bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular weight characterization of virgin and explanted polyester arterial prostheses
Authors: Maarek J. M. , Guidoin R. , Aubin M. , Prud'homme R. E.
Published: December 2004

The macromolecular properties of 17 virgin commercial arterial prostheses and a series of explanted prostheses, both manufactured from poly(ethylene terephthalate) (PET) yarns, have been studied by gel permeation chromatography (GPC) and by differential scanning calorimetry (DSC). Only small differences were found between the average molecular weights and the degree of crystallinity of the unused reference grafts. A broadening of the DSC curves was observed for the prostheses containing texturized yarns compared with those made solely from flat, untexturized yarns. This broadening may be due to greater heterogeneity of the crystal sizes caused by the texturizing process and to the use of two or more different yarns with dissimilar thermal histories in the same prosthesis. Average molecular weights of the explant series were significantly lower than those of the corresponding reference grafts but almost time independent. The polydispersity index and the degree of crystallinity of the explants remained constant as a function of time. These results are discussed in regard to others available in the literature.
Cytocompatibility of albuminated polyester fabrics
Authors: Sigot‐Luizard M. F. , Domurado D. , Sigot M. , Guidoin R. , Gosselin C. , Marois M. , Girard J. F. , King M. , Badour B.
Published: December 2004

An alternative to the usual technique of preclotting porous textile vascular prostheses prior to surgical implantation is to render them impermeable to blood by impregnation with a cross‐linked albumin filler matrix. This material subsequently becomes the foundation for cellular development. The compatibility of such impregnated fabrics with newly formed endothelial cells has been evaluated by an in vitro organotypic culture method. This technique enables the characterization and numeration of cells that develop on blood contact surfaces and enables determination of their rate of development. Woven, knitted, and velour fabrics were evaluated folllowing coating with albumin and either storage in Tyrode solution or 40% ethanol or desiccation by critical point drying. Preclotted cardiovascular repair fabrics prepared according to conventional surgical protocol served as controls. The identification of the newly formed cells was confirmed histologically. The most extensive and rapid cellular development was observed on the woven fabric and is believed may have resulted from the smoother surface topography of this substrate. Good cellular development was noted particularly on fabrics which had been stored in Tyrode solution. Ethanol had a deleterious effect on the apparent compatibility.
The activation of the complement system by polymer materials and their blood compatibility
Authors: Sevast'ianov V. I. , Tseytlina E. A.
Published: December 2004

The activation of the complement system by polymer materials and their blood compatibility. One of the negative effects of the clinical application of various blood‐containing biomedical devices is the activation of the complement system induced by a foreign surface. A method of determining the hemolytic activity of human serum complement before and after contact with polymers was chosen in order to elucidate the relationship between polymer surface types and the degree of complement activation. The complement activation of each donor proved to depend both on his own complement reactivity and the type of polymer surface. The role played by each constituent was estimated using the rate constants for spontaneous (ksp) and induced (kind) complement activation. The negative correlation (−0,88, p < 0,001) between the degree of irreversible adsorption of 131I‐serum albumin and relative kind was determined. Thus, we propose the use of kind for the criterion of conformation alterations of protein macromolecules induced by the adsorption/desorption processes on blood/surface interface, leading to complement activation.
The binding of metal salts and corrosion products to cells and proteins in vitro
Authors: Merritt K. , Brown S. A. , Sharkey N. A.
Published: December 2004

The binding of metal ions from salts and from corrosion products of 316 LVM stainless steel and MP‐35 to blood cells and serum proteins was studied in vitro. In the first series of experiments, metal salts were added to whole blood and then the blood separated into red cells, white cells, and serum. Nickel from nickel chloride or corrosion products of stainless steel bound in very small quantities to blood cells. Cobalt from cobalt chloride bound to both red cells and white cells. Chromium from chromic chloride (Cr3+) bound to cells in very small quantities whereas chromium from potassium dichromate (Cr6+) and corrosion products showed very high to binding to red cells and some binding to white cells. In a second series of experiments the blood was separated into its components and then the metal salts were added and the binding pattern was identical. In a third series of experiments serum which had interacted with the metal salts or corrosion products was separated into its components by isolectric focusing on polyacrylamide gels. Almost all of the metal, whatever the source, was detected in the albumin region of the gels indicating strong binding to albumin. These studies on the cell and protein binding of the metals help to explain the dissemination of corrosion products from the site of the implant and subsequent systemic responses by some individuals.
The fatigue strength of porous‐coated Ti–6% Al–4% V implant alloy
Authors: Yue S. , Pilliar R. M. , Weatherly G. C.
Published: December 2004

The fatigue behaviour of Ti‐6Al‐4V (extra low interstital) alloy coated with Ti‐6Al‐4V powder was investigated using rotating bending fatigue testing. It was found that the high cycle fatigue strength of porous coated specimens exhibited a substantial decrease compared to uncoated specimens of the same microstructure. Chemical analysis of the sintered surface revealed significant increases of interstitials compared to the bulk analysis, but it is concluded that this would not adversely affect the fatigue strength. Scanning electron microscopy revealed crack initiation close to particle/substrate contact interfaces and it is concluded that stress intensification due to these interface regions are major sources of weakness with respect to fatigue strength. Finally it was found that subjecting a polished Ti‐6Al‐4V specimen to the heat treatment required for sintering resulted in delineation of prior beta grain boundaries and it is suggested that this also contributes to the inferior fatigue strength of porous coated Ti‐6Al‐4V.
The antithrombotic effect of prostaglandin E1 immobilized on albuminated polymer matrix
Authors: Chandy Thomas , Sharma Chandra P.
Published: December 2004

