bluuebunny/crossref_metadata_2025_split huggingface dataset:
An in vivo method for the evaluation of catheter thrombogenicity
Authors: Solomon Donald D. , Arnold William L. , Martin Neil D. , Lentz David J. 
Published: December 2004

AbstractA new method has been developed to evaluate the relative thrombogenicity of vascular catheters. The technique provides a means to quantitatively differentiate between catheters made from different polymeric materials. Autologous In‐111 labeled platelets were infused into a dog model and catheters were then inserted into the external jugular vein of the dog. The neck region was scanned using gamma camera imaging. Comparisons between catheter materials were made using computer generated uptake slopes during the first 40 min of the scan. In addition to scintigraphy, visual assessment of thrombus deposition, thrombus weight, platelet deposition, and scanning electron microscopy were used to validate the technique. Poly(vinyl chloride), polyurethane, heparinized polyurethane, and silicone catheter materials were tested. It was found that heparinized polyurethane was the least thrombogenic of all materials evaluated.
Uptake of zinc and fluoride by several dentin components
Authors: Meryon S. D. , Jakeman K. J. 
Published: December 2004

AbstractThe uptake of zinc released from ZOE and Dispersalloy, and fluoride from ChemFil by different components of dentin was studied in vitro. These materials were placed over a 500‐m̈m layer of the dentin fraction in a simulated cavity, and the zinc and fluoride levels in the fraction and underlying solution determined after 7 days. Parallel studies were also carried out in which these components, alone in simulated cavities, were placed over solutions containing different concentrations of zinc and fluoride and the uptake determined after 24 h. Zinc uptake was considerably greater by the inorganic than the organic fractions used in this study. Uptake from ZOE was disproportionately higher than from Dispersalloy presumably reflecting the fact that the zinc in ZOE is more loosely bound. In addition the high zinc levels in collagen beneath this material may be attributed to the binding of the eugenol component. In contrast fluoride uptake was generally highest by the organic fractions with relatively low uptake by the inorganic fractions which is in contrast to previous studies. Uptake of zinc and fluoride from solution by these fractions was consistent with these findings. Thus zinc is more strongly bound by the inorganic and fluoride by the organic fractions of dentin.
Protein adsorption to polymer particles: Role of surface properties
Authors: Absolom D. R. , Zingg W. , Neumann A. W. 
Published: December 2004

AbstractAdsorption isotherms of four plasma proteins (fibrinogen, IgG, human serum albumin, and bovine serum albumin) using four different types of small particles as substrates (siliconized glass, Teflon, polyvinylchloride, and Nylon‐6, 6) are reported. The suspending liquid medium was phosphate‐buffered saline, with a surface tension higher than that of any of the proteins. In keeping with the thermodynamic expectations for these systems, protein adsorption decreases for all solids in sequence from fibrinogen (the most hydrophobic) to IgG, human serum albumin, and bovine serum albumin (the most hydrophilic). Furthermore, the extent of protein adsorption also decreases from the low surface tension (hydrophobic) to the higher surface tension solids, again as expected on thermodynamic grounds. There is one minor yet interesting exception to the thermodynamic pattern: In spite of the slightly lower surface tension of siliconized glass, the extent of protein adsorption is slightly higher to Teflon than to siliconized glass. This result is attributed to the theoretically well known phenomenon of “screening”.
Angular dependent ESCA and infrared studies of segmented polyurethanes
Authors: Grobe George L. , Gardella Joseph A. , Hopson Wendy L. , McKenna William P. , Eyring Edward M. 
Published: December 2004

