Biomaterials.info - Resources for Engineers

Record 4321 to 4340

Tricalcium phosphate solubilizing abilities of Trichoderma spp. in relation to P uptake and growth and yield parameters of chickpea (Cicer arietinum L.)
Rudresh, D. L., M. K. Shivaprakash, et al. (2005), Can J Microbiol 51(3): 217-22.
Abstract: Nine isolates of Trichoderma spp. were investigated for their ability to solubilize insoluble phosphate in Pikovskaya's broth and were compared with an efficient phosphate-solubilizing bacterium Bacillus megaterium subsp. phospaticum PB that was used as the reference strain. All 9 Trichoderma isolates were found to solubilize insoluble tricalcium phosphate to various extents. Trichoderma viride (TV 97) (9.03 microg x mL(-1)), Trichoderma virens (PDBCTVs 12) (9.0 microg x mL(-1)), and Trichoderma virens (PDBCTVs 13) (8.83 microg x mL(-1)) solubilized 70% of that solubilized by the reference strain Bacillus megaterium (12.43 microg x mL(-1)). Pot culture and field evaluations with Trichoderma harzianum (PDBCTH 10), Trichoderma viride (TV 97), and Trichoderma virens (PDBCTVs 12) using chickpea (Cicer arietinum L.) 'Annegeri-1' as the test plant and rock phosphate as the phosphorus source showed significantly increased P uptake in plants treated with Trichoderma harzianum (PDBCTH 10) followed by Trichoderma virens (PDBCTVs 12) and Trichoderma viride (TV 97). Inoculation of Trichoderma spp. also showed increased growth and yield parameters of chickpea compared with the uninoculated controls under both glasshouse and field conditions.

TRICOMED S.A.--Polish School of the Biomaterials
Raczynski, K. (2002), Polim Med 32(1-2): 3-12.

Trimethylated chitosans as non-viral gene delivery vectors: cytotoxicity and transfection efficiency
Kean, T., S. Roth, et al. (2005), J Control Release 103(3): 643-53.
Abstract: Chitosans are linear polysaccharides of natural origin that show potential as carriers in drug and gene delivery. Introducing quaternisation on the chitosan backbone renders the polymer soluble over a wider pH range and confers controlled cationic character. This study aims to investigate the effect of increasing quaternisation and therefore, positive charge on cell viability and transfection. Oligomeric and polymeric chitosans were trimethylated, the toxicity and transfection efficiency of these derivatives were tested with respect to increasing degree of trimethylation. The cytoxicity of polymer and oligomer derivatives alone and of their complexes with plasmid DNA were determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay on COS-7 (monkey kidney fibroblasts) and MCF-7 (epithelial breast cancer) cells. Transfection efficiency was investigated using the pGL3 luciferase reporter gene on the same cell lines. Complexes were characterised for their stability by gel electrophoresis. Cytotoxicity results showed that all derivatives were significantly less toxic than linear polyethylenimine (PEI). A general trend of increasing toxicity with increasing degree of trimethylation was seen. However, higher toxicity was seen in polymeric chitosan derivatives over oligomeric chitosan derivatives at similar degrees of trimethylation. All derivatives complexed pGL3 luc plasmid DNA efficiently at 10:1 ratio and three (TMO44, TMC57 and TMC93) were able to transfect MCF-7 cells with greater efficiency than PEI; 16, 23 and 50-fold, respectively. TMC57, TMC93 and all TMOs gave appreciable transfection of COS-7 cells.

Triple helical collagen-like peptides: engineering and applications in matrix biology
Koide, T. (2005), Connect Tissue Res 46(3): 131-41.
Abstract: Collagen, a large insoluble protein with a characteristic triple helical structure, is found as the most prominent component of extracellular matrix. The functions of collagen are not limited to providing mechanical strength to various tissues and organs as a structural protein, as it has been pointed out that collagen exhibits various biological functions through specific interactions with other macromolecules. However, the use of native triple helical collagen is often troublesome because of its insolubility and gelating properties. Instead, triple helical collagen-like peptides have been designed and are used as collagen surrogates in studies on collagen structure, stability, and biological functions including binding to other proteins and cultured cells. This article reviews recent progress in peptide design, synthesis, and the applications of collagen-like peptides in current matrix biology, while emphasizing the advantages of the peptide-based strategy.

Tubing extrusion made easier, part I
Ferrandino, M. (2004), Med Device Technol 15(8): 12-5.
Abstract: To produce tubing with consistent properties, it is important to know the material, understand the process, control the basics, and keep the goal, that is, the product in focus. Tips on controlling the process and producing the required results are provided in this two-part article. Part I focusses on the melt and material sensitivities.

Tubing extrusion made easier, Part II
Ferrandino, M. (2004), Med Device Technol 15(9): 20-3.
Abstract: An increased understanding of the primary elements will lead to greater control of the extrusion process. In the ongoing quest to produce tubing with consistent properties. Part II of this two-part article makes recommendations on best practice in barrel and screw design, compression ratios and dies.

Tubing loops as a model for cardiopulmonary bypass circuits: both the biomaterial and the blood-gas phase interfaces induce complement activation in an in vitro model
Gong, J., R. Larsson, et al. (1996), J Clin Immunol 16(4): 222-9.
Abstract: We describe here a model for the study of blood/surface and blood/air interaction as encountered in cardiopulmonary bypass (CPB) circuits. Polyethylene tubing was filled with serum or blood and closed end to end into loops whereby the volume of the remaining air bubble was inversely varied with respect to that of the fluid. The loops were rotated vertically in a water bath at 37 degrees C. The profiles of C3a, iC3, and TCC generation were similar to those observed at surgery, involving CPB. Soluble heparin and heparan sulfate inhibited both C3a and TCC formation, but surface-conjugated heparin had only a minor effect. Binding of C3 and/or C3 fragments to the heparin surface was much reduced compared to the amine matrix to which heparin was linked, but compared with the polyethylene surface the effect was less pronounced. These data suggest that, in addition to the biomaterial surface, the blood-gas interface seems to play an important role in the activation of complement and that this activation is inhibitable by high concentrations of soluble glucose aminoglycans.

Tumor necrosis factor and vascular endothelial growth factor induce endothelial integrin repertories, regulating endovascular differentiation and apoptosis in a human extravillous trophoblast cell line
Fukushima, K., S. Miyamoto, et al. (2005), Biol Reprod 73(1): 172-9.
Abstract: Angiogenesis is crucial in human development. Extravillous trophoblast (EVT) cells mimic endothelial cells in angiogenesis during endovascular differentiation, inducing a remodeling of spiral arteries that increases blood flow toward the intravillous space. We have previously shown that tumor necrosis factor (TNF) alpha regulates expression of ITGA6 and ITGA1, which are involved in cell survival, in the human EVT cell line TCL1. To further investigate endovascular differentiation, we examined the effects of vascular endothelial growth factor (VEGF), TNF, and extracellular matrix (ECM) on TCL1 cells. Seeded on Matrigel, TCL1 cells show tube-like formation that specifically recalls morphological changes in endothelial cells. Anti-ITGAV/ITGB3 antibodies significantly reduced the size of the capillary network (P < 0.05) on Matrigel and also suppressed TNF-induced apoptosis (P < 0.05) in TCL1 cells. VEGF induced expression of ITGAV/ITGB3 subunits and protein aggregation, as in the case of TNF, which in turn, induces synthesis of VEGF in TCL1 cells. Soluble FLT1 suppressed these activities in TCL1 cells, indicating that signals involving VEGF axis are essential for endovascular differentiation. These results suggest that TNF, VEGF, and ECM collaboratively regulate EVT behavior, including cell survival and endovascular differentiation, through integrin signaling during establishment and maintenance of successful human pregnancies.

Tuning compliance of nanoscale polyelectrolyte multilayers to modulate cell adhesion
Thompson, M. T., M. C. Berg, et al. (2005), Biomaterials 26(34): 6836-45.
Abstract: It is well known that mechanical stimuli induce cellular responses ranging from morphological reorganization to mineral secretion, and that mechanical stimulation through modulation of the mechanical properties of cell substrata affects cell function in vitro and in vivo. However, there are few approaches by which the mechanical compliance of the substrata to which cells adhere and grow can be determined quantitatively and varied independent of substrata chemical composition. General methods by which mechanical state can be quantified and modulated at the cell population level are critical to understanding and engineering materials that promote and maintain cell phenotype for applications such as vascular tissue constructs. Here, we apply contact mechanics of nanoindentation to measure the mechanical compliance of weak polyelectrolyte multilayers (PEMs) of nanoscale thickness, and explore the effects of this tunable compliance for cell substrata applications. We show that the nominal elastic moduli E(s) of these substrata depend directly on the pH at which the PEMs are assembled, and can be varied over several orders of magnitude for given polycation/polyanion pairs. Further, we demonstrate that the attachment and proliferation of human microvascular endothelial cells (MVECs) can be regulated through independent changes in the compliance and terminal polyion layer of these PEM substrata. These data indicate that substrate mechanical compliance is a strong determinant of cell fate, and that PEMs of nanoscale thickness provide a valuable tool to vary the external mechanical environment of cells independently of chemical stimuli.

Tuning the sol-gel microenvironment for acetylcholinesterase encapsulation
Sotiropoulou, S. and N. A. Chaniotakis (2005), Biomaterials 26(33): 6771-9.
Abstract: The effect of the sol-gel microenvironment on the activity of acetylcholinesterase, an enzyme of high bio-analytical interest, is presented and is correlated to the overall analytical performance of corresponding biosensors. The sol-gel membranes are initially optimized with respect to the catalyst and the TEOS:H2O ratio (r), for mechanical stability, porosity, and hydrophobicity as well as in terms of enzymatic activity. FT-IR and electrochemical impedance spectroscopy (EIS) are used to probe the configuration and rotational mobility of the enzyme within the sol-gel matrices. Overall, it is observed that the rotational mobility of the protein can be correlated with the sensitivity of the biosensor. Optimum biosensor performance is obtained for base-catalyzed sol-gels with r values close to 2. The biosensor has sensitivity of 2.5 microA/mm, a linear range of response between 1 and 3mm, response time of about 30s, and sensor-to-sensor reproducibility (RSD) of 3%. These analytical characteristics are far superior to previously reported sol-gel biosensors.

Two cases of subintimal angioplasty with proximal stent implantation for long superficial femoral artery occlusions
Min, P. K., Y. G. Ko, et al. (2005), Catheter Cardiovasc Interv 65(4): 540-3.
Abstract: Subintimal angioplasty is a simple and safe alternative to conventional intraluminal angioplasty for the recanalization of diffuse long femoropopliteal occlusions. However, long-term patency rates are unsatisfactory despite the high initial technical success rates. Two cases of occluded left superficial femoral arteries are presented in which subintimal angioplasty with proximal stent implantation was successfully performed. Self-expanding nitinol stents were placed at the proximal part of subintimal plane to maintain good inflow. In both cases, follow-up angiogram at 6 months demonstrated patent stents with good antegrade flow.

Two new plate nozzles for the production of alginate microspheres
Yang, F., K. Wang, et al. (2005), Int J Pharm 298(1): 206-10.
Abstract: Combining the Rayleigh-type jet break-up and two new plate nozzles, the alginate microsphere was produced. Spray generators made of syringe needle and laser-drilling nozzle plate and synthetic red stone nozzle plate were fabricated and contrasted. The above two plate nozzles provided lower liquid resistance and yield well. Furthermore, the more uniform microsphere was produced within a wider range of frequency by plate nozzles. Experiments using multiple-nozzle synthetic red stone plate was easy to feasible.

Two-dimensional patterning of thin coatings for the control of tissue outgrowth
Thissen, H., G. Johnson, et al. (2006), Biomaterials 27(1): 35-43.
Abstract: Control of the precise location and extent of cellular attachment and proliferation, and of tissue outgrowth is important in a number of biomedical applications, including biomaterials and tissue engineered medical devices. Here we describe a method to control and direct the location and define boundaries of tissue growth on surfaces in two dimensions. The method relies on the generation of a spatially defined surface chemistry comprising protein adsorbing and non-adsorbing areas that allow control over the adsorption of cell-adhesive glycoproteins. Surface modification was carried out by deposition of thin acetaldehyde and allylamine plasma polymer coatings on silicon wafer and FEP substrates, followed by grafting of a protein resistant layer of poly(ethylene oxide). Spatially controlled patterning of the surface chemistry was achieved by masking during plasma polymerization. XPS and AFM were used to provide evidence of successful surface modifications. Adsorption of the extracellular matrix protein collagen I followed by tissue outgrowth experiments with bovine corneal epithelial tissue for up to 21 days showed that two-dimensional control over tissue outgrowth is achievable with our patterning method over extended time frames. The method promises to be an effective tool for use in a number of in vitro and in vivo applications.

Two-dimensional thickness measurements based on internal reflection ellipsometry
Otsuki, S., K. Tamada, et al. (2005), Appl Opt 44(8): 1410-5.
Abstract: An imaging ellipsometer technique on internal reflection geometry that can measure the thickness distribution of a thin film possessing an assumed refractive index is described. Because a prism is used for the internal reflection geometry, it was theoretically predicted that angular derivation from the normal incidence on the prism surface affects only the psi value by a factor of 0.97 at maximum. Measurements were carried out for an optical system of silica substrate-TiO2 layer-silica layer-protein film-air, with a thin-film array of dried protein as the sample film. Thickness of the protein films was two-dimensionally estimated only from the measured map of the delta value by use of the simulated relationship between the thickness and the delta value. The thickness map obtained was coincident on the whole with the results according to a mechanical scanning. The detection limit was approximately +/- 0.2 nm. These findings validate the optical effect of a high-index additional layer to improve the sensitivity and precision of thickness measurements of the sample film on transparent substrates.

Two-layer film as a laser soldering biomaterial
Lauto, A., I. Kerman, et al. (1999), Lasers Surg Med 25(3): 250-6.
Abstract: BACKGROUND AND OBJECTIVES: A two-layer solder was developed to weld at low laser intensity and to provide a new method of measuring solder-tissue temperature. STUDY DESIGN/MATERIALS AND METHODS: A film solder consisted of a white layer (bovine serum albumin (BSA) and distilled water) and a black layer (BSA, carbon black (CB), and distilled water). This two-layer solder was used with a diode laser to weld sections of dog small intestine (lambda = 810 nm, power = 200 +/- 20 mW, radiation dose = 18 +/- 1 J/mg). Sections of intestine were welded only with one-layer black solders as control group. The temperature difference between the external solder surface and the tissue-solder interface was evaluated during welding. RESULTS: The two-layer solder performed welds as strong as the one-layer solder (approximately 0.12 N) but with less laser intensity on the black layer. The temperature difference between the external surface of the solder and the solder-tissue interface was significantly less for the two-layer solder than for the one-layer solder (approximately 6 degrees C and approximately 15 degrees C, respectively; P < 0.05). CONCLUSIONS: The two-layer solder appeared to be more efficient at soldering biomaterials than the one-layer solder. Furthermore, the heat diffusion from the black midplane of the two-layer solder decreased the difference in temperature recorded on the solder external surface and on the solder-tissue interface.

Two-month ciprofloxacin implants for multibacterial bone infections
Castro, C., C. Evora, et al. (2005), Eur J Pharm Biopharm 60(3): 401-6.
Abstract: A ciprofloxacin implant formulation composed of 12% hydroxyapatite, 36% tricalcium phosphate, 12% poly(DL-lactide) (PLA) and 40% ciprofloxacin was characterized in vivo for use in treatment of multibacterial bone infection. After the implant was inserted in the femur of rabbits, approximately 90% of the total ciprofloxacin was released within 8 weeks, maintaining therapeutic levels in the femur and tibia. Throughout the femoral cortex and marrow these remained higher than the minimum inhibitory concentrations (MIC) against the most common pathogens causing osteomyelitis. Levels in tibia cortex were also above MIC for 6 weeks. The implant was characterized in terms of polymer degradation and morphological and crystallographic changes. X-ray analyses confirmed the osteoconductivity and biocompatibility of these materials. The sequential changes in the femur were those of a normal surgical trauma reaction followed by a repair process. All the results confirmed that ciprofloxacin release is limited by its low solubility, and that implant erosion and bone ingrowth into the implants enhance the antibiotic release.

Two-stent techniques for the treatment of coronary bifurcations with drug-eluting stents
Iakovou, I. and A. Colombo (2005), Hellenic J Cardiol 46(3): 188-98.

Tyrosine derived polycarbonate membrane is useful for guided bone regeneration in rabbit mandibular defects
Asikainen, A. J., J. Noponen, et al. (2005), J Mater Sci Mater Med 16(8): 753-8.
Abstract: Standardized bilateral through-and-through defects (12x6 mm) were created extraorally in the mandibular angle of 18 New Zealand White rabbits. Animals were divided in to three groups (n=6) according to the intended healing time. On the left side, defects were covered with a poly(desaminotyrosyl-tyrosine-ethyl ester carbonate) (PDTE carbonate) membrane wrapped around the inferior border of the mandible and fixed with bioabsorbable sutures. On the right side, the defects were filled with a mesh made of bioactive glass 13-93 and 3 wt% chitosan. The defects were covered with the same membranes. Periosteal flap was sutured over the membrane. Radiographically, bone ingrowth was seen in all specimens at 12 weeks postoperatively. At 24 weeks, completely ossified area remained approximately at the same level as at 12 weeks, but the non-ossified area decreased to almost zero. However, the bioactive glass mesh did not improve the results. Nevertheless, enveloping the defect with PDTE carbonate membrane seemed to play a crucial role in new bone formation. Based on these results, we conclude that tyrosine polycarbonate is a promising new material for guided bone regeneration.

Tyrosine-PEG-derived poly(ether carbonate)s as new biomaterials. Part I: synthesis and evaluation
Yu, C. and J. Kohn (1999), Biomaterials 20(3): 253-64.
Abstract: Tyrosine PEG-derived poly(ether carbonate)s were prepared by condensation copolymerization with phosgene. The resulting polymers were random copolymers with weight average molecular weights from 40 000 to 200 000 dalton. Chemical structure and purity were confirmed by NMR and FTIR spectral analysis. General structure property correlations were established. The glass transition temperature decreased with increasing PEG content and increasing pendent chain length. When higher molecular weight PEG blocks were used, the glass transition temperature increased relative to identical polymers having shorter PEG blocks. The tensile modulus increased with decreasing PEG content, decreasing pendent chain length, and when longer PEG blocks were used. Water uptake and the rate of backbone degradation increased with increasing PEG content. Microspheres could be prepared by solvent evaporation techniques from copolymers with low PEG content. Release rate of pNA and FITC-dextran from the microspheres increased with increasing PEG content. While tyrosine-derived polycarbonates were excellent substrates for cell attachment and growth, the presence of only 5 mol% of PEG1000 led to low or no cell attachment in short-term cell culture with both rat lung fibroblasts and osteoblasts. The polymers were non-cytotoxic.

Tyrosine-PEG-derived poly(ether carbonate)s as new biomaterials. Part II: study of inverse temperature transitions
Yu, C., S. S. Mielewczyk, et al. (1999), Biomaterials 20(3): 265-72.
Abstract: Tyrosine-poly(alkylene oxide)-derived poly(ether carbonate)s represent a new group of degradable biomaterials that exhibit inverse temperature transitions. Poly(DTE co 70%PEG,1000 carbonate) was chosen as an example to study this special phase transition behavior of the polymers. The observed transition temperature varied slightly depending on the technique used, e.g. CD always gave a lower temperature than UV/Vis. CD and UV/Vis studies indicated that the transition temperature was both heating rate and concentration dependent. Thermodynamic parameters of the transition (enthalpy, entropy, and free energy) were determined by DSC. The molecularity of the transition was 2.6, as calculated from UV and DSC data. The transition temperature could be varied from 18 to 58 degrees C by changing the polymer structure. The new poly(ether carbonate)s may be used in medical applications such as injectable drug delivery formulations and bioresorbable barriers for the prevention of surgical adhesions.

First Page

Last Page