bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical characterization of commercially made carbon‐fiber‐reinforced polymethylmethacrylate
Authors: Saha S. , Pal S.
Published: December 2004

Acrylic bone cement is significantly weaker and of lower modulus of elasticity than compact bone. It is also weaker in tension than in compression. This limits its use in orthopedics to areas where tensile stresses are minimum. Many authors have shown that addition of small percentages of fiber reinforcement by hand mixing improved the mechanical properties significantly but with variable results. In this investigation we have examined the mechanical properties of machine‐mixed, commercially available carbon‐fiber‐reinforced bone cement. Appropriate samples of normal low‐viscosity cement and carbon‐fiber‐reinforced cement were prepared and tested mechanically. Carbon fiber increased the tensile strength and modulus by 30% and 35.8% respectively. The compression strength and modulus, however, increased by only 10.7%. Similarly, bending and shear strengths improved by 29.5% and 18.5%, respectively. Diametral compression strength, which is an indirect measure of tensile strength, however, showed only 6.2% improvement. The maximum temperature rise during polymerization was also reduced significantly by the fiber reinforcement.
Effect of pore size of porous bead carriers immobilizing antibody on IgE adsorption
Authors: Sato Hiroshi , Kidaka Teruhisa , Hori Masatake
Published: December 2004

Immunoglobulin E (IgE) adsorption was studied using antihuman IgE antibody immobilized on alkylamine glass carriers with different pore sizes (Controlled Pore Glass [CPG]®) to determine the effect of pore size on IgE adsorption in therapeutic immuno‐adsorbents. With a series of CPGs whose pore sizes were in the range of 170 to 1400 Å, CPGs possessing pore sizes larger than 500 Å had higher IgE adsorption. A CPG (500‐Å pore size) with the spacer arm 20 Å long did not give better IgE removal than CPG without the spacer arm, since the spacer prevented the immobilization of a sufficient amount of the antibody on the carrier because of steric hindrance. However, the antibodies, once immobilized on CPG with the spacer arm, bound the same amount of IgE molecules (antigens) as those immobilized on CPG without the spacer arm.
Crystallinity and solubility behavior of iron‐containing fluoridated hydroxyapatites
Authors: Okazaki Masayuki , Takahashi Junzo , Kimura Hiroshi
Published: December 2004

Iron‐containing fluoridated hydroxyapatites with various fluoride contents were synthesized at 80°C and pH 7.4 using FeCl2 · nH2O as a source of iron. The Fe2+ uptake of fluoridated apatites was independent of fluoride concentration in the solution. a‐Axis dimensions of Fe‐containing apatites decreased with the degree of fluoridation in addition to the decrease related to the substitution of Fe2+ ions. All Fe‐containing fluoridated apatites were less well crystallized than Fe‐free fluoridated apatites previously reported, although with increasing degree of fluoridation, the crystallinity behavior of the former apatites appeared analogous to that of the latter apatites. In contrast to this inhibited crystallinity behavior, the apparent solubility of Fe‐containing fluoridated apatites decreased more than that of Fe‐free fluoridated apatites at low fluoride content.
Antithrombogenic heparinized polyacrylonitrile copolymer
Authors: Miyama Hajime , Fujii Nobuyuki , Kuwano Atsushi , Nagaoka Syoji , Mori Yuichi , Noishiki Yasuharu
Published: December 2004

A new antithrombogenic polymer was synthesized by the photograft‐copolymerization of methoxypolyethyleneglycol methacrylate and dimethylaminoethyl methacrylate to polyacrylonitrile containing bromine atoms, and by quaternizing and heparinizing the graft‐copolymer.

Hydrophilicity and heparin content of the polymer could be controlled by changing the feed ratio of the acrylates to be grafted. The heparinized polymer showed excellent mechanical and antithrombogenic properties.
The biological performance of calcium phosphate ceramics in an infected implantation site: II. Biological evaluation of hydroxyapatite during short‐term infection
Authors: Van Blitterswijk C. A. , Bakker D. , Grote J. J. , Daems W. Th.
Published: December 2004

Macroporous hydroxyapatite was implanted submucosally in the rat middle ear and studied after intratympanic injection of a Staphylococcus aureus suspension. The middle ear infection was induced 1 week after the implantation, and the effects of infection on the middle ear and the implant material were evaluated after 1, 3, 7, and 14 days by light and electron microscopy. The findings in the infected middle ear with an implant corresponded well with those described for the infected middle ear cavity without an implant. The reactions of the tissue over the implant were similar to those of the original mucosa of the middle ear.

Bone was deposited on the implant and in its pores in relatively large quantities. Biodegradation, due at least partially to phagocytic activity of macrophages and multinucleated cells, was more prominent than previously found. This higher degree of biodegradation may be attributed to the use of the mucosal implantation technique, because this was the only point of divergence with respect to material or methods from earlier work reported by our group.

The present results, together with those published earlier, suggest that this material has promising features for use as a bone substitute in reconstructive middle ear surgery. Definitive conclusions on biological performance and biofunctionality will, however, have to await long term clinical trials.
Adsorption of plasma proteins to the derivatives of polyetherurethaneurea carrying tertiary amino groups in the side chains
Authors: Ito Yoshihiro , Sisido Masahiko , Imanishi Yukio
Published: December 2004

Polyetherurethaneureas carrying tertiary amino groups in the side chains were synthesized, quaternized, and heparinized. The adsorption of plasma proteins to the polyurethane derivatives was investigated using Fourier‐transform infrared, surface fluorescence, ultraviolet, and circular dichroism spectroscopy. Bovine γ‐globulin and bovine plasma fibrinogen were easily adsorbed to hydrophobic polyurethanes and denatured. It was found that the β structure was generated during the irreversible conformational change of the proteins on adsorption to hydrophobic polyurethane materials. On the other hand, bovine serum albumin was easily adsorbed to hydrophilic quaternized and heparinized polyurethanes without a serious conformational change. The conclusion was drawn that a polymer material that selectively adsorbs bovine serum albumin in a native state could be antithrombogenic.
Identification of proteins adsorbed from human plasma to glass bead columns: Plasmin‐induced degradation of adsorbed fibrinogen
Authors: Brash J. L. , Thibodeau J. A.
Published: December 2004

In a bead column experiment, attempts have been made to identify the proteins adsorbed from plasma onto a glass surface. Proteins adsorbed after a 3‐h contact time were eluted sequentially by 1 M tris buffer and SDS. Polyacrylamide gel electrophoresis of eluted proteins showed a multiplicity of components, and not all of these could be identified. Positive identifications were made by immunodiffusion against specific antibodies, band positions on electrophoresis gels, and location of radioactivity in gels when specific radiolabeled proteins were added to plasma. Proteins found were albumin, IgG, fibrinogen, plasminogen, and fibrinogen degradation products (FDP). A major component with an apparent molecular weight of 25,000 remains unidentified. It is unrelated to albumin, IgG, fibrinogen, factor XII, or plasminogen. Adsorbed fibrinogen was less degraded when experiments were performed with plasmas deficient in either plasminogen or factor XII. It is therefore concluded that FDP are formed by activation of adsorbed plasminogen, as was found previously for purified fibrinogen containing a trace of plasminogen.11 At least part of this activation is potentiated by the contact activation phase of plasma coagulation, in particular activated factor XII.
Influence of alloy composition on the hardening of silver–tin dental amalgam
Authors: Abbott J. R. , Miller D. R. , Netherway D. J.
Published: December 2004

The objective of the investigation was to examine the reactions of mercury with silver‐tin alloys with compositions spanning the phase fields β, (β + γ), γ, and (γ + Sn). The experimental methods employed include the application of light microscopy, scanning electron microscopy, and electron probe microanalysis. These techniques were used to investigate the mechanisms of reaction and to identify the nature and morphology of the reaction products formed on bulk specimens of the alloys. The progress and characteristics of the reactionsthat occur during hardening of amalgams prepared from powders of these alloys were monitored using a highsensitivity dilatometer. These results were correlated with direct observations on the development of the microstructures. The reaction of mercury with the β‐phase alloy occurred rapidly and resulted in a very marked and rapid expansion during the initial stages of hardening. γ‐Phase alloys, on the other hand, reacted more slowly and contracted markedly during hardening. The behavior of amalgams made from alloys with compositions lying between these two extremes appeared to be explicable in terms of the characteristics of the separate phases from which they were constituted.
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

