bluuebunny/crossref_metadata_2025 huggingface dataset:
Porosity in silver‐tin amalgams
Authors: Taylor Duane F.
Published: December 2004

Porosity has been determined metallographically for a series of spherical silvertin amalgams. The alloy consisted of separate size fractions of five compositions. Porosity was found to increase with increasing silver content and particle size, and was reduced by blending of large and small particle sizes. In blended alloys the porosity showed close correlation to the observed setting expansion.
Thermally induced stresses and rapid temperature changes in teeth
Authors: Barker Robert E. , Rafoth Robert F. , Ward Robert W.
Published: December 2004

The central theme of this paper revolves about an attempt to provide information and ideas that might be useful to persons interested in cryogenic dental procedures. However, a broad spectrum of thermal properties is also considered. For convenience a summary table is given for pertinent thermal and mechanical properties of dental materials. A point demonstrated is that observations which are of direct empirical utility to dentists often can be enhanced in value if viewed in terms of simple analytical models. For example, a tooth can be expected to be somewhere between a sphere and a long rod in its cooling or heating characteristics. The importance of the thermal diffusivity rather than thermal conductivity in transient phenomena is discussed. Some graphical techniques that circumvent mathematical difficulties are developed in detail. An isolated extracted tooth in contact with a coolant approaches to within 98% of its final temperature in less than 1 min but in the jaw, in contact with a cold (or hot) probe, the equilibration will take much longer. Thermally generated stresses, either due to differences in expansivities of the dentin and enamel or to large temperature gradients across a single component, can be quite large (comparable to the reported tensile strength, 9.3 MN/m2 for enamel) at cryogenic temperatures. Our observations and analysis make us believe that the reported strength of 9.3 MN/m2 is too low by at least an order of magnitude.
Lipid absorption by silicone heart valve poppets—in‐vivo and in‐vitro results
Authors: Carmen Raleigh , Mutha S. C.
Published: December 2004

Silicone rubber poppets, apparently without exception, will absorb lipid from the blood stream. In most cases, absorption is quite low and confined to simple lipids like cholesterol and cholesterol esters. A small percentage, however, absorb an unknown material in quantities sufficient to render them variant. This material appears to be an oxidation product of polyunsaturated fatty acids formed after their absorption into the poppet by the action of molecular oxygen. In vitro experiments supporting the in vivo findings are described.
Kinetics of bone growth into cylindrical channels in aluminum oxide and titanium
Authors: Predecki Paul , Stephan J. E. , Auslaender B. A. , Mooney Vert. L. , Kirkland K.
Published: December 2004

Samples of dense aluminum oxide, dense, porous, and surface‐oxidized titanium of varying surface roughness and containing long cylindrical channels 95–1000 μ in diameter were implanted in vivo in do femurs for periods of 2–8 weeks. The depth of ingrowth of calcified tissue into these channels was determined as a function of time, principally by electron microprobe.

The most rapid bone ingrowth was obtained with 500–, 525–, and 1000–μ diameter channels in all the titanium and aluminum oxide samples. However, the fraction of any given channel cross‐section filled with bone was observed to decrease as the channel diameter increased. In these channels, ingrowth depths of more than 2000 μ were often achieved in 4 weeks after which the rate of ingrowth levelled off somewhat. A certain degree of surface rougheness (greater than 20 μ in. a.a.) appeared to be necessary for fixation and ingrowth. Ingrowth of bone into the 95‐μ diameter channels was neglibile even after 18 weeks. The presence of interconnecting fine porosity per se, was found not essential for bone ingrowth nor does it have a major effect on ingrowth kinetics.
Biocompatibility of ceramic implants in soft tissue
Authors: Davis S. D. , Gibbons D. F. , Martin R. L. , Levitt S. R. , Smith J. , Harrington R. V.
Published: December 2004

The degradation and biocompatibility of seveal commercially available glasses, glass‐ceramics, and ceramics have been evaluated in soft tissue. Tissue compatibility was investigated by histological and toxicological determinations. Materials degration was evaluated by weight loss and surface replica electron microscopic techniques. High lead and arsenic‐selenium‐sulfur glasses are found to be unsuitable materials for implantation due to high corrosion and toxicity. Certain borosilicate glasses are also found unacceptable because of severe corrosion. Fused quartz, aluminosilicates, certain borosilicates, alkali resistant glass, soda‐lime glass, titania frit, arsenic trisulfide, lithium and magnesium aluminosilicate, glass‐ceramics, and calcium‐fluorapatite all appear to be well tolerated and seem acceptable for soft tissue implantation on the basis of the present data. Because of the lack of sensitivity of weight change as a parameter to measure low corrosion rates, we have no data on which to estimate the actual corrosion rate. The detailed changes in surface structurte produced during the corrosion process only provide information about the corrosion mechanism and may not be correlated with the corrosion rate. A more sensitive method to study low corrosion rates in glasses may be to use radioactive tracer techniques to measure the loss in radioactivity of glasses when implanted in the peritoneal cavity rather than subcutaneously.
Hard mathacrylic polymers. III. Copolymers of ethylene or trioxyethylene dimethacrylate with 2,2‐di(4‐methacryloxyphenyl)‐propane
Authors: Atusuta Mitsuru , Nakabayashi Nobuo , Masuhara Eiichi
Published: December 2004

