Self-indicating polymers: a pathway to intelligent materials.

Self-indicating polymers have emerged as a promising class of smart materials that possess the unique ability to undergo detectable variations in their physical or chemical properties in response to various stimuli. This article presents an overview of the most important mechanisms through which these materials exhibit self-indication, including aggregation, phase transition, covalent and non-covalent bond cleavage, isomerization, charge transfer, and energy transfer. Aggregation is a prevalent mechanism observed in self-indicating polymers, where changes in the degree of molecular organization result in variations in optical or electrical properties. Phase transition-induced self-indication relies on the transformation between different phases, such as liquid-to-solid or crystalline-to-amorphous transitions, leading to observable changes in color or conductivity. Covalent bond cleavage-based self-indicating polymers undergo controlled degradation or fragmentation upon exposure to specific triggers, resulting in noticeable variations in their structural or mechanical properties. Isomerization is another crucial mechanism exploited in self-indicating polymers, where the reversible transformation between the different isomeric forms induces detectable changes in fluorescence or absorption spectra. Charge transfer-based self-indicating polymers rely on the modulation of electron or hole transfer within the polymer backbone, manifesting as changes in electrical conductivity or redox properties. Energy transfer is an essential mechanism utilized by certain self-indicating polymers, where energy transfer between chromophores or fluorophores leads to variations in the emission characteristics. Furthermore, this review article highlights the diverse range of applications for self-indicating polymers. These materials find particular use in sensing and monitoring applications, where their responsive nature enables them to act as sensors for specific analytes, environmental parameters, or mechanical stress. Self-indicating polymers have also been used in the development of smart materials, including stimuli-responsive coatings, drug delivery systems, food sensors, wearable devices, and molecular switches. The unique combination of tunable properties and responsiveness makes self-indicating polymers highly promising for future advancements in the fields of biotechnology, materials science, and electronics.

Colloidal Polymer Nanoparticles as Smart Inks for Authentication and Indication of Latent Fingerprints and Scratch.

An environmentally friendly smart ink was developed by incorporating fluorescein into functionalized poly(methyl methacrylate) (PMMA) nanoparticles synthesized using an emulsifier-free emulsion copolymerization approach. The functional comonomers of 2-(dimethylamino)ethyl methacrylate (DMAEMA), acrylamide, hydroxyethyl methacrylate, and glycidyl methacrylate in 10 wt % with respect to methyl methacrylate were used to obtain the functionalized colloidal PMMA nanoparticles. Functional groups of the latex nanoparticles were characterized by Fourier-transform infrared spectroscopy. Field emission scanning electron microscopy results showed that all of the latex nanoparticles have nearly spherical morphologies with variations in size and surface smoothness due to the presence of different comonomers. Ultraviolet-visible and fluorescence spectra indicated that the fluorescein-doped latex nanoparticles containing the DMAEMA comonomer had the highest absorbance and fluorescence intensity. In the alkaline media, fluorescein turns to a dianion, showing a red shift and increased absorbance in the UV-vis spectroscopy. In addition, the electron inductive characteristics of the tertiary amine groups result in enhancing the conjugation of fluorescein molecules and increasing the fluorescence intensities. Therefore, the colloidal nanoparticles with amine functional groups were used in the formulation of a smart ink with applications in securing documents and fingerprints, encrypting banknotes and money, detecting latent fingerprints, crafting anticounterfeiting paper, and eventually providing optical detection and indication of surface scratches.

Fluorescent cellulosic composites based on carbon dots: Recent advances, developments, and applications.

Cellulose and its derivatives are highly applicable in advanced applications on the basis of fluorescence phenomena. Carbon dots (CDs) have also appealing properties, such as high photoluminescence, easy synthesis pathway, cheap source materials, chemical stability, and easy functionalization. In this regard, combination of luminescent CDs with natural cellulosic materials could adjust or expand its desirable properties and have advanced applications. This review summarizes chemical and physical incorporation of CDs and graphene quantum dots into different types of cellulosic materials to yield smart fluorescent materials with applications in films, catalysts, bioimaging, drug delivery, anticounterfeiting, and fluorescence chemosensors for sensing pH, temperature, cations, anions, glucose, and aromatic amines. The challenges and future directions in fluorescent materials based on CDs are also briefly discussed. We hope that these studies will provide more consideration and curiosity for chemists, biologists, and materials scientists working in the field of fluorescent and CDs-containing cellulosic materials.

Safety and efficacy of remote ischemic preconditioning in patients with severe carotid artery stenosis before carotid artery stenting: A proof-of-concept, randomized controlled trial.

Background: Remote ischemic preconditioning (RIPC) has been proposed as a possible potential treatment for ischemic stroke. This study aimed to investigate the frequency of micro-embolic brain infarcts after RIPC in patients with stroke who underwent elective carotid artery stenting (CAS) treatment. Methods: This study was managed at Shiraz University of Medical Sciences in southwest Iran. Patients undergoing CAS were randomly allocated into RIPC and control groups. Patients in the RIPC group received three intermittent cycles of 5-minute arm ischemia followed by reperfusion using manual blood cuff inflation/deflation less than 30 minutes before CAS treatment. Afterward, stenting surgery was conducted. Magnetic resonance imaging (MRI), including diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC), was acquired within the first 24 hours after CAS. Results: Seventy-four patients were recruited (79.7% men, age: 72.30 ± 8.57). Both groups of RIPC and control had no significant difference in baseline parameters (P > 0.05). Fifteen patients (40.5%) in the RIPC group and 19 (54.1%) patients in the control group developed restricted lesions in DWI MRI. In DWI+ patients, there were no significant differences according to the number of lesions, lesion surface area, largest lesion diameter, cortical infarcts percent, and ipsilateral and bilateral infarcts between the two groups. Conclusion: Although RIPC is a safe and non-invasive modality before CAS to decrease infarcts, this study did not show the advantage of RIPC in the prevention of infarcts following CAS. It may be because of the small sample size.

Polymer grafting on graphene layers by controlled radical polymerization.

In situ controlled radical polymerization (CRP) is considered as an important approach to graft polymer brushes with controlled grafting density, functionality, and thickness on graphene layers. Polymers are tethered with chain end or through its backbone to the surface or edge of graphene layers with two in situ polymerization methods of "grafting from" and "grafting through" and also a method based on coupling reactions known as "grafting to". The "grafting from" method relies on the propagation of polymer chains from the surface- or edge-attached initiators. The "grafting through" method is based on incorporation of double bond-modified graphene layers into polymer chains through the propagation reaction. The "grafting to" technique involves attachment of pre-fabricated polymer chains to the graphene substrate. Here, physical and chemical attachment approaches are also considered in polymer-modification of graphene layers. Combination of CRP mechanisms of reversible activation, degenerative (exchange) chain transfer, atom transfer, and reversible chain transfer with various kinds of grafting reactions makes it possible to selectively functionalize graphene layers. The main aim of this review is assessment of the recent advances in the field of preparation of polymer-grafted graphene substrates with well-defined polymers of controlled molecular weight, thickness, and polydispersity index. Study of the opportunities and challenges for the future works in controlling of grafting density, site-selectivity in grafting, and various topologies of the brushes with potential applications in stimuli-responsive surfaces, polymer composites, Pickering emulsions, coating technologies, and sensors is also considered.