Toward 4D Nanoprinting with Tip-Induced Organic Surface Reactions

Reactive Additive Capillary Stamping with Double Network Hydrogel-Derived Aerogel Stamps under Solvothermal Conditions

Integration of solvothermal reaction products into complex thin-layer architectures is frequently achieved by combinations of layer transfer and subtractive lithography, whereas direct additive substrate patterning with solvothermal reaction products has remained challenging. We report reactive additive capillary stamping under solvothermal conditions as a parallel contact-lithographic access to patterns of solvothermal reaction products in thin-layer configurations. To this end, corresponding precursor inks are infiltrated into mechanically robust mesoporous aerogel stamps derived from double-network hydrogels. The stamp is then brought into contact with a substrate to be patterned under solvothermal reaction conditions inside an autoclave. The precursor ink forms liquid bridges between the topographic surface pattern of the stamp and the substrate. Evaporation-driven enrichment of the precursors in these liquid bridges, along with their liquid-bridge-guided conversion into the solvothermal reaction products, yields large-area submicron patterns of the solvothermal reaction products replicating the stamp topography. For example, we prepared thin hybrid films, which contained ordered monolayers of superparamagnetic submicron nickel ferrite dots prepared by solvothermal capillary stamping surrounded by nickel electrodeposited in a second orthogonal substrate functionalization step. The submicron nickel ferrite dots acted as a magnetic hardener, halving the remanence of the ferromagnetic nickel layer. In this way, thin-layer electromechanical systems, transformers, and positioning systems may be customized.

Phenolic Resin Dual-Use Stamps for Capillary Stamping and Decal Transfer Printing

We report an optimized two-step thermopolymerization process carried out in contact with micropatterned molds that yields porous phenolic resin dual-use stamps with topographically micropatterned contact surfaces. With these stamps, two different parallel additive substrate manufacturing methods can be executed: capillary stamping and decal transfer microlithography. Under moderate contact pressures, the porous phenolic resin stamps are used for nondestructive ink transfer to substrates by capillary stamping. Continuous ink supply through the pore systems to the contact surfaces of the porous phenolic resin stamps enables multiple successive stamp-substrate contacts for lithographic ink deposition under ambient conditions. No deterioration of the quality of the deposited pattern occurs, and no interruptions for ink replenishment are required. Under a high contact pressure, porous phenolic resin stamps are used for decal transfer printing. In this way, the tips of the stamps' contact elements are lithographically transferred to counterpart substrates. The granular nature of the phenolic resin facilitates the rupture of the contact elements upon stamp retraction. The deposited phenolic resin micropatterns characterized by abundance of exposed hydroxyl groups are used as generic anchoring sites for further application-specific functionalizations. As an example, we deposited phenolic resin micropatterns on quartz crystal microbalance resonators and further functionalized them with polyethylenimine for preconcentration sensing of humidity and gaseous formic acid. We envision that also preconcentration coatings for other sensing methods, such as attenuated total reflection infrared spectroscopy and surface plasmon resonance spectroscopy, are accessible by this functionalization algorithm.

Dip-Pen Nanolithography(DPN): from Micro/Nano-patterns to Biosensing

Dip-pen nanolithography is an emerging and attractive surface modification technique that has the capacity to directly and controllably write micro/nano-array patterns on diverse substrates. The superior throughput, resolution, and registration enable DPN an outstanding candidate for biological detection from the molecular level to the cellular level. Herein, we overview the technological evolution of DPN in terms of its advanced derivatives and DPN-enabled versatile sensing patterns featuring multiple compositions and structures for biosensing. Benefitting from uniform, reproducible, and large-area array patterns, DPN-based biosensors have shown high sensitivity, excellent selectivity, and fast response in target analyte detection and specific cellular recognition. We anticipate that DPN-based technologies could offer great potential opportunities to fabricate multiplexed, programmable, and commercial array-based sensing biochips.

Evolution and applications of polymer brush hypersurface photolithography

Hypersurface photolithography creates arbitrary polymer brush patterns with independent control over feature diameter, height, and spacing between features, while controlling composition along a polymer chain and between features.

A review on spacers and membranes: Conventional or hybrid additive manufacturing?

Over the past decade, 3D printing or additive manufacturing (AM) technology has seen great advancement in many aspects such as printing resolution, speed and cost. Membranes for water treatment experienced significant breakthroughs owing to the unique benefits of additive manufacturing. In particular, 3D printing's high degree of freedom in various aspects such as material and prototype design has helped to fabricate innovative spacers and membranes. However, there were conflicting reports on the feasibility of 3D printing, especially for membranes. Some research groups stated that technology limitations today made it impossible to 3D print membranes, but others showed that it was possible by successfully fabricating prototypes. This paper will provide a critical and comprehensive discussion on 3D printing specifically for spacers and membranes. Various 3D printing techniques will be introduced, and their suitability for membrane and spacer fabrication will be discussed. It will be followed by a review of past studies associated with 3D-printed spacers and membranes. A new category of additive manufacturing in the membrane water industry will be introduced here, known as hybrid additive manufacturing, to address the controversies of 3D printing for membrane. As AM technology continues to advance, its possibilities in the water treatment is limitless. Some insightful future trends will be provided at the end of the paper.

A 3D-Printed Self-Adhesive Bandage with Drug Release for Peripheral Nerve Repair

Peripheral nerve injury is a common disease that often causes disability and challenges surgeons. Drug-releasable biomaterials provide a reliable tool to regulate the nerve healing-associated microenvironment for nerve repair. Here, a self-adhesive bandage is designed that can form a wrap surrounding the injured nerve to promote nerve regeneration and recovery. Via a 3D printing technique, the bandage is prepared with a special structure and made up of two different hydrogel layers that can adhere to each other by a click reaction. The nanodrug is encapsulated in one layer with a grating structure. Wrapping the injured nerve, the grating layer of the bandage is closed to the injured site. The drug can be mainly released to the inner area of the wrap to promote the nerve repair by improving the proliferation and migration of Schwann cells. In this study, the bandage is used to assist the neurorrhaphy for the treatment of complete sciatic nerve transection without obvious defect in rats. Results indicate that the self-adhesive capacity can simplify the installation process and the drug-loaded bandage can promote the repairing of injured nerves. The demonstrated 3D-printed self-adhesive bandage has potential application in assisting the neurorrhaphy for nerve repair.

Manipulable Metal Catalyst for Nanographene Synthesis

Performing bottom-up synthesis by using molecules adsorbed on a surface is an effective method to yield functional polycyclic aromatic hydrocarbons (PAHs) and nanocarbon materials. The intramolecular cyclodehydrogenation of hydrocarbons is a critical process in this synthesis; however, thus far, its elementary steps have not been elucidated thoroughly. In this study, we utilize the metal tip of a low-temperature noncontact atomic force microscope as a manipulable metal surface to locally activate dehydrogenation for PAH-forming cyclodehydrogenation. This method leads to the dissociation of a H atom of an intermediate to yield the cyclodehydrogenated product in a target-selective and reproducible manner. We demonstrate the metal-tip-catalyzed dehydrogenation for both benzenoid and nonbenzonoid PAHs, suggesting its universal applicability as a catalyst for nanographene synthesis.

Multifaceted aspects of charge transfer

Charge transfer and charge transport are by far among the most important processes for sustaining life on Earth and for making our modern ways of living possible. Involving multiple electron-transfer steps, photosynthesis and cellular respiration have been principally responsible for managing the energy flow in the biosphere of our planet since the Great Oxygen Event. It is impossible to imagine living organisms without charge transport mediated by ion channels, or electron and proton transfer mediated by redox enzymes. Concurrently, transfer and transport of electrons and holes drive the functionalities of electronic and photonic devices that are intricate for our lives. While fueling advances in engineering, charge-transfer science has established itself as an important independent field, originating from physical chemistry and chemical physics, focusing on paradigms from biology, and gaining momentum from solar-energy research. Here, we review the fundamental concepts of charge transfer, and outline its core role in a broad range of unrelated fields, such as medicine, environmental science, catalysis, electronics and photonics. The ubiquitous nature of dipoles, for example, sets demands on deepening the understanding of how localized electric fields affect charge transfer. Charge-transfer electrets, thus, prove important for advancing the field and for interfacing fundamental science with engineering. Synergy between the vastly different aspects of charge-transfer science sets the stage for the broad global impacts that the advances in this field have.

