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Record 2961 to 2980

Nerve conduits
Taras, J. S., V. Nanavati, et al. (2005), J Hand Ther 18(2): 191-7.
Abstract: The evolution of peripheral nerve repair is reviewed with respect to the development of the nerve conduit. The rationale and available scientific evidence to support the use of nerve conduits is presented. Therapy evaluation and treatment protocols for patients with peripheral nerve repairs with nerve conduits are detailed. The authors present clinical experience to date with 73 cases of peripheral nerves repaired with the NeuraGenR collagen nerve conduit.

Nerve growth factor expression by PLG-mediated lipofection
Whittlesey, K. J. and L. D. Shea (2006), Biomaterials 27(11): 2477-86.
Abstract: Biomaterials capable of efficient gene delivery provide a fundamental tool for basic and applied research models, such as promoting neural regeneration. We developed a system for the encapsulation and sustained release of plasmid DNA complexed with a cationic lipid and investigated their efficacy using in vitro models of neurite outgrowth. Sustained lipoplex release was obtained for up to 50 days, with rates controlled by the fabrication conditions. Released lipoplexes retained their activity, transfecting 48.2+/-8.3% of NIH3T3 cells with luciferase activity of 3.97x10(7)RLU/mg. Expression of nerve growth factor (NGF) was employed in two models of neurite outgrowth: PC12 and primary dorsal root ganglia (DRG) co-culture. Polymer-mediated lipofection of PC12 produced bioactive NGF, eliciting robust neurite outgrowth. An EGFP/NGF dual-expression vector identified transfected cells (GFP-positive) while neurite outgrowth verified NGF secretion. A co-culture model examined the ability of NGF secretion by an accessory cell population to stimulate DRG neurite outgrowth. Polymer-mediated transfection of HEK293T with an NGF-encoding plasmid induced outgrowth by DRG neurons. This system could be fabricated as implants or nerve guidance conduits to support cellular and tissue regeneration. Combining this physical support with the ability to locally express neurotrophic factors will potentiate regeneration in nerve injury and disease models.

Nerve growth factor mediates its pro-invasive effect in parallel with the release of a soluble E-cadherin fragment from breast cancer MCF-7/AZ cells
Dolle, L., M. J. Oliveira, et al. (2005), J Dairy Res 72 Spec No: 20-6.
Abstract: To define better the function of Nerve Growth Factor (NGF) in breast cancer progression, we investigated whether this polypeptide was able to induce breast cancer cell invasion. NGF inhibited aggregation of tumour cells through modulation of the E-cadherin/catenin complex function. In addition, NGF induced the breast cancer cells to invade into Matrigel. We focused our attention on how NGF prevents aggregation, in order to discover the signalling pathway that leads tumour cells to acquire the invasive phenotype. Moreover, studies on the identification of signalling pathways that are responsive for NGF-induced invasion will be basically described.

Neural tissue engineering: a self-organizing collagen guidance conduit
Phillips, J. B., S. C. Bunting, et al. (2005), Tissue Eng 11(9-10): 1611-7.
Abstract: We report a novel implantable device that will deliver a tethered aligned collagen guidance conduit containing Schwann cells into a peripheral nerve injury site. Cells (Schwann cells and fibroblasts) incorporated into tethered rectangular collagen gels contracted and resulted in uniaxial alignment. This tissue-engineered construct was tested in three-dimensional culture and demonstrated the ability to guide neurite extension from dissociated dorsal root ganglia. A silicone tube was adapted to provide tethering sites for an implantable construct such that uniaxial cell-generated tension resulted in the formation of a bridge of aligned collagen fibrils, with a resident Schwann cell population. The potential of this device for surgical nerve regeneration was assessed in a 5-mm defect in a rat sciatic nerve model. Neural regeneration through this device was significantly greater than in controls, demonstrating that this system has potential both as a simple robust clinical implant and as a three-dimensional engineered tissue model.