For intravascular implantation, a biofunctional surface seems to retard surface thrombosis upon synthetic materials. Prostaglandins, like PGI2, PGE1, and PGD2, etc., are believed to stimulate membrane‐bound adenyl cyclase and thereby raise intracellular levels of c‐AMP within platelets, which inhibit platelet adhesion and aggregation. A new procedure is suggested for the immobilization of prostaglandin E1 on an albuminated polymer matrix, through glutaraldehyde coupling. Materials thus prepared show dramatic antiplatelet effects, with regard to platelet adhesion, when compared with albumin‐immobilized surfaces. The affinity of various modified surfaces toward platelet adhesion is studied, using washed platelets suspended in Tyrode's solution. Octane contact angle studies are used to develop an understanding of the varied nature of bound substrates at equilibrium on polymer surfaces. These are studied at the solid/liquid interface, which is closest to in vivo conditions. The plasma recalcification time demonstrates the anticoagulant properties of various surfaces. A possible role of PGE1 in reducing platelet activity in the presence and absence of vitamin C is discussed. This technique may be used in the development of nonthrombogenic surfaces on existing biomedical polymers. Simultaneous pharmaceutical modification of the blood with vitamin C may enhance the blood compatibility of the surface.
Extracorporeal removal of specific antibodies by hemoperfusion through the immunosorbent agarose‐polyacrolein microsphere beads: Removal of anti‐bovine serum albumin in animals
Authors: Marcus Leon , Mashiah Aharon , Offarim Michael , Margel Shlomo
Published: December 2004

We describe (1) the production of a unique immunosorbent system, agarose‐polyacrolein microsphere beads (APAMB) for removal of a specific antibody, anti BSA, and (2) its efficacy in animal trials. This is a model system for hemoperfusive removal of specific antibodies or antigens directly from whole blood. The agarose beads (1.0 mm mean diameter) contain thousands of microspheres of 0.2 m̈m mean diameter. The microspheres which contain the ligand are encapsulated within an agarose matrix to confer physical strength, biocompatibility, spacial configuration, and porosity allowing rapid entry of plasma for reaction. Any antigen may be linked covalently to spacers on the polyacrolein microspheres to remove a specific antibody, or vice versa. Thus the APAMB remove specific molecules in contrast to the charcoal or ion exchange resins currently in use. Removal of antibody is efficient and rapid, therefore, short hemoperfusive times may be used. The beads are biocompatible; there are negligible decreases in RBC, WBC and platelets. Electrolytes and other soluble components also are minimally affected. Therapy, at the least palliative, of autoimmune disorders i.e., multiple myeloma, macroglobinemia, autohemolytic anemias, idiopathic thrombocytopenia, myasthenia gravis, rheumatoid arthritis, thyroiditis, glomerulonephritis, etc, is potentially available with this or its further improved versions.
In vivo biocompatibility studies. V. In vivo leukocyte interactions with biomer
Authors: Marchant R. E. , Miller K. M. , Anderson J. M.
Published: December 2004

A cage implant system was utilized to quantitatively and qualitatively characterize in vivo leukocyte interactions with cast Biomer. Scanning electron microscopy (SEM) in conjunction with cytochemical staining procedures were used to investigate the cellular events at the leukocyte/Biomer interface as well as in the inflammatory exudate over a 21‐day implantation period. SEM was used to characterize leukocyte morphology on the Biomer surface and the cytochemical stains were used to differentially count leukocytes and to demonstrate intracellular alkaline and acid phosphatase activity. The results showed that the population density of leukocytes on the Biomer surface diminished with implantation time. The population density of multinucleated foreign body giant cells remained constant with time, while the numbers of nuclei per giant cell increased. The differential analysis revealed that macrophages preferentially adhered to the Biomer surface compared to other leukocytes in the exudate. The phagocytic capability of all adherent leukocytes, including giant cells, decreased with time and this corresponded to changes in leukocyte morphology observed with SEM.
In situ replication techniques: II. Quantitative methodologies for replicate materials
Authors: Kusy R. P. , Whitley J. Q.
Published: December 2004

Because replicate materials have requirements different from those of recording or impression materials, quantitative methodologies were sought using commercial impression materials. Two satisfactory objective techniques resulted, a laser‐scattering and a capillary flow test. Using high‐resolution gratings to simulate tooth detail (<1 μm), the reproduction quality of 36 two‐stage replicas was determined in diffraction, reflection, and in an unblazed state. Using precision bore glass tubes (0.25, 0.5, 1, and 2 mm diameters) to simulate the high‐energy surface of enamel, the flow characteristics of nine elastomers (the first stage replicates) and four epoxies (the second stage replicates) were determined at isobaric conditions. Because the laser spot size was relatively large (0.6 mm) and the pressure differential was small (25 mm Hg), both the global resolution and the low shear rate characteristics could be measured. Of the commercial materials tested, Reprosil Light had the best combination of fluidity and resolution, regardless of which positive material was used. Although Permagum Low, Silene Wash, and Xantopren Blue scored high in one of the two tests, none of these materials could compare to Reprosil Light within the context described herein.
Assessment of thromboresistance of intravenous cannulae by 125I‐fibrinogen scanning
Authors: Lewis J. , Sweeney J. , Baldini L. , Friedland G. H. , Salzman E. W.
Published: December 2004

