Biomaterials.info - Resources for Engineers

Record 2621 to 2640

Is it time to remove the MemoryLens IOL from the market?
Apple, D. J., G. Kleinmann, et al. (2005), J Cataract Refract Surg 31(9): 1681-2.

Is there a need for plasticizer-free biomaterials in dialysis therapy?
Yakubovich, M. and J. Vienken (2000), Med Device Technol 11(10): 12-3, 18-21.
Abstract: The impact of plasticizers on general health is an extremely controversial subject. Most of the results in this area, especially those related to di-ethylhexyl-phthalate, are collected from animal studies and the extrapolation to humans is still controversial and difficult. This review of research findings explores the science of using soft polyvinyl(chloride). With particular reference to dialysis, it explains why some companies now offer products made of plasticizer-free biomaterials.

Is trehalose special for preserving dry biomaterials?
Crowe, L. M., D. S. Reid, et al. (1996), Biophys J 71(4): 2087-93.
Abstract: Simple sugars, especially disaccharides, stabilize biomaterials of various composition during air-drying or freeze-drying. We and others have provided evidence that direct interaction, an interaction that we believe is essential for the stabilization, between the sugar and polar groups in, for example, proteins and phospholipids occurs in the dry state. Some researchers, however, have suggested that the ability of the sugar to form a glass is the only requirement for stabilization. More recently, we have shown that both glass formation and direct interaction of the sugar and headgroup are often required for stabilization. In the present study, we present a state diagram for trehalose glass and suggest that the efficacy of this sugar for stabilization may be related to its higher glass transition temperatures at all water contents. We also show that trehalose and trehalose:liposome preparations form trehalose dihydrate as well as trehalose glass when rehydrated with water vapor. Formation of the dihydrate sequesters water, which might otherwise participate in lowering the glass transition temperature to below ambient. Because samples remain in the glassy state at ambient temperatures, viscosity is high and fusion between liposomes is prevented.

Isocyanato- and methacryloxysilanes promote Bis-GMA adhesion to titanium
Matinlinna, J. P., L. V. Lassila, et al. (2005), J Dent Res 84(4): 360-4.
Abstract: In dentistry, adhesion promotion with 3-methacryloyloxypropyltrimethoxysilane is usually sufficient, but its hydrolytic stability is a continuous concern. The hydrolytic stability of an alternative, 3-isocyanatopropyltriethoxysilane, was compared with that of conventional 3-methacryloyloxypropyltrimethoxysilane. Two silanes, both in 0.1 and 1.0 vol-% in ethanol-water, were evaluated in the attachment of an experimental bis-phenol-A-diglycidyldimethacrylate (Bis-GMA) resin to grit-blasted (with two different systems) titanium. Silane hydrolysis was monitored by FTIR spectrometry. Bis-GMA resin was applied and photo-polymerized on titanium. The specimens were thermocycled (6000 cycles, 5-55 degrees C). Surface analysis was carried out with scanning electron microscopy. Statistical analysis (ANOVA) showed that the highest shear bond was achieved with 0.1% 3-isocyanatopropyltriethoxysilane (12.5 MPa) with silica-coating, and the lowest with 1.0% 3-methacryloyloxypropyltrimethoxysilane (3.4 MPa) with alumina-coating. The silane, its concentration, and the grit-blasting method significantly affected the shear bond strength (p < 0.05). SEM images indicated cohesive failure of bonding, and, in conclusion, 3-isocyanatopropyltriethoxysilane is a potential coupling agent.

Isolation and characterization of osteoblast cultures from normal and osteopenic sheep for biomaterials evaluation
Torricelli, P., M. Fini, et al. (2000), J Biomed Mater Res 52(1): 177-82.
Abstract: Being very useful in the analysis of bone cell differentiation and activity, osteoblast cultures are also used in the in vitro biocompatibility study of new materials. The aim of this work was to evaluate sheep osteoblast cultures derived from normal and ovariectomized animals, and then to assess the in vitro biomaterial behavior on these cultures, taking into account the quality of bone where orthopedic devices are clinically used. For this purpose, we characterized sheep osteoblast cultures, isolated from iliac crest bone of normal (NB osteoblast culture) and osteopenic after ovariectomy (OB osteoblast culture) sheep. Moreover, we studied cell behavior when cultured on different biomaterials (titanium and two biological glasses, RKKP and AP40). Cell characterization at baseline demonstrated that both cultures (NB and OB) showed normal osteoblastic behavior. On the contrary, osteoblasts derived from osteopenic bone and cultivated on AP40 for 6 days revealed a different behavior in terms of both cell morphology and metabolic activity. Statistical analysis (one-way analysis of variance and Scheffe's post hoc multiple-comparison tests) revealed significant differences in Ca level (p<0.0005), MTT test (p<0.0005) and OC production (p<0.05). These in vitro tests demonstrated that sheep osteoblast cultures can be useful when determining biocompatibility and osteointegration of orthopedic materials, and also when evaluating for the presence of osteoporosis.

