Here we report a link between the interfacial structure and adhesive property of homopolymer chains physically adsorbed (i.e., via physisorption) onto solids. Polyethylene oxide (PEO) was used as a model and two different chain conformations of the adsorbed polymer were created on silicon substrates via the well-established Guiselin's approach: "flattened chains" which lie flat on the solid and are densely packed, and "loosely adsorbed polymer chains" which form bridges jointing up nearby empty sites on the solid surface and cover the flattened chains. We investigated the adhesion properties of the two different adsorbed chains using a custom-built adhesion testing device. Bilayers of a thick PEO overlayer on top of the flattened chains or loosely adsorbed chains were subjected to the adhesion test. The results revealed that the flattened chains do not show any adhesion even with the chemically identical free polymer on top, while the loosely adsorbed chains exhibit adhesion. Neutron reflectivity experiments corroborated that the difference in the interfacial adhesion is not attributed to the interfacial brodening at the free polymer-adsorbed polymer interface. Instead, coarse-grained molecular dynamics simulation results suggest that the tail parts of the loosely adsorbed chains act as "connector molecules", bridging the free chains and substrate surface and improving the interfacial adhesion. These findings not only shed light on the structure-property relationship at the interface, but also provide a novel approach for developing sticking/anti-sticking technologies through precise control of the interfacial polymer nanostructures.

We report that the nanometer-scale architecture of polymer chains plays a crucial role in its protein resistant property over surface chemistry. Protein-repellent (noncharged), few nanometer thick polymer layers were designed with homopolymer chains physisorbed on solids. We evaluated the antifouling property of the hydrophilic or hydrophobic adsorbed homopolymer chains against bovine serum albumin in water. Molecular dynamics simulations along with sum frequency generation spectroscopy data revealed the selforganized nanoarchitecture of the adsorbed chains composed of inner nematiclike ordered segments and outer brush-like segments across homopolymer systems with different interactions among a polymer, substrate, and interfacial water. We propose that this structure acts as a dual barrier against protein adsorption.

We here report that adsorbed chains composed of one of the constituent blocks can be used as a new surface modification approach to induce perpendicularly oriented lamellar microdomains in block copolymer thin films. A nearly symmetric polystyrene-block-poly­(methyl methacrylate) (PS-block-PMMA) diblock copolymer was used as a model. Densely packed PS- or PMMA-adsorbed chains of about 2–3 nm in thickness (“polymer nanocoatings”) were deposited on silicon (Si) substrates using a solvent-rinsing approach. Spin-cast films of 40 or 60 nm-thick PS-block-PMMA (equivalent to two or three interdomain spacings) were subsequently deposited onto the PS or PMMA nanocoatings. Grazing incidence small-angle X-ray scattering experiments revealed the formation of perpendicularly oriented lamellar microdomains within the entire films at 200 °C, where balanced interfacial interactions at the polymer–air interface were achieved. Additionally, X-ray photon correlation spectroscopy studies demonstrated the dynamics of the fully standing lamellar microdomains in the melt, which are coupled to cooperative interdomain movement. We demonstrate that the “neutrality” of the nanocoating is attributed to its noninteractive property against both blocks. This “structurally neutral” property prevents adsorption of the PS-block-PMMA chains on the bare Si substrate that causes the undesirable substrate field effect.

Solid films of deoxyribonucleic acid (DNA) containing a hydrated ionic liquid, choline dihydrogen phosphate (CDP), were prepared by a solvent-casting method. Thermal properties, aggregation structure, thermal molecular motion, and tensile properties of CDP-containing DNA films were examined by thermogravimetry (TG), wide-angle X-ray diffraction (WAXD) measurement, dynamic mechanical analysis (DMA), and tensile tests, respectively. The water retentivity of the films at room temperature was much improved with CDP. The packing density of DNA helical chains clearly depended on the amount of CDP in the film. A small amount of CDP contributed to the suppression of the BI → BII conformational transition and the cooperative motion of the DNA duplex in the film. The tensile properties of the film drastically changed in the presence of CDP. When the amount of hydrated CDP in the film increased, the mechanical response of the film changed from glassy-like to rubbery-like via a semicrystalline-like state. The above results make it clear that CDP plays two major roles as a water absorber and plasticizer in the DNA film. Thus, it can be concluded that the use of an ionic liquid as an additive significantly increases the possibility of using a DNA solid film as a structural material.

