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Biomimetic surfaces for control of cell adhesion to facilitate bone formation.

Cell adhesion to extracellular matrix ligands through integrin receptors plays a central role in bone formation and maintenance by anchoring cells and triggering signals that direct osteoblast proliferation and differentiation. Moreover, osteoblast adhesion to adsorbed, synthesized, or engineered extracellular ligands on synthetic surfaces is critical to numerous biomedical and biotechnological applications. Considerable research efforts have concentrated on the development of surfaces that promote osteoblast differentiation and bone formation. Emerging surface engineering approaches have focused on creating biomimetic substrates that target integrins to activate signaling pathways directing the osteoblast differentiation program. These initiatives generally rely on controlling the adsorption of extracellular matrix ligands or engineering synthetic supports presenting bioadhesive motifs from extracellular matrix proteins. These biomolecular approaches provide promising strategies for the engineering of robust biofunctional matrices that control cell adhesion and signaling and promote osteoblast proliferation, differentiation, and matrix mineralization.

Animals↗

Utilizing biomimetic oligopeptides to probe fibronectin-integrin binding and signaling in regulating macrophage function in vitro and in vivo.

Biomimetic oligopeptides were employed to elucidate the molecular mechanisms of fibronectin-integrin interaction in regulating macrophage function. Oligopeptides were designed based on of the functional structure of fibronectin and grafted onto a polymer network containing polyethyleneglycols. Macrophage adhesion was independent of the peptide identity that contained sequence RGD, PHSRN, PRRARV, or combinations thereof in an integrin-dependent fashion in vitro. However, integrin-dependent foreign body giant cell (FBGC) formation in vitro was highly dependent on both RGD and PHSRN in a single peptide formulation and with a specific orientation. In vivo results showed that peptide identity played a minimal role in modulating the host inflammatory response and adherent macrophage density. RGD-containing peptides mediated a rapid FBGC formation by 4 days of implantation by significantly increasing both the number of macrophages that participate in the cell fusion process and the rate of cell fusion. Both RGD and PHSRN domains were important in mediating FBGC formation at later implantation periods. In vitro intracellular signaling studies revealed that the requirement of protein tyrosine kinase and serine/threonine kinase activation and cross-talk compensation for macrophage adhesion dynamically varied with surfaces and culture time. Protein kinase C-dependent adhesion was related to RGD and PHSRN sequences, and to the sequence orientation thereof in a form of GGGRGDGGGGGGPHSRNG. Furthermore, we observed a multiple effect of the mitogen-activated protein kinase/extracellular-signal-regulated kinase signaling factor in mediating macrophage adhesion, which depended on the method of ligand immobilization. These findings represent a mechanistic correlation between the role of substrates and protein functional architectures in ligand-receptor recognition and post-ligation signaling events that control cellular behavior in vitro and in vivo.

Animals↗

Reactive intermediates in pesticide metabolism: peracid oxidations as possible biomimetic models.

Reactive intermediates generated by metabolic epoxidation, N-oxidation and S-oxidation are often identical to those obtained on peracid oxidation as illustrated by studies with a variety of pesticides. Epoxidation reactions carried out metabolically or with peracids lead to transitory or unstable epoxychrysanthemic acid, epoxycyclopentenolone and epoxyfuran derivatives from pyrethroids, and geranyl-derived diepoxides and epoxydiols from juvenoids. N-Oxidation with microsomal oxidases or peracids activates hydroxylamine ether proinsecticides and dimethylphosphoramide and aminodiphenyl ether promutagens, but the peracid system is not always a suitable biomimetic model. Sulphoxidations with peracids appear to give the same reactive intermediates as those involved in metabolism of S-alkyl thiocarbamate and S-methyl-triazinone herbicides, S-chloroallyl promutagens, and S-propyl phosphorothiolate and phosphinyliminodithiolane proinsecticides.

Biotransformation↗

Biomimetic polyesters and their role in ion transport across cell membranes.

Syntheses of biomimetic low-molecular weight poly-(R)-3-hydroxybutanoate mediated by three types of supramolecular catalysts are presented. The utility of these synthetic polyesters for preparation of artificial channels in phospholipid bilayers capable of sodium and calcium ion transport across cell membranes, is discussed. Further studies on possible applications of these bio-polymers for manufacturing drugs of prolonged activity are under way.

Cell Membrane↗

[Biomimetic oxidation of benzene by a polynuclear manganese complex [Mn12O12(CH3CO2)16(H2O)4] under mild conditions].

The possibility of monooxygenase enzymes biomimetic construction models with the use of polynuclear manganese complexes was shown. It was demonstration that benzene is oxidized by polynuclear manganese complex [Mn12O12(CH3CO2)16(H2O)4] in acetonitrile solution at room temperature and atmospheric pressure yielding phenol with the selectivity more than 80%. It was determined that the addition of air oxygen as the reoxidizer to the reaction mixture didn't transfer the reaction into the catalytic mode.

Benzene↗

[Biomimetic electrochemical synthesis of quinol-thioether conjugates: their implication in the serotonergic neurotoxicity of amphetamine derivatives].

Injection of 3,4-methylenedioxyamphetamine (MDA) or 3,4-methylenedioxymethylamphetamine (MDMA or ecstasy) directly into the brain fails to reproduce the long-term effects observed after peripheral administration, implying an essential role for systemic metabolites in the development of toxicity. However, the precise identity of the metabolites participating in MDA and MDMA-mediated serotonergic neurotoxicity remains unclear: neither 3,4-alpha-methyldopamine, nor N-methyl-alpha-methyldopamine, major metabolites, produce neurotoxicity following peripheral administration. In vivo, these metabolites are oxidized to the corresponding orthoquinones, that readily react with protein and nonprotein sulphydryls including glutathione (GSH). The resulting quinol-thioether conjugates exhibit a variety of toxicological activities, which can be regulated by intramolecular cyclisation reactions that occur subsequent to oxidation. The ability of quinol-thioether conjugates to redox cycle and produce reactive oxygen species provides a rationale for the potential role of these metabolites in MDA and MDMA neurotoxicity. A biomimetic one-pot synthesis of 5-(GSH-S-yl)-N-Me-alpha-Me-DA involving addition of GSH to the electrogenerated orthoquinone species, is reported to evaluate its in vivo potential neurotoxicity.

Amphetamines↗

Platelet adhesion to a biomimetic prosthesis prepared from canine arterial wall.

A biomimetic prosthesis was prepared from canine arterial wall by extraction with 70% formic acid. Under these conditions, the arterial architecture consisting of elastic lamella was conserved and the tensile strength was retained. Attachment of 51Cr-endothelial cells to the surface of the prosthesis was enhanced in the presence of collagen (50 micrograms/ml), fibronectin (20 micrograms/ml), and fibrinogen (500 micrograms/ml). These agents also enhanced the adhesion of 51Cr-platelets. However, preattachment of endothelial cells to prostheses prevented platelet adhesion.

Acetates↗

[The biomimetic oxidation of propiverine hydrochloride and 1-methyl-4-piperidylbenzilate].

The reaction of propiverinhydrochloride (1) and 1-methyl-4-piperidyl benzilate (2) with the biomimetic system manganese(III)-5,10,15,20-tetrakis(pentafluorophenyl)porphyrin chloride (MnTPFPPCl)/pyridine/hydrogen peroxide affords unchanged 1 and 2 and 15 potential metabolites, which were isolated and identified. These compounds are products of cleavage of the ester bond, of O-dealkylation, aromatic oxidation, respectively of decarboxylation, demethylation, and N-oxidation, Products were identified by TLC, UV, and MS in comparison with authentic samples. Thereby we found a nearly conformity with rat metabolism.

Animals↗

[Biomimetic oxidation of clemastine hydrogen fumarate].

The reaction of clemastine fumarate (1) with the biomimetic system manganese(III)-5,10,15,20-tetrakis(pentafluoro-water. The reaction of 1 in aqueous solution with manganese(III)-5,10,15,20-tetrakis (pentafluorophenyl)-beta-tetrasulfonatoporphyrin chloride (MnTPFPS4PCl) as catalyst additional generates products of aromatic hydroxylation. Products were identified by TLC, UV, and MS. Thereby we found a close conformity with rat metabolism.

Animals↗

Preparation of SBF with different HCO3- content and its influence on the composition of biomimetic apatites.

The bioactivity of bone and dental implant materials is usually tested in vitro using simulated body fluid (SBF). The composition of common SBF differs from that of blood plasma in that it has a higher Cl- and a lower HCO3- concentration, which affects the composition of in vitro formed bone-like apatite. Five different SBFs with a composition of 142 Na+, 5 K+, 2.5 Ca2+, 1 Mg2+, 1SO4(2-), 1HPO4(2-), and 136 (Cl-+HCO3-) mmol/l were prepared with HCO3- concentrations ranging from 5 to 27 mmol/l. The SBF solutions were prepared by mixing stable concentrated solutions, which increase the reproducibility of in vitro tests due to negligible changes of pH during preparation. The high stability of thus prepared SBF enables the evaluation of hydroxyapatite formation on the surface of bioactive materials without the negative effect of spontaneous precipitation. Furthermore, the use of concentrated solutions offers a facile way to prepare SBF with different ionic contents and thus modify the composition of Ca-P layers precipitated on the surface of the bioactive materials exposed to the SBF solutions. The SBF solutions were shown to be supersaturated with respect to slightly carbonated apatite. The Fourier transform infrared (FT-IR), Raman and X-ray analyses of the precipitated layers indicate that the HCO3- content in SBF influences the composition and structure of the calcium phosphates obtained. It can be supposed that as long as the HCO3- concentration in the testing solutions is lower than 20 mmol/l, only B-type HCA precipitates. At higher HCO3- concentrations, it can be assumed that A-type HCA forms as well considering FT-IR, Raman and X-ray measurements.