Isolation of intact elastin fibers devoid of microfibrils
Daamen, W. F., T. Hafmans, et al. (2005), Tissue Eng 11(7-8): 1168-76.
Abstract: Purification protocols for elastin generally result in greatly damaged elastin fibers and this likely influences the biological response. We here describe a novel protocol for the isolation of elastin whereby the fibers stay intact, and introduce the term "elastin fiber" for intact elastic fibers with elastin as their sole component. As opposed to elastic fibers, elastin fibers do not contain any microfibrils or associated molecules. Elastin fibers were isolated from equine elastic ligaments according to various protocols and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, amino acid quantification, immunofluorescence assay, transmission/scanning electron microscopy, and cellular reactivity in vivo. The optimal protocol comprised several extraction steps and trypsin digestion. Elastin fibers were free of contaminants and had a smooth, regular appearance. The cellular response to purified, intact elastin fibers was different in comparison with purified, but affected, fibers and to contaminated fibers. Intact fibers consisting only of elastin may be important for both fundamental and applied research, for example, tissue engineering, which need well-defined preparations to study the cellular biological effect of individual components.

Isolation, culture, and characterisation of human macular inner choroidal microvascular endothelial cells
Browning, A. C., T. Gray, et al. (2005), Br J Ophthalmol 89(10): 1343-7.
Abstract: AIM: To develop a method for the reliable isolation of adult human macular inner choroidal endothelial cells (ICECs) and to subsequently characterise them for their expression of a range of endothelial cell associated surface markers. METHOD: Human ICECs were isolated after manual dissection of maculas from fresh human posterior segments. Following enzyme digestion to form a single cell suspension, the ICECs were isolated using anti-CD31 coated Dynabeads. The isolated cells were grown in culture and examined for typical endothelial cell morphology, surface expression of vWf, CD 31, CD 105, VEGF receptors 1 and 2, and expression of E-selectin after stimulation with TNF-alpha. The cells were also examined for their ability to form fenestrations and capillary-like tubes in Matrigel. RESULTS: The method enabled the rapid isolation of viable cells that demonstrated typical endothelial cobblestone morphology in culture. The cells stained positive for CD31, vWf, CD105, VEGF receptors 1 and 2, and E-selectin (after stimulation with TNF-alpha). The cells stained negative for alpha smooth muscle actin and fibroblast surface protein. The cells also developed fenestrations when cultured on fibronectin coated plates and formed capillary-like tubes structures when cultured on Matrigel. CONCLUSIONS: This technique isolates cells from the human macular inner choroid that display features consistent with vascular endothelial cells. These cells could subsequently be used to further the understanding of the pathophysiological mechanisms of diseases of the inner choroid, such as choroidal neovascularisation.

Isolation, proliferation and differentiation of osteoblastic cells to study cell/biomaterial interactions: comparison of different isolation techniques and source
Declercq, H., N. Van den Vreken, et al. (2004), Biomaterials 25(5): 757-68.
Abstract: A sufficient amount of easily obtained and well-characterized osteoblastic cells is a useful tool to study biomaterial/cell interactions essential for bone tissue engineering. Osteoblastic cells were derived from adult and fetal rat via different isolation techniques. The isolation and in vitro proliferation of primary cultures were compared. The osteogenic potential of subcultures was studied by culturing them in osteogenic medium and compared with respect to alkaline phosphatase activity, nodule formation and mineralization potential. Calvaria cells were easier to obtain and the amount of cells released by enzymatic isolation was higher than for the long bone cells. The expansion of the cells in primary culture was highest for fetal calvaria cells compared to fetal and adult long bone cells. All cultures expressed high alkaline phosphatase activity except for calvaria cells obtained by spontaneous outgrowth. Enzymatic isolation of fetal calvaria and long bone cells favoured the osteogenic differentiation. Enzymatically isolated calvaria cells formed well-defined three-dimensional nodules which mineralized restricted to this area. On the contrary, cultures derived from fetal as well as adult long bones mineralized in ill-defined deposits throughout the culture and only formed occasionally nodular-like structures. The mineral phase of all osteoblastic cultures was identified as a carbonate-containing apatite. The present study demonstrates that considering the isolation method, proliferation capacity and the osteogenic potential, the enzymatically released fetal calvaria cells are most satisfactory to study cell/biomaterial interactions.

