The science and technology of the 21st century will rely heavily on the development of new materials. Such materials are expected to be innovative with regards to structure, functionality, and design. One concept in achieving this goal is what has been termed 'smart materials.' A smart material is defined as a material which has been atomically or molecularly engineered in such a way that the microstructure itself is imbued with embedded sensors, actuators, and control mechanisms, giving it the capability of sensing and responding to external stimuli in a predetermined and controlled fashion. Programs in this area have involved technological advances in a number of scientific disciplines inclusive of materials science, chemistry, biotechnology, molecular electronics, nanotechnology, etc. These have encompassed research themes into the design of polymeric materials which are capable of altering their mechanical and electrical properties when exposed to specific molecular species, the synthesis of amphiphlic molecules with easily modified ferroelectric, photochromic and nonlinear properties, the design of stress sensitive molecules capable of monitoring damage and redistributing stresses in composites, and the merging of biological and chemical technologies to create assemblies with signal transduction properties. This presentation highlights some of these activities.

The development of novel conducting polymer hydrogel composites has been pursued in the course of this work. It has been found that conducting polymers can be formed electrochemically within hydrogel structures. This enables the dimensions and shape of conducting polymer based structures to be easily modified. The resulting composites retain the properties of the hydrogels and also are electroactive. Preliminary work suggests that these structures show enhanced performance when used as electromolecular or electromechanical actuators.

Liquid crystal/polymer network composites are formed by mixing small amounts of mesogenic monomers and liquid crystals. The monomers are then photo-polymerized in liquid crystalline phases. The polymer networks, whose orientation is controlled by the surface alignment or external field, are anisotropic. Afterwards, we use the resultant ordered networks, influenced by the orientation of liquid crystals, to stabilize cholesteric textures and develop three different types of displays. A tunable chiral material (TCM), whose chirality can be photochemically altered by exposing the materials to UV light, is integrated into the production of a multicolor reflective cholesteric display.

An array of polymer grid triodes (PGTs) connected through a common grid functions as a 'plastic retina' which provides local contrast gain control for image enhancement. This device, made from layers of conducting polymers, functions as an active resistive network that performs center-surround filtering. The PGT array with common grid is a continuous analog of the discrete approach of Mead, with a variety of fabrication advantages and with a significant saving of 'real estate' within the unit cell of each pixel.

Reversible change in optical properties of ionic polymeric gels, 2-acrylamido-2-methylpropane sulfonic acid (PAMPS) and polyacrylic acid plus sodium acrylate cross-linked with bisacrylamide (PAAM), under the effect of an electric field is reported. The shape of a cylindrical piece of the gel, with flat top and bottom surfaces, changed when affected by an electric field. The top surface became curved and the sense of the curvature (whether concave or convex) depended on the polarity of the applied electric field. The curvature of the surface changed from concave to convex and vice versa by changing the polarity of the electric field. By the use of an optical apparatus, focusing capability of the curved surface was verified and the focal length of the deformed gel was measured. The effect of the intensity of the applied electric field on the surface curvature and thus, on the focal length of the gel are tested. Different mechanisms are discussed; either of them or their combination may explain the surface deformation and curvature. Practical difficulties in the test procedure and the future potential of the electrically adaptive and active optical lenses are also discussed. These adaptive lenses may be considered as smart adaptive lenses for contact lens or other optical applications requiring focal point undulation.

The thermomechanical properties of a thin film of shape memory polymer of polyurethane series were investigated experimentally. The results were summarized as follows: (1) Modulus of elasticity and yield stress are high below glass transition temperature T_g and low above T_g. The value of loss tangent is large in the vicinity of T_g. (2) The stress-strain curves vary significantly in the early cycles but slightly thereafter under cyclic deformation above T_g. (3) During the heating process after loading above T_g followed by unloading below T_g, strain is recovered in the vicinity of T_g. (4) Shape fixity with loading above T_g followed by unloading below T_g does not vary under thermomechanical cycling. (5) Creep strain is recovered after unloading above T_g. Creep residual strain below T_g is recovered in the vicinity of T_g during the heating process. (6) About a half of initial stress relaxes after a certain duration of time. Several applications of the polymers were introduced.

The dielectric properties of piezoelectric materials are important in many applications of piezoelectric materials, such as active structural control, underwater sonar, dielectric insulator, etc. The experimental measurement of dielectric properties of materials is usually done using commercial electrical impedance analyzer, LCR meter, or network analyzer, such as an HP 4194 impedance analyzer. The excitation voltage of these commercial analyzers is generally very low, e.g., 1.5 volts rms or under. However, the dielectric properties of piezoelectric materials (both dielectric constant and dielectric loss factor) can be very sensitive to the level of applied electric voltage (field). Since virtually all the applications of piezoelectric materials are under high field, it is important to develop measurement techniques to determine the voltage dependent dielectric material properties. This paper introduces a high- voltage/high-power electromechanical impedance analyzer developed based on a commercial electrical power analyzer/phase angle multimeter. The developed analyzer is then used to determine the dielectric constant and dielectric loss factor of G1195 PZT. The measurement results, dielectric constant and loss factor as a function of applied electric field, frequency, and ambient temperatures, are presented in the paper.

