|Articles about Biomaterials|
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| Effect of morphological features and surface area of hydroxyapatite on the fatigue behavior of hydroxyapatite-polyethylene composites
Joseph, R. and K. E. Tanner (2005), Biomacromolecules 6(2): 1021-6.
Abstract: The effect of surface area and morphological features of filler particles on the fatigue behavior of hydroxyapatite-filled high-density polyethylene composites was studied. Composites containing 40 vol % filler were injection-molded into tensile bars, gamma-irradiated, and subjected to sinusoidal tensile fatigue at a frequency of 2 Hz. To simulate the physiological environment, the tests were conducted at 37 degrees C in saline. Results showed that properties such as secant modulus, cyclic energy dissipation, dynamic creep strain, hysteresis loops, and even fracture surfaces differ depending on the morphology and surface area of the fillers used.
| Effect of morphological properties of transferred embryonic stages on tubal migration Implications for in vivo culture in the bovine oviduct
Wetscher, F., V. Havlicek, et al. (2005), Theriogenology 64(1): 41-8.
Abstract: In cattle, there is no practical method, which allows tubal transfer of pre-implantation embryos for routine in vivo culture as it has been established in sheep. The aim of our study was to perform tubal transfer by transvaginal endoscopy in synchronized heifers, in order to expose embryos at various embryonic stages to the physiological mechanisms of migration in the non-ligated oviducts. Various embryonic stages were transferred by transvaginal endoscopy into the oviducts of temporary recipients and were recovered on Day 7. The transfer of embryos in hyaluronate containing medium ("Hyaluronan"), zygotes stripped of cumulus ("Denuded Zygotes"), embryos embedded in cumulus ("Zygotes with Cumulus"), matured oocytes with capacitated spermatozoa ("GIFT") or embryos embedded in Na alginate ("Alginate") led to increasing recovery rates (13, 30, 56, 63 and 71%, respectively). However, the developmental rate on Day 7 was adversely affected (16, 11, 8, 16 and 8%), whereas the blastocyst rate on Day 8 showed more balanced results (17, 14, 18, 21 and 11%). Our data demonstrate that the structural properties of transferred embryos affect tubal migration and are crucial for subsequent in vivo culture. Embryos enclosed in cumulus cells or alginate synchronize more successfully with the oviductal transport systems than denuded stages or embryos in hyaluronate containing medium.
| Effect of nano-TiO(2) on strength of naturally aged seeds and growth of spinach
Zheng, L., F. Hong, et al. (2005), Biol Trace Elem Res 104(1): 83-92.
Abstract: The effects of nano-TiO(2) (rutile) and non-nano-TiO(2) on the germination and growth of naturally aged spinach seeds were studied by measuring the germination rate and the germination and vigor indexes of aged spinach seeds. An increase of these factors was observed at 0.25-4% nano-TiO(2) treatment. During the growth stage, the plant dry weight was increased, as was the chlorophyll formation, the ribulosebisphosphate carboxylase/oxygenase activity, and the photosynthetic rate. The best results were found at 2.5% nano-TiO(2). The effects of non-nano-TiO(2) are not significant. It is shown that the physiological effects are related to the nanometer-size particles, but the mechanism by which nano-TiO(2) improves the growth of spinach seeds still needs further study.
| Effect of nano-TiO2 on photochemical reaction of chloroplasts of spinach
Hong, F., J. Zhou, et al. (2005), Biol Trace Elem Res 105(1-3): 269-79.
Abstract: The effects of nano-TiO2 (rutile) on the photochemical reaction of chloroplasts of spinach were studied. The results showed that when spinach was treated with 0.25% nano-TiO2, the Hill reaction, such as the reduction rate of FeCy, and the rate of evolution oxygen of chloroplasts was accelerated and noncyclic photophosphorylation (nc-PSP) activity of chloroplasts was higher than cyclic photophosphorylation (c-PSP) activity, the chloroplast coupling was improved and activities of Mg2+-ATPase and chloroplast coupling factor I (CF1)-ATPase on the thylakoid membranes were obviously activated. It suggested that photosynthesis promoted by nano-TiO2 might be related to activation of photochemical reaction of chloroplasts of spinach.
| Effect of norcantharidin on proliferation and invasion of human gallbladder carcinoma GBC-SD cells
Fan, Y. Z., J. Y. Fu, et al. (2005), World J Gastroenterol 11(16): 2431-7.
