Table of contents

Science is one of the most robust conceptual constructs developed by human beings. Theoretical physical models have been developed involving the smallest and the largest systems over the full scale of the universe. At both extremes the models are predictive and include constant interactions between components.

Life evolved from systems of intermediate size in relation to the extremes of universal scale. Life, biological organs and cells only develop functions under chemical driving conditions. Natural organs can be considered as biological devices which are very efficient at transforming chemical energy at constant temperature into functions, unlike machines' servitude to the Carnot cycle. Inside any living cell thousands of simultaneous reactions occur. Every reaction promotes changes from reactants to products with subsequent changes to hundreds of intramolecular and intermolecular interactions. Moreover, most of those reactions link conformational changes of biopolymers with ionic and electronic movement driving water flow. Chemical reactions, intermolecular and intramolecular interactions involving conformational movements are outside the possibilities of current theoretical models. Theoretical descriptions of any living cell and predictions of its behaviour when unhealthy are unavailable within our scientific models.

Actuation of natural organs such as muscles involves, moreover, the chemical reaction ATP hydrolysis—simultaneous sensing processes which provide living creatures with a perfect consciousness of both the characteristics of their mechanical movements and their interactions with their environment: they are intelligent machines.

This constitutes the proximity paradox. We have been able to develop good and predictive theoretical models for subatomic or galactic systems, far removed from our everyday surroundings. Nevertheless, we are unable to predict the behaviour of the cells and organs that constitute our life and everyday environment, when invaded by a new virus. A very expensive trial and error (still pseudo-alchemic) procedure has to be initiated to try to enable ill people to get better.

Nowadays models from chemical kinetics do not include any quantification of either changes to the molecular interactions inside the system during reaction or structural information about the conformational changes brought about by enzymes or reactive proteins. From our point of view this is one the most important scientific challenges for the 21st century, involving responses to questions related to life, health and illness. Those responses, due to the magnitude of the challenge, can only be obtained by cooperative work involving chemists, physicist, engineers, biologists and clinicians.

Figure showing the full distance inside the universe. Small and large systems are submitted as `constant physical' interactions affording quite predictive models. Life is based on chemistry giving rise to simultaneous changes on all the molecular interactions included in the system: their interpretation is outside current chemical or physical models.

Most technological advances developed by human beings are inspired by biological systems, organs, or mechanisms present in living creatures. The main difference between human technology and natural organs is the changes in chemical composition occurring inside the wet natural organ during actuation: they are reactive, soft and wet materials. Our artificial machines are constructed of dry materials that maintain a constant composition under actuation.

This is the context proposed for the consecutive World Congresses on Biomimetics, Artificial Muscles & Nano-Bio and more specifically for the IVth Congress held in Torre Pacheco, Spain, 6–9 November 2007. The papers selected for this volume of Journal of Physics: Conference Series includes: dry and wet materials, chemically reactive or physically reactive materials, organic and inorganic materials, macroscopic films and nanoparticles. Different biomimicking devices: artificial muscles and actuators, sensors, electrochromic materials, and microscopic magnetic control of fluids are described under different experimental conditions. New models, including or avoiding chemical reactions are presented here. In this way new steps are being presented in an attempt to model biomimicking materials and devices. We expect that those biomimicking devices and models will, in the future, open the way to predict the behaviour of cells.

Thanks are due to the editorial and production team of Journal of Physics: Conference Series for their continued support and management of the review and preparation process in an entirely efficient and professional manner. Thanks are due to those institutions that have contributed in different ways to the final success of the meeting: MEC, ISE, UPCT, IBERNAM and the Autonomous Government of the Murcia Region. Special thanks go to all the participants who have contributed to this volume of Journal of Physics: Conference Series who are at the forefront of progress towards the biomimetics of materials, properties and models.

Toribio Fernández Otero

This is a co-publication with Bioinspiration and Biomimetics. The bulk of the papers, after peer review, are published in Journal of Physics: Conference Series. However a selection of papers, are published separately in a special issue of Bioinspiration and Biomimetics.