Keratin sponge: immobilization of lysozyme
Kurimoto, A., T. Tanabe, et al. (2003), J Biosci Bioeng 96(3): 307-9.
Abstract: A porous wool keratin sponge was used for immobilization of lysozyme, a model bioactive substance and was demonstrated to be a unique biomaterial in terms that the activity of lysozyme linked to the sponge through disulfide bond was gradually released, while lysozyme through thioether bond was stably maintained.

Key issues involved with the use of miniature specimens in the characterization of the mechanical behavior of polymeric biomaterials--a review
Lewis, G. (2002), J Biomed Mater Res 63(5): 455-66.
Abstract: This article is arranged in three parts. In the first, a brief history of the use of miniature specimens for characterizing the mechanical behavior of materials in general is given. In the second part, several trends in literature reports of small punch and small shear punch tests of ultra-high-molecular-weight polyethylene and acrylic bone cement specimens are examined critically. In this exercise, special attention is paid to one test metric; namely, the work to failure [which is the area under the punch load (P) versus punch displacement (Delta) plot up to the failure point]. In the third part of the article, seven key issues in this field are discussed. In each case, the gaps in the current knowledge base are pointed out. Among those issues are determination of sensitivity of test results to test variables, development of methods for converting P-Delta results to bulk material properties, and constitutive modeling of the mechanical behavior of a polymeric biomaterial, under both small punch and small shear punch loading.

Key points in the fixation of the craniofacial skeleton with absorbable biomaterial
Habal, M. B. and W. S. Pietrzak (1999), J Craniofac Surg 10(6): 491-9.

Key references in biomaterials: bone/biomaterial interface in orthopedic joint implants
Gruen, T. A. and A. Sarmiento (1984), J Biomed Mater Res 18(5): 577-99.

Key references in biomaterials: heart valve replacement
Schoen, F. J. and N. S. Braunwald (1983), J Biomed Mater Res 17(4): 715-29.

Kinetic analysis of photocatalytic oxidation of gas-phase formaldehyde over titanium dioxide
Liu, H., Z. Lian, et al. (2005), Chemosphere 60(5): 630-5.
Abstract: Degradation of formaldehyde with different initial concentration over titanium dioxide was carried out in a photocatalytic reactor. Photocatalytic rates were well described by the simplified Langmuir-Hinshelwood model. The kinetic analysis shows that the apparent first-order reaction coefficient is lower and half-life of photocatalysis is longer for low concentration than for high concentration formaldehyde. A network formation model of the photocatalytic products was established. Experimental results and analysis demonstrate that carbon dioxide concentration and carbon monoxide concentration in gas phase vary exponentially with the illumination time and may be even higher than gas-phase formaldehyde concentration if there is much pre-adsorbed formaldehyde in adsorption equilibrium on catalysts before illumination. Carbon monoxide is found to be one of the by-products during formaldehyde photooxidation.

Kinetics of fibrinogen and platelet adherence to biomaterials
Roohk, H. V., J. Pick, et al. (1976), Trans Am Soc Artif Intern Organs 22: 1-8.
Abstract: The initial task was to establish a conceptually and materially simple test procedure that could quantitate and evaluate the thrombogenic potential of a biomaterial surface. Since the primary events of thrombus formation on prosthetic surfaces are believed to involve the deposition of a plasma protein monolayer followed by platelet adhesion to its fibrinogen component, it seemed reasonable to focus on the binding kinetics of fibrinogen and platelets to a commonly used biomaterial. Employing solutions of 125I-fibrinogen in buffered saline, the adsorption characteristics of several types of biomedical tubing could be compared, and the competition and exchange among plasma proteins at surface binding sites of PVC were evaluated. Human platelets with 51Cr were found to adhere to PVC surfaces proportional to surface fibrinogen concentration, but only in the presence of plasma; the circulation of labelled platelets in buffered saline only resulted in significant adherence to the native surface, while surface fibrinogen was inhibitory. Physiological concentrations of albumin were the most effective in preventing both fibrinogen adsorption and platelet adherence. The most important consequence of this work, perhaps, is the many avenues of future experimentation discovered from this methodological approach, not only in the thrombogenic evaluation of a specific biomedical surface, but also in the delineation of thrombogenic sequelae in general.