Abstract: AIM: To investigate the effect of norcantharidin on proliferation and invasion of human gallbladder carcinoma GBC-SD cells in vitro and its anticancer mechanism. METHODS: Human gallbladder carcinoma GBC-SD cells were cultured by cell culture technique. The growth and the invasiveness of GBC-SD cells in vitro were evaluated by the tetrazolium-based colorimetric assay and by the Matrigel experiment and the crossing-river test. Expression of PCNA, Ki-67, MMP2 and TIMP2 proteins of GBC-SD cells was determined by streptavidin-biotin complex method. RESULTS: In vitro norcantharidin inhibited the growth and proliferation of GBC-SD cells in a dose- and time-dependent manner, with the IC50 value of 56.18 microg/mL at 48 h. Norcantharidin began to inhibit the invasion of GBC-SD cells at the concentration of 5 microg/mL, and the invasive action of GBC-SD cells was inhibited completely and their crossing-river time was prolonged significantly at 40 microg/mL. After treatment with norcantharidin, the expression of PCNA, Ki-67, and MMP2 was significantly decreased. With the increase in TIMP2 expression, the MMP2 to TIMP2 ratio was decreased significantly (P<0.05). CONCLUSION: Norcantharidin inhibits the proliferation and growth of human gallbladder carcinoma cells in vitro at relatively low concentrations by inhibiting PCNA and Ki-67 expression. Its anti-invasive activity may be the result of decrease in MMP2 to TIMP2 ratio and reduced cell motility.
| Effect of particle size of nanospheres and microspheres on the cellular-association and cytotoxicity of paclitaxel in 4T1 cells
De, S., D. W. Miller, et al. (2005), Pharm Res 22(5): 766-75.
Abstract: PURPOSE: To compare the effect of size of delivery systems on the cell-association and in vitro cytotoxicity of paclitaxel. METHODS: Four sizes of PLGA-paclitaxel particles were prepared to study the effect of particle size on the cell-association of paclitaxel in 4T1 monolayer in the presence, and absence, of BCRP inhibitor, endocytic inhibitor, and P-glycoprotein (P-gp) inhibitor. Paclitaxel cell-association studies were repeated in Caco-2, Cor-L23/R, and bovine brain microvessel endothelial cells (BBMECs), as well as the association of etoposide in 4T1 cells. Cytotoxicity of paclitaxel to 4T1 cells delivered in nanospheres was compared to microspheres. RESULTS: The concentration of paclitaxel and etoposide associated with 4T1 cells was 4.8 and 29 times greater, respectively, as the size increased from 310 to 2077 nm. Paclitaxel association consistently increased in Caco-2 and Cor-L23/R as the size of the delivery system increased. The endocytic inhibitor, 2-deoxyglucose, significantly decreased the cellular paclitaxel association when delivered by nanospheres but not microspheres. Consistent with the cell-association results, paclitaxel was thrice more cytotoxic to 4T1 cells when delivered in microspheres. CONCLUSIONS: Cell-association of paclitaxel increased in 4T1, Caco-2, and Cor-L23/R as particle size increased. Paclitaxel delivered from 1-mum microspheres was thrice more cytotoxic to 4T1 cells compared to the drug delivered from nanospheres or solution.
| Effect of passage number and matrix characteristics on differentiation of endothelial cells cultured for tissue engineering
Prasad Chennazhy, K. and L. K. Krishnan (2005), Biomaterials 26(28): 5658-67.
