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PubMed2002

Nucleation of biomimetic Ca-P coatings on ti6A14V from a SBF x 5 solution: influence of magnesium.

Biomimetic Calcium-Phosphate (Ca-P) coatings were applied by using 5 times concentrated Simulated Body Fluid (SBF x 5) using Carbon Dioxide gas. This process allows the deposition of a uniform Ca-P coating within 24 h. A previous study of our process emphasized the importance of hydrogenocarbonate ions (HCO-3), a crystal growth inhibitor. The aim of the present study was to investigate the role of the other crystal growth inhibitor present in SBF x 5, Magnesium (Mg2+), on the Ca-P coating formation. Several SBF x 5 solutions were prepared with various Mg2+ and HCO3 contents. No Ca-P deposits were detected on Ti6A14V substrate soaked for 24h in a Mg-free SBF x 5 solution, whereas by increasing HCO-3 content in a Mg-free SBF x 5 solution, a Ca-P coating developed on Ti6A14V substrate. Therefore, it appeared that Mg2+ has a stronger inhibitory effect on apatite crystal growth than HCO-3. Nevertheless, Mg2+ plays also another important role as suggested by depth profile X-ray Photoelectron Spectroscopy (XPS) of the Ca-P coating obtained from SBF x 5 solution. Ca2+ and Mg2+ contents increased significantly at the titanium/coating interface. Therefore, Ca2+ and Mg2+ initiated Ca-P coating from SBF x 5 solution. The relatively high interfacial concentration in Mg2+ favors heterogeneous nucleation of tiny Ca-P globules onto the substrate. So physical adhesion is enhanced at the early stage of the coating formation.

Alloys↗

PubMed2002

Preparation and histological evaluation of biomimetic three-dimensional hydroxyapatite/chitosan-gelatin network composite scaffolds.

A novel biodegradable hydroxyapatite/chitosan-gelatin network (HA/CS-Gel) composite of similar composition to that of normal human bone was prepared as a three-dimensional biomimetic scaffold by phase separation method for bone tissue engineering. Changing the solid content and the compositional variables of the original mixtures allowed control of the porosities and densities of the scaffolds. The HA granules were dispersed uniformly in the organic network with intimate interface contact via pulverizing and ultrasonically treating commercial available HA particles. Scaffolds of 90.6% porosity were used to examine the proliferation and functions of the cells in this three-dimensional microenvironment by culturing neonatal rat caldaria osteoblasts. Histological and immunohistochemical staining and scanning electron microscopy observation indicated that the osteoblasts attached to and proliferated on the scaffolds. Extracellular matrices including collagen I and proteoglycan-like substrate were synthesized, while osteoid and bone-like tissue formed during the culture period. Furthermore, the cell/scaffold constructs had good biomineralization effect after 3 weeks in culture.

Animals↗

PubMed2003

Proteins incorporated into biomimetically prepared calcium phosphate coatings modulate their mechanical strength and dissolution rate.

In a previous investigation, we demonstrated that when bovine serum albumin (BSA) is biomimetically co-precipitated with Ca(2+) and PO(4)(3-) ions upon titanium-alloy implants, it becomes incorporated into the crystal lattice and is not merely deposited on its surface. Moreover, the protein elicited a change in crystal structure from an octacalcium phosphate type to a carbonated apatite one, which bears a closer resemblance to natural bone mineral. In the present study, we investigated the dissolution rate and mechanical strength of such BSA-containing coatings as a function of protein concentration within the bathing medium (10 ng/ml to 1.0 mg/ml). BSA-containing coatings released Ca(2+) ions more slowly (5 ppm/min) than did non-BSA-containing ones (10 ppm/min), but this rate did not change as a function of protein concentration within the bathing medium. In contrast, the strength of coatings increased almost linearly as a function of protein concentration within the bathing medium, indicating that BSA incorporated into the crystal lattice enhances its mechanical strength in a concentration-dependent manner.

Alloys↗

PubMed2003

Indirect solid free form fabrication of local and global porous, biomimetic and composite 3D polymer-ceramic scaffolds.