Assessment of potentially thromboresistant polymers and other materials has been impeded by the lack of a simple and safe test procedure in man. This report describes the use of a portable gamma radiation detector to assess accumulation of 125I‐fibrinogen in thrombi related to intravenous cannulae. The method was first employed in 19 dogs and one sheep with FEP‐Teflon forelimb intraveneous cannulae which were scanned for up to 6 h after insertion. Results were compared with findings at post mortem examination. Eleven thrombi developed, nine of which emitted more than 3500 counts per minute; eight of these (89%) were detected by external scanning. The smallest thrombus detected weighed 0.7 mg. The method did not distinguish between thrombus and hematoma. Fifty FEP‐Teflon cannulae were then studied in 39 patients after injection of 100 μCi 125I‐fibrinogen. Cannulae and control sites were scanned twice daily and an independent blind clinical appraisal was performed by an experienced nurse. A rise in percentage uptake (count at a limb site/heart count × 100) of 20 or a difference of 40 between adjacent sites was regarded as a positive test. Scans became positive up to 30 h before clinical evidence of phlebitis was observed. The interval between insertion and thrombosis of both large and small cannulae detected by scanning was significantly shorter than that determined by clinical assessment (p < 0.001). Physical signs of phlebitis were noted with 58% of large cannulae (16 or 18 gauge) and 33% of small cannulae (22 gauge) at the time of removal. Positive 125I‐fibrinogen tests were obtained with 70% of large cannulae and 75% of small cannulae. 125I‐fibrinogen scanning is a safe simple sensitive technique to detect thrombosis related to intravenous cannulae. The test should enable comparisons of different cannula materials in man.
Long‐term behavior of bovine collagen membrane used as vascular substitute. Experimental study in rats
Authors: Chignier Elza , Eloy Rosy , Huc Alain , Gimeno René , Gleizal Claudine
Published: December 2004

The aim of the present study was to evaluate the sequence (1) of the immediate and (2) the mid/long‐term organization of the blood interface of a collagenous membrane used as vascular substitute in rats. The implants were prepared from calf skin type I insoluble collagen, obtained after acidic dispersion, in absence of chemical or tanning treatment. They were used to patch an aortic defect by means of microsurgical techniques. The animals were sequentially sacrificed for immediate hemocompatibility studies at 10 s, 30 s, 10 min, 3 h, and 6 h, for long‐term analyses of the organization of the blood material interface at the 7th, 15th, 45th, 60th, 90th day following the surgery and each month until 14 months after aortic replacement. The superficial immediate events at the blood patch interface demonstrated erythrocytes heavily engulfed in a thin but dense fibrin mesh both at the patch and at the adjacent aortic wall surfaces. Neither adherent platelet nor platelet aggregate were detectable on the collagen patch surface. This fibrinoerythrocytic membrane covered the patch completely at 60 s and at 3 h the deposit was limited to 5–6 erythrocyte layers as confirmed by histology. It did not further develop on the 7th day. At the blood‐collagen interface there progressively developed a tissue composed of active myofibroblasts, collagen bundles, and elastic fibers. After 4 months, nests of fibroendothelial cells were present, and between 6 and 14 months surface cell differentiation, although complete on the adjacent aorta was still incomplete on the bovine collagen patch, amorphous fibers, and fibroendothelial cells coexisting. Heterologous patch debris were still present 14 months after implantation and were associated with macroscopic and ultrastructural calcification, which need further investigations concerning the exact nature and mechanism of mineralization of vascular substitutes of biological nature.
The effect of surface treatments on the interface mechanics of LTI pyrolytic carbon implants
Authors: Thomas K. A. , Cook S. D. , Renz E. A. , Anderson R. C. , Haddad R. J. , Haubold A. D. , Yapp R.
Published: December 2004

A mechanical and histological evaluation of LTI pyrolytic carbon implants was undertaken to determine the effect of various surface treatments on the retention characteristics of the implants. Five types of surfaces were evaluated, including as‐deposited, fine grit‐blasted, coarse grit‐blasted, ground, and plasma oxygenated. The four surface treatments were chosen in an attempt to emulate the morphology of the as‐deposited implants. The implants were evaluated in vivo by placement transcortically in the femora of adult mongrel dogs for periods of 12 to 24 weeks. Although the as‐deposited implants exhibited the greatest interface strength at 12 weeks the results of mechanical testing after 24 weeks implantation indicated no statistically significant difference among the interface strength values or among the interface stiffness values of the implants. The histologic response of the implants was similar; while all implants exhibited areas of direct implant‐bone apposition, the as‐deposited implants exhibited this behavior to the greatest extent. Thus the ability to duplicate the biological response to the as‐deposited LTI carbon surface appears possible by one or more of the treatments evaluated.
Mechanical stability of elastomeric polymers for blood pump applications
Authors: Hayashi Kozaburo , Takano Hisateru , Matsuda Takehisa , Umezu Mitsuo
Published: December 2004

