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Second generation LEDs for the polymerization of oral biomaterials
Uhl, A., B. W. Sigusch, et al. (2004), Dent Mater 20(1): 80-7.
Abstract: OBJECTIVES: New blue, so called second generation light emitting diodes (LEDs) are now available with a high optical power output. These LEDs will potentially find widespread application in commercially available light curing units (LCUs). This study, therefore, investigated the curing performance of a prototype LCU containing one high power LED and a conventional halogen LCU (Polofil). METHODS: The performances of the LCUs were evaluated by measuring the Knoop hardness and depth of cure of the composites. Three dental composites were selected (Z100, Admira and Revolcin Flow) in a light (A2) and a dark shade (A3.5 or A4), respectively, and were polymerized for 40 s each. RESULTS: The LED prototype (irradiance=901 mW/cm2) achieved a statistically significantly greater (p<0.05) depth of cure than the halogen LCU (irradiance=860 mW/cm2) for all composites. Generally, there was no statistically significant difference in Knoop hardness on the top and bottom of a 2 mm thick disk for the composites Z100 and Admira if polymerized with the LED prototype or halogen LCU. The composite Revolcin Flow, however, showed in general a statistically significant lower Knoop hardness if polymerized with the LED LCU. SIGNIFICANCE: The present study shows that second generation LEDs have the potential to replace halogen LCUs if the composites are selected carefully. Furthermore, this study confirmed that the depth of cure test does not discriminate between LCU's performance for composites containing co-initiators, but the Knoop hardness test does.

Selection and interaction of biomaterials used in the construction of cardiac bioprostheses
Carrera San Martin, A., J. M. Garcia Paez, et al. (1998), J Biomed Mater Res 39(4): 568-74.
Abstract: The mechanical behavior of calf pericardium employed in the manufacture of cardiac bioprostheses was assessed according to the region from which it was selected. For this purpose, selected samples of the tissue were sewn with different types of commercially available sutures and subjected to tensile testing, the results of which were compared with the findings in selected, but not sutured, tissue used as a control. The results confirm a loss of resistance--that is, a reduction of the capacity of sutured samples of the biomaterial to withstand breakage stress compared with control samples. Taking into account the marked resistance to breakage of the suture thread, this phenomenon can only be explained as a consequence of the deleterious mechanical interaction between the suture and chemically treated pericardium. This interaction is illustrated by the shearing force which is responsible for the loss of resistance in the tested samples. These trials demonstrate that the results can be improved and the deleterious interaction diminished, although not eliminated, when the pericardium is selected from a given region.

Selection of biomaterials for middle and inner ear implants
Dormer, K. J., G. E. Bryce, et al. (1995), Otolaryngol Clin North Am 28(1): 17-27.
Abstract: In the selection of biomaterials for middle ear applications of implantable devices, certainly the site of implantation and the mass of the implant will dictate the choice of biomaterials. Hermetic sealing of an implant is best achieved by the use of metals, not polymers. Osteocompatibility of an ossicular implant can be enhanced by the incorporation of calcium phosphates such as hydroxyapatite coatings. Finally, osseointegration or osseofixation is neither necessary nor desirable for ossicular implants, because (1) they may need to be removed or replaced in the future and (2) their solid fixation to an ossicle is not necessary for the vibratory function of hearing amplification.

Selection of biomaterials for peripheral nerve regeneration using data from the nerve chamber model
Yannas, I. V. and B. J. Hill (2004), Biomaterials 25(9): 1593-600.
Abstract: Peripheral nerve regeneration has been studied in a variety of animal models. Of these, the nerve chamber model has clearly dominated. It has been used to generate a large base of data that, however, cannot be analyzed usefully due to lack of standardization of experimental conditions and assays. Lack of standardization of critical experimental parameters of the model has, however, greatly limited the opportunity to compare directly data from independent investigators; as a result, progress in understanding conditions for optimal nerve regeneration has been stunted. In this article, we provide an overview of the major experimental parameters that must be controlled in order to generate data from independent investigators that can be compared directly (normalized data). Such parameters include the gap length, animal species, and the identity of assays used to evaluate the product of the regenerative process. Use of the recently introduced concept of critical axon elongation, the gap length at which the probability of axonal outgrowth (reinnervation) across the gap is 50%, leads to generation of a normalized database that includes data from several independent investigators. Conclusions are drawn about the relative efficacy of the various biomaterials and devices employed. Nerve chamber configurations that had the highest regenerative activity were those in which the tube wall comprised collagen and certain synthetic biodegradable polymers rather than silicone, and was cell-permeable rather than protein-permeable. In addition, the following tube fillings showed very high regenerative activity: suspensions of Schwann cells; a solution either of acidic or basic fibroblast growth factor; insoluble ECM substrates rather than solutions or gels; polyamide filaments oriented along the tube axis; highly porous, insoluble analogs of the ECM with specific structure and controlled degradation rate.

