bluuebunny/crossref_metadata_2025 huggingface dataset:
A preliminary durability study of two types of low‐profile pericardial bioprosthetic valves through the use of accelerated fatigue testing and flow characterization
Authors: Schuster Paul R. , Wagner James W.
Published: December 2004

Bioprosthetic heart valves are being used more often because of certain advantages they have over artificial valves. The bioprostheses are less thrombogenic, cause a lower incidence of hemolysis, and usually fail in a slow progressive manner. A combination of flow characterization and accelerated testing was used to assess the durability of two types of pericardial valves, the Ionescu‐Shiley Low Profile Mitral and the Carpentier‐Edwards Low Profile Aortic valve. The flow characterization work was done in an aortic chamber designed for in vivo simulation. The function of the valve was monitored between different stages of the accelerated testing using laser Doppler anemometry. Accelerated testing was performed at 1300 cardiac cycles per minute, and physiologic conditions both in closing pressures and the ambient temperature were maintained. Results indicated a change in flow characteristics owing to cyclic loading of the leaflet tissue. The flow orifice increased over time leading to a decrease in peak velocity. Future developments in Doppler ultrasound may facilitate non‐invasive assessment of these peak velocity variations. Calcification of the tissue was not considered, since this was an in vitro study.
Effect of heparin–pva hydrogel on platelets in a chronic canine arterio‐venous shunt
Authors: Cholakis Cynthia H. , Zingg Walter , Sefton Michael V.
Published: December 2004

Polyvinyl alcohol (PVA) hydrogel, with or without heparin, was reactive towards canine platelets in a chronic artriovenous shunt as demonstrated by an increase in platelet regeneration time, a systemic decrease in platelet count and transient decrease in platelet serotonin content. Immobilized heparin (heparin–PVA) had no effect whereas unmodified polyethylene was found to be unreactive despite similar levels of platelet deposition as measured by SEM and a higher in vitro reactivity (J. Biomed. Mater. Res., this is sue). Tewnty‐centimeter lengths of hydrogel coated polyethylene tubing were inserted between the arterial and venous portions of the shunt and left in place for 4–6 days, without the complicating artifacts of anticoagulation, anesthesia, or surgical intervention. Regeneration time was measured as the return to normal platelet cyclooxygenase (co) activity after a single 240‐mg dose of aspirin, with co activity measured in vitro as malondialde hyde production. Although measuring new platelet production, regeneration time is an indirect measure of platelet consumption, so that the reduced regeneration time seen here was presumed to reflect enhanced material associated consumption and thromboembolism. Like other hydrogels, PVA does not appear to be “thromboadherent” but it does appear thrombogenic. Immobilized heparin had no additional effect, presumably because the platelet response was dominated by the reactivity of the underlying substrate.
The bovine pericardial xenograft: I. Effect of fixation in aldehydes without constraint on the tensile viscoelastic properties of bovine pericardium
Authors: Lee J. Michael , Haberer Sean A. , Boughner Derek R.
Published: December 2004

Tensile testing of tissue strips has been used to examine the effect of simple fixation in glutaraldehyde and formaldehyde on the viscoelastic properties of bovine pericardium. To assess tissue anisotropy, tissue strips were cut at 0°, 30°, 60°, and 90° relative to the base‐to‐apex direction. Fresh anterior pericardium was modestly anisotropic, being least extensible in the base‐to‐apex direction; however, fixation removed this anisotropy. Fixation also produced a marked change in the response of the material to initial cyclic loading during preconditioning. Overall extensibility of the fixed material was significantly greater than that for the fresh tissue, consistent with a 10.7% shrinkage in aldehydes calculated from strain at fracture data. Reductions in stress relaxation and creep after fixation were noted as well, consistent with intrafibrillar crosslinking. Cyclic hysteresis and ultimate tensile strength were unaffected. Since the observed changes in the stress–strain response were largely attributable to shrinkage, control of shrinkage by physical means would allow for engineering modification of bovine pericardial mechanics for controlled anisotropy.
Fracture behavior of urinary stones under compression
Authors: Ebrahimi F. , Wang F.
Published: December 2004

The fracture behavior of two types of urinary stones, namely struvite and calcium oxalate, during compression testing was studied. Scanning electron microscopy (SEM) was used to characterize the fracture surfaces. Both types of stone showed pseudo‐plastic behavior as indicated by their load‐displacement curve. The onset of nonlinear behavior was found to correspond to development of microcracks in the specimens. The compressive strength was defined as the stress calculated at the maximum load. In struvite samples, the maximum load corresponded with the development of large cracks parallel to the compressive axis. For oxalate stones a separation of the outer layer (crust) from the inner layer (core) marked the point of maximum load. The compressive strength of the struvite samples was found to depend on the orientation of lamellae relative to the loading axis. Struvite stones, when loaded parallel to the lamination direction showed a higher compressive strength than oxalate stones did. The fracture behavior and compressive strength of a model material (z‐brick) were also characterized and compared to those of the urinary stones.
Biomechanical considerations on some postoperative problems of directly anchored total hip replacements
Authors: Heimke G. , Stock D. , Büsing C. M. , Mallinckrodt D. V.
Published: December 2004