As a series of studies on the mechanical properties of materials used in cardiac prostheses, static and dynamic characteristics and stability of five kinds of elastomeric polymers have been studied by uniaxial tensile and fatigue tests in air at room temperature and in saline solution at 37°C. Of all materials tested in this study, Texin MD85A, a segmented polyether polyurethane, has the lowest flexibility under static and dynamic conditions, with relatively high strength. Hexsyn, a polyolefin rubber, is highly flexible with little stress relaxation. However, this material has very low tensile strength and short elongation, and shows unstable change in the elastic modulus during cyclic deformation. Avcothane 51, a copolymer of polyurethane and silicon, has unstable mechanical properties and gradually stiffens upon cyclic deformation. On the other hand, Biomer, a segmented polyether polyurethane, has high flexibility and shows the most stable behavior during cyclic deformation regardless of test environment. Toyobo TM5, a similar segmented polyurethane to Biomer, has higher strength and ductility than Biomer, although its static and dynamic flexibility are slightly worse and less stable than those of Biomer. These results indicate that Biomer and Toyobo TM5 are more suitable for flexible components of cardiac prostheses.
The mechanism of “primary mineralization” in the reaction of bone to injury and administration of implant
Authors: Sela J. , Bab I.
Published: December 2004

The purpose of the present article is to discuss the role of extracellular matrix vesicles as a marker of primary mineralization after injury to bone with or without the implantation of foreign artificial or biological materials.
The structure of bone apatite surfaces
Authors: Posner Aaron S.
Published: December 2004

This is a review of the surface chemistry of bone mineral and its synthetic counterpart hydroxypapatite. Small‐angle x‐ray scattering and low‐temperature nitrogen adsorption measurements show bone mineral surfaces range from 100 to 200 m2/g. The heats of adsorption of small molecules on bone and apatite surfaces show that these materials have polarizing surfaces which form strong bonds with polar and polarizable molecules. Water is hydrogen bonded to these surfaces with energies ranging from 23 Kcal/mol, for low coverage, to 11 Kcal/mol after two full layers; the latter value shows that after two monolayers the water is bonded as strongly to the solution as it is to the apatite surface. Stearic acid in cyclohexane adsorbs on bone and apatite surfaces in a closed‐packed manner with the straight‐chain molecules in parallel array with the end carboxyl groups hydrogen bonded to surface electronegative ions. Synthetic hydroxyapatite has long been used in chromatography because of the bonding capacity apatite surface has for certain proteins and polynucleotides. The metabolic interplay between bone mineral and the body results from the high magnitude and high reactivity of the mineral surface.
The interface of various glasses and glass ceramics with a bony implantation bed
Authors: Gross U. , Strunz V.
Published: December 2004

Basing on histomorphological evaluations and morphometrical quantifications in a standardized model experiment, a comparison is made between the reactions of skeletal tissues to various glasses, glassceramics and enamels. On the surface of these so‐called reactive biomaterials either a direct bonding to mineralized bone or also different amounts of osteoid or chondroid tissue formation can be observed, depending on the composition of the material. It is shown that (1) the solubility of the glasses cannot directly be related to the reactivity and the resulting bone bonding; (2) bone binds only to glasses with a controlled release of constituents and which exhibit a seam of extracellular matrix on their surface, in which normal primary mineralization can occur; (3) the release of constituents such as Al2O3, Ta2O5, ZrO2, or phosphates from the material can inhibit this normal mineralization and the transformation of chondroid tissue to bone; (4) if connective tissue instead of bone is present at the interface (either primarily or after bone remodelling), the dissolution (or corrosion) of the material may be no longer controllable, and the tissue reacts with a continuous inflammatory response to the corrosion products.
Bioglass coatings and bioglass composites as implant materials
Authors: Ducheyne P.
Published: December 2004

This article addresses three aspects of the mechanical and biological properties of bioreactive glasses. First, it describes the composition and the relationship between the composition and bonding and its influence on the bone bonding mechanism and the rate of bond formation. Second, the mechanical properties of bioglass are dealt with. It is shown that the approaches to use bioglass in highly stressed applications, have met with various degrees of success. Third, the issue of the effect of loading on the glass properties and, above all, on the glass bonding properties is discussed.
In vivo corrosion of sodium silicate glasses
Authors: Pernot François , Zarzycki Jerzy , Baldet Pierre , Bonnel François , Rabischong Pierre
Published: December 2004

Square‐shaped implants of various sodium silicate glasses were weighed and implanted intraperitoneally in rats for periods ranging from 8 to about 60 days. The implants were then removed and their aspect was compared to their aspect before exposure to physiological environment. The corrosion products were studied by x‐ray diffraction and electron microprobe analysis. Weight changes were also measured to calculate a biodegradation rate. The glass 66 S O (66.6 SiO2–33.3 Na2O) was strongly corroded, as early as after the first week. The nonsoluble degradation products formed a cocoon encapsulating the now smaller specimen. The analysis of the cocoon showed that it was made of a silica‐rich layer containing also calcium and phosphorus. In this layer the ratio Ca/P could correspond to that of an apatite. The biodegradation rate reached 71 × 10−4 g · cm−2 · day−1. The glass 75 SO (75 SiO2‐25 Na2O) was not so quickly corroded: Cracks appeared at the surface and progressively reached the center of the implants. There was no removable shell but a white deposit, adherent to the surface. This deposit contained silica and also calcium and phosphorus at the periphery. The biodegradation rate was only 2.6 × 10−4 g · cm−2 · day−1.
Pyruvic acid as an etching agent in clinical dentistry
Authors: Retief D. H. , Harris B. E. , Bradley E. L. , Denys F. R.
Published: December 2004