AbstractThe understanding of surface bonding and composition of complex polymer mixtures used for biomedical implant materials can be accomplished by a combination of techniques. In this study, vibrational spectroscopic probes of bulk and surface bonding and composition are combined with measurements with angular dependent X‐Ray Photoelectron Spectroscopy (XPS or ESCA). These data provide a detailed description in the surface composition of Biomer and Avcothane, commercially available biomedical grade polymers and model systems polydimethylsiloxane (DMS) and Avcomat, all of which have been cast as smooth films from solution. Impurities are observed segregated in the near surface region sampled by ESCA which are not observed in the surface infrared results. Both Attenuated Total Reflectance (ATR) and Photoacoustic (PA) sampling are utilized, ATR to provide a depth profile and demonstrate the higher surface sensitivity of PA sampling. The combined results describe the depth of segregation of DMS blocks in Avcothane, the presence of DMS within the topmost 20 Å in Biomer, and similar impurities in the model polymers. These results point out the need for multitechnique approach and the control of sample preparation and morphology in understanding complex polymer surfaces.
Characterization of UHMWPE hip cups run on joint simulators
Authors: Eyerer P. , Kurth M. , McKellup H. A. , Mittlmeier T. 
Published: December 2004

AbstractThe density and crystallinity of UHMWPE‐hip cups were investigated as a function of thickness from the inner stressed surface to the unstressed outer surface. The effects of mechanical strain and chemical reactions during simulation tests, and damage of the material due to pretreatments and storage, resulted in changes of the structure, as indicated by variations in the crystallinity. Independent of either the batch of UHMWPE supplied or the manufacturer and the type of simulator used, the individual samplesets showed a similar characteristic curve of density versus wall thickness. Infrared spectroscopic evaluations indicated the presence of oxidative degradation, and answers the question as to which areas of the polymers are changed by aging and which compounds are newly formed. The characteristic carbonyl groups were also determined. The concentration trend of carbonyl groups versus wall thickness obtained agrees surprisingly well with the locally determined density and crystallinity trend. As these compounds are formed by reactions which produce stable oxidative degradation products and also crosslinking, we have determined the degree of crosslinking. The determination of the soluble constituents after extraction showed lower degree of crosslinking on the surface than in the middle of the material. Hence it follows that on the surfaces oxidative chain scission is prevailing, whereas in the interior mainly crosslinking is developed. These results indicate that the samples used for the simulation tests had distinct differences in characteristics. Generally the results show that wear tests in joint simulators lead to property changes in UHMWPE which differ considerably from test results previously obtained on retrieved hip cups.
Physicochemical characterization of a hydrophilic microporous polyurethane vascular graft
Authors: Martz Hugues , Beaudoin Gilles , Paynter Royston , King Martin , Marceau Daniel , Guidoin Robert 
Published: December 2004

AbstractThere is still a need for a viable small‐diameter synthetic vascular graft. The expanded PTEE device appears to be the best presently available, but is still inferior to the autologous saphenous vein. Recently, a novel microporous, small‐diameter vascular graft fabricated from Mitrathane, a polyether urethane urea (PEUU), has been developed. In this article, we report the findings of an in vitro evaluation of the morphological, mechanical, and chemical properties of this new device. The results are compared with those of established vascular prostheses made from alternative materials including expanded PTFE and bovine heterograft, and with natural blood vessels. The PEUU graft displays good mechanical properties in spite of the presence of some structural defects or anomalies. In particular it compares favorably to the expanded PTFE device by providing both superior radial compliance and improved suture tearing strength.
Effects of periosteal activation agent on bone repair and ingrowth
Authors: Alberts L. Russell 
Published: December 2004

AbstractA substance that activates the resting periosteum (PAA) was applied to the periosteal surface in two different healing models using the femurs of 2‐kg male rabbits. The activation agent was applied to the periosteal surface over the sites of circular defects drilled through the lateral cortex in one model and over the sites of porous polyethylene implants placed in the lateral cortex and the medullary canal in the other model. Results failed to show that the agent either enhanced bone ingrowth into the porous implants or accelerated bony filling of the circular defects. However, there was indication of enhanced mineralization and periosteal callus formation as early as 24 h after application.
Fluorescence lifetime measurements using total internal reflection fluorimetry: Evidence for a conformational change in albumin adsorbed to quartz
Authors: Rainbow Mark R. , Atherton Stephen , Eberhart Robert C. 
Published: December 2004

