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The construction, measurement, and modeling of an artificial cochlea (ACochlea) are presented in this paper. An artificial basilar membrane (ABM) was made by depositing discrete Cu beams on a piezomembrane substrate. Rather than two fluid channels, as in the mammalian cochlea, a single fluid channel was implemented on one side of the ABM, facilitating the use of a laser to detect the ABM vibration on the other side. Measurements were performed on both the ABM and the ACochlea. The measurement results on the ABM show that the longitudinal coupling on the ABM is very strong. Reduced longitudinal coupling was achieved by cutting the membrane between adjacent beams using a laser. The measured results from the ACochlea with a laser-cut ABM demonstrate cochlear-like features, including traveling waves, sharp high-frequency rolloffs, and place-specific frequency selectivity. Companion computational models of the mechanical devices were formulated and implemented using a circuit simulator. Experimental data were compared with simulation results. The simulation results from the computational models of the ABM and the ACochlea are similar to their experimental counterparts.
In the paper we give a method for calculating the tractions (local forces) of the fluid motion determined by an incoming plane pressure wave on an artificial hair cell transducer structure. The sensing element of the transducer is a standing high aspect ratio cilium in the shape of a narrow thin curved beam (tape-like), which can be easily fabricated in micro-/nanotechnology. The method is based on considering the system of partial differential equations describing the motion of the compressible viscous fluid in an acoustic linearized approximation, and representation of the velocity field as a viscous acoustic single-layer potential. The boundary conditions, stating the cancellation of the velocity components on the solid beam, yield a two-dimensional (2-D) system of three integral equations over the beam's surface for the traction components. In the case of a narrow cilium, the system of integral equations furnishes a system of two 1-D integral equations over the symmetry curve of the structure for obtaining the tangential and normal components of the traction. This system is solved numerically by a finite (boundary) element method. The numerical code written for solving the problem was applied to some particular structures. The last structure is similar to the trichobothrium of a spider Cupiennius salei. The results obtained show that the curvature of the hair is enhancing sensitivity to flows directed normal to the main shaft of the hair confirming the assertion of Barth et al. [Philos. Trans. R. Soc. London, Ser. B 340, 445-461 (1993)].
Many organisms construct structural ceramic (biomineral) composites from seemingly mundane materials; cell-mediated processes control both the nucleation and growth of mineral and the development of composite microarchitecture. Living systems fabricate biocomposites by: (i) confining biomineralization within specific subunit compartments; (ii) producing a specific mineral with defined crystal size and orientation; and (iii) packaging many incremental units together in a moving front process to form fully densified, macroscopic structures. By adapting biological principles, materials scientists are attempting to produce novel materials. To date, neither the elegance of the biomineral assembly mechanisms nor the intricate composite microarchitectures have been duplicated by nonbiological processing. However, substantial progress has been made in the understanding of how biomineralization occurs, and the first steps are now being taken to exploit the basic principles involved.
The potent antileukemic plant principles triptolide and tripdiolide contain a characteristic hydrogen-bonded 9,11-epoxy-14beta-hydroxy system. They alkylate propanethiol in a process which involves opening of the epoxide function with neighboring hydroxyl assistance. The reaction may mimic the inhibition of tumor growth via selective alkylation of the thiol groups of key enzymes concerned with groth regulation.
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Living organisms construct various forms of laminated nanocomposites through directed nucleation and growth of inorganics at self-assembled organic templates at temperatures below 100°C and in aqueous solutions. Recent research has focused on the use of functionalized organic surfaces to form continuous thin films of single-phase ceramics. Continuous thin films of mesostructured silicates have also been formed on hydrophobic and hydrophilic surfaces through a two-step mechanism. First, under acidic conditions, surfactant micellar structures are self-assembled at the solid/liquid interface, and second, inorganic precursors condense to form an inorganic-organic nanocomposite. Epitaxial coordination of adsorbed surfactant tubules is observed on mica and graphite substrates, whereas a random arrangement is observed on amorphous silica. The ability to process ceramic-organic nanocomposite films by these methods provides new technological opportunities.
Individual phospholipid vesicles, 1 to 5 micrometers in diameter, containing a single reagent or a complete reaction system, were immobilized with an infrared laser optical trap or by adhesion to modified borosilicate glass surfaces. Chemical transformations were initiated either by electroporation or by electrofusion, in each case through application of a short (10-microsecond), intense (20 to 50 kilovolts per centimeter) electric pulse delivered across ultramicroelectrodes. Product formation was monitored by far-field laser fluorescence microscopy. The ultrasmall characteristic of this reaction volume led to rapid diffusional mixing that permits the study of fast chemical kinetics. This technique is also well suited for the study of reaction dynamics of biological molecules within lipid-enclosed nanoenvironments that mimic cell membranes.
A low molecular weight, lipophilic, copper coordination complex with superoxide dismutase-mimetic activity inhibited biochemical and biological actions of a tumor promoter in mouse epidermis. Such inhibitory effects implicate reactive oxygen species in the tumor promotion process.
A model that makes use of the cooperative organization of inorganic and organic molecular species into three dimensionally structured arrays is generalized for the synthesis of nanocomposite materials. In this model, the properties and structure of a system are determined by dynamic interplay among ion-pair inorganic and organic species, so that different phases can be readily obtained through small variations of controllable synthesis parameters, including mixture composition and temperature. Nucleation, growth, and phase transitions may be directed by the charge density, coordination, and steric requirements of the inorganic and organic species at the interface and not necessarily by a preformed structure. A specific example is presented in which organic molecules in the presence of multiply charged silicate oligomers self-assemble into silicatropic liquid crystals. The organization of these silicate-surfactant mesophases is investigated with and without interfacial silicate condensation to separate the effects of self-assembly from the kinetics of silicate polymerization.
In designing polymers that can act as tissue engineering templates it is beneficial to consider methods of mimicking the natural support structures used by the human body to guide the behavior and development of cells within tissues. The well-known RGD cell adhesion ligand provides a simple mechanism of creating polymer surfaces that mimic the extracellular matrix. This paper considers the methods that have been used to attach such motifs to synthetic polymers. In general there are two strategies: the formation of polymer-peptide hybrid molecules, or the immobilization of the ligand on the fabricated surface of the polymer. The three major synthetic strategies of creating polymer-peptide hybrids are reviewed.
The method of thin film preparation known as layer-by-layer assembly is of growing interest for current and envisioned developments in bionanotechnology. Here, cysteine-containing 32mer peptides have been designed, synthesized, purified, and used to prepare polypeptide films. A range of methods-quartz crystal microbalance, Fourier transform infrared spectroscopy, circular dichroism spectroscopy, and high-performance liquid chromatography-have been used to probe the effect of ionic strength and polymer secondary structure in solution on peptide self-assembly, and on secondary structure formation and disulfide bond cross-linking in the multilayer film. The amount of designed peptide deposited per adsorption step of film fabrication increased with increasing ionic strength, as with conventional polyelectrolytes. Secondary structure content changed from random coil to beta sheet on incorporation of peptides into a film. "Peptide-inherent" cross-linking by disulfide bond formation increased film stability at acidic pH. Conditions for disulfide stabilization have been optimized. The results contribute to exploration of the physical basis of peptide self-assembly broaden the scope of applications of layer-by-layer assembly, particularly where biocompatibility and stability are key design concerns, and provide a basis for mass production of custom polypeptide thin films of high stability, even in harsh environments.
The conditions of the use of the manganese/porphyrin/imidazole system needed to be improved in order to obtain larger amounts of models of metabolites. An increase of the oxidation yields and a better preservation of this catalytic system have been obtained on the examples of various alkanes, by an acid addition in the reaction mixture. Three manganoporphyrins were checked for evaluation of the reaction. These results were extended to molecules of therapeutical interest such as ibuprofen and phenylbutazone.
(+/-)-Galanthamine (1) was synthesized in excellent yield by applying PIFA-mediated oxidative phenol coupling of N-(4-hydroxy)phenethyl-N-(3',4',5'-trialkoxy)benzyl formamide (15b) as a key step. Because of the symmetrical characteristics of the pyrogallol moiety in the substrate (15b), the phenol coupling resulted in a sole coupling product except for volatile components from the oxidizing agent. On the basis of the successful results of the above strategy, (-)-galanthamine (1) was synthesized by employing a novel remote asymmetric induction, where conformation of the seven-membered ring in the product of the phenol coupling was restricted by forming a fused-chiral imidazolidinone ring with D-phenylalanine on the benzylic C-N bond of the tri-O-alkylated gallyl amino moiety. The conformational restriction and successive debenzylation of the protected hydroxyl groups on the pyrogallol ring caused diastereoselective cyclization to yield a cyclic ether having the desired stereochemistry for the synthesis of (-)-1.
Neomycin B has been found to block the binding of HIV-1 Rev protein to its viral RNA recognition site, thereby inhibiting the production of the virus. This paper describes the synthesis of analogues of neomycin B, which are potential anti-HIV compounds designed as inhibitors of Rev/RRE binding.
Dichloromethane containing metalloporphyrins [meso-tetraphenylporphyrinatomanganese(III) chloride (1) or meso-tetraphenylporphyrinatoiron(III) chloride (2)] and Bu4NClO4 was treated with an aqueous solution of NaOH (5%), and subjected to controlled potential electrolysis at -1.0 V (vs. S.C.E. (saturated calomel electrode)) in a divided cell after addition of diphenyl sulfide (3). Diphenyl sulfoxide (4) and diphenyl sulfone (5) were found in an electrolyzed solution as the reaction products. Results obtained from cyclic voltammetry and visible spectrometry suggested that the treatment of dichloromethane containing metalloporphyrins with the aqueous solution of NaOH did not change the fifth ligand of metalloporphyrins from Cl to OH. On the electrode, dissolved dioxygen was reduced to hydrogen peroxide. Compounds 1 and 2 catalyze the oxidation of 3 by hydrogen peroxide without imidazole. Compound 2 showed higher selectivity than compound 1.
The process of bone growth, regeneration, and remodeling is mediated, in part, by the immediate cell-matrix environment. Osteoblast stimulating factor-1 (OSF-1), more commonly known as pleiotrophin (PTN), is an extracellular matrix-associated protein, present in matrices, which act as targets for the deposition of new bone. However, the actions of PTN on human bone progenitor cells remain unknown. We examined the effects of PTN on primary human bone marrow stromal cells chemotaxis, differentiation, and colony formation (colony forming unit-fibroblastic) in vitro, and in particular, growth and differentiation on three-dimensional biodegradable porous scaffolds adsorbed with PTN in vivo. Primary human bone marrow cells were cultured on tissue culture plastic or poly(DL-lactic acid-co-glycolic acid) (PLGA; 75:25) porous scaffolds with or without addition of recombinant human PTN (1 pg-50 ng/ml) in basal and osteogenic conditions. Negligible cellular growth was observed on PLGA scaffold alone, generated using a super-critical fluid mixing method. PTN (50 microg/ml) was chemotactic to human osteoprogenitors and stimulated total colony formation, alkaline phosphatase-positive colony formation, and alkaline phosphatase-specific activity at concentrations as low as 10 pg/ml compared with control cultures. The effects were time-dependent. On three-dimensional scaffolds adsorbed with PTN, alkaline phosphatase activity, type I collagen formation, and synthesis of cbfa-1, osteocalcin, and PTN were observed by immunocytochemistry and PTN expression by in situ hybridization. PTN-adsorbed constructs showed morphologic evidence of new bone matrix and cartilage formation after subcutaneous implantation as well as within diffusion chambers implanted into athymic mice. In summary, PTN has the ability to promote adhesion, migration, expansion, and differentiation of human osteoprogenitor cells, and these results indicate the potential to develop protocols for de novo bone formation for skeletal repair that exploit cell-matrix interactions.