Copolymers of 2,2‐di(4‐methacryloxyphenyl) propane and several glycol dimethacrylates were studied to develop a suitable polymer for crown and bridge restorations and artifical bone. The physical properties of copolymers—hardness, abrasion resistance, compressive strength, and water sorption—were measured. These properties were markedly improved by introduction of highly crosslinked structure.
Antithrombogenic characteristics of cathodically polarized copper prostheses
Authors: Gileadi E. , Stanczewski B. , Parmeggiani A. , Lucas T. , Ranganathan M. , Srinivasan S. , Sawyer P. N.
Published: December 2004

In previous studies from our laboratories, it was shown that metals and alloys which register negative potentials in blood vs. the normal hydrogen electrode (NHE) tend to be antithrombogenic, while those with positive potentials are invariably thrombogenic. Of the metals, only the corrodible ones fall in the first group and the noble ones in the second. Blood compatible metals appear to be essential for some types of medical devices. This paper deals with a novel approach of maintaining an implanted metallic prostheses at a negative potential. A copper vascular prostheses in a dog was made the cathode in a polarizing circuit, which in addition consists of a smal mercury battery, a resistor and an auxiliary electrode. Such experiments were conducted in three animals, and the potentials ranged from −60 to −160 mV/NHE. The three dogs were sacrificed after 6, 8, and 14 days and the tubes were examined. All tubes were free of thrombus deposits; minimal junctional thrombi were found. Two copper tubes with no polarizing circuit and registering positive potentials were occluded after 8 and 14 days, respectively. Histologic and electron‐microscopic studies of the thrombus deposits in tubes at spontaneous potentials and of the junctional thrombus deposits in the tube at negative potentials showed similar structures. The present experiments further confirm the view that the potential across the conductive material‐blood interface is a more basic parameter than the chemical nature of the surface in determining its blood‐compatible characteristic.
Effect of surface materials on shear‐induced hemolysis
Authors: Lampert Richard H. , Williams Michael C.
Published: December 2004

A rotating shearing device with interchangeable discs of various metals and plastics was used to induce hemolysis in human blood. Durations of shear ranged from 4 to 5000 sec, thereby defining the overall hemolysis kinetics for the test materials. Data are presented as ΔC (relative plasma hemoglobin increase) vs. time t, and fitted to the relation ΔC = Atβ. It is found that A = A(β) and β is correlated with the critical surface energy of the plastics. Based on this evidence and reports of plasma protein adsorption, a partial explanation is proposed for shear‐induced hemolysis in this low‐stress regime (under 500 dynes/cm2).
Reaction of oral mucous membranes to selected dental materials
Authors: Lilly G. E. , Cutcher J. L. , Jendresen M. D.
Published: December 2004

This study was undertaken to evaluate the comparative reaction of oral mucous membrances to topical exposure to selected liquid dental materials. Elven adult mongrel dogs and five different liquid dental materials (50% citric acid, mercury, 50% phosphoric acid, eugenol and methyl methacrylate) were selected for this study. Each material was applied bilaterally to a specific area of the ventral surface of the tongue for 5 min. Sites were examined at 30 min and visual observations recorded. Animals were sacrificed 24 hr after application. hematoxylin and eosin stained microsections were examined without knowledge of the material used. Citric acid and phosphoric acid were associated with the most severe response, characterized clinically by surface necrosis and histologically by a dense, diffuse, neutrophilic infiltrate. Eugenol was associated with erythema, and in some cases, ulcers, with a moderate diffuse inflammatory infiltrate, histologically. Methyl methacrylate resulted in immediate surface dehydration followed by mild erythema with mild local inflammatory infiltration. Mercury produced no observable clinical or microscopic tissue response. This is a simple method for evaluating acute mucous membrane toxicity which may be used for screening liquid dental materials.
Amalgamation reaction of tin, silver, and dental alloy (Ag3Sn)
Authors: Okabe Toru , Ling Fu‐Wen , Hochman Robert F.
Published: December 2004

The reactions between liquid mercury and high purity tin, silver, and silver‐tin dental alloy (Ag3Sn) were studied at 30°C. Polyhedral‐shaped crystals formed both on the tin and Ag3Sn specimens, while no crystalites were detected on the surface of the silver. The crystals on the tin Surface were identified as γ2 by x‐ray diffraction methods. Electron microprobe data revealed that the polyhedral crystals which formed on the Ag3Sn consisted only of the silver‐mercury compound which dissolved a small amount of tin (Ag 28.5, Hg 71.1, Sn 0.4 wt. %). The diffusion profile for the Hg‐Ag3Sn system demonstrated that silver atoms migrate much faster than tin atoms in Ag3Sn, both at the surface and in the area close to the mercury‐penetrated grain boundaries. It is clearly demonstrated that the bulk and grain‐boundary diffusion of silver is a major factor in the clinical setting reaction of dental amalgam.
Artifical skin. II. Pluronic F‐127 silver nitrate or silver lactate gel in the treatment of thermal burns
Authors: Nalbandian Robert M. , Henry Raymond L. , Wilks Harvey S.
Published: December 2004

