bluuebunny/crossref_metadata_2025 huggingface dataset:
Porous acrylic cement
Authors: Rijke A. M. , Rieger M. R. , McLaughlin R. E. , McCoy S.
Published: December 2004

The use of acrylic bone cement has a number of shortcomings, viz., high curing temperatures that can cause thermal necrosis, release of toxic monomer, and a less than perfect cement‐to‐bone bond. However, by modifying the cement composition through the addition of a soluble, nontoxic filler such as sucrose or tricalcium phosphate which does not impair the workability of the material during surgery, a significant improvement in the performance of the cement can be achieved.

Because the filler replaces part of the acrylic components, less heat is generated during curing while the filler itself acts as a heat sink. Also, less monomer, proportional to the amount replaced by the filler, diffuses from the implant site.

Upon elution of the filler, a porous cement will be obtained provided that a critical minimum percentage loading is exceeded so that the filler crystals will make physical contact with each other. The value of this percentage depends on both crystal modification and size. In the 125–175 μm sucrose crystal size range, the critical minimum percentage lies in the range of 20–28 wt % loading. Above 30%, the interconnecting pore size increases sharply to a value which allows good tissue ingrowth into the pores.

The introduction of filler and pores causes a drop in strength, but the diametral tensile strength of modified cement containing up to 40% pores and sucrose lies between .7 and 1.5 kg/mm2, respectively, which is still in the same range as that of bone.
Human platelet and fluorochemical interaction
Authors: Kmetzo James J. , Peter Stein T. , Wallace Herbert W.
Published: December 2004

Since the fluorochemicals have become of interest for the development of artificial red blood cells, oxygenators, liquid breathing, and as a radiographic contrast medium, their interaction with biological substances is of importance. Fresh human platelets were placed in contact with four different fluorochemicals for a period of 50 min. The platelet function as measured by aggregation was determined before and after fluorochemical contact. Appropriate controls were also evaluated. No significant differences were found between the aggregation of platelets contacted with fluorochemicals and the aggregation of platelets from the same donor unexposed to fluorochemicals.
Clinical influences on bone cement monomer release
Authors: Bayne Stephen C. , Lautenschlager Eugene P. , Greener Evan H. , Meyer Paul R.
Published: December 2004

Monomer losses for two self‐curing acrylic cements were similar via laboratory serial weighing experiments. Both the P/L ratio and mixing duration substantially influenced subsequent monomer losses, but ambient temperature variation during mixing had little effect. Greater losses were encountered during the mixing and setting intervals than during the molding interval. Patient potential exposure to monomer occurs during the molding and setting intervals; therefore, handling procedures reducing losses in these intervals are important to the surgeon.

The least monomer loss during both molding and setting occurred at the manufacturers' recommended P/L ratio, which strongly indicated the need to mix all contents supplied. Mixing loss increased with amount of spatulation. However, once the mass was well mixed (about 300 steady spatulations), no further decreases in the molding and setting interval losses were promoted by overmixing. Because of the lower monomer loss rate during the molding interval, postponed cement insertion may not be warranted in light of losing mechanical locking efficiency. The actual ramifications of a threefold reduction in potential patient exposure (3.5 down to 1.2 wt % of total monomer) via modified handling techniques have not yet been clinically evaluated.
Histologic response to porous PMMA implant materials
Authors: Nathanson Dan , Gettleman Lawrence , Schnitman Paul , Shklar Gerald
Published: December 2004

Poly(methyl methacrylate) as used in polymer replica tooth implants was fabricated into 6 × 6 mm cylindrical specimens and cured in either an air oven, pressure pot, autoclave, or microwave oven. Polymer porosity was achieved by means of either (1) intrinsic foaming agents, or (2) compacting different sizes of large beads with a minimum of monomer, with dense PMMA used as a control. Specimens were then implanted in the long bones of baboons.

Histology of thin‐sectioned and ground specimens from the sacrificed animals revealed complete tissue ingrowth into implanted material made of medium and large PMMA beads, very superficial ingrowth into material containing foaming agents and anorganic bone chips, and no ingrowth into dense PMMA implants.

None of the implants were rejected or caused chronic inflammation. The effect on histologic response of the different curing methods could not be distinguished.
The biocompatibility of materials for internal fixation of fractures
Authors: Brown Stanley A. , Mayor Michael B.
Published: December 2004

Surgically produced fractures of rabbit tibiae were internally stabilized with in tramedullary rods of stainless steel (316LVM), titanium (6A1,4V), polyacetal (Delrin), and polyamide (Nylon 101). Periodic radiographs were taken until sacrifice at 16 weeks after fracture. Structural properties of the tibiae were determined in torsion with the rods in situ, and then the tissue was prepared for histology or microradiography.

