摘要:

AbstractSurface chemical analysis of two commercially available polyurethanes, i.e., Avcothane and Biomer was carried out by electron spectroscopy for chemical analysis (ESCA). The depth which is subject to analysis is in the range of 50–100 Å. The variables studied in this study are the difference in exposure to air or to the mold substrate during the solvent casting process. Model compounds such as a pure polydimethylsiloxane, polyether soft segment and hard segment copolymer were used to identify and assign various ESCA peaks. The air facing surface of Avcothane which is the blood contacting surface is found to be covered mostly with polydimethylsiloxane polymer, with a small amount of polyether soft segment mixed with silicone. Therefore, the hard segment of the polyurethanes is hidden beneath the blood contact surface in Avcothane. In Biomer films, the air facing surface contains a greater concentration of polyether soft segment than the substrate surface. These results are consistent with our previous results obtained by Fourier transform IR internal reflection studies and Auger electron spectrosco

ISSN:0021-9304    

DOI:10.1002/jbm.820130202

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe importance of surface charge in foreign body carcinogenesis was evaluated by implanting in C3H/HeJ male mice, bipolar polystyrene thermoelectrets formed in variously charged electrical fields. Charged electrets had tumor rates similar to control groups. The cumulative probability of tumor development was highest in the charged electret group being 0.58 at 133 weeks after implantation. The tumor rate for all charged electrets was 27% as compared to 17% and 6% for the control groups. The latent period of tumor induction varied little between groups and averaged approximately 700 days. No conclusions regarding the tumorigenic effect of electropositive versus electronegative (body) sides of the electret. An occasional tumor (2/25) arose on both sides of a single electret. The antigenicities of tumors tested by excise and challenge techniques were weak. The immunologic relationship between top and bottom growing tumors on a single electret could not be adequately determined because of the weak antigenicity.

ISSN:0021-9304    

DOI:10.1002/jbm.820130203

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

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

ISSN:0021-9304    

DOI:10.1002/jbm.820130204

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe hemolytic potential of pure ethylene oxide in solution was evaluated as a function of initial ethylene oxide concentration in three test systems, diluted whole blood in isotonic saline, erythrocytes washed and resuspended in isotonic saline, and erythrocytes washed and resuspended in isotonic phosphate buffer. Concentrations of 2 mg/ml (2000 ppm) were necessary before cell lysis was observed in either of the isotonic saline systems. This value increased to 10 mg/ml (10,000 ppm) in the isotonic buffer system. Efforts have been made to correlate the hemolysis and cell culture toxicity of residual ethylene oxide in five medical materials to the toxicity of pure ethylene oxide. Only materials exhibiting a low order of inherent toxicity showed any correlation. In poly(vinyl chloride) tubing containing 1.8 and 2.1 mg ethylene oxide per gram of materials, a small amount of toxicity was seen in the cell culture system but toxicity was absent in the hemolysis test.

ISSN:0021-9304    

DOI:10.1002/jbm.820130205

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe excellent corrosion resistance of titanium and its alloys to physiological chloride solutions is well documented. Occasionally, however, titanium compounds have been found in tissue adjacent to titanium implants. These findings were reported to be unrelated to wear processes, suggesting that either the metal or its passive film was dissolving. The unpredictability of these findings further suggests that preimplantation surface treatments and/or variations in the physiological environment may be factors. To determine a mechanism by which titanium can be released from an implant a study was initiated which employed electrochemical techniques, Auger electron spectroscopy (AES), and replica transmission electron microscopy (RTEM). Specifically, the purpose was to characterize the passive film on titanium and Ti‐6Al‐4V, and to determine if there is dissolution of the film or metal in a static unstressed state. Passive film behavior of commercially pure titanium, Ti‐6Al‐4V and nitrided Ti‐6Al‐4V was studied by anodic polarization and pulse potentiostatic capacitance techniques in Ringer's solution at 37°C with and without physiological additions of several amino acids. Solution Po2,pH, and specimen surface finish were varied to include all probablein vivoconditions. In all tests, potentiostatic anodic polarization of each material yielded potential‐current density curves which showed passivity over the entire experimental range. This range greatly exceeded the oxygen‐reduction reversible electrode potential. No breakdown potentials were observed. The passive current density was not significantly affected by varying the experimental parameters. AES as well as charge and capacitance measurements showed that the electrochemical reaction which occurred was growth of the passive film. The data indicated that the effective electrochemical area of each specimen was less than its geometrical area, and was dependent on bothpH and surface finish. The findings of this study showed that, under static conditions, titanium and Ti‐6Al‐4V should withstand exposure to physiological chloride solutions at body temperature indefinitely. Furthermore, the findings are consistent with a model of the implant surface inwhich the naturla air oxide that initially forms on an abraded implant surface is comprised of microscopic oxide needles. It is proposed that (i) the needless canbe broken off or dissolvedin vivo, providing the source of the titanium sometimes found in tissue adjacent to an implant, and (ii) use of certain pretreatments may remove the needles prior to surgery, resulting in the more common case in which titanium is nto

