bluuebunny/crossref_metadata_2025 huggingface dataset:
Heparinized styrene‐butadiene‐styrene elastomers
Authors: Goosen Mattheus F. A. , Sefton Michael V.
Published: December 2004

A heparinized high‐strength elastomer has been developed which is potentially useful as a nonthrombogenic vascular prosthesis. A surface hydroxylated styrene‐butadiene‐styrene (SBS) block copolymer with at least 40% extent of reaction after glow‐discharge cleaning was coated with a 20% acetylated polyvinyl alcohol/heparin mixture containing glutaraldehyde and magnesium chloride. After curing at 80°C for 100 min, the polyvinyl alcohol, heparin, and hydroxylated SBS were covalently bound to each other by acetal bridges. The effects of the various substrate and coating parameters were optimized to achieve very strong adhesion between the coating layer and the surface hydroxylated SBS. Heparin was not leached from the surface of the new material using 3M saline at pH 7.4 despite a detection limit of 10−5 μg heparin/cm2 min. Prolonged partial thromboplastin times of greater than 1200 sec were observed (control: PTT = 120 sec). Preliminary ex vivo testing using a simple arteriovenous shunt in the leg of a rabbit showed good thromboresistance. The heparinized SBS shunt chamber remained patent for more than two hours without desorption of heparin. It was concluded that surface hydroxylated SBS heparinized by acetal coupling owed its thromboresistance to the heparin covalently bound to the surface and not to a microenvironment of heparin in solution at the blood/material interface.
The fabrication of artifacts out of glassy carbon and carbon‐fiber‐reinforced carbon for biomedical applications
Authors: Jenkins G. M. , Grigson C. J.
Published: December 2004

Polymeric carbons1 are produced by the carbonization of a wide range of organic polymeric systems. We have concentrated on the fabrication of two types of polymeric carbons, glassy carbon and carbon‐fiber‐reinforced carbon (CFRC), both involving phenolic resin precursors. We describe herein the technology which enables us to make dental implants and heart valves out of glassy carbon. We also show how carbon‐fiber‐reinforced carbon can be made in the form of rods and plates for orthopedic use and molded before firing to produce complex, rigid, individually sculptured shapes suitable for maxillofacial bone replacement. The mechanical properties will be discussed in relation to the structure of these various forms of polymeric carbon.

The main purpose of the work is to show that the technology of polymeric‐carbon manufacture is essentially simple and the manufacturing process is readily carried out in laboratories which have already been equipped to fabricate standard dental prostheses.
Time‐Dependent phase changes in Cu‐rich amalgams
Authors: Marshall Sally J. , Marshall Grayson W.
Published: December 2004

Cu‐rich amalgams represent a significant change in amalgam alloy formulation which may result in enhanced performance. Significantly, these systems reduce or eliminate the γ2 phase. This work studied the phase changes which occurred from one hour to six months in 13 commercial amalgams by x‐ray diffraction. This included 9 two‐particle or blend systems and 4 single‐particle systems. γ2 was found in all systems, but was reduced or eliminated on storage at 37°C at rates which varied from system to system. During γ2 elimination, the Cu6Sn5 content correspondingly increased, indicating that solid‐state reaction occurs for up to six months in some systems.
The influence of grain size on the fatigue behavior of annealed 316 LVM stainless steel
Authors: Clemens D. , Galante J. , Rostoker W.
Published: December 2004

Experimental tests demonstrate that there is a sharp drop in resistance to fatigue fracture when the grain size is increased from 75 to 150 μm. This is at least a partial explanation for fatigue fractures of the stems of total hip‐joint prostheses reported in the literature. It is also shown that plastic strains associated with fatigue stressing increase with increasing grain size so that loosening of the bone cement embedment may also be part of the premature failure process.
Bending properties of wire‐reinforced bone cement for applications in spinal fixation
Authors: Saha Subrata , Kraay Matthew J.
Published: December 2004

PMMA beam specimens were tested in four‐point bending to determine if the bending strength of acrylic bone cement, as used in posterior spinal fusion, could be improved by metal‐wire reinforcement. The result showed that the load‐carrying capacities of 1‐ and 0.5‐mm diam stainless‐steel‐wire‐reinforced PMMA specimens in bending were significantly higher than similar unreinforced normal PMMA samples. On an average, steel reinforcement comprising approximately 1% of the cross‐sectional area of the PMMA specimens caused a 15% increase in bending strength. Even after the cement fractured, the reinforcing wires still sustained an appreciable amount of bending moment, thus preventing catastrophic failure of cement alone.
A comparative study of poly(glycolic acid) and catgut as suture materials. Histomorphology and mechanical properties
Authors: Pavan Andrea , Bosio Maurizio , Longo Tito
Published: December 2004

