Glucose-responsive microgels with a core-shell structure

Microgel-Based Smart Materials: How Do You Design a Microgel?

Microgels, which are submicrometer- to micrometer-sized hydrogels, have been investigated for more than four decades and are now widely applied in modern advanced smart materials. The "smartness" of microgel-based materials is attributed to their material composition, cross-linking strategy, and responsiveness to stimuli. These characteristics are inherently influenced and constrained by the fabrication method, which, in turn, affects the properties of the resulting microgel particles. While numerous studies have reported on the applications of microgels, the translation of fundamental research findings into practical applications remains limited. For example, while recent research in biomedical applications has focused on controlled and smart drug release based on novel environmentally responsive mechanisms, this Review highlights that the responsiveness still requires further refinement in terms of selectivity and precision. Moreover, the variety of drugs that can be used remains limited, and as this Review clarifies, microgel-based materials frequently do not possess adequate biocompatibility for biomedical applications. This Review initially summarizes the relationship between microgel synthesis techniques and their resulting properties. Furthermore, we observe that recent reports on the applications of microgels fall primarily into the categories of sensing, separation, biomedical applications, and additive manufacturing. These reports highlight recent advances in microgel applications; however, several challenges specific to each application area still need to be addressed. For instance, improving sensitivity and selectivity is a key concern in the sensing field. This Review identifies these challenges and proposes future directions for the advancement of microgel-based smart materials.

Glucose-Responsive Materials for Smart Insulin Delivery: From Protein-Based to Protein-Free Design

Over the last four decades, glucose-responsive materials have emerged as promising candidates for developing smart insulin delivery systems, offering an alternative approach to treating diabetes. These materials replicate the pancreas's natural "closed loop" insulin secretion function by detecting changes in blood glucose levels and releasing insulin accordingly. This perspective highlights the evolution of glucose-responsive materials from protein-based materials, such as glucose oxidase (GOx), and glucose-binding proteins, such as concanavalin A (ConA), to protein-free materials, including phenylboronic acid (PBA) and their applications in smart insulin delivery. We first describe protein-based glucose-responsive systems that depend on different macromolecules, including enzymes and proteins, that interact directly with glucose to promote insulin release. However, these systems encounter significant stability, scalability, and immunogenicity challenges. In contrast, protein-free systems include hydrogels, nanogels/microgels, and microneedle patches, offering long-term stability and storability. In this direction, we discuss the design principles, mechanisms of glucose/pH sensitivity, and the disintegration of both protein-based and protein-free systems into different glucose environments. Finally, we outline the key challenges, potential solutions, and prospects for developing smart insulin delivery systems.

Development of 3D Printed pNIPAM-Chitosan Scaffolds for Dentoalveolar Tissue Engineering

While available treatments have addressed a variety of complications in the dentoalveolar region, associated challenges have resulted in exploration of tissue engineering techniques. Often, scaffold biomaterials with specific properties are required for such strategies to be successful, development of which is an active area of research. This study focuses on the development of a copolymer of poly (N-isopropylacrylamide) (pNIPAM) and chitosan, used for 3D printing of scaffolds for dentoalveolar regeneration. The synthesized material was characterized by Fourier transform infrared spectroscopy, and the possibility of printing was evaluated through various printability tests. The rate of degradation and swelling was analyzed through gravimetry, and surface morphology was characterized by scanning electron microscopy. Viability of dental pulp stem cells seeded on the scaffolds was evaluated by live/dead analysis and DNA quantification. The results demonstrated successful copolymerization, and three formulations among various synthesized formulations were successfully 3D printed. Up to 35% degradability was confirmed within 7 days, and a maximum swelling of approximately 1200% was achieved. Furthermore, initial assessment of cell viability demonstrated biocompatibility of the developed scaffolds. While further studies are required to achieve the tissue engineering goals, the present results tend to indicate that the proposed hydrogel might be a valid candidate for scaffold fabrication serving dentoalveolar tissue engineering through 3D printing.

