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PubMed1978

Corrosion behavior of cast and forged cobalt-based alloys for double-alloy joint endoprostheses.

An ideal combination of mechanical and corrosion properties of long-term implants such as joint endoprostheses has yet to be found. Besides being resistant to pitting and crevice attack, which can lead to corrosion fatigue and stress corrosion cracking failures, the implant material must be highly resistant to wear and abrasion. Two cobalt-based alloys, wrought CoNiMoTi and air-cast CoCrMo, were subjected to a number of selected in vitro electrochemically and chemically accelerated corrosion tests in chloride-containing solutions with wrought AISI-316L used as a reference alloy. A limited number of immersion tests in FeCl3 and acidified FeCl3 solutions were also conducted. It is found that the mechanical properties of wrought CoNiCrMoTi alloy qualify it as a substitute for cast CoCrMo alloy and wrought AISI-316L in anchorage shaft production for all types of joint endoprostheses. Wrought CoNiCrMoTi has a higher resistance to fatigue cracking compared with cast CoCrMo and is as resistant to selective corrosion phenomena such as stress corrosion cracking.

Alloys↗
PubMed1995

Effect of carbon content on the resistance to localized corrosion of as-cast cobalt-based alloys in an aqueous chloride solution.

The effect of carbon content on the resistance to localized corrosion of ASTM-F75, as-cast cobalt-based alloys, was studied using potentiostatic polarization tests in Ringer's solution. Critical pitting potentials were estimated from the potentiostatic polarization curves and were found to increase with decreasing carbon content. The highest resistance to pitting corrosion observed at low C contents was attributed to a greater chemical and microstructural homogeneity in the as-cast condition. The results of the investigation led to the conclusion that the use of low C content ASTM-F75 as-cast alloys in the manufacture of orthopedic implants may result in a lower release rate of corrosion products which should improve the "in vivo" performance of the implants.

Alloys↗
PubMed2005

Bioactive and biocompatible pieces of HA/sol-gel glass mixtures obtained by the gel-casting method.

Hydroxyapatite (HA)/glass mixtures have shown a faster bioactive behaviour than HA itself. On the other hand, the gel-casting method is a simple and reproducible colloidal method to produce ceramic pieces with complex shapes. In this work, pieces of HA/glass mixtures were prepared by the gel-casting method. A study for obtaining concentrated slurries of these mixtures is reported; the bioactivity and biocompatibility of the obtained pieces have been studied also. The influence of pH, dispersant concentration, the content and milling of glass, and the way to prepare the suspensions were investigated. The lowest viscosity and better rheological properties were achieved with the lowest glass content, when the glass was added after the dispersion of the HA powder and when the glass was not milled after calcination. Fluid suspensions with a high solid content (50 vol.%) could be prepared and well-shaped pieces were obtained from these slurries. These pieces showed in vitro bioactive behavior in simulated body fluid; additionally, the proliferation and spreading assays with osteoblastic cells (HOS) showed that the pieces are biocompatible. The results obtained indicate that the gel-casting of HA/glass mixtures produces bioactive and biocompatible pieces with the required shapes. Therefore, these materials could be good candidates for clinical applications and scaffolds for tissue engineering.

Biocompatible Materials↗
PubMed2006

Characterization and bioactivity of tape-cast and sintered TCP sheets.

The purpose of this study was to investigate the influence of sintering temperature on in vivo and in vitro bioactivities of sintered tricalcium phosphate (TCP) sheets prepared by the tape casting technique. Green sheets of beta-TCP prepared by tape casting were sintered for 2 h in a furnace at atmospheric pressure, at five different sintering temperatures: 900, 1000, 1100, 1150, and 1200 degrees C. Measurement of X-ray diffraction and Fourier transform infrared spectrometry showed the presence of alpha-tricalcium phosphate phase in the TCP sheet sintered at 1200 degrees C, in addition to beta-TCP phase. As compared with the other sintered TCP sheet, the TCP sheet sintered at 1200 degrees C demonstrated a lower dissolution rate in phosphate buffered saline solution at 37 degrees C and pH 7.4 over 24 weeks, and more amount of apatite formation in Hanks' balanced salt solution with pH 7.4 was observed. After 4 weeks' implantation of sintered TCP sheets into tibial diaphyses of rabbits, the bone-sheet contact of the TCP sheet sintered at 1200 degrees C was significantly higher than that of the TCP sheet sintered at 900 degrees C. These results indicate that a flat sintered TCP sheet prepared by tape casting is a promising material for a bone substitute.