The “quality” of poly(glycolic acid) as an absorbable suture material was investigated in comparison with catgut. Tissue reactions to poly(glycolic acid) and plain catgut were examined histomorphologically at different time intervals after implantation in rats, and compared. Four mechanical properties were also examined as relevant quality factors: elastic stiffness, tensile strength, toughness, and percent elongation at rupture of the suture material per se (unknotted). The variation of these properties in poly (glycolic acid) implants was followed since their insertion in the tissues. Histological behavior and mechanical properties appear to be more closely correlated in the case of poly(glycolic acid) than in the case of catgut, as a consequence of a greater regularity of tissue reaction towards the synthetic material. Both tissue reaction and tensile properties variation are independent of size in the case of the braided poly(glycolic acid) sutures examined. Elastic stiffness and tensile strength decrease steadily in time; toughness and ultimate elongation display an increase up to a maximum within one day since implantation, and then decrease.
In vivo evaluation of a high‐strength, high‐ductility stainless steel for use in surgical implants
Authors: Syrett Barry C. , Davis Edward E.
Published: December 2004

A high‐strength, high‐ductility, austenitic stainless steel has been evaluated for use in surgical implants by performing in vivo tests in rats, rabbits, dogs, and rhesus monkeys. This stainless steel, a TRIP (TRansformation Induced Plasticity) steel containing about 4% Mo, was compared with two alloys in current clinical use: Type 316L stainless steel and cast Vitallium. Compared with the other two alloys, cast Vitallium generally had higher resistance to corrosion and superior biocompatibility in all animals. The tests in rats and dogs indicated that the corrosion resistances of the TRIP steel and the Type 316L stainless steel were similar and that the tissue reactions caused by these alloys were also similar. However, in rhesus monkeys, the TRIP steel was shown to be susceptible to stress‐corrosion cracking and much more susceptible to crevice corrosion than Type 316L stainless steel. Limited tests in rabbits supported the observation that the TRIP steel is susceptible to stress‐corrosion cracking. These inconsistencies in the in vivo tests underline the need for a reevaluation of the popular test techniques and of the animals commonly chosen for assessing the suitability of candidate implant materials. The “worst case” results from the rhesus monkey tests were entirely consistent with previous results obtained from in vitro studies. However, further work must be performed before the behavior of metals in humans, rhesus monkeys, or any other animal, can be predicted with confidence from an in vitro test program.
The effects of radiation sterilization on the properties of ultrahigh molecular weight polyethylene
Authors: Nusbaum H. J. , Rose R. M.
Published: December 2004

The effects of radiation sterilization on ultrahigh molecular weight polyethylene were explored by freeze fractures, electron spin resonance, absorption of aqueous media, density measurements, small‐angle and wide‐angle x‐ray scatter, differential scanning calorimetry, infrared and ultraviolet‐visible spectrometry, static and dynamic mechanical properties measurements, mechanical fatigue measurements, and standard environmental stress cracking measurements. The rate of fluid absorption increased significantly due to the appearance of carbonyl groups. As the fluids were absorbed, density increased and small‐angle x‐ray scatter (SAXS) intensity diminished slightly, as expected. Small changes in mechanical properties (e.g., tensile properties and dynamic spectrum) were always consistent with the cross‐linking which occurs after irradiation; the only significant mechanical deterioration was in the fatigue properties. The nonspherulitic, inhibited crystallinity which characterized this material and which is responsible for its excellent static resistance to environmental stress cracking was not at all changed.
Durability of the bond between bone and various 2‐cyanoacrylates in an aqueous environment
Authors: Brauer G. M. , Kumpula J. W. , Termini D. J. , Davidson K. M.
Published: December 2004

The durability of the bond strength developed between 2‐cyanoacrylate esters and bone has been determined by aging specimens in water. One‐day bond strength of the isobutyl and isomeric amyl 2‐cyanoacrylates varied from 6.2 to 7.2 MPa. The strength of the bond decreased on storage or on thermocycling in water. Hydrolytic stability increased with increasing length of the alkyl ester group. After a six‐month storage in water the various amyl 2‐cyanoacrylates retained from 70% to 73% of their one‐day bond strength. Pretreatment of the bone surface prior to application of the adhesive did not prove beneficial. The cured 2‐cyanoacrylate can be removed from the substrate surface by appropriate solvents. Thus, it is not bonded covalently to bone. The bond strength, especially of the isobutyl and amyl 2‐cyanoacrylates to bone in an aqueous environment, appears to be superior to other adhesives. Provided these monomers are biocompatible, they may be useful clinically where an intermediate‐term adhesion is desired.
Tissue response to surface‐treated tantalum implants: Preliminary observations in primates
Authors: Meenaghan Michael A. , Natiella Joseph R. , Moresi John L. , Flynn Harry E. , Wirth John E. , Baier Robert E.
Published: December 2004