Rational Design and Development of Polymeric Nanogels as Protein Carriers

Proteins have gained significant attention as potential therapeutic agents owing to their high specificity and reduced toxicity. Nevertheless, their clinical utility is hindered by inherent challenges associated with stability during storage and after in vivo administration. To overcome these limitations, polymeric nanogels (NGs) have emerged as promising carriers. These colloidal systems are capable of efficient encapsulation and stabilization of protein cargoes while improving their bioavailability and targeted delivery. The design of such delivery systems requires a comprehensive understanding of how the synthesis and formulation processes affect the final performance of the protein. This review highlights critical aspects involved in the development of NGs for protein delivery, with specific emphasis on loading strategies and evaluation techniques. For example, factors influencing loading efficiency and release kinetics are discussed, along with strategies to optimize protein encapsulation through protein-carrier interactions to achieve the desired therapeutic outcomes. The discussion is based on recent literature examples and aims to provide valuable insights for researchers working toward the advancement of protein-based therapeutics.

A Review of Research Progress on the Performance of Intelligent Polymer Gel

Intelligent polymer gel, as a popular polymer material, has been attracting much attention for its application. An intelligent polymer gel will make corresponding changes to adapt to the environment after receiving stimuli; therefore, an intelligent polymer gel can play its role in many fields. With the research on intelligent polymer gels, there is great potential for applications in the fields of drug engineering, molecular devices, and biomedicine in particular. The strength and responsiveness of the gels can be improved under different configurations in different technologies to meet the needs in these fields. There is no discussion on the application of intelligent polymer gels in these fields; therefore, this paper reviews the research progress of intelligent polymer gel, describes the important research of some intelligent polymer gel, summarizes the research progress and current situation of intelligent polymer gel in the environment of external stimulation, and discusses the performance and future development direction of intelligent polymer gel.

Temperature-Dependent Nanomechanical Properties of Adsorbed Poly-NIPAm Microgel Particles Immersed in Water

The temperature dependence of nanomechanical properties of adsorbed poly-NIPAm microgel particles prepared by a semibatch polymerization process was investigated in an aqueous environment via indentation-based atomic force microscopy (AFM) methods. Poly-NIPAm microgel particles prepared by the classical batch process were also characterized for comparison. The local mechanical properties were measured between 26 and 35 °C, i.e., in the temperature range of the volume transition. Two different AFM tips with different shapes and end radii were utilized. The nanomechanical properties measured by the two kinds of tips showed a similar temperature dependence of the nanomechanical properties, but the actual values were found to depend on the size of the tip. The results suggest that the semibatch synthesis process results in the formation of more homogeneous microgel particles than the classical batch method. The methodological approach reported in this work is generally applicable to soft surface characterization in situ.

One-pot HTST synthesis of responsive fluorescent ZnO@apo-enzyme composite microgels for intracellular glucometry

Responsive fluorescent microgels, that can selectively, reversibly, and rapidly convert the fluctuation in intracellular glucose level into fluorescence signal, have the potential use for intracellular glucometry to promote the understanding of physiology. Herein, we report one-pot synthesis of such a responsive fluorescent composite microgels, which is made of a representative apo-enzyme, apo-glucose oxidase (apo-GOx), interpenetrated in a composite gel network that is comprised of ZnO quantum dots covalently bonded onto crosslinked poly(ethylene glycol) dimethacrylate. The key of this one-pot synthesis is applying a high-temperature short-time heating (HTST) method, so that the naturally dynamic profile of apo-GOx can be maintained and harnessed on the composite microgels to allow the highly selective response to glucose over a glucose concentration range of 0-20 mM. While the composite microgels can undergo volume phase transitions and convert both an increase and a decrease in glucose concentration into fluorescence signal shortly (<1 s), the changes in average hydrodynamic diameter and fluorescence of the composite microgels can be fully reversible even after twenty cycles of adding/removing glucose, indicating a reversible and rapid time response to the glucose concentration variations. With the composite microgels as biosensors, the fluorescence of the composite microgels embedded in the model cancer cells B16F10 can be modulated in response to intracellular glucose level variations, which are derived from a change in glucose concentration in the culture medium by an external supply, or that can be triggered by biochemical reactions (with the β-galactosidase catalysed hydrolysis of lactose as a model reaction for achieving increased glucose levels, and the GOx catalysed oxidation of glucose for achieving decreased glucose levels).