AbstractWe have modified the total internal reflectance fluorimetry (TIRF) method to determine, indirectly, quantum fluorescence yield and thus infer structural changes of adsorbed plasma proteins. We employed a frequency multiplied Nd: YAG pulse laser to excite tryptophan residues of bovine serum albumin (BSA), measuring the resulting fluorescence lifetimes. BSA adsorbed on quartz was investigated at normal pH and under acidic (pH 3.8) conditions at which albumin shape change has been established in bulk solution. Albumin adsorbed at pH 7.2 has a slightly lower lifetime than the bulk solution value, reflecting a population of both native and isomerized forms. Gently washing the adsorbate surface significantly reduces fluorescence lifetime, suggesting retention of more tenacious, conformationally altered molecules. Vigorous washing further reduces fluorescence lifetimes to values close to those obtained in bulk under acidic conditions. Similar alterations in fluorescence lifetimes were observed for heat‐denatured albumin. These results support the hypothesis that adsorbed albumin exists in the form of a two‐layer deposit, each with a possibly different structure. A loosely held layer, consisting of BSA microaggregates and including partially unfolded molecules, exists on the undisturbed surface and is partially removed by gentle washing. Vigorous washing removes all but the most tightly held protein, which exists in a possibly further unfolded configuration. The decrease in fluorescence lifetime of adsorbed BSA implies a corresponding change in quantum yield. A change in quantum yield of BSA tryptophan fluorophors implies that measuring adsorbed protein concentration by intrinsic fluorescence is unreliable.
Reversible morphological and functional abnormalities of RINm5F cells cultured on polystyrene sulfonate beads
Authors: Aubert N. , Reach G. , Serne H. , Jozefowicz M. 
Published: December 2004

AbstractRINm5F cells (an insulin‐secreting cell line) were cultured on PSSO3Na microbeads under static conditions. The cells grown on plastic wells or slower, depending on the intial cell concentration. With both supports, it was similarly influenced by the fetal calf serum concentration in the culture medium, and protein content per cell was identical. However, no spreading was observed when cells were cultured on microbeads. RINm5F cells cultured on plastic wells responded to arginine + theophylline and to leucine + theophylline by a significant increase in insulin secretion. By contrast, in cells cultured on PSSO3Na microbeads, the increase in this secretion was only slight or nil. All these abnormalities were reversible. Thus, when cells cultured on microbeads were detached and seeded on plastic wells, normal spreading and insulin secretion were observed. Lastly, PSSO3Na beads had an acute suppressive effect on insulin secretion by cells cultured on plastic wells. This study provides an example of cell‐biomaterial interaction in which cell growth is possible, but with altered cell function.
Slow crack propagation in composite restorative materials
Authors: Montes‐G. G. Marcos , Draughn Robert A. 
Published: December 2004

AbstractThe double‐torsion test technique was used to study slow crack propagation in a set of dental composite resins including two glass‐filled and two microfilled materials. The microstructure within each pair was the same but one of the resins was self‐curved and the other photocured. The fracture behavior was dependent on the filler concentration and the presence of absorbed water. Wet materials fractured by slow crack growth in the range of crack velocity studied (10−7 to 10−3 m/s), and the microfilled composites, which contain a lower concentration of inorganic filler, had lower stress intensity factors (K1c) than the glass‐filled composites tested. Dry specimens of the microfilled materials and the selfcured, glass‐filled composite also showed unstable, stick‐slip fracture behavior indicative of a crack blunting mechanism which leads to an elevation of the stress intensity factor for crack initiation over K1c for stable crack growth. The plasticizing effect of water increased the viscoelastic response of the materials measured by the slope of curves of slow crack growth. Analysis of fracture surfaces showed that cracks propagated at low velocities (10−7 to 10−5 m/s) by the apparent failure of the filler/matrix interfacial bond, and absorbed water affected the strength or fracture resistance of the interface. At high crack velocities the properties of the composite depend on the properties of the polymeric matrix, the filler, and the filler volume fraction, but at low velocities the interface is the controlling factor in the durability of these composites exposed to an aqueous environment.
Theoretical and experimental analysis of cellular adhesion to polymer surfaces
Authors: Strong A. B. , Stubley G. D. , Chang G. , Absolom D. R. 
Published: December 2004