UV-responsive cyclic peptide progelator bioinks

We describe cyclic peptide progelators which cleave in response to UV light to generate linearized peptides which then self-assemble into gel networks. Cyclic peptide progelators were synthesized, where the peptides were sterically constrained, but upon UV irradiation, predictable cleavage products were generated. Amino acid sequences and formulation conditions were altered to tune the mechanical properties of the resulting gels. Characterization of the resulting morphologies and chemistry was achieved through liquid phase and standard TEM methods, combined with matrix assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS).

Development of Dip-Pen Nanolithography (DPN) and Its Derivatives

Dip-pen nanolithography (DPN) is a unique nanofabrication tool that can directly write a variety of molecular patterns on a surface with high resolution and excellent registration. Over the past 20 years, DPN has experienced a tremendous evolution in terms of applicable inks, a remarkable improvement in fabrication throughput, and the development of various derivative technologies. Among these developments, polymer pen lithography (PPL) is the most prominent one that provides a large-scale, high-throughput, low-cost tool for nanofabrication, which significantly extends DPN and beyond. These developments not only expand the scope of the wide field of scanning probe lithography, but also enable DPN and PPL as general approaches for the fabrication or study of nanostructures and nanomaterials. In this review, a focused summary and historical perspective of the technological development of DPN and its derivatives, with a focus on PPL, in one timeline, are provided and future opportunities for technological exploration in this field are proposed.

Close-packed silane nanodot arrays by capillary nanostamping coupled with heterocyclic silane ring opening

We report the parallel generation of close-packed ordered silane nanodot arrays with nanodot diameters of few 100 nm and nearest-neighbor distances in the one-micron range.

Spatially resolved acyl transfer on surface by organo-catalytic scanning probe nanolithography (o-cSPL)

Local and catalytic acyl transfer for multipatterning of surfaces.

Groundbreaking research done in the area of nanolithography makes it a versatile tool to produce nanopatterns for a broad range of chemical surface functionalization or physical modifications. We report for the first time an organocatalytic scanning probe nanolithography (o-cSPL) approach. Covalent binding of an organocatalyst on the apex of an atomic force microscope (AFM) tip gives way to a system that allows the formation of locally defined acylated-alcohol patterns on self-assembled monolayers (SAMs). With resolutions comparable to those of other cSPL methods, this first example of o-cSPL holds promise for future applications of bottom-up nanolithography set-ups employing this novel technique.

Ordered Topographically Patterned Silicon by Insect-Inspired Capillary Submicron Stamping

Insect-inspired capillary submicron stamping and subsequent surface-limited metal-assisted chemical etching (MACE) with ammonium bifluoride as a HF source are employed for the high-throughput production of ordered topographically patterned silicon (tpSi). Insect feet often possess hairy contact elements through which adhesive secretion is deployed. Thus, arrays of adhesive secretion drops remain as footprints on contact surfaces. Stamps for insect-inspired capillary submicron stamping having surfaces topographically patterned with contact elements mimic the functional principles of such insect feet. They contain spongy continuous nanopore networks penetrating the entire stamps. Any ink (organic or aqueous) may be supplied from the backside of the nanoporous stamps to the contact elements. We generated ordered arrays of submicron AgNO₃ dots extending square millimeters on Si by manual stamping with cycle times of a few seconds under ambient conditions; at higher load, ordered holey AgNO₃ films were obtained. Surface-limited MACE correspondingly yielded either macroporous tpSi or Si pillar arrays. Inkjet printing of polymer solutions onto the tpSi yielded patterns of polymer blots conformally covering the tpSi. Such blot patterns could potentially represent a starting point for the development of persistent and scratch-resistant identity labels or quick response codes on silicon surfaces.

Large-Area Patterning of Metal Nanostructures by Dip-Pen Nanodisplacement Lithography for Optical Applications

Au nanostructures are remarkably important in a wide variety of fields for decades. The fabrication of Au nanostructures typically requires time-consuming and expensive electron-beam lithography (EBL) that operates in vacuum. To address this challenge, this paper reports the development of massive dip-pen nanodisplacement lithography (DNL) as a desktop fabrication tool, which allows high-throughput and rational design of arbitrary Au nanopatterns in ambient condition. Large-area (1 cm² ) and uniform (<10% variation) Au nanostructures as small as 70 nm are readily fabricated, with a throughput 100-fold higher than that of conventional EBL. As a proof-of-concept of the applications in the opitcal field, we fabricate discrete Au nanorod arrays that show significant plasmonic resonance in the visible range, and interconnected Au nanomeshes that are used for transparent conductive electrode of solar cells.