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Solar cells: later rather than sooner
Moser, J. E. (2005), Nat Mater 4(10): 723-4.

Sol-gel synthesis of a multifunctional, hierarchically porous silica/apatite composite
Andersson, J., S. Areva, et al. (2005), Biomaterials 26(34): 6827-35.
Abstract: In this study, a degradable, hierarchically porous silica/apatite composite material is developed from a simple low-temperature synthesis. Mesoporosity is induced in the silica portion by the use of supramolecular templating. The template is further removed by calcination. Firstly, hydroxyapatite is synthesized through a sol-gel method at near room temperature conditions. After the mineralization process, the crystal surface is coated with a mesoporous silica matrix using the templates already present in the bulk solution. The material is characterized by XRD, N(2)-sorption, FT-IR, SEM/EDS, and TEM. The coating layer is distributed fairly homogeneously over the apatite surface and the coating thickness is easily adjustable and dependent on the amount of added silica precursor. The hybrid material is shown to efficiently induce calcium phosphate formation under in vitro conditions and simultaneously work as a carrier system for drugs.

Sol-gel-derived biomaterials of silica and carrageenans
Shchipunov, Y. A. (2003), J Colloid Interface Sci 268(1): 68-76.
Abstract: A new precursor, tetrakis(2-hydroxyethyl) orthosilicate (THEOS), introduced by Hoffmann et al. (J. Phys. Chem. B 106 (2002) 1528-1533), was used to synthesize monolithic hybrid biomaterials on the basis of silica and three main types of carrageenans, kappa-, iota-, and lambda-carrageenans. The advantage of THEOS over the currently applied TEOS and TMOS is in its complete solubility in water. This negated the need to add organic solvents, thus excluding a denaturating effect on biopolymers. In their turn, carrageenans introduced into the precursor solution made use of common catalysts unneeded to trigger the sol-gel transition. It was found that they promoted the mineralization, acting as a template for the inorganic component. The kinetics of sol-gel processes, mechanical properties, phase behavior, and structure of novel hybrid biomaterials were studied by dynamic rheology, differential scanning calorimetry, and scanning electron microscopy. The material properties were regulated by both the precursor and carrageenan. The increase of silicate concentration led to a rise in the stiffness and brittleness of the material, whereas the polysaccharide addition made it softer and more elastic. It was shown that the formation and properties of mixed gels were determined by the nature of carrageenan. kappa-Carrageenans brought about shrinkage of hybrid materials that led to water separation, while iota- and lambda-carrageenans did not induce the syneresis. This is in line with the difference in polysaccharide properties when they are in aqueous solutions without silicate. Furthermore, kappa- and iota-carrageenans experienced a thermoreversible phase transition in the hybrid materials owing to the helix-coil transition. This resulted in a step like change in the mechanical properties of mixed systems in the corresponding temperature range. lambda-Carrageenan is a nongelling polysaccharide, which is why the rheological parameters of its hybrid gel were unchanged with the temperature. It was found that the polysaccharides modified the structure of silica-based materials. They transformed a three-dimensional network of connected silica particles into that consisting of crossed fibers.

Sol-gel-modified titanium with hydroxyapatite thin films and effect on osteoblast-like cell responses
Kim, H. W., H. E. Kim, et al. (2005), J Biomed Mater Res A 74(3): 294-305.
Abstract: Titanium (Ti) surface was coated with hydroxyapatite (HA) films via the sol-gel method. The coating properties, such as crystallinity and surface roughness, were controlled and their effects on the osteoblast-like cell responses were investigated. The film crystallinity was controlled with different heat treatment temperatures (400, 500, and 600 degrees C): Also the surface roughness was changed by using different heating rates (1 and 50 degrees C/min). The obtained sol-gel films had a dense and homogeneous structure with a thickness about 1 mum. The film heat-treated at higher temperature had enhanced crystallinity (600>500>>400 degrees C), while retaining similar surface roughness. When heat-treated rapidly (50 degrees C/min), the film became quite rough, with roughness parameters being much higher (4-6 times) than that obtained at a low heating rate (1 degrees C/min). The dissolution rate of the film decreased with increasing crystallinity (400>>500>600 degrees C), and the rougher film had slightly higher dissolution rate. The attachment, proliferation, and differentiation behaviors of human osteosarcoma HOS TE85 cells were affected by the properties of the films. On the films with higher crystallinity (heat treated over 500 degrees C), the cells attached and proliferated well and expressed alkaline phosphatase (ALP) and osteocalcin (OC) to a higher degree as compared to the poorly crystallized film (heat treated at 400 degrees C). On the rough film, the cell attachment was enhanced, but the ALP and OC expression levels were similar as compared to the smooth films.