Anions↗

Bottom-up design of biomimetic assemblies.

Nature has evolved the ability to assemble a variety of molecules into functional architectures that can specifically bind cellular ligands. Mimicking this strategy requires the design of a set of multifaceted molecules, where elements that direct assembly were conjugated to biologically specific components. The development of functional molecular building-blocks that assemble to form compartments for therapeutics addresses the desire to have controllable morphologies that interact with biological interfaces at nanometer length scales. The practical application of such 'bottom-up' assemblies requires the ability to predict the type of aggregated structure and to synthesize molecules in a highly controlled fashion. This bottom-up approach results in a molecular platform that mimics biological systems with potential for encapsulating and delivering drug molecules.

Binding Sites↗

Nanotechnology and biomimetic methods in therapeutics: molecular scale control with some help from nature.

Nanoscale science and engineering has provided new avenues for engineering materials with macromolecular and even molecular precision. In particular, researchers are beginning to mimic biological systems, achieving molecular scale control via self-assembly and directed assembly techniques. Fabrication and manipulation with macromolecular and molecular precision have led and will lead to the development of novel materials, and these materials will facilitate the fabrication of micro- and nanoscale devices, such as self-regulated micro- and nanoscale drug delivery devices that combine diagnostic and therapeutic actions for instantaneous administration of therapy. As the field of nanoscale science and engineering matures, technologies that will revolutionize the way health care is administered will continue to be developed.

Biomimetic Materials↗

Thermal assembly of a biomimetic mineral/collagen composite.

A strategy is described for exploiting temperature driven self-assembly of collagen and thermally triggered liposome mineralization to form a mineralized collagen composite from an injectable precursor fluid. Optical density and rheological experiments demonstrated the formation of a collagen gel when acid-soluble type I collagen solutions (1-7 mg/ml) were heated to 24-30 degrees C. Scanning calorimetry experiments demonstrated that mixtures of calcium- and phosphate-loaded liposomes composed of dipalmitoylphosphatidylcholine (90 mol%) and dimyristoylphosphatidylcholine (10 mol%) were stable at room temperature but formed calcium phosphate mineral when heated above 35 degrees C, a consequence of the release of entrapped salts at the lipid chain melting transition. The formation of calcium phosphate mineral induced by triggered release of calcium and phosphate was detected as an endothermic transition (deltaH=6.2+/-1.1 kcal/mol lipid) near the lipid chain melting transition (Tm=37 degrees C). Combining an acid-soluble collagen solution with calcium- and phosphate-loaded liposomes resulted in a liposome/collagen precursor fluid, which when heated from room temperature to 37 degrees C formed a mineralized collagen gel. The dynamic storage modulus of the collagen scaffold increased upon mineralization, and direct nucleation of mineral from the collagen scaffold was detected by electron microscopy.

Biomimetic Materials↗

Aggregation during coniferyl alcohol polymerization in pectin solution: a biomimetic approach of the first steps of lignification.

Coniferyl alcohol was polymerized in pectin solution in order to mimic the lignification that is the final step of biosynthesis of plant cell wall. Dehydrogenated polymers (DHP = coniferyl alcohol polymers = synthetic lignin) interact with pectin to form hydrophobic clusters as monitored by pyrene fluorescence spectroscopy. The structure of these clusters was studied during the polymerization of synthetic lignin by static and quasielastic light scattering and small angle neutron scattering experiments. We show that synthetic lignin and pectin contribute to the same clusters, but the inner structure of these clusters is very heterogeneous and displays three phases. One observes a segregation between well separated pectin and lignin rich phases at length scales below approximately 30 nm. As a corollary of this segregation, clusters embody a large amount of solvent. On average, the density of the polymer rich phase (lignin plus pectin) inside clusters increases while its specific surface area decreases throughout the polymerization process. These results are discussed with respect to in vivo lignification of the plant cell wall.

Biomimetic Materials↗

Multilayer biomimetics: reversible covalent stabilization of a nanostructured biofilm.

Designed polypeptides and electrostatic layer-by-layer self-assembly form the basis of promising research in bionanotechnology and medicine on development of polyelectrolyte multilayer films (PEMs). We show that PEMs can be formed from oppositely charged 32mers containing several cysteine residues. The polypeptides in PEMs become cross-linked under mild oxidizing conditions. This mimicking of disulfide (S-S) bond stabilization of folded protein structure confers on the PEMs a marked increase in resistance to film disassembly at acidic pH. The reversibility of S-S bond stabilization of PEMs presents further advantages for controlling physical properties of films, coatings, and other applications involving PEMs.

Amino Acid Sequence↗