Samples of capacitor grade tantalum were surface‐treated by a variety of methods. These surface treatments allowed testing of the same basic material which was millfinished, metallurgically polished, electrochemically oxidized, sintered with a porous surface, and glow‐discharged. Surface characterization was accomplished by contact angle measurements, Scanning Electron Microscopy, energy‐dispensed x‐ray analysis, and internal reflection spectroscopy. Subsequent to characterization, the material was surgically implanted in the subperiosteal region of the mandible, the buccal mucosa, and the subcutaneous paravertebral region of the back of Macaca speciosa (stumptail monkey). The tissue reaction at intervals of up to three weeks was evaluated morphologically and ultrastructurally. Significant differences in tissue response were noted at the interfaces with glow‐discharge‐treated versus lower surface energy samples. Adjacent to the glow‐discharge‐treated implants, two distinct tissue zones were identified. Zone #1, nearest the implant, exhibited an increased cellularity. This consisted of 4–5 layers of highly active mesenchymal cells or fibroblast‐like cells with spindle‐shaped nuclei and prominent cytoplasmic features. At various foci along the interface, hyperchromatic nuclear forms were noted to project into the space left by removal of the implant. These observations, coupled with a predominance of intercellular ground‐substance material and less collagen at the interface, may indicate some form of bioadhesion. The deeper Zone #2 was 2–3 times as thick and consisted of typical fibroblastic cells with a lamellar configuration, bordered by an occasional delicate‐lined space. Independent of implantation site or surface texture, all other implants showed occasional multinucleated giant cells and a decrease in the cellular character of Zone #1. Both zones were reduced in thickness and composed of more mature fibroblasts. Some specimens exhibited intracytoplasmic vacuolization. It may be concluded, therefore, that surface‐free energy of the implanted specimens played a significant role in inducing differential tissue response to otherwise similar pure metal samples.
Influence of methyl methacrylate on quantitative gel diffusion assay of immunoglobulins
Authors: Petty William
Published: December 2004

Infection is not a common problem following implant surgery using the bone cement, polymethyl methacrylate. When infection occurs, its often disastrous results makes for major complications. Many methods have been used in an attempt to reduce bacterial contamination at the time of implant surgery, but little attention has been given to the problem of possible effects of implant materials on the immune mechanisms of the host. In the experiments reported here, the in vitro effect of methyl methacrylate monomer on human immunoglobulins was determined using a quantitative gel diffusion technique. When methyl methacrylate monomer was added to serum samples containing immunoglobulin, it caused no statistically significant change in the immunoglobulin concentration of immunoglobulin‐G, immunoglobulin‐A, or immunoglobulin‐M. It is possible that methyl methacrylate could affect other types of antigen antibody reactions which may be important in resisting infection, but the evidence reported here indicates that in low concentrations, methyl methacrylate monomer does not affect the normal reactivity of immunoglobulins of the G, M, or A class.
Release characteristics of dibucaine dispersed in konjac gels
Authors: Nakano Masahiro , Takikawa Kaori , Arita Takaichi
Published: December 2004

A possible use of konjac gel for sustained release of drugs was examined in a monolithic system containing dibucaine. Dibucaine was dispersed in the gel which was prepared by gelation of the konjac flour in a borax solution at 60°. The cumulative amount of the drug released plotted against the square root of time was linear in the monolithic system. This relationship was in agreement with that expected from the theoretical equation for planar configuration. The mechanism of the release of the drug from the gel may be considered to be a leaching of the drug by the permeating fluid. The release profile from dried konjac gel was similar to that from undried gel, but that from unwarmed gel showed a deviation from linearity although sustained release was similarly obtained.
In vitro and in vivo evaluations of dacron velour and knit prostheses
Authors: Sawyer P. N. , Stanczewski B. , Hoskin G. P. , Sophie Z. , Stillman R. M. , Turner R. J. , Hoffman H. L.
Published: December 2004

Dacron velour and knit prostheses were compared with respect to long‐term patency when used as canine aortic implants. These grafts were rated, according to the average numerical value of six equally weighted criteria, in decreasing order of performance: velour I, velour II, circular knit III, velour IV, circular knit V, warp‐knit VI, warp‐knit VII and VIII, warp‐knit IX and warp‐knit X. In general, compacting and crimping methods using halogenated hydrocarbons produced the least successful grafts. Grafts of identical brand but compacted and crimped by different methods exhibited different patencies. No true healing of any of the grafts was observed. Layered deposits of inner fibrous capsule were formed at rates and thicknesses c a acteristic for each type of graft employed. A functioning Dacron femoral‐popliteal bypass removed from a human after 9 months exhibited inner and outer fibrous capsules similar to those from canine implants.
In vitro heterogeneous degradation of poly(n‐alkyl α‐cyanoacrylates)
Authors: Vezin W. R. , Florence A. T.
Published: December 2004

Methods by which in vitro heterogeneous phase degradation rates of the poly(n‐alkyl α‐cyanoacrylates) have been directly obtained are described. The data indicate that the rates of degradation in aqueous buffer solutions depend not only upon pH of the medium and length of the monomer alkyl side chain, but also critically upon polymer particle specific surface, particle size, polymer molecular weight, and molecular weight distribution. A modification of the currently held theory of degradation of these polymers is required, and postulated.
The influence of design parameters on calcar stresses following femoral head arthroplasty
Authors: Cook S. D. , Klawitter J. J. , Weinstein A. M.
Published: December 2004

