Electronically modulated biological functions of molecular interfaced enzymes and living cells

Graphene-polymer hybrid nanostructure-based bioenergy storage device for real-time control of biological motor activity

We report a graphene-polymer hybrid nanostructure-based bioenergy storage device to turn on and off biomotor activity in real-time. In this strategy, graphene was functionalized with amine groups and utilized as a transparent electrode supporting the motility of biomotors. Conducting polymer patterns doped with adenosine triphosphate (ATP) were fabricated on the graphene and utilized for the fast release of ATP by electrical stimuli through the graphene. The controlled release of biomotor fuel, ATP, allowed us to control the actin filament transportation propelled by the biomotor in real-time. This strategy should enable the integrated nanodevices for the real-time control of biological motors, which can be a significant stepping stone toward hybrid nanomechanical systems based on motor proteins.

A biofuel cell with electrochemically switchable and tunable power output

An electroswitchable and tunable biofuel cell based on the biocatalyzed oxidation of glucose is described. The anode consists of a Cu(2+)-poly(acrylic acid) film on which the redox-relay pyrroloquinoline quinone (PQQ) and the flavin adenine dinucleotide (FAD) cofactor are covalently linked. Apo-glucose oxidase is reconstituted on the FAD sites to yield the glucose oxidase (GOx)-functionalized electrode. The cathode consists of a Cu(2+)-poly(acrylic acid) film that provides the functional interface for the covalent linkage of cytochrome c (Cyt c) that is further linked to cytochrome oxidase (COx). Electrochemical reduction of the Cu(2+)-poly(acrylic acid) films (applied potential -0.5 V vs SCE) associated with the anode and cathode yields the conductive Cu(0)-poly(acrylic acid) matrixes that electrically contact the GOx-electrode and the COx/Cyt c-electrode, respectively. The short-circuit current and open-circuit voltage of the biofuel cell correspond to 105 microA (current density ca. 550 microA cm(-2)) and 120 mV, respectively, and the maximum extracted power from the cell is 4.3 microW at an external loading resistance of 1 kOmega. The electrochemical oxidation of the polymer films associated with the electrodes (applied potential 0.5 V) yields the nonconductive Cu(2+)-poly(acrylic acid) films that completely block the biofuel cell operation. By the cyclic electrochemical reduction and oxidation of the polymer films associated with the anode and cathode between the Cu(0)-poly(acrylic acid) and Cu(2+)-poly(acrylic acid) states, the biofuel cell performance is reversibly switched between "ON" and "OFF" states, respectively. The electrochemical reduction of the Cu(2+)-polymer film to the Cu(0)-polymer film is a slow process (ca. 1000 s) because the formation and aggregation of the Cu(0)-clusters requires the migration of Cu(2+) ions in the polymer film and their reduction at conductive sites. The slow reduction of the Cu(2+)-polymer films allows for the controlling of the content of conductive domains in the films and the tuning of the output power of the biofuel cell. The electron-transfer resistances of the cathodic and anodic processes were characterized by impedance spectroscopy. Also, the overall resistances of the biofuel cell generated by the time-dependent electrochemical reduction process were followed by impedance spectroscopy and correlated with the internal resistances of the cell upon its operation.

Biostability of electrically conductive polyester fabrics: an in vitro study

The biostability of a series of polypyrrole (PPy)-coated polyester fabrics was investigated in an in vitro model. PPy-coated sample fabrics were incubated in saline at 37 degrees C for 1 and 2 weeks. After each period of incubation, the surface electrical resistivity of the sample fabrics was measured to monitor the changes caused by the incubation. Redoping was then performed by immersing the sample fabrics in a 1N HCl solution at room temperature for 30 min, which was followed by another measurement of the surface resistivity. The surface morphology of the sample fabrics was observed by scanning electron microscopy. The surface chemical composition of the fabrics and the oxidation of nitrogen in PPy were measured with X-ray photoelectron spectroscopy. The surface electrical resistivity of the PPy-coated fabrics was found to increase with the progress of incubation, which was mainly caused by dedoping and uptake of oxygen. This increase was nonlinear and accelerated with time. The surface resistivity of most of the samples was retained in the range of 10(3)-10(4) Omega/square after 1 week of incubation, which was considered suitable for short-term electrical stimulation applications. Physical deterioration represented by the cracking and delamination of the PPy coating was occasionally observed on the sample fabrics showing the most significant increase of resistivity. Further improvement of the stability of conductivity is highly desirable.