Precise control over scaffold material, porosity, and internal pore architecture is essential for tissue engineering. By coupling solid free form (SFF) manufacturing with conventional sponge scaffold fabrication procedures, we have developed methods for casting scaffolds that contain designed and controlled locally porous and globally porous internal architectures. These methods are compatible with numerous bioresorbable and non-resorbable polymers, ceramics, and biologic materials. Phase separation, emulsion-solvent diffusion, and porogen leaching were used to create poly(L)lactide (PLA) scaffolds containing both computationally designed global pores (500, 600, or 800 microm wide channels) and solvent fashioned local pores (50-100 microm wide voids or 5-10 microm length plates). Globally porous PLA and polyglycolide/PLA discrete composites were made using melt processing. Biphasic scaffolds with mechanically interdigitated PLA and sintered hydroxyapatite regions were fabricated with 500 and 600 microm wide global pores. PLA scaffolds with complex internal architectures that mimicked human trabecular bone were produced. Our indirect fabrication using casting in SFF molds provided enhanced control over scaffold shape, material, porosity and pore architecture, including size, geometry, orientation, branching, and interconnectivity. These scaffolds that contain concurrent local and global pores, discrete material regions, and biomimetic internal architectures may prove valuable for multi-tissue and structural tissue interface engineering.

Biomechanical Phenomena↗

PubMed2001

Redox and ligand exchange reactions of potential gold(I) and gold(III)-cyanide metabolites under biomimetic conditions.

Biomimetic pathways for the oxidation of [Au(CN)(2)](-), a gold metabolite, and further cyanation of the gold(III) products to form Au(CN)(4)(-) were investigated using 13C NMR and UV-Visible spectroscopic methods. Hypochlorite ion, an oxidant released during the oxidative burst of immune cells, was employed. The reaction generates mixed dicyanoaurate(III) complexes, trans-[Au(CN)(2)X(2)](-), where X(-) represents equilibrating hydroxide and chloride ligands, and establishes the chemical feasibility of dicyanoaurate oxidation by OCl(-) to gold(III) species. This oxidation reaction suggests a new procedure for synthesis of H[Au(CN)(2)Cl(2)]. Reaction of trans-[Au(CN)(2)X(2)](-) (X(-)=Cl(-) and Br(-)) or [AuCl(4)](-) with HCN in aqueous solution at pH 7.4 leads directly to [Au(CN)(4)](-) without detection of the anticipated [Au(CN)(x)X(4-x)](-)intermediates, which is attributed to the cis- and trans-accelerating effects of the cyanides. The reduction of [Au(CN)(4)](-) by glutathione and other thiols is a complex, pH-dependent process that proceeds through two intermediates and ultimately generates [Au(CN)(2)](-). These studies provide further insight into the possible mechanisms of an immunogenically generated gold(I)/gold(III) redox cycle in vivo.

Cyanates↗

PubMed2002

The fate of the biomimetic cation triaqua-mu-oxohexapropionatotrichromium(III) in rats.

The synthetic biomimetic triaqua-mu-oxohexapropionatotrichromium(III) nitrate when given intravenously to rats lowers fasting blood plasma triglycerides and cholesterol concentrations; thus, the cation has the potential to serve as a therapeutic agent. Its ability to function in vivo presumably is dependent on its ability to mimic the action of the natural, bioactive, chromium-binding oligopeptide chromodulin in stimulating insulin receptor kinase activity. Consequently, the cation should be incorporated into insulin-sensitive cells intact. Thus, the fate of the 51Cr-labeled complex during the first 24 h after injection in tissues, blood, urine, and feces was followed. The complex appears to be readily incorporated into tissues and cells. In hepatocytes, the cation is efficiently transported into microsomes where its concentration reaches a maximum in approximately 2 h.

Animals↗

PubMed2001

Synthetic biomimetic supra molecular Biovector (SMBV) particles for nasal vaccine delivery.

For the optimal delivery of antigens to mucosal tissues, especially as nasal sprays, protein antigen alone is often not sufficient. A clear need for nasal delivery systems has therefore evolved, especially for Influenza A vaccines. Such technologies will be even more essential for new modern vaccines based on recombinant antigens. Here we describe synthetic biomimetic supra molecular Biovector (SMBV) which have proven in preclinical and clinical evaluation to be suitable candidates for the delivery of nasal vaccines. They also demonstrate the potential to work with multiple antigens and furthermore allow combination with adjuvants. These Biovectors can associate with internal or lipid layer membrane proteins and peptides due to their charged polysaccharide core. The mimicry with viruses is also provided through their size of 60-80 nm, which allows sterilization by filtration. This makes them an ideal tool for the development of modern nasal vaccines, as they have shown to be able to induce the desired types of humoral immunity (serosal and mucosal immunity, IgA and IgG antibodies) as well as cellular immunity (CD4 and CD8 responses).

Adjuvants, Immunologic↗

PubMed1991

Catalytic antibodies and biomimetics.

Of the various approaches being studied to mimic the catalytic properties of enzymes, catalytic antibody research is advancing most rapidly and successfully; the discovery of new reactions and new catalytic antibody-producing haptenic structures continues unabated. One of the highlights of the past year was the design and synthesis of a catalytically active peptide. The overall area of catalytic antibodies and biomimetics will be prominent in future biotechnological applications, as further advances are made and the nature of the catalyzed reactions becomes better understood.

Antibodies↗

PubMed1996

Molecularly imprinted polymers for bioanalysis: chromatography, binding assays and biomimetic sensors.

The field of molecular imprinting has undergone rapid expansion in recent years, and applications have been demonstrated for imprinted materials in separations, analysis and catalysis. The range of compounds that has been imprinted has also expanded. Imprinted polymers have been used for the chromatographic separation of amino acids, sugars, drugs and nucleotides. Drugs have been measured using imprinted polymers as antibody substitutes in radioligand binding assays. Applications are being found for imprinted polymers in biomimetic sensing devices and sensors. Particularly interesting developments from the past year include ligand binding assays for morphine in aqueous buffers with similar specificity to antibody-based assays and the imprinting of cholesterol using a novel procedure in which the template is covalently bonded to the monomer during polymerization, but after cleavage, rebinds the polymer only by non-covalent interactions.

Journal Article↗

PubMed2000

Metalloporphyrin catalyzed oxidation of N-hydroxyguanidines: a biomimetic model for the H2O2-dependent activity of nitric oxide synthase.

A chemical model for the H2O2 promoted oxidation by nitric oxide synthase (NOS) has been developed. Biomimetic oxidations were carried out using H2O2 and tetrakis(perfluorophenyl)porphyrinato-iron(III) chloride (FeTPPF20) as a catalyst. Similarly to NOS our model system produces Ndelta-cyanoornithine, citrulline and NO from NOHA and did not oxidize arginine itself. Based on these results we propose a peroxide shunt to be involved in the catalytic cycle of NOS. To the best of our knowledge this is the first chemical system that semiquantitatively mimics NOS activity.

Catalysis↗

PubMed1999

Biomimetic degradation of lignin and lignin model compounds by synthetic anionic and cationic water soluble manganese and iron porphyrins.

The biomimetic oxidation of 5-5' condensed and diphenylmethane lignin model compounds with several water soluble anionic and cationic iron and manganese porphyrins in the presence of hydrogen peroxide is reported. The oxidative efficiency of manganese and iron meso-tetra(2,6-dichloro-3-sulphonatophenyl) porphyrin chloride (TDCSPPMnCl and TDCSPPFeCl, respectively), meso-tetra-3-sulphonatophenyl porphyrin chloride (TSPPMnCl) and manganese meso-tetra(N-methylpyridinio)porphyrin pentaacetate (TPyMePMn(CH3COO)5) was compared on the basis of the oxidation extent of the models tested. Manganese porphyrins were found more effective in degrading lignin substructures than iron ones. Among them the cationic TPyMePMn (CH3COO)5, never used before in lignin oxidation, showed to be the best catalyst. The catalytic activity of porphyrins in hydrogen peroxide oxidation of residual kraft lignin was also investigated. The use of quantitative 31P NMR allowed the focusing on the occurrence of different degradative pathways depending on the catalyst used. TPyMePMn(CH3COO)5 was able to perform the most extensive degradation of the lignin structure, as demonstrated by the decrease of aliphatic hydroxyl groups and carboxylic acids. Noteworthy, no significant condensation reactions occurred during manganese porphyrins catalyzed oxidations of residual kraft lignin, while in the presence of iron porphyrins a substantial increase of condensed substructures was detected.

Anions↗

PubMed1999

Reaction of dopamine with D-glyceraldehyde under biomimetic conditions: stereoselective formation of tetrahydroisoquinolines and rate-accelerating effects of transition metal ions.

In 0.05 M phosphate buffer, pH 7.4, and at 37 degrees C, dopamine underwent a smooth Pictet-Spengler condensation with D-glyceraldehyde and D,L-glyceraldehyde-3-phosphate to afford diastereoisomeric tetrahydroisoquinolines. In the case of D-glyceraldehyde 1a/1b were formed in ca. 2:1 ratio. Treatment with carbonyldiimidazole converted 1a and 1b into the corresponding oxazinoisoquinolinones 2a and 2b which were separated and stereochemically characterised by NMR analysis. Transition metal ions commonly occurring in biological systems (e.g. Cu2+ and Fe3+) markedly accelerated the formation of 1a-1b without affecting the product ratio. Mechanistic evidence suggested the reversible generation of Schiff base intermediates, detected by 1H NMR, which undergo stereoselective cyclisation according to the Felkin-Anh model. Metal-chelation at the catechol group facilitates the rate-determining nucleophilic attack to the imine moiety by enhancing the electron density at the site of cyclisation. These results highlight an apparently overlooked effect of transition metal ions on the Pictet-Spengler reaction under biomimetic conditions and provide a chemical basis to postulate a role of carbohydrate metabolites as modulatory agents of dopaminergic neurotransmission via conversion to potentially bioactive tetrahydroisoquinoline derivatives.

Acceleration↗

PubMed2003

Microstructure, mechanical, and biomimetic properties of fish scales from Pagrus major.

The fish scale of Pagrus major has an orthogonal plywood structure of stratified lamellae, 1-2 microm in thickness, consisting of closely packed 70- to 80-nm-diameter collagen fibers. X-ray diffraction, energy-dispersive X-ray analysis, and infrared spectroscopy indicate that the mineral phase in the scale is calcium-deficient hydroxyapatite containing a small amount of sodium and magnesium ions, as well as carbonate anions in phosphate sites of the apatite lattice. The tensile strength of the scale is high (approximately 90 MPa) because of the hierarchically ordered structure of mineralized collagen fibers. Mechanical failure occurs by sliding of the lamellae and associated pulling out and fracture of the collagen fibers. In contrast, demineralized scales have significantly lower tensile strength (36 MPa), indicating that interactions between the apatite crystals and collagen fibers are of fundamental importance in determining the mechanical properties. Thermal treatment of fish scales to remove the organic components produces remarkable inorganic replicas of the native orthogonal plywood structure of the fibrillary plate. The biomimetic replica produced by heating to 873 K consists of stratified porous lamellae of c-axis-aligned apatite crystals that are long, narrow plates, 0.5-0.6 microm in length and 0.1-0.2 microm in width. The textured inorganic material remains intact when heated to 1473 K, although the size of the constituent crystals increases as a result of thermal sintering.

Animals↗

PubMed1998

Biomimetic processing of calcium phosphate coating.

Most ceramics used in surgical implantation are better tolerated by the body environment than other biomaterials, particularly metals. However, the broader application of ceramics is limited because they are brittle and prone to catastrophic failure. By contrast. naturally produced ceramic organic biocomposites can possess mechanical properties which make them suitable for use as biomaterials. An example would be the mollusc shell, where an inorganic phase grows onto a charged and organised organic template. This natural biomineralization provides a calcium carbonate phase with satisfactory mechanical properties appropriate for surgical implantation. It is reported how Langmuir Blodgett films have been used as organic templates for calcium phosphate crystallization. Three different Langmuir Blodgett Films: omega tricosenoic acid, stearic acid and octadecylamine have been investigated. The Langmuir Blodgett Films produced had methyl (CH3) and calcium carboxylate (CaCOO) as functional groups. Atomic force microscopy and scanning electron microscopy shows that calcium phosphate crystallization occurs in a similar manner to natural biomineralization. The calcium carboxylate head group appears to have a physical influence on the morphology and distribution of the calcium phosphate crystals. Under the experimental conditions tested, the calcium carboxylate functional head group controls calcium phosphate crystallization by a biomimetic approach. This study strongly suggests that this approach has the potential for producing high performance ceramics comparable with those made by mollusc shells.

Calcium Phosphates↗

PubMed2000

Methane monooxygenase and its related biomimetic models.

The past year has seen significant advances in the understanding of the dioxygen-activating chemistry of non-heme diiron enzymes, such as methane monooxygenase. Recent spectroscopic and structural studies on various biomimetic model compounds have provided new and valuable insights into this enzyme's mechanism of action and the important dioxygen-activation process.

Catalysis↗

PubMed2002

Chemical models for cytochrome P450 as a biomimetic metabolic activation system in mutation assays.

