bluuebunny/crossref_metadata_2025_split huggingface dataset:
Immobilization of enzymes for medical uses on plastic surfaces by radiation‐induced polymerization at low temperatures
Authors: Kaetsu Isao , Kumakura Minoru , Asano Masaharu , Yamada Akio , Sakurai Yasuhisa 
Published: December 2004

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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