Biomaterials.info - Resources for Engineers

Record 3481 to 3500

Rationalising the design of polymeric thermoresponsive biomaterials
Rochev, Y., D. O'Halloran, et al. (2004), J Mater Sci Mater Med 15(4): 513-7.
Abstract: We investigated the cell adhesion and growth of a series of thermoresponsive copolymers of N-isopropylacrylamide (NIPA) and N-tert-butylacrylamide (NtBA) above their lower critical solubility temperatures (LCST). It was found that cell adhesion and growth on the solvent cast films improved with increasing the NtBA content in the copolymers. The improvement was dependent on cell line. The surfaces of copolymers were analysed by atomic force microscopy. The topography of polymer films was not dependent on composition. The differences in the cell attachment and growth were attributed to the variation of surface energy with composition. The surface energy of copolymers decreased with the increase in the NtBA content. We conclude that poly(N-isopropylacrylamide) (poly(NIPA)) is a relatively poor substrate for cell growth and proliferation. However, its ability to support cell growth can be significantly improved by suitable modification.

Rationalizing the design of polymeric biomaterials
Angelova, N. and D. Hunkeler (1999), Trends Biotechnol 17(10): 409-21.
Abstract: Polymers are a promising class of biomaterials that can be engineered to meet specific end-use requirements. They can be selected according to key 'device' characteristics such as mechanical resistance, degradability, permeability, solubility and transparency, but the currently available polymers need to be improved by altering their surface and bulk properties. The design of macromolecules must therefore be carefully tailored in order to provide the combination of chemical, interfacial, mechanical and biological functions necessary for the manufacture of new and improved biomaterials.

Re: "Localized inferior orbital fibrosis associated with porcine dermal collagen xenograft orbital floor implant"
Avery, C., J. P. Hayter, et al. (2005), Ophthal Plast Reconstr Surg 21(3): 249; author reply 249-51.

Re: The polyurethane foam covering the Meme Breast Prosthesis: a biomedical breakthrough or a biomaterial tar baby?
Santerre, J. P., R. S. Labow, et al. (1992), Ann Plast Surg 29(5): 477-8.

Reaction characteristics of a tooth-bleaching agent containing H2O2 and NaF: in vitro study of crystal structure change in treated hydroxyapatite and chemical states of incorporated fluorine
Tanizawa, Y. (2005), J Cosmet Sci 56(2): 121-34.
Abstract: This in vitro study was performed to elucidate the reaction mechanism of sodium fluoride (NaF), which is added to tooth-bleaching agents to lessen the adverse effect of hydrogen peroxide (H2O2) on teeth. Both hydroxyapatite (HAP) and dihydrated dicalcium phosphate (DCPD), model substances for dental hard tissues, dissolved easily in a simple H2O2 solution. In the H2O2/NaF solutions, however, fluorine compounds that could not be identified by X-ray diffraction (XRD) due to the smallness of the products were formed on the surface of the HAP. X-ray photoelectron spectroscopy (XPS) studies demonstrated that fluoridated hydroxyapatite (FHAP) was formed on HAP, and that calcium fluoride (CaF2) formation was accelerated by increasing the concentrations of fluorine and H2O2 along with the partial dissolution of HAP. In H2O2/NaF solution, DCPD also transformed easily to FHAP and CaF2, which are favorable to the remineralization process on the tooth surface. Thus, the mechanism of NaF was elucidated, and its use together with H2O2 for tooth bleaching was proved to be effective. Methodologically, the XPS two-dimensional plot made it possible for the first time to directly estimate the ratio of FHAP and CaF2 in the reaction products, in contrast to the conventional wet-analytical method, which is simply based on the difference in solubility of the two components.

Reactions to biomaterials: the good, the bad, and ideas for developing new therapeutic approaches
Ashammakhi, N. (2005), J Craniofac Surg 16(2): 195-6.