Fine scale lead zirconate titanate (PZT) fibers were fabricated from sol-gel processed viscous 'sol' using spinning methodology developed for the continuous production of glass and carbon fibers. Subsequent drying and firing at temperatures above 700 degrees Celsius resulted in phase pure perovskite fibers with diameters ranging from 30 to 70 micrometers. The dense fibers were comprised of sub-micron grains at sintering temperatures below 1000 degrees Celsius, growing to 2 - 3 micrometers at 1200 degrees Celsius. The dielectric properties of the sol-gel derived fibers were comparable with that of bulk ceramics for both undoped and modified PZT compositions. Relevant to mechanical properties, however, the fine scale PZT fibers exhibited fracture strengths on the order of 50 MPa, well below that of structural fiber materials, e.g. Al₂O₃, limiting their potential use in active structural composites.

Optomechanical actuation was achieved reversibly using highly oriented pyrolytic graphite intercalated with bromine (1.9 mol% Br₂). White light from a 150 W tungsten-halogen lamp was used for optomechanical switching. The displacement was approximately 4 micrometers and occurred only along the c-axis of the graphite. The rise and fall times were approximately 15 s. The origin of the optomechanical effect is the reversible exfoliation of the near surface region of the intercalated graphite.

Electrorheological (ER) fluids are fine semi-conducting particles in a non-conducting carrier fluid, which can alter their observed physical characteristics upon application of an external electric field. They are sometimes referred to as 'smart materials' and would appear to be of scientific and industrial interest. Theoretical responSe of a two degree of freedom system utilizing an ER damper is shown. This model could be representative of a quarter vehicle system, or a vibration absorber.

Ti-Ni shape memory alloys with nearly equiatomic compositions were made by three types of production methods, i.e., rolling, drawing and sputtering methods. These methods were used for making thin plates 0.1 mm thick, thick and thin wires 1.0 mm and 0.08 mm in diameter, and thin films 0.007 mm thick, respectively. These specimens were annealed at 673 K, 773 K, and 873 K in order to investigate the affect of annealing temperature on the shape memory characteristics in each specimen. The shape memory characteristics were compared among these specimens in order to investigate the effect of the production method.

The thermomechanical properties of shape memory effect and superelasticity due to the martensitic transformation and the R-phase transformation of TiNi shape memory alloy were investigated experimentally. The transformation line, recovery stress and fatigue property due to both transformations were discussed for cyclic deformation. The thermomechanical properties due to the R-phase transformation were excellent for deformation with high cycles.

Artificial muscles made with polyacrylonitrile (PAN) fibers are traditionally activated in electrolytic solution by changing the pH of the solution by the addition of acids and/or bases. This usually consumes a considerable amount of weak acids or bases. Furthermore, the synthetic muscle (PAN) itself has to be impregnated with an acid or a base and must have an appropriate enclosure or provision for waste collection after actuation. This work introduces a method by which the PAN muscle may be elongated or contracted in an electric field. We believe this is the first time that this has been achieved with PAN fibers as artificial muscles. In this new development the PAN muscle is first put in close contact with one of the two platinum wires (electrodes) immersed in an aqueous solution of sodium chloride. Applying an electric voltage between the two wires changes the local acidity of the solution in the regions close to the platinum wires. This is because of the ionization of sodium chloride molecules and the accumulation of Na⁺ and Cl^- ions at the negative and positive electrode sites, respectively. This ion accumulation, in turn, is accompanied by a sharp increase and decrease of the local acidity in regions close to either of the platinum wires, respectively. An artificial muscle, in close contact with the platinum wire, because of the change in the local acidity will contract or expand depending on the polarity of the electric field. This scheme allows the experimenter to use a fixed flexible container of an electrolytic solution whose local pH can be modulated by an imposed electric field while the produced ions are basically trapped to stay in the neighborhood of a given electrode. This method of artificial muscle activation has several advantages. First, the need to use a large quantity of acidic or alkaline solutions is eliminated. Second, the use of a compact PAN muscular system is facilitated for applications in active musculoskeletal structures. Third, the PAN muscles become electrically controllable and therefore the use of such artificial muscles in robotic structures and applications becomes more feasible. A muscle is designed such that it is exposed to either Na⁺ or Cl^- ions effectively. Muscle contraction or expansion characteristics under the effect of the applied electric field are discussed.

Two different types of biomolecular network systems have been designed to respond to the environmental conditions. One is the calmodulin and enzyme (phosphodiesterase, PDE) that activates phosphodiesterase through the conformational change in responding calcium ion. Calmodulin was genetically engineered to be fused with glutathione-S-transferase (GST). Calmodulin/GST fused protein was self-assembled on the gold surface through glutathione. The calmodulin/GST protein layer exhibited an ability to modulate the PDE activity in a solution phase depending on the calcium ion concentration. The other is the engineered gene structure that produces firefly luciferase in responding environmental pollutants. A TOL plasmid, encoding a binding protein xyl R for xyline and a marker enzyme firefly luciferase, has been implemented in a bacterial cell. The whole cell responded to environmentally hazardous substances such as xylene in emitting light.

In conventional biochemistry, there has been no method to allow space-resolved access to a particular position in a molecule. This is due partly to a lack of the molecular manipulation method. A chain like macromolecule, such as DNA, takes randomly coiled conformation and fluctuates due to Brownian motion. Hence, to allow external access, it has to be immobilized with a proper conformation first. The authors use high-intensity high-frequency electric field (less than or equal to 10⁶ V/m, approximately equals 1 MHz) created in micro-machined electrodes to (1) stretch a flexible molecule, (2) align parallel to the field, and/or (3) position onto a substrate either electrically or with the use of molecular bindings. It has been shown that DNA is stretched to full length (0.34 nm per base) under the electrostatic field. Once stretch-and- positioned, position-dependent modifications become possible. It is demonstrated that (1) a stretched DNA can be cut at arbitrary position by ultra-violet laser beam, (2) local temperature rise created by a laser manipulated-and-heated microbead induces pin-point conformational change of a bacterial flagellum ('tail'). The spatial resolution enabled by the electrostatic stretch-and-positioning will find applications not only in biochemical assays, in particular DNA sequencing, but also in the basic research of biomolecular interactions.