Uncemented total hip replacements have resulted in a higher incidence of postoperative complaints than cemented ones. The theoretical explanation of these not well defined discomforts is based on the differences of the stress and strain fields around the distal portions of the femoral components. While the noncemented stems are press‐fitted and most of them tapered distally, thus creating hoop stresses and strains in the surrounding cortical bone, the shrinkage of the cement prevents these mechanical irritations. The relatively sudden disappearance of these discomforts within the first 2 postoperative years is attributed to the shift of the main zone of load transmission from the distal to the proximal portion of the stems following bone remodeling.
Generation of IL1‐like activity in response to biomedical polymer implants: A comparison of in vitro and in vivo models
Authors: Miller Kathleen M. , Rose‐Caprara Veronica , Anderson James M.
Published: December 2004

Of the many factors determining host biocompatibility responses to implanted biomedical polymers, the cellular interactions at the tissue/material interface have been recognized to be some of the most important. The present study has combined results both from an in vitro cell culture system and from an in vivo animal model to examine this host response. In vitro results suggest that a variety of polymer materials can differentially activate human monocytes to produce a protein(s) having different biological activites. The polymers tested induce the production of the regulatory inflammatory protein interleukin 1 as well as a factor that enhances fibroblast proliferation and collagen synthesis. The observed activities of these factors appear to be related but not identical, and are dependent upon the specific polymer. Evaluation of exudate and tissue responses to these same polymer materials in an in vivo model are also presented. Both in vitro and in vivo results support the hypothesis that monocyte/macrophage activation with subsequent synthesis of regulatory factors such as interleukin 1 plays a significant role in determining the host response to biomedical polymer implants.
The influence of calcium phosphate ceramics and glass‐ceramics on cultured cells and their surrounding media
Authors: Hyakuna Katsufumi , Yamamuro Takao , Kotoura Yoshihiko , Kakutani Yoshiaki , Kitsugi Toshiaki , Takagi Haruki , Oka Masanori , Kokubo Tadashi
Published: December 2004

The cytotoxicity of hydroxyapatite (HA), tricalcium phosphate (TCP), and two types of phosphate (TCP), and two types of apatite‐containing glass‐ceramics designated A · W‐GC and A · W · CP‐GC was evaluated by the direct contact method using V79 cells. Compatibility of the cells was assessed as a function of cellular attachment and subsequent growth using scanning electron microscopy. Although all of the tested materials have surfaces available for cellular attachment, cell growth was markedly inhibited by HA sintered at 600°C and 900°C, and slightly inhibited by HA sintered at 1200°C, TCP and the glass‐ceramics. In attempts to clarify the cause of this toxicity, the interactions of the ceramics with culture medium was assessed by measurement of calcium (Ca), inorganic phosphate (P), magnesium (Mg), pH and albumin content in the medium. The grade of toxicity corresponded to the degree of reduction of Ca, P, and albumin in the medium. Furthermore, surface reactions of the ceramics were demonstrated to vary in both mode and degree depending on their chemical structure and level of microporosity. Thus, the surface reactivity of ceramic materials should be always taken into account in discussing their biocompatibility in vivo.
Duplex stainless steels for osteosynthesis devices
Authors: Cigada A. , Rondelli G. , Vicentini B. , Giacomazzi M. , Roos A.
Published: December 2004

The austenitic stainless steels used today for the manufacture of osteosynthesis devices are sensitive to crvice corrosion. In this study the corrosion properties of some duplex stainless steels were evaluated and compared to traditional austenitic stainless steels. According to our results the following ranking was established: 23Cr4Ni < AISI 316L < ASTM F138 < 22Cr5Ni3Mo < 27Cr31Ni3.5Mo < 25Cr7Ni4MoN. In particular the results showed that the high‐performance 25Cr7Ni4MoN duplex stainless steel, with high molybdenum and nitrogen contents, can be considered not susceptible to crevice corrosion in the human body. The duplex stainless steels have also better mechanical properties at the same degree of cold working compared with austenitic stainless steels. Hence the 25Cr7Ni4MoN duplex stainless steel can be considered a convenient substitute of ASTM F138 for orthopedic and osteosynthesis devices.
Enhanced adherence of human adult endothelial cells to plasma discharge modified polyethylene terephthalate
Authors: Pratt Kerri J. , Williams Stuart K. , Jarrell Bruce E.
Published: December 2004

Human adult aortic endothelial cell attachment to polyethyleneterephthalate (PET as mylar film) was examined in vitro. PET was examined in both the unmodified form (PET −) and in a modified form (PET +) that had undergone plasma discharge surface modification (PDSM). These surfaces were compared to unmodified tissue culture polystyrene (PS −). The kinetics of attachment and the force of attachment using the rotating disc were determined as a function of surface and substrate protein applied to the surface. Four proteins—fibronectin, collagen I/III, collagen IV/V, and laminin—were added and compared to saline pretreatment. The most significant variable affecting attachment was the time of incubation. When corrected for time, PET + demonstrated significantly superior attachment kinetics when compared to PET − in most cases. These kinetics were similar to those seen on PS−. Fibronectin precoating of the surface greatly enhanced attachment kinetics on PET + and PS− but to a much lesser degree on PET−. The fibronectin effect was synergistic with PDSM, suggesting that PDSM enhances protein adsorption on the surface. The force of attachment was generally independent of incubation time and surface/substrate combination except for laminin precoating. Taken together, these data indicate that human endothelial cell adherence to PET may be significantly enhanced by PDSM and surface precoating with fibronectin. Attachment occurs rapidly and, once attached, the cells demonstrate a very firm attachment force capable of resisting shear stresses up to 90 dynes/cm2.
Interaction of human serum lipoproteins with biomaterials
Authors: Jayakumari N. , Chitra M. , Iyer K. Subramonia
Published: December 2004

