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At least 217 records · Page 12Linked to original sources
PubMed2006

Biomimetic porous scaffolds made from poly(L-lactide)-g-chondroitin sulfate blend with poly(L-lactide) for cartilage tissue engineering.

A novel biodegradable graft copolymer chondroitin sulfate-grafted poly(L-lactide) (CS-PLLA) was synthesized. The graft copolymer was blended with PLLA to form biomimetic porous scaffolds. Natural CS was introduced into the polyester matrix to promote the proliferation of cells. Three-dimensional spongelike scaffolds were fabricated by a combination of salt leaching and solvent casting methods. The morphology of the scaffolds was observed with scanning electron microscopy with an average pore size between 50 and 250 microm, and its porosity was high (>85%). Compression analysis indicated that the mechanical properties of the scaffold were adequate to support the proliferation of cells. The hydrophilicity increased with an increase in the copolymer content in the blend, as determined by measuring the contact angle. Hematoxylin and eosin, Masson, and Safranin-O staining showed that cells formed a chondro tissue gradually. Histological results revealed that abundant cartilaginous matrixes surrounded spherical chondrocytes in the center of the explants. Chondrocytes cultured in this extracellular-matrix-like scaffold maintained a round morphology phenotype, characterized by a significant quantity of extracellular matrixes of sulfated glycosaminoglycans and collagens. Additionally, phenotypic gene expression (reverse transcriptase-polymerase chain reaction) indicated that chondrocytes expressed transcripts that encoded type II collagen and aggrecan and generated sulfated glycosaminoglycans.

Aggrecans↗
PubMed2007

Synthetic biomimetic hydrogels incorporated with ephrin-A1 for therapeutic angiogenesis.

Eph receptors and ephrin ligands are essential for vascular development and angiogenic remodeling. In this work, we developed biomimetic poly(ethylene glycol)-diacrylate hydrogels incorporated with ephrin-A1 and examined their angiogenic properties. Ephrin-A1 was covalently immobilized on the surface of hydrogels by chemical modification and photopolymerization. Ephrin-A1 immobilized on hydrogels was found to retain its capacity to stimulate endothelial cell adhesion in a dose-dependent manner as similar findings were observed on polystyrene culture wells pre-adsorbed with ephrin-A1. Cell adhesion stimulated by ephrin-A1 was abolished by treatment with soluble RGDS and anti-alpha(v)beta3 integrin but not anti-alpha(v)beta5 integrin antibodies, suggesting that ephrin-A1 activates cell adhesion through alpha(v)beta3 integrins. Also, surface immobilized ephrin-A1 was found to induce endothelial tubule formation with luminal diameters ranging 5-30 microm on hydrogels. The results of these studies demonstrate that pro-angiogenic properties of ephrin-A1 are preserved in hydrogels and suggest potential applications of this hydrogel system in regenerative medicine and tissue engineering.

Biocompatible Materials↗
PubMedDate not supplied

Effects of epidermal growth factor on fibroblast migration through biomimetic hydrogels.

We have previously reported on the development and use of synthetic hydrogel extracellular matrix (ECM) analogues that can be used to study the mechanisms of migration. These biomimetic hydrogels consist of bioinert poly(ethylene glycol) diacrylate derivatives with proteolytically degradable peptide sequences included in the backbone of the polymer and adhesion peptide sequences grafted into the network. Cells adhere to the hydrogel via interaction between the grafted adhesion ligands and receptors on the cell surface. The cells migrate through the three-dimensional system by secreting the appropriate proteolytic enzymes, which are involved in cell migration and are targeted to the peptide sequences incorporated in the backbone of the polymer. It was observed that cell migration has a biphasic dependence on adhesion ligand concentration, with optimal migration at intermediate ligand levels. In this study, we demonstrate that we can covalently attach epidermal growth factor (EGF) to PEG and graft them into the hydrogels. It was observed that EGF when tethered maintained mitogenic activity. It was also observed that fibroblast migration significantly increased in the presence of the grafted EGF through the collagenase-sensitive hydrogels. In addition, the increase in migration was found to be independent from the proliferative response of the cells. These synthetic ECM analogues allow one to systematically control identities and concentrations of biomolecules and are useful tools to study mechanisms of cell migration.

Biocompatible Materials↗
PubMedDate not supplied

Synthetic low-density lipoprotein, a novel biomimetic lipid supplement for serum-free tissue culture.

Lipid supplementation in serum-free tissue culture employs solubilization techniques to permit the addition of lipids, but these systems are potentially cytotoxic and do not present lipid in a natural form. In this research a simplified preparation method for synthetic low-density lipoprotein (sLDL) has been developed that involves microfluidization of a solvent lipid solution in a simple aqueous solution. This produces material with size and zeta potential characteristics similar to those of native LDL. sLDL supplementation in tissue culture media provides cholesterol concentrations higher than those achieved by 10% serum supplementation and existing chemically defined lipid supplements. sLDL stimulates NS0 and U937 cellular proliferation in completely serum-free media, the former in a lipid concentration dependent manner that is also related to both the receptor peptide structure employed and its concentration on the particle. The greatest NS0 cellular proliferation was obtained at the highest cholesterol concentration tested (0.5 mg/mL), which was 10 times higher than the cholesterol concentration achieved by standard 10% serum supplementation. U937 cellular proliferation was influenced by variation of sLDL's fatty acid constituents with a natural mixture producing maximal effect. Cell uptake studies in NS0 with fluorescently labeled sLDL indicated that assimilation is reduced by competition from native LDL. The planktonic nature of NS0 cell growth meant that cell binding and uptake experiments were difficult to conduct because of cellular aggregation. However, sLDL-induced U937 proliferation is ablated by the presence of an anti-LDL receptor antibody. The results indicate that sLDL uptake is via the LDL receptor and that sLDL can function as a lipid supplement for serum-free media capable of supplementation to cholesterol concentrations up to 0.5 mg/mL. Cellular uptake studies also suggest that sLDL will be useful for the targeting and delivery of materials to cells. sLDL therefore represents a new and promising synthetic biomimetic alternative to native LDL with multiple applications.

Animals↗
PubMed2004

A hybrid density functional study of O-O bond cleavage and phenyl ring hydroxylation for a biomimetic non-heme iron complex.

Density functional calculations using the B3LYP functional have been used to study the reaction mechanism of [Fe(Tp(Ph2))BF] (Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate; BF = benzoylformate) with dioxygen. This mononuclear non-heme iron(II) complex was recently synthesized, and it proved to be the first biomimetic complex reproducing the dioxygenase activity of alpha-ketoglutarate-dependent enzymes. Moreover, the enthalpy and entropy of activation for this biologically interesting process were derived from kinetic experiments offering a unique possibility for direct comparison of theoretical and experimental data. The results reported here support a mechanism in which oxidative decarboxylation of the keto acid is the rate-limiting step. This oxygen activation process proceeds on the septet potential energy surface through a transition state for a concerted O-O and C-C bond cleavage. In the next step, a high-valent iron-oxo species performs electrophilic attack on the phenyl ring of the Tp(Ph2) ligand leading to an iron(III)-radical sigma-complex. Subsequent proton-coupled electron-transfer yields an iron(II)-phenol intermediate, which can bind dioxygen and reduce it to a superoxide radical. Finally, the protonated superoxide radical leaves the first coordination sphere of the iron(III)-phenolate complex and dismutates to dioxygen and hydrogen peroxide. The calculated activation barrier (enthalpy and entropy) and the overall reaction energy profile agree well with experimental data. A comparison to the enzymatic process, which is suggested to occur on the quintet surface, has been made.

Biomimetic Materials↗
PubMed2003

Total synthesis of Elisabethin A: intramolecular Diels-Alder reaction under biomimetic conditions.

We describe the first total synthesis of the marine diterpenoid elisabethin A. The synthesis uses (S)-hydroxy-2-methyl-propionate as the chiral starting material, which is elaborated into a dienyl-iodide and added to an aryl acetic acid ester via enolate alkylation. The hydroquinoid system is oxidized to the quinone which serves as the dienophile in a highly stereocontrolled intramolecular Diels-Alder addition. This IMDA reaction, which to our knowledge is the first one to employ a terminal (Z)-diene, proceeds under biomimetic conditions (water, ferrichloride as the oxidant, room temperature) with high yield and stereoselectivity. The Diels-Alder adduct is transformed into the natural product via a three-step sequence including selective hydrogenation, base-catalyzed epimerization of the cis- into the trans-decalin system and O-demethylation.

Animals↗
PubMed2003

A selective biomimetic tweezer for noradrenaline.

The new highly preorganized tweezer molecule 1 binds noradrenaline in polar solvents with unprecedented specificity. It uses a biomimetic recognition pattern and rejects almost all other neurotransmitters. LB experiments on a film balance reflect the same selectivity if 1 is incorporated into a stearic acid monolayer.

Alkynes↗
PubMed2003

Intramolecular charge transfer and biomimetic reaction kinetics in galactose oxidase model complexes.

One-electron oxidation of two structurally similar CuII-diphenolate complexes, 1 and 2, creates EPR-silent CuII-phenoxyl complexes [1]+ and [2]+ that mimic the oxidized form of the enzyme galactose oxidase (GOase). Both model complexes display novel NIR absorptions assigned to phenolate-phenoxyl charge transfer that resemble a tyrosinate-tyrosyl charge-transfer band observed in the enzymatic system. [1]+ and [2]+ react with benzyl alcohol to form 0.5 equivs of benzaldehyde per complex; biomimetic reduction to CuI-phenol complexes is not observed, but such species may exist transiently. Initial kinetic studies show that [2]+ reacts faster with benzyl alcohol than does [1]+, despite being a significantly weaker oxidant (DeltaE degrees = 370 mV). This acceleration is ascribed to mechanistic differences: [2]+ appears to bind substrate prior to the rate-determining step. Large, nonclassical kinetic isotope effects confirm C-H bond cleavage as the rate-determining step in the reactions of both [1]+ and [2]+ with benzyl alcohol, as is the case for GOase.

Benzyl Alcohol↗
PubMed2004

Design and photochemical characterization of a biomimetic light-driven Z/E switcher.

Protonated Schiff bases (PSBs) of polyenals constitute a class of light-driven switchers selected by biological evolution that provide model compounds for the development of artificial light-driven molecular devices or motors. In the present paper, our primary target is to show, through combined computational and experimental studies, that it is possible to approach the design of artificial PSBs suitable for such applications. Below, we use the methods of computational photochemistry to design and characterize the prototype biomimetic molecular switchers 4-cyclopenten-2'-enylidene-3,4-dihydro-2H-pyrrolinium and its 5,5'-dimethyl derivative both containing the penta-2,4-dieniminium chromophore. To find support for the predicted behavior, we also report the photochemical reaction path of the synthetically accessible compound 4-benzylidene-3,4-dihydro-2H-pyrrolinium. We show that the preparation and photochemical characterization of this compound (together with three different N-methyl derivatives) provide both support for the predicted photoisomerization mechanism and information on its sensitivity to the molecular environment.

Biomimetic Materials↗
PubMed2004

Biomimetically inspired total synthesis and structure activity relationships of 1-O-methyllateriflorone. 6 pi electrocyclizations in organic synthesis.

The total synthesis of 1-O-methyllateriflorone (2) is described. The construction of the cage-like domain of the molecule involved a biomimetic Claisen/Diels-Alder cascade, whereas the novel spiroxalactone framework was generated by an intramolecular Michael reaction within precursor 16a involving the carboxylate residue as the nucleophile. This finding might bear on the biosynthetic pathway by which nature forms lateriflorone. Described herein is also an interesting cascade sequence involving facile 6 pi electrocyclizations which leads to complex benzopyran systems. The biological evaluation of a small library of lateriflorone analogues and related systems establishing the first SAR within this class of compounds is also included. Among the most active compounds against tumor cells are 2, 16b, 56, 58, and 59.

Benzopyrans↗
PubMed2004

A biomimetic approach to the rocaglamides employing photogeneration of oxidopyryliums derived from 3-hydroxyflavones.

A unified biomimetic approach to the aglain-forbaglin-rocaglamide classes of natural products is reported. The approach involves photogeneration of oxidopyryliums via excited-state intramolecular proton transfer (ESIPT) of 3-hydroxyflavones followed by [3+2] dipolar cycloaddition to the aglain core. An alpha-ketol (acyloin) rearrangement was employed to transform the aglain core to the rocaglamide framework. This approach was successfully used for the synthesis of the natural product (+/-)-methyl rocaglate.

Benzofurans↗
PubMed2005

Albumin-conjugated corrole metal complexes: extremely simple yet very efficient biomimetic oxidation systems.

