuir M. E. , Vartanian H. , McHardy J. 
Published: December 2004

AbstractThe ideal electrode for stimulation of the nervous system is one that will inject charge by purely capacitive processes. One approach is to exploit the type of metal‐oxide combination used in electrolytic capacitors, e.g., Ta/Ta2O5. For this purpose, fine tantalum wire (0.25 mm diam) was etched electrolytically at constant current in a methanol solution of NH4Br containing 1.5 wt % H2O. Electrolytic etching produced a conical tip with a length of ca. 0.5 mm and shaft diameters ranging from 0.10 to 0.16 mm. The etched electrodes were anodized to 10 V (vs. SCE) in 0.1 vol % H3PO4. The capacitance values normalized to geometric area of etched electrodes ranged from 0.13 to 0.33 μF mm−2. Comparison of these values to the capacitance of “smooth” tantalum anodized to 10 V (0.011 μF mm−2) indicated that the degree of surface enhancement, or etch ratio, was 12–30. The surface roughness was confirmed by scanning electron microscopy studies which revealed an intricate array of irregularly shaped surface projections about 1–2 μm wide. The etched electrodes were capable of delivering 0.06–0.1 μC of charge with 0.1 ms pulses at a pulse repetition rate of 400 Hz when operated at 50% of the anodization voltage. This quantity of charge corresponded to volumetric charge densities of 20–30 μC mm−3 and area charge densities of 0.55–0.88 μC mm−2. Charge storage was proportionately higher at higher fractional values of the formation voltage. Leakage currents at 5 V were ca. 2 nA. Neither long‐term passive storage (1500 h) nor extended pulsing time (18 h) had a deleterious effect on electrode performance. The trend in electrical stimulation work is toward smaller electrodes. The procedures developed in this study should be particularly well‐suited to the fabrication of even smaller electrodes because of the favorable electrical and geometric characteristics of the etched surface.
Endothelial cell labeling with indium‐111‐oxine as a marker of cell attachment to bioprosthetic surfaces
Authors: Sharefkin John B. , Lather Carole , Smith Michael , Rich Norman M. 
Published: December 2004

AbstractCanine vascular endothelium labeled with indium‐111‐oxine was used as a marker of cell attachment to vascular prosthetic surfaces with complex textures. Primarily cultured and freshly harvested endothelial cells both took up the label rapidly. An average of 72% of a 32 μCi labeling dose was taken up by 1.5 × 106 cells in 10 min in serum‐free medium. Over 95% of freshly labeled cells were viable by trypan blue tests and only 5% of the label was released after 1 h incubations at 37°C. Labeled and unlabeled cells had similar rates of attachment to plastic dishes. Scanning electron microscopic studies showed that labeled cells retained their ability to spread on tissue culture dishes even at low (1%) serum levels. Labeled endothelial cells seeded onto Dacron or expanded polytetrafluoroethylene vascular prostheses by methods used in current surgical models could be identified by autoradiography of microscopic sections of the prostheses, and the efficiency of cell attachment to the prosthesis could be measured by gamma counting. Indium‐111 labeling affords a simple and rapid way to measure initial cell attachment to, and distribution on, vascular prosthetic materials. The method could also allow measurement of early cell loss from a flow surface in vivo by using external gamma imaging.
In vivo and in vitro studies of the stress‐corrosion cracking behavior of surgical implant alloys
Authors: Bundy K. J. , Marek M. , Hochman R. F. 
Published: December 2004

AbstractBehavior of implant alloys exposed simultaneously to tensile stresses and corrosion environments has been examined. In the in vivo studies, a stainless steel and a titanium alloy exhibited cracklike freatures when loaded to the yield stress σy and implanted for 16 weeks. A cobalt‐chromium alloy stressed beyond σy exhibited them in plastically deformed areas. A cobalt‐chromium‐nickel‐molybdenum alloy appeared to be immune. In vitro samples loaded to various stress levels were immersed in Ringer's solution at 37°C. Half of them were subjected to applied anodic potentials; the remaining control group was not. The applied potentials were dc potentials of magnitude similar to those generated by bioelectric effects. No attempt was made to duplicate time dependence or wave forms. Cracklike features were observed in the stainless steel and in the titanium alloy loaded to or beyond σy and polarized for 38 weeks. None were observed below σy. For the controls, no cracklike features were observed at any stress level after 53 1/2 weeks. Polarization measurements and potential versus time measurements were performed to study possible mechanisms for crack propagation. These investigations suggest that the in vivo corrosion environment is more severe than a 37°C Ringer's solution because of the influence of both bioelectric effects and organic constituents. The implications of these studies for the performance of prosthetic devices is discussed.