Human serum was incubated with representative portions of polyvinyl chloride (PVC) blood storage bags and vascular prostheses. The in vitro interaction process with lipo‐protein was followed by polyacrylamide gel electrophoresis (PAGE) using sudan black and nitroblue tetrazolium (NBT) in the prestaining procedure. Densitometric scan of all the lipoprotein bands in serum after incubation with PVC bag material when prestained with sudan black showed remarkable increase in intensity. However, in the same experiment when NBT was used for prestaining no increase in the intensity of any of the lipoprotein bands could be observed. Since sudan black is known to bind cholesterol specifically we suggest that a molecular unfolding occurs when lipoprotein interacts with PVC bag material. When similar experiments were carried out with vascular prosthesis there was conspicuous decrease in the intensity of the high‐density lipoprotein (HDL) band especially when stained with NBT. This indicates preferential adhesion of HDL during interaction with vascular prosthesis.
Study of the osteoconductive properties of bioactive glass fibers
Authors: Pazzaglia Ugo E. , Gabbi C. , Locardi B. , Di Nucci A. , Zatti G. , Cherubino P.
Published: December 2004

Bioactive glass fibers have been prepared and implanted in cortical defect and in muscle. The fibers can act as a substrate for bone apposition, when implanted in a cortical defect, and become incorporated in the new bone matrix. The same results were obtained when fibers were implanted in a muscle pouch together with bone marrow cells. An intense inflammatory reaction was observed when bioactive glass fibers were implanted in muscle; the reaction was milder when fibers were implanted in bone or in muscle together with bone marrow cells. This fact supports the hypothesis that osteogenic cells adhere in an early phase to the substrate and prevent recognition of the foreign material by inflammatory cells. This appears to be a fundamental condition for direct bone matrix apposition on the surface of fibers.
Amphiphilic networks: II. Biocompatibility and controlled drug release of poly[isobutylene‐co‐2‐(dimethylamino)ethyl methacrylate]
Authors: Chen Dianja , Kennedy Joseph P. , Kory Martha M. , Ely Daniel L.
Published: December 2004

Biocompatibility and diffusional characteristics of recently synthesized unique amphiphilic newtworks, i.e., copolymers of methaycryloyl‐capped polysiobutylene (MA‐PIB‐MA) with 2‐(dimethylamino)‐ethyl methacrylate (DMAEMA) have been examined. Excellent biocompatibility and biostability were obtained after 7 weeks with films containing 53–58% MA‐PIB‐MA implanted dorsally or abdominally in rats. In contras, neworks with higher or lower MA‐PIB‐MA contents showed decreased biocompatibility. These amphiphilic networks were also studied as potential implantable drug release systems. Bromophenol blue and folic acid were used as model compounds for drug release. Diffusion of these chemicals from loaded networks into water showed a marked pH dependence. Under specific well‐defined conditions (MA‐PIB‐MA/DMAEMA content, pH, time range) release was observed to be independent of time (zero‐order release).
Desorption and exchange properties of adsorbed albumin on apatite. Influence of long‐term interfacial residence times
Authors: Mura M. J. , Behr S. , Voegel J. C.
Published: December 2004

A technique using 125‐I‐labeled proteins was employed to study static adsorption properties and slow exchange and desorption processes of human albumin in contact with synthetic hydroxyapatite beads. With the aid of a thermostated “minicolumn,” the adsorption isotherm was obtained during a so‐called multiadsorption process, and could be described by a Langmuir adsorption model (K = 1.10 × 1010 cm3 · mol−1). All kinetic desorption and exchange experiments could be fitted by a simple exponential function of time. No influence of long‐term interfacial residence times on characteristic relaxation times or percentage of desorbed or exchanged proteins could be detected in the present system. On the other hand, as compared to the low surface coverage domain, the small percentage of desorbable and high percentage of exchangeable molecules in the adsorption plateau domain was attributed to a bimolecular exchange process.
Effects of synthetic calcium phosphates on the 3h‐thymidine incorporation and alkaline phosphatase activity of human fibroblasts in culture
Authors: Orly I. , Grégoire M. , Menanteau J. , Dard M.
Published: December 2004

Gingival fibroblasts were cultured with four different calcium phosphate minerals (hydroxyapatite, whitlockite, b̃‐tricalcium phosphate, and octocalcium phosphate). 3H‐thymidine incorporation into DNA and alkaline phosphatase specific activity were determined after different incubation periods. As a consequence of the phagocytosis of calcium phosphates crystals, we pointed out, compared to control, a stimulation of the rate of 3H‐thymidine incorporation and sharp decreases in alkaline phosphatase activity. The magnitude of the alkaline phosphatase activity inhibition was observed to be increased with the solubility of the materials. We propose that the effects of calcium phosphates on alkaline phosphatase and 3H‐thymidine incorporation could be calcium‐mediated events, resulting from intracellular dissolution of phagocytized materials. We suggest that in vitro determination of 3H‐thymidine incorporation and alkaline phosphatase activity, which are highly sensitive tests, could be involved in evaluation procedures of calcium phosphates biomaterials.
Immobilization and characterization of β‐galactosidase in thermally reversible hydrogel beads
Authors: Park Tae Gwan , Hoffman Allan S.
Published: December 2004