Glucose-Responsive Insulin and Delivery Systems: Innovation and Translation

Type 1 and advanced type 2 diabetes treatment involves daily injections or continuous infusion of exogenous insulin aimed at regulating blood glucose levels in the normoglycemic range. However, current options for insulin therapy are limited by the risk of hypoglycemia and are associated with suboptimal glycemic control outcomes. Therefore, a range of glucose-responsive components that can undergo changes in conformation or show alterations in intermolecular binding capability in response to glucose stimulation has been studied for ultimate integration into closed-loop insulin delivery or "smart insulin" systems. Here, an overview of the evolution and recent progress in the development of molecular approaches for glucose-responsive insulin delivery systems, a rapidly growing subfield of precision medicine, is presented. Three central glucose-responsive moieties, including glucose oxidase, phenylboronic acid, and glucose-binding molecules are examined in detail. Future opportunities and challenges regarding translation are also discussed.

New Developments in Medical Applications of Hybrid Hydrogels Containing Natural Polymers

New trends in biomedical applications of the hybrid polymeric hydrogels, obtained by combining natural polymers with synthetic ones, have been reviewed. Homopolysaccharides, heteropolysaccharides, as well as polypeptides, proteins and nucleic acids, are presented from the point of view of their ability to form hydrogels with synthetic polymers, the preparation procedures for polymeric organic hybrid hydrogels, general physico-chemical properties and main biomedical applications (i.e., tissue engineering, wound dressing, drug delivery, etc.).

Sugar-responsive Pickering emulsions mediated by switching hydrophobicity in microgels

HYPOTHESIS

Pickering emulsions stabilized by soft and responsive microgels can demulsify on demand upon microgel collapse. The concept has been explored with simple model microgels such as poly(N-isopropylacrylamide) (pNIPAM) and their derivatives, but the role of functionalization is largely unexplored.

EXPERIMENTS

Saccharide-responsive phenylboronic-modified microgels are used as Pickering emulsion stabilizers. Emulsion stability and microgel organization at drop surface are studied as a function of saccharide concentration. Better insight into their behavior at interfaces is gained through adsorption kinetics and Langmuir film studies at air-water interface.

FINDINGS

The functionalization of water-swollen microgels by phenylboronic functions imparts some hydrophobicity to the structure, at the origin of additional internal cross-links analogous which rigidify the structure compared to non-functionalized microgels, as proved by their slow adsorption kinetics and poor interfacial compressibility. Upon boronate ester formation with diol groups of the saccharide, the hydrophobic character of the phenylboronic acid decreases, increasing the adsorption kinetics and their interfacial compressibility. Emulsions are stable in the presence of saccharide, given the high deformability of the yet-hydrophilic microgels, and mechanically unstable with less deformable particles in low saccharide concentration. The hydrophobic-hydrophilic switch acts as a trigger to tune the microgel stabilizing properties.

Hybrid Microgels for Catalytic and Photocatalytic Removal of Nitroarenes and Organic Dyes From Aqueous Medium: A Review

Polymer microgels loaded with inorganic nanoparticles have gained much attention as catalytic systems for reduction of toxic chemicals. Enhanced catalytic properties of hybrid microgels are related to the stimuli responsive nature of microgels and extraordinary stability of nanoparticles within network of polymer microgels. Catalytic properties of hybrid microgels can be tuned very easily by slight variation in environmental conditions. Herein we have reviewed catalytic reduction of toxic chemicals such as nitroarenes and organic dyes in the presence of appropriate hybrid microgel catalytic systems under different operating conditions of reaction. Recent advancements in catalytic behavior of hybrid microgels with special emphasis on their ability to catalytically degrade various toxic chemicals has been presented in this review.