Solid films of blended poly(vinyl alcohol)/poly(vinyl pyrrolidone) for topical S-nitrosoglutathione and nitric oxide release
Seabra, A. B., L. L. da Rocha, et al. (2005), J Pharm Sci 94(5): 994-1003.
Abstract: Nitric oxide (NO) is responsible for biological actions in mammals, ranging from the control of arterial pressure to immunological responses. In this study, S-nitrosoglutathione (GSNO), a spontaneous NO donor, was incorporated in solid films of blended poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) comprising a biomaterial with potential for the local delivery of NO. In dry conditions, the extinction of the absorption bands of GSNO was correlated with the increase of the absorption band of its dimmer, GS-SG, implying NO release through the homolytic cleavage of the S-N bond. Mass spectrometry was used to confirm and to monitor the release of free NO from solid PVA/PVP-GSNO films to the gas phase. Kinetic measurement based on the Griess reaction was used to show that solid PVA/PVP-GSNO films are also capable of releasing both NO and GSNO to aqueous solution trough diffusion. Storage experiments have shown that GSNO is highly stabilized in the dry PVA/PVP matrix. The results indicate that GSNO-containing PVA/PVP films may be used for delivering free NO and/or GSNO topically and controllably.

Solid-phase microextraction for qualitative and quantitative determination of migrated degradation products of antioxidants in an organic aqueous solution
Burman, L., A. C. Albertsson, et al. (2005), J Chromatogr A 1080(2): 107-16.
Abstract: Low molecular weight aromatic substances may migrate out from plastic packaging to their contents, especially if they consist of organic aqueous solutions or oils. It is, therefore, extremely important to be able to identify and quantify any migrated substances in such solutions, even at very low concentrations. We have in this work investigated and evaluated the use of solid-phase microextraction for the specific task of extraction from an organic aqueous solution such as a simulated pharmaceutical solution consisting of 10 vol.% ethanol in water. The goal was furthermore to investigate the possibility of simultaneously identifying and quantifying the substances in spite of differences in their chemical structures. Methods were developed and evaluated for extraction both with direct sampling and with headspace sampling. Difficulties appeared due to the ethanol in the solution and the minute amounts of substances present. We have shown that a simultaneous quantification of migrated low molecular weight degradation products of antioxidants using only one fibre is possible if the extraction method and temperature are adjusted in relation to the concentration levels of the analytes. Comparions were made with solid-phase extraction.

Solution technique to incorporate polyethylene oxide and other water-soluble polymers into surfaces of polymeric biomaterials
Desai, N. P. and J. A. Hubbell (1991), Biomaterials 12(2): 144-53.
Abstract: A simple solution technique was used to incorporate polyethylene oxide (PEO, of 5000, 10,000, 18,500, and 100,000 g/mol) and other water-soluble polymers such as polyvinylpyrrolidone and polyethyl oxazoline into the surfaces of commonly used biomedical polymers such as polyethylene terephthalate, a polyurethane (Pellethane 2363-80AE), and polymethylmethacrylate. The presence of the water-soluble polymers on these surfaces was verified by using contact angle analysis and ESCA. Protein adsorption studies, fibroblast adhesion assays, and whole blood perfusions over these polymers showed that the surface modified with PEO 18,500 was the most effective in reducing all the tested biological interactions. It was concluded that PEO 18,500 had a chain length that was optimal, using this technique for surface incorporation, to reduce protein adsorption and hence prevent protein-mediated biological interactions.