Neurite bridging across micropatterned grooves
Goldner, J. S., J. M. Bruder, et al. (2006), Biomaterials 27(3): 460-72.
Abstract: After injury, regenerating axons must navigate complex, three-dimensional (3D) microenvironments. Topographic guidance of neurite outgrowth has been demonstrated in vitro with culture substrates that contain micropatterned features on the nanometer-micron scale. In this study we report the ability of microfabricated biomaterials to support neurite extension across micropatterned grooves with feature sizes on the order of tens of microns, sizes relevant to the design of biomaterials and tissue engineering scaffolds. Neonatal rat dorsal root ganglion (DRG) neurons were cultured on grooved substrates of poly(dimethyl siloxane) coated with poly-L-lysine and laminin. Here we describe an unusual capability of a subpopulation of DRG neurons to extend neurites that spanned across the grooves, with no underlying solid support. Multiple parameters influenced the formation of bridging neurites, with the highest numbers of bridges observed under the following experimental conditions: cell density of 125,000 cells per sample, groove depth of 50 microm, groove width of 30 microm, and plateau width of 200 microm. Bridges were formed as neurites extended from a neuron in a groove, contacted adjacent plateaus, pulled the neuron up to become suspended over the groove, and the soma translocated to the plateau. These studies are of interest to understanding cytoskeletal dynamics and designing biomaterials for 3D axon guidance.

Neurogenesis and neuronal communication on micropatterned neurochips
Bani-Yaghoub, M., R. Tremblay, et al. (2005), Biotechnol Bioeng 92(3): 336-45.
Abstract: Neural networks are formed by accurate connectivity of neurons and glial cells in the brain. These networks employ a three-dimensional bio-surface that both assigns precise coordinates to cells during development and facilitates their connectivity and functionality throughout life. Using specific topographic and chemical features, we have taken steps towards the development of poly(dimethylsiloxane; PDMS) neurochips that can be used to generate and study synthetic neural networks. These neurochips have micropatterned structures that permit adequate cell positioning and support cell survival. Within days of plating, cells differentiate into neurons displaying excitability and communication, as evidenced by intracellular calcium oscillations and action potentials. The structural and functional capacities of such simple neural networks open up new opportunities to study synaptic communication and plasticity.

Neurotrophin releasing single and multiple lumen nerve conduits
Yang, Y., L. De Laporte, et al. (2005), J Control Release 104(3): 433-46.
Abstract: Tissue engineering strategies for nerve repair employ polymer conduits termed guidance channels and bridges to promote regeneration for peripheral nerve injury and spinal cord injury, respectively. An approach for fabrication of nerve conduits with single and multiple lumens capable of controlled release of neurotrophic factors was developed. These conduits were fabricated from a mixture of poly(lactide-co-glycolide) (PLG) microspheres and porogen (NaCl) that was loaded into a mold and processed by gas foaming. The porosity and mechanical properties of the constructs were regulated by the ratio of porogen to polymer microsphere. The neurotrophin, nerve growth factor (NGF), was incorporated into the conduit by either mixing the protein with microspheres or encapsulating the protein within microspheres prior to gas foaming. A sustained release was observed for at least 42 days, with the release rate controlled by method of incorporation and polymer molecular weight. Released NGF retained its bioactivity, as demonstrated by its ability to stimulate neurite outgrowth from primary dorsal root ganglion (DRG). In vivo results indicate that conduits retain their original architecture, and allow for cellular infiltration into the channels. Polymer conduits with controllable lumen diameters and protein release may enhance nerve regeneration by guiding and stimulating neurite outgrowth.