Pluronic F‐127 was found to be an effective base for the bactriocidal agent silver nitrate or silver lactate following 18–22% surface area full thickness thermal burns. Some protection was afforded by Pluronic F‐127 alone, attesting to its biological activity as an artificial skin. The bacteriocidal agents, however, further enhanced the effectiveness of the dressing as an artificial skin. No inhibition of skin growth and repair was noted and the dressing was equally effective against Psuedomonas aeruginosa and Proteus mirabilis. Indication that natural defense mechanisms in addition to surface infection needs attention was also noted. Conclusion was reached that Pluronic F‐127 is an ideal base for bacteriocidal agents in the treatment of full thickness thermal wounds. In addition, the Pluronic F‐127 dressing with silver nitrate or silver lactate showed promise as an effective biological artificial skin against electrolyte imbalance, heat loss, and bacterial invasion.
Subacute toxicity testing of biomaterials using histopathologic evaluation of rabbit muscle tissue
Authors: Turner J. E. , Lawrence W. H. , Autian J.
Published: December 2004

A group of 12 materials was evaluated for tissue compatibility via a sequential histopathologic evaluation of the rabit muscle response to the implanted materials. Tissue samples were obtained daily for 7 days and weekly for 12 weeks to follow the time course of the response. Some cytotoxic samples revealed a rapid and marked response of relatively short duration, whereas others tended to produce a sustained or a long‐term, intermittent inflammatory and/or necrotic response. These effects also demonstrated the suitability of 7 days as a satisfactory time period for routine evaluation of rabbit muscle reaction to implanted materials. The histopathologic evaluation of the response was compared with a gross evaluation of the implant site and an independent test of the material by tissue culture (agar–overlay method).
Drug‐incorporated silicone discs as sustained release capsules. I. Chloroqine diphosphate
Authors: Fu J. C. , Kale A. K. , Moyer D. L.
Published: December 2004

Quantitative investigation of the rate of diffusion (in vitro) of chloroquine diphosphate, an antimalarial drug, from silicone rubber (Silastic) discs is reported here. The viscosity of the polymer is reduced to facilitate the formation of a more homogeneous drug‐polymer mixture from which the discs are made. The average quantity of drug released daily from these vulcanized silicone rubber discs is measured as a function of the amount of drug initially incorporated in the polymeric mass. Discs with 9 and 36 mg of chloroquine diphosphate incorporated continue to release drug in microgram quantities for a period of over four months. The presence of low viscosity silicone fluid (20 centistokes) in the discs was found to cause no significant alteration in the drug release rate. The effect of agitation of the fluid in which the discs are immersed is also investigated. Results from samples prepared from different batches of polymer showed comparable results, indicating the rather homogeneous nature of the polymer‐drug system. All samples showed high release rates during the first few days followed by much lower and more or less constant drug release on subsequent days over a period of months.

Concentrations of the drug in the eluant is determined spectrophotometrically by utilizing the 220‐ and 343‐mμ peaks of chloroquine diphosphate as well as spectrofluorometrically by measuring the percent fluorescence at 405 mμ (360‐mμ excitation).
Local reaction to polyurethane—a comparative study in the mouse, rat, and rabbit
Authors: Rigdon R. H.
Published: December 2004

The local reaction to polyurethane (Thurane foam‐rigid type) varies significantly in the subcutaneous tissue of the mouse, rat, and rabbit. Polymorphonuclear leucocytes concentrated at the periphery of the particles of polyurethane in the mouse in conspicuous numbers for as long as 550 days. In the rat leucocytes were infrequent and in the rabbit they were absent. The mechanism by which this variation occurs is unknown. It is suggested that it may be attributed to an electrical phenomena with variations in different hosts. There was an accumulation of pigment in the local inflammatory reaction apparently resulting from a degeneration of the polyurethane as well as degeneration of erythrocytes. The amount of this pigment varied significantly in the mouse, rat, and rabbit. Proliferation of large fibroblast‐like cells, apparently originating from adjacent striated muscle, occurred in the mouse but was absent in the rat and rabbit, another significant, variation in the reaction of the mouse to polyurethane when compared to that in the rat and rabbit.
Biological tolerance of ionogenic hydrophilic gels
Authors: Šprincl L. , Vacík J. , Kopeček J.
Published: December 2004

The long‐term biological tolerance of hydrophilic gels containing ionogenic groups was investigated on animals (rats and pigs). The basic polymeric skeletons of poly(glyco1 monomethacrylate) and poly (N‐ethyl methacrylamide) were modified by introducing acidic (carboxylic) and basic (tert‐amino) groups, or both groups at a time. Introduction of both groups at a time in the molar ratio yielded an electroneutral polymer of ionogenic character.

In all groups investigated here the implant was encapsulated by a fine capsule of collagen fibrous tissue; no signs of proliferation were observed. No calcification took place.