Kinetics of gelation and thermal sensitivity of N-isobutyryl chitosan hydrogels
Felix, L., J. Hernandez, et al. (2005), Biomacromolecules 6(5): 2408-15.
Abstract: N-Acylation of chitosan with carboxylic anhydrides in dilute acetic acid/methanol has been a well documented strategy to selectively modify chitosan. Although this reaction is known to lead to irreversible gel formation, the kinetics and mechanism of this process have not so far been addressed. To this purpose, gel formation during the N-isobutyrylation of chitosan was investigated as a function of the reaction stoichiometry (R), chitosan concentration, and temperature by small deformation oscillatory rheology. Gel formation follows closely the chemical reaction and it proceeds predominantly under second-order kinetics as established from the dependence of critical gel time, t(gel), on R and concentration. The activation energy value derived from t(gel) vs 1/T data (E(a) = 68.29 +/- 1.80 kJ/mol) was almost identical to values reported for the chitosan N-acetylation reaction in previous studies. An excess isobutyric anhydride is suggested to be necessary for nucleation and hydrophobic association. The potential application of N-isobutyrylchitosan (NIBC) hydrogels in the design of thermally sensitive materials is also demonstrated.

Kinetics of ultrasonic disinfection of Escherichia coli in the presence of titanium dioxide particles
Kubo, M., R. Onodera, et al. (2005), Biotechnol Prog 21(3): 897-901.
Abstract: The ultrasonic disinfection of Escherichia coli was carried out in the presence of anatase-type TiO2 particles, and the effectiveness of the combination of ultrasonic irradiation with TiO2 addition was verified. The rate constant was determined from the plot of the common logarithm of the survival cell ratio versus the ultrasonic irradiation time using first-order kinetics. In the absence of particles, the rate constant was proportional to the ultrasonic power. When ultrasonic disinfection was carried out in the presence of TiO2 particles, which have a radical generation ability, the rate of disinfection was remarkably faster than that in the absence of TiO2. In the presence of silica particles, which have no radical generation ability, the rate of disinfection was the same as that in the absence of TiO2. These results suggest that the radical generation ability of TiO2 appeared as a result of the ultrasonic irradiation. The effect of the amount of TiO2 on the rate of disinfection was also examined. The rate constant for disinfection in the presence of TiO2 was saturated to a certain value and was represented using the Langmuir-type equation. The proposed model well describes the effects of the ultrasonic power and the amount of TiO2 on the rate constant for disinfection.

Knitted dacron grafts used for abdominal aortic reconstruction: sizing references
Alonso-Perez, M., R. J. Segura, et al. (2001), Vasc Surg 35(6): 457-61.
Abstract: This study was undertaken to analyze immediate and mid-term knitted Dacron graft dilation and to establish which parameters should be taken as a reference when aortic graft dilation is evaluated. A Dacron knitted microvel double velour vascular graft (Hemashield Gold) was implanted in 30 patients with aneurysmal (19 cases, 63%) or occlusive (11 cases, 37%) aortic disease. The stems of bifurcated prostheses (27 patients, 90%) and tube grafts (3 patients, 10%) were measured. The package sizing (labelled size) was compared with the external diameter measured intraoperatively with a slide caliper, prior to implantation and after complete clamp release. Additional measurements were obtained by ultrasound 1 and 6 months after implantation, and in 16 cases (53% of the patients) ultrasound and computed tomography (CT) were performed at the end of the first year. The means of the measurements were compared using Student's t test for matched pairs. The statistical significance level was set at p values < 0.05. There was a statistically significant difference between the package sizing (15.3 +/- 1.1 mm) and the external diameter measured prior to implantation (18.7 +/- 1.3 mm); and with the external diameter following implantation (19.6 +/- 1.4 mm), (p < 0.01). External diameters measured prior to grafting and following implantation (after complete clamp release), when compared with the manufacturer's size, showed a mean increase in graft diameter of 3.4 mm (22%) and 4.3 mm (28%), respectively. There were no statistical differences between the external diameter measured after clamp release (19.6 +/- 1.4 mm) and the size determined by ultrasound 4 weeks (19.3 +/- 1.2 mm) and 6 months (19.8 +/- 1.5 mm) following surgery (p values 0.11 and 0.56, respectively). Considering size after clamp release as a reference (19.6 +/- 1.4 mm), an almost significant (p = 0.08) increase in the diameter (0.7 +/- 1.5 mm) was obtained at the end of the first year when the measurement was performed with ultrasound. However, when the measurement was performed by CT at the end of the first year, the differences (0.9 +/- 1.6 mm) revealed statistical relevance (p = 0.04). There was no statistically significant difference between the sizes obtained by ultrasound (20.3 +/- 2.1 mm) and by CT (20.5 +/- 2.2 mm) at the end of the first year (p values 0.07). The package sizing is not a reliable parameter for choosing the size of knitted Dacron grafts. Immediate increase in diameter noted in Dacron grafts is caused by discrepancies between the package sizing and the measured diameter after clamp release during implantation, and by an initial adaptation of the textile structure. This must be taken into account for an accurate investigation of the immediate graft dilation rate, and if further follow-up is contemplated, a measurement to be taken as a reference should be performed by ultrasound or CT in the immediate postoperative period.

Label-free detection of protein-ligand interactions by the quartz crystal microbalance
Janshoff, A. and C. Steinem (2005), Methods Mol Biol 305: 47-64.
Abstract: In recent years the quartz crystal microbalance (QCM) has been accepted as a powerful technique to monitor adsorption processes at interfaces in different chemical and biological research areas. In the last decade, the investigation of adsorption of biomolecules on functionalized surfaces turned out to be one of the paramount applications of the QCM comprising the interaction of nucleic acids, specific molecular recognition of protein-receptor couples, and antigen-antibody reactions realized in immunosensors. The advantage of the QCM technique is that it allows for a label free detection of molecules. This is a result of the fact that the frequency response of the quartz resonator is proportional to the increase in thickness of the adsorbed layer. However, in recent years it became more and more evident that quartz resonators used in fluids are more than mere mass or thickness sensors. The sensor response is also influenced by viscoelastic properties of the adhered biomaterial, surface charges of adsorbed molecules and surface roughness. These phenomena have been used to get new insights in the adhesion process of living cells and to understand their response to pharmacological substances by determining morphological changes of the cells. In this chapter we describe a protocol to explore the kinetics and thermodynamics of specific interactions of different proteins such as lectins and annexins with their ligands using receptor bearing solid supported lipid bilayers.

Lack of OH in nanocrystalline apatite as a function of degree of atomic order: implications for bone and biomaterials
Pasteris, J. D., B. Wopenka, et al. (2004), Biomaterials 25(2): 229-38.
Abstract: Using laser Raman microprobe spectroscopy, we have characterized the degree of hydroxylation and the state of atomic order of several natural and synthetic calcium phosphate phases, including apatite of biological (human bone, heated human bone, mouse bone, human and boar dentin, and human and boar enamel), geological, and synthetic origin. Common belief holds that all the studied phases are hydroxylapatite, i.e., an OH-containing mineral with the composition Ca10(PO4)6(OH)2. We observe, however, that OH-incorporation into the apatite crystal lattice is reduced for nanocrystalline samples. Among the biological samples, no OH-band was detected in the Raman spectrum of bone (the most nanocrystalline biological apatite), whereas a weak OH-band occurs in dentin and a strong OH-band in tooth enamel. We agree with others, who used NMR, IR spectroscopy, and inelastic neutron scattering, that-contrary to the general medical nomenclature-bone apatite is not hydroxylated and therefore not hydroxylapatite. Crystallographically, this observation is unexpected; it therefore remains unclear what atom(s) occupy the OH-site and how charge balance is maintained within the crystal. For non-bone apatites that do show an OH-band in their Raman spectra, there is a strong correlation between the concentration of hydroxyl groups (based on the ratio of the areas of the 3572 deltacm(-1) OH-peak to the 960 deltacm(-1) P-O phosphate peak) and the crystallographic degree of atomic order (based on the relative width of the 960 deltacm(-1) P-O phosphate peak) of the samples. We hypothesize that the body biochemically imposes a specific state of atomic order and crystallinity (and, thus, concentration of hydroxyl) on its different apatite precipitates (bone, dentin, enamel) in order to enhance their ability to carry out tissue-specific functions.

First Page

Last Page