Animals↗
PubMed2004

SEM/EDS evaluation of porcelain adherence to gold-coated cast titanium.

The adhesion between titanium and dental porcelain is related to the diffusion of oxygen to the reaction layer formed on cast-titanium surfaces during porcelain firing. The diffusion of oxygen could be suppressed by coating the titanium surface with a thin gold layer. This study characterized the effects of gold coating on titanium-ceramic adhesion. ASTM grade II CP titanium was cast into a MgO-based investment (Selevest CB, Selec). The specimen surfaces were air abraded with 110-microm Al(2)O(3) particles. Gold coating was applied on titanium surfaces by three methods: gold-paste (Deck Gold NF, Degussa-Ney) coating and firing at 800 degrees C for three times, single gold-paste coating and firing followed by sputter coating (40 mA, 500 s), and sputter coating (40 mA, 1000 s). Surfaces only air abraded with Al(2)O(3) particles were used as controls. An ultra-low-fusing dental porcelain (Vita Titankeramik, Vident) was fused on titanium surfaces. Specimen surfaces were characterized by SEM/EDS and XRD. The titanium-ceramic adhesion was evaluated by a biaxial flexure test (N = 8), and area fraction of adherent porcelain (AFAP) was determined by EDS. Numerical results were statistically analyzed by one-way ANOVA and the Student-Newman-Keuls test at alpha = 0.05. SEM fractography showed a substantial amount of porcelains remaining on the gold-sputter-coated titanium surfaces. A new Au(2)Ti phase was found on gold-coated titanium surface after the firing. Significantly higher (p <.05) AFAP values were determined for the gold-sputter-coated specimens compared to the others. No significant differences were found among the other groups and the control. Results suggested that gold coatings used in this study are not effective barriers to completely protect titanium from oxidation during the porcelain firing, and porcelain adherence to cast titanium can be improved by gold-sputter coating used in the present study.

Dental Porcelain↗
PubMed2005

Mechanical properties of cast Ti-Hf alloys.

This study examined the mechanical properties of a series of Ti-Hf alloys. Titanium alloys with 10 to 40 mass % Hf were made with titanium and hafnium sponge in an argon-arc melting furnace. Specimens cast into magnesia-based investment molds were tested for yield strength, tensile strength, percentage elongation, and modulus of elasticity. Vickers microhardness was determined at 25 to 600 microm from the cast surface. X-ray diffractometry was also performed. Commercially pure Ti (CP Ti) and pure Ti prepared from titanium sponge were used as controls. The data (n = 5) were analyzed with a one-way ANOVA and the Student-Newman-Keuls test (alpha = 0.05). The diffraction peaks of all the metals matched those for alpha Ti; no beta phase peaks were found. Alloys with Hf > or = 25% had significantly (p < 0.05) higher yield and tensile strength compared to the CP Ti and pure Ti. There were no significant differences (p > 0.05) in elongation among all the Ti-Hf alloys and CP Ti, whereas the elongation of alloys with Hf > or = 30% was significantly (p < 0.05) lower than that of the pure Ti. The cast Ti-Hf alloys tested can be considered viable alternatives to CP Ti because they were stronger than CP Ti and had similar elongation.

Alloys↗
PubMed2007

Effects of airborne-particle abrasion, sodium hydroxide anodization, and electrical discharge machining on porcelain adherence to cast commercially pure titanium.

