We use a microfluidic approach to fabricate gelatin fibers with controlled sizes and cross-sections. Uniform gelatin microfibers with various morphologies and cross-sections (round and square) are fabricated by increasing the gelatin concentration of the core solution from 8% to 12%. Moreover, the increase of gelatin concentration greatly improves the mechanical properties of gelatin fibers; the Young's modulus and tensile stress at break of gelatin (12%) fibers are raised about 2.2 and 1.9 times as those of gelatin (8%) fibers. The COMSOL simulations indicate that the sizes and cross-sections of the gelatin fibers can be tuned by using a microfluidic device with four-chevron grooves. The experimental results demonstrate that the decrease of the sheath-to-core flow-rate ratio from 150 : 1 to 30 : 1 can increase the aspect ratio and size of ribbon-shaped fibers from 35 μm × 60 μm to 47 μm × 282 μm, which is consistent with the simulation results. The increased size and shape evolution of the cross-section can not only strengthen the Young's modulus and tensile stress at break, but also significantly enhance the tensile strain at break. Disciplines Applied Mechanics | Biology and Biomimetic Materials | Biomechanical Engineering | Polymer and Organic MaterialsComments This is a manuscript of an article published as Bai, Zhenhua, Janet M. Mendoza Reyes, Reza Montazami, and Nastaran Hashemi. "On-chip development of hydrogel microfibers from round to square/ribbon shape."We use a microfluidic approach to fabricate gelatin fibers with controlled sizes and cross sections. Uniform gelatin microfibers with various morphologies and cross sections (round and square) are fabricated by increasing the gelatin concentration of core solution from 8 % to 12 %. Moreover, the increase of gelatin concentration greatly improves the mechanical properties of gelatin fibers; the Young's modulus and tensile stress at break of gelatin (12 %) fiber are raised about 2.2 and 1.9 times as those of gelatin (8 %) fiber. The COMSOL simulations indicate that the size and cross section of gelatin fiber can be tuned by microfluidic device with four-chevron grooves. The experiment results demonstrate that the decrease of sheath-to-core flow-rate ratio from 150:1 to 30:1 can increase the aspect ratio and size of ribbon-shaped fiber from 35 µm × 60 µm to 47 µm × 282 µm, which consists well with the simulation results. The increased size and shape evolution of cross section can not only strengthen the Young's modulus and tensile stress at break, and also significantly enhance tensile strain at break.

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We have measured the optical absorption characteristics of copper oxide single crystals in the range from 1.1 to 2.0 eV. The crystals were annealed at various oxygen pressures at high temperatures and quenched to room temperature. A major, broad, previously unknown absorption peak was found at 1.6 eV which we relate to the formation of copper inclusions in the oxide. Although experimental data on thin copper films agree with our assumptions, we cannot reconcile our results with scattering theory of small metal spheres embedded in a dielectric. Agreement between scattering theory and optical absorption may be achieved for nonspherical particles for which as yet no other experimental evidence exists.

The interference modulated reflection spectra R(1) at normal incidence for amorphous GeSe, semiconducting films, deposited by thennal evaporation, were obtained in the spectral region from 400nm to 2200nm. The straightforward method proposed by Minkov, which is based on the use of the extrema of the interference fringes R(1), has been applied in order to obtain both the real and imaginary parts of the complex refractive index, It and k, respectively, and the film thickness, d. Thickness measurements made by a surface-profiling stylus have also been carried out to cross-check the results obtained by the optical method. The dispersion of n is discussed in terms of the single-oscillator Wemple-DiDomenico model.

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