Neutrophil polarization and immunoelectrophoresis assays in the study of complement activation by biomaterials
Remes, A. and D. F. Williams (1991), Biomaterials 12(6): 607-13.
Abstract: The neutrophil polarization assay, a technique used to measure chemotaxis, was adapted to examine complement activation. Complement activation in serum which had been incubated with metallic and polymeric biomaterials was examined using the neutrophil polarization assay and immunoelectrophoresis assay. In agreement with previous publications, nylon activated the complement cascade, but PTFE did not. The neutrophil polarization assay was found to be the most sensitive technique for examining complement activation by endotoxin but the immunoelectrophoresis assay is the technique most sensitive for detecting complement activation by cobalt powder. In both assays, complement activation was not detected in serum incubated with chromium powder. However, serum incubated with silver and nickel powder stimulated neutrophils to polarize indicating that these powders may activate complement.

Neutrophil survival on biomaterials is determined by surface topography
Chang, S., Y. Popowich, et al. (2003), J Vasc Surg 37(5): 1082-90.
Abstract: PURPOSE: Cardiovascular device-centered infections are a major cause of hospital morbidity, mortality, and expense. Caused by opportunistic bacteria, this phenomenon is thought to arise because of a defect in neutrophil bacterial killing. We have shown that neutrophils that adhere to polystyrene remain viable, whereas neutrophils that adhere to the vascular biomaterials expanded polytetrafluoroethylene (ePTFE) and Dacron undergo a rapid nonapoptotic death. This study was designed to test the hypothesis that surface topography is a determinant of the nonapoptotic death response of neutrophils to biomaterials. METHODS: We took advantage of the ease with which a polystyrene surface can be manipulated to examine the effect of surface topography on neutrophil viability. Neutrophils were exposed to smooth or roughened polystyrene surfaces both in vivo and in vitro. Changes in cell membrane permeability and production of reactive oxygen species by individual cells were monitored with fluorescent dyes. RESULTS: Host cells and isolated human neutrophils died rapidly after adhesion to roughened polystyrene. Neutrophils adherent to roughened surfaces produced more reactive oxygen intermediates than those adherent to smooth surfaces and were first to die. The cell death response precipitated by expanded polytetrafluoroethylene, Dacron, or the roughened surfaces was significantly reduced with treatment of the neutrophils with catalase, diphenylene iodonium, or the src kinase inhibitor PP2 before adhesion. CONCLUSIONS: Neutrophil adhesion to roughened materials triggers rapid production of reactive oxygen species and precipitates a nonapoptotic cell death. Understanding the material properties that trigger these responses is essential to development of the next generation of implantable biomaterials.

New antiinfectious biomaterials. Ciprofloxacin containing polyurethanes as potential drug delivery systems to prevent foreign-body infections
Schierholz, J. M., A. Rump, et al. (1997), Arzneimittelforschung 47(1): 70-4.
Abstract: Device related infections are an increasing problem since foreign materials are used in modern medicine. Ciprofloxacin-HCl salt (CAS 86393-32-0) and lipophilic ciprofloxacin-betaine (Bay o 9867) incorporated into polyurethanes by solvent casting technique were studied in order to develop antiinfectious properties of this biomaterial. Drug release rates, bacterial colonization and morphological features of the polymerciprofloxacin combinations were studied and the physico-chemical mechanisms of the delivery were discussed. Ciprofloxacin salt showed a fast initial release rate, whereas ciprofloxacin-betaine was characterized by a more continuous release behaviour. A higher diffusity of the lipophilic ciprofloxacin-betaine in the polymer could be shown as compared to its salt incorporated into the polyurethane. The high initial burst effect of the hydrochloride antibiotic was caused by its high solubility in the elution medium. Bacterial colonization to the antibiotic-loaded polyurethanes was inhibited effectively only by preparations showing a slower but more sustained drug release. Scanning electron microscopy (SEM) demonstrated that the polyurethane-antibiotic combination was most homogenous for ciprofloxacin-betaine. Polyurethane material loaded with ciprofloxacin salt showed crystals at the surface and a granular structure of the polymeric matrix. Crystalline structure of the drug on polymeric surfaces varied with loading concentration and lipophilicity. Physico-chemical similarity of the polymeric material and the antibodies is important for the homogeneity of the polymer-antibiotic combinations. High homogeneity is required for a sustained and prolonged release and effective inhibition of bacterial colonization.