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

Systems that are intelligent have the ability to sense their surroundings, analyze, and respond accordingly. In nature, many biological systems are considered intelligent (e.g., humans, animals, and cells). For man-made systems, artificial intelligence is achieved by massively sophisticated electronic machines (e.g., computers and robots operated by advanced algorithms). On the other hand, freestanding materials (i.e., not tethered to a power supply) are usually passive and static. Hence, herein, the question is asked: can materials be fabricated so that they are intelligent? One promising approach is to use stimuli-responsive materials; these "smart" materials use the energy supplied by a stimulus available from the surrounding for performing a corresponding action. After decades of research, many interesting stimuli-responsive materials that can sense and perform smart functions have been developed. Classes of functions discussed include practical functions (e.g., targeting and motion), regulatory functions (e.g., self-regulation and amplification), and analytical processing functions (e.g., memory and computing). The pathway toward creating truly intelligent materials can involve incorporating a combination of these different types of functions into a single integrated system by using stimuli-responsive materials as the basic building blocks.

Ferulic acid-based reactive core–shell latex by seeded emulsion polymerization

A recently revisited biobased styrenic monomer, acetyl-protected 4-vinylguaiacol (AC4VG), was used for the synthesis of partially biobased, functional core–shell polymers.

Construction of dual-functional polymer nanomaterials with near-infrared fluorescence imaging and polymer prodrug by RAFT-mediated aqueous dispersion polymerization

The performance of functional polymer nanomaterials is a vigorously discussed topic in polymer science. We devoted ourselves to investigating polymer nanomaterials based on near-infrared (NIR) fluorescence imaging and polymer prodrug in this study. Aza-boron dipyrromethene (BODIPY) is an important organic dye, having characteristics such as environmental resistance, light resistance, high molar extinction coefficient, and fluorescence quantum yield. We incorporated it into our target monomer, which can be polymerized without changing its parent structure in a polar solvent and copolymerized with water-soluble monomer to improve the solubility of the dye in an aqueous solution. At the same time, the hydrophobic drug camptothecin (CPT) was designed as a prodrug monomer, and the polymeric nanoparticles (NPs) with NIR fluorescence imaging and prodrug were synthesized in situ in reversible addition-fragmentation chain transfer (RAFT)-mediated aqueous dispersion polymerization. The dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed the final uniform size of the dual-functional polymeric NPs morphology. The dual-functional polymeric NPs had a strong absorption and emission signal in the NIR region (>650 nm) based on the fluorescence tests. In consideration of the long-term biological toxicity, confocal laser scanning microscopy (CLSM) results indicated that the dual-functional NPs with controlled drug content exhibited effective capability of killing HeLa cells. In addition, in vivo imaging of the dual-functional NPs was observed in real time, and the fluorescent signals clearly demonstrated the dynamic process of prodrug transfer.

The synthesis of a contraction-type glucose-sensitive microgel working at physiological temperature guided by a new glucose-sensing mechanism

A new glucose-sensing mechanism was proposed, guided by which a contraction-type glucose-sensitive microgel working at physiological temperature was synthesized successfully.

Biomolecule-Responsive Hydrogels in Medicine

Recent advances and applications of biomolecule-responsive hydrogels, namely, glucose-responsive hydrogels, protein-responsive hydrogels, and nucleic-acid-responsive hydrogels are highlighted. However, achieving the ultimate purpose of using biomolecule-responsive hydrogels in preclinical and clinical areas is still at the very early stage and calls for more novel designing concepts and advance ideas. On the way toward the real/clinical application of biomolecule-responsive hydrogels, plenty of factors should be extensively studied and examined under both in vitro and in vivo conditions. For example, biocompatibility, biointegration, and toxicity of biomolecule-responsive hydrogels should be carefully evaluated. From the living body's point of view, biocompatibility is seriously depended on the interactions at the tissue/polymer interface. These interactions are influenced by physical nature, chemical structure, surface properties, and degradation of the materials. In addition, the developments of advanced hydrogels with tunable biological and mechanical properties which cause no/low side effects are of great importance.