Solvent environment modulates effects of glutaraldehyde crosslinking on tissue-derived biomaterials
Gratzer, P. F., C. A. Pereira, et al. (1996), J Biomed Mater Res 31(4): 533-43.
Abstract: Bioprosthetic materials utilized in the construction of heart valves and vascular grafts possess limited performance and viability in vivo. This is due (in part) to the failure of these materials to mimic the mechanical properties of the host tissue they replace. If bioprosthetic materials could be engineered to meet the mechanical performance required in vivo, the functional lifetime of implants would be increased. In this study, glutaraldehyde/solvent solutions of decreasing dielectric constant (polarity) were utilized to modify the properties of crosslinked collagen in whole bovine pericardial tissue. Solvents included phosphate buffer, methanol, 95% (w/w) ethanol, n-propanol, and n-butanol. Exogenous crosslinking was verified in collagen by thermal denaturation tests and amino acid analyses. Tensile mechanical behavior of collagenous pericardial samples was found to depend upon the dielectric constant (polarity) of the glutaraldehyde/solvent solutions employed; however, treatment in the solvents alone had little, if any, effect. As the dielectric constant of the solvents decreased, three mechanical properties were systematically altered: plastic strain fell from a mean of 8.9 +/- 1.5% (buffer) to 1.6 +/- 0.4% (n-butanol); strain at fracture increased from 32.2 +/- 2.6% (buffer) to 55.6 +/- 4.6% (n-butanol); and percent stress remaining after 1000-s stress relaxation from an 80-g initial load fell from 86.3 +/- 1.1% (buffer) to 76.9 +/- 1.0% (n-butanol). Crosslinking using a glutaraldehyde/n-butanol solution produced materials with tensile mechanical behavior that was very close to that of fresh tissue; however, the flexural properties of the treated tissue were different from those of fresh tissue. This decoupling of the flexural and tensile mechanical behaviors of crosslinked bioprosthetic materials is unique to this form of treatment. The observed phenomena may be the results of conformational changes in collagen facilitated by polar/nonpolar interactions with the solvent that are "locked in" by the action of glutaraldehyde. This technique may aid in the "customized" design of mechanical properties in tissue-derived biomaterials.

Solvent for removing silicone oil from intraocular lenses: experimental study comparing various biomaterials
Dick, H. B. and A. J. Augustin (2000), J Cataract Refract Surg 26(11): 1667-72.
Abstract: PURPOSE: To evaluate the effectiveness of a perfluorocarbon-perfluorohexyloctane (PFHO)-in removing silicone oil from different intraocular lenses (IOLs) and determine whether any removal technique enhances the removal of silicone oil. METHODS: Six IOL materials were analyzed: standard poly(methyl methacrylate) (PMMA), heparin-surface-modified (HSM) PMMA, AcrySof, 2 polyHEMAs with different water contents, and a second-generation SLM-2 silicone. One or 2 microL of a highly viscous silicone oil (5700 cs) was applied to the center of each IOL optic. Perfluorohexyloctane (2 mL) was then used to remove the silicone oil by 1 of 3 techniques: immersion of the IOL in PFHO; irrigation of the silicone oil with a small, blunt cannula; mechanical wiping with a PFHO-saturated Merocel swab (used only when irrigation failed). Next, each IOL was examined by light and scanning electron microscopy. The expanse of silicone oil residue remaining on the IOLs was objectively quantified using an integrated computerized analysis system combined with energy-dispersive spectrometry. RESULTS: After application of 1 microL silicone oil, immersion in PFHO did not remove silicone oil from any IOL material. Irrigation with PFHO removed the silicone oil from the HSM PMMA and polyHEMA IOLs, but oil remained on the other lens materials. Mechanical wiping was necessary to remove the oil from the PMMA, AcrySof, and silicone IOLs. Attempts to remove 2 microL of silicone oil produced similar results. Although mechanical wiping of the AcrySof IOL removed all silicone oil, a slight residue remained on the PMMA and silicone IOLs. The PFHO irrigation removed significantly more silicone oil from the HSM PMMA than the unmodified PMMA IOL (P =.001). More silicone oil was removed from polyHEMA IOLs than from the AcrySof or silicone IOLs (P =.05). CONCLUSION: Although PFHO can remove silicone oil, it is of limited usefulness. The effectiveness of PFHO depends on the removal technique, IOL material, and amount of silicone oil present. Based on these results, we recommend PFHO irrigation followed by mechanical wiping with a PFHO-saturated swab.

Solvent-free vapor-phase photografting of acrylamide onto poly(ethylene terephthalate)
Wirsen, A., H. Sun, et al. (2005), Biomacromolecules 6(5): 2697-702.
Abstract: Poly(ethylene terphthalate) (PET) films were photografted under reduced pressure in a solvent-free vapor of acrylamide and a co-initiator, benzophenone. Characterization of grafted samples by ESCA and contact angles showed that the grafting increased with grafting time and temperature. The amide groups obtained by the acrylamide grafting were converted into amine groups by the Hofmann rearrangement to be used in coupling reactions. The amine groups were confirmed by reaction with pentafluorobenzoyl chloride, which provides a fluorine label for ESCA. Surface grafting of polymeric substrates in the vapor phase induced by plasma or high energy and UV irradiation is reviewed.