Abstract: Cells can sense the physical and chemical properties of artificial materials used as scaffolds for tissue engineering and regulate their behavior. Therefore, biomimetic and biospecific molecules are coated on materials to regulate function of cells on the tissue-engineered product. These bioactive molecules can be attached in a defined spectrum, concentration and spatial distribution in order to control adhesion, growth, viability, differentiation, and function of the cells. When autologous cells are used for tissue engineering, initially limited cells obtained may often need an amplification of cell number by passage in tissue culture before they are seeded on a biomaterial or scaffold. We have conducted this study to understand how the characteristics of bioactive molecule coating might affect proliferation, apoptosis and differentiation when endothelial cell (EC) is serially passaged. Proliferation was assessed by proliferating cell nuclear antigen (PCNA) staining along with counting of cells harvested from confluent monolayer. Apoptosis was assessed by Annexin V staining and differentiation by semi quantitative reverse transcriptase polymerase chain reaction (RT-PCR) for von Willebrand factor (vWF) expression and quantification of its release using enzyme linked immunosorbant assay (ELISA), and thrombogenicity by comparing platelet adhesion to EC monolayer Dacron grafts (DG) with specific protein coating. The results indicate that ECs easily lose its proliferation potential when they are cultured repeatedly on gelatin, turn apoptotic and over express the prothrombotic protein- vWF. Whereas, when it is grown on a matrix composed of fibrin, fibronectin, gelatin and vascular EC growth factor (VEGF), the cells retained their ability to proliferate, remained viable and were relatively less thrombogenic, even when passage number progressed. It is concluded that if ECs are grown on the composite matrix that mimics natural vessel scaffold, the cell number can be amplified without affecting its normal physiological function and may be used to generate effective tissue-engineered cardiovascular constructs.
| Effect of pH on production of virulence factors by biofilm cells of Pseudomonas aeruginosa
Harjai, K., R. K. Khandwahaa, et al. (2005), Folia Microbiol (Praha) 50(2): 99-102.
Abstract: Effect of pH on production of extracellular virulence factors of Pseudomonas aeruginosa grown on catheter in biofilm was determined. Alginate and proteinase production was higher at pH 8; in contrast, siderophores (pyochelin and pyoverdin) were synthesized more intensively at pH 5.
| Effect of processing route and acetone pre-treatment on the biostability of pellethane materials used in medical device applications
Taylor, J. E., P. R. Laity, et al. (2005), Biomaterials 26(33): 6467-76.
Abstract: Thermoplastic polyurethanes, such as Pellethane 2363 80A (Pel80A) and Pellethane 2363 55D (Pel55D) are widely used in the medical device industry because of their biological and mechanical properties. However, premature failure in such devices has been observed and attributed to environmental stress cracking (ESC). The current work investigates the possibility of reducing ESC via bulk morphology manipulation. This can be achieved through various processing routes such as solvent-casting (SC) and hot-press quenching (HPQ). The effect of stress on the bulk morphology of Pel55D and Pel80A was evaluated using small-angle X-ray scattering (SAXS) in conjunction with tensile testing. SC samples exhibited greater phase separation compared with HPQ samples. Alignment of hard segment domains became apparent around the point of yield. Onset of ESC with respect to SC and HPQ routines was determined using the Zhao-Stokes glass-wool test with optical (OM) and environment scanning electron microscopy (ESEM). Improvement in biostability of Pel80A was found in HPQ samples compared to those that were SC. A secondary objective of this work was to investigate the effect of acetone pre-treatment on surface morphology. High resolution imaging of acetone treated and untreated SC Pel80A showed significant differences in surface morphology.
| Effect of protein concentration on rate of closure of ameroid constrictors in vitro
Monnet, E. and A. Rosenberg (2005), Am J Vet Res 66(8): 1337-40.