Cooperation between the electrical conductivity and hygroscopic nature of conducting polymers can provide an insight into the development of a new class of electro-active polymer (EAP) actuators or soft robots working in ambient air. In this paper, we describe an 'origami' actuator fabricated by folding a sheet of conducting 'paper'. The principle lies in the electrically induced changes in the elastic modulus of a humidosensitive conducting polymer film through reversible sorption and desorption of water vapor molecules, which is responsible for amplifying a contraction of the film (∼ 1%) to more than a 100-fold expansion (> 100%) of the origami actuator. Utilizing the origami technique, we have fabricated a biomorphic origami robot by folding an electrochemically synthesized polypyrrole film into the figure of an accordion shape, which can move with a caterpillar-like motion by repeated expansion and contraction at a velocity of 2 cm min^-1.

Described are the state of the art on designing and developing a microgripper using ionic polymer metal composites (IPMCs), an electroactive material, as an actuator to grasp and manipulate micro-sized flexible and rigid objects and yet also serve as a sensor for position feedback control. IPMCs, as a material, are compliant and can work in both wet and dry environments. This makes it ideally suited for both industrial operations, e.g., building microsystems from MEMS components, as well as for a variety of bio-micromanipulation tasks, e.g., bacterium and cell handling. We derive a theoretical force model for the microgripper. The model estimates that an IPMC finger of dimensions 5mm × lmm × 0.2mm exerts a force of 85 μN when grasping a solder ball of 15mg. We experimentally measure the load carrying capacity of the IPMC microgripper. Furthermore, we show empirically that the relationship between load carry capability and the length of microgripper fingers is linear. Experiments with three different microgripper finger shapes show that load carrying performance is related to the area of the finger rather than the shape. This implies that manufacturing ease favours microgrippers with tapered fingers. Finally, we show how flexible objects (hydrogel crystals in this case) are grasped with this IPMC microgripper.

We have developed a new type of electroactive polymer actuator film that is made of composite materials consisting of carbon nanoparticles and binder polymers. The actuator film can operate in two modes of actuation, the 'charge accumulation mode,' or the 'self-heating mode.' The former operates in an electrolyte solution when the voltage is applied against a counter electrode due to the charge accumulated on the electric double layer formed at the surface of the carbon nanoparticles. The latter operates in air owing to the thermal expansion caused by Joule heating. The actuator film is easily fabricated using casting or printing methods.

Research on electromechanical characterization of non-uniformly charged IPMCs is quasi-absent. This has limited their use to only those devices where the IPMC is completely covered with electrode surfaces (uniformly charged). In this paper, we develop a theoretical study for electromechanical characterization of non-uniformly charged IPMCs. A continuum model taking into account the gravitational forces, important for large IPMCs, is presented. Based on this approach, FEM analysis of IPMC devices using Comsol Multiphysics is introduced in a very simple way. Three devices have been studied, comparing the analytical model results with those ones obtained from a FEM analysis.

Further development of mechanical devices based on conducting polymers; require a precise understanding of their mechanical response, i.e. their control, under a controlled external current. In this work, we show some results for the relation between the electrical current consumed in the electrochemical process and the mechanical work developed by a freestanding polypyrrole strip, when it is subjected to a stretching force (stress). Under these conditions, from the results obtained in this work, we observe how it results almost impossible to predict a straight relationship between mechanical work and current consumed in the electrochemical process. In addition, we will quantify the variation of the mechanical properties of the free standing polypyrrole strip associated with the oxidation state of the polymer by measuring its Young's modulus.