The objective of this study was to evaluate the use of pyruvic acid as an alternative etching agent to phosphoric acid (H3PO4). Solutions containing 5, 10, 15, 20, 25, and 30 m/m % pyruvic acid and 50% m/m H3PO4 were prepared. The tensile bond strengths of a composite resin to enamel surfaces etched with the respective etching agents were determined. The rates of etching of enamel surfaces by each of the etching solutions were evaluated. Unground and polished enamel surfaces were etched with the respective etching solutions and the surfaces examined by scanning electron microscopy. The tensile bond strengths of the resin to enamel surfaces etched with 10–30% pyruvic acid exceeded those obtained on enamel surfaces etched with 50% H3PO4. The rates of etching of all the pyruvic acid solutions were significantly less than that of H3PO4. Well‐defined etching patterns were observed on the enamel surfaces etched with all the etching solutions. The results of this laboratory study suggest that pyruvic acid may be a suitable alternative to phosphoric acid as an etching agent in clinical dentistry.
Biodegradation of and tissue reaction to 50:50 poly(DL‐lactide‐co‐glycolide) microcapsules
Authors: Visscher G. E. , Robison R. L. , Maulding H. V. , Fong J. W. , Pearson J. E. , Argentieri G. J.
Published: December 2004

The biodegradation of the copolymer 50:50 poly(DL‐lactide‐CO‐glycolide)‐lypressin microcapsules was studied by light and electron microscopic methods and 14C release. Intramuscular injection sites of microcapsules in rats were studied by dissecting and conventional light microscopy as well as scanning (SEM) and transmission electron microscopy. A minimal localized acute myositis was seen initially at the injection sites. By Day 4, a few small foreign body giant cells were present participating in the minimal foreign body response. Later the inflammatory cells decreased and the individual microcapsules were walled off by immature fibrous connective tissue and large syncytial foreign body giant cells. By Day 35, definitive changes in some microcapsules, consisting of a granular and slightly eroded appearance of the internal matrix, were seen by SEM. By Day 42, the outer rims of the microcapsules were extensively eroded. At Day 56, the inflammatory and connective tissue reactions were almost completely resolved and biodegradation continued so that only remnant pieces of the microcapsules were present at Day 63. The morphologic picture correlated well with loss of 14C radioactivity, which could no longer be detected at the injection sites on Day 56. Phagocytosis did not seem to be an important factor in the biodegradation.
Metallographic texture analysis of dental materials by polarizing microscopy in the incidental light
Authors: Newesely H. , Rabe H.
Published: December 2004

Incidental polarized light microscopy can be used for the optical analysis of crystal phases with similar anisotropic behavior or preferred textures in polished sections. In this method, the vibration mode of the reflected light is determined by remarkable interference colors in the microscope using a compensator plate. The application of this method for the analysis of dental materials is demonstrated with amalgams and gold‐reduced alloys. As a prerequisite, a modified procedure for preparing suitable polished sections of inhomogenous materials is described. Employing this optical and a crystallographic computing method, more detailed information about the way of element replacement in the course of the chemical reaction can be obtained. The results of these investigations also warrant the assumption that coherent crystal intergrowth which prefers low indicated and closely packed lattice directions, gives rise to a good adhesive strength of the bonding in the alloy.
The structure of highly crosslinked poly(2‐hydroxyethyl methacrylate) hydrogels
Authors: Peppas Nikolaos A. , Moynihan Humphrey J. , Lucht Lucy M.
Published: December 2004

Films were prepared by reaction of HEMA monomer with the crosslinking agent ethyleneglycol dimethacrylate (EGDMA) at crosslinking ratios, X, of 0.005, 0.01, 0.0128, 0.025, and 0.050 mol EGDMA/mol HEMA in the presence of 40 wt. % water at 60°C for 12 h. These membranes were subsequently swollen in water at 37°C and their structure analyzed using a modified Gaussian distribution equation of equilibrium swelling. The calculated values of Mc varied between 800 and 3700 daltons, which corresponded to a correlation length of the mesh size ζ of 16.2 to 35.6 Å. The structural analysis and diffusive studies of PHEMA membranes indicate that the recent determinations of Mc for PHEMA by Migliaresi et al. (C. Migliaresi, L. Nicodemo, L. Nicolais, and P. Passerini), “Physical characterization of PHEMA gels,” J. Biomed. Mater. Res., 15, 307 (1981) and others are not accurate. The methods presented can also be used for analysis of any highly crosslinked polymer network produced by simultaneous polymerization and crosslinking reactions.
The blood compatibility of chitosan and N‐acylchitosans
Authors: Hirano Shigehiro , Noishiki Yasuharu
Published: December 2004