Abstract: OBJECTIVE: To evaluate the effect of protein concentration on rate of closure of ameroid constrictors in vitro. SAMPLE POPULATION: Twenty-four 3.5-mm ameroid constrictors. PROCEDURE: Ameroid constrictors were equally allocated into 4 treatment groups; constrictors were placed in saline (0.9% NaCl) solution (control) or plasma diluted with saline solution to obtain protein concentrations of 1.5, 3, or 6 g/dL. Ameroid constrictors were incubated for 27 days. A digital camera was used to image ameroid constrictors in culture at 1, 6, 11, 16, 21, and 27 days, and the lumen diameter of each constrictor was measured. RESULTS: None of the rings were completely closed at 27 days. Mean final lumen diameter was 0.205 +/- 0.22 mm. Mean final lumen diameter of constrictors in the control group was significantly larger than that of constrictors in the 1.5, 3, and 6 g/dL groups. Constrictors in the 1.5 g/dL group closed to a larger diameter than that of constrictors in the 6 g/dL group. Constrictors in the control group had the smallest overall change in lumen diameter, compared with constrictors in the 3 and 6 g/dL groups. Constrictors in the 1.5 g/dL group had a significant decrease in overall lumen diameter, compared with constrictors in the 3 and 6 g/dL groups. The diameter of the ameroid lumen was a function of time and protein concentration. CONCLUSIONS AND CLINICAL RELEVANCE: High plasma protein concentrations resulted in rapid closure of the ameroid constrictor lumen. Complete closure of ameroid constrictors may not be attributable to imbibition of casein.
| Effect of pulsed ultrasound in combination with gentamicin on bacterial viability in biofilms on bone cements in vivo
Ensing, G. T., B. L. Roeder, et al. (2005), J Appl Microbiol 99(3): 443-8.
Abstract: AIMS: The aim of this study is to investigate whether pulsed ultrasound (US) in combination with gentamicin yields a decreased viability of bacteria in biofilms on bone cements in vivo. METHODS AND RESULTS: Bacterial survival on bone cement in the presence and absence of ultrasound was compared in a rabbit model. Two bone cement samples with an Escherichia coli ATCC 10798 biofilm were implanted in a total of nine rabbits. In two groups bone cement discs loaded with gentamicin, freshly prepared and aged were used, and in one group unloaded bone cement discs in combination with systemically administered gentamicin. Pulsed ultrasound with a frequency of 28.48 kHz and a maximum acoustic intensity of 500 mW cm(-2) was applied continuously from 24 h till 72 h postsurgery on one of the two implanted discs. After euthanization and removal of the bacteria from the discs, the number of viable bacteria were quantified and skin samples were analysed for histopathological examination. Application of ultrasound, combined with gentamicin, reduced the viability of the biofilms in all three groups varying between 58 and 69% compared with the negative control. Histopathological examinations showed no skin lesions. CONCLUSIONS: Ultrasound resulted in a tendency of improved efficacy of gentamicin, either applied locally or systemically. Usage of ultrasound in this model proved to be safe. SIGNIFICANCE AND IMPACT OF THE STUDY: This study implies that ultrasound could improve the prevention of infection immediately after surgery, especially because the biomaterials, gentamicin and ultrasound used in this model are all in clinical usage, but not yet combined in clinical practice.
| Effect of recombinant human bone morphogenetic protein-2 in an absorbable collagen sponge with space-providing biomaterials on the augmentation of chronic alveolar ridge defects
Barboza, E. P., A. L. Caula, et al. (2004), J Periodontol 75(5): 702-8.
Abstract: BACKGROUND: Recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable collagen sponge (ACS) carrier has been shown to support significant bone formation in the craniofacial skeleton. When used as an onlay, however, rhBMP-2/ACS may become compressed with limited resulting bone formation. The objective of this study was to evaluate the effect of two space-providing biomaterials, bioactive glass (BG) and demineralized/mineralized bone matrix (DMB), on rhBMP-2/ACS induced alveolar ridge augmentation. METHODS: Bilateral alveolar ridge defects were produced in the mandible in six mongrel dogs. rhBMP-2/ACS with biomaterials was surgically implanted into contralateral defects in four animals. Treatments were alternated between jaw quadrants in consecutive animals. Two animals received rhBMP-2/ACS or sham-surgery in contralateral defects. The animals were injected with fluorescent bone labels to monitor bone formation. Clinical evaluations were made at ridge augmentation and 12 weeks post-implantation when the animals were euthanized and block biopsies collected for histopathologic evaluation. RESULTS: Sham-surgery produced limited horizontal alveolar augmentation (0.1 +/- 0.6 mm). Implantation of rhBMP-2/ACS resulted in alveolar augmentation amounting to 2.2 +/- 1.8 mm. Alveolar augmentation in sites receiving rhBMP-2/ACS with DMB or BG was 2-fold greater compared to rhBMP-2/ACS alone averaging 4.4 +/- 1.3 and 4.6 +/- 1.5 mm, respectively. The DMB biomaterial appeared substituted by newly formed bone. The BG particles were observed imbedded in bone or encapsulated in dense connective tissue without associated bone metabolic activity. Fluorescent light microscopy suggested that the new bone was formed within 4 weeks. CONCLUSION: The bioglass and demineralized/mineralized bone matrix biomaterials utilized in this study in combination with rhBMP-2/ACS supported clinical and histological ridge augmentation.