β‐Galactosidase has been immobilized within thermally reversible hydrogel beads and has been studied in batch and packed bed reactor systems. The enzyme was entrapped in a copolymer hydrogel of N‐isopropylacrylamide (NIPAAm) and acrylamide (AAm) as beads were formed in an inverse suspension polymerization. A reversible deswelling and reswelling of the hydrogel matrix was induced by first warming and then cooling through 37–40°C, which is the lower critical solution temperature, LCST, of the backbone copolymer. The optimum temperature for maximum activity of the immobilized enzyme‐gel bead system was found to be 30–357deg;C in a batch mode and 40°C in a packed bed reactor, which were both below the 50°C optimum for the free enzyme. These differences are understandable, since the mass transfer rates of substrate and product within the pores of the gel matrix are controlled mainly by the temperature, so therefore it is the temperature which governs the overall activity of the immobilized enzyme system. It was also found that when the operational temperature in the packed bed reactor was cycled between temperatures below (35°C) and above (45°C) the copolymer gel LCST, the activity of the immobilized enzyme almost fully recovered after each cycle. In fact, the enzyme‐gel system exhibited a complete “shut‐off” in activity at 50°C which was the temperature where the free enzyme showed its maximum activity. The thermal cycling operation of LCST enzyme‐gel beads can be used to enhance overall activity and productivity of a packed bed reactor, when compared to isothermal operation of this reactor. This is due to the thermally induced “pumping” which enhances mass transfer rates of substrate in and product out of the gel beads.
Sepsis of vascular catheters. II: In vitro disinfection of colonized tubing
Authors: Dennis Melvin B. , Jones Douglas R. , Tenover Fred C.
Published: December 2004

Preparatory to development of in situ disinfection of implanted catheters, silicone rubber tubing colonized by incubation with Staphylococcus aureus, Staphylococcus epidermidis, or Klebsiella pneumoniae was used to test the efficacy of various chemicals in vitro. Protocols sterilizing all segments colonized for 24 h (n = 30) were immersion into 50% povidone iodine for 5 and 60 min, 100% povidone iodine for 5, 15, and 60 min, 1.2 × 103 ppm chlorine dioxide for 15 and 60 min, and 1.2 × 103 ppm chlorine dioxide buffered to pH 5.1 for 60 min. Immersion in up to 2% chlorhexidine, 7.4% formaldehyde, or 6% sodium hypochlorite for up to 60 min failed to sterilize all segments. None of 117 control segments were sterilized. Segments colonized for seven days were sterilized by immersion into 100% povidone iodine for 15 or 60 min. Use of 1.2 × 103 ppm chlorine dioxide for 60 min sterilized 97% of segments tested. Lower concentrations and shorter exposure times failed to sterilize all segments. Eighteen silicone rubber catheters, colonized on the outer surface, were all sterilized within 24 h by a chlorine dioxide solution placed in the lumen and diffusing through the wall to kill the bacteria.
The influence of calcium phosphate biomaterials on human bone cell activities. An in vitro approach
Authors: Grégoire M. , Orly I. , Menanteau J.
Published: December 2004

An in vitro method is described to assess the influence of synthetic calcium phosphate powders on osteoblast activities. Human osteoblast cell cultures were established from iliac crest. MC3T3‐E1, an established osteogenic cell line, was employed as a control. Scanning and transmission electron microscopic observations clearly demonstrated the internalization of particles of calcium phosphate by the two osteoblast cell populations. As a consequence to the phagocytotic process, RNA transcription and protein synthesis were stimulated, as indicated by the measurements of labeled uridine, leucine and proline uptakes. From these data, it is proposed that such an in vitro model, using one of the specific cell types involved in the tissue responses to implants, could be useful to assess the biological response at the cell–biomaterial interaction.
Preparation of spherical encapsulation of activated carbons and their adsorption capacity of typical uremic toxins
Authors: Lee Chau‐Jen , Hsu Shih‐Tong
Published: December 2004

A method has been designed for making spherical microencapsulation of activatedcarbon particles for use in the removal of metabolic wastes and/or toxins from blood. This bench‐scale method was able to make better uniformity in particle size, and at a higher particle production rate. The material properties such as particle size, particle porosity, electromicroscopy of surface morphology, surface hardness, and pore‐size distribution were characterized in order to conclude with their adsorption capacity for specific toxin solutes. The performance characteristics of these self‐prepared particle encapsulation was also evaluated against the commercially available hemoperfusion particles, e.g., Kuraray's DHP (Japan). The encapsulation particles were also coated with polyhydroxyethyl methacrylate (PHEMA) for blood compatibility purpose.
The histological effects of the implantation of different sizes of polyethylene particles in the rabbit tibia
Authors: Goodman S. B. , Fornasier V. L. , Lee J. , Kei J.
Published: December 2004