A segment of silk polyfilament suture [No. 2‐0(USP)], ca. 10 cm long, was coated with a thin membrane (2–6 μm) of chitosan, N‐acetylchitosan, or N‐hexanoylchitosan. The suture was directly inserted into the lumen of dog's peripheral veins. The in vivo blood compatibility of these membranes was macroscopically determined from the blood coagulum formed on the membrane surface at 2 h. An intense thick blood coagulum formed on the chitosan membrane surface and a thin blood coagulum formed on N‐acetylchitosan membrane surface, but no blood coagulum formed on N‐hexanoylchitosan membrane surface.
The intracellular degradation of poly(ε‐caprolactone)
Authors: Woodward S. C. , Brewer P. S. , Moatamed F. , Schindler A. , Pitt C. G.
Published: December 2004

Poly(ε‐caprolactone) [PEC], a biodegradable aliphatic polyester, undergoes a two‐stage degradation process: The first lengthy phase involves nonenzymatic hydrolytic cleavage of ester groups, the second phase beginning when the polymer is more highly crystalline, and of low molecular weight. The cellular events of the second phase were examined by implanting gelatin capsules containing 25 mg of low molecular weight (Mn 3000) PEC powders, 106 to 500 μm, in rats. PEC fragments ultimately were degraded in phagosomes of macrophages and giant cells, the process requiring less than 13 days for completion at some sites. PEC was also identified within fibroblasts. These studies support the intracellular degradation of PEC as the principal pathway of degradation once the molecular weight of the aged polymer is reduced to 3000 or less.
Polymers for the controlled release of macromolecules: Effect of molecular weight of ethylene‐vinyl acetate copolymer
Authors: Hsu Terry Tsong‐Pin , Langer Robert
Published: December 2004

Matrices composed of ethylene‐vinyl acetate copolymer (EVAc) have been used for controlled delivery of macromolecular bioactive agents. Three EVAc samples of different molecular weight (MW) were selected from solution fractionated samples. The polymer MW is a sensitive factor in affecting the release rate of bovine serum albumin (BSA); the higher the MW of EVAc, the slower the release rate. Depending on the degree of hydrophilicity of the device, the relatively hydrophilic drug particles would cause various degrees of swelling pressure upon water uptake. The relatively hydrophobic EVAc carrier would impose different degrees of restrictive force as determined by polymer MW. The interaction between the restrictive force of the carrier and the swelling pressure of the drug particles is a key factor in affecting the drug release kinetics. As a result, the selection of the polymer carrier can be used to affect the kinetics of a controlled release device.
Optical properties of esthetic restorative materials and natural dentition
Authors: Cook Wayne D. , McAree Deborah C.
Published: December 2004

The diffuse reflectance spectra of dental ceramic and composite resin specimens were analyzed by the Kubelka–Munk (K–M) theory of light scattering materials. This enabled the prediction of the spectra and color of differing thicknesses of these materials on various backgrounds, which were in good agreement with observation. The reflectance spectra of natural enamel and dentine sections were also measured on white and black backgrounds. This allowed the calculation of the K–M scattering (S) and absorption (K) parameters, which were compared with those of the restorative materials. The Chroma of these tooth sections increased slightly with the age of the patient, but the Hue and Value showed no systematic variation. Comparisons of the measured Munsell color for a range of composite resins and ceramics with that of the natural tooth sections showed that they generally exhibited a similar range of colors.
Biocompatibility test procedures for materials evaluation in vitro. II. Objective methods of toxicity assessment
Authors: Johnson H. J. , Northup S. J. , Seagraves P. A. , Atallah M. , Garvin P. J. , Lin L. , Darby T. D.
Published: December 2004

Methods of assessing the biocompatibility of materials for use in medical devices were evaluated. Ten materials were tested using quantative, objectively graded in vitro biochemical and functional assays employing four cell lines (CCL 1, 74, 76, and 131) used in previous work and five primary cell types (human lymphocytes, polymorpho‐nuclear leukocytes, and mixed leukocytes, mouse macrophages, and mouse embryo). The biochemical methods (DNA synthesis, protein synthesis, and ATP activity) demonstrated good agreement in toxicity ranking of the materials, regardless of which cell culture was used and, also, the cell cultures responded similarly for each method. Methods that measured functional characteristics of cells (adhesion and phagocytosis) were highly sensitive but had low toxicity ranking agreement and reproducibility. Assays (defined as method and cell culture combinations) using cell lines were more reproducible than assays using primary cell types. Significant differences in sensitivity were noted among the assay systems for particular material types. The in vitro assays were more sensitive to differences in material composition than was a 90‐day assay by subcutaneous implantation in rats.
A segmented polyurethane composite prosthetic anterior cruciate ligament in vivo study
Authors: Peterson Christopher J. , Donachy James H. , Kalenak Alexander
Published: December 2004

A segmented polyurethane prosthetic anterior cruciate ligament prototype has been developed and its in vivo integrity assessed in canine subjects. Prosthetic ligaments surgically implanted for 3, 4, 6, 8, 12, and 16 months were assessed clinically in living subjects, at time of autopsy, and microscopically postautopsy. It was found that the ligaments were adequate in strength to provide stability and last for periods up to 16 months. Notching of the ligaments was observed at two designated friction points.
Effect of drug–vinyl copolymer delivery composites on the rat prostate
Authors: Yoshida Masaru , Asano Masaharu , Kaetsu Isao , Yamanaka Hidetoshi , Nakai Katsuyuki , Yuasa Hisako , Shida Keizo
Published: December 2004