The results demonstrated that fracture remodeling was adversely affected by the metal rods. New bone was seen to have formed over the ends of the metal rods, and cortical bone resorption was observed in the fracture region, suggestive of transfer of mechanical stress to the rods, resulting in stress shielding of the diaphysis. Negligible osseous response to the polymeric rods was observed; fracture callus remodeling was extensive. The torsional test results demonstrated that fractures with polymeric rods were significantly stronger and tougher than those with metallic rods. With the exception of titanium, the strength of healed fractures was inversely related to the elastic moduli of the implant materials.
Neurocranial reconstruction using an elastomer‐coated cloth mesh and bone grafting
Authors: Leake D. , Habal M. , Maniscalco J. , Freeman S.
Published: December 2004

The purpose of this report is to present our 5‐year experience in reconstructing large bony defects in the cranial vault of 16 patients. The method employs an alloplastic implant device made of elastomer‐coated cloth mesh, used in conjunction with bone grafting [D. L. Leake and M. Habal, J. Biomed. Mater. Res., 10, 555 (1976)]. The cranial defects ranged in size from 6 × 6 cm to 15 × 17 cm. The defects were in the frontal, temporoparietal, and occipital regions. Particularly challenging was the frontal‐orbital region involving the superciliary ridges. The alloplastic implant provides controlled contour of the bone graft material while providing strength and stability during healing. The implant has adequate but not complete rigidity, allowing adaptability in the operating room. The elastomer used is a polyetherurethane. Any biocompatible cloth mesh can be used, but Dacron [poly(ethylene terephthalate)] was chosen because of its extensive implant history.

Contrasted with reconstruction using only bone, where as many as half of the cases had uneveness and were found to be aesthetically unsatisfactory, the technique described here has resulted in aesthetically excellent results and an intact neurocranium in the 16 patients studied thus far.
Stress relaxation of dental amalgam alloys
Authors: Huget Eugene F. , De Simon Laszlo B. , Hertert Robert S.
Published: December 2004

Short‐term stress relaxation of four dental amalgam alloys was studied. Test materials included two conventional lathe‐cut restoratives, a spherical alloy, and a dispersed phase product. Specimens were 24‐hr‐old 4 × 8‐mm cylinders. The specimens were compressed and held at constant strain on development of a stress (S0) of 28 MN/m2. Subsequent stress relaxation (Dt) was recorded for 60 sec. Data were obtained at eight nominal temperatures between 0 and 55°C.

Over the experimental temperature range, fractional stress losses at 60 sec (Dt/S0/60) for specimens made from lathe‐cut alloys increased from 10% to 58%. The spherical material and the dispersed phase alloy showed fractional stress losses (Dt/S0/60) ranging from 9% to 47% and 9% to 31%, respectively.

It would appear that particle morphology and alloy composition affect stress‐relaxation behavior of dental amalgam. Stress decay patterns enhance significantly the mechanical characterization of amalgam alloys.
Surface texture and strength of vitreous carbon–poly(methyl methacrylate) dental implant materials
Authors: Hodosh Milton , Gettleman Lawrence , Shklar Gerald , Povar Morris
Published: December 2004

A study has been carried out on the surface texture and the strength of several dental implant materials composed of vitreous carbon microballoons (6, 24, and 48 wt %) and poly(methyl methacrylate). Two sizes of microballoons were used—particle size less than 100 μm and particle size greater than 100 μm. Square wafers of the materials (10 × 10 × 1 mm) were studied with the surface sandblasted in half of the specimens. SEM studies revealed a rough porous surface with scattered moderately sized deep cavities in the 6% and 24% specimens with an increase in the number of cavities in the 24% specimens. The 48% specimens revealed a rough, porous surface composed of large shallow craters.

Prepared specimens of the materials, processed by a gas‐fired air oven and by a microwave oven, were tested for compressive strength and tensile strength using an Instron Universal Testing Machine. Compressive strengths of the various mixtures were similar, but mixtures using VC particle size over 100 μm demonstrated somewhat reduced compressive strength. Tensile strengths of the mixtures decreased significantly as the amount of VC increased, with a 20% reduction at 24 wt % and a 45% reduction at 48 wt %.
Adsorption of plasma proteins on hydrophobic surfaces. II. Fibrinogen and fibrinogen‐containing protein mixtures
Authors: Bagnall Robert David
Published: December 2004

The adsorption of fibrinogen from single solution and from mixed solution with albumin and γ‐globulin has been followed at the air–buffer, isooctane–buffer, and methylene iodide–buffer interfaces by the pendant drop technique. Fibrinogen is shown to form substantial coherent films on isooctane and methylene iodide, suggesting considerable unfolding and lateral association. From this, a novel hypothesis has been proposed to account for the dominance of fibrinogen adsorption from mixed solutions on certain hydrophobic surfaces, in which the spreading pressure of rapidly unfolding fibrinogen molecules is sufficient to desorb other plasma proteins.
Can a small blood vessel prosthesis be derived from heterologous foreign body reactive tissue?
Authors: Schoen F. J. , Normann S. J. , Brunswick R. A. , Diacoff G. R.
Published: December 2004

This study investigated as a small diameter vascular replacement the tissue formed adjacent to an implanted cylindrical foreign body, heterologously transplanted. Grafts of 4 mm i.d. were grown in rabbits and transplanted to dogs as segmental carotid and femoral artery replacements. These maintained 50% patency after 3 weeks. Variables in the further development of this concept are discussed.
Thermally induced time dependence of mechanical properties in biomedical grade polyurethanes
Authors: Wilkes G. L. , Dziemianowicz T. S. , Ophir Z. H. , Artz E. , Wildnauer R.
Published: December 2004