The second part of the work consisted in an investigation of the tolerance of heterogeneous poly(glyco1 monomethacrylate) gels containing ionogenic groups,basic, acidic, and ampholytic, with continuously changing porosity. The microporous polymers (50–60% water in the starting mixture) were healed‐in as compact gels by encapsulation with collagen fibrous tissue. The macroporous polymers (70% of water and more in the starting mixture) were encapsulated with a capsule of collagen fibrous tissue, from which newly formed capillaries,serous exudate and numerous cells penetrated into the implant. The more porous the material, the broader the zone of cellulization. In microporous polymers there was no calcification; in macroporous, calcification occurred in the margin of the implant or in its center. In contrast with other authors' findings,no effect of the chemical composition within the concentration range investigated upon the way of healing‐in or calcification could be observed; only the effect of physical factors was evident.
Thromboembolic sequelae to indwelling Silastic cannulas in sheep arteries
Authors: Andrews Edwin J. , Hughes Howard C.
Published: December 2004

In sheep, chronic arterial cannulation with Silastic has led to thrombus formation and to intimal fibroplasia of a type not previously reported. Concurrent infection resulted in septic embolization to the brains and eyes on the same side as the cannulated vessels. The histopathology is described in detail.
Use of organ cultures to evaluate biodegradation of polymer implant materials
Authors: Hegyeli Andrew F.
Published: December 2004

An in vitro organ culture method was developed for the study of biodegradation of surgical implant materials. This method gives valuable information in less than 24 hr in the case of rapidly biodegradable materials such as poly(lactic acids) and poly(alkyl 2‐cyanoacrylates). These data correlate well with the results of long‐term in‐vivo implantation studies. The organ culture technique can be used for the study of metabolism of polymers including the formation of volatile metabolites during biological degradation. Finally, histological and electron microscopic studies of the exposed organ slices can give indication of the formation of toxic metabolites during the biological degradation process.
Scanning electron microscopic study of surface changes on biodegradable sutures
Authors: Ruderman Robert J. , Bernstein Emil , Kairinen Eila , Hegyeli Andrew F.
Published: December 2004

Topographical changes which occur during the degradation of suture materials were studied by scanning electron microscopy. Potentially absorbable sutures were compared with those known to be absorbable. Loops of plain catgut, chromic catgut, polylactic acid, polyglycolic acid, polyester “A” and polyester “B” were implanted subcutaneously in rats for periods ranging from 2 to 14 weeks. They were removed and examined without further treatment. Specific and localized structural defects were observed to develop in the implant materials. In some cases the time required for development of these defects indicated that although they can be assumed to play a role in the ultimate dissolution of the material, these flaws are not necessarily responsible for the early loss of mechanical properties which have been observed by others. The implications of these observations for the development and evaluation of synthetic surgical repair materials are discussed.
Biomechanical evaluation of bone‐porous material interfaces
Authors: Nilles J. L. , Coletti J. M. , Wilson C.
Published: December 2004

An investigation was undertaken to correlate mechanical strengths of various bone‐porous material interfaces with the type and degree of osseous ingrowth. Intracortical cylinders of porous and nonporous metals, ceramics, polymers, and carbon were implanted into canine long bones and examined at 3, 6, and 12 weeks. Reflected and transmitted light microscopy were used to study bone ingrowth. Electron microprobe analysis and tetracycline labelling were used to characterize the degree of mineralization of the ingrowth. Shear strengths of bone‐porous material interfaces were measured on cylinders forced out in compression. Microhardness traverses were made across the interfaces. Readily identifiable bone was shown by histology in many porous specimens. Mineralization was found to various depths in all the porous specimens. The porous metals displayed the greatest interfacial shear strengths and hardnesses, with values from one‐ to two‐thirds that of cortical bone. Changes occurred in the ingrowth region, a bone‐metal composite, which suggest a reduction of elastic mismatch.
Estimation of the permeability of cellulosic membranes from solute dimensions and diffusivities
Authors: Farrell Peter C. , Babb Albert L.
Published: December 2004

Permeability data were obtained for commercial regenerated cellulose (Cuprophan PT–150) in isotonic saline at 37°C in a dual closed‐loop dialysis cell. Eighteen radioactively labeled monodisperse solutes of widely differing chemical and physical properties, and ranging in molecular weight from 60 (urea) to 1355 (vitamin B12), were evaluated and the permeabilities of these solutes have been successfully correlated with various solute characteristics.

Correlations were established between membrane mass transfer resistances (or effective membrane diffusivities) and:(1) characteristic molecular radii determined from both molal volume at normal boiling point (MVNBP) and hydrodynamic theory and (2) molecular diffusivities in saline. Membrane resistance data reported elsewhere for other cellulosic membranes were also found to correlate well with both MVNBP radii and liquid diffusivities.

The correlations for Cuprophan have the following form:

where Deff = effective membrane diffusivity (cm2/sec), r2 = MVNBP radius (Å), and Ds is saline diffusivity (cm2/sec). Similar correlations were established for other membranes. It should be feasible to use these and similar correlations to predict membrane permeabilities (for a given membrane) from known solute characteristics without resorting to laboratory measurements.