Selective protein adsorption on micro-textured P-type and N-type silicon wafers
Lukas, S. J. and J. Ahmed (2005), Biomed Sci Instrum 41: 181-6.
Abstract: There has recently been a great deal of effort put towards the development of bioMEMS-based electrochemical biosensors for use in implantable devices. Currently, the primary issue limiting the lifespan of implantable sensors is protein and cell adhesion (biofouling) to the sensor surface, which impedes the sensor's access to analyte. To better understand this problem, it would be useful to have an understanding of how silicon-based microdevices interact with proteins in a physiological environment. To help answer this question, we investigated the interactions of proteins with microtextured silicon wafers. Bulk micromachining techniques were used to create micro-textures that varied between 5 and 80 microns in size nd spacing. We used n-type and p-type silicon wafers with a <100> crystal orientation. Shapes such as rectangles, circles, and triangles were fabricated that were recessed into the silicon substrate. The features were estimated to be between 3 and 8 microns in depth. After the features were created, the wafers were coated with a layer of silicon dioxide. Once fabrication was complete, the wafers were incubated in vitro ith fluorescently tagged Albumin (500 microg/ml in Phosphate-Buffered Saline, PBS) for 5 minutes. The wafers were then rinsed with PBS solution and viewed using an epifluorescence microscope. Albumin adsorbed selectively onto the micropatterned wafers. Depending on the type of wafer we found that albumin adsorbed selectively onto either the bulk surface, the sidewalls, or the bottom of the etched feature.

Selective targeting of antibody-conjugated nanoparticles to leukemic cells and primary T-lymphocytes
Dinauer, N., S. Balthasar, et al. (2005), Biomaterials 26(29): 5898-906.
Abstract: In the present study, surface-modified nanoparticles based on biodegradable material were used for antibody coupling in order to get a selective drug carrier systems. Gelatin nanoparticles were prepared by a desolvation process. Sulfhydryl groups were introduced which enabled the linkage of NeutrAvidin (NAv). Antibodies specific for the CD3 antigen on lymphocytic cells were conjugated to the nanoparticles surface. The binding of biotinylated anti-CD3 antibody was achieved by NAv-biotin-complex formation. Cellular binding and uptake were determined by flow cytometry and confocal laser scanning microscopy (CLSM). Cell-type-specific targeting of anti-CD3-conjugated nanoparticles into CD3-positive human T-cell leukemia cells and primary T-lymphocytes could be shown. Celluar uptake and effective internalization of antibody-conjugated nanoparticles into CD3 expressing cells were demonstrated. Uptake rates of about 84% into T-cell leukemia cells were observed. To confirm selectivity of T-cell targeting, competition experiments were carried out adding excessive free anti-CD3 prior to nanoparticle incubation leading to significantly reduced cellular uptake of antibody-conjugated nanoparticles. Further analysis on the mechanism of uptake confirmed a receptor-mediated endocytotic process. Protein-based nanoparticles conjugated with an antibody against a specific cellular antigen hold promise as selective drug delivery systems for specific cell types.

Selective versus exclusive use of sirolimus-eluting stent implantation in multivessel coronary artery disease
Chu, W. W., S. W. Rha, et al. (2005), Catheter Cardiovasc Interv 65(4): 473-7.
Abstract: Sirolimus-eluting stents (SESs; Cypher) have demonstrated a significant reduction in restenosis rates when compared to bare metal stents (BMSs). The purpose of this study was to evaluate the strategy of exclusive use of two SESs versus the combination of one BMS and one SES for two-vessel coronary artery disease (CAD). It was found that the selective use of one SES combined with one BMS in patients undergoing percutaneous coronary intervention that requires more than one stent is safe, feasible, and associated with favorable procedural, 30-day, and 6-month clinical outcomes when compared to the exclusive use of SESs.