The time dependence of the mechanical properties of segmented urethanes as well as urethane‐urea systems were monitored after the materials had been given a short thermal treatment followed by rapid cooling. Both linear and crosslinked materials were studied but the major focus was on many of the common biomedical grade urethanes. As had been noted in earlier studies on nonmedical segmented urethanes from this laboratory, many of the biomedical grade materials also showed time‐dependent changes in mechanical properties that can be directly related to time‐dependent changes in the degree of domain structure (microphase separation) that may occur in these segmented copolymers. Interestingly, those systems possessing significant amounts of urea linkage show little or no significant time‐dependent changes in structure or properties following thermal treatment. The effect of chemical crosslinking can also influence the domain formation process and its thermal stability. The ramifications of these time dependent effects may have bearing on the biomaterial applications of segmented urethane polymers.
Thrombus formation and microaggregate removal during extracorporeal membrane oxygenation
Authors: Guidoin R. G. , Kenedi R. M. , Trudell L. , Galleti P. , Blais P.
Published: December 2004

Contemporary microporous membrane oxygenators have adequate gas transfer capacity and even prolonged oxygenation is relatively atraumatic to the blood elements. However, even with adequate heparinization, thrombus formation still takes place, albeit to a lesser degree than in direct blood‐gas contact devices. In this work, scanning electron microscopy of the dissected devices in the extracorporeal circuit was performed on devices used during four aorto‐coronary bypasses and two cardiac valve replacements. Membrane surfaces remained free of major deposits although thrombotic material could still be observed in parts of the oxygenators and the filters. Blood filtration from the cardiotomy reservoir may be more critical as it removes surgical debris and cells injured by suction which appear to enhance thrombus formation within the oxygenator. The return line arterial filter appears more useful as a bubble remover; its value appears much diminished as microemboli do not leave the device in large quantities.
Adsorption of human serum albumin to amberlite XAD‐7 resin
Authors: Ton H. Y. , Hughes R. D. , Silk D. B. A. , Williams Roger
Published: December 2004

In the present study the conditions leading to tight binding of human serum albumin to the Amberlite XAD‐7 resin without the use of chemical coupling agents have been defined. Optimal binding (10.97 mm/kg dry XAD‐7) was achieved at pH 5.0 and adsorption conformed to a Langmuir isotherm. Theoretical analysis of the data suggest adsorption of a monolayer of albumin which is suported by the absence of visual surface coating on scanning electron micrographs. Binding of human serum albumin was reduced when two chemical coupling agents, glutaraldehyde and carbodiimide were included in the human serum albumin solution, the elution of adsorbed HSA from the resins under severe flow conditions was reduced, and the amount eluted was minimal in all instances.
Role of catheter surface morphology on intravascular thrombosis of plastic catheters
Authors: Libsack Craig V. , Kollmeyer Kenneth R.
Published: December 2004

The role of catheter surface roughness in initiation and propagation of intravascular catheter thrombosis was studied in dogs, utilizing the scanning electron microscope. Catheters were inserted in major arteries and veins for 200 min and the animals then sacrificed. Catheter segments, both with and without associated thrombi, were scrutinized with the scanning electron microscope. No correlation was found between catheter surface roughness and thrombus formation, suggesting that the inherent chemical characteristics of the catheter is most important in the initiation of intravascular catheter thrombus formation.
Sustained drug delivery systems. I. The permeability of poly(ϵ‐caprolactone), poly(DL‐lactic acid), and their copolymers
Authors: Pitt Colin G. , Jeffcoat A. Robert , Zweidinger Ruth A. , Schindler Anton
Published: December 2004

The maximum steady state flux, diffusion coefficients, and solubilities of five contraceptive steroids in homopolymers and copolymers of ϵ‐caprolactone and DL‐lactic acid were determined. The permeabilities of polymers of ϵ‐caprolactone were comparable to silicone rubber and, by inference, are suitable for the construction of drug delivery devices. Poly(DL‐lactic acid) was 104 times less permeable, although its permeability was significantly enhanced by additives.
In vitro blood compatibility of glycosaminoglycan‐precipitated collagens
Authors: Silver F. H. , Yannas I. V. , Salzman E. W.
Published: December 2004

Precipitation of bovine hide collagen by chondroitin 6‐sulfate at low pH and subsequent crosslinking enhances the blood compatibility of native collagen. Both dehydrothermal crosslinking and complexation with chondroitin 6‐sulfate separately decrease the platelet‐aggregating activity of collagen. Crosslinking also decreases the number of free acidic and free basic residues on collagen, which suggests that crosslinking involves these residues in condensation reactions with formation of intrachain and interchain synthetic peptide bonds. Clotting times for collagen precipitated with chondroitin 6‐sulfate indicate the this surface does not activate or interfere with coagulation via either the intrinsic or extrinsic pathway. These findings support further consideration of collagen modified by chondroitin 6‐sulfate as a blood compatible material.
Surface ultrastructure and pressure dynamics of tracheal tube cuffs
Authors: Wu Wen‐Hsien , Arteaga Margaret , Mlodozeniec Arthur R. , Poppers Paul J.
Published: December 2004

