The Pathway to Intelligence: Using Stimuli-Responsive Materials as Building Blocks for Constructing Smart and Functional Systems

Multitasking polyamine/ferrioxalate nano-sized assemblies: thermo-, photo-, and redox-responsive soft materials made easy

Responsive nanomaterials have emerged as key components in materials sciences. Herein, we report the one-step preparation of multi-stimuli responsive polyamine-salt aggregates (PSA) by ionically crosslinking polyethylenimine with potassium ferrioxalate (FeOx). The unique properties of FeOx enables a novel class of soft nanomaterial that disassembles by exposure to light, reducing environments and temperature.

Surface Plasmon Resonance-Enhanced Photoacoustic Imaging and Photothermal Therapy of Endogenous H2 S-Triggered Au@Cu2 O

Smart theranostics agents triggered by endogenous H₂ S with combined activated photoacoustic imaging and photothermal therapy can improve the diagnosis and treatment of colon cancer. However, the low theranostic performance of the current smart theranostics agents after the triggering step has limited their further application. In this work, the theranostic performance of endogenous H₂ S-triggered Au@Cu₂ O for the diagnosis and treatment of colon cancer, which is generated from the localized surface plasmon resonance coupling effect between a noble metal (Au) and a semiconductor (Cu₂ O), is investigated. Compared with Cu₂ O, the prepared H₂ S-triggered Au@Cu₂ O shows a significantly stronger absorption at the near-infrared region, such as a ≈2.1 times change at 808 nm, giving a photothermal conversion efficiency increase of ≈1.2 times. More importantly, Au@Cu₂ O still exhibits good photoacoustic imaging contrast and photothermal properties for treatment of colon cancer in vivo even at very low injection doses. This work not only investigates an endogenous H₂ S-triggered Au@Cu₂ O theranostic agent with enhanced theranostic performance for colon cancer but also provides a novel strategy for designing high-performance theranostic agents.

Smart Composite Hydrogels with pH-Responsiveness and Electrical Conductivity for Flexible Sensors and Logic Gates

Stimuli-responsive conductive hydrogels have a wide range of applications due to their intelligent sensing of external environmental changes, which are important for smart switches, soft robotics, and flexible sensors. However, designing stimuli-responsive conductive hydrogels with logical operation, such as smart switches, remains a challenge. In this study, we synthesized pH-responsive conductive hydrogels, based on the copolymer network of acrylic acid and hydroxyethyl acrylate doped with graphene oxide. Using the good flexibility and conductivity of these hydrogels, we prepared a flexible sensor that can realize the intelligent analysis of human body motion signals. Moreover, the pH-responsive conductive hydrogels were integrated with temperature-responsive conductive hydrogels to develop logic gates with sensing, analysis, and driving functions, which realized the intellectualization of conductive hydrogels.

Flexible Films for Smart Thermal Management: Influence of Structure Construction of a Two-Dimensional Graphene Network on Active Heat Dissipation Response Behavior

In recent years, the development and wide application of micro-electronic technology brings forward high demands for active thermal management systems. However, such systems are not only costly, but also usually tethered, and need constant power to operate. To avoid such a limitation, smart thermal management systems have been developed to achieve active thermal management. Here, inspired by the temperature control principle of a butterfly, a shape memory polymer was used to endow the thermally conductive graphene-polymer hybrid film with intelligence. As the device temperature reaches 60 °C, the bud-shaped hybrid film started to bloom, which is a visually active heat dissipation process. As a result, this active process promoted the thermal management capacity of the hybrid film and increased the temperature-raising time of the light-emitting diode. Through the construction of a bilayer structure, the transmission channel for phonon transfer was optimized, which lead the hybrid film to attain a remarkable thermal conductivity of 21.83 W·m^-1·K^-1 with 30 wt % graphene. This graphene-polymer hybrid film shows potential application in the smart thermal management field.

Synthesis and physicochemical properties of dual-responsive acrylic acid/butyl acrylate cross-linked nanogel systems

HYPOTHESIS

A cross-linked amphiphilic nanogel containing a high mole% of hydrophilic pH-responsive moiety can provide enhanced functionality regarding stimuli-responsiveness, water-dispersibility, hydrophobic substance loading, and structural stability under harsh environmental conditions. These nanogels could be synthesized using a one-pot procedure for large-scale applications. Moreover, the interplay of various interaction forces in these colloidal systems is being investigated.

EXPERIMENTS

Model nanogels consisting of acrylic acid-butyl acrylate-ethylene glycoldimethacrylate were synthesized using an emulsion copolymerization via a seeded semi-batch process under an acidic condition. The structures were assessed by Fourier transform infrared spectroscopy and potentiometric-conductometric titrations. Zeta potential, field-emission scanning electron microscopy, and transmission electron microscopy were used to evaluate the dispersion stability, size distribution, and structural distribution, respectively. Their stimuli-responsive behavior was studied by combining static and dynamic light scattering and titration analyses.

FINDINGS

Monodisperse nanospheres of approximately 150 nm were successfully prepared by implementing a one-pot practical pathway. These nanogels displayed a dual thermo- and pH-responsive behavior, reflecting the high efficiency of physical cross-linking make it ideal for drug delivery and oil industry applications. Moreover, a novel symmetric pH-activated morphology transformation behavior was revealed. Accordingly, a compositional distribution was proposed and assessed by exploring the polymerization process.

Peptide Tectonics: Encoded Structural Complementarity Dictates Programmable Self-Assembly

Programmable self-assembly of peptides into well-defined nanostructures represents one promising approach for bioinspired and biomimetic synthesis of artificial complex systems and functional materials. Despite the progress made over the past two decades in the development of strategies for precise manipulation of the self-assembly of peptides, there is a remarkable gap between current peptide assemblies and biological systems in terms of structural complexity and functions. Here, the concept of peptide tectonics for the creation of well-defined nanostructures predominately driven by the complementary association at the interacting interfaces of tectons is introduced. Peptide tectons are defined as peptide building blocks exhibiting structural complementarity at the interacting interfaces of commensurate domains and undergoing programmable self-assembly into defined supramolecular structures promoted by complementary interactions. Peptide tectons are categorized based on their conformational entropy and the underlying mechanism for the programmable self-assembly of peptide tectons is highlighted focusing on the approaches for incorporating the structural complementarity within tectons. Peptide tectonics not only provides an alternative perspective to understand the self-assembly of peptides, but also allows for precise manipulation of peptide interactions, thus leading to artificial systems with advanced complexity and functions and paves the way toward peptide-related functional materials resembling natural systems.

Functional materials: making the world go round

This themed issue includes a collection of articles on functional materials.

Boron-based stimuli responsive materials

Representative types of boron-based molecular systems that respond to external stimuli such as temperature, pressure, light, or chemicals (oxygen, acid, base etc.) are described in this review article. The boron molecules are classified according to their operating mechanisms, with emphasis on systems, which are based on switchable boron-donor bonds and switchable excited states.

The evolution of spiropyran: fundamentals and progress of an extraordinarily versatile photochrome

Spiropyrans have played a pivotal role in the emergence of the field of chromism following their discovery in the early 20th century, with almost ubiquitous use in materials applications especially since their photochromism was discovered in 1952.