Membrane activation energies were also computed for eight solutes by measuring the variation in permeation rate through Cuprophan between 5 to 50°C. Unexpectedly, it was observed that the solute activation energies were not dominated by the activation energy of the membrane but revealed significant differences between solutes.
The effect of movement on the bonding of porous metal to bone
Authors: Cameron Hugh U. , Pilliar Robert M. , Macnab Ian
Published: December 2004

An attempt has been made to define the conditions with respect to movement under which porous metal will bond to bone. It has already been shown that bone will grow into the pore of porous Vitallium under static conditions and under conditions of micromovement, as when stressed by the pull of a tendon. An experiment is described in which porous Vitallium staples were inserted across an unstable osteotomy site. No bonding occurred indicating that bone ingrowth will not occur in the presence of movement of this order of magnitude.

The implication of this observation in the design of porous coated endoprostheses is that some form of initial mechanical fixation is required, and this fixation must remain rigid for four months to allow bone ingrowth.
The redistribution of mercury as observed in the phase transformations in amalgams
Authors: Reynolds C. L.
Published: December 2004

An investigation has been conducted to observe the effect of heat treatment on mercury loss and structural transitions in clinically used amalgams, as well as the individual phases composing dental amalgam. Pure Ag2Hg3 readily loses mercury and transforms to the β1 phase while the remaining amalgams are somewhat more stable. Since essentially no weight loss is observed in clinically used alloys, the mercury, liberated by the γ1 decomposition, reacts with excess Ag3Sn to form a self‐perpetuating reaction, explaining the increases in the β1 and γ2 phases in the Ag3Sn and “True Dentalloy” amalgams. That is, the mercury has redistributed itself within the amalgam.
Studies related to the fracture of partial dentures—fractography of cobalt‐chromium alloys
Authors: Bates J. F. , Scott J.
Published: December 2004

The fracture surfaces of specimens of a cobalt‐chromium alloy fractured in a conventional testing machine have been compared with similar specimens fractured by fatigue. Notched bar impact tests were also carried out and the surfaces of the specimens compared to those fractured in tension and by fatigue. Results show a brittle failure in all cases, although some change in the rate of crack propagation was evident in the fatigue specimens. Clinical evidence suggests that failure of partial dentures is due to bad castings, but some evidence is produced to show that fatigue cannot be eliminated as a cause of failure.
Some observations on the dielectric properties of cardiovascular implant materials
Authors: Milligan Herbert L. , Cleminshaw William T. , William Edmark K.
Published: December 2004

Bioelectric charge transfer between blood and the vascular wall appears to play a significant role in maintaining vascular homeostasis. Since the surface charge characteristics of the vessel wall are a function of the dielectric properties of the material, a study was made of the dielectric characteristics of various ion permeable materials and their relationship to electrokinetic phenomena and thrombogenicity. The dielectric properties of the ion permeable materials and of animal tissue were determined and found to be strikingly similar. Several models of electrodiffusion phenomena are reviewed with respect to dielectric properties. The electro‐osmotic characteristics of animal tissue and ion permeable materials were investigated, and it was found that animal tissue exhibited electro‐osmotic characteristics to a greater degree than did any other man‐made materials. The propensity of a material to electro‐osmose could not be predicted from the dielectric properties. In addition, no correlation could be found between thrombogenicity and dielectric properties. Dielectric relaxation phenomena is reviewed, and its possible contribution to nonthrombogenicity through the generation of a uniform, constant wall surface charge is presented. It is concluded that to mimic the ion content and mobility characteristics of animal tissue, as determined by dielectric properties, is insufficient to preclude thrombus formation.
An electrical resistance study of the precipitation reaction in a gold‐platinum‐iron alloy
Authors: Sims Julius R. , Blumenthal Robert N. , O'Brien William J.
Published: December 2004

The aging reaction of a 90 wt‐% gold, 10 wt‐% platinum alloy with nominal iron concentrations of 0.04, 0.08, and 0.16 wt‐% iron has been studied using electrical resistance measurements. The electrical resistance was measured as a function of temperature from 300 to 750°C. A decrease in electrical resistance was observed occurring at 350 to 450°C, when heating the solution treated and water quenched specimens containing iron. Subsequent heating and cooling curves follow the gold‐platinum standard. Isothermal electrical resistance measurements were made as a function of time. The data from the specimen containing a nominal iron concentration of 0.16 wt‐% iron was analyzed using the Johnson‐Mehl equation. The shape parameter n was found to vary as a function of aging temperature from n = 0.6 to n = 1. These results have been rationalized in terms of a model involving precipitation of FePt3 at dislocations (400°C) and FePt3 in the shape of a rod at 500°C.
Water and hydrogels
Authors: Jhon Mu Shik , Andrade J. D.
Published: December 2004

The apparent biocompatibility of many synthetic and natural aqueous gel materials has encouraged their study and testing for a wide variety of biomedical device applications. Many of the physical and in particular the interfacial properties of such gels are highly dependent on the organization of water within and on the surface of the hydrogel. Water is an important component of such gels, varying from about 30 to nearly 100 wt‐%, yet the role of water in the gels has been virtually ignored. This paper briefly reviews the nature of water structure in pure bulk water, in solutions, and at interfaces. Polywater or anomalous water is also briefly reviewed. Evidence is presented that the water in many hydrogel systems can exist in at least three different, structurally distinct forms. A hypothesis is presented which can be used to evaluate and study the nature of water in bulk hydrogels. Consideration is also given to the role of organized water at the hydrogel surface on the interfacial properties of such systems.
The in vivo and in vitro corrosion products of dental amalgams
Authors: Otani Hiroshi , Jesser William A. , Wilsdorf Heinz G. F.
Published: December 2004

The purpose of this investigation is to clarify the role of the component phases of dental amalgam in a corrosive environment and to analyze the corrosion products at various stages of formation predominantly by means of x‐ray diffraction methods and energy dispersive x‐ray spectroscopy. The study encompassed in vivo as well as in vitro experiments.