Tissue reaction to polypyrrole-coated polyester fabrics: an in vivo study in rats

Electrically conductive polypyrrole is very attractive for tissue engineering because of its potential to modulate cellular activities through electrical stimulation. However, its in vivo behaviors have not been fully studied. This paper investigates the in vivo biocompatibility and biostability of PPy-coated polyester fabrics. Three PPy-coated fabrics were prepared using phosphonylation (PPy-Phos), plasma activation (PPy-Plas), and plasma activation plus heparin treatment (PPy-Plas-HE). Virgin and fluoropassivated fabrics (F-PET) were controls. The specimens were implanted subcutaneously in the back of rats for 3-90 days, then harvested and processed for enzymatic, histological, and morphological analyses. A noninvasive MRI method was used to continuously monitor the inflammation. The level of acid and alkaline phosphatase showed a similar or a less intensive cellular reaction by the PPy-coated fabrics, when compared to the controls. Histology supported the enzymatic results and showed a fast collagen infiltration at 28 days for the PPy-Phos fabric. MRI reported an overall decrease of inflammation over time, with the PPy-coated fabrics showing a similar or mild inflammation in contrast to the non-coated fabrics. PPy clusters and excessive PPy laminary coating on the PPy-Plas and PPy-Plas-HE were lost with the implantation. This experiment suggests a similar in vivo biocompatibility of the PPy-coated and noncoated polyester fabrics and the importance of achieving a thin, uniform PPy coating.

In vitro biocompatibility study of electrically conductive polypyrrole-coated polyester fabrics

This study investigated the basic biocompatibility aspects of two types of polypyrrole (PPy)-coated polyester fabrics for possible use as vascular prostheses. These PPy-coated fabrics, PPy-Phos and PPy-Plas, were sterilized with ethylene oxide (EO) and the following characterizations were performed: surface morphology by scanning electron microscope, EO residuals analysis by the headspace method, acute systemic toxicity in the mouse model, hemolysis, blood coagulation time, viability and proliferation of endothelial cells measured with the WST-1 method, and activation of polymorphonuclear (PMN) cells indicated by the specific expression of interleukin 8 mRNA measured by reverse transcription polymerase chain reaction. Virgin polyester fabrics, expanded poly(tetrafluoroethylene) (ePTFE), and medical-grade Bionate 80A poly(carbonate urethane) were used as references in the cell culture experiments. The PPy-coated fabrics revealed different surface morphologies by showing more PPy lamina and clusters on the PPy-Plas. Neither of the PPy-coated fabrics had an adverse effect on hemolysis and coagulation time, and they did not cause any acute systemic toxicity. The EO residual level was as low as 5 ppm or less, which is considered quite acceptable. Although exhibiting a relatively low initial cell adhesion at 24 h, the two PPy-coated samples showed no cytotoxicity at 72 and 168 h. Bionate 80A and ePTFE recorded cytotoxicity at 72 and 168 h, respectively. The virgin fabrics also demonstrated a decrease of viable cells at 72 h that was not significant. The activation of PMN cells induced by both PPy-coated fabrics, the ePTFE, and the negative control was significantly lower than that induced by their respective tumor necrosis factor-alpha controls. These results therefore highlighted the potential of PPy-coated fabrics for use as cardiovascular prostheses. It was suggested that cell adhesion moieties should be incorporated into the PPy/fabric composite to increase cell adhesion and subsequent cell proliferation.