A radiation polymerized drug–vinyl copolymer delivery composite (0.8 mm in diameter, 3 mm long) was inserted into the right‐lobe ventral prostate (I), into the right testis (II), and subcutaneously (III) into the back of male Wistar rats. The implantation was carried out over a period of 12 weeks maximum. From the relationship between the site of surgical insertion of the implant and the physiologic response (as measured by the decrease in the weight of the prostatic organs, e.g., ventral prostates, dorsolateral prostates, and seminal vesicles), it was found that in an AA560‐containing composite (36 μg daily), the physiologic response is increased in order of (III) > (II) > (I). The same tendency was observed in the Estracyt‐containing composite system (15 μg daily). The difference in the physiologic response owing to the site of surgical insertion of the implant was not observed in an E2‐17β‐containing composite (6 μg daily), although this composite showed the strongest physiologic response. No physiologic response in rats with CMA‐containing composite (28 μg daily) was noted.
A modification of the cell culture agar diffusion test using fluoresceindiacetate staining
Authors: Schmalz G. , Netuschil L.
Published: December 2004

In order to reduce the uncertainties involved in the morphologic evaluation of the cell culture agar diffusion test, the originally recommended neutral red stain was replaced by fluoresceindiacetate (FDA). This stain proved to be nontoxic in the concentrations used in this study (0.002%). Toxicity tests with phenol, formalin, and methylmethacrylate monomer revealed results corresponding to literature evaluations by other methods. Since FDA makes cell metabolism visible and easily accessible to automated evaluation techniques, it presents certain advantages over the morphologic evaluation using the neutral red stain.
Auger electron spectroscopic studies of stainless‐steel implants
Authors: Sundgren J.‐E. , Bodö P. , Lundström I. , Berggren A. , Hellem S.
Published: December 2004

Auger electron spectroscopy together with scanning electron microscopy has been used to study the interface between stainlesssteel implants and human tissue. The thickness and nature of the oxide layer on the implants have been found to depend on the location of the implants in the body. Before implantation, the oxide layer is about 50 Å thick, consisting mainly of chromium oxide. For implants located in cortical bone the thickness of the interfacial oxide layer remains unaffected, while it increases by a factor of three to four on samples located in bone marrow. In both these cases calcium and phosphorus are incorporated in the oxides. Implants located in soft tissue have an interfacial oxide layer with a thickness of about one and one‐half times that on an unimplanted sample. On these samples, calcium and phosphorus are not found, but occasionally sulfur is found in the oxide layer. All these samples originated from the oral region of the body; the reason for this finding, however, is not known at present time. The interactions between the implants and human tissues resulting in the observed changes of the implant surfaces are discussed in terms of oxygen pressures and metabolic activity.
Mechanical properties and biomechanical compatibility of porous titanium for dental implants
Authors: Asaoka Kenzo , Kuwayama Norihiko , Okuno Osamu , Miura Ishi
Published: December 2004

Titanium powder with a granule diameter of 420–500 μm was prepared and porous titanium specimens were made from this powder. The mechanical properties of these specimens were examined. The compressive strength and low cyclic compressive fatigue strength were 182 and 40 MPa, respectively. Fractography was also observed by scanning electron microscopy. Typical fatigue characteristics of the bonding areas of the powder were observed. In addition, porous‐titanium‐coated dental implants with pure titanium cores were prepared. The compressive strength of the material used was 230 MPa, fatigue strength not being improved. Biomechanical stress calculations using the finite element method were made using a model that employed the use of the material implanted in alveolar bone. Shear stress at the implant–bone interface as well as compressive stress concentrations in the bone was calculated. The most suitable elastic modulus for the dental implant was then estimated from these calculations. Finally, based on these results, the use of porous titanium for dental implants was assessed.
Divanillates and polymerizable vanillates as ingredients of dental cements
Authors: Stansbury J. W. , Brauer G. M.
Published: December 2004

Vanillate esters with multifunctional groups that react with metal oxides to give chainextended molecules have been synthesized. Divanillates were obtained from vanillic acid and the corresponding polymethylenediols. Methacryloylethyl vanillate (MEV) and vanillyl methacrylates were prepared respectively from hydroxyethyl vanillate or vanillyl alcohol and methacryloyl chloride. The properties of cements prepared with liquids incorporating these compounds were determined. Liquids containing divanillates dissolved in the reactive chelating agent o‐ethoxybenzoic acid (EBA) when mixed with zinc oxide powders harden within a few minutes. The resulting cements have a tensile strength much higher than the commonly used zinc oxide–eugenol cements, have low solubility, do not inhibit polymerization, and adhere well to metallic substrates. Similarly, liquids with MEV as an ingredient yield cements with excellent strength and good adhesion to stainless steel and composites. Their brittleness can be overcome by addition of an oligomeric methacryloylethyl vanillate to the liquid or silanized glass to the powder ingredient. These cements, subject to their biocompatibility to oral tissues, could be most useful for a number of dental applications.
Beryllium localization in base metal dental casting alloys
Authors: Covington J. S. , McBride M. A. , Slagle W. F. , Disney A. L.
Published: December 2004

