摘要:

AbstractXenograft valves of glutaraldehyde‐treated bovine pericardial tissue have been claimed to be an excellent choice for the replacement of malfunctioning human heart valves. These valves exhibit low thrombogenicity, hemodynamic function, and transvalvular gradients superior to their mechanical and tissue counterparts. However, there are differences of opinion concerning the immunogenic properties of these valvular devices. This study was conducted to evaluate the immune reactivity of such implants. Data obtained indicated that whole xenograft sections of both untreated and treated valvular tissue remain immunogenic following initial and secondary subcutaneous implantations in rabbits. Homologous and cross‐reacting antibodies were detected by means of indirect hemagglutination test 30 days after initial implantation of the grafts. Presence of cellular immune response as judged by skin reaction and leukocyte migration inhibition tests indicated that glutaraldehyde treatment of tissues does not destroy cellular immunity. Data obtained also suggest that chemical modification of such implants by glutaraldehyde probably alters, but does not abolish some antigenic determinant sites on the tissue surface. Glutaraldehyde treatment of bovine pericardial tissue does not render the tissue immunologically in

ISSN:0021-9304    

DOI:10.1002/jbm.820190103

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractCharacterization of microphase separated structure, interaction with blood components such as lipids, and fatigue behavior after immersion in blood components were carried out for segmented poly(urethaneureas). The materials studied were Biomer and segmented poly(urethaneurea) (TU‐Mn) composed of hard segment with 4,4′‐diphenylmethane diisocyanate (MDI)‐ethylenediamine (EDA) or 4,4′‐diaminodiphenylmethane (DAM) and soft segment with MDI‐polytetramethylene glycol (PTMG) [Mnof 856, 1350, and 2000]. Small‐angle x‐ray scattering, wide‐angle x‐ray diffraction, and dynamic viscoelastic measurements revealed that these materials showed the state of microphase separation. TU‐Mnwith PTMG ofMn= 856 shows the partial phase mixing between hard and soft segments, and phase separation was improved with an increase ofMnof PTMG. Biomer has the characteristics of stronger aggregation of hard segment than that of TU‐Mn. All the specimen showed lipid absorption, but the amount of absorption decreased remarkably after precoating on the specimen surface with serum albumin. Lipid absorption of the specimen was confirmed by dynamic viscoelastic and IR measurements. In the case of segmented poly(urethaneurea) which did not immersed in lipids solution, their fatigue strength are sufficient for application to artificial heart systems. However, fatigue strength of the TU‐Mnseries was decreased drastically after absorption of lipids. On the other hand, Biomer did not show a decrease of fatigue strength after lipid absorption. The reduction of fatigue strength in the TU‐Mnseries after lipid absorption will be attributed to the weak aggregation of hard segment domain. This reduction of fatigue strength in the TU‐Mnseries is characterized by formation of microcrack and mirror zone in fatigue fractured specimen. As the precoating of the specimen surface with serum albumin inhibits the absorption of lipids, the reduction of fatigue strength was not observed for the specimen precoated with serum albumin even after immersing the TU‐Mnseri

ISSN:0021-9304    

DOI:10.1002/jbm.820190104

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractBecause 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 describe

ISSN:0021-9304    

DOI:10.1002/jbm.820190105

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractSurfaces of amorphous carbon, polystyrene, and polycarbonate were exposed to solutions of fibrinogen, a modified fibrinogen which lacked the alpha chain protuberance, and serum albumin. The results were studied by electron microscopy. The exposures occurred in a well characterized flow environment at a shear rate of 135/s. All three protein species formed a film when adsorbed to carbon films. When the proteins were adsorbed to polystyrene surfaces, formation of a network was observed. Polycarbonate surfaces adsorbed the proteins both as a network and as a continuous film. It was observed that the nature of the adsorption process depended upon the specific combination of molecule and material. For example, on carbon, individual fibrinogen molecules retain their trinodular structure and adsorb randomly until a monolayer forms. On polystyrene, the individual fibrinogen molecules appear as globules and a network forms before complete coverage occurs.

ISSN:0021-9304    

DOI:10.1002/jbm.820190106

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe reproducible regulation of release of a macromolecule (bovine serum albumin) from biocompatible polymer systems has been demonstrated. Small magnetic spheres or cylindrical magnets were embedded within the polymer matrix which was then subjected to an oscillating magnetic field. In this fashion baseline release rates could be increased 5‐ to 10‐fold with 5–10% standard error. Parameters critical to the regulation of this release included the position, orientation, and magnetic strength of the embedded objects and the amplitude and frequency of the applied magnetic field. Scanning electronmicrographs of the polymer matrix surface reveal that a gap, approximately 100/μm wide, is formed between the embedded object and adjacent polymer material after repeated exposure to an oscillating magnetic

ISSN:0021-9304    

DOI:10.1002/jbm.820190107

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe creep of microspecimens of posterior dental composites was studied using a torsional creep apparatus. Shear stresses were maintained for 3 h and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50°C and four torque levels. The effect of conditioning the specimens in water up to 8 weeks was studied. The posterior composites exhibited linear viscoelastic behavior at low deformations. They had higher shear moduli and greater resistance to creep than conventional and microfilled composites. In aging experiments, maximum shear moduli occurred when specimens were 48 h to 1 week old. Subsequent softening was attributed to water absorption. Residual strain was highest when the composites were stressed within 24 h of initiating polymerization. Residual strain was very low in specimens 48 h to 8 weeks of age

ISSN:0021-9304    

DOI:10.1002/jbm.820190108

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

ISSN:0021-9304    

DOI:10.1002/jbm.820190109

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

ISSN:0021-9304    

DOI:10.1002/jbm.820190102

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY