Unidirectionally aligned line patterns driven by entropic effects on faceted surfaces

A simple, versatile approach to the directed self-assembly of block copolymers into a macroscopic array of unidirectionally aligned cylindrical microdomains on reconstructed faceted single crystal surfaces or on flexible, inexpensive polymeric replicas was discov-
ered. High fidelity transfer of the line pattern generated from the microdomains to a master mold is also shown. A single-grained line patterns over arbitrarily large surface areas without the use of top-down techniques is demonstrated, which has an order parameter typically in excess of 0.97 and a slope error of 1.1 deg. This degree of perfection, produced in a short time period, has yet to be achieved by any other methods. The exceptional alignment arises
from entropic penalties of chain packing in the facets coupled with the bending modulus of the cylindrical microdomains. This is shown, theoretically, to be the lowest energy state. The atomic crystalline ordering of the substrate is transferred, over multiple length scales, to the block copolymer microdomains, opening avenues to large-scale roll-to-roll type and nanoimprint processing of perfectly patterned surfaces and as templates and scaffolds for
magnetic storage media, polarizing devices, and nanowire arrays.

Multifunctional Lipid Multilayer Stamping

Nanostructured lipid multilayers on surfaces are a promising biofunctional nanomaterial. For example, surface-supported lipid multilayer diffraction gratings with optical properties that depend on the microscale spacing of the grating lines and the nanometer thickness of the lipid multilayers have been fabricated previously by dip-pen nanolithography (DPN), with immediate applications as label-free biosensors. The innate biocompatibility of such gratings makes them promising as biological sensor elements, model cellular systems, and construction materials for nanotechnology. Here a method is described that combines the lateral patterning capabilities and scalability of microcontact printing with the topographical control of nanoimprint lithography and the multimaterial integration aspects of dip-pen nanolithography in order to create nanostructured lipid multilayer arrays. This approach is denoted multilayer stamping. The distinguishing characteristic of this method is that it allows control of the lipid multilayer thickness, which is a crucial nanoscale dimension that determines the optical properties of lipid multilayer nanostructures. The ability to integrate multiple lipid materials on the same surface is also demonstrated by multi-ink spotting onto a polydimethoxysilane stamp, as well as higher-throughput patterning (on the order of 2 cm2 s−1 for grating fabrication) and the ability to pattern lipid materials that could not previously be patterned with high resolution by lipid DPN, for example, the gel-phase phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or the steroid cholesterol.

Synthesis of Monodisperse, Covalently Cross-Linked, Degradable “Smart” Microgels Using Microfluidics

The development of a robust method for the synthesis of highly monodisperse microgels cross-linked with degradable covalent bonds offers the potential for fabricating microgels with the highly controllable porosities, cell interactions, and degradation half-lives required for biomedical applications. A microfluidic chip is designed that enables the on-chip mixing and emulsification of two reactive polymer solutions (hydrazide and aldehyde-functionalized carbohydrates) to form monodisperse, hydrazone cross-linked microgels in the size range of ≈40–100 μm. The device can be run continuously for at least 30 h without a significant drift in particle size. The resulting microgels have a homogeneous bulk composition and can swell and deswell as the solvent conditions change in predictable ways based on the chemistry of the reactive polymers used, thereby enabling improved control over both the chemistry and morphology of the resulting microgels relative to other reported approaches. The in situ gelation chemistry used facilitates rapid microgel formation within the droplets without requiring the use of UV light or heating to initiate polymerization, thus making this approach of particular potential utility in cell encapsulation or drug delivery (as demonstrated).

Elastomeric Origami: Programmable Paper-Elastomer Composites as Pneumatic Actuators

The development of soft pneumatic actuators based on composites consisting of elastomers with embedded sheet or fiber structures (e.g., paper or fabric) that are flexible but not extensible is described. On pneumatic inflation, these actuators move anisotropically, based on the motions accessible by their composite structures. They are inexpensive, simple to fabricate, light in weight, and easy to actuate. This class of structure is versatile: the same principles of design lead to actuators that respond to pressurization with a wide range of motions (bending, extension, contraction, twisting, and others). Paper, when used to introduce anisotropy into elastomers, can be readily folded into 3D structures following the principles of origami; these folded structures increase the stiffness and anisotropy of the elastomeric actuators, while being light in weight. These soft actuators can manipulate objects with moderate performance; for example, they can lift loads up to 120 times their weight. They can also be combined with other components, for example, electrical components, to increase their functionality.

Inkjet-Printed Graphene Electronics

We demonstrate inkjet printing as a viable method for large-area fabrication of graphene devices. We produce a graphene-based ink by liquid phase exfoliation of graphite in N-methylpyrrolidone. We use it to print thin-film transistors, with mobilities up to 95 cm2 V–1 s–1, as well as transparent and conductive patterns, with 80% transmittance and 30 kΩ/□ sheet resistance. This paves the way to all-printed, flexible, and transparent graphene devices on arbitrary substrates.

Receptor-Mediated Delivery of Magnetic Nanoparticles across the Blood–Brain Barrier

A brain delivery probe was prepared by covalently conjugating lactoferrin (Lf) to a poly(ethylene glycol) (PEG)-coated Fe3O4 nanoparticle in order to facilitate the transport of the nanoparticles across the blood–brain barrier (BBB) by receptor-mediated transcytosis via the Lf receptor present on cerebral endothelial cells. The efficacy of the Fe3O4-Lf conjugate to cross the BBB was evaluated in vitro using a cell culture model for the blood–brain barrier as well as in vivo in SD rats. For an in vitro experiment, a well-established porcine BBB model was used based on the primary culture of cerebral capillary endothelial cells grown on filter supports, thus allowing one to follow the transfer of nanoparticles from the apical (blood) to the basolateral (brain) side. For in vivo experiments, SD rats were used as animal model to detect the passage of the nanoparticles through the BBB by MRI techniques. The results of both in vitro and in vivo experiments revealed that the Fe3O4-Lf probe exhibited an enhanced ability to cross the BBB in comparison to the PEG-coated Fe3O4 nanoparticles and further suggested that the Lf-receptor-mediated transcytosis was an effective measure for delivering the nanoparticles across the BBB.

Free-floating hydrogel-based rafts supporting a microarray of functional entities at fluid interfaces

In the present paper, we report a method for fabricating a macroscopic, free-floating device that supports a microarray of molecular functional entities. Therefore, the fabrication process developed by us combines bottom-up and top-down microfabrication strategies for a spatially controllable integration of molecular entities into the macroscopic device. For application, the generated device is transferred to fluid interfaces. Through a combined experimental and theoretical study, we demonstrate that the microscopic cavities of the intrinsically hydrophilic comb-shaped mesh structure enable the flotation of the device at a water–air interface of a sessile droplet due to surface tension effects. The design of the functionalized and free-floating device affords a long-term stable approach with respect to a chemical patterning of this fluid interface without loss of the lateral arrangement of the functional entities over time.