A 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

The 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

Adsorption 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

The 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

The 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

There 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

A 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

We 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

RINm5F 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

The 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

An 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

An 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

The 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

The 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

A 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

Using 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

This 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.
The effects of pore size and endothelial cell seeding upon the performance of small‐diameter e‐PTFE vascular grafts under controlled flow conditions
Authors: Boyd Kevin L. , Schmidt Steven , Pippert Todd R. , Hite Scott A. , Sharp William V.
Published: December 2004

The purpose of this study was to determine the effects of endothelial cell seeding and graft internodal distance upon the performance of 4‐mm‐ID e‐PTFE grafts during acute reduced blood flow conditions. PTFE grafts especially manufactured with three different mean internodal distances (28, 40, and 52 μm) were evaluated. Fifteen dogs (n = 5 for each design of PTFE graft) underwent bilateral carotid artery replacements with 6 cm lengths of 4‐mm‐ID PTFE grafts. In each dog one graft was seeded with enzymatically derived endothelial cells; the contralateral graft was nonseeded. All grafts were evaluated 5 weeks postoperatively. Dogs with bilaterally patent grafts were subsequently subjected to flow conditions through the graft that were maintained at 30% of the initial flow rates for 4 hr. Following controlled low flows the grafts were excised and assessed for patency, thrombus‐free surface area, inner capsule thickness and prostacyclin production. Endothelial cell seeding of these small‐diameter e‐PTFE vascular grafts improved patency and thrombus‐free surface areas in grafts of all pore sizes, with these parameters being greatest in the 40‐μm grafts. Inner‐capsule healing in these grafts was controlled and related to the pore size. PGI2 production was improved in endothelial cell seeded grafts of all pore sizes. However, neither endothelial cell seeding nor graft pore size affected the performance of these e‐PTFE grafts under conditions of reduced blood flows.
Calcium phosphate‐coated porous titanium implants for enhanced skeletal fixation
Authors: Rivero D. P. , Fox J. , Skipor A. K. , Urban R. M. , Galante J. O.
Published: December 2004

Porous titanium fiber implants for cementless skeletal fixation by bone ingrowth were treated with a calcium phosphate coating applied by a plasma flame‐spray technique. In a paired experiment, treated and control implants were inserted in the humeri and olecranons of 36 adult dogs for periods of 1, 2, 4, and 6 weeks. After the animals were sacrificed, a biomechanical evaluation of the strength of skeletal fixation of the implants and a histologic evaluation of bone ingrowth was done. The mean shear strength of skeletal fixation at four weeks for the calcium phosphate‐coated implants was 24% greater (p < .01) than for paired controls. No difference in strength of fixation between treated and control implants was present at other time periods. The osteoconductive properties of the ceramic coating were demonstrated by bone forming in direct contact with the calcium phosphate coating on the metal fibers of the treated implants. No significant increase for the volume of bone ingrowth was established for treated implants compared to paired controls at any time period.
Cell morphology, proliferation and collagen synthesis of human fibroblasts cultured on sepiolite–collagen complexes
Authors: Olmo Nieves , Lizarbe Maria A. , Turnay Javier , Müller Klaus P. , Gavilanes José G.
Published: December 2004

The growth and morphology as well as collagen biosynthesis of human fibroblasts obtained and cultured on sepiolite–collagen complexes have been studied. No differences on cell morphology and growth properties nor collagen synthesis were observed when compared with standard culture substrates. The type I/type III ratio of biosynthesized collagen by fibroblasts cultured on sepiolite–collagen complexes was about 5–6 with no difference when compared to control conditions. This normal behavior was also observed for the type I/type III procollagens. According to these studies the sepiolite–collagen complexes do not modify the studied features of the fibroblasts.
Endothelialization of polymer surfaces
Authors: Absolom D. R. , Hawthorn L. A. , Chang G.
Published: December 2004