Self-assembled monolayers and polymer brushes in biotechnology: current applications and future perspectives
Senaratne, W., L. Andruzzi, et al. (2005), Biomacromolecules 6(5): 2427-48.
Abstract: The chemistry and topography of a surface affect biological response and are of fundamental importance, especially when living systems encounter synthetic surfaces. Most biomolecules have immense recognition power (specific binding) and simultaneously have a tendency to physically adsorb onto a solid substrate without specific receptor recognition (nonspecific adsorption). Therefore, to create useful materials for many biotechnology applications, interfaces are required that have both enhanced specific binding and reduced nonspecific binding. Thus, in applications such as sensors, the tailoring of surface chemistry and the use of micro or nanofabrication techniques becomes an important avenue for the production of surfaces with specific binding properties and minimal background interference. Both self-assembled monolayers (SAMs) and polymer brushes have attracted considerable attention as surface-active materials. In this review, we discuss both of these materials with their potential applications in biotechnology. We also summarize lithographic methods for pattern formation using combined top-down and bottom-up approaches and briefly discuss the future of these materials by describing emerging new applications.

Self-assembling biomaterials: liquid crystal phases of cholesteryl oligo(L-lactic acid) and their interactions with cells
Hwang, J. J., S. N. Iyer, et al. (2002), Proc Natl Acad Sci U S A 99(15): 9662-7.
Abstract: We report here on the synthesis and characterization of a series of self-assembling biomaterials with molecular features designed to interact with cells and scaffolds for tissue regeneration. The molecules of these materials contain cholesteryl moieties, which have universal affinity for cell membranes, and short chains of lactic acid, a common component of biodegradable tissue engineering matrices. The materials were synthesized in good yields with low polydispersities in the range of 1.05-1.15, and their characterization was carried out by small-angle x-ray diffraction, transmission electron microscopy, electron diffraction, differential scanning calorimetry, and atomic force microscopy. These molecular materials form layered structures that can be described as smectic phases and can also order into single-crystal stacks with an orthorhombic unit cell. Their layer spacings range from 58 to 99 A, corresponding to bilayers of oligomers with an average of 10 and 37 lactic acid residues, respectively. The self-organized layered structures were found to promote improved fibroblast adhesion and spreading, although the specific mechanism for this observed response remains unknown. The ability of self-assembling materials to present ordered and periodic bulk structures to cells could be a useful strategy in tissue engineering.

Self-assembling short oligopeptides and the promotion of angiogenesis
Narmoneva, D. A., O. Oni, et al. (2005), Biomaterials 26(23): 4837-46.
Abstract: Because an adequate blood supply to and within tissues is an essential factor for successful tissue regeneration, promoting a functional microvasculature is a crucial factor for biomaterials. In this study, we demonstrate that short self-assembling peptides form scaffolds that provide an angiogenic environment promoting long-term cell survival and capillary-like network formation in three-dimensional cultures of human microvascular endothelial cells. Our data show that, in contrast to collagen type I, the peptide scaffold inhibits endothelial cell apoptosis in the absence of added angiogenic factors, accompanied by enhanced gene expression of the angiogenic factor VEGF. In addition, our results suggest that the process of capillary-like network formation and the size and spatial organization of cell networks may be controlled through manipulation of the scaffold properties, with a more rigid scaffold promoting extended structures with a larger inter-structure distance, as compared with more dense structures of smaller size observed in a more compliant scaffold. These findings indicate that self-assembling peptide scaffolds have potential for engineering vascularized tissues with control over angiogenic processes. Since these peptides can be modified in many ways, they may be uniquely valuable in regeneration of vascularized tissues.

Self-assembly of small molecules affords multifunctional supramolecular hydrogels for topically treating simulated uranium wounds
Yang, Z., K. Xu, et al. (2005), Chem Commun (Camb)(35): 4414-6.
Abstract: Two types of therapeutic agents, which have discrete yet complementary functions, self-assemble into nanofibers in water to formulate a new supramolecular hydrogel as a self-delivery biomaterial to reduce the toxicity of uranyl oxide at the wound sites.

Self-complementary peptides for the formation of collagen-like triple helical supramolecules
Koide, T., D. L. Homma, et al. (2005), Bioorg Med Chem Lett 15(23): 5230-3.
Abstract: Collagen is acknowledged as one of the most prominent biomaterials on account of its high biocompatibility and biostability. The development of artificial collagens to replace the animal-derived collagens presents a challenge in the formation of safer and highly functionalized biomaterials. Here, a novel peptide-based system for obtaining collagen-like supramolecules via a spontaneous self-assembling process is described. The designed collagen-like peptides are self-complementary trimers in which each of the 24-mer peptide strands is tethered by two cystine knots forming a staggered arrangement. Their self-assembling ability in aqueous solution was analyzed by circular dichroism, ultrafiltration, and laser diffraction particle size estimation. The obtained results indicate that the staggered trimers form large supramolecular architectures through intermolecular triple helix-formation.

