Stimuli-transition of hydrophobicity/hydrophilicity in o-nitrobenzyl ester-containing multi-responsive copolymers: Application in patterning and droplet stabilization in heterogeneous media

Photo-Controllable Smart Hydrogels for Biomedical Application: A Review

Nowadays, smart hydrogels are being widely studied by researchers because of their advantages such as simple preparation, stable performance, response to external stimuli, and easy control of response behavior. Photo-controllable smart hydrogels (PCHs) are a class of responsive hydrogels whose physical and chemical properties can be changed when stimulated by light at specific wavelengths. Since the light source is safe, clean, simple to operate, and easy to control, PCHs have broad application prospects in the biomedical field. Therefore, this review timely summarizes the latest progress in the PCHs field, with an emphasis on the design principles of typical PCHs and their multiple biomedical applications in tissue regeneration, tumor therapy, antibacterial therapy, diseases diagnosis and monitoring, etc. Meanwhile, the challenges and perspectives of widespread practical implementation of PCHs are presented in biomedical applications. This study hopes that PCHs will flourish in the biomedical field and this review will provide useful information for interested researchers.

Stimuli-responsive destructible polymeric hydrogels based on irreversible covalent bond dissociation

Covalently crosslinked stimuli-destructible hydrogels with the ability of irreversible bond dissociation have attracted great attentions due to their biodegradability, stability against hydrolysis, and controlled solubility upon insertion of desired triggers.

Photoswitchable surface wettability of ultrahydrophobic nanofibrous coatings composed of spiropyran-acrylic copolymers

HYPOTHESIS

Light-controlling of surface characteristics in polymeric coatings has been a significant research area because of its potential application in development of smart surfaces. Wettability of light-responsive polymeric coatings based on spiropyran photochromic compound could be tuned by light irradiation. This is mainly because of spiropyran isomerization between the hydrophobic and hydrophilic states.

EXPERIMENTS

Light-responsive latex nanoparticles containing spiropyran moieties were synthesized by semi-continuous emulsion copolymerization of acrylate monomers, which have different chain flexibility depending on the copolymer composition. Photochromic properties of spiropyran in stimuli-responsive latex nanoparticles displayed dependence of photochromism intensity and its kinetics to flexibility of the polymer chains in addition to the polarity of media. Photoswitchable surface wettability of the spiropyran-containing acrylic copolymer coatings was investigated, where the photo-responsive coatings were prepared by solution casting and electrospinning methods.

FINDINGS

The photoswitchable coatings prepared by solution casting and electrospinning methods showed significant differences in their physical characteristics and especially surface wettability. The polymeric coatings displayed water droplet contact angles in the range of 60-93°, which could reversibly be switched to 55-86° upon UV light (365 nm) illumination as a result of isomerization of the hydrophobic spiro form to the zwitterionic merocyanine form. The nanofibrous coatings prepared by electrospinning method displayed higher contact angles in the range of 120-136°, which was switched to 78-105° upon UV light irradiation. The developed photo-responsive coatings displayed highly-efficient photoswitching between the two hydrophobic and hydrophilic states as a response to UV and visible light irradiation. The photoswitchable nanofibrous coatings displayed ultrahydrophobic characteristics, where the colored water droplets were stable on their surface and could easily be adsorbed by a cellulosic tissue. In summary, the photoswitchable nanofibrous coatings could be applied for design and development of ultrahydrophobic materials with the ability of photo-controlling of surface wettability by light irradiation with tunable intensity.

Photoluminescent and Chromic Nanomaterials for Anticounterfeiting Technologies: Recent Advances and Future Challenges

Counterfeiting and inverse engineering of security and confidential documents, such as banknotes, passports, national cards, certificates, and valuable products, has significantly been increased, which is a major challenge for governments, companies, and customers. From recent global reports published in 2017, the counterfeiting market was evaluated to be $107.26 billion in 2016 and forecasted to reach $206.57 billion by 2021 at a compound annual growth rate of 14.0%. Development of anticounterfeiting and authentication technologies with multilevel securities is a powerful solution to overcome this challenge. Stimuli-chromic (photochromic, hydrochromic, and thermochromic) and photoluminescent (fluorescent and phosphorescent) compounds are the most significant and applicable materials for development of complex anticounterfeiting inks with a high-security level and fast authentication. Highly efficient anticounterfeiting and authentication technologies have been developed to reach high security and efficiency. Applicable materials for anticounterfeiting applications are generally based on photochromic and photoluminescent compounds, for which hydrochromic and thermochromic materials have extensively been used in recent decades. A wide range of materials, such as organic and inorganic metal complexes, polymer nanoparticles, quantum dots, polymer dots, carbon dots, upconverting nanoparticles, and supramolecular structures, could display all of these phenomena depending on their physical and chemical characteristics. The polymeric anticounterfeiting inks have recently received significant attention because of their high stability for printing on confidential documents. In addition, the printing technologies including hand-writing, stamping, inkjet printing, screen printing, and anticounterfeiting labels are discussed for introduction of the most efficient methods for application of different anticounterfeiting inks. This review would help scientists to design and develop the most applicable encryption, authentication, and anticounterfeiting technologies with high security, fast detection, and potential applications in security marking and information encryption on various substrates.