Polymerization and surface analysis of electrically-conductive polypyrrole on surface-activated polyester fabrics for biomedical applications

A new synthetic route is reported for the synthesis and covalent bonding of electrically conductive polypyrrole to a poly(ethylene terephthalate) fabric. It involves a three-step process including surface phosphorylation and graft polymerization from the gaseous phase. In the first step, the fibre surfaces are activated using phosphorus trichloride. Then, 1-(3-hydroxypropyl) pyrrole is introduced and grafted to the phosphorus chloride to create an ester bond between the fibres and the pyrrole. Finally, the pyrrole-grafted fibres are dipped in an aqueous FeCl3 catalyst and exposed to pyrrole monomer vapor for the final polymerization. This last step creates an electrically conductive polypyrrole layer covalently linked to the poly(ethylene terephthalate) fibres. ESCA analysis indicates a high degree of phosphorylation and grafting of the anchor molecules. Scanning electron microscopy reveals an overall smooth and uniform surface coating of polypyrrole on the polyester fibres. The use of ATR-FTIR spectroscopy is not able to distinguish between polypyrrole-coated and non-coated fabrics because of the extremely thin polypyrrole layer. Measurements of dynamic surface wetting indicated that the polypyrrole-coated fabric is more hydrophilic than the untreated control. With values for surface resistivity in the range 10(4)-10(5) ohmz/square, such polypyrrole-coated fabrics are considered attractive candidates for biomedical applications.

Reagentless biosensors based on self-deposited redox polyelectrolyte-oxidoreductases architectures

Reagentless fructose and alcohol biosensors have been produced with a versatile enzyme immobilisation technique which mimics natural interactions and flexibility of living systems. The electrode architecture is built up on electrostatic interactions by the sequential adsorption of redox polyelectrolytes and redox enzymes giving rise to the efficient transformation of substrate fluxes into electrocatalytic currents. All investigated multilayer structures were self-deposited on 3-mercapto-1-propanesulfonic acid monolayers self-assembled on gold electrodes. Fructose dehydrogenase, horseradish peroxidase (HRP) and the couple HRP-alcohol oxidase were electrochemically connected with a cationic poly[(vinylpyridine)Os(bpy)2Cl] redox polymer (RP) interface in a layer-by-layer self-deposited architecture. The dependence of the distance on the electrochemical response of this interface was also studied showing a clear decrease in the Faradaic current when the distance to the electrode surface was increased. The sensitivities obtained for each biosensor were 19.3, 58.1 and 10.6 mA M(-1) cm(-1) for fructose, H2O2 and methanol, respectively. The sensitivity values can be easily controlled by a rational deposition and manipulation of the charge in the catalytic layers. The electrostatic assembly of the electrochemical interface and the catalytic layers resulted in integrated biochemical systems in which mass transfer diffusion and heterogeneous catalytic and electron transfer steps are efficiently coupled and can be easily manipulated.

Patterning neuronal and glia cells on light-assisted functionalised photoresists

A common photosensitive polymeric material used in semiconductor microlithography (diazo-naphto-quinone/novolak resist) was pattern-exposed with near-UV light to create carboxylic-rich areas on the polymer surface. The patterned surfaces were further functionalised via: (1) the anchorage of peptides for specific cell-attachment or cell-detachment functions; or (2) the diffusion of silicon rich chemical species to achieve the cell detachment. Pairs of antagonistic surface characteristics controlled the cell attachment: (1) amino-rich or carboxylic-rich surfaces; and (2) hydrophilic or hydrophobic surfaces; in which the former promoted the adhesion. It was found that common microlithographic materials and techniques can be upgraded to allow an effective control of the lateral organisation of the artificial arrays of neuronal and glia cells.

Interface analysis in biosensor design

In a survey, the analytical tools to characterise and optimise properties and stabilities of interfaces in thin film biosensors are discussed. After an introduction to microscopic and spectroscopic techniques and different transducers, case studies are presented. They concern bioaffinity sensors with particular emphasis on biomimetic recognition structures, catalytic sensors, transmembrane sensors, cell sensors, and the ambitious goal of addressing individual biomolecular function units.