Cell membranes play a vital role in energy conversion, information processing and signal transduction. This is owing to the fact that most physiological activities involve lipid bilayer- based receptor-ligand interactions. Some of the outstanding examples are ATP synthesis, ion transport, antigen-antibody binding, and gated channels. One approach to study these interactions in vitro is facilitated by employing artificial BLMs (bilayer lipid membranes). Our current efforts have been focused on ion and/or molecular selectivity and specificity using recently available self-assembled BLMs on solid support (i.e. s-BLMs) which, with their enhanced stability, greatly aid in research areas of membrane biochemistry, biophysics, and cell biology as well as in biosensor designs and molecular devices development. In this report, our recent work along with the experiments done in collaboration with others on s-BLMs are presented.

The development of enzyme electrodes plays a major role in the performance of an electrochemical biosensor. In this paper, we describe two generic methods for efficient immobilization of enzymes or biomolecules at the electrode surface. These methods are based on physical entrapment of the enzymes during biochemical polymerization of phenols and electrochemical copolymerization of aromatic diamines with enzymes that are covalently coupled to the monomer. Both of these techniques have proven to be chemically mild and provide efficient polymer matrices for the fabrication of enzyme electrodes. Enzymes including horseradish peroxidase, alkaline phosphatase and glucose oxidase have been immobilized in these polymeric matrices and used for electrochemical as well as colorimetric detection of various substrates. Response times of the order of 5 - 10 seconds and sensitivities of the order of mM have been achieved with these electrodes. The use of these immobilization techniques towards the development of microelectrode arrays for multianalyte sensors is also discussed.

New biocomposites with dynamically active properties were synthesized containing the conducting electroactive polymer, polypyrrole, dextran sulphate and a range of proteins. These composites have a hydrophilic matrix with a high water content and confer on the conducting polymer several properties useful in the design of new 'smarter' biomaterials. The composite is an excellent surface for the culture of mammalian cells. Inclusion of the polyelectrolyte also allows incorporation of protein and control of its release by reducing the polypyrrole backbone. These properties were exploited to incorporate nerve growth factor into a composite of polypyrrole and sulphated polysaccharide and after reduction to cause release of the nerve growth factor and thereby stimulate phaeochromocytoma cells to differentiate. Inclusion of polyelectrolyte also allows the incorporation of whole relatively intact cells into a polymer composite. This was demonstrated by the incorporation of human erythrocytes into the composite. The electrochemical properties of the composite were maintained raising the possibility that they could be used as the basis of an electrochemical biosensor for the detection of blood cell antigens. These new composite polymers showing protein release could be used not only as vehicles to deliver proteinaceous pharmaceuticals but also to communicate with mammalian cells during critical phases of their growth and development. The immobilization of mammalian cells in the composites could not only form the basis of biosensors but can also be used for many other applications where immobilized cells are required. Moreover the ability to control the dynamic properties of the composite and possibly the cells within it could be exploited to advantage.

Oriented assembly and interfacial electron transfer of flavin coenzymes on titanium dioxide (TiO₂) electrodes have been studied to develop the smart enzyme sensors or reactors. It was demonstrated that FMN and FAD were chemically adsorbed via phosphate moiety on TiO₂ surface in weak acidic solutions to make monolayers. Quasi reversible slow electron transfer was observed on the FMN or FAD-adsorbed TiO₂ electrodes. It was further demonstrated that the FMN-assembled TiO₂ electrode electrochemically catalyzed the oxidation of NADH. The FMN-assembled TiO₂ was then combined with some dehydrogenases and NADH to perform amperometric sensing for enzyme substrates. The results suggest that the assembled flavin coenzyme might be promising for a nanospace interface to achieve electrochemical communication between redox active biomolecules and the metal oxide electrodes.

In this paper a Nafion^TM polyelectrolyte ion-exchange membrane (IEM) was used as a propulsion fin for robotic swimming structures such as a boat or fish-like object swimming in water or aqueous medium. The Nafion membrane was chemically plated with platinum. The resulting membrane was cut in a strip to resemble a fish-like caudal fin for propulsion. A small function generator circuit was designed and built to produce approximately plus or minus 2.0 V amplitude square wave at varying frequency up to 50 Hz. The circuit board was mounted on a buoyant styrofoam shaped like a boat or a tadpole. The fin was attached to the rear of the boat. By setting the signal frequency to the desired value and thereby setting the frequency of bending oscillation of the membrane, a proportional forward propulsion speed could be obtained. The speed was then measured using a high speed camera. Several theoretical hydrodynamic models were then presented to characterize speed-frequency of the forward motion using available theories on biological fish motion. The results were compared to experimental data which showed close agreement. It turned out that the forward speed of the object was directly proportional to the product of frequency and amplitude of the fin oscillation as in biological fishes. This relation was further simplified by keeping the voltage constant and therefore amplitude of the oscillation. The proportionality constant could be measured for a known geometry of the fin-boat assembly and reactivity of the Nafion membrane used. The system as a whole presented an autonomous robotic swimming structure with frequency modulated propulsion to investigate application of polyelectrolyte hydrogel membranes and their effect on hydrodynamic behavior of an undulating swimming object. As in fishes the thrust force of the robot was generated by evolution of vortices on the sides of the undulating fin. For a constant forward speed, this thrust is equal to the drag force due to geometry and skin friction of the swimming robot. It was observed that regardless of the laminar or turbulent flow pattern around the robot the relation between speed and frequency holds. This research was a proof of concept for investigating fish propulsion known best for undulatory swimming motion, using polyelectrolyte ion-exchange-metal composite membrane.