| Effect of salts on the properties of aqueous sugar systems, in relation to biomaterial stabilization. 1. Water sorption behavior and ice crystallization/melting
Mazzobre, M. F., M. P. Longinotti, et al. (2001), Cryobiology 43(3): 199-210.
Abstract: Trehalose and sucrose, two sugars that are involved in the protection of living organisms under extreme conditions, and their mixtures with salts were employed to prepare supercooled or freeze-dried glassy systems. The objective of the present work was to explore the effects of different salts on water sorption, glass transition temperature (T(g)), and formation and melting of ice in aqueous sugar systems. In the sugar-salt mixtures, water adsorption was higher than expected on the basis of the water uptake by each pure component. In systems with a reduced mass fraction of water (w less-than-or-equal 0.4), salts delayed water crystallization, probably due to ion-water interactions. In systems where > 0.6, water crystallization could be explained by the known colligative properties of the solutes. The glass transition temperature of the maximally concentrated matrix (T(g)') was decreased by the presence of salts. However, the actual T(g) values of the systems were not modified. Thus, the effect of salts on sorption behavior and formation of ice may reflect dynamic water-salt-sugar interactions which take place at a molecular level and are related to the charge/mass ratio of the cation present without affecting supramolecular or macroscopic properties.
| Effect of several sterilisation techniques on homogeneous self assembled monolayers
Fleith, S., A. Ponche, et al. (2005), Colloids Surf B Biointerfaces 44(1): 15-24.
Abstract: Understanding how cells sense their environment and are able to regulate their metabolism is of great importance for the success of biomaterials implantation. Self assembled monolayers (SAMs) are in use nowadays to model the surface of such materials. They permit the control of different surface parameters (like chemistry, surface energy and topography) enabling to get a greater insight in cells behaviour when interacting with surfaces and thus, in the future, to enhance surface properties of biomaterials. As sterilisation is the compulsory step for in vitro and in vivo assays with living biological materials, it is important to know how SAMs react under sterilisation techniques in use on biomaterials. In this work, the effect of three types of sterilisation techniques: gamma-irradiation, mostly used on biomaterials, dry heat and steam autoclaving, have been investigated on NH2 and CH3 terminated SAMs. Gamma-irradiation destructs drastically the NH2 and partially the CH3 monolayers by producing oxidative compounds (COOH, C=O, C-OH). The main product induced by gamma-irradiation on NH2 monolayers is carboxylic acid, whereas CH3 shows an important increase in the amount of alcoholic groups. This difference in deterioration is assumed to be due to the higher stability of the CH3 monolayer. Steam autoclaving to a lesser extent gives the same results on NH2 monolayers. Dry heat seems to be the most reliable technique, which can be used on such surfaces as it removes physically adsorbed organic contaminants without affecting the integrity of the surface.
| Effect of solid/solution ratio on apatite formation from CaSiO3 ceramics in simulated body fluid
Iimori, Y., Y. Kameshima, et al. (2004), J Mater Sci Mater Med 15(11): 1247-53.