The outer and inner surfaces of six commercial endotracheal tube cuffs were characterized using scanning electron microscopy (SEM) and energy dispersive x‐ray analysis. Lateral tracheal wall pressure (LWP) was measured at various steps of cuff inflation using a mock‐trachea system. The surface characteristics of the cuffs were found to vary widely. The surface of the Lanz cuff was relatively smooth but showed a regular array of circular depressions 0.8 μm in diameter. Uniform spheres also 0.8 μm in diameter were distributed through the thickness of the membrane. The American Hi‐Lo cuff surface was also relatively smooth but was covered widely with flakes of material which x‐ray showed to be a clay‐like substance containing aluminum, silica, and potassium. The Harlake cuff was covered widely with roughly spherical, 5‐μm‐diam particles, probably starch granules. The membrane itself was smooth even at 3,000X. The Foregger cuff had a rough surface and was covered with the same clay‐like particles seen on the American cuff. The inner surface with irregular, uneven areas were surrounded by fissures. The Rusch Armored tube cuff was completely covered by a continuous 2‐μm‐thick chlorinated coating. The surface was highly convoluted and irregular. The three cuff membranes showing relatively smooth surfaces, Lanz, American and Harlake, also produced relatively low LWP at various points of cuff inflation. While we have no data to indicate that cuff surface smoothness correlates with tracheal morbidity, it would seem prudent to select cuffs that produce low LWP's with smooth surfaces for clinical use.
Design of an artificial skin. II. Control of chemical composition
Authors: Yannas I. V. , Burke J. F. , Gordon P. L. , Huang C. , Rubenstein R. H.
Published: December 2004

Detailed methodology is described for the reproducible preparation of collagen‐glycosaminoglycan (GAG) membranes with known chemical composition. These membranes have been used to cover satisfactorily large experimental full‐thickness skin wounds in guinea pigs over the past few years. Such membranes have effectively protected these wounds from infection and fluid loss for over 25 days without rejection and without requiring change or other invasive manipulation. When appropriately designed for the purpose, the membranes have also strongly retarded wound contraction and have become replaced by newly synthesized, stable connective tissue. In our work, purified, fully native collagen from two mammalian sources is precipitated from acid dispersion by addition of chondroitin 6‐sulfate. The relative amount of GAG in the coprecipitate varies with the amount of GAG added and with the pH. Since coprecipitated GAG is generally eluted from collagen fibers by physiological fluids, control of the chemical composition of membranes is arrived at by crosslinking the collagen‐GAG ionic complex with glutaraldehyde, or, alternately, by use of high‐temperature vacuum dehydration. Appropriate use of the crosslinking treatment allows separate study of changes in membrane composition due to elution of GAG by extracellular fluid in animal studies from changes in composition due to enzymatic degradation of the grafted or implanted membrane in these studies. Exhaustive in vitro elution studies extending up to 20 days showed that these crosslinking treatments insolubilize in an apparently permanent manner a fraction of the ionically complexed GAG, although it could not be directly confirmed that glutaraldehyde treatment covalently crosslinks GAG to collagen. By contrast, the available evidence suggests strongly that high‐temperature vacuum dehydration leads to formation of chemical bonds between collagen and GAG. Procedures are described for control of insolubilized and “free” GAG in these membranes as well as for control of the molecular weight between crosslinks (Mc). The insolubilized GAG can be controlled in the range 0.5–10 wt. % while “free” GAG can be independently controlled up to at least 25 wt. %; Mc can be controlled in the range 2500–40,000. Studies by infrared spectroscopy have shown that treatment of collagen‐GAG membranes by glutaraldehyde or under high‐temperature vacuum does not alter the configuration of the collagen triple helix in the membranes. Neither do these treatments modify the native banding pattern of collagen as viewed by electron microscopy. Collagen‐GAG membranes appear to be useful as chemically well‐characterized, solid macromolecular probes of biomaterial‐tissue interactions.
Fracture toughness concept applied to methyl methacrylate
Authors: Sih G. C. , Berman A. T.
Published: December 2004

Polymethyl methacrylate bone cement is tested at the Institute of Fracture and Solid Mechanics Laboratory, Lehigh University. Standard tensile coupon and compact tension specimens are molded under varying conditions of temperature and pressure. Test results are obtained for the strength and toughness of bone cement involved in total hip replacement operations.
Radioactive tracer technique for monitoring of microleakage: An interim report
Authors: Crisp Stephen , Wilson Alan D.
Published: December 2004

A diffusion apparatus for the measurement and monitoring of microleakage is described. Radioactive ions are used to measure the diffusion across a section of a filled tooth. A study was made of the sealing ability of some amalgams and a composite resin filling material.
Measurement of the activation time for platelet adhesion to foreign surfaces
Authors: Predecki Paul , Life L. , Russell P. A. , Newman M. M.
Published: December 2004

An apparatus is described which permitted a perfusant (lactated Ringer's solution) to be passed through a porous sample in a pulsatile manner with a square wave pressure profile. The “on” time, “off” time, number of cycles and pressure amplitude were separately controllable. Using this apparatus and immersing the sample in stirred, heparinized, human blood, there was a certain “off” time below which platelet adhesion to the sample abruptly ceased. The values of this “off” time, termed the activation time ta for platelet adhesion were ∼0.5 sec for 0.2 μm pore size cellulose diacetate/nitrate (millipore filter) and ˜0.3 sec for 0.2 μm polycarbonate (nuclepore filter). After a single cycle with a 5 sec “off” time, adhered platelets on both these materials showed pseudopodia, varying degrees of spreading and membrane perforation.
Methyl methacrylate concentrations in tissues adjacent to bone cement
Authors: Petty William
Published: December 2004