Sn, which came from only the γ2 phase, was found to be the sole or main constituent that contributes to the formation of the corrosion products. \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SnO} \cdot {\textstyle{1 \over 2}}{\rm H}_2 {\rm O} $\end{document} constituted the majority of the corrosion products formed in the early stages. SnO appeared in corrosion products more than 14 days old.
Adhesion of synthetic organic polymer on soft tissue. I. A fast setting polyurethane adhesive
Authors: Llewellyn‐Thomas E. , Wang P. Y. , Cannon J. S.
Published: December 2004

Conventional polyurethane prepolymers have been shown to adhere to living biological tissues. However, their setting is not sufficiently expedient to permit convenient applications in vivo. A prepolymer prepared from the highly reactive 6‐chloro‐2,4,5‐trifluoro‐1,3‐phenylene diisocyanate, castor oil, and a trace of pyridine has afforded an adhesive which sets in about 2 min in vivo. The fast setting has resulted in poor adhesion on biological tissue. The bonding has been improved by the inclusion of tolylene diisocyanate in the composition without affecting the fast curing rate of the prepolymer. The dispersion of the adhesive and its cohesion after solidification have been adjusted by other minor additives. Preliminary evaluation on animals indicates that this adhesive is most useful as a hemostatic coating in hepatic lacerations.
Diffusion of anti‐tumor drugs through membranes from hydrophilic methacrylate gels
Authors: Drobník J. , Špaček P. , Wichterle O.
Published: December 2004

Permeation parameters of four anti‐tumor drugs across membranes prepared from hydrophilic methacrylate gels were measured and compared with the permeation of NaCl. It was found that by increasing the ratio of butyl methacrylate (BMA) to hydroxyethyl methacrylate (HEMA), the rate of diffusion can be lowered to practically zero at 20% BMA. However, this decrease is different with various drugs due to the interaction of the drug with the gel. Differences by a factor of two were found in our set of drugs. Therefore, each new drug should be tested in this way. In addition a routine testing of dialysing devices by an NaCl solution is suggested as a method for detecting technological imperfections and calibrating the deviations from standard parameters. A chemical modification of the membrane is recommended as the best way for controlling the permeation rate.
Aeration of medical plastics
Authors: Tock Richard M. , Chen Yang Chin
Published: December 2004

Because the metabolic reaction that gives ethylene oxide its sterilizing qualities also takes place with human protein, it is imperative that any residual gas be removed before the sterilized material is used on the patient. This paper presents a method of estimating aeration time required following sterilization of polyvinyl chloride (PVC) to reduce toxic residues to a desired level. The method proposed involves calculation of the coefficient of diffusivity, and the use of a simplified diffusion equation to estimate aeration time.
Adhesion of red cells to foreign surfaces in the presence of flow
Authors: Mohandas N. , Hochmuth R. M. , Spaeth E. E.
Published: December 2004

A controlled surface shear stress produced by laminar flow in a rotating disk or parallel plate flow system has been used to study red cell adhesion to glass, siliconized glass, polythylene and Teflon. The results indicate that the shear stress at the surface must exceed a minimum critical value before cells will detach, and that this minimum critical shear stress increases as the time of cellsurface contact is increased. The results also indicate that the minimum critical shear stress for detachment from clean surfaces correlates with the critical surface tension of the material for the four materials studied. Studies with proteincoated surfaces indicate that albumin causes a moderate reduction in the strength of adhesion. The magnitude of the effect was found to be influenced significantly by the substratum material.
A combined metallurgical and histological study of tissue‐prosthesis interactions in orthopedic patients
Authors: Williams D. F. , Meachim G.
Published: December 2004

Metallurgical and histological examinations of implants and adjacent tissue removed from orthopedic patients have been performed in a series of 190 cases. The results have been correlated with clinical findings where possible. The two major factors to emerge from this study were that many stainless steel implants corrode in the body and that titanium implants release titanium into the local tissue, which may become discolored.

Severe cases of corrosion in stainless steel implants were attributed to faulty manufacturing technique and poor implant usage. This corrosion was frequently associated with crystal‐like “microplates” in the tissue and lead to clinically significant effects in some cases. Less severe cases of corrosion were almost invariably associated with interfaces between components. Susceptibility to this corrosion may be minimised by improvements in design and materials specification.