Abstract: The effect of the solid/solution (S/S) ratio on apatite formation from CaSiO3 ceramics in simulated body fluid (SBF) was investigated. CaSiO3 ceramics with a Ca/Si ratio of 0.91 were prepared by sintering CaSiO3 powder coprecipitated from ethanol solutions of Ca(NO3)2. 4H2O and Si(OC2H5)4 using NH4OH as the precipitant. These ceramics were reacted with SBF at S/S ratios of 1.0, 2.5 and 8.3 mg/ml at 36.5 degrees C for various times. Formation of apatite was observed at all the S/S ratios after soaking for 1 day. The amount and microstructure of the apatite obtained at a S/S ratio of 8.3 mg/ml, however, differed largely from the product formed at the other two S/S ratios. The apatite formed at S/S = 8.3 mg/ml was of smaller particle size, formed in smaller amount and with less preferred orientation of the (001) of apatite crystals compared with those formed at S/S = 1.0 and 2.5 mg/ml. An increase of Ca and decrease of the P components occurred in the soaked SBF at S/S = 8.3 mg/ml, the changes being much more marked than with the other two S/S ratios. These differences in the concentration changes in SBF at different S/S ratios are attributed to the difference in the apatite formation from the CaSiO3 ceramics.
| Effect of starch-based biomaterials on the in vitro proliferation and viability of osteoblast-like cells
Marques, A. P., H. R. Cruz, et al. (2005), J Mater Sci Mater Med 16(9): 833-42.
Abstract: The cytotoxicity of starch-based polymers was investigated using different methodologies. Poly-L-lactic acid (PLLA) was used as a control for comparison purposes. Extracts of four different starch-based blends (corn starch and ethylene vinyl alcohol (SEVA-C), corn starch and cellulose acetate (SCA), corn starch and polycaprolactone (SPCL) and starch and poly-lactic acid (SPLA70) were prepared in culture medium and their toxicity was analysed. Osteoblast-like cells (SaOs-2) were incubated with the extracts and cell viability was assessed using the MTT test and a lactate dehydrogenase (LDH) assay. In addition DNA and total protein were quantified in order to evaluate cell proliferation. Cells were also cultured in direct contact with the polymers for 3 and 7 days and observed in light and scanning electron microscopy (SEM). LDH and DNA quantification revealed to be the most sensitive tests to assess respectively cell viability and cell proliferation after incubation with starch-based materials and PLLA. SCA was the starch blend with higher cytotoxicity index although similar to PLLA polymer. Cell adhesion tests confirmed the worst performance of the blend of starch with cellulose acetate but also showed that SPCL does not perform as well as it could be expected. All the other materials were shown to present a comparable behaviour in terms of cell adhesion showing slight differences in morphology that seem to disappear for longer culture times.The results of this study suggest that not only the extract of the materials but also their three-dimensional form has to be biologically tested in order to analyse material-associated parameters that are not possible to consider within the degradation extract. In this study, the majority of the starch-based biomaterials presented very promising results in terms of cytotoxicity, comparable to the currently used biodegradable PLLA which might lead the biocompatibility evaluation of those novel biomaterials to other studies.
| Effect of storage duration on tensile bond strength of acrylic or silicone-based soft denture liners to a processed denture base polymer
Mese, A., K. G. Guzel, et al. (2005), Acta Odontol Scand 63(1): 31-5.
Abstract: OBJECTIVE: To investigate the effect of storage duration on the tensile bond strength of acrylic and silicone-based denture base materials with liners either heat-cured or auto-cured. MATERIAL AND METHODS: The denture liners investigated were Vertex soft (acrylic-based, heat-cured), Coe soft (acrylic-based, auto-cured), Molloplast-B (silicone-based, heat-cured), and Mollosil plus (silicone-based, auto-cured). The soft liner specimens were 10 x 10 x 3 mm and were processed between two PMMA blocks. They were tested following immersion in water at 37 degrees C for 1 day, 1 week, and 1, 3, and 6 months. Tensile bond strength was measured using a universal testing machine (Testometric Micro 500) at a crosshead speed of 20 mm/min (n = 10 specimens per experimental group). Multiple ANOVA and Tukey HSD were used to analyse the data at a pre-set alpha of 0.05. RESULTS: The results indicate that the tensile bond strength of acrylic-based soft liners is greater than that of silicone-based materials. The bond strength of all lining materials decreases with storage duration; the decrease being greatest for the acrylic-based soft liners. The decrease in bond strength of the auto-cured materials is greater than that of the heat-cured products. CLINICAL SIGNIFICANCE: Comparison of the materials in this study indicates that the silicone-based, heat-cured soft liner is superior, based on the tensile bond strength property. Use of silicone-based, heat-cured soft liners may provide better clinical success over a long period. These laboratory results need to be verified by clinical testing.
| Effect of synovial fluid, phosphate-buffered saline solution, and water on the dissolution and corrosion properties of CoCrMo alloys as used in orthopedic implants
Lewis, A. C., M. R. Kilburn, et al. (2005), J Biomed Mater Res A 73(4): 456-67.