AbstractAn exact discrete numerical solution to the Grabowski model for predicting cell adhesion to polymer surfaces is discussed. The solution technique allows the possibility of taking into account cell–cell interactions within the flow situation and the multistep process involved in thrombus formation. The proposed solution also allows modification of the wall reaction rate model into a two specie reaction rate which distinguishes between the kinetics of contact adhesion and irreversible adhesion. The solution allows determination of effective diffusivity (De) and surface reaction rate (k) constants. Use of the model to examine available experimental data results in the following conclusions: (1) static or dynamic cell adhesion cannot be considered to be diffusion limited; (2) for flow conditions De is a monotonically increasing function of shear rate; (3) under static, i. e., zero flow conditions, De appears to be markedly larger than for flow conditions.
A rapid in vitro test of the in vivo healing potential of vascular prostheses
Authors: Mathisen Sven R. , Coan Daniel E. , Sauvage Lester R. , Wu Hong‐De , Wechezak Arlene R. , Goff Steven G. 
Published: December 2004

AbstractAn in vitro method for comparing the penetration of bovine fibroblasts seeded on the external surface of porous vascular prostheses was devised. The effects of water porosity reduction and differing manufacturing constructions (warp‐knit Dacron, woven Dacron and polytetrafluoroethylene) on the ability of the bovine fibroblasts to penetrate transmurally was investigated. Of the warp‐knit external‐veloured Dacron prostheses, the highest porosity 140‐denier prototype had the highest luminal surface cell count and the lowest porosty 280‐denier prototype the lowest luminal surface cell count. The intermediate prototypes had values between these two extremes. The woven Dacron prostheses which were of even lower porosity but with a much thinner wall, had cell counts midway between the 140‐denier and the 280‐denier prototypes. The microporous polytetrafluoroethylene prostheses did not allow fibroblast penetration despite adherence of cells to the outer surface. These findings agree with in vivo healing studies of the same materials in the descending thoracic aorta of the dog, demonstrating that this rapid in vitro assay method can help predict the healing potential of a vascular prosthesis.
Adsorption of N‐phenylglycine on hydroxyapatite: Role in the bonding procedure of a restorative resin to dentin
Authors: Misra D. N. , Johnston A. D. 
Published: December 2004

AbstractThe adsorption of N‐phenylglycine (NPG) onto synthetic hydroxyapatite from ethanol solutions was studied to elucidate the role of surface‐active moieties in determining the character of adsorption, and to explore the role of NPG in a bonding procedure of restorative resin to dentin. The adsorption isotherm of N‐phenylglycine is reversible (and Langmuirian) from ethanol (99.8%). At maximum adsorption the phenyl rings of the adsorbed molecules lie flat on the surface and the carboxylate oxygens and amino nitrogens are anchored to the surface. The N‐phenylglycine serves as an amine accelerator since the peroxide containing monomer polymerizes with the adsorbate‐covered apatite. The diametral tensile strength of this composite is approximately equal to the composite filled with untreated apatite. The role of various factors contributing to adhesive strength in the bonding procedure is also discussed.
Plasma sprayed coatings of hydroxylapatite
Authors: De Groot K. , Geesink R. , Klein C. P. A. T. , Serekian P. 
Published: December 2004

AbstractThe technique of plasma spraying has been applied to deposite a thin, dense layer of hydroxylapatite onto a titanium substrate. Bond strength of such apatite coatings with the substrate have been measured, as well as the (absence of) influence of the coating process on fatigue properties of the substrate. Animal studies showed similar histological reactions to apatite coatings as to (well documented) apatite bulk materials.
The effect of surface macrotexture and hydroxylapatite coating on the mechanical strengths and histologic profiles of titanium implant materials
Authors: Thomas Kevin A. , Kay John F. , Cook Stephen D. , Jarcho Michael 
Published: December 2004