The aim of this study was to determine the effect of airborne-particle abrasion (APA), sodium hydroxide anodization (SHA), and electrical discharge machining (EDM) on cast titanium surfaces and titanium-porcelain adhesion. Ninety titanium specimens were cast with pure titanium and the alpha-case layer was removed. Specimens were randomly divided into three groups. Ten specimens from each group were subjected to APA. SHA was applied to the second subgroups, and the remaining specimens were subjected to the EDM. For the control group, 10 specimens were cast using NiCr alloy and subjected to only APA. Surfaces were examined by using scanning electron microscope and a surface profilometer. Three titanium porcelains were fused on the titanium surfaces, whereas NiCr specimens were covered with conventional porcelain. Titanium-porcelain adhesion was characterized by a 3-point bending test. Statistical analysis showed that the porcelain-metal bond strength of the control group was higher than that of the titanium-porcelain system (p < 0.05). There were no significant differences between the bond strengths of titanium groups (p 0.05), except the bond strengths of Noritake Super Porcelain TI-22 groups on which APA and SHA were applied (p < 0.05). SHA and EDM as surface treatment did not improve titanium-porcelain adhesion when compared to APA.

Chromium Alloys↗
PubMed1983

Circulatory pathways in the sinusal spleen of the dog, studied by scanning electron microscopy of microcorrosion casts.

Scanning electron microscopy of microcorrosion casts was used to visualize circulatory pathways in the sinusal spleen of dog. The examination of contracted versus dilated organs and variations of the volume of material injected gave an indication of flow dynamics. Minimal injections of material into contracted spleens produced filling of mainly the fastest routes for flow, whereas injections into dilated spleens primarily filled slower routes. This procedure yielded a more complete, three-dimensional picture of the arterial, intermediate, and venous pathways as a whole, and of the relative amounts of flow through different arterial routes. Evidence of flow from capillary lumina out into ellipsoid sheaths was plentiful in casts from dilated spleens, but rare in casts from contracted organs. The pattern of flow within and out of the marginal sinus has been elucidated: A circumferential filling occurs first, followed by a flow that radiates outward into the marginal zone and red pulp. Venous sinuses filled via two routes in addition to the generally accepted path from the reticular meshwork via fenestrations in sinus walls. First, many venous sinuses extending out from the marginal sinus and surrounding marginal zone originated as open-ended tubes continuous with the reticular spaces of the marginal sinus or marginal zone. Second, direct connections of arterial capillaries with venous sinuses in the red pulp were found. Evidence indicating that some mechanism is controlling the flow via these routes is discussed. The strikingly different arrangement of venous sinuses in the subcapsular region is demonstrated.

Animals↗
PubMed1983

The intermediate circulation in the nonsinusal spleen of the cat, studied by scanning electron microscopy of microcorrosion casts.

Scanning electron microscopy of microcorrosion casts was used to visualize circulatory pathways of the intermediate circulation in nonsinusal spleen of cat. The marginal sinus (MS) around lymphatic nodules is a distinct vascular space which fills preferentially before the filling of the marginal zone (MZ) and surrounding red pulp occurs. The MS, which has a plentiful vascular supply, does not usually enclose the nodule completely. From the MS, flow occurs radially outwards into the MZ. Corrosion casts and histological sections both showed that a diversity of forms of the MZ exists: The thickness of MZ and the arrangement of its reticulum vary among nodules and between different areas of the same nodule, from a complete absence to a region of up to 50 microns in width. No direct arteriovenous connections were found (in contrast to dog spleen: Schmidt et al., '83b). Aside from capillary endings in the MS and MZ, all arterial capillaries terminate in the reticular spaces of the red pulp, i.e., the circulation appears to be entirely "open." From each capillary termination a great variety of flow pathways through the reticular meshwork to the pulp venules is available; some of these routes are quite long but others may involve distances as short as 15-25 microns. Evidence of flow into ellipsoid sheaths was abundant in casts from dilated spleens, but scarce in contracted spleens. In contrast to the extensive system of interconnected venous sinuses in dog spleen, the pulp venules found in cat spleen are nonanastomosing, shorter, and much smaller in caliber, and all receive flow freely from the reticular meshwork via open ends and fenestrations in their walls.

Animals↗
PubMed1976

Vinyl acetate casts of emphysematous rat lungs.