New approaches to biomaterials design
Kohn, J. (2004), Nat Mater 3(11): 745-7.
Abstract: The adoption of combinatorial and computational methods in biomaterials design is a highway towards the discovery and realization of tailored polymeric materials to satisfy the specific requirements of many diverse biomedical or prosthetic applications.

New biocomposite [biphasic calcium phosphate/ poly-DL-lactide-co-glycolide/biostimulative agent] filler for reconstruction of bone tissue changed by osteoporosis
Ignjatovic, N., Z. Ajdukovic, et al. (2005), J Mater Sci Mater Med 16(7): 621-6.
Abstract: Biphasic calcium phosphate-poly-DL-lactide-co-glycolide composite biomaterial with and without biostimulative agents (protein-rich plasma or fibrin) was synthesised in the form suitable for reconstruction of bone defects. The composite used as filler was obtained by precipitation in solvent-non-solvent systems. The material, calcium phosphate granules covered by polymer, was characterised by wide-angle X-ray structural analysis, scanning electron microscopy, infrared spectroscopy and differential scanning calorimetry. Reparation of bone tissue damaged by osteoporosis was investigated in vivo on rats. The method applied enabled production of granules of calcium phosphate-poly-DL-lactide-co- glycolide composite biomaterial of average diameter 150-200 mum. Histological analysis confirmed recuperation of the alveolar bone, which osteoporosis-induced defects were repaired using composite biomaterial. By addition of biostimulative agents, intensity of osteogenesis increases accompanied by the formation of regular, new bone structure.

New biodegradable amphiphilic block copolymers of epsilon-caprolactone and delta-valerolactone catalyzed by novel aluminum metal complexes. II. Micellization and solution to gel transition
Yang, J., L. Jia, et al. (2005), Macromol Biosci 5(9): 896-903.
Abstract: In our previous study [J. Yang, L. Jia, L. Yin, J. Yu, Z. Shi, Q. Fang, A. Cao, Macromol. Biosci. 2004, 4, 1092.], new biodegradable copolymers of diblock methoxy poly(ethylene glycol)-block-poly(epsilon-caprolactone) and methoxy poly(ethylene glycol)-block-poly(delta-valerolactone), and triblock poly(epsilon-caprolactone)-block-poly(ethylene glycol)-block-poly(epsilon-caprolactone) and poly(delta-valerolactone)-block-poly(ethylene glycol)-block-poly(delta-valero-lactone) bearing narrow molecular weight distributions and well-defined block architectures were reported to be prepared with our original aluminum metal complex templates. This work will continue to report new investigations on their water solubility, and reversible thermal responsive micellization and solution to gel transition in distilled water. Among the new synthesized copolymers (P1-P23), seven diblock or triblock samples (P3, P6, P7, P11, P12, P19, and P21) with higher hydrophilic building block populations were revealed to be water soluble under ambient temperature. By means of UV spectrophotometer attached with a thermostat, important parameters as critical micellization mass concentrations (CMCs) and critical micellization temperatures (CMTs) were characterized for these new amphiphile dilute aqueous solution with the aid of an lipophilic organic dye probe of 1,6-diphenyl-1,3,5-hexatriene (DPH). Furthermore, the critical gelation temperatures (CGTs) were simultaneously investigated for these water-soluble block copolymers via a tube tilting method. It was found that the CMC, CMT, and CGT were strongly affected by the population and nature of the hydrophobic building blocks, and a higher hydrophobicity of the new amphiphilic block copolymer finally led to lower CMC and CMT, and higher CGT. In addition, the salts of KBr and NaCl were found to play as a salt-out effect on the solution to gel transition for the diblock P6 and triblock P11, exhibiting an interesting tunable gelation temperature close to 35-42 degrees C. These results will pave new possibility for the synthesized block structural amphiphiles as potential biomaterials to be applied in vivo.