Glucose-responsive insulin release: Analysis of mechanisms, formulations, and evaluation criteria

Diabetes mellitus has become one of the biggest medical challenges affecting millions of people globally. Alternative treatments for diabetes are currently being intensively investigated to improve the treatment efficacy and life qualities for diabetic patients. Glucose-responsive insulin release (GRIR) systems have exhibited tremendous potential to improve the normal glycemic control and to reduce the incidence of hyperglycemia and hypoglycemia, which further reduces potential complications in diabetic patients. In a given GRIR drug formulation, accuracy, response time, and reversibility of the GRIR functions are three key features enabling potential seamless control of blood glucose level. Nevertheless, there is significant challenge preventing current GRIR formulations from achieving them. This review article analyzes the most updated literature and provides insights on the impact of GRIR mechanisms, and formulations on these key features, and the relevant in vitro and in vivo evaluation methods to test these functions.

The Potential of Stimuli-Responsive Nanogels in Drug and Active Molecule Delivery for Targeted Therapy

Nanogels (NGs) are currently under extensive investigation due to their unique properties, such as small particle size, high encapsulation efficiency and protection of active agents from degradation, which make them ideal candidates as drug delivery systems (DDS). Stimuli-responsive NGs are cross-linked nanoparticles (NPs), composed of polymers, natural, synthetic, or a combination thereof that can swell by absorption (uptake) of large amounts of solvent, but not dissolve due to the constituent structure of the polymeric network. NGs can undergo change from a polymeric solution (swell form) to a hard particle (collapsed form) in response to (i) physical stimuli such as temperature, ionic strength, magnetic or electric fields; (ii) chemical stimuli such as pH, ions, specific molecules or (iii) biochemical stimuli such as enzymatic substrates or affinity ligands. The interest in NGs comes from their multi-stimuli nature involving reversible phase transitions in response to changes in the external media in a faster way than macroscopic gels or hydrogels due to their nanometric size. NGs have a porous structure able to encapsulate small molecules such as drugs and genes, then releasing them by changing their volume when external stimuli are applied.

UCST-Type Thermosensitive Hairy Nanogels Synthesized by RAFT Polymerization-Induced Self-Assembly

While lower critical solution temperature (LCST)-type thermosensitive nanogels have been intensively studied, the upper critical solution temperature (UCST)-type versions are much less explored. This communication reports a method for the synthesis of zwitterionic UCST nanogels by reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly in water-organic solvent mixtures. The nanogels were prepared by RAFT polymerization of 3-dimethyl(methacryloyloxyethyl)ammonium propanesulfonate, whose polymer is known to exhibit UCST behavior in water, conducted in ethanol-water mixtures at 70 °C using poly(poly(ethylene glycol) methyl ether methacrylate) as a macro-chain transfer agent (CTA) and a difunctional monomer as cross-linker. At a sufficiently high ethanol content in reaction media, spherical hairy nanogels with a single size distribution were obtained. These nanogels exhibited reversible heating-induced swelling and cooling-induced shrinking, consistent with the expected UCST behavior. The hydrodynamic size, volume changing ratio, and transition temperature of nanogels can be tuned by varying ethanol content in solvent mixtures, molar ratio of monomer-to-macro-CTA, and amount of cross-linker. Hairy nanogels were also successfully synthesized using a water-THF mixture as medium. The use of water-organic solvent mixtures as reaction media allowed for facile incorporation of a hydrophobic fluorescent monomer to make functional UCST nanogels.