Some considerations on biomaterials and bone
Zaffe, D. (2005), Micron 36(7-8): 583-92.
Abstract: Osteoinduction is a property not traditionally attributed to Calcium Phosphate ceramics. Histologic, SEM and X-ray microanalyses of a biopsy of pulmonary alveolar microlithiasis allow to discredit this opinion. Bone, even lamellar type, was ectopically formed on microliths undergoing osteoclastic erosion. The SEM and X-ray microanalyses of coral granules implanted in humans indicate an osteoconductive property for both Calcium and Phosphorus. Analysis of in vitro allows to propose an enhancement of the osteocapability of coral. Lamellar bone formation in the near absence of loads undermines the opinion which sees a correlation between lamellar bone and mechanical loads. Analysis of the bone surrounding an uncemented titanium hip prosthesis highlights that both remodeled and newly formed bone have lamellae oriented parallel to prosthesis surfaces, i.e. orthogonal to loads, as opposed to that of lamellar bone of osteons which are oriented parallel to loads. Analysis of longitudinal sections of cortical bone under polarized light points out that lamellae are displaced parallel to the cement line surface both in the conic end of osteons and in Volkman's canals with thick wall, i.e. undergoing sloped load directions. In conclusion, there may be a relationship between lamellae formation and gravity.

Some current problems and new dimensions of polymeric biomaterials for blood-contacting applications
Bruck, S. D. (1978), Biomater Med Devices Artif Organs 6(1): 57-76.

Some factors affecting properties of elastin-fibrin biomaterial
Barbie, C., C. Angibaud, et al. (1989), Biomaterials 10(7): 445-8.
Abstract: The elasticity, mechanical strength and permeability of a new biomaterial made of elastin and fibrin were investigated. It was shown that gamma-irradiation to sterilize the product, and sulphur derivatives (Merceptyl, thiourea, cystein) working as reticulating agents modified these properties. Depending on whether or not the biomaterial needs to be stiff, strong or elastic both physical processes could intervene separately or together. The good permeability of this material allows it to be used in several surgical fields as a true artificial connective matrix.

Some interactions of blood with tubular biomaterials
Mason, R. G., W. H. Zucker, et al. (1975), Biomater Med Devices Artif Organs 3(1): 57-95.
Abstract: Native human blood was exposed to polyethylene, poly(vinyl chloride), and Silastic tubing for varying time intervals, following which the relative degree of activation of the intrinsic coagulation system and alterations in cell counts were determined. The effects of pre-exposure of Silastic to purified albumin, high-density lipoprotein, or protein polysaccharide upon subsequent reactivity of blood with these surfaces was determined. In addition, the effects of aspirin, dextran, heparin, and Warfarin on reactivity of blood with Silastic were determined. In each case, changes in coagulation and cell counts were correlated with ultrastructural features of test surfaces following their exposure to blood. Pre-exposure of Silastic to purified proteins had relatively little effect upon subsequent reactivity with blood, while the presence of antithrombotic agents produced numerous changes.

Some methods for in vitro estimation of the blood compatibility of biomaterials
Mason, R. G. (1972), Bull N Y Acad Med 48(2): 407-24.

Some philosophies for standardizations of biomaterials and related devices
Yokobori, T. (1994), Biomed Mater Eng 4(4): 341-3.
Abstract: From the viewpoint of the target of biomaterials, the needs for biomedical reliability as well as development of novel function is discussed. Some approaches to guidelines or standardization of biomaterials and the related devices are pointed out.

Sonocatalytic degradation of methyl orange in the presence of (nanometer and ordinary) anatase TiO2 powders
Wang, J., B. D. Guo, et al. (2005), J Environ Sci (China) 17(3): 414-8.
Abstract: The nanometer and ordinary anatase titanium dioxide (TiO2) powders were adopted as the sonocatalysts for the degradation of methyl orange used as a model compound for the first time. It was found that the sonocatalytic degradation effect of methyl orange in the presence of TiO2 powder were much better than that without TiO2, but the sonocatalytic activity of the nanometer anatase TiO2 particle was obviously higher than that of ordinary anatase TiO2 particle. Although there are many factors influencing sonocatalytic degradation of methyl orange, the experimental results showed that the best degradation ratio of methyl orange could be obtained when the experimental conditions were: initial concentration 15 mg/L, nanometer anatase TiO2 adding amount 750 mg/L, ultrasonic frequency 40 kHz, output power 50 W, pH = 3.0 and temperature 40 degrees C within 150 min. In addition, the catalytic activity of reused nanometer anatase TiO2 catalyst was also studied and found to decline gradually comparing with initial nanometer anatase TiO2 catalyst. All experiments indicated that the method of the sonocatalytic degradation of organic pollutants in the presence of TiO2 powder was an advisable choice for non- or low-transparent organic wastewaters.

