Preparation and characterization of pH-responsive and thermoresponsive hybrid microgel particles with gold nanorods

Determination of Aminophylline in Human Serum Using Hydrogel Microspheres for Coupled Surface-Enhanced Raman Spectroscopy (SERS) and Solid-Phase Extraction

Aminophylline (AMP) is a bronchodilator. The therapeutic and toxic doses are very close. Therefore, therapeutic drug monitoring (TDM) of AMP is essential in clinical practice. Microgels were synthesized by free radical precipitation polymerization. Silver@poly(N-isopropyl acrylamide) (Ag@PNIPAM) hybrid microgels were obtained by loading silver (Ag) nanoparticles into the three-dimensional network of the microgels by in situ reduction. The microgel is a three-dimensional reticular structure with tunable pore size, large specific surface area, and good biocompatibility, which can be used as a sorbent for solid-phase extraction (SPE) of target molecules in complex matrices and as a surface-enhanced Raman spectroscopy (SERS) substrate. We optimized the conditions affecting SERS enhancement, such as silver nitrate (AgNO3) concentration and SPE time, according to the SERS strategy of Ag@PNIPAM hybrid microgels to achieve label-free TDM for trace AMP in human serum. The results showed good linearity between the logarithmic concentration of AMP and its SERS intensity in the range of 1-1.1 × 102 µg/mL, with a correlation coefficient (R2) of 0.9947 and a low detection limit of 0.61 µg/mL. The assay accuracy was demonstrated by spiking experiments, with recoveries ranging from 93.0 to 101.8%. The method is rapid, sensitive, reproducible, requires simple sample pretreatment, and has good potential for use in clinical treatment drug monitoring.

Fabrication of attapulgite-based dual responsive composite hydrogel and its efficient adsorption for methyl violet

In this work, attapulgite (ATP)-based dual sensitive poly (N-isopropylacrylamide-co-acrylic acid) composite hydrogel, P(NIPAM-co-AA)/ATP, was prepared by free radical polymerization. The prepared composite hydrogel was characterized via methods of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), zeta potential analysis and Brunauer, Emmett, and Teller (BET) etc. The composite hydrogel showed pH and temperature sensitive behaviour, with lower critical solution temperature (LCST) of 35°C and highest swelling occurred at pH 8.0. The adsorption of methyl violet (MV) can be controlled by the hydrogel responsiveness, and 95.78% of MV can be removed at pH 8.0 and 35°C. The addition of a small amount of ATP (3 Wt%) can improve the swelling ratio and adsorption capacity. Kinetic analysis demonstrated that the experimental data were best fitted to the pseudo-second order model. Isotherm analysis showed that the equilibrium data followed Langmuir model with the adsorption capacity of 168.35 mg g^-1. In addition, the composite hydrogel has high adsorption selectivity for cationic dyes, and MV-loaded hydrogel is easy to regenerate, which can be used for successive adsorption cycles. These results demonstrate that the composite hydrogel has potential application in dye wastewater treatment.

Fabrication of Chlorophyll-Incorporated Nanogels for Potential Applications in Photothermal Cancer Therapy

Nanogels have been widely used in biomedical applications, such as carriers for hyperthermia cancer treatment, drug delivery, and imaging. Owing to the enhanced permeability and retention effect, nanogels have shown a great potential in cancer therapy. In this study, sodium copper chlorophyllin (SCC), a low cytotoxicity and biodegradable photothermal agent, was copolymerized with a nanogel of N-[3-(dimethylamino)propyl]methacrylamide. The nanogels could produce heat under exposure to a green laser with a 532 nm wavelength. The positively charged nature of the nanogels enhanced the endocytosis of the nanogels. The cell mortality was greatly enhanced with the treatment of the SCC-containing nanogels and green light illumination. Our results suggest the potential of SCC-containing nanogels in photothermal cancer therapy.

Functional Stimuli-Responsive Gels: Hydrogels and Microgels

One strategy that has gained much attention in the last decades is the understanding and further mimicking of structures and behaviours found in nature, as inspiration to develop materials with additional functionalities. This review presents recent advances in stimuli-responsive gels with emphasis on functional hydrogels and microgels. The first part of the review highlights the high impact of stimuli-responsive hydrogels in materials science. From macro to micro scale, the review also collects the most recent studies on the preparation of hybrid polymeric microgels composed of a nanoparticle (able to respond to external stimuli), encapsulated or grown into a stimuli-responsive matrix (microgel). This combination gave rise to interesting multi-responsive functional microgels and paved a new path for the preparation of multi-stimuli "smart" systems. Finally, special attention is focused on a new generation of functional stimuli-responsive polymer hydrogels able to self-shape (shape-memory) and/or self-repair. This last functionality could be considered as the closing loop for smart polymeric gels.

Multi-Responsive Behaviors of Copolymers Bearing N-Isopropylacrylamide with or without Phenylboronic Acid in Aqueous Solution

Continuing efforts to develop novel smart materials are anticipated to upgrade the quality of life of humans. Thermo-responsive poly(N-isopropylacrylamide) and glucose-responsive phenylboronic acid-typical representatives-are often integrated as multi-stimuli-sensitive materials, but few are available for side-by-side comparisons with their properties. In this study, both copolymers bearing N-isopropylacrylamide (NIPAAm), with or without 3-acrylamidophenylboronic acid (AAPBA), were synthesized by free radical polymerization, and characterized by Fourier transform infrared spectrometry, nuclear magnetic resonance hydrogen spectroscopy and gel permeation chromatography. Dynamic light scattering was used to analyze and compare the responsive behaviors of the copolymers in different aqueous solutions. Atomic force microscopy was also employed to investigate the apparent morphology changes with particle sizes. The results demonstrated that the introduction of NIPAAm endowed the composite materials with thermosensitivity, whereas the addition of AAPBA lowered the molecular weight of the copolymers, intensified the intermolecular aggregation of the nanoparticles, reduced the lower critical solution temperature (LCST) of the composites, and accordingly allowed the copolymers to respond to glucose. It was also concluded that the responding of smart copolymers to operating parameters can be activated only under special conditions, and copolymer dimension and conformation were affected by inter/intramolecular interactions.

Temperature-Responsive Polymer Microgel-Gold Nanorods Composite Particles: Physicochemical Characterization and Cytocompatibility

In this paper, we report an easy route for preparing new metal nanorod-polymer composites consisting of gold nanorods, Au NRs, and temperature responsive copolymer "microgel" particles. The microgel particles of ~200 nm in size, which contain carboxylic acid groups, were prepared by surfactant-free emulsion polymerization of a selected mixture made of N-isopropylacylamide and acrylic acid in the presence of a cross-linker N,N'-methylenebisacrylamide. The electrostatic interactions between the cationic cetyltrimethylammonium bromide (CTAB) stabilized Au NRs and anionic microgel particles were expected to occur in order to prepare stable Au NRs-microgel composite particles. The optical and structural characterization of the composite was achieved using UV-Vis spectroscopy, Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and dynamic light scattering (DLS). TEM image shows that Au NRs are attached on the surface of the microgel particles. Dynamic light scattering measurements prove that the composite particles are temperature responsive, which means the particles undergo a decrease in size as the temperature increases above its phase transition temperature. In vitro cytotoxicity of the composite materials were tested by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), Lactate dehydrogenase (LDH), and hemolysis assay, which showed non-toxicity (biocompatibility).

Review on synthesis, properties, characterization, and applications of responsive microgels fabricated with gold nanostructures

In this article, the classification, synthesis, properties, and applications of responsive microgels fabricated with gold (Au) nanostructures have been systematically reviewed. Microspheres, core-shell, core-shell-shell, hollow rings, and yolk-shell are different types of hybrid microgels containing Au nanostructures that have been reported in the literature. Hybrid microgels have tunable properties of both Au nanomaterial and smart polymeric material. Due to this unique combination, hybrid microgels containing Au nanomaterial are potential candidates for applications in drug delivery, photothermal therapy, glucose sensing, insulin delivery, catalysis, photonics, and ultrasensitive analyte analysis. Recent research progress in the design, characterization, and applications of Au nanomaterial containing smart polymer microgels has been described here. Many gaps in the literature and future perspectives of Au nanomaterial-based hybrid microgels have been highlighted in this review, which will be helpful for the people working in this area to plan their future work.

Fast and facile one-step synthesis of monodisperse thermo-responsive core–shell microspheres and applications

Highly monodisperse PMMA microspheres covered with a thermo-responsive shell were synthesized in a single step by means of photoinitiated RAFT dispersion polymerization at room temperature.

Highly efficient surface-enhanced Raman scattering substrate formulation by self-assembled gold nanoparticles physisorbed on poly(N-isopropylacrylamide) thermoresponsive hydrogels

Employing thermoresponsive hydrogels as scaffolding material for noble metal surface loading might be useful for the fabrication of surface-enhanced Raman scattering (SERS) surfaces. Here, we report on a new, reproducible, and simple approach to engineer poly(N-isopropylacrylamide) (PNIPAAm) hydrogel surfaces optimized for physisorption of gold nanoparticles (AuNPs). The advantage of this approach consists of the simple mechanism by which AuNPs are adsorbed on hydrogel templates, without sophisticated chemical treatments for their conjugation with the hydrogel. The resulting PNIPAAm-40 nm AuNP modes demonstrate that this approach gives the capability to tune the interparticle distance and, therefore, to control and modulate SERS affinity upon temperature changing.