Self-expanding metal stents in the palliation of malignant dysphagia: outcome analysis in 100 consecutive patients
Elphick, D. A., B. A. Smith, et al. (2005), Dis Esophagus 18(2): 93-5.
Abstract: SUMMARY. Patients with inoperable esophageal malignancy often undergo palliative self-expanding metal stent insertion. This analysis of cases shows that although such stents provide good palliation of dysphagia, complications frequently occur. Complications reported were pain after insertion, bleeding, food bolus impaction, stent migration and increased gastroesophageal reflux. Furthermore, in patients with esophageal adenocarcinoma, survival was less if the distal end of the stent entered the stomach, rather than lying entirely within the esophagus. Reduced survival, in this group with gastroesophageal junction tumors, may be a result of increased gastroesophageal reflux leading to pulmonary aspiration. Stents incorporating an antireflux valve have been shown to reduce symptomatic gastroesophageal reflux. It may be that such valves offer a survival advantage where stent insertion ablates the function of the lower esophageal sphincter. Further studies are needed to assess the role of antireflux stents on survival in patients with gastroesophageal junction tumors.

Self-organization of skin cells in three-dimensional electrospun polystyrene scaffolds
Sun, T., S. Mai, et al. (2005), Tissue Eng 11(7-8): 1023-33.
Abstract: Much research in tissue engineering focuses on the synthesis of complex three-dimensional polymer scaffolds containing functional biomolecules to which cells are introduced. Typical scaffolds for skin tissue engineering are macroscopically porous with struts or fibers approximately 10 microm thick at a packing fraction of approximately 0.1. We made a polystyrene scaffold without cell signaling or spatial information by electrospinning and studied the growth of skin fibroblasts, keratinocytes, and endothelial cells, as single and cocultured populations in the presence and absence of fetal calf serum. In the absence of serum, keratinocytes, fibroblasts, and endothelial cells did not grow when cultured alone. However, when fibroblasts were cocultured with keratinocytes and endothelial cells, expansion of keratinocytes and endothelial cells occurred even in the absence of serum. Furthermore, cells displayed native spatial three-dimensional organization when cultured at an air-liquid interface, even when all three cell types were introduced at random to the scaffold. This study shows that coculture with fibroblasts enables keratinocytes and endothelial cells to proliferate without serum, but also to self-organize according to the native epidermal-dermal structure given the symmetry-breaking field of an air-liquid interface.

SEM fractography studies of porous vitreous carbon: a candidate biomaterial
Tarr, R. R. (1979), J Biomed Mater Res 13(5): 717-27.
Abstract: A new porous vitreous carbon material under development for use in orthopedic applications was investigated. Specimens were machined to appropriate sizes and fractured in one of the following modes: compression, cantilevered bending, or axial torsion. Scanning electron microscopy (SEM) was used to examine surface and internal features. Characteristics of a brittle, glassy material were noted. Findings included internal voids which appeared as craters, patches of whiskerlike fibrils, and edge impurities. Numerous microcracks caused by mechanical shaping and handling were the most remarkable structural defects. Pore channels which would allow bony ingrowth ranged in size from 50--500 micrometers with the majority between 200 and 300 micrometers. This study of porous vitreous carbon points to the need for stricter quality control in manufacturing, alternative methods for shaping and handling, and careful consideration in design and usage of a brittle material with marginal limits of safety for biomedical applications.

SEM observation of collagen fibrils secreted from the body surface of osteoblasts on a CO3apatite-collagen sponge
Hirata, I., Y. Nomura, et al. (2005), Dent Mater J 24(3): 460-4.
Abstract: The secretion of collagen by osteoblasts was observed by scanning electron microscopy (SEM). Osteoblast-like cells were cultured on a CO3apatite-collagen sponge reinforced with a porous HAp frame. After three days' incubation, a number of newly created matrix fibrils, forming a network structure, were observed at the cell surface. SEM also showed that osteoblasts secreted collagen fibrils from their membrane, and that the collagen fibrils were twisted together. When collagen in an aqueous sol solution was sprayed onto the extremely smooth surface of a mica plate to support the secretion of osteoblasts, a collagen network structure could be clearly observed with atomic force microscopy (AFM). With this in vitro phenomenon, we could confirm the formation of collagen network structure without biological function. Therefore, it was suggested that the CO3apatite-collagen sponge used in this study is a favorable scaffold biomaterial, on which osteoblasts could produce the unmistakable, characteristic extracellular matrix for mineralization. For therapeutic use of hard tissue biomaterials, collagen formation as an extracellular matrix (ECM) is very important because mineralization is subsequent to ECM.