Abstract: The corrosion and dissolution of high- and low-carbon CoCrMo alloys, as used in orthopedic joint replacements, were studied by immersing samples in phosphate-buffered saline (PBS), water, and synovial fluid at 37 degrees C for up to 35 days. Bulk properties were analyzed with a fine ion beam microscope. Surface analyses by X-ray photoelectron spectroscopy and Auger electron spectroscopy showed surprisingly that synovial fluid produced a thin oxide/hydroxide layer. Release of ions into solution from the alloy also followed an unexpected pattern where synovial fluid, of all the samples, had the highest Cr concentration but the lowest Co concentration. The presence of carbide inclusions in the alloy did not affect the corrosion or the dissolution mechanisms, although the carbides were a significant feature on the metal surface. Only one mechanism was recognized as controlling the thickness of the oxide/hydroxide interface. The analysis of the dissolved metal showed two mechanisms at work: (1) a protein film caused ligand-induced dissolution, increasing the Cr concentration in synovial fluid, and was explained by the equilibrium constants; (2) corrosion at the interface increased the Co in PBS. The effect of prepassivating the samples (ASTM F-86-01) did not always have the desired effect of reducing dissolution. The release of Cr into PBS increased after prepassivation. The metal-synovial fluid interface did not contain calcium phosphate as a deposit, typically found where samples are exposed to calcium rich bodily fluids.
| Effect of the M(s) transformation temperature on the wear behaviour of NiTi shape memory alloys for articular prosthesis
Pena, J., E. Solano, et al. (2005), Biomed Mater Eng 15(4): 289-93.
Abstract: The main objective of this work has been the characterisation and correlation of the wear behaviour of the NiTi shape memory alloys in their different phases. The weight losses for the different alloys in function of the present phase, and of the M(s) transformation temperature are studied. Adhesive wear tests, Pin-on-Disk, according to the ASTM-G99 standard have been carried out. The thermoelastic martensitic transformations that cause the super-elastic effect, the reorientation and coalescence of martensitic plates and the damping effect promotes a high ability to accommodate large deformations without generating permanent damages that causes the wear. The resulting plastic deformation may be accumulated during wear process without generating fracture. The results show that the wear resistance is mainly dependent of the M(s) transformation temperature for both alloys. For the NiTi alloys also the Ni atomic percentage and the hardness of the alloys are important parameters in the wear behavior.
| Effect of thermal treatments on tensile strength of commercially cast pure titanium and Ti-6Al-4V alloys
da Rocha, S. S., G. L. Adabo, et al. (2005), J Mater Sci Mater Med 16(8): 759-66.
Abstract: Heating titanium structures is assumed to relieve tensions induced by the casting process as well as possibly optimizing some mechanical properties. The aim of this investigation was to evaluate the effect of thermal treatments on tensile strength of commercially pure titanium (CP Ti) and Ti-6Al-4V alloy. Thirty dumbbell rods, with diameters of 3.0 mm at the central segment and lengths of 42 mm, were cast for each metal using the Rematitan System. CP Ti and Ti-6Al-4V specimens were randomly divided into three groups of ten: a control group that received no thermal treatment and two test groups. One (T1) was heated at 750 degrees C for 2 h and the other (T2) was annealed at 955 degrees C for 1 h and aged at 620 degrees C for 2 h. Tensile strength was measured with a universal testing machine (MTS model 810). Tensile strength means and standard deviations were statistically compared using a Kruskal-Wallis test at a alpha=0.05 significance level. No statistically significant differences in tensile strength were observed among CP Ti groups. For the Ti-6Al-4V alloy, the control and T1 groups revealed statistically higher tensile strengths when compared to the T2 group, with no significant difference between the control and T1 groups.
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