Emphysema was induced in rats by chronic exposure to a papain aerosol according to established methods. The emphysematous changes were evaluated by previously described histological and biochemical parameters and by a new method employing infiltration of the lungs with vinyl acetate to make casts of the air spaces of the pulmonary tree. The weights and gross and microscopic appearance of the casts demonstrated the emphysematous changes in lungs of the papain-treated rats. Vinyl acetate casting may offer a new and useful tool in evaluating experimental induction of emphysema in rats.

Acetates↗
PubMed2005

A model of muscle atrophy using cast immobilization in mice.

We describe a new cast-immobilization protocol to induce muscle atrophy in the lower hindlimb muscles of mice. Bilateral cast immobilization for 2 weeks in a shortened position resulted in a significant loss of muscle size and strength in the soleus and extensor digitorum longus. The availability of a model of cast immobilization in mice may benefit future studies targeting genetic or cell therapy interventions of muscle atrophy in transgenic and mutant mice strains.

Animals↗
PubMed1987

Capillary sprouts in ovaries of immature superstimulated golden hamsters: a SEM study of microcorrosion casts.

A new polyester resin of low viscosity was used to study the three-dimensional structure of capillary sprouts of mature follicles and of corpora lutea. Vascular microcorrosion casts were obtained from ovaries of immature golden hamsters between days 4 and 7 after stimulation with pregnant mares' serum gonadotrophin (PMSG). On days 4 and 5 after PMSG, a nodular appearance of the organ was due to mature follicles and corpora lutea. Capillary sprouts were seen as dead-ending structures originating from the thecal capillary network. The sprouts were either concentrated around (follicle type 1) or towards (follicle type 2) the center of the antrum. Increased vascular permeability resulted in resin leakage only in type 2. Intact corpora lutea were characterized by radially grown capillary sprouts. Regressing corpora lutea showed a marked reduction of the vascular bed as displayed by filling defects in casts on day 6 and 7 after PMSG. It is assumed that: 1. Dead-ending capillary structures, resin leakage, and filling defects are not always artifacts of the microcorrosion cast technique, but can express functional microcirculatory changes. 2. The concentric growth of thecal capillary sprouts may be related to the presence of an intact follicular basal membrane, and the radial growth of sprouts be taken as a sign of a digested basal membrane.

Animals↗
PubMed1998

Passage of a large bowel cast caused by acute ischemia: report of two cases.

PURPOSE: We report two cases of spontaneous anal passage of a large bowel 'cast' caused by acute ischemic injury. METHODS: Clinical, laboratory, endoscopic, and pathologic features were reviewed, and the literature was searched for similar cases. RESULTS: An 85-year-old male who had undergone aortic surgery recovered from rectosigmoid ischemia after undergoing a descending colostomy. A 74-year-old male with severe pancreatitis developed a postischemic sigmoid stricture but did not have operative treatment before death of pneumonia three months after the episode. A literature review revealed six cases of passage of a large bowel cast. In the eight total patients, infarcted muscularis propria was found in seven specimens, five patients had a diversion procedure, and seven survived. CONCLUSION: Passage of a large bowel cast is an extraordinary complication of ischemia that often requires diverting surgery, and most patients survive the ischemic injury.

Acute Disease↗
PubMedDate not supplied

Comparison of theoretical and experimental particle diffusion data within human airway casts.

The dose delivered to airway cells is a critical factor whether one is addressing the therapeutic (i.e., positive) effects of inhaled pharmacologic agents or the toxic (i.e., negative) effects of pollutants. In this study, theoretical models describing particle deposition have been compared with experimental data from the literature. In the simulations, airways can be either rough-or smooth-walled to be consistent with human lungs which can be either lined by cartilaginous rings (i.e., rough) or muscle (i.e., smooth). Particle motion for rough-walled airways within generations I = 1-6 is calculated using the formula proposed by Martonen et al. (1). For smooth-walled airways within generations I = 7-10, particle motion is calculated using the formula proposed by Martonen et al. (2). Theoretical predictions of particle deposition efficiencies are not only in agreement with the overall best fit empirical correlation presented by Cohen and Asgharian (3) over a wide range of dimensionless diffusion parameters, but also match individual experimental measurements (only available in I = 1-6) with regard to effects of the parameters of particle size, flow rate, and airway dimensions. The mean difference in the ratio of experimental-to-theoretical particle diffusion values is 0.9 for a flow rate of 18 L/min and 1.1 for a flow rate of 34 L/min (i.e., the difference is only about 10%) within the upper airways of the casts (airway generations I = 1-6), the mean difference for the whole casts was much greater. This may be attributed to the uncertainty of flow conditions in the peripheral airways as a result of the trimmed nature of the casts. Overall, the findings suggest that the model can be a valuable component of aerosol therapy and risk assessment protocols, especially to address effects of enhanced deposition of pharmacologic drugs and radionuclides at sites within the human tracheobronchial tree.