Titanium levels in excess of 2,000 ppm were found in the tissue in 3 cases out of 19 analysed, no specimen of a control series showing greater than 100 ppm. Histological sections showed accumulations of intracellular particles of exogenous origin. The evidence that such titanium release and particle accumulation causes clinically significant effects is only minimal but it is possible that systemic distribution of titanium and remote hypersensitivity effects could arise.
Tissue reaction to metallic wear and corrosion products in human patients
Authors: Winter George D.
Published: December 2004

Tissues from around surgical implants have been examined by optical microscopy and electron microscopy and by electron diffraction and x‐ray spectrographic techniques. The presence of small alloy fragments and carbides worn from cobalt‐chromium total joint replacements was confirmed. These foreign bodies had been phagocytosed by macrophages and there were no indications that the tissues were damaged by their presence. In 13 of 44 specimens there were granulomatous foci related apparently to the presence of numerous minute particles of unknown composition which had elicited vigorous macrophage reactions.

In tissues near stainless steel joints too there were particles of the naked alloy taken up by macrophages and again the fibrous tissue appeared unaffected.

Typically the tissues near to stainless steel implants are affected by cytosiderosis. It is deduced that the iron released by corrosion from stainless steel is processed by macrophages locally and there is formed a mixture of hydrated ferric oxides similar to hemosiderin. This may be looked upon as a detoxication mechanism. There is evidence that in some specimens the limit of tissue tolerance for stored iron has been exceeded locally with consequent pathological changes.

Another common deposit around stainless steel implants occurs in large plaques. It attracts giant cells and there is evidence that it is fibrotic and cytotoxic.
Transcutaneous implants: Reactions of the skin‐implant interface
Authors: Winter George D.
Published: December 2004

One method of providing an artificial limb for an amputee might be to attach the external prosthesis directly to the skeleton but a major problem is the behavior of the tissues at the point where the prosthesis penetrates the skin surface. Preliminary experiments have been carried out using small flexible implants in porcine skin to study the principles involved. It is confirmed that the epidermis grows down into the dermis around the nonporous materials and the implant‐skin junction is unstable and readily becomes infected. It was found that polytetrafluorethylene with pores of 10 μm diameter and hydron sponge with pores of 40 μm diameter became invaded by fibrous tissue and this appeared to prevent the migration of epidermis alongside the implants and a stable ring of epidermal tissue was formed near the skin surface. A review of other situations where epidermal migration is taking place suggests that epidermis is able to migrate through damaged collagenous tissue, possibly with the help of leucocytic enzymes, but that epidermal cell movement is halted when the epidermal sheet is confronted by heathly collagen bundles.
The role of porous polymeric materials in prosthesis attachment
Authors: Sauer Barry W. , Weinstein Allan M. , Klawitter Jerome J. , Hulbert Samuel F. , Leonard Ralph B. , Bagwell Joseph G.
Published: December 2004

Polymeric materials are becoming increasingly popular as prosthetic materials in orthopedic surgery. One of these materials, polyethylene, is capable of being fabricated in a porous form suitable for tissue ingrowth. Porous polyethylene appears to be well suited for prosthesis attachment when bonded to its solid form of other prosthetic materials. Extensive bone growth into porous cylindrical specimens implanted in the canine femur has occurred as early as four weeks. Ingrown tissues appear normal and there is minimal inflammatory response. Mechanical strength of the porous material, though not as great as that of the solid material, does appear to be sufficient for certain orthopedic applications. Current research is directed toward determining interfacial strengths and the mechanical properties of the porous polyethylene‐bone composite.
Study of early sheath development using static nongliding implants
Authors: Hunter James M. , Steindel Carl , Salisbury Roger , Hughes David
Published: December 2004

Clinical studies will permit only small sections of tendon sheaths to be removed for biopsy at restricted levels as the sheaths were to be used for tendon grafting. In active gliding programs, biopsy has been limited to small sheath sections in immediate relation to the distal or proximal anastomosis where gliding motion may be induced or minimal. In the passive gliding programs, biopsy has been limited to the most proximal segments where considerable folding of the sheath occurs or cul‐de‐sac buckling of the implant may produce irritation.

As these were the only practical clinical sources of sheath sections for biopsy and study, the authors felt that a comparison study of sheath development in animals would broaden our understanding in humans. With this objective in mind, three canine laboratory studies were carried out where, for pure purposes of investigation, entire sheath sections were removed at designated time intervals for study.

The flexible implants were well accepted, affording the opportunity to observe development of early sheaths in a controlled connective tissue environment, free from the stress of joint motion.

The semi‐rigid implants showed equal acceptance in side‐by‐side tissue level of the same dog as the flexible implant. This influenced changes in artificial tendon development from extrusion to the more exacting mold fabrication. It seemed evident that the degree of increase in stiffness of the new artificial tendons to gain a superior surface for gliding and increased strength would not change tissue acceptance providing flexibility was maintained.

The cellular response in this study did not seem to represent a foreign body phenomena but an orderly acceptance of the soft tissue environment to the smooth surface of the inert implant.

It is concluded that this study confirmed in animals the clinical findings of Mayer, Bunnell, Milgram, and Carroll.