The amount of methyl methacrylate monomer present in bone tissue immediately adjacent to implanted bone cement that has polymerized in vivo has been determined. Poly(methyl methacrylate) was implanted into the distal femoral condyle of the dog and allowed to polymerize. At various times following polymerization, samples were removed and sections adjacent to the cement were cut and subjected to homogenization followed by liquid gas chromatographic determination of the amount of methyl methacrylate monomer present. The highest concentration of methyl methacrylate monomer present in bone tissue was 0.140% in the 1000 μm of bone tissue adjacent to bone cement immediately after polymerization of the cement. The concentration was very similar (0.137%) 1 hr after cement polymerization, but dropped off rapidly following that with no free methyl methacrylate monomer present in bone tissue adjacent to cement after 4 hr following cement polymerization.
Interaction of human α‐thrombin with artificial surfaces and reactivity of adsorbed α‐thrombin
Authors: Chuang H. Y. K. , Mohammad S. F. , Sharma N. C. , Mason R. G.
Published: December 2004

Thrombin adsorbed onto Cuprophane or poly(vinyl chloride) (PVC) was shown to be inactive with respect to amidase activity. Desorbed thrombin from these two artificial surfaces showed only low amidase activity. However, in the presence of albumin, the surface‐bound thrombin appeared to exhibit increased amidase activity. This apparent activity may be due to the action of thrombin displaced from the surfaces by albumin. Thrombin bound to Cuprophane or PVC was shown to be capable of reacting with antithrombin III (AT III) only in the presence of heparin. On the other hand, AT III bound to Cuprophane or PVC was unable to react with thrombin in either the absence or presence of heparin. Fibrin formation on or at surfaces was demonstrated by phase contrast microscopy when Cuprophane or PVC pretreated with thrombin and carefully rinsed was incubated in a fibrinogen solution. This fibrin formation is time dependent and likely is the result of direct interaction of adsorbed thrombin with fibrinogen in solution. Glass, Cuprophane, and PVC pretreated with thrombin were shown to attract more platelets than respective untreated surfaces. The enhancing effect of adsorbed thrombin on platelet adhesion was similar to the enhancing effect of adsorbed fibrinogen. Thrombin adsorbed onto PVC and crosslinked by glutaraldehyde treatment was shown to be antigenically active with a 125I‐labeled monospecific antithrombin IgG produced in rabbits. No other plasma proteins adsorbed singly or from plasma or serum onto PVC reacted significantly with the antithrombin IgG preparation. The possible significance of these observations is discussed.
Design of an artificial skin. Part III. Control of pore structure
Authors: Dagalakis N. , Flink J. , Stasikelis P. , Burke J. F. , Yannas I. V.
Published: December 2004

Several methods are compared for preparing collagen‐glycosaminoglycan (GAG) membranes of high or low porosity. Collagen‐GAG membranes have been used to cover satisfactorily large experimental full‐thickness skin wounds in guinea pigs over the past few years. Methods studies as means for controlling pore size are confined to purely physical processes which do not require use of additives or chemical reagents to form the porous membrane. We find that membranes, initially swollen in distilled water or saline, shrink linearly to no less than 94% of original dimension after freeze drying; to 75% after critical point drying (from CO2, following water‐ethanol exchange); and to 41% of original dimension following air drying from the swollen state. Scanning electron microscopic study of the pore structure resulting from each drying procedure confirms our major conclusion: A carefully designed freeze drying process, two variants of which are described in detail, yields membranes with the highest mean pore size, as measured by quantitative stereological procedures. Critical point drying gave significantly more shrinkage and a lower mean pore size than either one of the two freeze drying procedures used.
Factors affecting surgical alloy/bone cement interface adhesion
Authors: Keller John C. , Lautenschlager Eugene P. , Marshall Grayson W. , Meyer Paul R.
Published: December 2004

Interfaces were formed between acrylic bone cement and three commonly used surgical alloys (316L SS, CoCrMo, and Ti6A14V), in an attempt to further define cementation parameters of acrylic bone cement for use in orthopaedic surgery. Metal/cement interfaces were made at three distinct times during the setting cycle of the cement and were cured for 1 hr, 1 day, and 1 week. The metals were prepared with roughly polished or finely polished prepassivated surfaces. Tensile bond strengths and residual cement on metal coverage data indicated that, for each metal system, interfaces created prior to and at the onset of the dough stage formed superior interfaces for implanation compared to those formed late in the dough stage. Furthermore, electropolishing plus prepassivation offered a more efficient bonding surface than mechanical polishing.
The use of 99Tc‐pyrophosphate for imaging and measuring of calcification caused by implanted polymers
Authors: Cífková I. , Šprincl L.
Published: December 2004