This study examines the histological effects of different sizes of polyethylene particles implanted into the rabbit tibia. Seventeen mature New Zealand white female rabbits were allocated into three groups. Group 1 (5 rabbits) received polyethylene particles averaging approximately 16 μm in diameter, implanted into the right proximal tibia through a drill hole. Group 2 (5 animals) received particles averaging 26 μm, and Group 3 (7 rabbits) received particles averaging 67 μm. The left tibia was drilled but not implanted. Animals were sacrificed after 16 weeks. Histological analysis disclosed decreased hematopoietic activity within the left tibial drill hole. In all groups, the right tibia demonstrated positively birefringent polyethylene particles surrounded by, and within (smaller particles), histiocytes and giant cells in a fibrous tissue stroma. Statistical analysis disclosed more fibrocytes and less marrow cells at the interface of Group 3 (largest particles) compared to Group 1 and 2. Larger polyethylene particles, being less readily phagocytosed, appear to produce more fibrous encapsulation, compared to particles of a smaller size. The histological reaction stimulated by the different sizes of polyethylene particles resembled the membrane surrounding loose joint arthroplasties in humans.
Stiffness and strength tailoring of a hip prosthesis made of advanced composite materials
Authors: Chang Fu‐Kuo , Perez Jose Luis , Davidson James A.
Published: December 2004

This work is concerned with the design of hip prostheses using advanced fiber reinforced composite materials. The major focus of the study is to evaluate how the stiffness and strength of composite hip prostheses can be affected by variations in ply orientation and stacking sequence for a selected manufacturing method. This investigation involved both analytical and experimental work. An analytical model was developed which consists of a stress analysis and a failure analysis. A finite element program was developed during the course of the investigation for analyzing stresses, strains, and deformations of composite stems with a simplified configuration. Failure and mode of failure were predicted by appropriately selected failure criteria. Experiments were also performed on T300/976 graphite/epoxy composites to verify the analysis and the computer calculations. Both testing and analysis accounted for the various combinations of in‐plane and out‐of‐plane (torsion) loading that can act on the prosthetic hip. Simplified composite stems with a 120 layer thickness were fabricated and tested. An excellent agreement was found between the measured strain data and the numerical calculations. Using the program, parametric studies were performed. It was found that an optimal design of hip stems can be achieved by using advanced fiberreinforced composite materials, but great care must be taken when selecting the appropriate ply orientation and stacking sequence for a chosen fabrication method.
In vitro and in vivo studies of heparinized‐collageno‐elastic tubes
Authors: Senatore Fred , Shankar Hariharan , Chen Jyh‐Herng , Avantsa Srinivas , Feola Mario , Posteraro Robert , Blackwell Eric
Published: December 2004

Heparin was covalently coupled to collageno‐elastic grafts (CET) derived from lamb carotid arteries, by using the crosslinking agent 1‐ethyl‐3 (3‐dimethylaminopropyl) carbodiimide (EDC). The collagenous grafts were pretreated with various aminating agents in order to enhance the number of available binding sites on the collagen surface. By varying the EDC/heparin weight ratio, the pH of the immobilization media, and the pretreatment agent, a global search pattern maximized heparin loading at 3.90 ± 0.36 USP heparin/cm2 collagenous graft surface when the EDC/heparin ratio was 2:1 at a pH of 1.5 with 1 M hydroxylamine sulfate as the pretreatment agent. Heparinized CETs were superior to nonheparinized CETs by exhibiting both enhanced antiplatelet activity in using an in vitro differential recirculation reactor with chromium‐51 tagged platelets and enhanced patency when interposed in canine carotid arteries. Both antiplatelet activity and patency duration for heparinized CETs were independent of heparin loading.
Preparation and evaluation of radiopaque hydrogel microspheres based on PHEMA/iothalamic acid and PHEMA/iopanoic acid as particulate emboli
Authors: Jayakrishnan A. , Thanoo B. Chithambara , Rathinam K. , Mohanty M.
Published: December 2004

Highly porous poly(2‐hydroxyethyl methacrylate) (PHEMA) microspheres prepared by suspension polymerization of 2‐hydroxyethyl methacrylate (HEMA) in presence of polymeric diluents such as poly(methyl methacrylate) (PMMA) in toluene and poly(tetramethylene glycol) (PTMG) were made radiopaque by esterification of the reactive hydroxyl groups with iothalamic acid and iopanoic acid, two radiopaque substances clinically used. Of the various solvents and catalysts examined, tetrahydrofuran (THF) and N,N′‐dimethyl paratoluidine (DMPT) were found to be best for obtaining a high degree of conversion. More than 30 wt% iodine could be bound to the microspheres which made them sufficiently radiopaque to be imaged radiographically. Microspheres retained their porosity, swelling ability, hydrophilicity, and surface morphology to a significant extent after iodination. Preliminary implantation studies of such microspheres subcutaneously in rats have shown no adverse tissue reactions over a 6‐month period. It is suggested that these microspheres would prove to be useful as particulate emboli in endovascular embolization.
Adhesive bonding of denture base resins to plastic denture teeth
Authors: Suzuki Shiro , Sakoh Mitsuo , Shiba Akihiko
Published: December 2004

The adhesive bonding of denture teeth to denture base resins in dentures with conventional acrylic teeth and crosslinked plastic teeth was investigated. The dentures with highly crosslinked plastic teeth such as SR‐Orthosit, Crystal ND, and Mitel‐OM showed poor bonding at the tooth/base resin interface using the conventional bonding method. Elimination of the alginate mold lining material in the conventional bonding method effectively improved bonding at the tooth/base resin interface. The application of 4‐META adhesive bonding agents to the denture teeth improved the interface bonding of highly crosslinked plastic teeth and the denture base. Dentures with Orthosit and Mitel showed differences in bonding ability when two different adhesives were used.
The effect of glass‐ceramic implants on matrix vesicle calcification after two weeks of rat tibial bone healing
Authors: Müller‐Mai C. , Amir D. , Wendland H. , Schwartz Z. , Sela J. , Gross U.
Published: December 2004