Sonochemical deposition of Au nanoparticles on titania and the significant decrease in the melting point of gold
Pol, V. G., G. Wildermuth, et al. (2005), J Nanosci Nanotechnol 5(6): 975-9.
Abstract: In this article, sub-micron size particles of titania were coated by a nanosized gold particles with the aid of power ultrasound. We could achieve a uniform coating of gold nanoparticles on a titania surface with a maximum gold loading of 10 wt%. In addition, we report on the experimental evidence for a significant decrease in the melting point of gold nanoparticles (<2 nm) by approximately 850 degrees C from that of the bulk material.

Sonoelastographic imaging of interference patterns for estimation of the shear velocity of homogeneous biomaterials
Wu, Z., L. S. Taylor, et al. (2004), Phys Med Biol 49(6): 911-22.
Abstract: The shear wave velocity is one of a few important parameters that characterize the mechanical properties of bio-materials. In this paper, two noninvasive methods are proposed to measure the shear velocity by inspecting the shear wave interference patterns. In one method, two shear wave sources are placed on the opposite two sides of a sample, driven by the identical sinusoidal signals. The shear waves from the two sources interact to create interference patterns, which are visualized by the vibration sonoelastography technique. The spacing between the pattern bands equals half of the shear wavelength. The shear velocity can be obtained by taking the product of the wavelength and the frequency. An alternative method is to drive the two vibration sources at slightly different frequencies. In this case, the interference patterns no longer remain stationary. It is proved that the apparent velocity of the moving patterns is proportional to the shear velocity in the medium. Since the apparent velocity of the patterns can be measured by analysing the video sequence, the shear velocity can be obtained thereafter. These approaches are validated by a conventional shear wave time-of-flight approach, and they are accurate within 4% on various homogeneous tissue-mimicking phantoms.

Sorption mechanisms of zinc on hydroxyapatite: systematic uptake studies and EXAFS spectroscopy analysis
Lee, Y. J., E. J. Elzinga, et al. (2005), Environ Sci Technol 39(11): 4042-8.
Abstract: The systematics and mechanisms of Zn uptake by hydroxyapatite (HAP) in preequilibrated suspensions open to PCO2 were characterized using a combination of batch sorption experiments, X-ray diffraction (XRD), and extended X-ray absorption fine structure spectroscopy (EXAFS) over a wide range of pH and Zn concentrations. Sorption isotherms of Zn(II) on HAP at pH 5.0 and 7.3 show an initial steep slope at low Zn(II) concentrations, followed by a plateau up to [Zn] < approximately 750 microM, suggesting Langmuir-type behavior. At [Zn] > 750 microM, a sharp rise in the pH 5.0 isotherm suggests precipitation, whereas slight continued uptake in the pH 7.3 isotherm is suggestive of an additional uptake mechanism. The sorption isotherm at pH 9.0 shows a steep uptake step at [Zn] < or = 0.8 microM, followed by an increasing linear trend up to [Zn] = 5 microM, without any indication of a maximum, suggesting that precipitation is an important uptake process at this pH. Zn K edge EXAFS results show a first oxygen shell at 1.96-1.98 +/- 0.02 A in sorption samples with [Zn]tot < or = 250 microM at pH 5.0, 7.3, and 9.0, consistent with tetrahedral coordination. EXAFS results reveal additional P and Ca neighbors that support formation of an inner-sphere Zn surface complex where the Zn is coordinated to surface P04 tetrahedra in a corner-sharing bidentate fashion, bridging a Ca atom. In contrast, EXAFS and XRD data indicate that precipitation of Zn3(PO4)2-4H2O (hopeite) dominates the mode of Zn uptake at [Zn]tot > or = 3 mM at pH 5.0. Principal component analysis and linear combination fits of EXAFS data reveal a mixture of inner-sphere Zn surface complexation and precipitation of Zn5(OH)6(CO3)2 (hydrozincite) in sorption samples for [Zn]tot = 5 mM at pH 7.3 and for [Zn]tot = 1 mM at pH 9.0.

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Last Modified: 8 February 2006