Biocompatible deoxyribonucleic acid (DNA), with high mechanical strength, was employed as the substrate for a Ag nanowire (Ag NW) pattern and then used to fabricate flexible resistor-type memory devices. The memory exhibited typical write-once-read-many (WORM)-type memory features with a high ON/OFF ratio (10), long-term retention ability (10 s) and excellent mechanical endurance.

Here we present a microengineered soft-robotic in vitro platform developed by integrating a pneumatically regulated novel elastomeric actuator with primary culture of human cells. This system is capable of generating dynamic bending motion akin to the constriction of tubular organs that can exert controlled compressive forces on cultured living cells. Using this platform, we demonstrate cyclic compression of primary human endothelial cells, fibroblasts, and smooth muscle cells to show physiological changes in their morphology due to applied forces. Moreover, we present mechanically actuatable organotypic models to examine the effects of compressive forces on three-dimensional multicellular constructs designed to emulate complex tissues such as solid tumors and vascular networks. Our work provides a preliminary demonstration of how soft-robotics technology can be leveraged for in vitro modeling of complex physiological tissue microenvironment, and may enable the development of new research tools for mechanobiology and related areas.

Double‐stranded deoxyribonucleic acids (DNAs) were intermolecularly cross‐linked using 2,5‐hexanedione under reductive amination conditions in aqueous phase. Cross‐linking points between DNAs were directly observed by atomic force microscopy in conjunction with a conventional gel electrophoresis analysis. While DNA chains near cross‐linking points were denatured, DNA chains not near cross‐linking points maintained B‐form double strands. A transparent and self‐supported film of cross‐linked DNA (DNA‐c) was obtained by a simple solvent‐casting method. The tensile properties of DNA‐c films were much better than those of non‐cross‐linked DNA (DNA‐n) films due to the presence of the cross‐linking portions. Structural analyses based on wide‐angle X‐ray diffraction measurements revealed that the reorientation of DNA‐c was remarkably restricted by the introduction of cross‐linking points.

Liquid crystal-nanoparticle (LC-NP) hybrid systems allow synergistic interactions between LC matrixes with anisotropic alignment and NP dopants with versatile functionalities. A uniform, well-dispersed, and highly stable thermotropic LC-NP mixture paves the way for further applications. In this work, a linear promesogenic ligand and two types of dendritic promesogenic ligands with alkyl or oligo ethylene glycol (OEG) chains are designed and synthesized to facilitate incorporating NPs into the thermotropic 4-cyano-4′-pentylbiphenyl (5CB) LC matrix. A comparison study between the linear and the dendritic ligands on the capability to promote miscibility and stability of NPs in LCs is conducted. Miscibility test results show that the linear ligand and the OEG-chained dendrimer both perform well in uniformly dispersing NPs in LCs. Dynamic assemblies of NPs assisted by dendritic ligands and driven by aligning and equilibrating of mesogens are captured, showing the potential of manipulating the assembly of NPs through external thermal stimuli. The stability test shows that both types of dendrimers can significantly enhance the shelf-life time and thermal stability of NPs compared to the linear ligand. In particular, Au NPs capped with OEG-chained dendrimers are stable in 5CB for 6 months at room temperature and over 10 h at 50 °C. The synthesis of dendritic ligands is highly modulated and can be generalized onto NPs with different dimensions and properties. Tied by the dendritic promesogenic ligands, this LC-NP hybrid system with good uniformity and stability could be further applied to tunable optical displays, responsive materials, etc.