ISSN:0021-9304    

DOI:10.1002/jbm.820130206

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe fatigue behavior of alumina and bioglass‐coated alumina was determined in air and biological test environments by the dynamic fatigue test technique in which strength is measured as a function of stressing rate. The good correlation found between the test data and fracture mechanics theory indicates that fatigue failure is controlled by the slow crack growth of preexisting flaws and that fracture mechanics theory can be used in making failure predictions for alumina and bioglass‐coated alumina in biological environments. Thus, it is believed that lifetime predictions can be made for ceramic implants on the basis of short‐term test data utilizing fracture mechanics princ

ISSN:0021-9304    

DOI:10.1002/jbm.820130207

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractCurrent practice in the manufacture of Co‐Cr‐Mo alloy total hip prostheses is the use of a solution treatment to increase the ductility of the as‐cast alloy. This study is concerned with the reactions encountered during solution treatment at temperatures between 1165–1270°C. These reactions, including incipient melting, a carbide transformation fromM23C6toM6C and sigma‐phase formation, have bene examined using both qualitative and quantitative metallographci techniques, and are shown to influence the production of a single phase microstructure. As a res8lt, an optimum temperature for solution treatment of 1220°C has been determined. It is futher proposed that a reduction in the carbon content of this alloy would improve its solution treatme

ISSN:0021-9304    

DOI:10.1002/jbm.820130208

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThein vitrodeformation failure behavior of the conventional and the recent high copper dental amalgams is studied under different strain rates. The conventional silver‐tin amalgams exhibited significant slow compressive flow at low strain rates, but failed catastrophically at the higher loading rates. On the other hand, amalgams containing highest copper contents showed no compressive flow and failed ctastrophically at all the loading rates. The slow compressive flow in the conventional dental amalgams indicate that dislocations may play an important role in the deformation process of the amalgams at the lower strain rate

ISSN:0021-9304    

DOI:10.1002/jbm.820130209

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractPlasma polymerized ethylene (PPE), styrene (PPS), and chlorotrifluoroethylene (PPCTFE) were synthesized by exposing the monomeric gases to an inductively coupled radio frequency “glow‐discharge” field. The polymer films were deposited on poly(dimethyl) siloxane (medical grade Silastic®), which was then surgically implanted in rat paravertebral muscle for periods up to 84 weeks. The biocompatibility of the plasma deposited films and uncoated Silastic® was evaluated by qualitative (graded inflammatory cell response) and quantitative (connective tissue capsule thickness) techniques as a function of time. The morphological features of the connective tissue capsule and the plasma polymerized films were examined by SEM after 75 weeks of implantation. Results showed that the acute inflammatory cell migration around PPS and PPCTFE was at a maximum in 2 weeks, decaying to control levels in 4 to 8 weeks. The PPE response was judged as less than the control response up to 4 weeks. After 8 weeks no qualitative difference could be detected between the plasma polymerized films and Silstic®. On the other hand, a quantifiable change in fibrous capsule response as a function of time and material was noted until 24 weeks. From these data we conclude that these types of films do not elicit an untoward foreign body reaction at a skeletal muscle implant site

ISSN:0021-9304    

DOI:10.1002/jbm.820130210

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

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

ISSN:0021-9304    

DOI:10.1002/jbm.820130211

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY