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Record 3961 to 3980

Tech.Sight. Bioelectronics. Biomaterials for sensors, fuel cells, and circuitry
Willner, I. (2002), Science 298(5602): 2407-8.

Technique of left main stenting is dependent on lesion location and distal branch protection
Wood, F., E. Bazemore, et al. (2005), Catheter Cardiovasc Interv 65(4): 499-503.
Abstract: The purpose of this study was to review our experience with left main stenting and evaluate initial results with drug-eluting stents (DESs). Drug-eluting stents delivered with contemporary techniques could change the traditional surgical approach to patients with significant left main disease. One hundred sixty-one patients underwent left main stenting (100 bare metal, 61 drug-eluting) after being excluded from surgery. In group A, disease was confined to the ostium or main stem; in group B, disease involved the bifurcation. Patients were classified as either unprotected (U) or protected (P) depending on the presence of a patent bypass graft. Study endpoints were any major adverse cardiac event (MACE). In-hospital MACE was 6% with no deaths; 74% of patients in group A underwent direct stenting, whereas 89% of the patients in group B had predilatation performed prior to stent implantation. A total of 98% of patients in BU had kissing balloon inflations after stent deployment; provisional side-branch stenting was required in one patient. V-stenting was performed in 13% of patients in group BU. The 1-year mortality in the bare metal stent group was 9% with the majority of deaths in group BU. There was one noncardiac death in the DES group at 6 months and five patients (8.2%) underwent target vessel revascularization for restenosis. Event-free survival at 6 months in group BU treated with DESs was 87%. Significant left main disease presents a spectrum of angiographic abnormalities and different interventional techniques are required depending on lesion location and distal protection. Although in-hospital complications with left main stenting were low in this single-center study, follow-up events were common in patients treated with bare metal stents. A randomized multicenter trial will be required to determine whether drug-eluting stents will improve survival in patients with left main disease.

Techniques to investigate cellular and molecular interactions in the host response to implanted biomaterials
Hunt, J. A., P. J. McLaughlin, et al. (1997), Biomaterials 18(22): 1449-59.
Abstract: Evaluation of the host response to implanted materials requires systematic, objective investigations of responses at both the cellular and molecular levels. This article explains the basis behind two technologies: antibody and molecular techniques, which will give valuable information when applied to investigations of cells and molecules involved in the host biomaterial interaction. Such investigations are well underway, and a number of groups are now studying well characterised cell markers or molecules to evaluate the host response to biomaterials. Here we outline current technologies for the development of antibodies as tools to study cell markers or molecules, including those for which reagents are not yet available and DNA based technologies, whose continued application should prove an invaluable adjunct to existing approaches. These technologies may be particularly valuable to investigations focusing on newly characterised cytokines, receptors or cell adhesion molecules and subsequently provide a way forward for the production of advanced biomaterials.

Technological advances in nanoscale biomaterials: the future of synthetic vascular graft design
Miller, D. C., T. J. Webster, et al. (2004), Expert Rev Med Devices 1(2): 259-68.
Abstract: Currently, autologous veins are the first choice for patients in need of bypass grafting materials. However, due to either pre-existing conditions or previous bypass surgery, some patients lack the necessary amount of host tissue for such procedures. Unfortunately, current synthetic vascular grafts of less than 6 mm in diameter have been plagued by a variety of problems. For this reason, there has been significant research aimed at finding more suitable small-diameter vascular graft materials. In order to improve vascular cell functions on such synthetic materials, several techniques are currently under development that attempt to mimic the natural nanometer architecture of the vascular basement membrane. This review presents several processes including colloidal lithography, chemical etching, electrospinning and solid free-form fabrication that could play a role in the future of vascular nanostructured biomaterial development.

Technological issues for the development of more efficient calcium phosphate bone cements: a critical assessment
Bohner, M., U. Gbureck, et al. (2005), Biomaterials 26(33): 6423-9.
Abstract: The first calcium phosphate cements (CPCs) were discovered in the 1980s. Two decades later, the interest for these materials is still rising. The goal of the present document is to review the most recent achievements in the field and to analyze future directions in research and development.

Technology development for medical implants
Hodgins, D. (2005), Med Device Technol 16(5): 19-20.
Abstract: Work on new technologies for biomaterials and an implantable power source for implants is described here. Common requirements have been identified to start the development of technological solutions that can be applied to a range of products.

Temperature-responsive hydroxybutyl chitosan for the culture of mesenchymal stem cells and intervertebral disk cells
Dang, J. M., D. D. Sun, et al. (2006), Biomaterials 27(3): 406-18.
Abstract: Temperature-responsive polymers are attractive candidates for applications related to injectable delivery of biologically active therapeutics, such as stem cells. In this study, we evaluate the potential of thermosensitive hydroxybutyl chitosan (HBC) as a biomaterial for the culture of human mesenchymal stem cells (hMSC) and cells derived from the intervertebral disk, with the eventual goal of using the HBC polymer as an injectable matrix/cell therapeutic. Conjugation of hydroxybutyl groups to chitosan renders the polymer water soluble and thermally responsive. Below its lower critical solution temperature, a solution of HBC can be maintained indefinitely in its solvated state. Upon exposure to a 37 degrees C environment, within 60 s, a 3.8 wt% HBC solution rapidly forms a gel that can be maneuvered with forceps. Upon cooling, the gel once again is able to revert to its solvated state. The gel exhibits a dramatic increase in both G' and G'' with increasing temperature, signifying a temperature-dependent enhancement of gel mechanical properties. Although a solid structure upon gelation, due to its physical nature of polymer interaction and gel formation, the gel exhibits a fluid-like viscoelastic behavior when exposed to shear stresses of up to 10% strain, with both G' and G'' approaching zero with increasing shear stress. Formulations of HBC gels presented in this study have gelation temperatures ranging from 13.0 to 34.6 degrees C and water contents of 67-95%. Minimal cytotoxicity in MSC and disk cell cultures was observed with these polymers up to a concentration of 5 wt%. Detection of metabolic activity, genetic analysis of synthesized mRNA, and histological staining of MSC and disk cell cultures in these gels collectively indicate cell proliferation without a loss in metabolic activity and extracellular matrix production. This study suggests the potential of HBC gel as an injectable carrier for future applications of delivering therapeutics to encourage a biologically relevant reconstruction of the degenerated disk.

Template-directed self-assembly and growth of insulin amyloid fibrils
Ha, C. and C. B. Park (2005), Biotechnol Bioeng 90(7): 848-55.
Abstract: The formation of amyloid aggregates in tissue is a pathological feature of many neurodegenerative diseases and type II diabetes. Amyloid deposition, the process of amyloid growth by the association of individual soluble amyloid molecules with a pre-existing amyloid template (i.e., plaque), is known to be critical for amyloid formation in vivo. The requirement for a natural amyloid template, however, has made amyloid deposition study difficult and cumbersome. In the present work, we developed a novel, synthetic amyloid template by attaching amyloid seeds covalently onto an N-hydroxysuccinimide-activated surface, where insulin was chosen as a model amyloidogenic protein. According to ex situ atomic force microscopy observations, insulin monomers in solution were deposited onto the synthetic amyloid template to form fibrils, like hair growth. The fibril formation on the template occurred without lag time, and its rate was highly accelerated than in the solution. The fibrils were long, over 2 mum, and much thinner than those in the solution, which was caused by limited nucleation sites on the template surface and lack of lateral twisting between fibrils. According to our investigations using thioflavin T-induced fluorescence, birefringent Congo red binding, and circular dichroism, fibrils grown on the template were identified to be amyloids that formed through a conformational rearrangement of insulin monomers upon interaction with the template. The amyloid deposition rate followed saturation kinetics with respect to insulin concentration in the solution. The characteristics of amyloid deposition on the synthetic template were in agreement with previous studies performed with human amyloid plaques. It is demonstrated that the synthetic amyloid template can be used for the screening of inhibitors on amyloid deposition in vitro.

Template-synthesized protein nanotubes
Hou, S., J. Wang, et al. (2005), Nano Lett 5(2): 231-4.
Abstract: A layer-by-layer deposition strategy for preparing protein nanotubes within the pores of a nanopore alumina template membrane is described. This method entails alternately exposing the template membrane to a solution of the desired protein and then to a solution of glutaraldehyde, which acts as cross-linking agent to hold the protein layers together. The number of layers of protein that make up the nanotube walls can be controlled at will by varying the number of alternate protein/glutaraldehyde cycles. After the desired number of layers have been deposited on the pore walls, the alumina template can be dissolved to liberate the protein nanotubes. We show here that glucose oxidase nanotubes prepared in this way catalyze glucose oxidation and that hemoglobin nanotubes retain their heme electroactivity. Furthermore, for the glucose oxidase nanotubes, the enzymatic activity increases with the nanotube wall thickness.

Tensile creep properties of interpenetrating networks containing gelatin and poly(ethylene glycol) diacrylate
Toth, M., K. Williams, et al. (2005), J Biomater Sci Polym Ed 16(7): 925-32.
Abstract: The tensile creep properties of an interpenetrating networks (IPN) system containing polyanionic ethylenediaminetetraacetic dianhydride (EDTAD)-modified gelatin and poly(ethylene glycol) diacrylate (PEGdA) of 600 or 2000 Da at various weight ratios were determined under different pH and load levels. A computerized creep testing device was designed following ASTM D2990 and validated to establish the environment-dependent structure-function relationship of IPNs. IPNs containing PEGdA 2000 Da or EDTAD-modified gelatin showed less strain than those formulated with PEGdA 600 Da or unmodified gelatin, respectively. IPN formulated with 40 wt% gelatin showed higher strain than those with 50 or 30 wt% gelatin. Increasing strain in IPN was observed with increasing load level. IPN strain was higher at pH 7 when compared to pH 4 or 10. The creep characteristics of this complex macromolecular system are dependent on both environmental and composition factors.

Testing biomaterials
Milthorpe, B. K. and K. Schindhelm (1986), Australas Phys Eng Sci Med 9(1): 33-7.

Testing biomaterials by the in-situ evaluation of cell response
Manso, M., S. Ogueta, et al. (2002), Biomol Eng 19(2-6): 239-42.
Abstract: In this work, we describe a technique for the in-situ observation of cells adhered on opaque biomaterial surfaces. The visualisation of the morphology of cells adhered onto a surface allows to derive nuclear apoptotic signs or even the existence of organisation between groups of these cells. The technique is based on the use of an auto-immune reaction combined with a fluorescent agent that allows a direct inspection of the cell behaviour. The versatility of the technique is demonstrated by presenting several examples with different cultured cells (human chondrosarcome cells (CSRCs) and pluripotential mesenchymal stem cells (MSCs) from bone marrow) seeded over two different Ti-based surfaces (TiO(2) and TiN, respectively). These in-vitro observations are compared with the behaviour of the same cells on bare TiAlV alloy. From our results it is concluded that both TiO(2) and TiN surfaces show enhanced biological responses.

Testing of biomaterials, accelerated ageing
Prodinger, A., S. Krausler, et al. (1985), Life Support Syst 3 Suppl 1: 444-7.
Abstract: The residual elongation is a critical property of materials used for manufacturing diaphragms of artificial hearts. It is therefore important to check goods received or to control manufactured diaphragms, whether their creep properties are within the required limits. Ordinary creep tests take at least several months, while the release of goods received or diaphragms manufactured should be possible within a few days. Acceleration of the creep test by increasing the test temperature permits an estimation whether the creep properties of a material are within the required limits within a week.

Testing of bone-biomaterial interfacial bonding strength: a comparison of different techniques
Wang, X., A. Subramanian, et al. (1996), J Biomed Mater Res 33(3): 133-8.

Testing the utility of rationally engineered recombinant collagen-like proteins for applications in tissue engineering
Ito, H., A. Steplewski, et al. (2005), J Biomed Mater Res A
Abstract: Collagens are attractive proteins as materials for tissue engineering. Over the last decade, significant progress has been made in developing technologies for large-scale production of native-like human recombinant collagens. Yet, the rational design of customized collagen-like proteins for smart biomaterials to enhance the quality of engineered tissues has not been explored. We mapped the D4 domain of human collagen II as most critical for supporting migration of chondrocytes and used this information to genetically engineer a collagen-like protein consisting of tandem repeats of the D4 domain (mD4 collagen). This novel collagen has been utilized to fabricate a scaffold for support of chondrocytes. We determined superior qualities of cartilaginous constructs created by chondrocytes cultured in scaffolds containing the mD4 collagen in comparison to those formed by chondrocytes cultured in bare scaffolds or those coated with wild-type collagen II. Our results are a first attempt to rationally engineer collagen-like proteins with characteristics tailored for specific needs of cartilage engineering and provide a basis for rational engineering of similar proteins for a variety of biomedical applications. (c) 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005.

Texture analysis from synchrotron diffraction images with the Rietveld method: dinosaur tendon and salmon scale
Lonardelli, I., H. R. Wenk, et al. (2005), J Synchrotron Radiat 12(Pt 3): 354-60.
Abstract: A Rietveld method is described which extracts information on crystal structure, texture and microstructure directly from two-dimensional synchrotron diffraction images. This is advantageous over conventional texture analysis that relies on individual diffraction peaks, particularly for low-symmetry materials with many overlapping peaks and images with a poor peak-to-background ratio. The method is applied to two mineralized biological samples with hydroxylapatite fabrics: an ossified pachycephalosaurid dinosaur tendon and an Atlantic salmon scale. Both are measured using monochromatic synchrotron X-rays. The dinosaur tendon has very strongly oriented crystals with c-axes parallel to the tendon direction. The salmon scale displays a weak texture.

The activation of human plasma prekallikrein as a hemocompatibility test for biomaterials. II. Contact activation by EVAL and EVAL-SMA copolymers
Guerra, G. D., N. Barbani, et al. (1993), J Biomater Sci Polym Ed 4(6): 643-52.
Abstract: The activation of human plasma prekallikrein (PKK) to kallikrein (KK), induced by the contact of blood with foreign materials, is a useful in vitro hemocompatibility test. Kallikrein is easily detected by its reaction with the chromogenic substrate H-D-Pro-Phe-Arg-pNA, which releases p-nitroaniline, revealed by its absorption at 405 nm. This test, which was already carried out by evaluating PKK activation by the 'end-point' method, has been carried out in this work by the more accurate 'initial velocity' method, i.e. by evaluating the activation from the initial rates of the KK-substrate reaction. The tests were carried out on the following materials: borosilicate glass (as a high-activation reference material), silicone (as a low-activation reference material), the commercial biomaterial Cardiothane 51, three graft copolymers synthesized in our laboratory by reacting ethylene-vinyl alcohol copolymer (EVAL) with styrene-maleic anhydride copolymer (SMA), and EVAL itself. A mathematical treatment based on a simple kinetic model has been used for a first-approximation evaluation of the PKK-activating power of the materials tested. The quite low activating power of the EVAL-SMA copolymers, which are easily processable into water-permeable hollow fibers, suggests the possibility of their use in blood dialyzers.

The actuation of a biomimetic poly(vinyl alcohol)poly(acrylic acid) gel
Marra, S. P., K. T. Ramesh, et al. (2002), Philos Transact A Math Phys Eng Sci 360(1791): 175-98.
Abstract: Active polymer gels expand and contract in response to certain environmental stimuli, such as the application of an electric field or a change in the pH level of the surroundings. This ability to achieve large, reversible deformations with no external mechanical loading has generated much interest in the use of these gels as biomimetic actuators and "artificial muscles". In previous work, a thermodynamically consistent finite-elastic constitutive model has been developed to describe the mechanical and actuation behaviours of active polymer gels. The mechanical properties were characterized by a free-energy function, and the model uses an evolving internal variable to describe the actuation state. In this work, an evolution law for the internal variable is determined from free actuation experiments on a poly(vinyl alcohol)poly(acrylic acid) (PVAPAA) gel. The complete finite-elastic/evolution law constitutive model is then used to predict the response of the PVA-PAA gel to isotonic and isometric loading and actuation. The model is shown to give relatively good agreement with experimental results.

The aggregation behavior of O-carboxymethylchitosan in dilute aqueous solution
Zhu, A., M. B. Chan-Park, et al. (2005), Colloids Surf B Biointerfaces 43(3-4): 143-9.
Abstract: O-Carboxymethylchitosan (OCMCS) is a kind of biocompatible derivatives of chitosan whose water solubility is strongly dependent on the degree of carboxymethylation. The OCMCS with 100 carboxymethyl groups and 75 amino groups per 100 anhydroglucosamine units of OCMCS was synthesized by the reaction of chitosan and monochloroacetic. When OCMCS was dissolved in water, its solution was neutral and OCMCS behaved like a weak polyanionic polyeclectrolyte because most of carboxylic groups were not dissociated in neutral aqueous solution. The aggregation behavior of OCMCS in aqueous solution was studied by surface tensiometry, steady-state fluorescence spectroscopy and viscometry. The critical aggregation concentration (cac) of OCMCS was determined to be between 0.042 mg/ml and 0.050 mg/ml. The possible aggregation mechanism of OCMCS in water was elucidated.

The anti-oxidative properties of alpha-tocopherol in gamma-irradiated UHMWPE with respect to fatigue and oxidation resistance
Shibata, N. and N. Tomita (2005), Biomaterials 26(29): 5755-62.
Abstract: Although addition of an antioxidant (alpha-tocopherol) is reported to prevent delamination in ultrahigh molecular weight polyethylene (UHMWPE) knee components, contribution of alpha-tocopherol as an antioxidant to the improvement of long-term fatigue performance of UHMWPE is an unknown mechanism. To solve this problem, bi-directional sliding fatigue tests were performed for gamma-irradiated (25 kGy), gamma-irradiated (25 kGy) with 0.3 wt% alpha-tocopherol added, and gamma-irradiated (25 kGy) with 0.3 wt% tocopheryl acetate added UHMWPE specimens. Internal defect initiation was quantified with scanning acoustic tomography (SAT). Also, oxidation index and crystallinity were obtained from infrared absorption spectra measured using Fourier transform infrared (FT-IR) microscopy. Only gamma-irradiated UHMWPE specimens resulted in severe fatigue fractures. alpha-Tocopherol-added UHMWPE specimens showed significantly lower projected area ratio of defects (1.80+/-0.82) than did gamma-irradiated (7.0+/-2.29) and tocopheryl acetate-added ones (8.50+/-2.01). The oxidation index of gamma-irradiated UHMWPE specimens (0.111+/-0.0052) was extremely higher compared to those of doped ones; 0.0179+/-0.0026 and 0.0144+/-0.0069 for alpha-tocopherol-added and tocopheryl acetate-added ones, respectively. The crystallinity of gamma-irradiated UHMWPE specimens (57.5+/-1.16) was lower compared to those of doped ones; 60.3+/-0.72 and 60.4+/-1.38 for alpha-tocopherol-added and tocopheryl acetate-added ones, respectively. The incorporation of alpha-tocopherol significantly improves the long-term fatigue performance of gamma-irradiated UHMWPE with oxidation stability. Also, the addition of alpha-tocopherol controls macromolecular structures resulting in the improvement of fatigue performance of UHMWPE.

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