Type, size and distribution of extracellular matrix vesicles (MV), known mediators of primary calcification, were studied around bone‐bonding and metal‐oxide containing, nonbonding, glass‐ceramic implants. This was performed in order to further understand the different effects of implants on bone healing. At 14 days after implantation in adult rat tibial bone the effects of different implants on MV were studied by transmission electron microscopy and computerized morphometry. A total number of 4607 MV in 245 electron micrographs were counted and grouped according to diameter, distance from the calcifying front, and classified as four types: “empty,” “amorphous,” “crystal,” and “rupture.” The sequence of types according to diameter and distance was recorded as follows around both implants tested: “rupture” MV were the closest to the front with the largest diameter, followed by “crystal,” “amorphous,” and “empty,” MV with the largest distance from the front and the smallest diameter. Most vesicles were concentrated in a distance of less than 2.4 μm from the front and between diameters of 0.06 μm and 0.22 μm. The noncalcified extracellular matrix around bone‐bonding implants contained more MV than the matrix around the nonbonding type (26.24 MV/10 μm2 and 18.76 MV/10μm2). MV distribution according to type showed that around bonding implants ther was a higher percentage of “crystal” and a lower percent age of “rupture” when compared to the nonbonding type. These results indicate that bonding implansts affect osteoblastic function by increasing tht vesicular number and retardation of intravesicular crystal fromation. It might be suggested that bonding implants induce an increase in the process of primary calcification and a decreased rate of crystal formation resulting with the highest organization of the healing bone.
Compositional analysis of biomer
Authors: Belisle Jon , Maier Susan K. , Tucker Joseph A.
Published: December 2004

Biomer, a segmented polyether polyurethane, has been analyzed via hydrolysis/gas chromatography to determine its composition. In addition to the previously reported 4,4′‐methylene bis(phenyl isocyanate) (MDI), polytetramethylene glycol (PTMO), and ethylenediamine, we now report the presence of diethylamine, 1,3‐diaminocyclohexane and poly(diisopropylaminoethyl methacrylate‐co‐decyl methacrylate), Biomer's cloudy insoluble phase. In addition, a method is presented to characterize the methacrylate additive by molecular weight based on GPC. Also found by chromatography were the antioxidants Santowhite Powder and BHT. XPS shows no Si (silicone) on the Biomer surface, and a total chloride analysis reports no chloride (<0.03%). Time‐of‐flight SIMS data suggest evidence for the methacrylate additive at the surface, and mass spectroscopy can be interpreted as evidence for a diaminocyclohexane.
Line analysis of interface layer on dentin by means of electron‐probe microanalysis
Authors: Fukushima Tadao , Horibe Takashi
Published: December 2004

Three types of brominated methacrylates, SBPPM, BPylM, and BNEM, were synthesized. The distribution of Br, Ca, and Fe at the interface between dentin treated with the 10‐3 solution and resin containing these monomers was analyzed using an electron‐probe microanalyzer (EPMA) in order to predict the composition and thickness of the interface layer on dentin for the corresponding unbrominated methacrylates. There was no significant difference between the brominated and unbrominated methacrylates in either the bond strength to the treated dentin or in the thickness of the interface layer on dentin observed with a scanning electron microscope (SEM). The thickness determined with EPMA was equivalent to that observed with SEM. The concentration of each brominated methacrylate in the interface layer was higher than the original concentration in the resin monomers, and BNEM showed higher concentration than the others. The presence of Fe in the layer was confirmed by EPMA.
Platelet adherence and detachment: A flow study with a series of hydroxyethyl methacrylate‐ethyl methacrylate copolymers using video microscopy
Authors: Feuerstein Irwin A. , Buchan Sue M. , Horbett Thomas A. , Hauch Kip D.
Published: December 2004

The adhesion and detachment of platelets were studied on glass coatings of a series of copolymers of hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA). Observations of the interactions of mepacrine labelled washed platelets with these surfaces from a flowing (500 s−1 wall shear rate) suspension in Tyrode's solution containing albumin and red cells were made with epifluorescent video microscopy (EVM). Total platelet adhesion, including platelets which adhere on first contact and platelets which attach temporarily before adhesion, and the number of detaching platelets were minimal for the 0 and 20% EMA copolymers, reached a maximum for the 50% EMA copolymer and showed reduced values for the 80% and 100% EMA copolymers. For the 50, 80, and 100% EMA copolymers, the adhesion values expressed, as a percentage of total contacting platelets, were not different. Albumin adsorption to these copolymers shows a continuous increase from the 0% to the 100% EMA copolymer. It is likely that the peak in platelet adhesion at the 50% EMA composition is related to: low protein adsorption on the 0 and 20% EMA copolymers, too little albumin adsorption to block adhesion on the 50% EMA copolymer, and full‐scale blocking on the 80 and 100% EMA copolymers due to greater albumin adsorption.
Novel polyfunctional silanes for improved hydrolytic stability at the polymer–silica interface
Authors: Nishiyama Norihiro , Ishizaki Tsutomu , Horie Kozo , Tomari Masato , Someya Minoru
Published: December 2004

