This PDF file contains the front matter associated with SPIE Proceedings Volume 7401, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Humans have always sought to imitate the human appearance, functions and intelligence. Human-like robots, which for many years have been a science fiction, are increasingly becoming an engineering reality resulting from the many advances in biologically inspired technologies. These biomimetic technologies include artificial intelligence, artificial vision and hearing as well as artificial muscles, also known as electroactive polymers (EAP). Robots, such as the vacuum cleaner Rumba and the robotic lawnmower, that don't have human shape, are already finding growing use in homes worldwide. As opposed to other human-made machines and devices, this technology raises also various questions and concerns and they need to be addressed as the technology advances. These include the need to prevent accidents, deliberate harm, or their use in crime. In this paper the state-of-the-art of the ultimate goal of biomimetics, the development of humanlike robots, the potentials and the challenges are reviewed.

Bio-Mimicking/Bio-Inspiration: How can we not be inspired by Nature? Life has evolved on earth over the last 3.5 to 4 billion years. Materials formed during this time were not toxic; they were created at low temperatures and low pressures unlike many of the materials developed today. The natural materials formed are self-assembled, multifunctional, nonlinear, complex, adaptive, self-repairing and biodegradable. The designs that failed are fossils. Those that survived are the success stories. Natural materials are mostly formed from organics, inorganic crystals and amorphous phases. The materials make economic sense by optimizing the design of the structures or systems to meet multiple needs. We constantly "see" many similar strategies in approaches, between man and nature, but we seldom look at the details of natures approaches. The power of image processing, in many of natures creatures, is a detail that is often overlooked. Seldon does the engineer interact with the biologist and learn what nature has to teach us. The variety and complexity of biological materials and the optical systems formed should inspire us.

Plants have evolved unusual tissue optical properties, not surprising as creatures of light. These are astonishingly sophisticated, involving both micro- and nanostructures. Microstructures refract, scatter, and channel light in plant tissues, to produce concentrations and gradients of light within, and to remove undesired portions of the electromagnetic spectrum. Nanostructures use the different refractive indices of both cellulosic walls and bi-lipid membranes to interfere with light, multiple layers producing intense constructive coloration and reduced fluxes within tissues. In a tropical sedge now under analysis, structures may include silica. Recently discovered surface diffraction gratings produce strong directionally sensitive coloration that assist in pollinator visitation. Although some of these properties have obvious applications, most await appreciation by creative scientists to produce new useful devices.

Multilayer interference phenomenon has been widely applied to various optical components that have highly wavelength-selective properties in reflection and transmission. In nature, some animals also take advantage of a similar mechanism for the coloration of their brilliant bodies. However, natural examples of multilayer thin-film structure are often modified in some structural aspects, and the modifications have been found to cause interesting optical effects. Recently, we found such an example, highly curved multilayer structure, in the wing scale of the Madagascan sunset moth. In this paper, we report the extended study of this subject. First, we will review the structural characteristics and various optical phenomena that occur on the wing of the moth. Second, inspired by the coloration mechanism of the moth wing, we newly consider multilayer designs for the color plates that change their colors depending on the analyzing direction of polarization.

Structural colors are non-pigment colors that originate from the scattering of light from ordered microstructures, thin films, and even irregular arrays of scatterers. Examples include the flashing sparks of colors in opals and the brilliant hues of some butterflies such as Morpho rhetenor. Structural colors arise in nature from one or more of a palette of physical mechanisms that are now understood quite well and can be implemented industrially to produce structurally colored paints, fabrics, and cosmetics.

A range of different beetles exhibits brilliant colours and metallic sheen. One of the most spectacular species is the Plusiotis resplendens from Central America with gold metal appearance. The beetle shells are made from chitin and have a number of unique properties that apart from spectacular aesthetic effects include metal sheen from non-metal surfaces combined with electric and thermal insulation. The reflection mechanism has been studied by a number of authors and is well understood. Basically there are 2 different reflection principles. One is the multilayer reflector where alternating layers have high and low refractive index. The other is the Bouligand structure where birefringent chiral nanofibres are organised in spiral structures. The paper describes work done to explore different approaches to mimic these structures using polymer based materials and production methods that are suitable for more complex double curved geometry. One approach is to use alternating layers of 2 different polymers applied by dipping and another is applying cholesteric liquid crystals in paint. However, none of them can yet make the desired metal-looking free-form surfaces.