AbstractA mechanical and histological evaluation of uncoated and hydroxylapatite‐coated titanium implant materials was performed. Cylindrical implants of uncoated commercially pure (CP) titanium and hydroxyl‐apatite‐coated Ti‐6Al‐4V alloy were studied using a transcortical model, with implants evaluated after periods of 3,5,10, and 32 weeks. All implants had a surface macrotexture consisting of a series of semicircular annular grooves, approximately 750 m̈m in maximum depth. The attachment characteristics of interface shear stiffness and interface shear strength were determined by mechanical push‐out testing. Nondecalcified histologic and microradiographic techniques, with implants in situ, were used to evaluate the response to the implant materials and the presence of the surface macrotexture. Mechanical testing results indicated that the hydroxyl‐apatite‐coated implants exhibited significantly greater values of maximum interface shear strength than the uncoated implants after all time periods. Interface shear stiffness was also significantly greater at all time periods for the hydroxylapatite‐coated implants as compared to the uncoated implants. Histological evaluation after 3 weeks revealed an osteoid layer covering on all areas coated with the hydroxylapatite material; mineralization of this layer appeared to be complete after 10 weeks. In all cases, longer‐term implants demonstrated mineralization of interface bone directly onto the hydroxylapatite coating, and in no case was a fibrous layer observed between the hydroxylapatite coating and the interface bone. Sections from the uncoated CP titanium implants revealed a thin fibrous layer present in nearly all areas. Only isolated regions of direct bone‐implant apposition were observed for the uncoated implants. The presence of this fibrous tissue layer, however, apparently did not adversely affect the development of considerable attachment strength. The results from this study indicate that the hydroxylapatite coating can significantly increase the attachment strength of implants which rely upon bone apposition for fixation. In addition, the hydroxylapatite coating provides an osteophilic surface for bone deposition, and allows for a more rapid development of implant‐bone attachment.
A comparative scanning electron microscopic study on degradation of absorbable ligating clips in vivo and in vitro
Authors: Chegini N. , Hay D. L. , von Fraunhofer J. A. , Masterson B. J. 
Published: December 2004

AbstractUsing scanning electron microscopy, the degradation characteristics of two absorbable ligating clips, Absolok (polydioxanone) and Lactomer (poly‐L‐lactide‐co‐30%‐glycolide) have been studied under in vivo and in vitro conditions. The rate of Absolok clip degradation was significantly greater than that of Lactomer clip degradation both in vitro and in vivo. The rate of degradation of Lactomer clips significantly increased and they showed a greater change in proportion of breakdown in vivo than in vitro compared to Absolok clips. The Absolok clip breakdown began with the formation of surface undulations which later developed into fissures. The undulations appeared on the clip surface as early as 7 days and by 2 weeks developed into fissures. The initial appearance of the fissures was at the edge of the clips particularly at the mating surface. The thickness of layers forming the fissures gradually decreased and by 15 weeks the layers appeared as very thin sheets of materials. The high energy areas (locking and molding points) were more resistant to breakown and the remains of the clips were still present 25 weeks after initiation of the experiments. The Lactomer clips showed very little sign of degradation in vitro even after 10 weeks of incubation. However, in the in vivo experiments undulations formed on the clip surface as early as 2 weeks postimplantation. These clips also showed fissures similar to those observed on Absolok clips.
Normal wound healing compared to healing within porous Dacron implants
Authors: Schreuders Paul D. , Salthouse Thomas N. , von Recum Andreas F. 
Published: December 2004

AbstractThis study examined the hypothesis that healing within porous implants differs from that in normal connective tissue. Special attention was given to extracellular components including collagen, reticular fibers, and ground substance, and to enzymes associated with activated macrophages. Using Dacron velour and the rabbit as host, the healing of normal connective tissue and that of the tissue/implant interface were histologically compared 10 and 28 days postimplantation. The results exhibited significant differences between connective tissue healing, implant capsule formation, and granulation tissue generation. The healing of connective tissue and implant capsule formation were essentially complete at 28 days. However, tissue inside the implant was qualitatively different and did not significantly change between 10 and 28 days. It was characterized by macrophages and giant cells, a predominantly acid mucopolysaccharide ground substance, and qualitatively fewer and less well defined collagen and reticular fibers were observed than in normal wound healing. Thus we conclude that the connective tissue inside Dacron velour does not resemble normal connective tissue after 10 or 28 days of healing. Furthermore, the collagen never fully matures into orderly bundles, a phenomenon which may be related to an altered mucopolysaccharide composition and a diminished reticular network. The lysosomal enzymatic activity of the macrophages and perhaps the giant cells at the tissue/implant interface may be linked to these differences.