Determining the fundamental mechanisms underlying tissue formation and wound healing allows for bio-inspired approaches that leverage the best practices of biology, as decided upon by millions of years of evolution. To gain insight into how tissue is built, we have studied the interactions between two of the principal proteins found in connective tissues: collagen and fibronectin. We have confirmed a binding affinity in solution, which supports a reciprocal relationship whereby the assembly pathway of one catalyzes the other. The molecular synergy enables complex extracellular matrix formation with a range of mechanical properties.
Color is a signature visual feature in nature; however, the ability to trigger color change in the presence of different environmental stimuli is unique to only a handful of species in the animal kingdom. We exploit the natural color-changing properties of the predominant pigment in arthropods and cephalopodsxanthommatin (Xa)and describe its utility as a new broad-spectrum electrochromic material. To accomplish this goal, we explored the spectroelectrochemical properties of Xa adsorbed to an indium-doped tin oxide-coated substrate chemically modified with poly(3,4-ethylene dioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS). We identified a synergistic role between PEDOT:PSS and Xa that contributed to its absorption profile, which could be modulated across multiple cycles. By varying the ratio of the two electroactive components, we also altered the perceived visible color of Xa-based devices, which cycled from different shades of red to yellow under reducing and oxidizing potentials, respectively. Together, our data illustrate the utility of Xa-based devices as new broad-spectrum electrochromic materials.
A laser-mediated methodology for standoff infrared detection of threat chemicals is described in this article. Laser-induced thermal emissions (LITE) from vibrationally excited residue of highly energetic material (HEM) deposited on substrates were detected remotely. Telescope-based Fourier transform infrared (FT-IR) spectroscopy measurements were carried out on substrates containing small amounts of HEM at surface concentrations of 5-200 μg/cm(2). Target substrates of various thicknesses were heated remotely using a carbon dioxide laser, and their mid-infrared (mid-IR), thermally stimulated emission spectra were recorded after heating. The telescope was configured from reflective optical elements to minimize emission losses in the mid-IR frequencies. Spectral replicas were acquired at distances from 4 to 64 m using an FT-IR interferometer at 4 cm(-1) resolution. The laser power, laser exposure times, and acquisition time of the FT-IR interferometer were adjusted to improve the detection and identification of samples. The advantages of increasing the thermal emission were easily observed in the results. The signal intensities were proportional to the thickness of the coated surface (a function of the surface concentration) as well as the laser power and laser exposure time. The limits of detection obtained for the HEM studied were 140-21 μg/cm(2) at 4 m. Detection was achieved at 64 m for a surface concentration of 200 μg/cm(2).
The highly energetic material (HEM) hexahydro-1,3,5-trinitro-s-triazine, also known as RDX, has two stable conformational polymorphs at room temperature: α-RDX (molecular conformation of −NO2 groups: axial–axial–equatorial) and β-RDX (molecular conformation of −NO2 groups: axial–axial–axial). Both polymorphs can be formed by deposition on stainless steel substrates using spin coating methodology. α-RDX is the most stable crystal form at room temperature and ambient pressure. However, β-RDX, which has been reported to be difficult to obtain in bulk form at room temperature, was readily formed. Reflection–absorption infrared spectroscopy measurements for RDX-coated stainless steel substrates provided spectral markers that were used to distinguish between the conformational polymorphs on large surface areas of the substrates. Raman microspectroscopy was employed to examine small areas where the intensity was proportional to the height of the structures of RDX. Spectral features were interpreted and classified by using principal component analysis (PCA). The results from these spectral analyses provided good correlation with the values reported in the literature. Conditions to generate predominantly β-RDX crystalline films as a function of the spin coating rotational speed on these substrates were obtained. PCA was also applied to predict percentages of polymorphs present in experimental samples. Applications of the results obtained suggest the modification of existing vibrational spectroscopy based spectral libraries for defense and security applications. Understanding the effects of polymorphism in HEMs will result in the attainment of higher confidence limits in the detection and identification of explosives, especially at trace or near trace levels.
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