Drops can be moved in complex patterns on superhydrophobic surfaces using a reconfigured computer-controlled x-y metrology stage with a high degree of accuracy, flexibility, and reconfigurability. The stage employs a DMC-4030 controller which has a RISC-based, clock multiplying processor with DSP functions, accepting encoder inputs up to 22 MHz, provides servo update rates as high as 32 kHz, and processes commands at rates as fast as 40 milliseconds. A 6.35 mm diameter cylindrical NdFeB magnet is translated by the stage causing water drops to move by the action of induced magnetization of coated iron microspheres that remain in the drop and are attracted to the rare earth magnet through digital magnetofluidics. Water drops are easily moved in complex patterns in automated digital magnetofluidics at an average speed of 2.8 cm/s over a superhydrophobic polyethylene surface created by solvent casting. With additional components, some potential uses for this automated microfluidic system include characterization of superhydrophobic surfaces, water quality analysis, and medical diagnostics.

Most previous studies on H₂S were devoted to its toxic effects. However, recently there have been increasing evidences which show that endogenously generated H₂S in specific mammalian tissues has certain significant positive physiological effects such as a neuromodulator and vasorelaxant in a membrane receptor-independent manner. In order to know the functions of endogenous H₂S, low concentration and high accuracy measurement of H₂S is a must. Furthermore, this measurement is desired to be real-time and non-invasive. It is reported that low concentration and nano quantity of H₂S can be detected in water solutions and sera using carbon nanotubes with the fluorescence by confocal laser scanning microscopy. However, because of the Brownian motion of the small particle (carbon nanotube), a control system must be developed to track the movement of the particle in fluids. In this paper, we present a study to track a carbon nanotube which absorbs H₂S in water or serum using a Raman microscope or confocal laser scanning microscope. In particular, we developed a novel control system for this task. Simulation has shown that our system works very well.

Among the different ways of synthesizing fiber and tubular micro and nanostructures, some top-down methods resort to electro-hydrodynamic forces to smoothly stretch liquids interfaces down to such small size scales. The well-known electrospinning technique, commonly used to fabricate micro and nanofibers of a broad variety of materials, is now expanded to fabricate coaxial fibers upon the generation of electrified coaxial jets instead of single jets. We briefly report different types of micro and nano structures that may be fabricated with this new technique termed co-electrospinning.

Carbon nanotube has a high potential to be used as a biosensor and drug carrier. However, its binding behaviour with proteins needs to be studied before the full potential of carbon nanotube in biological studies can be realized. Although many studies have been conducted to characterize the affinity of functionalized carbon nanotube to various types of proteins, our present study for the first time reported that hemoglobin can bind with non-functionalized carbon nanotube, and this binding can be identified by Raman spectrum. Further, this binding has not change, Raman luminescence with specific excitation and emission wavelengths. The immediate application of these findings is to use non-functionalized carbon nanotube as a biosensor to measure H₂S in blood in which hemoglobin takes about 37% of the total blood volume. Other potential uses of non-functionalized carbon nanotube to bind selective groups of proteins are also hinted.

A functionalized nanohydrogels have been synthesized by two step procedure. The first step implies an inverse microemulsion polymerization of p-nitro phenol acrylate (NPA) and N-isopropylacrylamide (NIPA) using Aerosol (AOT) as a surfactant and ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent. The polymerization reaction was performed in presence of an oil-soluble salt to reduce the dimensions of the micellar diameter. The second step includes a chemical functionalization by nucleophilic substitution reaction over the carbonyl groups. The average particle diameter and the particle size distribution of the nanohydrogels were measured in acetone at 25°C by quasielastic light scattering (QLS) showing average diameter of 22 nm. The nanogels were characterized by FTIR-ATR, ¹HNMR, UV-vis spectroscopy and DSC.

The dual polymer configuration is commonly used when constructing electrochromic devices (ECDs) due to the expected electrochemical stability and enhanced optical properties. In this configuration, two different polymers are used which are optically complementary. Herein we report the construction and characterization of dual-type ECDs using poly(3, 4-ethylenedioxythiophene) (PEDOT) and poly[3, 6-bis(2-(3, 4-ethylenedioxy)thienyl)-N-methylcarbazole] (PBEDOT-NMCz) as the two complementary electrochromic polymers for the device. A variety of gel electrolyte solutions were prepared and evaluated for these devices. The use of ionic liquids within these gels imparted interesting properties, including long lifetimes, and thermal stability of devices. Switching speeds for the various devices, as well as optical contrasts, were also obtained for the gel electrolytes containing different amounts of ionic liquid as plasticizer.