Polyfunctional silanes were designed to promote the formation of a stable multisilane layer on the silica surface. The hydrolytic stability of polyfunctional silanes at the interface between silica and polymeric resin was investigated using conventional tensile testing. The specimens were immersed in boiling water and a decrease was observed in the tensile bonding strength of polymeric resin against the silane‐treated silica surface as the immersion time increased. The failure mechanism changes from cohesive failure of the matrix resin to failure of the interface. The time necessary to start the interfacial failure is dependent on the silane concentration in the treating solution and the number of silicone functional groups within the silane molecules. The silane with two silicone functional groups is more stable at the interface between silica and polymeric resin than those which have mono‐ or trisilicone functional groups.
Preparation of thermo‐responsive polymer membranes. I
Authors: Nozawa Iwao , Suzuki Yosuke , Sato Shuji , Sugibayashi Kenji , Morimoto Yasunori
Published: December 2004

Two types of liquid crystal (LC)‐entrapped membranes, (a) polymer alloyed membranes and (b) LC‐adsorbed membranes, were investigated for the purpose of developing the drug delivery systems (DDS) with thermal stimuli responsing. Polymer alloyed membranes were obtained by polymerizing acrylic monomers in presence of LC and LC‐adsorbed membrane were obtained by adsorbing LC into porous hydrophobic polymer membrane. It was made clear from the indomethacin permeation experiments below and above the gel‐liquid crystal phase transition temperature of the LC that the extent of thermo‐sensitivity for LC‐adsorbed membranes was greater than that for the alloyed membrane. The permeability ratio (38°C vs. 32°C) was found to be about 120 with the LC‐adsorbed membrane. It was suggested from the results that the LC‐adsorbed membrane was one of the useful candidates as a thermo‐responsive system for DDS.
A laboratory model to quantitate the resistance of collagen vascular grafts to biodegradation
Authors: Megerman Joseph , Reddy Esphiran , L'Italien Gilbert J. , Warnock David F. , Abbott William M.
Published: December 2004

Recent reports have shown that despite extensive preclinical testing, vascular grafts of biological origin undergo severe biodegradation and aneurysm formation after two or more years of implantation in man. The purpose of this study was to develop a laboratory model to quantitate and correlate the stability of crosslinked collagen grafts in vitro and in vivo. This resistance to biodegradation was assessed by measuring changes in suture pullout force and sample weight in response to controlled digestion with bacterial collagenase, in 0.5‐cm‐long cylindrical graft segments (chemically processed bovine carotid artery and human umbilical cord vein) that were implanted in the rat subcutis for 2 to 12 weeks. Scar tissue was removed from the explants by brief enzymatic digestion, a process that was inhibited when graft segments had become infected. Changes in dry weight were more consistent than were changes in wet weight; drying the graft segments had no effect on their degradation in vivo or in vitro. Intact cylindrical rings suffered somewhat less damage than did opened, flattened cylinders. Graft degradation increased markedly with implantation time, and was detected after only 3 weeks. We conclude that the rat subcutis model, when combined with controlled enzymatic digestion, first to remove scar tissue and then to challenge structural integrity, provides an accelerated assay by which to predict the stability of collagen vascular grafts.
Use of a phosphophoryn‐Ca+2‐collagen composition that mimics a mineralization front in unicortical defects in long bones
Authors: Sauk John J. , Van Kampen Craig L.
Published: December 2004

The present study was designed to ascertain if dynamic ionic matrices that mimic the mineralization front could be used as active scaffolds for bone repair. Dentinal phosphophoryn calcium salts were extracted from unerupted bovine dentin using chatopic buffers and EDTA. The phosphophoryns were subsequently isolated following precipitation with CaCl2. The phosphophoryn‐Ca+2 salts were then mixed with pepsin solubilized bovine skin collagen and lyophilized into hardened sponges. Three groups of 4 beagle dogs were employed such that one leg served as an experimental test site for a mechanical wound, while the contralateral leg served as a control. Animals were sacrificed at 1, 3, and 6 month intervals. The test specimens were harvested, fixed, and processed for routine histology, examined with image histomorphometric analysis, and scored. Tabulation of these data indicated that phosphophoryn‐Ca+2‐collagen enhances the repair of mechanically formed osseous defects in the distal femur of beagle dogs. This enhanced rate of bone repair was manifest by earlier filling of bony voids with osteoid and trabecular bone. Eventually, this process was followed by recortification of the surface defects. These data suggest that components derived from a mineralization front may influence bone formation in unicortical defects within long bones.
Effects of fibroblasts and basic fibroblast growth factor on facilitation of dermal wound healing by type I collagen matrices
Authors: Marks Michael G. , Doillon Charles , Silvert Frederick H.
Published: December 2004

Healing of large open dermal wounds is associated with decreased values of the tensile strength even up to 6 months postwounding. Results of previous studies have shown that healing is facilitated in the presence of a type I collagen sponge by promoting deposition of newly synthesized large‐diameter collagen fibers parallel to the fibers of the sponge. In this study healing is evaluated in dermal wounds treated with a collagen sponge seeded with fibroblasts or coated with basic fibroblast growth factor (bFGF).Experimental results indicate that the presence of a collagen sponge results in increased wound tensile strength and increased collagen fiber diameters in the upper dermis 15 days post‐wounding in an excisional guinea pig dermal wound model. In comparison, dermal wounds treated with collagen sponges seeded with fibroblasts or coated with bFGF showed increased tensile strengths 15 days postimplantation and increased degree of reepithelialization. These results indicate that fibroblast seeding and bFGF coating in conjunction with a type I collagen sponge matrix facilitate early dermal and epidermal wound healing.
In vitro degradation of a poly(ether urethane) by trypsin
Authors: Bouvier M. , Chawla A. S. , Hinberg I.
Published: December 2004