A two‐dimensional finite element model (FEM) was used to investigate the effect of various prosthesis design parameters on stresses along the proximal medial aspect of the femur. Strain calculations were compared to reported experimentally measured strains for an intact femur and femur containing a prosthesis in an effort to verify the FEM results. The results of the study indicated that stress levels in the medical aspect of the femur approaching those of the intact femur are possible with a device having an elastic modulus similar to bone. It was found that acrylic bone cement had little effect on stress profiles in the medial aspect when compared to stresses for devices utilizing a direct bone to implant attachment mechanism. It was also found that reduction in implant stem length and elastic modulus of tissue present at the prosthesisbone interface could be used to increase stresses in the medial aspect; however, their effects were not as dramatic as reducing the elastic modulus of the stem material.
Oxygen permeability of carbon‐surfaced microporous membranes
Authors: Borovetz Harvey S. , Mateer David D. , Hardesty Robert L. , Haubold Axel D.
Published: December 2004

A study was conducted to measure the permeability to oxygen (PmO2) of microporous membranes coated with ultra‐low‐temperature isotropic (ULTI) carbon. Carbon‐surfaced membranes were fabricated by application of a thin complete layer (0.7 to 1.7 microns thick) of ULTI carbon onto one surface of a microporous substrate. Based upon the average values of 27 measurements in a diffusion cell, a mean reduction in PmO2 of only 10% results following the treatment of the microporous substrate with ULTI carbon. The values for PmO2 are not dependent upon the thickness of the carbon film over the range of film thickness of 0.7 to 1.7 microns. When coupled with the known antithrombotic characteristics of ULTI carbon, an oxygenator incorporating carbon‐surfaced microporous membranes has the potential for use in clinical extracorporeal membrane oxygenation (ECMO).
Academic Focus: Graduate study in biological materials at Northwestern University
Authors: Greener E. H. , Marshall G. W.
Published: December 2004

This is the first of a series of presentations which we will publish irregularly. This new dimension in the literature will be of considerable interest to the many academicians involved in the teaching of biomedical sciences.—Ed.
Time‐temperature behavior for creep of dental amalgam
Authors: Greener E. H. , Szurgot K. , Lautenschlager E. P.
Published: December 2004

From 0 to 24 hours at an initial static stress of 34.5 MPa and in the temperature range of 0 to 60°C, the creep behavior of four different one‐week‐old dental amalgams was monitored in a recently developed minispecimen creep apparatus. In most instances the behavior could not be described by a linear relationship. Therefore, the usefulness of calculating creep rate based upon only two times, i.e., 1 and 4 hours, must be questioned. On the other hand, the observed creep kinetics were found to follow accepted nonlinear models of dislocation/obstacles interactions which may be thermally activated.
Immobilization of enzymes for medical uses on plastic surfaces by radiation‐induced polymerization at low temperatures
Authors: Kaetsu Isao , Kumakura Minoru , Asano Masaharu , Yamada Akio , Sakurai Yasuhisa
Published: December 2004

The immobilization of some medically useful enzymes were studied by means of radiation‐induced polymerization at −78°C. Glucose oxidase and glucose peroxidase were immobilized in the form of thin membranes inside polyvinyl chloride tubes and on polyethylene films; these membranes showed considerable activity yield, as well as good activity retention. Two effective methods were adopted to improve the surface properties of the base materials and to facilitate firm immobilization by coating: that is, an undercoating method followed by radiation curing of the undercoating and an irradiation grafting method with a monomer. Both were tested with good results. An immobilization of urokinase was also carried out successfully by similar methods. The thrombogenicity of the immobilized urokinase showed a remarkable effect on thrombus formation.
Platelet adhesion onto artificial red blood cells
Authors: Muramatsu Nabuhiro , Kondo Tamotsu
Published: December 2004

Several kinds of polyamide microcapsules containing mammalian hemolysate were prepared by making use of the interfacial polycondensation reaction between diamines and terephthaloyl dichloride and their blood compatibility in terms of platelet adhesion was examined aiming at their ultimate clinical use as artificial red blood cells. It was found that rabbit platelets adhere onto the hemolysate‐loaded microcapsules in the presence of the plasma, while no platelet adhesion takes place in the absence of the plasma. This was interpreted as indicating an important role of plasma components in platelet adhesion. Moreover, platelet adhesion was observed to be facilitated by negative charges on the surface of the hemolysate‐loaded microcapsules; the more negatively the surface was charged, the more easily the platelets adhered onto the surface. Finally, the present method of assessing platelet adhesion suggested the possibility of its use for the kinetic study of platelet adhesion since it allowed us to make numerical evaluation of platelet adhesion as a function of time.
Butt joint versus bevelled gold margin in metalceramic crowns
Authors: McLean J. W. , Wilson A. D.
Published: December 2004

The merits of a butt joint versus a bevelled margin are reexamined. It is shown that only acute bevels are effective in reducing the marginal diffusion of plaque acid. However, acute gold bevels may give rise to other major problems in avoiding distortion of the gold during firing of the porcelain, and finishing and cementing the crown.
Piezoelectric ceramic implants: A feasibility study
Authors: Park J. B. , von Recum A. F. , Kenner G. H. , Kelly B. J. , Coffeen W. W. , Grether M. F.
Published: December 2004