A variety of animals emit light, either for intraspecific signalling, for predator repulsion or for using their own vision system in total darkness. As the design of light-emitting diodes has revealed, light extraction from a high refractive index medium is difficult because transmission is limited by total internal reflection. Surface roughness is needed to attempt avoiding this limitation. The optical structure of the bioluminescent organs of fireflies is investigated and the possible role of inhomogeneities for improving the efficiency of the radiative emission is considered. This analysis shows that the light extraction in this complex structure is essentially doubled, compared to the extraction in a reference system consisting of an homogeneous chitinous medium terminated by a flat surface. The inequal fitting of the scales and the lowering of the average refractive index in the photocytes accounts for most of the improvement.

The biomimetic approach seeks to incorporate designs based on biological organisms into engineered technologies. Biomimetics can be used to engineer machines that emulate the performance of organisms, particularly in instances where the organism's performance exceeds current mechanical technology or provides new directions to solve existing problems. For biologists, an adaptationist program has allowed for the identification of novel features of organisms based on engineering principles; whereas for engineers, identification of such novel features is necessary to exploit them for biomimetic development. Adaptations (leading edge tubercles to passively modify flow and high efficiency oscillatory propulsive systems) from marine animals demonstrate potential utility in the development of biomimetic products. Nature retains a store of untouched knowledge, which would be beneficial in advancing technology.

Viscous coupling between filiform hair sensors of insects and arthropods has gained considerable interest recently. Study of viscous coupling between hairs at micro scale with current technologies is proving difficult and hence the hair system has been physically scaled up by a factor of 100. For instance, a typical filiform hair of 10 μm diameter and 1000 μm length has been physically scaled up to 1 mm in diameter and 100mm in length. At the base, a rotational spring with a bonded strain gauge provides the restoring force and measures the angle of deflection of the model hair. These model hairs were used in a glycerol-filled aquarium where the velocity of flow and the fluid properties were determined by imposing the Reynolds numbers compatible with biological system. Experiments have been conducted by varying the separation distance and the relative position between the moveable model hairs, of different lengths and between the movable and rigid hairs of different lengths for the steady velocity flow with Reynolds numbers of 0.02 and 0.05. In this study, the viscous coupling between hairs has been characterised. The effect of the distance from the physical boundaries, such as tank walls has also been quantified (wall effect). The purpose of this investigation is to provide relevant information for the design of MEMS systems mimicking the cricket's hair array.

The male of the beetle Hoplia coerulea is known for its spectacular blue-violet iridescence. The blue coloration is caused by the presence of an interesting photonic structure inside the scales which cover the dorsal parts of the insect's body. This structure can be described as the stacking of chitin plates supporting arrays of parallel rods. The change of colour of this structure with humidity is investigated, as well as its response to some other external conditions, such as mechanical strain.

The tissue engineering focuses on synthesis or regeneration of tissues and organs. The hierarchical structure of nearly all porous scaffolds on the macro, micro- and nanometer scales resembles that of engineering foams dedicated for technical applications, but differ from the complex architecture of long bone. A major obstacle of scaffold architecture in tissue regeneration is the limited cell infiltration as the result of the engineering approaches. The biological cells seeded on the three-dimensional constructs are finally only located on the scaffold's periphery. This paper reports on the successful realization of calcium phosphate scaffolds with an anatomical architecture similar to long bones. Two base materials, namely nano-porous spray-dried hydroxyapatite hollow spheres and tri-calcium phosphate powder, were used to manufacture cylindrically shaped, 3D-printed scaffolds with micro-passages and one central macro-canal following the general architecture of long bones. The macro-canal is built for the surgical placement of nerves or larger blood vessels. The micro-passages allow for cell migration and capillary formation through the entire scaffold. Finally, the nanoporosity is essential for the molecule transport crucial for signaling, any cell nutrition and waste removal.

Human teeth are anisotropic composites. Dentin as the core material of the tooth consists of nanometer-sized calcium phosphate crystallites embedded in collagen fiber networks. It shows its anisotropy on the micrometer scale by its well-oriented microtubules. The detailed three-dimensional nanostructure of the hard tissues namely dentin and enamel, however, is not understood, although numerous studies on the anisotropic mechanical properties have been performed and evaluated to explain the tooth function including the enamel-dentin junction acting as effective crack barrier. Small angle X-ray scattering (SAXS) with a spatial resolution in the 10 μm range allows determining the size and orientation of the constituents on the nanometer scale with reasonable precision. So far, only some dental materials, i.e. the fiber reinforced posts exhibit anisotropic properties related to the micrometer-size glass fibers. Dental fillings, composed of nanostructures oriented similar to the natural hard tissues of teeth, however, do not exist at all. The current X-ray-based investigations of extracted human teeth provide evidence for oriented micro- and nanostructures in dentin and enamel. These fundamental quantitative findings result in profound knowledge to develop biologically inspired dental fillings with superior resistance to thermal and mechanical shocks.