New biomaterials and methods for craniofacial bone defect: chondroid bone grafts in maxillary alveolar clefts
Kawata, T., S. Kohno, et al. (2000), J Craniofac Genet Dev Biol 20(1): 49-52.
Abstract: The purpose of this study was to evaluate autogenous osteogenic marrow within chondroid bone grafts in simulated alveolar defects of mice in order to determine the ability of the graft material to effectively close the cleft from an osseous standpoint and to observe the effect of the grafting procedure. Critical-sized defects were made in the premaxillary bones of male mice using a surgical trephine and a low-speed dental engine as a model of the maxillary alveolar cleft for testing bone-inductive agents. Premaxillary trephine defects were not repaired by fibrous tissue or bone formation 30 days after operation. This nonhealing bony wound of the premaxilla in mice may be useful as a model for studying the effect of bone-inductive agents on the healing of alveolar clefts. Distraction osteogenesis is a recently advanced principle of bone lengthening in which a long bone separated by osteotomy is subjected to slow progressive distraction using an external fixation device. The osteotomy site was surrounded by an external callus consisting of hyaline cartilage. The callus contained a lot of chondroid bone. The transplant bone within chondroid bone was characterized by bone formation and remodeling 30 days after transplantation. Throughout the experiment, our findings demonstrated, for the first time, that the transplant bone that contains chondroid bone may be used clinically in relation to craniofacial bone defects to improve the treatment of bone grafts.

New biomaterials through surface segregation phenomenon: new quaternary ammonium compounds as antibacterial agents
Nohr, R. S. and J. G. Macdonald (1994), J Biomater Sci Polym Ed 5(6): 607-19.
Abstract: Five new trisiloxane quaternary ammonium compounds were synthesized from hydrotrisiloxane with allyl glycidyl ether to yield the epoxy function. Various amines were then reacted to yield trisiloxane amines which were further reacted to methyl substitute or oxidize the beta-carbons in order to provide thermal stability. These new compounds were employed as melt additives in a nonwoven polypropylene fiber extrusion process to produce, through surface segregation, a new biomaterial with antibacterial properties.

New blood vessel formation and expression of VEGF receptors after implantation of platelet growth factor-enriched biodegradable nanocrystalline hydroxyapatite
Kilian, O., V. Alt, et al. (2005), Growth Factors 23(2): 125-33.
Abstract: Vascular endothelial growth factor (VEGF) plays a key role for the interaction of osteoblasts and endothelial cells and, therefore, is an important factor for the osteointegration of bone substitutes. The aim of the current work was to study the effects of platelet growth factors (PLF) on new blood vessel formation and VEGF-receptors expression pattern in bone defects filled with nanocrystalline hydroxyapatite (HA) paste in miniature-pigs. Conventional histology, RT-PCR for VEGF and receptors mRNA, Western blot analysis, immunohistochemical staining and quantitative assessment of newly formed vessels was performed. HA enriched with platelet growth factor (HA/PLF+) led to an up-regulation of VEGF-R1 synthesis, a slightly enhanced number of newly formed vessels with higher sprouting activity compared with HA without PLF (HA/PLF-) filling defects. These observation are most likely attributable to a stimulating effect of TGF-ss from the platelet factor on VEGF expression in osteoblasts.

New challenges in biomaterials
Peppas, N. A. and R. Langer (1994), Science 263(5154): 1715-20.
Abstract: Significant opportunities and challenges exist in the creation and characterization of biomaterials. Materials have been designed for contact with blood, as replacements for soft and hard tissues, as adhesives, and as dental materials. Current methods of synthesis and characterization of these materials are outlined. Approaches for controlling the interface between tissue and biomaterials and ways in which the engineered materials may contribute to medicine are considered.