Pyrophosphate labeled with 99Tc was evaluated as an indicator of the calcification which occurs after implantation of polymeric materials in rats. Poly(2‐hydroxyethyl methacrylate), both porous and homogeneous, had been implanted. 99Tc pyrophosphate was applied intravenously to rats in intervals from 14 days to 15 months. Scintigraphy, x‐ray examination, and histology were carried out. The ratio of specific activity in the capsule around the implant to specific activity in the reference tissue was determined. The cumulation of activity was parallel with the development of calcification as revealed by histology. The method can be used not only in the screening test of new polymeric materials, but also in a quantitative determination of the degree of calcification in general.
The use of polyamide coatings for selective adsorption control on activated charcoal
Authors: Wicks S. R. , Richardson N. E. , Meakin B. J.
Published: December 2004

Polymer‐coated, activated charcoal granules have found considerable use for the direct detoxification of blood in cases of uraemia and drug overdose. Although polymer coating materials are presently selected for their biocompatibility, more selective polymers could be used to increase the adsorption capacity for specific drugs and toxins. To gain an understanding of the fundamental factors influencing these adsorbent systems, we have investigated a possible selective coating material, nylon 6 and studied its influence on adsorption rates of simple model compounds when applied as a thin coat to activated charcoal granules. Thermodynamic studies have shown that phenolic compounds interact with the polymer by a hydrogen bonding mechanism, whereas nonphenolic compounds probably bind less strongly due to Van der Waals type interactions. Kinetic studies have shown that the selectivity of charcoal granules for phenolic compounds was increased by coating the granules with a thin layer of nylon 6. The increase in selectivity is probably a result of the different binding mechanism between solute and the polymer. These studies have shown that possible selective coatings may be evaluated more effectively on the basis of simple preliminary drug‐plastics interaction studies.
Experimental design in the clinical evaluation of amalgam restorations
Authors: Goldberg Jon , Munster Edward , Rydinge Elisabeth , Sanchez Luis , Lambert Kenneth
Published: December 2004

In a clinical evaluation of marginal deterioration, 475 amalgram restorations were equally distributed in a 6 × 4 × 2 × 3 factorial design, based on alloy, operator, tooth, and number of restored surfaces. All factors except the last had a statistically significant effect after 6, 12 and 18 months. There were no consistent two‐way interactions over time.
Effect of applied dc currents on experimental tumor growth in rats
Authors: Habal Mutaz B.
Published: December 2004

Morris Hepatoma experimental tumor in ACI rats is treated with small anodal direct current via an implantable power pack unit. There was major retardation in tumor growth when the treatment was started early. There was enhancement of tumor growth when the treatment was started early and then was discontinued. There was no statistical difference in growth control of the experimental tumor when the electrotherapy was given after the half‐life of the tumor was achieved. This last point will be the most important to the clinician scientist, for it simulates the clinical situation that faces the treating physician.
Adsorption of proteins from plasma to a series of hydrophilic‐hydrophobic copolymers. I. Analysis with the in situ radioiodination technique
Authors: Horbett Thomas A. , Weathersby Paul K.
Published: December 2004

The adsorption of proteins affects cellular interactions with foreign surfaces and thus plays an important role in determining the biocompatibility of implants. Previous studies have indicated differences in the affinity of various proteins for a given polymer, and differences in the affinity of fibrinogen for a series of polymers varying in hydrophilicity. These studies suggest that differences in the composition of the protein layer adsorbed to polymers from plasma might exist. To examine this hypothesis, the proteins adsorbed from plasma to a series of polymers varying in hydrophilicity were analyzed with the iodogram technique. Copolymers of hydroxyethyl methacrylate and ethyl methacrylate made by the radiation grafting technique were exposed to plasma for 0.5 or 150 min. The adsorbed proteins were iodinated, eluted with SDS, and separated with polyacrylamide gel electrophoresis. Fibrinogen, immunoglobulin G, hemoglobin, and a peak tentatively ascribed to prothrombin were the major proteins detected. Very little iodine was incorporated into adsorbed albumin, even though it was shown to be present by a separate experiment using dye binding. The fraction of total radioactivity associated with each of nine proteins was found to vary markedly and systematically among the surfaces. The distribution of radioactivity into the proteins was very different on 0.5 and 150‐min plasma exposed polymers. The results reflect both compositional differences in the adsorbed protein layer on the polymers and differences in the accessibility of proteins to the labeling reagent in the adsorbed state. Differences in the organization of the adsorbed protein layer may play a key role in determining whether cell surface receptors can come in contact with the specific plasma protein able to further stimulate the cell.
The in vitro and in vivo behavior of urokinase immobilized onto collagen‐synthetic polymer composite material
Authors: Watanabe S. , Shimizu Y. , Teramatsu T. , Murachi T. , Hino T.
Published: December 2004

With a view to developing biomaterials for semipermanent substitution, we have studied a composite material constituted with collagen and a synthetic polymer which possesses high tissue compatibility. This collagen—synthetic polymer composite was applied as a support for immobilization of enzymes for the purpose of providing a material surface with biological function. The enzymes, urokinase and trypsin, were successfully bound to the collagen membrane layer which had been activated by acyl azide formation of its carboxyl groups. The enzyme‐bearing composite material showed excellent catalytic activity toward a protein substrate as well as a low‐molecular‐weight synthetic substrate. The immobilized urokinase was characterized enzymatically and compared with native urokinase. The apparent affinity of immobilized urokinase for the substrate was slightly decreased, but its intrinsic kinetic properties were not significantly affected. No decrease in its esterase activity was observed both on repeated use and on long‐term storage, and its fibrinolytic activity was stable on heat or disinfection treatment. When this urokinase‐bearing composite material was applied into rabbit blood vessels, its in vivo fibrinolytic activity was maintained. Thus, enzyme—collagen—synthetic polymer composites may find wide application for biomaterials and artificial organs as functional biomaterials.
Biodegradation of a poly(α‐amino acid) hydrogel. I.In vivo
Authors: Dickinson H. R. , Hiltner A. , Gibbons D. F. , Anderson J. M.
Published: December 2004