Administration, Inhalation↗
PubMed2005

Drug release from cast films of ethylene vinyl acetate (EVA) copolymer: Stability of drugs by 1H NMR and solid state 13C CP/MAS NMR.

The study utilizes an oral biocompatible material based on ethylene vinyl acetate copolymer (EVA) designed to release drugs in vitro at therapeutic levels over several days. We examined the drug stability during film casting process using proton and solid state NMR techniques. The drug-loaded EVA films were prepared from the dry sheet obtained by solvent (dichloromethane) evaporation of polymer casting solutions. Drugs tested include chlorhexidine diacetate (CDA), doxycycline hydrochloride (DOH), tetracycline hydrochloride (TTH) and nystatin (NST). Drug release from the films was examined for at least 14 days in 10 ml ddH2O (NST in water/ethanol (4:1)) which was replaced daily. Changes in optical density were followed spectraphotometrically. Effect of temperature on rate measurements was studied and the energies of activation (E*) were calculated using Arrhenius plots. Effect of EVA copolymer composition on CDA release rate was also investigated. The enhanced rates with temperature increase may be attributed to the formation of channels with increased geometry in the polymer. The highest E* observed for CDA compared to DOH and TTH may be related to their average molecular weights. Spectral analyses for CDA and NST revealed that the chemical and physical structures of the drugs remained unaffected during the film casting process.

Biocompatible Materials↗
PubMed2005

Fabrication of hydroxyapatite ceramics with controlled pore characteristics by slip casting.

Porous hydroxyapatite (HAp) ceramics with controlled pore characteristics were fabricated using slip casting method by mixing PMMA with HAp powder. The optimum conditions of HAp slip for slip casting was achieved by employing various experimental techniques, zeta potential and sedimentation, as a function of pH of the slips in the pH range of 4-12. HAp suspensions displayed an absolute maximum in zeta potential values and a minimum in sedimentation height at pH 11.5. The optimal amount of dispersant for the HAp suspensions was found at 1.0 wt% according to the viscosity of 25 vol% HAp slurry. The rheological behaviour of HAp slurry displays a shear-thinning behavior without thixotropy, which is needed in slip casting processing. The pore characteristics of sintered porous hydroxyapatite bioceramics can be controlled by added PMMA particle size and volume. The obtained ceramics exhibit higher strength than those obtained by dry pressing.

Biocompatible Materials↗
PubMed1983

An apparatus for the simultaneous casting of large numbers of uniform cylindrical polyacrylamide gels.

An apparatus for the simultaneous casting of a large number of cylindrical polyacrylamide gels is described. Gels can be cast that are uniform with respect to length, loading-surface flatness, and internal polymerization properties. The basis of the method is casting the gels as an inverted single block which totally excludes oxygen from gel-loading surfaces during polymerization.

Acrylic Resins↗
PubMed1983

An improved technique for producing casts of the internal structure of hard tissues, including some observations on human dentine.

A method for producing plastic casts of the internal structure of dentine has been described by Marten, Hallsworth and Buckley, J. Microsc. 112, 345-352 (1978). The main drawback of the method is that the casts collapse when they are air-dried. In the present investigation a freeze-drying technique was used to eliminate this problem. In addition, subtle variations in methodology were necessary to produce optimal casts of different hard tissues. These are described in detail and initial observations of the internal structure of human coronal and radicular dentine are also included. Special attention was given to the structure of Tomes' granular layer.

Bone and Bones↗