A piezoelectric ceramic has been investigated as a direct substitute for hard tissues. Barium titanate (BaTiO3) powder was slipcast and fired at 1430°C for 2 hr, then made piezoelectric by polarizing. After 16 and 86 days of implantation in the cortex of the femoral midshafts, the femora with test specimens were sectioned into about 4‐cm lengths. Their voltage outputs were measured under cyclic load at 1 Hz. The present results show that the voltage gradient at the implant surface is 0.15 mV/mm for the 16‐day implantation with a 445‐N (100‐lbs.) load. This in turn can give rise to about 0.01 μA current flow in the adjacent area of the 16‐day implant. The 86‐day implant showed an order of magnitude higher voltage output compared to the 16‐day implant with the same magnitude of loads. This is probably due to the “load‐transfer” efficiency through the implants, since the voltage output is directly proportional to the actual load transferred to the implant. The more bone implant interface matures, the better the load transfer occurs through the implant, resulting in higher voltage output.
Growth inhibition of cultured fibroblasts by cobalt and nickel
Authors: Bearden L. J. , Cooke F. W.
Published: December 2004

It is known that tissues surrounding the site of an implanted prosthetic alloy are exposed to increased concentrations of the metals comprising the alloy. However, the exact identity and concentration of such metallic products are usually unknown, thus limiting the possibilities for quantifying any observed toxicological response to the metals. This report describes some of the effects of increased concentrations (7.5–30 μg/ml; 1–5 × 10−4M) of cobalt (as CoCl2·6H2O) and of nickel (as NiCl2·6H2O) on the growth and morphology of cultured mouse fibroblasts. Ultrafiltration experiments indicated that much of the total Co or Ni present in cell culture medium could become bound to macromolecular serum components of the medium. Morphological changes and depressions in the cell growth rate were found to result from high concentrations (15–30 μg/ml) of either Co or Ni. However, lower concentrations of nickel may have produced some stimulation of cell growth, whereas all concentrations of Co studied were found to depress the rate of cell growth. The growth rate of actively proliferating fibroblasts was quite sensitive to variations in the concentration of either cobalt or nickel. Increased concentrations of cobalt or nickel, therefore, might also affect the normal reconstructive activity of fibroblasts in vivo.
The effect of bacteria on absorbable sutures
Authors: Williams David F.
Published: December 2004

In vitro and in vivo experiments were performed on polyglycolic acid and plain catgut sutures to study the effects of bacteria on their rate of degradation. Experiments with Strep, mites, E. coli and Staph. albus in culture showed that the polyglycolic acid sutures degraded faster in broth controls than in a broth containing bacteria as measured by the loss in breaking strength. No difference was observed with the catgut. Polyglycolic acid sutures in subcutaneous sites in rats inoculated with Staph. albus again degrade slower than in similar wounds which were not deliberately infected. With high bacterial counts, the catgut showed the reverse trend although no differences were noted at lower counts.
Methodological assessments of subcutaneous implantation techniques
Authors: Marion L. , Haugen E. , Mjör I. A.
Published: December 2004

Results from 197 subcutaneous implants on rats and 40 on mice of three different dental biomaterials were studied with emphasis on methodological evaluations. The types of implants employed allowed a differentiation between the materials based on the tissue reactions induced, but the degree of response recorded depended on the technique and the animal employed. The main problems encountered were the effect of operative trauma in short‐term experiments, loss of material/tissue interface, dislodgement or tearing of sections if the materials remained in situ, folding and distortion of tissue, and difficulties in orientation of specimens for sectioning. The tube implant supplied with a window and sectioned perpendicularly on the long axis of the tube gave the least methodological problems. This “window technique” is therefore recommended as the method of choice for subcutaneous implantations. Cell density evaluations allowed quantitative determinations of the cellular response.
Fracture toughness of denture base acrylics
Authors: Stafford G. D. , Huggett R. , Causton B. E.
Published: December 2004

Two types of fracture toughness specimen, the tapered cleavage (TC) and single edge notch (SEN), are compared. Their reproducibility, accuracy, and ease of preparation are investigated. The fracture toughness of four types of acrylic resin, heat cured, autopolymerized, injection molded, and high impact resistant, has been determined by one or both of the above methods. High impact acrylic proved too ductile for either of the specimens to be used to assessK1c; however, these deviations from brittle behavior were revealed by the tests and some insight into impact resistance was gained. The SEN specimens proved capable of distinguishing between the fracture toughness characteristics of the four types of denture base acrylics and proved easy to fabricate. The TC specimens proved difficult to fabricate requiring specialized equipment; however, once made, the specimens revealed more of the fracture process than did the SEN specimens.
Thermal expansion of dental alloys and porcelains
Authors: Fairhurst Carl W. , Anusavice Kenneth J. , Hashinger Delora T. , Ringle Robert D. , Warren Twiggs S.
Published: December 2004