A new hydrogel material has been prepared by crosslinking a hydrophilic, nonionic poly(amino acid), poly(2‐hydroxyethyl‐L‐glutamine). The material properties of the hydrogel can be controlled by variation in the crosslink density, and the swelling ratio was found to be a sensitive and convenient method for measuring the extent ofin vivobiodegradation of implanted specimens. Degradation of the material was observed only during the first 2 weeks of subcutaneous implantation in rats, and is attributed to hydrolysis by proteolytic enzymes released during the acute and chronic stages of the normal inflammatory response.
The in‐vitro degradation of poly(glycolic acid) sutures — effect of pH
Authors: Chu C. C.
Published: December 2004

Tensile strength of poly(glycolic acid) suture (PGA) of size 2–0 was examined as a function of three pH levels, 5.25,7.44, and 10.09 of the buffer. Cord and yarn grip was used to eliminate grip‐induced failure of breaking strength tests. It was found that Dexon sutures degraded significantly faster in pH = 10.09 buffer than the other two lower pH buffers. There was no significant difference in degradation rate at pH = 5.25 and 7.44. At 7 days, PGA sutures lost almost half of its original tensile strength at pH = 10.09, while the same sutures still remained more than 95% of their original breaking strength at buffers of pH = 5.25 and 7.44. After 21 days, no trace of sutures could be detected in the buffer of pH = 10.09 while about 20% strength still remained in the buffers of pH = 7.44 and 5.25. Cage effect in the crystalline phase and pH dependent hydrogen bonding were introduced to explain the difference in degradation phenomenon of PGA at buffers of various pH.
Toxicology and biocompatibility of bioglasses
Authors: Wilson June , Pigott G. H. , Schoen F. J. , Hench L. L.
Published: December 2004

Evidence for the lack of toxicity of various bioglass formulations has been deduced from studies carried out, both in vivo and in vitro, in several different centers. Recent studies of the authors, described here, include testing of solid bioglass implants in the soft tissues of rats and rabbits for time periods of up to eight weeks. Two new techniques are described for the toxicological testing of particulate biomaterials. These tests, which involve rat peritoneal macrophages in culture and a mouse pulmonary biomaterial embolus model, indicate the biocompatibility of bioglass powders. Thus, the surface activity so critical in bone adhesion is without toxic effect in nonosseous tissues in contact with solid bioglass implants. Should wear occur and produce particulate bioglass, the material should be eliminated without consequence.
Work hardening and forming behavior of cast dental alloys
Authors: Baran George , Woodland Everan C.
Published: December 2004

The work hardening characteristics of several casting alloys were determined from true stress‐true strain data. A regression technique was used to fit the data to linear or nonlinear mathematical expressions. Manipulation of the expressions made it possible to calculate the work necessary to deform the alloys. Several nonprecious alloys proved to be as easy to cold form as a conventional, high gold containing alloy.
SEM ultrastructure studies of N‐acyl‐ and N‐benzylidene‐chitosan and chitosan membranes
Authors: Hirano Shigehiro , Tobetto Kenzi , Noishiki Yasuharu
Published: December 2004

Fine ultrastructures of the cross sections of membranes, which are derived from chitosan and utilizable as artificial kidney, are examined by scanning electron microscopy (SEM). Three types of unique ultrastructure of the membrane cross sections are present: N‐acylchitosan membranes [N‐acetyl (1), N‐propionyl (2), N‐butyryl (3), N‐pentanoyl (4), N‐hexanoyl (5), N‐octanoyl (6), and N‐benzoyl (7)], N‐benzylidenechitosan membranes (8) and chitosan membranes (9). The vertical cross sections of membranes 1–7 consist of orderly arranged layers that are formed by an assembly of particle units of fibrils. Neither fibrils nor layers are present and a smooth surface is characteristic of the cross sections of (8). On the other hand, the particle units of fibrils are absent and a nappy rough surface is characteristic of the cross sections of (9). N‐Acetylation of (9) affords the particle units of fibrils that are disorderly oriented. Low‐ and middle‐molecular compounds (MW < 2000) pass through small pores among these fibrils present in orderly arranged layers of the membranes. Properties of these N‐acylchitosan membranes well meet the requirements of artificial kidney membranes.
Surface roughness and edge geometries in hemolysis with rotating disk flow
Authors: Monroe Joseph M. , True Douglas E. , Williams Michael C.
Published: December 2004