Investigation of dissolution of base metal dental casting alloy constituents in aqueous solutions revealed an unexpectedly high level of beryllium as compared with the other constituents. Analysis of atomic emission spectroscopy is presented here showing the outer surface (0–100 Å) is decidedly enriched in beryllium as compared with the bulk composition of the alloy. This localization is consistent in all samples and forms of the alloy tested.
Leaching of tobramycin from PMMA bone cement beads
Authors: von Frauhofer J. A. , Polk H. C. , Seligson D.
Published: December 2004

The in vitro leaching characteristics of tobramycin from acrylic resin (PMMA) bone cement beads have been determined by a radioimmune assay. Tobramycin was incorporated at two concentrations into bone cement beads fabricated from three commercial brands of acrylic resin. Antibiotic leaching followed a curvilinear relationship of the form X · Y = A · X + B · Y. All beads showed similar tobramycin leaching rates over time but the initial amount of leached material differed with the amount of tobramycin incorporated in the bead and the source of the PMMA bone cement. The data indicate that tobramycin‐impregnated PMMA beads permit antibiotic leaching at a controlled rate compatible with possible clinical application.
Fibronectin binding properties of bacteriologic petri plates and tissue culture dishes
Authors: Bentley Kevin L. , Klebe Robert J.
Published: December 2004

With the aid of a monoclonal antibodybased ELISA assay, the fibronectin binding properties of poly(styrene) bacteriologic and tissue culture petri plates were studied. After treatment of the plastics with serum, both the rate of fibronectin binding and the maximum amount of fibronectin bound were found to be lower for bacteriologic than tissue culture plates. In contrast, when treated with purified fibronectin rather than serum, bacteriologic and tissue culture plates bound fibronectin equally well. Thus, serum proteins are more effective in inhibiting fibronectin binding to bacteriologic petri plates than to tissue culture dishes. The fibronectin binding properties of plastic substrata could be enhanced by oxidation with H2SO4 or diminished by dissolution and recasting of tissue culture dishes. Thus, the fibronectin binding properties of bacteriologic and tissue culture dishes can be interconverted. Plastics with enhanced fibronectin binding properties (tissue culture plates) were found to be hydrophilic and good substrates for cell attachment and growth while plastics with decreased fibronectin binding characteristics were found to be hydrophobic and poor substrates for cell attachment and growth. The cell‐adhesive properties of bacteriologic and tissue culture plastic substrata were found to vary during incubation with cells. While cells remained firmly attached and spread on tissue culture plastics over a period of 5 days or more, previously attached cells gradually detached from bacteriologic plastics at incubation times beyond 12 h. The gradual detachment of cells from bacteriologic plates probably explains the poor properties of bacteriologic plastics for the growth of anchorage‐dependent cells, in particular.
Antithrombogenicity and oxygen permeability of block and graft copolymers of polydimethylsiloxane and poly(α‐amino acid)
Authors: Kumaki T. , Sisido M. , Imanishi Y.
Published: December 2004

A‐B‐A‐type block copolymers consisting of poly(α‐amino acid) as A component and polydimethylsiloxane as B component and graft copolymers consisting of polydimethylsiloxane as trunk polymer and poly(α‐amino acid) as branch polymer were synthesized. γ‐Benzyl‐L‐ or DL‐glutamate, ε‐benzyloxycarbonyl L‐lysine, and sarcosine were used as α‐amino acid. Different microphase‐separated structures were found on the film surface according to the copolymer composition and the casting conditions. In vitro antithrombogenicity test showed higher antithrombogenicity of block or graft copolymers than homopolymers. The best antithrombogenicity was independent of the kind of α‐amino acid and the degree of polymerization of copolymers. The best ratio was 65–75% in block copolymer and 40–50% in the case of graft copolymer. The oxygen permeability of block and graft copolymer film was intermediate between those of homopolymers and varied with changing the composition of the copolymer. These experiments showed that the microphase‐separated structure on the film surface was most important both for the antithrombogenicity and oxygen permeability of these copolymer films.
Development of a prosthetic venous valve
Authors: Hill R. , Schmidt S. , Evancho M. , Hunter T. , Hillegass D. , Sharp W.
Published: December 2004

The pathology of thrombophlebitis primarily results from the obliteration of venous valves in the lower extremities. The objective of this study was to develop a prosthetic venous valve that could be implanted in the human femoral system to ameliorate the deleterious effects of thrombophlebitis. Prosthetic venous valves were produced from two materials: Pellethane valves were fabricated from a dip‐casting process; umbilical vein valves were produced by a fixation process. The valves were evaluated as implants within the external jugular veins of 10 research dogs. Each animal was implanted with one Pellethane valve in one external jugular vein and one umbilical vein venous valve in the contralateral jugular vein. Each valve was positioned over a stainless‐steel cylinder that had been implanted into the jugular veins in such a manner that there existed no blood–cylinder interaction. Patency of the valves was determined by X‐ray venography at 24, 48, and 72 h and at 5 and 8 days postoperatively. All of the umbilical vein venous valves were occluded by the end of 48 h, whereas two of the Pellethane venous valves remained patent for at least 5 days but were occluded at 8 days. The results of this study suggest the possibility of success of Pellethane valve implants in the venous circulation and indicate future directions for study.