The effect of a porous sol-gel matrix on the optical limiting characteristics of chloroaluminum phthalocyanine (CAP) has been investigated. Excited state singlet-singlet absorption processes are found to be responsible for the fast response characteristics (ps to ns) for CAP doped xerogel glasses. Subsequent inter-system crossing and triplet-triplet absorption processes are responsible for the persistent absorbance (ns to ms) determined by the ISC rate and the phosphorescent lifetime of CAP. Inhomogeneous spectral broadening of CAP in the xerogel matrix relative to alcohol solutions was found to have a significant affect on the relative linear (i.e. ground state) versus non-linear (i.e. optically induced excited state) absorption processes. In addition, the faster absorption recovery observed for CAP in a silica xerogel relative to ethanol solution was attributed to an increased rate of electronic to vibrational internal conversion in the xerogel matrix. Porous xerogel glasses doped with sensor chromophores have also been in investigated as a novel cladding for fiber optic chemical sensor devices. The lower refractive index of the sol-gel film makes it a suitable cladding material while the porous channels allow analytes to diffuse into the evanescent field region where they are detected by changes in the photophysics of analyte sensitive chromophores.

We report new results on continuous wave Nd:YAG laser deposition of Cadmium Sulfide (CdS) thin films. Cadmium Sulfide has useful piezoelectric, optoelectric, photo-conductive and semiconductive properties. CdS films have been deposited on various substrates including Soda-lime silicate glass (SLS), NaCl, Alumina (corundum) and copper coated formvar. The thin films were analyzed using x-ray diffraction, SEM, EDS, TEM, and UV/visible transmission spectra.

It is well known that light has the ability to carry large amounts of information by virtue of its high intrinsic bandwidth and transmission speed. We report on a new class of mechanical fiber devices that are powered by light. In particular, we show that a sensor, logic unit, and actuator function can be built into a mesoscopic polymer optical fiber: The stress sensor converts stress to light, the logic element manipulates the light according to a preprogrammed response, and the actuator provides mechanical displacement. A device that combines all three of these devices into a single monolithic unit can be designed to perform many different smart mechanical and optical logic functions. Furthermore, because optical devices use no electronic components, they allow for highly interconnected architectures of multiple units that result in ultrasmart operation. Such associations of devices, when embedded in a host material, would form an ultrasmart material. We report on the multistable operation of a highly miniaturized vibration stabilizer in a polymer fiber and show that it has an ultrafast photomechanical response. The theory behind the response is also discussed.

The smart materials based on spatial modulation of the chemical nature of gels have been synthesized. The modulation is achieved by interpenetrating only part of one gel network with another gel network. Therefore, these gels have an internally heterogeneous, or modulated structure. The simplest modulated structure is a bigel. The bending of the bigel has been studied as a function of temperature. A theoretical model has been used to analyze the bending stress in the bigels. A variety of shapes, including sinusoidal and spiral ones, of the gels at various temperatures can be obtained by designing the modulation pattern of the system. The novel gel functions obtained from the modulation method are based on the fact that the volumes of different gels are sensitive to different environmental aspects.

The combination of sensing and actuating technologies within composite structures without affecting their structural performance is a major problem in the development, and acceptance, of smart materials technologies. A technique has been developed which uses a woven polyester cloth material, patterned with thin, integral, conductors to create a flexible, composite compatible, method of distributing electrical power throughout a structural panel. The cloths can be considered as printed circuit boards for inclusion within composite structures. It is capable of distributing power throughout a structure in a predetermined, controlled manner. This allows embedded components to be accurately positioned and many external connections to be made to the structure, via a PCB like connector, at a convenient position. The technique therefore considerably simplifies the construction of complex systems. The technology is demonstrated with reference to a piezoelectric actuated composite structure.

Presented are new definitions and interpretations for smartness and intelligence associated with materials, structures, and material systems (MS & MS). These newly proposed definitions complement and augment the present notion of smart and/or intelligent materials, structures and material systems, as accepted by our scientific community. These new definitions numerically quantify the concepts of smartness and intelligence for materials, structures and material systems. In this context amino acid sequences and structures such as proteins are proposed to be the smartest material family and are given an MSQ of 1000. Correspondingly, ribonucleic acid sequences such as RNA and DNA macromolecular assemblies and structures are proposed to be the most intelligent material family and are given an MIQ of 1000. In the same category the proteins are given an MIQ of about 700. Ionic polymeric gels, shape memory alloys, electromagnetic (electrostrictive, piezoelectric, ferroelectric, ferromagnetic) materials, electrorheological fluids and magnetorheological fluids are then categorized under this hierarchy of smart/intelligent materials with MSQs and MIQs of smaller values. A similar classification is also applied to smart/intelligent structures with reference to simple cells such as bacteria and viruses such as T4 Bacteriophages. A number of examples are presented and the corresponding MSQs and MIQs are estimated to show that materials, structure and material systems can truly be numerically categorized in connection with their smartness and intelligence and thus be compared with biological and botanical structures and material systems.