Novel resistive gas sensors based on single-walled carbon nanotube (SWNT) networks as the active sensing element nave been investigated for gas detection. SWNTs networks were fabricated by airbrushing on alumina substrates. As-produced- and Pd-decorated SWNT materials were used as sensitive layers for the detection of NO₂ and H₂, respectively. The studied sensors provided good response to NO₂ and H₂ as well as excellent selectivities to interfering gases.

The elaboration of a sensitive taste sensor for discrimination of different soft drinks is very important in food industry. The short review of taste sensors described in the literature is presented. Two types of potentiometric taste sensors, one with lipophilic compound-polymer membranes (ISE) and the other with lipid polymer membrane and a conducting polymer film (All solid state electrode, ASSE) were tested in appropriate taste solutions. Five channel ISE sensor was examined in acid, sour and sweet solutions. This sensor was sensitive to bitter and sour substances and not too sensitive to sucrose concentration. It was successfully used for discrimination of different kind of soft drinks. Four channel ASSE sensor was examined in sour solutions. It was found that stability and sensitivity of ASSE are lower than ISE. Therefore, it seems that the previous one cannot be applied in taste sensor.

Electrochromic nanofibers of conducting polymer (terthiophene) have been deposited over a conventional paper sheet by means of the electrospinning technique, and subsequently photopatterned by means of UV radiation. The synthesis of a processable precursor copolymer with a norbornylene matrix and pendant units of terthiophene makes the electrospinning process available, and allows for chemical or electrochemical crosslinking of the precursor copolymer to obtain a conducting polymer. The inclusion of photocrosslinkable units (methacrylate) in the precursor copolymer also allows for photopatterning of the material. This was applied to obtain patterns on the paper which can be chemically oxidized or reduced resulting in electrochromic characters. SEM images of the conducting polymer nanofibers together with the cellulose fibers show how these materials can be attached to textile fibers, adding new functionalities that are reminiscent of the chameleonic abilities of some living creatures.

In this study, slow relaxation (SR) associated with the electroreduction of polyaniline (PAn) films during polarization to high cathodic potentials was investigated by cyclic voltammetry technique. Anodic voltammetric currents were used as experimental variable to indicate the relaxation occurring in PAn films deposited electrochemically on the Pt electrode surface.

The dependence of SR on polymer film thickness, waiting potential, and mobility of the doped anion was investigated.

Percolation threshold potential for heteropolyanion doped PAn was estimated to be between 150 and 200 mV depending on polymer thickness on the electrode surface.

A new model of the conducting to insulating conversion is described by the percolation theory and mobility gap changes during the process.

The oxidation kinetics of films of the conducting polymer PEDOT-C1O4 after electrochemical reduction by polarization at increasing cathodic potential was studied by potential steps. The response i/t presents a maximum at intermediate oxidation times. At the maximum the reaction occurs under chemical kinetic control following the expected current variations from the Chemical and Electrochemical Kinetics, when reactant concentrations or temperatures are changed. The obtained activation energy of the oxidation present two ranges as a function of the cathodic potential of prepolarization: constant values after prepolarization at low cathodic potentials and a lineal variation after prepolarization at increasing high cathodic potentials. According with the conformational relaxation model during electrochemical reduction the polymer shrinks, closes and packs the conformational structure. The activation energy for the subsequent oxidation includes two terms: the constant chemical activation energy and the conformational energy required to relax the packed polymeric structure. The conformational energy only appears after prepolarization at more cathodic potentials than the closing potential where more packed conformations were obtained. The conformational activation energy accounts the energetic requirements to relax and unfold the polymeric chains generating the required free volume to lodge balancing counterions; meanwhile the chemical activation energy accounts the energetic requirements for the electrochemical reaction to occur.