Linear Stiffness Tuning in MEMS Devices via Prestress Introduced by TiN Thin Films

Stiffness tuning is crucial for micro/nanoscale devices to achieve advanced functionalities such as bistability, which enables efficient energy harvesting, large motion actuation, and programmable mechanical properties. Prestress implemented by thin films is one of the effective approaches for stiffness control; however, it is rarely used in practice because of the poor controllability in traditional thin film materials. Here, we demonstrate robust stiffness tuning on a microelectromechanical system (MEMS) sensor by using prestress in titanium nitride (TiN) thin films. Benefiting from the atomic peening effect, TiN exhibits linearly controllable prestress, which provides direct access to zero and negative stiffness in the mechanical device, resulting in multiple functionalities, including significantly enhanced sensitivity near zero-stiffness and bistable snapping behavior as stiffness becomes negative. The demonstrated technique can be a powerful tool to manipulate mechanical behaviors and facilitate exceptional sensing and actuating functionalities for micro/nanoscale devices

Hierarchical Assembly of siRNA with Tetraamino Fullerene in Physiological Conditions for Efficient Internalization into Cells and Knockdown

Delivery of siRNA is a key technique in alternative gene therapy, where the siRNA cargo must be effectively loaded onto a tailor-designed carrier molecule and smoothly unloaded precisely upon arrival at the target cells or organs. Any toxicity issues also need to be mitigated by suitable choice of the carrier molecule. A water-soluble cationic fullerene, tetra­(piperazino)[60]­fullerene epoxide (TPFE), was previously shown to be nontoxic and effective for lung-targeted in vivo siRNA delivery by way of agglutination-induced accumulation. We found in this in vitro study that hierarchical reversible assembly of micrometer-sized TPFE–siRNA–serum protein ternary complexes is the key element for effective loading and release, and stabilization of otherwise highly unstable siRNA under the physiological conditions. The amphiphilic TPFE molecule forms a sub-10 nm-sized stable micelle because of strong cohesion between fullerene molecules, and this fullerene aggregate protects siRNA and induces the hierarchical assembly. Unlike popularly used polyamine carriers, TPFE is not toxic at the dose used for the siRNA delivery

Hierarchically Structured Fullerene C₇₀ Cube for Sensing Volatile Aromatic Solvent Vapors

We report the preparation of hierarchically structured fullerene C₇₀ cubes (HFC) composed of mesoporous C₇₀ nanorods with crystalline pore walls. Highly crystalline cubic shape C₇₀ crystals (FC) were grown at a liquid–liquid interface formed between <i>tert</i>-butyl alcohol and C₇₀ solution in mesitylene. HFCs were then prepared by washing with isopropanol of the FC at 25 °C. The growth directions and diameters of C₇₀ nanorods could be controlled by varying washing conditions. HFCs perform as an excellent sensing system for vapor-phase aromatic solvents due to their easy diffusion through the mesoporous architecture and strong π–π interactions with the sp² carbon-rich pore walls. Moreover, HFCs offer an enhanced electrochemically active surface area resulting in an energy storage capacity 1 order of magnitude greater than pristine C₇₀ and fullerene C₇₀ cubes not containing mesoporous nanorods

Suppression of Myogenic Differentiation of Mammalian Cells Caused by Fluidity of a Liquid–Liquid Interface

There is growing evidence to suggest that the prevailing physical microenvironment and mechanical stress regulate cellular functions, including adhesion, proliferation, and differentiation. Moreover, the physical microenvironment determines the stem-cell lineage depending on stiffness of the substrate relative to biological tissues as well as the stress relaxation properties of the viscoelastic substrates used for cell culture. However, there is little known regarding the biological effects of a fluid substrate, where viscoelastic stress is essentially absent. Here, we demonstrate the regulation of myogenic differentiation on fluid substrates by using a liquid–liquid interface as a scaffold. C2C12 myoblast cells were cultured using water–perfluorocarbon (PFC) interfaces as the fluid microenvironment. We found that, for controlled in vitro culture at water–PFC interfaces, expression of <i>myogenin</i>, myogenic regulatory factors (MRF) family gene, is remarkably attenuated even when myogenic differentiation was induced by reducing levels of growth factors, although <i>MyoD</i> was expressed at the usual level (MyoD up-regulates myogenin under an elastic and/or viscoelastic environment). These results strongly suggest that this unique regulation of myogenic differentiation can be attributed to the fluid microenvironment of the interfacial culture medium. This interfacial culture system represents a powerful tool for investigation of the mechanisms by which physical properties regulate cellular adhesion and proliferation as well as their differentiation. Furthermore, we successfully transferred the cells cultured at such interfaces using Langmuir–Blodgett (LB) techniques. The combination of the interfacial culture system with the LB approach enables investigation of the effects of mechanical compression on cell functions

Supramolecular Differentiation for Construction of Anisotropic Fullerene Nanostructures by Time-Programmed Control of Interfacial Growth

Supramolecular assembly can be used to construct a wide variety of ordered structures by exploiting the cumulative effects of multiple noncovalent interactions. However, the construction of anisotropic nanostructures remains subject to some limitations. Here, we demonstrate the preparation of anisotropic fullerene-based nanostructures by supramolecular differentiation, which is the programmed control of multiple assembly strategies. We have carefully combined interfacial assembly and local phase separation phenomena. Two fullerene derivatives, <b>PhH</b> and <b>C12H</b>, were together formed into self-assembled anisotropic nanostructures by using this approach. This technique is applicable for the construction of anisotropic nanostructures without requiring complex molecular design or complicated methodology

Vortex-Aligned Fullerene Nanowhiskers as a Scaffold for Orienting Cell Growth

A versatile method for the rapid fabrication of aligned fullerene C₆₀ nanowhiskers (C₆₀NWs) at the air–water interface is presented. This method is based on the vortex motion of a subphase (water), which directs floating C₆₀NWs to align on the water surface according to the direction of rotational flow. Aligned C₆₀NWs could be transferred onto many different flat substrates, and, in this case, aligned C₆₀NWs on glass substrates were employed as a scaffold for cell culture. Bone forming human osteoblast MG63 cells adhered well to the C₆₀NWs, and their growth was found to be oriented with the axis of the aligned C₆₀NWs. Cells grown on aligned C₆₀NWs were more highly oriented with the axis of alignment than when grown on randomly oriented nanowhiskers. A study of cell proliferation on the C₆₀NWs revealed their low toxicity, indicating their potential for use in biomedical applications