The role that substrate surface properties play in influencing the extent of endothelialization of polymer surfaces has been investigated. For a wide range of polymer surfaces, the degree of endothelialization cells is directly related to polymer surface tension: increased endothelialization occurring with increasing substrate surface tension. As a result of adsorption of the proteins in the culture media, the surface properties of the polymers are altered considerably. The protein‐coated polymers were characterized by means of liquid–liquid contact angle measurements under non‐denaturing conditions. A striking correlation is observed between the degree of endothelialization and the measured dextran contact angle. The degree of endothelial cell spreading is not related to polymer surface tension. Cell morphology and extracellular matrix production, however, are influenced by substrate surface properties.
Cellular morphology and distribution on a stretching blood–material interface
Authors: McMillin Carl R. , Malladi Madhusudan R. , Ott Donald W. , Evancho Michelle M. , Schmidt Steven P.
Published: December 2004

In order to investigate the interactions of cellular elements and protein on constantly deforming (fatiguing) blood contact surfaces, a series of ex vivo canine arteriovenous shunt experiments were conducted. While fresh blood was flowing through Silastic tubing shunts, portions of the tubing were stretched 20 to 60% at a frequency of 20 to 90 cycles per minute for 10 to 90 min. The surfaces of the tubing that were stretched were compared with control tubing surfaces taken from the arterial side of the test segment using scanning electron microscopy and interference phase contrast microscopy.

Approximately the same number of platelets were deposited on the stretched as on the unstretched portions of the tubing in the ten minute experiments. On the control portions of the tubing, the platelets were deposited singly and uniformly in what appeared to be a fairly inactivated state. On the stretched tubing, more pseudopod extension and aggregation was observed. In these preliminary experiments, no differences were noted as a function of frequency of stretch. As the blood contact time and the percent stretch were increased, only nonuniform, scattered aggregations of platelets, and platelets mingled with fibrin were seen. Significant numbers of spread white blood cells were observed on many of the segments of Silastic tubing stretched 20% for as short a time as 15 min. Granulocytes have occasionally been reported on less hemocompatible biomaterials after exposure to canine blood. This helps to confirm that substrate stretching of 20–60% had an adverse effect on the blood compatibility of the Siliastic tubing.
Estimation of surface‐bound heparin activity: A comparison of methods
Authors: Chandler W. L. , Solomon D. D. , Hu C. B. , Schmer G.
Published: December 2004

We compared two assays for estimating the amount of active heparin bound to a catheter surface: (1) a kinetic assay based on the inactivation of thrombin by antithrombin III, and (2) thrombin uptake. Both assays were used to estimate the amount of heparin activity on a series of catheters coated with no heparin, covalently bound heparin, and ionically bound heparin. The kinetic assay produced estimates of surface‐bound heparin activity and showed that some binding methods resulted in destruction of most of the heparin's biologic activity. In contrast, the thrombin uptake assay did not correlate with the amount of heparin activity on the catheter surface. Substantial thrombin uptake was found on surfaces coated with no heparin or inactive heparin, while low thrombin uptake was found on surfaces with high levels of heparin activity in the kinetic assay. We conclude that: (1) a kinetic assay based on the heparin accelerated inactivation of thrombin by antithrombin III can be used to estimate the amount of active heparin bound to a catheter surface, and (2) thrombin uptake studies do not correlate with heparin activity and do not predict which heparin binding method will result in the highest concentration of active heparin on the catheter surface.
Separation of B‐ and T‐lymphocytes by cellular adsorption chromatography using poly(2‐hydroxyethyl methacrylate)/polyamine graft copolymer as column adsorbent
Authors: Maruyama A. , Tsuruta T. , Kataoka K. , Sakurai Y.
Published: December 2004

A series of poly(2‐hydroxyethyl methacrylate)/polyamine graft copolymers (HA copolymers) were examined as an adsorbent for cellular adsorption chromatography in order to separate cell populations with high efficacy. The capability of each copolymer sample to selectively adsorb rat lymphocyte subpopulations (B‐cells and T‐cells) was evaluated by applying a lymphocyte suspension to a copolymer‐coated glass bead column. A separation factor (AB/AT) greater than 5.0 was achieved for the HA copolymer, compared to 1.9 and 1.1 for homopolymers of poly(2‐hydroxyethyl methacrylate) and of a polyamine (poly(N,N‐diethylaminoethylstyrene)), respectively. By loading a rat lymphocyte suspension containing B‐cells (28%) and T‐cells (72%) through the HA copolymer column, more than 60% of T‐cells in 90% purity or more were recovered in the effluent.
Thermomechanical study of Ni‐Ti alloys
Authors: Lee J. H. , Park J. B. , Andreasen G. F. , Lakes R. S.
Published: December 2004