In this paper we explore the issue of fire and explosion in natural phenomena with a view to biomimetic applications. We study two examples. One area is the area of trees which use fire to propagate their seeds - the Monterey, Bishop and Knobcone pine (all in the US Pacific Northwest) have this ability which means that the cones remain closed for long periods of time. Some, such as the Knobcone will only open under high temperature such as in a fire. There are other pines such as the Banksia (Australia) which also operate in the same way. It is possible that these material features could have benefit to the community in developing fire proof materials. Another example of fire and explosion in nature is the bombardier beetle. This insect has the remarkable ability that it can resist an attacker with a powerful jet of hot, toxic fluid. It reacts small amounts of hydroquinone with hydrogen peroxide in the presence of the catalysts catalase and peroxidase and the spray is then ejected from combustion chambers in its rear end. Recent work has demonstrated that certain parts of the anatomy are in fact inlet and outlet valves and that the intake and exhaust valve mechanism involves a repeated (pulsating) steam explosion. The research has shown the characteristics of these ejections and an experimental rig mimicking the major physics of the beetle ejection system has been built which shows clearly the importance of the valve system for getting good spray characteristics.

Biological systems such as butterflies and beetles have developed highly elaborate photonic crystals to create their striking coloration. Especially, examples of the weevil and longhorn families (Curculionidae and Cerambycidae, respectively) possess a range of interesting three-dimensional photonic crystal structures operating at visible wavelengths, including non-close-packed lattices of cuticular spheres and diamond-based architectures. A low-temperature sol-gel bio-templating method was developed, to transform bio-polymeric photonic crystals into heat and photo-stable silica and titania inorganic structures. The fabricated oxide-based structures display good structural and optical properties.

The characteristic brilliant green iridescence of beetles of the species Lamprocyphus augustus arises from the elaborate multidomain photonic structure of its exoskeleton. The conformal-evaporated-film-by-rotation (CEFR) technique was used to conformally coat the exoskeletons of L. augustus specimen with GeO_x thin films. The exoskeletal surface structure was found to be accurately replicated at the micro-scale by the coatings. Moreover, the reflectance spectrums of an uncoated exoskeleton and a conformally coated exoskeleton turned out to display comparable overall characteristics in the visible and the near-infrared regimes, confirming that the structure of the exoskeleton was replicated with high fidelity by the coating, thus preserving its optical functionality. An attempt to fabricate a freestanding replica of an exoskeleton by immersion of a coated exoskeleton in an aqueous solution of orthophosphoric acid yielded encouraging results.

The eyes and wings of some species of moth are covered in arrays of subwavelength pillars that have been tuned over millions of years of evolution to reflect as little sunlight as possible. We are investigating ways of exploiting this to reduce reflection from the surfaces of silicon solar cells. Here, we report on the experimental realization of biomimetic antireflective moth-eye arrays in silicon using a technique based on nanoimprint lithography and dry etching. Areas of 1cm x 1cm have been patterned and analysis of reflectance measurements predicts a loss in the performance of a solar cell of only 6.5% compared to an ideal antireflective coating. This compares well with an optimized single layer Si₃N₄ antireflective coating, for which an 8% loss is predicted.

While technology relies on components defined in a fixed position on a rigid substrate, nature prefers soft substrates, and allows components to move significantly during morphogenesis. Taking inspiration from biological fabrication, we have developed a technique, called active polymer nanofabrication, which utilizes thermally active polymers to create complex nanoplasmonic substrates designed for molecular detection. We demonstrate the ability of active polymer nanofabrication to create ultra-dense nanoplasmonic prism arrays (plasmonic nanoflowers), and correlate changes in array morphology with optical properties. We investigate the associated changes in local electromagnetic fields with finite element analysis. Finally, we demonstrate the ability of active polymers to deform macroscopically while retaining nanostructure morphology. We expect these properties will make active polymer nanofabrication useful for a wide range of nanoplasmonic devices.