Judging biocompatibility of materials with blood includes assessment of hemolysis resulting from flow in contact with those materials. Such hemolysis is influenced in part by the surface roughness and specific hydrodynamic features of the device used. Using a rotating‐disk device, with polyethylene disks and human blood, it was shown that roughness under 4 μm has negligible effect and that hemolysis increases sharply for roughness above about 11 μm. Gross roughness (65 μm) causes qualitatively different hemolysis kinetics but not as severe hemolysis as extrapolated from low‐roughness data. In the disk geometry, the corner is a key region which generates high hemolysis and thus minor alterations cause hemolytic variations which may tend to obscure materials influences. A series of corner‐beveled polycarbonate disks were tested in comparison with the normal square corner and were found always to cause greater hemolysis. Tapering the bevel inward, so the taper angle was on the order of 2°−4°, reduced hemolysis relative to the 45° bevel but still was more hemolytic than the flat disk. Evidence suggests that glassy plastics can be machined with more reproducibility at the corners than plastics above their Tg such as polyethylene. General device design problems regarding hemolysis are discussed.
Irradiation crosslinking of the polytetrapeptide of elastin and compounding to dacron to produce a potential prosthetic material with elasticity and strength
Authors: Urry D. W. , Harris R. D. , Long M. M.
Published: December 2004

The poly(tetra peptide), H‐ (L·Val1‐L·Pro2‐Gly3‐Gly4)n‐L·Val‐OMe, which is a recurring sequence in tropoelastin the precursor protein of the elastic fiber, has been irradiation crosslinked to produce an elastomeric material with limited strength. When a material such as a Dacron fabric is impregnated by the coacervate phase of the poly(tetra peptide) prior to irradiation crosslinking at 50 Mrad, the crosslinked product exhibits stress–strain curves with good elastomeric properties and high strength. In addition to the stress‐strain curves, the material is characterized by scanning electron microscopy.
Evaluation of a chemical technique for determining the oxygen permeability of synthetic membranes
Authors: Alexander B. , Fleming J. S.
Published: December 2004

The biocompatibility and high gas transfer characteristics of gas‐permeable membranes have led to their use for total and supportive cardiopulmonary bypass. The gas transfer rates, particularly of oxygen, have previously been measured with sophisticated apparatus and this has restricted accurate measurements to a few laboratories. A simple chemical technique for measuring the oxygen permeability of synthetic membranes is described, in which sodium hydrosulfite is used to provide the highest possible oxygen gradient and the volume of oxygen crossing the membrane is measured volumetrically. Results agreed with those obtained with orthodox apparatus and replacement of the reducing agent with blood gave much lower oxygen transfer rates demonstrating the rheological influences of the blood upon oxygen transfer.
The influence of heparinized polymers on the retention of platelets aggregability during storage
Authors: Mori Yuichi , Nagaoka Shoji , Kikuchi Tetsuya , Tanzawa Hiroshi
Published: December 2004

The change in aggregability of the platelets stored in the storage tube fabricated from a newly developed heparinized hydrophilic polymer (H‐RSD) has been studied in comparison with plasticized poly(vinyl chloride) (PVC) which is widely used for blood bags. Rabbit blood was directly withdrawn into the storage tube containing an anticoagulant from the carotid. Then the tube was mechanically sealed with screw cocks and centrifugated to prepare platelet‐rich plasma (PRP) in the tube and again mechanically clamped to separate the PRP from the residual precipitate. The PRP was stored in situ in the storage tube at room temperature under agitation. During storage, the change in the aggregability of the PRP induced by adenosine diphosphate (ADP) was studied and the morphological change in the platelets adhered onto the inner surface of the storage tube was observed by scanning electron microscopy. In the H‐RSD tube, the aggregability was maintained during two‐day storage, while in the PVC tube, the aggregability was completely lost after one‐day storage. The scanning electron microscopic studies demonstrated that the reduction in the aggregability of the stored platelets is closely correlated with the morphological deformation of the platelets adhered onto the surface of the storage tube.
Wetting characteristics and blood clotting on surfaces of acylated chitins
Authors: Kaifu Katsuaki , Komai Takashi
Published: December 2004

Various acylated chitins, including formyl, acetyl, propionyl, butyryl, caproyl, capryl, lauroyl, and benzoylchitin, were evaluated as materials for blood contact surfaces by means of contact angle and blood‐clotting time measurements. Critical surface tensions of acylated chitins varied within the range of 20–30 dyn cm−1 and were dependent on the length of the acyl side chains. Furthermore, the dispersion and nondispersion components of the surface tension show remarkable differences which are dependent on the type of acyl group attached to chitin. The chitin derivative with 2.0 acetyl groups per N‐acetylglucosamine residue gave values of the dispersive and nondispersive components of the surface tension that are very close to those obtained for glutaraldehyde‐treated umbilical cord vessels. All of the acylated chitin surfaces show longer clotting times than the original chitin surface.
Correlation between strength of bonding to enamel and mechanical properties of dental composites
Authors: Boyer Daniel B. , Chalkley Yvonne , Chan Kai Chiu
Published: December 2004

The strength of bonding of dental composites to enamel was measured in shear. The compressive strength, proportional limit, elastic modulus, and tensile strength of the composites were measured for correlation with the bond strength. Conventional and microfilled composites with a range of filler concentrations were studied. The densities of the composites and their fillers and the concentrations of the fillers were determined. The mechanical properties that were most highly correlated with bond strength to enamel were proportional limit and elastic modulus. Tensile strength and filler concentration had lower correlation coefficients, and compressive strength was not correlated with bond strength. Using unfilled resins as bonding agents between the composites and enamel resulted in increased bond strength with half of the composites.