Materials and design of nanostructured broadband light absorbers for advanced light-to-heat conversion.

Light-to-heat conversion systems have been attracting growing research interest in the last few decades, due to their highly intriguing photothermal properties and their wide applications ranging from biomedical applications to solar energy harvesting to mechanical actuators. In general, because the light-to-heat conversion efficiency depends strongly on the absorbing material, significant efforts have been focused on fabricating broadband light absorbers. However, there are several challenges associated with the design and fabrication of light absorbers, such as minimizing heat loss, and optimizing the broadband light absorption and omnidirectional light absorption. Thus, the rational design of enhanced light absorbers is critical to achieve efficient light absorption over a broad wavelength range. In this paper, we introduce the basic theory of light absorption and heat transfer, then summarize fundamental understanding of representative light-to-heat conversion agents including carbon-based, semiconductor-based and plasmonic metal-based materials and structures, and highlight state-of-the-art structural designs towards the development of broadband light absorbers. In addition, the practical applications of these materials and designs are also discussed.

Biosafe, Eco-Friendly Levan Polysaccharide toward Transient Electronics.

New options in the material context of transient electronics are essential to create or expand potential applications and to progress in the face of technological challenges. A soft, transparent, and cost-effective polymer of levan polysaccharide that is capable of complete, programmable dissolution is described when immersed in water and implanted in an animal model. The results include chemical analysis, the kinetics of hydrolysis, and adjustable dissolution rates of levan, and a simple theoretical model of reactive diffusion governed by temperature. In vivo experiments of the levan represent nontoxicity and biocompatibility without any adverse reactions. On-demand, selective control of dissolution behaviors with an animal model demonstrates an effective triggering strategy to program the system's lifetime, providing the possibility of potential applications in envisioned areas such as bioresorbable electronic implants and drug release systems.

Hydrophilic Chlorin e6-Poly(amidoamine) Dendrimer Nanoconjugates for Enhanced Photodynamic Therapy.

In photodynamic therapy (PDT), chlorin e6 (Ce6), with its high phototoxic potential and strong absorption of visible light, penetrates deeply into photodamaged tissue. However, despite this fact, the direct application of Ce6 to PDT has been limited by its low water solubility and poor cancer cell localization. To ameliorate this situation, we report herein on the use of a hydrophilic nanoconjugate (DC) comprised of Ce6 and poly(amidoamine) dendrimer, which improves the water solubility and intracellular uptake of Ce6, thereby enhancing PDT efficacy. The synthesis of DC was verified by ¹H nuclear magnetic resonance (NMR) analysis, and the coupling ratio of Ce6 introduced onto DC was 2.64. The prepared DC was spherical, with an average diameter of 61.7 ± 3.5 nm. In addition, the characteristic ultraviolet-visible absorption bands of DC in distilled water were similar to those of free Ce6 in dimethyl sulfoxide (DMSO), indicating that the Ce6 chromophore did not change upon conjugation. Investigation using fluorescence spectroscopy and confocal microscopy revealed a greater intracellular uptake of DC than of Ce6 alone. Moreover, DC exhibited significantly increased phototoxicity to human cervical cancer cells, mostly because of apoptotic cell death. These results imply that DC is a candidate for the clinical treatment of PDT.

On-Demand Drug Release from Gold Nanoturf for a Thermo- and Chemotherapeutic Esophageal Stent.

Stimuli-responsive delivery systems for cancer therapy have been increasingly used to promote the on-demand therapeutic efficacy of anticancer drugs and, in some cases, simultaneously generate heat in response to a stimulus, resulting in hyperthermia. However, their application is still limited due to the systemic drawbacks of intravenous delivery, such as rapid clearance from the bloodstream and the repeat injections required for sustained safe dosage, which can cause overdosing. Here, we propose a gold (Au)-coated nanoturf structure as an implantable therapeutic interface for near-infrared (NIR)-mediated on-demand hyperthermia chemotherapy. The Au nanoturf possessed long-lasting doxorubicin (DOX) duration, which helps facilitate drug release in a sustained and prolonged manner. Moreover, the Au-coated nanoturf provides reproducible hyperthermia induced by localized surface plasmon resonances under NIR irradiation. Simultaneously, the NIR-mediated temperature increase can promote on-demand drug release at desired time points. For in vivo analysis, the Au nanoturf structure was applied on an esophageal stent, which needs sustained anticancer treatment to prevent tumor recurrence on the implanted surface. This thermo- and chemo-esophageal stent induced significant cancer cell death with released drug and hyperthermia. These phenomena were also confirmed by theoretical analysis. The proposed strategy provides a solution to achieve enhanced thermo-/chemotherapy and has broad applications in sustained cancer treatments.

A semi-permanent and durable nanoscale-crack-based sensor by on-demand healing.

Although sensitivity and durability are desirable in a sensor, both of them cannot be easily achieved. Site-specific and effective signal acquisition on the limited area of a sensor inevitably allows fatigue accumulation and contamination. For example, an ultrasensitive nanoscale-crack-based sensor for detecting a mechanical stimulus with tremendous sensitivity (a gauge factor greater than 2000 under 2% strain), yet limited durability (up to a few thousand stretching cycles in tensile tests) has been presented previously. Herein, we suggest a simple yet robust nanoscale-crack-based sensor that achieves remarkable durability through the use of a self-healable polymer. The self-healable polymer helps the crack gap recover and maintain high stability for 1 million cycles under 2% strain. Moreover, site-specific recovery with infrared light irradiation was demonstrated with monolithic arrayed sensors. The proposed strategy provides a unique solution to achieving highly enhanced durability and high mechanosensitivity, which are typically incompatible.

Surface energy-tunable iso decyl acrylate based molds for low pressure-nanoimprint lithography.

We presented surface energy-tunable nanoscale molds for unconventional lithography. The mold is highly robust, transparent, has a minimized haze, does not contain additives, and is a non-fluorinated isodecyl acrylate and trimethylolpropane triacrylate based polymer. By changing the mixing ratio of the polymer components, the cross-linking density, mechanical modulus, and surface energy (crucial factors in low pressure ((1-2) × 105 N m-2) low pressure-nanoimprint lithography (LP-NIL)), can be controlled. To verify these properties of the molds, we also characterized the surface energy by measuring the contact angles and calculating the work of adhesion among the wafer, polymer film, and mold for successful demolding in nanoscale structures. Moreover, the molds showed high optical clarity and precisely tunable mechanical and surface properties, capable of replicating sub-100 nm patterns by thermal LP-NIL and UV-NIL.

Designs and processes toward high-aspect-ratio nanostructures at the deep nanoscale: unconventional nanolithography and its applications.

The patterning of high-resolution-featured deep-nanoscale structures with a high aspect ratio (AR) has received increasing attention in recent years as a promising technique for a wide range of applications, including electrical, optical, mechanical and biological systems. Despite extensive efforts to develop viable nanostructure fabrication processes, a superior technique enabling defect-free, high-resolution control over a large area is still required. In this review, we focus on recent important advances in the designs and processes of high-resolution nanostructures possessing a high AR, including hierarchical and 3D patterns. The unique applications of these materials are also discussed.