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.

We have demonstrated a novel method for the preparation of a fluorescence-based pH sensor by combining the plasmon resonance band of Ag core and pH sensitive dye (HPTS). A thickness-variable silica shell is placed between Ag core and HPTS dye to achieve the maximum fluorescence enhancement. At the shell thickness of 8 nm, the fluorescence intensity increases 4 and 9 times when the sensor is excited at 405 and 455 nm, respectively. At the same time, the fluorescence intensity shows a good sensitivity toward pH value in the range of 5-9, and the ratio of emission intensity at 513 nm excited at 455 nm to that excited at 405 nm versus the pH value in the range of 5-9 is determined. It is believed that the present pH sensor has the potential for determining pH real time in the biological sample.

The useful functionalization and self-assembly of two-dimensional layered materials like hydrotalcite (LDH) are critical for the wide application of nanomaterials. In this work, some self-assembled Langmuir films of ion-exchanged LDH and dyes with different molecular structures were prepared by the Langmuir–Blodgett (LB) technique. The aggregation states of used dye molecules on the surface of the obtained membrane and the structures/properties of the membrane were studied. The hydroxyethyl sulfonate-inserted LDH (LDH-Ise) nanosheets were able to induce the dye formation of highly ordered H- and/or J-aggregate structures. Surface-enhanced Raman scattering (SERS) spectroscopy results demonstrated the uniformity and repeatability of the film. Interestingly, the good acid–base gas response characteristics of present LDH-Ise/dye LB films were investigated by UV–vis and Fourier transform infrared (FT-IR). The present research work provides new clues for the development of gas sensors and chemical switches as well as the preparation of effective functional self-assembled films.

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A microfluidic platform was used to fabricate polyvinyl alcohol microfibers with various morphology and mechanical properties.