Controlling Chemical Reactions by Short, Intense Mid-Infrared Laser Pulses: Comparison of Linear and Circularly Polarized Light in Simulations of ClCHO⁺ Fragmentation

Enhanced mode selective fragmentation of oriented ClCHO⁺ → Cl + HCO⁺, H + ClCO⁺, HCl⁺ + CO with linear polarized intense mid-IR pulses was demonstrated in our previous computational study (J. Phys. Chem. Lett. 2012, 3, 2541). Simulations of angle-dependent strong field ionization of ClCHO indicate the ionization rate in the molecular plane is nearly twice as large as perpendicular to the plane, suggesting a degree of planar alignment can be obtained experimentally for ClCHO⁺, starting from neutral molecules. Classical trajectory calculations with a 4 cycle 7 μm laser pulse (peak intensity of 1.26 × 10¹⁴ W/cm²) show that circularly polarized light with the electric field in the plane of the molecule deposits more energy and yields larger branching ratios for higher energy fragmentation channels than linearly polarized light with the same maximum field strength. These results suggest circularly polarized mid-IR pulses can not only achieve control on reactions but also provide an experimentally accessible implementation

Biomimetic Microfluidic Device for in Vitro Antihypertensive Drug Evaluation

Microfluidic devices have emerged as revolutionary, novel platforms for in vitro drug evaluation. In this work, we developed a facile method for evaluating antihypertensive drugs using a microfluidic chip. This microfluidic chip was generated using the elastic material poly­(dimethylsiloxane) (PDMS) and a microchannel structure that simulated a blood vessel as fabricated on the chip. We then cultured human umbilical vein endothelial cells (HUVECs) inside the channel. Different pressures and shear stresses could be applied on the cells. The generated vessel mimics can be used for evaluating the safety and effects of antihypertensive drugs. Here, we used hydralazine hydrochloride as a model drug. The results indicated that hydralazine hydrochloride effectively decreased the pressure-induced dysfunction of endothelial cells. This work demonstrates that our microfluidic system provides a convenient and cost-effective platform for studying cellular responses to drugs under mechanical pressure

Stretchable and Micropatterned Membrane for Osteogenic Differentation of Stem Cells

Stem cells have emerged as potentially useful cells for regenerative medicine applications. To fully harness this potential, it is important to develop in vitro cell culture platforms with spatially regulated mechanical, chemical, and biological cues to induce the differentiation of stem cells. In this study, a cell culture platform was constructed that used polydopamine (PDA)-coated parafilm. The modified parafilm supports cell attachment and proliferation. In addition, because of the superb plasticity and ductility of the parafilm, it can be easily micropatterned to regulate the spatial arrangements of cells, and can exert different mechanical tensions. Specifically, we constructed a PDA-coated parafilm with grooved micropatterns to induce the osteogenic differentiation of stem cells. Adipose-derived mesenchymal stem cells that were cultured on the PDA-coated parafilm exhibited significantly higher osteogenic commitment in response to mechanical and spatial cues compared to the ones without stretch. Our findings may open new opportunities for inducing osteogenesis of stem cells in vitro using the platform that combines mechanical and spatial cues

Fabrication of Uniform Casein/CaCO₃ Vaterite Microspheres and Investigation of Its Formation Mechanism

Uniform Casein/CaCO₃ microspheres were fabricated with well tuned properties and the formation mechanism based on the templating effect of casein micelles was proposed. In bone tissue engineering, vaterite microspheres were promising because of the biocompatibility and easy fabrication. Here Casein/CaCO₃ microspheres were precipitated by mixing CaCl₂ and Na₂CO₃ solutions under stirring in the presence of casein. All samples were mainly in vaterite, composed of aggregates of nanosized crystals. With the increase of casein concentration, the amount of calcite and microsphere size decreased while the loading content of casein increased, suggesting that casein induced the formation of vaterite and also stabilized the crystal phase. The formation mechanism was further investigated. With the increase of CaCl₂ amount, the size of the forming microspheres increased while the zeta potential was stabilized, the polycrystalline nature was shown, and the presence of Ca inside microspheres was confirmed. Hence, the formation mechanism based on casein micelles which demonstrated the template effect was proposed. Casein/CaCO₃ microspheres enhanced the deposition of hydroxyapatite crystals and sample II-8 was tested as the most cytocompatible on mesenchymal stem cells. The properties of Casein/CaCO₃ microspheres could be well controlled; for better performance in bone tissue engineering, formation of composite scaffolds may be preferred

Microfluidic Generation of Polydopamine Gradients on Hydrophobic Surfaces

Engineered surface-bound molecular gradients are of great importance for a range of biological applications. In this paper, we fabricated a polydopamine gradient on a hydrophobic surface. A microfluidic device was used to generate a covalently conjugated gradient of polydopamine (PDA), which changed the wettabilty and the surface energy of the substrate. The gradient was subsequently used to enable the spatial deposition of adhesive proteins on the surface. When seeded with human adipose mesenchymal stem cells, the PDA-graded surface induced a gradient of cell adhesion and spreading. The PDA gradient developed in this study is a promising tool for controlling cellular behavior and may be useful in various biological applications

The Frequency Spectral Properties of Electrode-Skin Contact Impedance on Human Head and Its Frequency-Dependent Effects on Frequency-Difference EIT in Stroke Detection from 10Hz to 1MHz - Fig 6

<p>(a)(b) The contact impedance of all subjects at all electrodes. The dashed lines represent the measurement results of the electrodes at the forehead. (c)(d) The measurement results of electrochemical impedance and conductive gel impedance in the case of conductive gel with the thickness of 0.4 mm.</p

The effects of contact impedance on the boundary voltages because of imbalance between contact impedances.

<p>The effects of contact impedance on the boundary voltages because of imbalance between contact impedances.</p

Measuring circuit of contact impedance.

<p>In this study, an impedance analyzer was used, and the voltage excitation mode (500 mV) was applied.</p

The dielectric parameters of head tissues, hemorrhagic tissue and ischemic tissue.

<p>The dielectric parameters of head tissues, hemorrhagic tissue and ischemic tissue.</p

Reconstructed results of the ischemic stroke and the effects of the contact impedance.

<p><b>The contact impedance imbalance was simulated by varying the resistor in series with Electrode 1</b>.</p