The consistent orderly development of the new sheaths formed in response to the static implants is impressive. The authors believe the appearance of these histologic sections are likely correlations with the development of new sheaths around the Hunter Tendon Prosthesis during the three–four week postoperative period when the hand is resting in a functional dressing.
Sheath formation in response to limited active gliding implants (animals)
Authors: Hunter James M. , Subin David , Minkow Frederick , Konikoff John
Published: December 2004

Experiments were conducted to further the understanding of tendon reconstructive surgery.

A series of 20 dogs was used for replacement of the forepaw extensor carpi radialis tendon (a single tendon only is present in the dog) with active gliding tendon implants. The implants were attached distally and proximally so that new tendon prosthetic designs could be studied as well as new sheath development under gliding conditions.

The results, recorded in this paper, show that a “gliding implant” can convert a nonspecific bed of connective tissue or scar into a specific living envelope comparable to a tendon sheath system. This system has been shown to be capable of lubricating and supporting a gliding artificial implant while augmenting normal tendon function. Degrees of active and passive gliding can take place for indefinite periods, providing the mechanical and dynamic capabilities of the new system are understood and controlled. The mature sheath will show a predictable physiologic response to unfavorable stimuli.

Further evidence that the new gliding system functions as a physiologic sheath is borne out by the fact that the implant can be replaced in Stage II by a long free tendon graft. The graft is apparently supported in part by fluid nutrition and filmy adhesions between the distal and proximal anastomosis.
Physical characteristics of setting of acrylic bone cements
Authors: Lautenschlager E. P. , Moore B. K. , Schoenfeld C. M.
Published: December 2004

An investigation was conducted to determine the general physical characteristics of self‐curing acrylic resin systems in terms of their potential utilization in total hip arthroplasty.

Exothermic temperature, working and setting times were monitored with thermocouples placed in acrylic masses insulated via a Teflon mold. Mechanical strengths were run in an Instron testing machine. The same trends were noted in all systems studied.

As thickness or mass increased, the maximum temperature and the setting time increased. As the powder to liquid ratio increased (thereby relatively less liquid), the maximum temperature, set times and dough times decreased, while the working time was essentially unaffected. As the ambient temperature decreased, the maximum temperature decreased while the dough, working and setting times increased.

The mechanical strengths of the systems cured at one atmosphere are low compared to high temperature and pressure curing. Flowability of the materials decreases quickly as final set time is approached.

Although trends are similar in many self‐curing acylic systems minors shifts in complex proprietary compositions can produce a wide span or working and setting times. Because the surgical team controls such parameters as the mass employed, the amount of liquid introduced, and the ambient temperature it is important that they continuously re‐evaluate their handling procedures particularly if new acrylic cements would be introduced.
The potential for poly‐α‐amino acids as biomaterials
Authors: Anderson J. M. , Gibbons D. F. , Martin R. L. , Hiltner A. , Woods R.
Published: December 2004

Poly‐α‐amino acids have been investigated for possible use in a wide variety of biomedical applications. These range from dialysis membranes to artificial skin substitutes to degradable sutures. The large number of available α‐amino acids potentially provides an extremely large number of poly‐α‐amino acids. The majority of materials investigated to date are copolymers composed of two components, one of which usually provides the desired property for the given application.

This paper deals with the further examination of a series of γ‐benzyl‐L‐glutamate‐L‐leucine copolymers. Evidence is provided on the effect of these copolymers on the biological environment as determined by implantation in rats up to 200 days. In vitro tests were also performed and the effect of these tests on the stress‐strain properties of one of the copolymers is presented.

Preliminary evidence on biodegradable copolymer films is also included. These materials have free γ‐carboxyl groups on the glutamate components.
Pyrolytic biocarbon materials
Authors: Olcott Eugene L.
Published: December 2004

Carbon is one of the most attractive biomaterials in many respects. Recent developments in high strength carbon materials for the aerospace industry have led to new forms of carbon which have good structural properties. Several of these, based on a vapor‐de‐posited pyrolytic graphite matrix, are described. A needle‐like silicon‐carbide strengthened pyrolytic graphite has been implanted in rabbits and chimpanzees with encouraging results. Applications are being sought.
Multiphase MP35N alloy for medical implants
Authors: Younkin C. N.
Published: December 2004

The biomaterials engineer of today has an extremely limited choice of approved metallic implant alloys with which to conduct his studies. There is essentially no incentive for larger companies to initiate basic research in the biomaterials field. New alloys which would have the best chance of developing as biomaterials would be “spin‐off” alloys from somewhat related industries and currently in production. MP35N is just such a spin‐off alloy with a background of years of in‐vitro testing and use in corrosive environments. When compared to the desired implant material requirements, the material properties required of MP35N for present applications readily indicate its potential use as a biomaterial.

It is a castable alloy which exhibits good as‐cast ductility. In the wrought condition, yield strength levels from 60,000 to over 310,000 psi are possible with accompanying good ductility characteristics. Excellent stress corrosion cracking resistance and improved fatigue strength over present cast implant material are also characteristic of MP35N. Results, to date, from in‐vivo tests indicate tissue compatibility of MP35N at least comparable to HS‐21 (Vitallium).

Possible medical applications for MP35N would include hip and knee joints, bone plates, heart pacer electrodes, suture wire and clips, and Endosseous blade implants.