Characterizing viscoelastic properties of synthetic and natural fibers and their coatings with a torsional pendulum.

Characterizing and understanding the viscoelastic mechanical properties of natural and synthetic fibers is of great importance in many biological and industrial applications. Microscopic techniques such as micro/nano indentation have been successfully employed in such efforts, yet these tests are often challenging to perform on fibers and come with certain limitations in the interpretation of the obtained results within the context of the macroscopic viscoelasticity in the fiber. Here we instead explore the properties of a series of natural and synthetic fibers, using a freely-oscillating torsional pendulum.

Multilayer tubes that constrict, dilate, and curl in response to stimuli.

Tubular structures in nature have the ability to respond to their environment-for example, blood vessels can constrict or dilate, thereby regulating flow velocity and blood pressure. These tubes have multiple concentric layers, with each layer having a distinct composition and properties. Inspired by such natural structures, we have synthesized responsive multilayer tubes in the laboratory without resorting to complex equipment such as a 3-D printer.

Thermally and pH-responsive gelation of nanoemulsions stabilized by weak acid surfactants.

Nanoemulsions are widely used in applications such as in food products, pharmaceutical ingredients and cosmetics. Moreover, nanoemulsions have been a model colloidal system due to their ease of synthesis and the flexibility in formulations that allows one to engineer the inter-droplet potentials and thus to rationally tune the material microstructures and rheological properties. In this article, we study a nanoemulsion system in which the inter-droplet interactions are modulated by temperature and pH.

Thermoresponsive nanoemulsion-based gel synthesized through a low-energy process.

Thermoresponsive nanoemulsions find utility in applications ranging from food to pharmaceuticals to consumer products. Prior systems have found limited translation to applications due to cytotoxicity of the compositions and/or difficulties in scaling-up the process. Here, we report a route to thermally gel an oil-in-water nanoemulsion using a small amount of FDA-approved amphiphilic triblock Pluronic copolymers which act as gelling agents.

Nature-Inspired Hydrogels with Soft and Stiff Zones that Exhibit a 100-Fold Difference in Elastic Modulus.

Many biological materials, such as the squid beak and the spinal disc, have a combination of stiff and soft parts with very different mechanical properties, for example, the elastic modulus (stiffness) of the stiffest part of the squid beak is about 100 times that of the softest part. Researchers have attempted to mimic such structures using hydrogels but have not succeeded in synthesizing bulk gels with such large variations in moduli. Here, we present a general approach that can be used to form hydrogels with two or more zones having appreciably different mechanical characters.

Extrusion-Based 3D Printing of Hierarchically Porous Advanced Battery Electrodes.

A highly porous 2D nanomaterial, holey graphene oxide (hGO), is synthesized directly from holey graphene powder and employed to create an aqueous 3D printable ink without the use of additives or binders. Stable dispersions of hydrophilic hGO sheets in water (≈100 mg mL ) can be readily achieved. The shear-thinning behavior of the aqueous hGO ink enables extrusion-based printing of fine filaments into complex 3D architectures, such as stacked mesh structures, on arbitrary substrates.

Enzyme-Triggered Folding of Hydrogels: Toward a Mimic of the Venus Flytrap.

External triggers such as pH or temperature can induce hydrogels to swell or shrink rapidly. Recently, these triggers have also been used to alter the three-dimensional (3-D) shapes of gels: for example, a flat gel sheet can be induced to fold into a tube. Self-folding gels are reminiscent of natural structures such as the Venus flytrap, which folds its leaves to entrap its prey.