The relationship between strain and the fractional increase in electrical resistance ((Delta) R/R_o) of piezoresistive polyether-sulfone-matrix composite strain sensors was found to be much more linear and less noisy when the electrically conducting filler was 0.1 micrometer-diameter carbon filaments rather than the conventionally used 10 micrometer- diameter carbon fibers. For the fiber composite, the non-linearity manifested itself as (Delta) R/R_o increasing reversibly with increasing compressive strain -- an effect opposite to and occurring on top of piezoresistivity. This effect was absent in the filament composite. Furthermore, the percolation threshold was lower for the filament composite than the fiber composite. For both filament and fiber composites, (Delta) R/R_o became more negative as cycling progressed up to approximately 10 cycles and then stabilized, though the effect was more significant for the latter.

Real-time monitoring of fatigue damage and dynamic strain in a continuous unidirectional carbon fiber polymer-matrix composite by longitudinal electrical resistance measurement was achieved. The resistance R decreased reversibly upon tensile loading in every cycle, thus providing dynamic strain monitoring. The peak R in a cycle irreversibly increased as fatigue damage occurred, due to fiber breakage. At 55% of the fatigue life, the peak R started to increase in spurts. At 89% of the fatigue life, the peak R started to increase continuously from cycle to cycle, but gradually. At 99.9% of the fatigue life, the peak R started to increase rapidly, both continuously and in spurts. The last spurt occurred at 99.997% of the fatigue life.

The influence of different factors (structure of a film-forming solution, the content ofa polymer, a method of introducing of a polyacid and its concentration, the moisture content of a film and heat treatment) on the formation of sensors based on polyvinyl alcohol (PVA)-heteropolyacid composites is examined. Such materials are sensitive to temperature and an electric field. Different sensitivity of films is associated with the formation of intermolecular complexes of different structure, including those containing water molecules. The complex fonnãtion depends on the process conditions. It is established that the complexation leads to the formation of associates and to an increase in the molecular mobility of macromolecules and their fragments. Rheological, optical and dielectric methods have been employed to evaluate the structure and properties of the thus obtained fluids and the films produced on their basis. Keywords: composites, complexes, associates, films, polyvinyl alcohol (PVA), heteropolyacids, sensors, technologies.

We report work on the fabrication of smart materials with two unique strategies: (1) self- assembly and (2) laser stereolithography. Both methods are akin to the processes used by biological systems. The first one is ideal for pattern development and the fabrication of miniaturized units in the submicron range and the second one in the 10 micrometer to 1 mm size range. By using these miniaturized units as building blocks, one can also produce smart material systems that can be used at larger length scales such as smart structural components. We have chosen to focus on two novel piezoceramic systems: (1) high-displacement piezoelectric actuators, and (2) piezoceramic hydrophone composites possessing negative Poisson ratio matrices. High-displacement actuators are essential in such applications as linear motors, pumps, switches, loud speakers, variable-focus mirrors, and laser deflectors. Arrays of such units can potentially be used for active vibration control of helicopter rotors as well as the fabrication of adaptive rotors. In the case of piezoceramic hydrophone composites, we utilize matrices having a negative Poisson's ratio in order to produce highly sensitive, miniaturized sensors. We envision such devices having promising new application areas such as the implantation of hydrophones in small blood vessels to monitor blood pressure. Negative Poisson ratio materials have promise as robust shock absorbers, air filters, and fasteners, and hence, can be used in aircraft and land vehicles.

The orb-web weaving spiders produce a broad range of high performance structural fibers (i.e. silks) with mechanical properties that are superbly matched to their function. Our interest in these materials stems both from an interest in the biology of the spiders and the design of their webs and also from a desire to discover principles of mechanical design of protein-based structural materials that can guide the development of novel bio-engineered materials. All spiders produce silks, but the orb-web weaving spiders are unique in their ability to produce seven different silks, each from distinct gland/spinneret complexes. Considering the wide diversity of spider species, there is likely to be an enormous range of material properties available in spider silk. However, at present, we only have information on two species of spiders, and only two of their seven silks have been studied in any detail. These are: (1) the silk produced by the major ampullate gland, which forms the safety-line or dragline of the spider and also is used to form the frame of its orb-web, and (2) the viscid silk produced by the flagelliform gland, which forms the glue-covered catching spiral of the web. In this paper we describe several aspects of the mechanical design of the dragline and viscid silks produced by the spider Araneus diadematus.

Studies of major ampullate silk (MAS), especially the secretions and fibers produced by the spider Nephila clavipes (golden orb weaver), have yielded several results of potential value to the materials scientist/engineer. There are lessons to be learned about synthesis, processing and microstructural design of high-tensile polymer fibers. The 'smart' aspect of silk production in nature concerns the ability of the spider to rapidly process a concentrated, viscous aqueous solution of silk protein (stored in the gland) into water-insoluble fiber on demand. This process centers on the assembly of a shear-sensitive supramolecular liquid crystalline phase by aggregation of the solubilized globular protein molecules.