A preliminary study was conducted to demonstrate the usefulness of the combined technique of differential scanning calorimetry (DSC) and mechanical testing for the shape memory metals of 54NiTi and 53NiTiCo(3%) alloys. The DSC technique was used to measure precise transformation temperatures and the amount of thermal energy required for the corresponding phase transformation. The degree of plastic deformation by bending and the effect of alloying (such as Co) were studied with combined DSC and mechanical property measurements.
The study of thermal and gross morphologic properties of polyglycolic acid upon annealing and degradation treatments
Authors: Chu C. C. , Browning A.
Published: December 2004

The objective of this study is to alter the fiber morphology of a linear aliphatic polyester, polyglycolic acid, by annealing treatment and to examine the changes of its degradation properties. The annealing was done at 150°C, 170°C, and 190°C, and the specimens were annealed in four different strained conditions, freely hung, 0, 1, and 10%. After annealing treatments, the specimens were subject to in vitro hydrolytic degradation by immersing them in phosphate‐buffer solution of pH 7.4 at 37°C for up to 28 days. The thermal properties and gross morphology of the specimens were obtained. It was found that annealing treatments resulted in initial higher levels of crystallinity, which, in turn, influenced the hydrolytic degradation of the fiber. Among all the annealing conditions, the freely hung specimens annealed at 190°C exhibited the most pronounced annealing effect on hydrolytic degradation, and was consistent with the observed gross morphologic changes. The change in the characteristics of fiber structure (i.e., the return to the stage of less oriented conformation upon freely hung annealing) was thought to be the cause.
Effect of delay between tissue harvest and glutaraldehyde pretreatment on mineralization of bovine pericardium used in bioprosthetic heart valves
Authors: Maranto Anthony R. , Schoen Frederick J.
Published: December 2004

There is concern that delayed glutaraldehyde treatment of bioprosthetic tissue could potentiate calcification by autolytic generation of mineralization nuclei. This study investigated the effects on mineralization of variable delays between harvest of bovine pericardium and initial glutaraldehyde treatment, using tissue implanted subcutaneously in rats for 21 days. Susceptibility to mineralization increased statistically but only modestly with delays to 34 h. This suggests that mineralization will not be significantly inhibited by rapid treatment of otherwise properly handled tissue and that clinically important prevention of calcification will require more dramatic means.
The use of dense alumina–alumina ceramic combination in total hip replacement
Authors: Boutin P. , Christel P. , Dorlot J.‐M. , Meunier A. , de Roquancourt A. , Blanquaert D. , Herman S. , Sedel L. , Witvoet J.
Published: December 2004

The purpose of this article was to review the laboratory and clinical performances since 1970 of a total hip prosthesis using alumina–alumina combination. The chemical and physical properties of dense alumina ceramic were studied in relation to biocompatibility, mechanical strength, and surface properties. Through the examination of 35 retrieved implants, it was found that the long‐term success of alumina–alumina total hip replacement depends on both the ceramic microstructure (small grain size with uniform distribution, minimum porosity, absence of inclusions) and implant geometry (sphericity deviation ±1 μm, radius tolerance between components 7–10 μm). Alumina component wear and fractures have disappeared with the use of high‐performance materials and severe manufacturing quality control. Examination of human biopsies from well‐fixed prostheses showed that alumina particles deposits increase with time with only a low‐grade macrophagic reaction. When loosening occurred, an inflammatory reaction appeared; this reaction was less striking than with loose metal–polyethylene prostheses, however. The long‐term behavior of cementless alumina cup fixation depends upon initial positioning and stability; survivorship analysis of the cemented ceramic cups showed an 88% survival probability after 8 years with a 1.6% average annual probability of revision. The percentage of surviving was 100% after 8 years in patients who were less than 50 years old. Aseptic loosenings occurring at the cup–cement interface were assumed to be related to stress protection secondary to the high rigidity of the ceramic leading to a weakening of the spongious bone supporting the cement mantle. Good bone stock quality as well as high‐quality ceramic appear to be the prerequisites for durable fixation of alumina sockets.