DNA damage is a critical factor in carcinogenesis. The Ames assay is a short-term test that screens for DNA-damaging agents. To be detected in the assay, most carcinogens require oxidation by cytochrome P450, a component of the liver homogenate preparation (S9 mix) that is traditionally used to metabolize promutagens to an active form in vitro. A combination of iron(III) porphyrin plus an oxidant activates many promutagens by mimicking cytochrome P450 metabolism. We previously reported that the mutagenicity of the N-nitrosodialkylamines was detected following reaction with tetrakis(pentafluorophenyl)porphyrinatoiron(III) chloride (Fe(F(5)P)Cl) plus tert-butyl hydroperoxide (t-BuOOH), which yielded the same alcohols and aldehydes as the enzymatic reaction. In the present study, to extend the scope of biomimetic models, we tested the mutagenicity of other carcinogens exposed to chemical oxidation systems.We investigated the optimal assay conditions for the models in Salmonella typhimurium TA1538, a strain sensitive to frame-shift mutagens. We activated 2-aminofluorene (AF), benzo[a]pyrene (B[a]P), a tryptophane pyrolysate 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), and 2-acetylaminofluorene (AAF) with Fe(F(5)P)Cl plus an oxidant-t-BuOOH, m-chloroperoxybenzoic acid (mCPBA), or magnesium monoperoxyphthalate (MPPT)-and we noted the effect of three solvents-acetonitrile (CH(3)CN),1,4-dioxane, and N,N-dimethylformamide (DMF)-on AF activation. All the promutagens became mutagenic in the presence of Fe(F(5)P)Cl plus an oxidant, with the effectiveness of the oxidant varying with the chemical. Aromatic amines, for example, showed the strongest mutagenicity with t-BuOOH whereas polycyclic hydrocarbons showed the strongest mutagenicity with mCPBA. All the promutagens were mutagenic in the presence of Fe(F(5)P)Cl plus MPPT. For AF activation, the order of effectiveness of the solvents was CH(3)CN>1,4-dioxane>DMF. The results suggested that these systems would serve as useful models for microsomal activating systems.

2-Acetylaminofluorene↗

PubMed2001

A biomimetic approach to artificial photosynthesis: Ru(II)-polypyridine photo-sensitisers linked to tyrosine and manganese electron donors.

The paper describes recent advances towards the construction of functional mimics of the oxygen evolving complex in photosystem II (PSII) that are coupled to photoinduced charge separation. Some key principles of PSII and artificial systems for light-induced charge accumulation are discussed. Systems are described where biomimetic electron donors--manganese complexes and tyrosine--have been linked to a Ru(II)-polypyridine photosensitiser. Oxidation of the donors by intramolecular electron transfer from the photo-oxidised Ru(III) complex has been studied using optical flash photolysis and EPR experiments. A step-wise electron transfer Mn(III,III)-->tyrosine Ru(III) has been demonstrated, in analogy to the reaction on the donor side of PSII. Electron transfer from the tyrosine to Ru(III) was coupled to tyrosine deprotonation. This resulted in a large reorganisation energy and thus a slow reaction rate, unless the tyrosine was hydrogen bonded or already deprotonated. A comparison with analogous reactions in PSII is made. Finally, light-induced oxidation of a manganese dimer linked to a Ru(II)-photosensitiser has been observed. Preliminary results suggest the possibility of photo-oxidising manganese dimers in several steps, which is an important advancement towards water oxidation.

Dimerization↗

PubMed1999

A biomimetic phospholipid/alkanethiolate bilayer immobilizing uricase and an electron mediator on an Au electrode for amperometric determination of uric acid.

A biomimetic bilayer membrane immobilizing uricase (urate oxidase; EC 1.7.3.3) (UOx) and a redox agent of 1-methoxy-5-methylphenazinium (MMP) was fabricated on an Au electrode substrate with use of the Au substrate coated with a self-assembled monolayer of n-octanethiolate (OT/Au) and L-alpha-phosphatidylcholine beta-oleoyl-gamma-palmitoyl (PCOP). The preparation was carried out by successively immersing an Au electrode substrate in an ethanol solution of OT, an MMP aqueous solution, and a suspension of proteoliposome formed by PCOP containing UOx and MMP. The prepared electrode exhibited such fast steady amperometric responses to uric acid as to allow its determination within 20 s after injecting uric acid, indicating that UOx-catalyzed electrochemical oxidation of uric acid was accomplished with assistance of electron mediation by MMP between UOx and the Au substrate. An increase in the response currents with increasing concentration of uric acid was obtained in a concentration range of uric acid found in healthy human blood. Any interference in the current response that is caused by direct anodic oxidation of uric acid or ascorbic acid was not observed at the prepared sensor electrode because the densely packed bilayer effectively blocked the diffusion of these substrates toward the Au surface, making it possible to determine amperometrically uric acid at the electrode with high precision.

Electrochemistry↗