All oriented polymers (net axial orientation function greater than 0.7) possess a microfibrillar morphology and all show significant fibrillation upon failure. Typical microfibrillar dimensions are 10 Nm in diameter and of essentially infinite length. Synthetic fibers comprise the most common form of oriented polymers, and all synthetic fibers possess a hierarchical structure in the sense that they possess a structural repeat of fiber symmetry from the molecular to the macroscopic. The microstructure of synthetic fibers is comprised of crystalline and non-crystalline elements. The choice of polymer and the details of the processing conditions control the ratio of crystalline to non-crystalline units, the net orientation associated with each phase (or subphase), and the connections between them. The microstructure of the typical 100 angstrom diameter microfibril can be between them. The microstructure of the typical 100 angstrom diameter microfibril can be described as an array of crystalline (or at least, mesogenically correlated) and non-crystalline elements in series. The ordered portions of the fibrils are characterized by size (normally 100s of angstrom by about 100 angstrom), net orientation and the nature of the order-disorder interface. While an equilibrium polymer crystal is comprised of fully extended chains, kinetic conditions during practical crystallization almost inevitably cause the chains to fold, forming thin lamellar structures with the chains parallel to the thin dimension. The regular nature of this folding and the concentration of tie molecules between lamellae is still debated in the literature, it is clear that tie molecule formation and less regular fold surfaces are aided by fast crystallization and chain orientation during or prior to the crystallization event. The thickness of the lamellar crystals is a function of the time and temperature of crystallization and lamellar crystals are subject to perfecting and thickening during annealing. (truncated)

Wood is one of the nation's leading raw materials and is used for a wide variety of products, either directly as wood, or as derived materials in pulp and paper. Wood is a biological material and evolved to provide mechanical support and water transport to the early plants that conquered the land. Wood is a tissue that results from the differentiation and programmed cell death of cells that derive from a tissue known as the vascular cambium. The vascular cambium is a thin cylinder of undifferentiated tissue in plant stems and roots that gives rise to several different cell types. Cells that differentiate on the internal side of the cambium form xylem, a tissue composed in major part, of long thin cells that die leaving a network of interconnected cell walls that serve to transport water and to provide mechanical support for the woody plant. The shape and chemical composition of the cells in xylem are well suited for these functions. The structure of cells in xylem determines the mechanical properties of the wood because of the strength derived from the reinforced matrix of the wall. The hydrophobic phenolic surface of the inside of the cell walls is essential to maintain surface tension upon which water transport is based and to resist decay caused by microorganisms. The properties of wood derived from the function of xylem also determine its structural and chemical properties as wood and paper products. Therefore, the physical and chemical properties of wood and paper products also depend on the morphology and composition of the cells from which they are derived. Wood (xylem cell walls) is an anisotropic material, a composite of lignocellulose. It is a matrix of cellulose microfibrils, complexed with hemicelluloses, (carbohydrate polymers which contain sugars other than glucose, both pentoses and hexoses), embedded together in a phenolic matrix of lignin. The high tensile strength of wood in the longitudinal direction, is due to the structure of cellulose and the orientation of the cellulose microfibrils. Lignin provides the embedding matrix that imparts compressive strength and flexibility. The water conducting cells in xylem, the tracheids, are long thin cells, which become the fibers of paper when the lignin is removed from wood during the papermaking process. The length of the tracheids and the thickness of the walls have important effects on the properties of paper that is produced. The past two decades have marked a revolutionary period in biological sciences due to the development of gene splicing techniques. These methods have led to the directed engineering of organisms to develop new industrial products. The technology has been used to produce a wide variety of new pharmaceuticals and transgenic plants and animals. This technology is now also being applied to forest trees.

Bicontinuous mesophases are mesoporous structures that divide space into several interpenetrating, continuously connected volumes. The length scales of the pores are typically in the tens of nanometer range, which offers opportunities for the use of these materials in nanoscale fabrication of structural composites or surface-active mesoporous structures. Use of these materials has been limited in the past because they were typically liquid crystals made of surfactant and water. This situation is rapidly changing due to recent successes in making bicontinuous mesophases out of more durable materials, such as polymers or silica, and in fabricating structures with a variety of morphologies. An overview is presented of the structural morphology, energetic considerations, and five different routes of fabrication for bicontinuous mesophases, for example, mesophases made of surfactants and water, block copolymers, polymerizable surfactants, polymerizable fluids in surfactant liquid crystals, and silica.

The cyanobacteria are photosynthetic procaryotes that employ a mechanism of photosynthesis which is essentially identical to the systems found in plant chloroplasts and the eukaryotic green algae. Cyanobacteria can drive photosynthesis with light energy from a broad region of the visible spectrum (500 - 650 nm wavelength) that is not available to plants and green algae, which are limited to the narrow band of light energy that is absorbed by chlorophyll (660-680 nm). The light-harvesting capacity of the cyanobacteria is a function of a complex protein structure that resides on the surface of the photosynthetic membrane in contact with the PSII chlorophyll reaction centers. This light-harvesting complex is called a phycobilisome and functions as a protein scaffold for a rigid array of chromophores that absorbs light energy and transfers it to chlorophyll. The chromophores are linear tetrapyrroles (the bilins) that are covalently attached to the biliproteins, which comprise 80 - 85% of the total phycobilisome mass. There are three major classes of spectrally distinct biliproteins [phycoerythrin (PE), (lambda) _max equals 565 nm; phycocyanin (PC), (lambda) _max equals 617 nm; and allophycocyanin (AP), (lambda) _max equals 650 nm] and their spatial organization within the phycobilisome creates an array of donor and acceptor chromophores that is optimized for resonance energy transfer to chlorophyll on a picosecond timescale and at close to 100% efficiency. The cyanobacteria can exert control over the biliprotein composition of the phycobilisomes in response to both light quality and light quantity, and they do so primarily by light-responsive transcription control mechanisms. The biosynthesis and assembly of a phycobilisome is an interesting example of self-assembly in a complex protein system. A phycobilisome from Synechocystis sp. strain 6701 can contain 400 proteins derived from a repertoire of 16 different polypeptides that includes the (alpha) and (beta) subunits for each major biliprotein and the achromic linker proteins that mediate assembly throughout the structure. The biliprotein subunit structures all show an identical motif that is reflected by significant amino acid sequence similarities across the different classes. Since phycobilisomes can comprise up to 40% of the cyanobacterial dry mass, assembly of these complexes must occur in the presence of high localized concentrations of components that are very similar in structure. That phycobilisome assembly is an efficient process with no evidence of significant misassembly suggests that effective molecular recognition during phycobilisome biosynthesis is based upon the subtle differences between subunits of different class biliproteins. We are using a protein engineering approach to examine structural features that mediate molecular recognition in two of the earliest steps of phycobilisome assembly, the docking of (alpha) and (beta) subunits and the selective attachment of chromophores.