An extremely simple biomimetic oxidation system, consisting of mixing metal complexes of amphiphilic corroles with serum albumins, utilizes hydrogen peroxide for asymmetric sulfoxidation in up to 74% ee. The albumin-conjugated manganese corroles also display catalase-like activity, and mechanistic evidence points toward oxidant-coordinated manganese(III) as the prime reaction intermediate.

Animals↗
PubMed2004

Phosphoryl choline introduces dual activity in biomimetic ionomers.

Dual activity of phosphoryl choline (PC) functional poly(trimethylene carbonate) (PTMC) was found which induces the zwitterionic biomimetic PC group to form physical cross-links with ionomers in the bulk, and at the same time enrich at the surface of cast films. The formation of zwitterionic domains from a bifunctional PC-PTMC-PC (ionomer) provided firm films with a low elastic modulus in contrast to the tacky PTMC starting material (Mn approximately 3900 g/mol) with poor mechanical performance. In addition, the ionomer possessed improved hemocompatible properties that was explained by the enrichment of PC at the surface, suggesting a way to tailor the mechanical performance of biodegradable PTMC-based ionomers while providing its bioactivity. Tailored elasticity while maintaining hemocompatibility of a biodegradable ionomer should be of particular interest for a variety of in vivo applications.

Biocompatible Materials↗
PubMed2004

Biomimetic catalytic system driven by electron transfer for selective oxygenation of hydrocarbon.

Hydrocarbon oxyfunctionalization is a crucial industrial process. Most metallic catalysts require higher temperatures and often show lower selectivities. One of the intellectual approaches is the mimicry for bio-oxidation. We have established a biomimetic system with a nonmetallic redox center, composed of anthraquinones, N-hydroxyphthalimide, and zeolite HY, for selective hydrocarbon oxygenation by molecular oxygen. Selectivity of 95.8% for acetophenone and 66.2% conversion were accomplished for oxygenation of ethylbenzene at temperatures as low as 80 degrees C. The redox cycle, driven by one-electron transfer and product orientation by Zeolite HY, opens up the possibility of mimicking bio-oxidation under mild conditions.

Biomimetic Materials↗
PubMed2004

Biomimetic enantioselective total synthesis of (-)-siccanin via the Pd-catalyzed asymmetric allylic alkylation (AAA) and sequential radical cyclizations.

(-)-Siccanin (1), a natural product possessing significant antifungal properties, was synthesized enantioselectively via a biomimetic route. This synthetic route features two sequential radical cyclizations: a Ti(III)-mediated radical cyclization of epoxyolefin 48 to construct the B-ring, and a Suarez reaction to establish the tetrahyrofuran ring. Chiral chroman moiety of siccanin was prepared based on our recent development of the Pd-catalyzed asymmetric allylic alkylation (AAA) of phenol trisubstituted allyl carbonates. Several other members of the siccanin family were also synthesized including siccanochromenes A (2), B (3), E (6), F (7), and the methyl ether of siccanochromene C (55). These studies may shed light on the biosynthesis of this novel family of compounds.

Alkylation↗
PubMed2004

Biomimetic monoacylation of diols in water. Lanthanide-promoted reactions of methyl benzoyl phosphate.

The direct monoacylation of diols by acyl phosphate monoesters in water is a biomimetic analogy to the enzymic aminoacylation of tRNA by aminoacyl adenylates. Without catalysis, acyl phosphate monoesters react rapidly with amines but very slowly with water and alcohols. Lanthanide ions dramatically and selectively facilitate the base-catalyzed monoacylation of diols in water by methyl benzoyl phosphate (MBP), a typical acyl phosphate monoester, in neutral solutions where reactive amines are protonated and unreactive. The reaction patterns and reactivity of various diols with MBP in the presence of lanthanides are consistent with a mechanism that involves internal addition from the conjugate base of the bis-bidentate complex of the lanthanide with the diol and MBP. The method is also applicable to reactions of nucleosides as evidenced by the selective monoacylation of the 2'- or 3'-hydroxyl group of adenosine, without reaction of the 5'-hydroxyl group or the 6-amino group. Analogues of adenosine without the diol are unreactive. This suggests that the method will selectively monoacylate the hydroxyl groups at the unique diol in tRNA that forms the 3'-terminus.

Acylation↗