The effect of thermal coefficient of expansion (α) mismatch on porcelain‐metal bonding is frequently referred to in the dental literature. Thermally induced stresses may develop at metal‐porcelain system interfaces due to differences in the coefficients of thermal expansion of the porcelains, metals, and metal oxides. The objective of this research is to characterize alloy and porcelain expansion behavior as a first step in developing a more specific definition of thermal compatibility. It is clear from comparisons of porcelain data and alloy data that the porcelain has expansion characteristics which are quite different from those of the alloys. The overall differences in values between these alloys and porcelains constitute a mismatch. First run dilatometric heating measurements for porcelain yield large differences between ΔL/L and α values as compared to cooling measurements. For a comparison of alloy and porcelain expansion characteristics, data should be obtained at several temperatures up to the glass transition temperature (Tg) of the porcelain.
Immunological evaluation of the tumorigenic response to implanted polymers
Authors: Habal Mutaz B. , Powell Marie L. , Schimpff Robert D.
Published: December 2004

This short report concentrates on a close look at the immunological status of experimental animals which were implanted with a known dose of tumor and polymer implant. The implanted polymers used represented the most common biocompatible materials employed in current surgery. The immunological studies all were done in vitro on the cellular level. The studies suggested that there is a noticeable change of the immune system when inorganic biocompatible polymers are used in experimental animals.
Permeability properties of gels and membranes derived from chitosan
Authors: Hirano Shigehiro , Tobetto Kenji , Hasegawa Masahiro , Matsuda Noriaki
Published: December 2004

A series of membranes was prepared by air‐drying the thin layers of N‐acyl‐ and N‐arylidene‐chitosan gels. Their flow rates of water and permeabilities of various compounds were examined. N‐Acylchitosan membranes were stable in both dilute acid and alkali, but N‐arylidene‐chitosan membranes were unstable in dilute acid. N‐Acetylchitosan membranes were stable in formic acid at room temperature for up to 7 hr. The flow rates of water through N‐acetylchitosan membranes were 10.0–23.6 × 10−3 ml/cm2 min under a pressure of 3 kg/cm2, and were unchanged by the membrane thickness (12–60 μm). The increase of carbon numbers for N‐acyl groups caused a slight decrease in the flow rates, and the flow rates were decreased by partial O‐acetylation of N‐acetylchitosan membranes. The flow rate of water through chitosan membranes (thickness 30–35 μm) was 7.1 × 10−4 ml/cm2 min, which was decreased by an increase in the membranes thickness. Low‐molecular‐weight compounds (MW < 2900) passed through these membranes, but high molecular‐weight compounds (MW > 13,000) did not pass through.
Kinetic and thermodynamic aspects of platelet adhesion from suspension to various substrates
Authors: Neumann A. W. , Hum O. S. , Francis D. W. , Zingg W. , Van Oss C. J.
Published: December 2004

Kinetics of platelet adhesion from suspension to various substrates leads to Langmuir isotherm types of curves, both for suspensions in which the platelets were isolated by means of gel filtration as well as by centrifuging and washing. The level of platelet adhesion increases with increasing surface tension of the substrate. These results cannot be explained on the basis of the theoretical transport model of Ruckenstein et al. The plot of the platelet adhesion at equilibrium vs. γsv brings the observations in yet closer agreement with thermodynamic predictions based on free energy calculations than was found previously for the adhesion of platelets after short contact times between platelet suspension and substrate.
Trace fluoride and its role in enamel mineralization
Authors: Finkelstein Mark J. , Nancollas George H.
Published: December 2004

A highly reproducible seeded crystal growth method has been used to study enamel mineralization in the presence of traces of fluoride ion. The resulting increased rate of remineralization over a range of calcium phosphate supersaturation may be attributed to the formation of surface fluorapatite.
Mechanical properties of the soft contact lens of poly(methyl methacrylate‐N‐vinylpyrrolidone)
Authors: Hosaka S. , Yamada A. , Tanzawa H. , Momose T. , Magatani H. , Nakajima A.
Published: December 2004

The mechanical properties of the hydrogel membrane of poly(methyl methacrylate‐N‐vinylpyrrolidone) were studied for the purpose of making soft contact lenses for extended wear. The dependence of tensile fracture energy, flexibility, and recovery from deformation on the water content and thickness of the hydrogel membrane was studied. Reducing the thickness of a lens was found to exert a more advantageous effect than increasing its water content on maximizing the tensile fracture energy under the condition of an adequate supply of oxygen to the cornea through the contact lens. As long as its water content is controlled between 63 and 78%, the contact lens made of poly(methyl methacrylate‐N‐vinylpyrrolidone) has the flexibility on the same order as that of conventional soft contact lenses of poly(2‐hydroxyethyl methacrylate). The rate of recovery from deformation increases with water content, and the residual elongation is negligible in the range of water content over about 70%. It is concluded that practical requirements for use of these contact lenses, determined by these three mechanical properties, can be satisfied at the same time if the water content of the contact lens is adjusted at about 70%.
Materials design analysis of the prosthetic anterior cruciate ligament
Authors: Chen E. H. , Black J.
Published: December 2004