Skin from the lizard, Anolis carolinensis, carries a molecular photosensor and will, in response to visible light, change from bright green to dark brown within minutes. The color/albedo change, involving control of three types of pigment cell, exhibits the sensor, effector, and function aspects of a smart functional system.

Genetic engineering and targeted chemical modification are being used to produce polypeptides with pore-forming activity that can be triggered or switched on-and-off by biochemical, chemical or physical stimuli. The principal target of our studies has been the (alpha) -hemolysin ((alpha) HL) from the bacterium Staphylococcus aureus. The remodeled hemolysins include protease-activated pores, metal-regulated pores, pores that are activated by chemical alkylation and pores that are turned on with light. These polypeptides have several potential applications. For example, they might serve as components of sensors or they might be useful for mediating the controlled release of encapsulated drugs.

We have focused our research on biologically derived materials to gain insight into new types of materials with novel functions and new assembly and processing methods associated with these materials. Biological systems offer prototypical capabilities in sensing and responding to the environmental changes. The material designs, synthesis, regulation and assembly involved in these sensing and response processes should offer materials engineers incredible opportunities in the molecular-level design of new 'smart' materials with functions not achievable today. Specific examples are cited from our own studies that explore the biosynthesis, processing and properties of novel biological materials. It is our expectation that through the elucidation of the nature of these materials and the processes by which these materials are formed that new directions to the design of 'smart' functions may be garnered.

Conventional synthetic membranes, fashioned for the most part from rather unremarkable polymeric materials, are essentially passive structures that achieve various industrial and biomedical separations through simple and selective membrane permeation processes. Indeed, simplicity of membrane material, structure, and function has long been perceived as a virtue of membranes relative to other separation processes with which they compete. The passive membrane separation processes -- exemplified by micro- and ultrafiltration, dialysis, reverse osmosis, and gas permeation -- differ from one another primarily in terms of membrane morphology or structure (e.g., porous, gel-type, and nonporous) and the permeant transport mechanism and driving force (e.g., diffusion, convection, and 'solution/diffusion'). The passive membrane separation processes have in common the fact that interaction between permeant and membrane material is typically weak and physicochemical in nature; indeed, it is frequently an objective of membrane materials design to minimize interaction between permeant and membrane polymer, since such strategies can minimize membrane fouling. As a consequence, conventional membrane processes often provide only modest separation factors or permselectivities; that is, they are more useful in performing 'group separations' (i.e., the separation of different classes of material) than they are in fractionating species within a given class. It has long been recognized within the community of membrane technologists that biological membrane structures and their components are extraordinarily sophisticated and powerful as compared to their synthetic counterparts. Moreover, biomembranes and related biological systems have been 'designed' according to a very different paradigm -- one that frequently maximizes and capitalizes on extraordinarily strong and biochemically specific interactions between components of the membrane and species interacting with them. Thus, in recent years synthetic membrane scientists have become intrigued with the notion of mimicking biological membrane structure and function where feasible -- and with 'activating' membranes by incorporating various biocatalytic or adsorptive entities within them. Generally, the objective has been to render synthetic membranes capable of performing separations more selectively or of increasing the range of function (e.g., chemical conversion) that they are capable of carrying out. At this point, the design of a number of novel synthetic membrane structures and processes has been guided by precedents afforded by biological systems. Several examples of this strategy as applied to synthetic membrane and membrane process development are enumerated.

Smart functions in biological systems are discussed from the perspective of the temperature at which inverse transitions of hydrophobic folding and assembly occur in response to increases in the temperature. The design of advanced materials is demonstrated in terms of the capacity to control the temperature, T_t, at which the inverse temperature transitions occur by controlling polymer hydrophobicity and by utilizing an associated hydrophobic-induced pKa shift. A smart material is recognized as one in which the material is responsive to the particular variable of interest, to the particular change in the variable that is required, and under the required conditions of temperature, pH, pressure, etc. By the proper design of the polymer, it is demonstrated that two distinguishable smart functions can be coupled such that an energy input that alters one function causes a change in the second function as an output. To become coupled the two distinguishable functions need to be part of the same hydrophobic folding domain. By way of example, a protein-based polymer was designed to carry out the conversion of electrochemical energy to chemical energy, i.e., electro-chemical transduction, under specified conditions of temperature and pH. This design approach utilizes the (Delta) T_t-mechanism of free energy transduction.