Semiconducting biomaterials: current status and future perspectives
Buckberry, L. and S. Bayliss (2001), Med Device Technol 12(5): 14-20.
Abstract: The ability to truly interface living cells with intelligent semiconducting biomaterials will launch new post-digital technology involving biologically interfaced medical devices. This article examines the potential of porous silicon for use in cell-interfaced electronic devices.

Semisynthetic hydrophilic polyals
Papisov, M. I., A. Hiller, et al. (2005), Biomacromolecules 6(5): 2659-70.
Abstract: Non-bioadhesive, fully biodegradable soluble polymers would be very instrumental in advanced biomedical applications, such as gene and drug delivery and tissue engineering. However, rational development of such materials is hindered by the complexity of macromolecule interactions with biological milieu. The prevalence of carbohydrates in naturally occurring interface structures suggests an alternative, biomimetic approach. Interface carbohydrates, regardless of their biological function, have common non-signaling substructures (e.g., acetal and ketal groups, secondary and primary alcohols). We hypothesized that hydrophilic polymers (polyals) consisting of acyclic units built of non-signaling carbohydrate substructures would be highly biocompatible and non-bioadhesive, while intrachain acetal or ketal groups would enable nonenzymatic biodegradation upon uptake by cells. Acyclic hydrophilic polyals can be prepared via either polymerization of suitable monomers or lateral cleavage of cyclic polyals (e.g., polysaccharides). In this study, model polyals were produced via lateral cleavage of polyaldoses and polyketoses. Best results were achieved using dextran B-512 as a precursor. The resultant poly[hydroxymethylethylene hydroxymethylformal], in agreement with the hypothesis, demonstrated excellent biological properties and technological flexibility. Materials of this type can potentially have several applications in pharmacology and bioengineering.

Separation of bioactive biflavonoids from Rheedia gardneriana using chitosan modified with benzaldehyde
Girardi, L. G., M. Morshc, et al. (2005), Z Naturforsch [C] 60(5-6): 408-10.
Abstract: This paper shows the influence of benzenic groups on the chitosan surface for the separation of bioactive biflavonoids from Rheedia gardneriana leaves The yield of the biflavonoids using chitin modified with benzaldehyde (CH-Bz) as adsorbent in column chromatography was higher than that achieved with silica gel and chitosan. The presence of benzenic groups decreases the polarity of chitosan and consequently the interaction of hydrogen bonding between phenolic hydroxyl (OH) of biflavonoids and amine groups of the adsorbent. Therefore, the separation of these compounds appears to be the result of hydrophobicity and pi-pi interaction among electrons from the aromatic ring in sorbent and biflavonoid molecules.

Sequential formation of covalently bonded hydrogel multilayers through surface initiated photopolymerization
Kizilel, S., E. Sawardecker, et al. (2006), Biomaterials 27(8): 1209-1215.
Abstract: A novel method for the sequential formation of hydrogel multilayers is described. Formation of the first layer is based on surface initiated photopolymerization of hydrogel precursors on eosin derivatized surfaces. In order to attach subsequent layers it is necessary to be able to functionalize intermediate hydrogel layers with eosin. In the present work, this is accomplished by introducing poly(ethylene glycol) amino acrylate (NH(2)-PEG-Acr) along with other hydrogel precursors such as poly(ethylene glycol) diacrylate (PEG-DA) on the intermediate layers. The pendant amine groups allow functionalization of the intermediate layers with eosin for subsequent photopolymerization of new hydrogel layers. The process can be repeated sequentially to construct multilayered hydrogel membranes. The NH(2)-PEG-Acr monomer can be formed by coupling cysteamine to PEG-DA by a conjugate addition reaction. The approach to multilayer formation could allow the incorporation of specific functionalities or compositions within each hydrogel layer so that multifunctional membranes can be formed. It could also be implemented, through proper photopatterning procedures, for the formation of 3-D hydrogel structures. The mild photopolymerization conditions employed using visible (514nm), rather than ultraviolet light would make this technique especially attractive for tissue engineering, drug delivery, biomaterials, biosensor development and other situations where the elements incorporated are sensitive to UV light exposure.

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Last Modified: 8 February 2006