In vitro enzymatic degradation of nonporous films of segmented poly(etherurethane) (Pellethane 2363–80AE) was investigated by incubating the biomaterial in concentrated trypsin solutions for 5 months at room temperature. Chemical degradation of films was monitored by surface analysis techniques such as Fourier transform infrared spectroscopyattenuated total reflectance and electron spectroscopy for chemical analysis. This latter technique proved to be much superior in detecting chemical changes. Extraction of films with methanol and characterization of the extracts by gel permeation chromatography revealed the presence of low‐molecular‐weight polymers. Results have shown that trypsin has the ability to induce degradation in PEU, the soft segment being most affected, particularly the CH2O bond of the either linkages.
The stabilization of fibrillar collagen matrices with 3,4‐dihydroxyphenylalanine
Authors: Gade Jay N. , Fellman Jack H. , Peter Bentley J.
Published: December 2004

Pepsin‐treated type I collagen fibrils were reconstituted by warming to 37°C in the presence of DOPA at a concentration of 1 × 10−3M. Following a 1‐1.5‐h lag period tdhe “gels” became progressively stabilized as indicated by an inability to disperse these at 0°C. Following 24 h of incubation at 37°C, the DOPA‐collagen gels were insoluble in dilute acetic acid even under denaturing conditions. The effect on both gel stability and solubility was concentration‐dependent and was maximum at 1 × 10−3M. Gel solubility changes were significant, with the greatest change occurring between concentrations of 3.1 × 10−5M. DOPA exposure did not alter the fibrillar banding pattern seen at the electron microscopic level. Collagen felts prepared by lyophilization of DOPA‐collagen gels demonstrated an increase in shrinkage temperature which after 24 h exceeded that of rat tail tendon. Preformed collagen felts incubated for 24 h in the presence of 1 mM DOPA also had a greatly increased shrinkage temperature. Pepsin‐treated collagen control felts were consistently unstable at 37°C. The tensile properties of DOPA‐collagen felts were altered with respect to control felts in a time dependent manner. The wet tensile strength increased to four times that of control after 3 days of incubation at 37°C. Matrix extensibility initially increased to 1.5 times that of control felts after 4 days of incubation at 37°C, but decreased to below control values following 6 additional days of incubation. These properties suggest that DOPA may be useful as a stabilizing agent of collagen biomedical prostheses.
Dental implant materials. I. Some effects of preparative procedures on surface topography
Authors: Smith D. C. , Pilliar R. M. , Chernecky R.
Published: December 2004

The effect of different treatments for preparing implant materials was examined by scanning electron microscopy and by contact angle measurements. The materials examined were Ti6Al4V alloy, Co‐Cr‐Mo alloy, Al2O3, and synthetic hydroxyapatite. Samples were prepared with solid or porous surfaces of these materials. These were detergent‐cleaned and then either autoclaved (steam sterilization), radiationsterilized, nitric acid‐etched, or plasmacleaned. The results of wettability studies indicated marked changes in surface energy corresponding to the different preparation methods, and differences in surface morphology were also observed. These differences could have significant consequences onin vivoimplant behaviour as mediated by tissue‐implant interactions.
Student research award in the undergraduate, Master candidate category, or health science degree candidate category, 17th annual meeting of the society for biomaterials, scottsdale, AZ may 1–5,1991. Characterization of the interface in the plasma‐sprayed HA coating/Ti‐6Al‐4V implant system
Authors: Filiaggi M. J. , Coombs N. A. , Pilliar R. M.
Published: December 2004

The successful use of plasma‐sprayed hydroxyapatite (HA) coatings on Ti‐alloy implants for implant‐to‐bone fixation requires strong adherence of the ceramic coating to the underlying metal substrate. In this study, the metal‐ceramic interface was evaluated using mechanical, chemical, and structural characterization methods. Evaluations of an HA‐coated Ti‐6A1‐4V implant system using a modified short bar technique for interfacial fracture toughness determination revealed relatively low fracture toughness values. Additionally, conventional tensile bond strength testing indicated much lower values than previously reported. Using high resolution electron spectroscopic imaging, evidence of chemical bonding was revealed at the plasmasprayed HA/Ti‐6AI‐4V interface, though bonding was primarily due to mechanical interlock at the interface. This study illustrates the benefits of, and the need for, a multilevel approach to evaluate and improve these plasma‐sprayed ceramicme tai subst rate interfaces.
Formation of 4,4′‐methylenedianiline in polyurethane potting materials by either γ‐ray or autoclave sterilization
Authors: Shintani Hideharu , Nakamura Akitada
Published: December 2004

In this experiment, we found that a potential carcinogen, 4,4′‐methylenedianiline (MDA), was produced from γ‐ray irradiated potting materials, medical thermosetting polyurethane (PU). γ‐Ray irradiated PUs were immersed in either methanol or in equine serum. The time course of MDA leached from the potting materials and other variables were compared. A significant relationship was noted between the amount extracted and the rigidity of the potting material. The accumulated amount of extracted MDA (a few ppm in the original sample) increased with increasing irradiation dose by a second‐order equation. One sample indicated reduced MDA elution after irradiation in the early stage. MDA extraction with serum was 82–87% that with methanol. In one case, MDA leaching into serum in the early stage was higher than that into methanol. Autoclave sterilization did not promote MDA formation, thus indicating that autoclaving would be preferable.