Composite materials have found a number of structural applications but their use in the electronics industry has been relatively limited. As the advantages and disadvantages of electroceramic composites are better understood, we can expect this picture to change. In this paper we review some of the composite sensor and actuator studies carried out in our laboratory during the past two decades. These functional composites make use of a number of underlying ideas including connectivity patterns leading to field and force concentration; the use of periodicity and scale in resonant structures; the symmetry of composite structures and its influence on physical properties; polychromatic percolation and coupled conduction paths; varistor action and other interfacial effects; sum, combination, and product properties; coupled phase transformation phenomena; and the important role that porosity and inner composites play in composite materials. These ideas provide a basic understanding of functional composites and have been discussed previously. In the present paper, we describe several composite piezoelectrics and their applications. Several of these transducers mimic the geometries of the sound-sensing organs of fish: elongated feelers, vibrating air bladders, and spherical inner ears.

Molecular self-assembly is a strategy for nanofabrication that involves designing molecules and supramolecular entities so that shape-complementarity causes them to aggregate into desired structures. Self-assembly has a number of advantages as a strategy: first, it carries out many of the most difficult steps in nanofabrication -- those involving atomic-level modification of structure -- using the very highly developed techniques of synthetic chemistry. Second, it draws from the enormous wealth of examples in biology for inspiration: self-assembly is one of the most important strategies used in biology for the development of complex, functional structures. Third, it can incorporate biological structures directly as components in the final systems. Fourth, because it requires that the target structures be the thermodynamically most stable ones open to the system, it tends to produce structures that are relatively defect-free and self-healing. Self-assembly also poses a number of substantial intellectual challenges. The brief summary of these challenges is that we do not yet know how to do it, and cannot even mimic those processes known to occur in biological systems at other than quite elementary levels. In addition, there are issues of function in self-assembled aggregates that need solution. The most promising avenues for self-assembly are presently those based on organic compounds, and organic compounds, as a group (although with exceptions), are electrical insulators; thus, many ideas for information processing and electrical/mechanical transduction will require either fundamental redesign in going from the macroscopic systems presently used to self-assembled systems, or the development of new types of organic molecules that show appropriate properties. This talk outlines some of these issues, and illustrates one of the approaches to self-assembled structures that has been particularly successful: that is, self- assembly on surfaces. There are now a range of different molecular systems that self-assemble -- that is, form ordered, monomolecular structures -- by the coordination of molecules to surfaces. These systems -- self-assembled monomlayers (SAMs) -- are reasonably well understood, and increasingly useful technologically. The crucial dimension in SAMs is the thickness perpendicular to the plane of the monolayer: this dimension, and the composition along this axis, can be controlled very simply at the scale of 0.1 nm by controlling the structures of the molecules making up the monolayer. (truncated)

The interfacial chemistry between inorganic ceramics and defined organic surfaces is the focus of intense investigation. Partially compressed Langmuir-Blodgett monolayers of anionic porphyrins have been used as modified nucleation sites for calcium carbonate. The porphyrin monolayer has an ordered array of carboxylates, and hence the system serves as a minimalist template for the modeling of complex biogenic acidic glycoproteins for biomineralization. The initial results suggest the formation of calcite with morphologically distinct calcitic rhombs with truncated, 3-edged corners and intricately articulated facial cavities. Stearic acid monolayers yield distinctly different calcite crystals, indicative that the geometrically defined carboxylate array is probably important. Phosphatidylcholine vesicles have been used as a tool for the formation of membrane encapsulated iron-oxides. Gramicindin A ion channels have been embedded in vesicles to kinetically alter the formation and growth of iron oxides, starting with intravesicular ferrous chloride. The results indicate that the presence of ion channels lead to the formation of magnetite vis-a-vis maghemite formation in vesicles lacking the ion channels. The use of ion channels has important implications in probable signal transduction processes during biomineralization pathways.

Nature uses cellular materials in applications requiring strength while, simultaneously, minimizing raw materials requirements. Minimizing raw materials is efficient both in terms of the energy expended by the organism to synthesize the structure and in terms of the strength- to-weight ratio of the structure. Wood is the most obvious example of cellular bio-materials, and it is the focus of other presentations in this symposium. The lightweight bone structure of birds is another excellent example where weight is a key criterion. The anchoring foot of the common muscle [Mytilus edulis] whereby it attaches itself to objects is a further example of a biological system that uses a foam to fill space and yet conserve on raw materials. In the case of the muscle the foam is water filled and the foot structure distributes stress over a larger area so that the strength of the byssal thread from which it is suspended is matched to the strength of interfacial attachment of the foot to a substrate. In these examples the synthesis and fabrication of the cellular material is directed by intercellular, genetically coded, biochemical reactions. The resulting cell sizes are microns in scale. Cellular materials at the next larger scale are created by organisms at the next higher level of integration. For example an African tree frog lays her eggs in a gas/fluid foam sack she builds on a branch overhanging a pond. The outside of the foam sack hardens in the sun and prevents water evaporation. The foam structure minimizes the amount of fluid that needs to be incorporated into the sack and minimizes its weight. However, as far as the developing eggs are concerned, they are in an aqueous medium, i.e. the continuous fluid phase of the foam. After precisely six days the eggs hatch, and the solidified outer wall re-liquefies and dumps the emerging tadpoles into the pond below. The bee honeycomb is an example of a cellular material with exquisite periodicity at millimeter length scales. The cellular structure provides strength through geometric regularity and functions as both honey storage vessels and incubators.