New chitosan-degrading strains that produce chitosanases similar to ChoA of Mitsuaria chitosanitabida
Yun, C., D. Amakata, et al. (2005), Appl Environ Microbiol 71(9): 5138-44.
Abstract: The betaproteobacterium Mitsuaria chitosanitabida (formerly Matsuebacter chitosanotabidus) 3001 produces a chitosanase (ChoA) that is classified in glycosyl hydrolase family 80. While many chitosanase genes have been isolated from various bacteria to date, they show limited homology to the M. chitosanitabida 3001 chitosanase gene (choA). To investigate the phylogenetic distribution of chitosanases analogous to ChoA in nature, we identified 67 chitosan-degrading strains by screening and investigated their physiological and biological characteristics. We then searched for similarities to ChoA by Western blotting and Southern hybridization and selected 11 strains whose chitosanases showed the most similarity to ChoA. PCR amplification and sequencing of the chitosanase genes from these strains revealed high deduced amino acid sequence similarities to ChoA ranging from 77% to 99%. Analysis of the 16S rRNA gene sequences of the 11 selected strains indicated that they are widely distributed in the beta and gamma subclasses of Proteobacteria and the Flavobacterium group. These observations suggest that the ChoA-like chitosanases that belong to family 80 occur widely in a broad variety of bacteria.

New connective tissue attachment formation on various biomaterials implanted in roots
Takata, T., K. Katauchi, et al. (1994), Int J Oral Maxillofac Implants 9(1): 77-84.
Abstract: To determine whether connective tissue attachment can occur on implant materials by repopulating periodontal ligament (PDL)-derived cells and whether the new connective tissue attachments formation is influenced by the type of implant materials, periodontal tissue regeneration on four materials implanted into root cavities of cat canines was observed under conditions where PDL-derived cells could populate the surface of the materials. New connective tissue attachment occurred on bioactive materials such as bioglass and hydroxyapatite, while little or no cementum deposition was seen on bioinert materials such as titanium alloy and partially stabilized zirconium. Results showed that PDL-derived cells can form new connective tissue attachments on implant materials and that the formation of new connective tissue attachment is influenced by bioactivity of the materials.

New evidences of glass transitions and microstructures of soy protein plasticized with glycerol
Chen, P. and L. Zhang (2005), Macromol Biosci 5(3): 237-45.
Abstract: Soy protein isolate (SPI) and glycerol were mixed under mild (L series) and severe (H series) mixing conditions, respectively, and then were compression-molded at 140 degrees C and 20 MPa to prepare the sheets (SL and SH series). The glass transition behaviors and microstructures of the soy protein plasticized with glycerol were investigated carefully by using differential scanning calorimetry and small-angle X-ray scattering. The results revealed that there were two glass transitions in the SPI/glycerol systems. When the glycerol contents ranged from 25 to 40 wt.-%, all of the SL- and SH-series sheets showed two glass transition temperatures (T(g1) and T(g2)) corresponding to glycerol-rich and protein-rich domains, respectively. The T(g1) values of the sheets decreased from -28.5 to -65.2 degrees C with an increase of glycerol content from 25 to 50 wt.-%, whereas the T(g2) values were almost invariable at about 44 degrees C. The results from wide-angle X-ray diffraction and small-angle X-ray scattering indicated that both protein-rich and glycerol-rich domains existed as amorphous morphologies, and the radii of gyration (R(g)) of the protein-rich domains were around 60 nm, a result suggesting the existence of stable protein domains. The results above suggest that protein-rich domains were composed of the compact chains of protein with relatively low compatibility to glycerol and glycerol-rich domains consisted of relative loose chains that possessed good compatibility with glycerol. The significant microphase separation occurred in the SPI sheets containing more than 25 wt.-% glycerol, with a rapid decrease of the tensile strength and Young's modulus. [illustration in text].

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