Reactive oxygen species produced upon photoexcitation of sunscreens containing titanium dioxide (an EPR study)
Brezova, V., S. Gabcova, et al. (2005), J Photochem Photobiol B 79(2): 121-34.
Abstract: Commercial sunscreen products containing titanium dioxide were irradiated with lambda>300 nm and the formation of oxygen- (OH, O2.-/.OOH) and carbon-centered radicals was monitored by EPR spectroscopy and spin trapping technique using 5,5-dimethyl-1-pyrroline N-oxide, alpha-phenyl-N-tert-butylnitrone (PBN), alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone as spin traps, and free nitroxide radical 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl. The photoinduced production of singlet oxygen was shown by 4-hydroxy-2,2,6,6-piperidine. The generation of reactive oxygen radical species upon irradiation of sunscreens significantly depends on their composition, as the additives present (antioxidants, radical-scavengers, solvents) can transform the reactive radicals formed to less harmful products. The continuous in situ irradiation of titanium dioxide powder, recommended for cosmetic application, investigated in different solvents (water, dimethyl sulfoxide, isopropyl myristate) resulted in the generation of oxygen-centered reactive radical species (superoxide anion radical, hydroxyl and alkoxyl radicals).

Reactivity of blood with biomaterials in vitro: evaluation of some in vitro test systems for estimation of the blood compatibility of biomaterials
Mason, R. G. and B. A. Shinoda (1975), Biomater Med Devices Artif Organs 3(3): 383-409.
Abstract: Several different in vitro tests designed to estimate the degree of compatibility of blood with biomaterials have been examined to determine possible effects of donor or donor-material interaction. Statistical evaluation of data was performed, and adequate data were collected with each different test system to render such evaluation meaningful. Isolated examples of donor and donor-material interaction were detected, but these proved to be minor or insignificant in each case. Data are presented for each of the in vitro test systems examined to indicate the number of replicate determinations required for observed differences to be significant at the 5% level.

Real time observation of platelet adhesion to opaque biomaterial surfaces under shear flow conditions
Furukawa, K., T. Ushida, et al. (1999), J Biomed Mater Res 46(1): 93-102.
Abstract: We developed a new system which enables direct observation of platelet adhesion on opaque biomaterials under shear flow conditions, by combining a thin quartz cone which produces laminar shear flows, with an upright epifluorescence microscope which visualizes stained platelets through the rotating cone. This is the first report on the observation of platelets adhered to opaque biomaterials in real time under shear flow conditions. The direct observation of platelet adhesion to expanded polytetrafluoroethylene (ePTFE) as an opaque biomaterial revealed that the kinetics of platelet adhesion to ePTFE depended greatly on shear stresses, showing that the shear stress of 5.0 dyne/cm2 induced higher adhesiveness of platelets to ePTFE than that of either 0.1 or 15 dyne/cm2. The observation also showed a difference in platelet adhesiveness among ePTFEs with different fibril lengths--0, 3.2, 18, and 35 microm--indicating that ePTFEs with shorter fibril length had lower adhesiveness of platelets under a shear stress of 5.0 dyne/cm2. It is indispensable for analyzing the phenomena of platelet adhesion to opaque biomaterials to observe in real-time rolling, adhesion, and detachment of platelets under shear stresses without disturbing shear flow conditions. The results showed that the mechanical and optical design of the system could serve this purpose.

Recent advances and current developments in tissue scaffolding
Yarlagadda, P. K., M. Chandrasekharan, et al. (2005), Biomed Mater Eng 15(3): 159-77.
Abstract: A bio-scaffold can be broadly termed as a structure used to substitute an organ either permanently or temporarily to restore functionality. The material that can be used varies with the application intended. Tissue engineering is one such application demanding certain requirements to be met before it is applied. One of the applications in tissue engineering is the tissue scaffold, which provides either a permanent or temporary support to the damaged tissues/organ until the functionalities are restored. A biomaterial can exhibit specific interactions with cells that will lead to stereotyped responses. The use of a particular material and morphology depends on various factors such as osteoinduction, osteoconduction, angiogenesis, growth rates of cells and degradation rate of the material in case of temporary scaffolds, etc. The current work reviews the state of art in tissue scaffolds and focuses on permanent scaffold materials and applications with a brief overview of temporary scaffold materials and their disadvantages.

Recent advances in biodegradable nanocomposites
Pandey, J. K., A. P. Kumar, et al. (2005), J Nanosci Nanotechnol 5(4): 497-526.
Abstract: There is growing interest in developing bio-based products and innovative process technologies that can reduce the dependence on fossil fuel and move to a sustainable materials basis. Biodegradable bio-based nanocomposites are the next generation of materials for the future. Renewable resource-based biodegradable polymers including cellulosic plastic (plastic made from wood), corn-derived plastics, and polyhydroxyalkanoates (plastics made from bacterial sources) are some of the potential biopolymers which, in combination with nanoclay reinforcement, can produce nanocomposites for a variety of applications. Nanocomposites of this category are expected to possess improved strength and stiffness with little sacrifice of toughness, reduced gas/water vapor permeability, a lower coefficient of thermal expansion, and an increased heat deflection temperature, opening an opportunity for the use of new, high performance, lightweight green nanocomposite materials to replace conventional petroleum-based composites. The present review addresses this green material, including its technical difficulties and their solutions.

Recent advances in biomaterials
Suh, H. (1998), Yonsei Med J 39(2): 87-96.
Abstract: Biomaterials for medical use have been developed in accordance with progress of the fields of medicine, biochemistry, material science, and pharmaceutics. Advances in the medicine have changed the concept of surgery from the deletion of damage tissue for the preservation of the remaining healthy tissue to the reconstruction or replacement of damaged tissue by promoting regeneration of the natural tissue. All the materials used in medicine should be biocompatible. Conventional materials such as metals, ceramics, and synthetic polymers are usually bioinert and support the structural defects. But recently introduced biomaterials are designed to provide biological functions as much a possible by mimicking natural tissue structures.

Recent advances in functionalization of mesoporous silica
Vinu, A., K. Z. Hossain, et al. (2005), J Nanosci Nanotechnol 5(3): 347-71.
Abstract: Mesoporous silica with regular geometries have been recently paid much attention owing to their scientific importance and great potentials in practical applications such as catalysis, adsorption, separation, sensing, medical usage, ecology, and nanotechnology. Especially, applications often require immobilization of the related functional groups in the mesopores. In order to achieve desire applications, modification of these mesoporous silica are indispensable. In this review, recent progresses of functionalization of mesoporous silica are comprehensively summarized. In the first parts, advances in three major methods, grafting (post-synthetic modification), co-condensation (direct synthesis), and techniques related with periodic mesoporous organosilicates, are explained. In the latter parts, new concepts for functionalization of mesoporous silica including functional template method and lizard template method are introduced. Most of the examples described here have been published in a new millennium.

Recent advances in the design of titanium alloys for orthopedic applications
Guillemot, F. (2005), Expert Rev Med Devices 2(6): 741-8.
Abstract: To increase an orthopedic implant's lifetime, research trends have included the development of new titanium alloys made of nontoxic elements with suitable mechanical properties (low Young's modulus - high fatigue strength), good workability and corrosion resistance. In accordance with the background on titanium and metallic biomaterials, recent interesting developments in titanium-based biomaterials are reported in this review, with a special emphasis on the design of new metastable beta-titanium alloys for orthopedic applications. In addition, as the concept of titanium alloys can now be regarded as relatively old, having emerged at the beginning of the 1980s, the author suggests some future directions that would permit the emergence of a new generation of titanium implants.

Recent development of polymer nanofibers for biomedical and biotechnological applications
Zhang, Y., C. T. Lim, et al. (2005), J Mater Sci Mater Med 16(10): 933-46.
Abstract: Research in polymer nanofibers has undergone significant progress in the last one decade. One of the main driving forces for this progress is the increasing use of these polymer nanofibers for biomedical and biotechnological applications. This article presents a review on the latest research advancement made in the use of polymer nanofibers for applications such as tissue engineering, controlled drug release, wound dressings, medical implants, nanocomposites for dental restoration, molecular separation, biosensors, and preservation of bioactive agents.