Repair or replacement of the damaged anterior cruciate ligament (ACL) is a significant clinical problem. A design utilizing ultrahigh‐molecular‐weight polyethylene (UHMWPE) was developed and marketed by an orthopaedic device manufacturer. Mechanical failure rates of greater than 10%/year postoperatively raised the issue of the adequacy of UHMWPE in that design. A study has been made to estimate the forces in the human anterior cruciate ligament for young, middle age, and older patients and to thus derive the minimum materials requirements for a now withdrawn prosthetic anterior cruciate ligament (PACL) design. It is concluded that UHMWPE does not possess adequate yield, creep, or fatigue properties to meet the design. Furthermore, consideration of the varying requirements on the PACL, due to differences in age and activity levels of patients, suggest that a band‐type design offers a better possibility of achieving adequate materials performance in the ACL prosthetic replacement.
Single crystal alumina for dental implants and bone screws
Authors: Kawahara Harukyuki , Hirabayashi Masaya , Shikita Takuji
Published: December 2004

When ground to a suitable form, flexural strength of single crystal alumina (Al2O3) decreases to as low as one third the strength of the intact crystal. This flexural strength decrease is, however, recovered by chemical etching at a high temperature to eliminate surface defects caused by grinding. By using this strength recovery treatment, various types of single crystal implants with fine structure were able to be designed. Four kinds of single crystal bone screws and single crystal dental implants of screw and anchor type were designed. Flexural strength and impact strength of the implants were measured.
The characteristics of anticoagulation by covalently immobilized heparin
Authors: Miura Yoshiharu , Aoyagi Sadayoshi , Kusada Yasuyo , Miyamoto Kazuhisa
Published: December 2004

The reactions of covalently immobilized heparin, abbreviated as I‐Hep, with thrombin or Factor Xa were investigated both in the presence and absence of antithrombin III, AT III. Although I‐Hep was able to bind to thrombin, the complex formation of thrombin and I‐Hep did not affect the thrombin activity when measured by using a small artificial substrate, a peptide‐MCA. Similarly, Factor Xa bound to I‐Hep, but the activity of Factor Xa was not decreased in the absence of AT III, when a peptide‐MCA was used for Factor Xa assay. Thrombin bound to I‐Hep in much larger amounts than Factor Xa. Thrombin and Factor Xa were instantaneously inhibited by AT III in the presence of soluble heparin. However, when I‐Hep was used instead of soluble heparin, instantaneous inhibition was not observed. When a natural, high‐molecular‐weight substrate was used for assay, the results were dependent on the structure of the immobilization carrier. Heparin immobilized on Sepharose 4B or Poly HEMA showed considerable prolongation of plasma recalcification time. However, heparin immobilized on the surface of PVA fiber did not prolong plasma recalcification time.
Characterization of graft polymers for biomedical applications
Authors: Ratner Buddy D.
Published: December 2004

Graft copolymer systems have frequently been suggested for biomedical applications. Since the properties of polymers are altered by the grafting process, thorough characterization is critical, particularly for the surface region of these copolymers. This review briefly discusses the grafting process and then describes characterization procedures for graft copolymers. Gravimetric characterization, thermodynamic measurements, surface chemistry analysis, and surface topographical analysis are considered in detail. Also, the relevance of materials characterization for predicting and understanding the biocompatibility response is discussed. Most of the analytical techniques described are applicable to all biomaterials and should be considered for the routine characterization of materials which will be interfaced with biological systems.
Tissue response to dense apatite implants in rats
Authors: Denissen H. W. , de Groot K. , Makkes P. Ch. , van den Hooff A. , Klopper P. J.
Published: December 2004

Dense (97–99.9%) hydroxylapatite ceramics were implanted in muscle and bone tissue of rats. The aim of this study was to compare apatite implant material made of commercially available powder with laboratory powder prepared in a painstaking manner. Biocompatibility, biostability, and adherence to bone were evaluated. In muscle tissue the implants were found to be encapsulated with a very thin connective tissue layer. Implantation in excavated bone tissue resulted with new bone directly deposited against the implant surface, irrespective of the type of hydroxylapatite used. When the implants were protruding from the bone surface, bone appeared to grow up to the edge of the protruding part of the implant. A very strong bonding developed; push‐out tests indicated that the bone fractured but never at the interface. Histologic studies proved that a sleeve of newly formed bone closely encased the implant, regardless of shape. It was concluded that dense apatite ceramics are fully compatible with the tibia of the rat and that no degradation of the implant material occurred for intervals of up to 6 months after implantation. The very strong bonding without mechanical retention indicated continuity between artificial hydroxylapatite and natural bone. No difference was found between the biological behavior of the hydroxylapatites prepared from commercial or laboratory starting powders.
Special Report: The interfacial behavior of biomaterials, 1979
Authors: Hench L. L.
Published: December 2004

In this excellent and analytical article, the immediate past President of the Society for Biomaterials reviews some of the most salient aspects of the Biomaterials scientists' work. His observations and comments are significant and crystallize current thought succinctly and with intelligence.—Ed.
Effects of roughness on the thrombogenicity of a plastic
Authors: Hecker J. F. , Edwards R. O.
Published: December 2004

