tide were made with the peptide Ac±GCRD±GPQG¯IWGQ±DRCG±NH 2 , with 2 lg/gel VEGF 165 within. Prior to gelation, the mixed liquid precursors were imbibed into an open pore polyurethane sponge, 5 mm diameter, 2 mm thick. The disks were implanted subcutaneously, dorsally in the rat, and were explanted after 13 days, fixed, and analyzed by immunohistochemistry. Tissue sections were stained for blood vessels with antibodies specific for a-smooth muscle actin and counterstained with hematoxylin. Photoimages were taken with a Zeiss Axioscope at the 2.5 and 10 magnifications. Colloidal crystals are three-dimensionally periodic lattices of monodispersed, spherical colloids such as polymer latexes and silica spheres.[1] The ability to crystallize colloidal particles allows one to obtain functionality not only from the constituent material of the colloids, but also from the long-range COMMUNICATIONS 892

This article describes an elastic silicone sheet with reversible tuning structural color. The sheet has a thin layer of cubic close-packed, ccp, colloidal particles embedded in poly(dimethylsiloxane), PDMS, elastomer. The array of ccp (111) planes diffracts light of selective wavelengths according to Bragg's law. This is responsible for the structural color of the PDMS sheet. Because the sheet was stretched in the horizontal direction, it was reduced in size in the vertical direction. As a result, the lattice distance of ccp (111) planes decreased, and the reflected wavelength of light shifted to shorter wavelengths. For example, the peak of reflection was tuned from 589 to 563 nm as a function of sheet elongation. The peak position decreased linearly with deformation when the deformation was within 20% of its elongation. Accordingly, the color of the PDMS sheet changed from red to green. When the mechanical strain on the PDMS sheet was released, the peak returned to its original position, and the color of the PDMS sheet also changed back to red. Tuning the color of the PDMS sheet is a reversible and repeatable process. The novel PDMS sheet has the potential to be applied to mechanical strain sensing.

This article describes the fabrication and characterization of colloidal crystals whose stop bands could be varied through the application of a liquid. Such a colloidal crystal was generated by infiltrating the voids within an opaline lattice of polystyrene beads with a liquid prepolymer to poly(dimethylsiloxane), followed by thermal curing. When a liquid (e.g., a silicone fluid, hexane, or octane) capable of swelling the elastomer matrix was applied to the surface of this crystal, the lattice constant and thus the wavelength of Braggdiffracted light was increased. For instance, the color of light diffracted from a colloidal crystal made of 175 nm polystyrene beads could be varied from violet to green, orange, and red simply by swelling it with different solvents. On the basis of this mechanism, we further demonstrated a photonic paper/ink system where color patterns could be conveniently generated on the surface of a thin film of colloidal crystal by writing with a Pilot pen, by screen printing, or by microcontact printing with an elastomer stamp. To fully illustrate the potential of this paper/ink system, we have demonstrated the fabrication of photonic papers as large as 75 cm 2 in area, supported on both rigid substrates and flexible Mylar films. By judicially choosing the diameter of the polystyrene beads, it was also possible to adjust the color initially displayed by a photonic paper to any wavelength within the spectral region from ultraviolet to near-infrared. As a result, the photonic papers could be fabricated to appear as colorless while the written patterns displaying a shiny color, or vice versa.

Flexible polymer laser devices excited by low‐threshold optical light are fabricated from colloidal crystals (CCs; see figure). The laser‐cavity structure consists of a light‐emitting layer sandwiched between two polymer CC films. Optical excitation with a green beam brings about emission with a red beam. This process allows the production of ultralightweight, low‐cost, flexible, and easily processible all‐plastic lasers.

In this paper, the key topics of tunable structural color in biology and material science are overviewed. Color in biology is considered for selected groups of tropical fish, octopus, squid and beetle. It is caused by nanoplates in iridophores and varies with their spacing, tilting angle and refractive index. These examples may provide valuable hints for the bioinspired design of photonic materials. 1D multilayer films and 3D colloidal crystals with tunable structural color are overviewed from the viewpoint of advanced materials. The tunability of structural color by swelling and strain is demonstrated on an example of opal composites.