Recent results on functional polymers and macromonomers of interest as biomaterials or for biomaterial modification
Ferruti, P., E. Ranucci, et al. (1994), Biomaterials 15(15): 1235-41.
Abstract: Different families of functionalized polymers with potential as biomaterials, or for biomaterial modification, have been investigated. In particular, degradation studies have been performed on poly(amidoamines), a family of polymers obtained by polyaddition of amines to bisacrylamides, and endowed with heparin-complexing ability. Some new poly(amidoamines) with more resistance towards hydrolytic degradation than traditional ones have been discovered. Other ter-amino polymers deriving from the polyaddition of ter-amino functionalized bis-thiols to bis-acrylic esters, or other activated unsaturated compounds, have been studied. Their quaternarization products have been proven, in a parallel work, to act as powerful antimicrobial agents. By performing in situ the polyaddition reaction, semi-interpenetrated networks based on silicone rubber and the same polymers have been prepared. Finally, end-functionalized amphiphilic oligomers have been prepared by radical polymerization techniques, and their use for enzyme modification considered.

Recent studies on biomembrane structure and biomaterials
Haris, P. I., B. Hall, et al. (1990), Prog Clin Biol Res 343: 1-13.

Recombinant human elastin polypeptides self-assemble into biomaterials with elastin-like properties
Bellingham, C. M., M. A. Lillie, et al. (2003), Biopolymers 70(4): 445-55.
Abstract: Processes involving self-assembly of monomeric units into organized polymeric arrays are currently the subject of much attention, particularly in the areas of nanotechnology and biomaterials. One biological example of a protein polymer with potential for self-organization is elastin. Elastin is the extracellular matrix protein that imparts the properties of extensibility and elastic recoil to large arteries, lung parenchyma, and other tissues. Tropoelastin, the approximately 70 kDa soluble monomeric form of elastin, is highly nonpolar in character, consisting essentially of 34 alternating hydrophobic and crosslinking domains. Crosslinking domains contain the lysine residues destined to form the covalent intermolecular crosslinks that stabilize the polymer. We and others have suggested that the hydrophobic domains are sites of interactions that contribute to juxtaposition of lysine residues in preparation for crosslink formation. Here, using recombinant polypeptides based on sequences in human elastin, we demonstrate that as few as three hydrophobic domains flanking two crosslinking domains are sufficient to support a self-assembly process that aligns lysines for zero-length crosslinking, resulting in formation of the crosslinks of native elastin. This process allows fabrication of a polymeric matrix with solubility and mechanical properties similar to those of native elastin.

Recombinant microbial systems for the production of human collagen and gelatin
Baez, J., D. Olsen, et al. (2005), Appl Microbiol Biotechnol 69(3): 245-52.
Abstract: The use of genetically engineered microorganisms is a cost-effective, scalable technology for the production of recombinant human collagen (rhC) and recombinant gelatin (rG). This review will discuss the use of yeast (Pichia pastoris, Saccharomyces cerevisiae, Hansenula polymorpha) and of bacteria (Escherichia coli, Bacillus brevis) genetically engineered for the production of rhC and rG. P. pastoris is the preferred production system for rhC and rG. Recombinant strains of P. pastoris accumulate properly hydroxylated triple helical rhC intracellularly at levels up to 1.5 g/l. Coexpression of recombinant collagen with recombinant prolyl hydroxylase results in the synthesis of hydroxylated collagen with thermal stability similar to native collagens. The purified hydroxylated rhC forms fibrils that are structurally similar to fibrils assembled from native collagen. These qualities make rhC attractive for use in many medical applications. P. pastoris can also be engineered to secrete high levels (3 to 14 g/l) of collagen fragments with defined length, composition, and physiochemical properties that serve as substitutes for animal-derived gelatins. The replacement of animal-derived collagen and gelatin with rhC and rG will result in products with improved safety, traceability, reproducibility, and quality. In addition, the rhC and rG can be engineered to improve the performance of products containing these biomaterials.

Reconstruction of human hair dermal papilla with microencapsulation in vitro
Li, Y., C. M. Lin, et al. (2005), J Dermatol Sci 38(2): 107-9.

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