Tubings extruded from one batch of polyvinylchloride resin at five temperatures ranging from 110 to 205°C were tested for thrombogenicity in the saphenous vein and aorta of sheep. There was more thrombus in both the vein and aorta on tubings extruded at lower temperatures. The surface areas of renal infarction were smaller when lower temperature tubings were inserted into the aorta. Scanning electron microscopy showed that lower extrusion temperatures caused greater roughness on the tubings. This greater roughness was confirmed by roughness measurements. It is suggested that the association which has been demonstrated between roughness and thrombus formation might be due to the degree of adhesion of the thrombus to the surface rather than to differences in thrombogenicity.
The effects of drug and water incorporation upon some physical properties of cold cured acrylic
Authors: Thaw M. , Addy M. , Handley R.
Published: December 2004

The addition of drugs to the cold cured acrylics has been demonstrated to variably affect their mechanical properties. This study investigated the effects, to the mechanical properties of a cold cured denture base material, of the addition of drugs and water. Chlorhexidine acetate was incorporated into the denture reline material at 10% w/w in the polymer phase of the material. Specimens also contained 10, 20, or 30% water w/w in the monomer phase of the material with or without the drug. The hardness of the specimens decreased with the addition of water to drug containing or drug‐free specimens. Furthermore, there was a significant reduction in the modulus of elasticity of the material with the addition of drugs and water or water alone, which was progressive as the amount of water increased. The load at fracture was similarly reduced as the water incorporation increased. The results demonstrated the considerable effects drug and water incorporation had upon the material. However, this would not negate the use of the material in the oral cavity in the reline or rebase situation employing existing prostheses. Moreover, the reduction in material strength may have the advantage of progressive loss of material with a resulting improved release pattern of the contained drug.
Interface mechanics of porous titanium implants
Authors: Clemow A. J. T. , Weinstein A. M. , Klawitter J. J. , Koeneman J. , Anderson J.
Published: December 2004

The interfacial shear properties of bone tissue growth into porous coated Ti‐6A1‐4V femoral implants have been examined as a function of the pore size of the porous surface. Three particle size range powders (297 μm, 420–500 μm, 595–707 μm) were used to fabricate cylindrical implants which were inserted into the femoral medullary canal of dogs for 6 months. Push‐out tests on the removed femurs are reported and reveal: (i) that those implants residing in cortical bone exhibited significantly higher shear properties than the equivalent implants in cancellous bone and (ii) that the interfacial shear strength and stiffness decreased with increasing pore diameter within the range 175–325 μm. The extent of bone ingrowth into the surface of the implants was measured using quantitative optical microscopic techniques. This indicated that the percentage of bone which had grown into the surface was inversely proportional to the square root of the pore size and that further the shear properties of the interface were proportional to the extent of bone in‐growth.
Finite element temperature analysis of a total hip replacement and measurement of PMMA curing temperatures
Authors: Swenson Lyle W. , Schurman David J. , Piziali Robert L.
Published: December 2004

Analytical and experimental studies were performed to examine some characteristics of poly(methyl methacrylate) bone cement in the context of total hip replacement. Proceeding from fundamental principles of balance of energy and heat conduction, three simulation models of total hip replacement, using the finite‐element method of numerical analysis, were used to predict the temperature response in the femoral prosthesis, cement, cancellous bone, and bone‐cement interface. When cement collars are a centimeter or less in thickness, the models predict little likelihood of permanent bone thermal necrosis. In addition, laboratory experimental results indicate that peak temperatures attained in Simplex‐P and Palacos‐R cement specimens are nearly identical and that adding 0.5 and 1.0 g of the antibiotic gentamicin to Palacos‐R has negligible influence on peak temperature. Experimental results also indicate that cooling cement specimens to 8°C extends the set time, which in turn could significantly increase the likelihood of stemcement loosening during surgery.
Piezoelectric ceramic implants: in vivo results
Authors: Park J. B. , Kelly B. J. , Kenner G. H. , von Recum A. F. , Grether M. F. , Coffeen W. W.
Published: December 2004

The suitability of barium titanate (BaTiO3) ceramic for direct substitution of hard tissues was evaluated using both electrically stimulated (piezoelectric) and inactive (nonpolarized) test implants. Textured cylindrical specimens, half of them made piezoelectric by polarization in a high electric field, were implanted into the cortex of the midshaft region of the femora of dogs for various periods of time. Interfacial healing and biocompatibility of the implant material were studied using mechanical, microradiographical, and histological techniques. Our results indicate that barium titanate ceramic shows a very high degree of biocompatibility as evidenced by the absence of inflammatory or foreign body reactions at the implant‐tissue interface. Furthermore, the material and its surface porosity allowed a high degree of bone ingrowth as evidenced by microradiography and a high degree of interfacial tensile strength. No difference was found between the piezoelectric and the electrically neutral implant‐tissue interfaces. Possible reasons for this are discussed. The excellent mechanical properties of barium titanate, its superior biocompatibility, and the ability of bone to form a strong mechanical interfacial bond with it, makes this material a new candidate for further tests for hard tissue replacement.