Determination of Glycoproteins by a Self-Assembled 4-Mercaptophenylboronic Acid Film on a Quartz Crystal Microbalance

Glycosylation plays an important part in many biological processes. However, many glycoproteins are either of low abundance or covered by other components in biological samples. Hence, developing new methods to measure the glycoproteins with both high efficiency and low detection limit is important. In this work, a self-assembled 4-mercaptophenylboronic acid film was coated on a quartz crystal microbalance chip. By optimizing the reaction time and the concentration of 4-mercaptophenylboronic acid, a sensor that specifically responded to glycoproteins was created. Then, several parameters for the prepared sensor were investigated and the working curve for representative glycoprotein-transferrin was established. The linearity range was from 50 to 400 ng/mL and the detection limit was 21.0 ng/mL. The sensor was used to detect transferrin in artificial urine samples. This sensor has a low detection limit of glycoproteins requiring only a small amount of samples, and thus has potential applications in both pharmaceutical and medical areas.

Swelling of glucose-responsive gels functionalized with boronic acid

A model is developed for the elastic response of a glucose-sensitive gel functionalized with boronic acid under swelling in aqueous solutions of glucose with various pH. A gel is treated as a three-phase medium composed of a solid phase (partially ionized polymer network), solvent (water), and solute (mobile glucose molecules and ions). Constitutive equations are derived by means of the free energy imbalance inequality for three-dimensional deformation with finite strains. Numerical analysis demonstrates the ability of the model to describe the effects of pH, molar fraction of glucose, and concentration of functional groups on equilibrium water uptake diagrams under unconstrained and constrained swelling.

Temperature-Responsive Smart Nanocarriers for Delivery Of Therapeutic Agents: Applications and Recent Advances

Smart drug delivery systems (DDSs) have attracted the attention of many scientists, as carriers that can be stimulated by changes in environmental parameters such as temperature, pH, light, electromagnetic fields, mechanical forces, etc. These smart nanocarriers can release their cargo on demand when their target is reached and the stimulus is applied. Using the techniques of nanotechnology, these nanocarriers can be tailored to be target-specific, and exhibit delayed or controlled release of drugs. Temperature-responsive nanocarriers are one of most important groups of smart nanoparticles (NPs) that have been investigated during the past decades. Temperature can either act as an external stimulus when heat is applied from the outside, or can be internal when pathological lesions have a naturally elevated termperature. A low critical solution temperature (LCST) is a special feature of some polymeric materials, and most of the temperature-responsive nanocarriers have been designed based on this feature. In this review, we attempt to summarize recent efforts to prepare innovative temperature-responsive nanocarriers and discuss their novel applications.

Stimuli-responsive nanogel composites and their application in nanomedicine

Nanogels are nanosized crosslinked polymer networks capable of absorbing large quantities of water. Specifically, smart nanogels are interesting because of their ability to respond to biomedically relevant changes like pH, temperature, etc. In the last few decades, hybrid nanogels or composites have been developed to overcome the ever increasing demand for new materials in this field. In this context, a hybrid refers to nanogels combined with different polymers and/or with nanoparticles such as plasmonic, magnetic, and carbonaceous nanoparticles, among others. Research activities are focused nowadays on using multifunctional hybrid nanogels in nanomedicine, not only as drug carriers but also as imaging and theranostic agents. In this review, we will describe nanogels, particularly in the form of composites or hybrids applied in nanomedicine.

Bioinspired synthesis of poly(phenylboronic acid) microgels with high glucose selectivity at physiological pH

A microgel that is more sensitive towards glucose than to other saccharides is made of 4-vinylphenylboronic acid crosslinked withN,N′-bis(propene)perylene-3,4,9,10-tetracarboxyldiimide.

Glucose-responsive microgels based on apo-enzyme recognition

Glucose-responsive microgels that can undergo reversible and rapid volume phase transitions were made of apo-glucose oxidase interpenetrated in a poly(N-isopropylacrylamide) network.

Saccharide-induced modulation of photoluminescence lifetime in microgels

Sugar-responsive microgels based on boronic acid derivative and incorporating [Ru(bpy)₃]²⁺ as a luminescent reporter, exhibit very long lifetimes and unusually high quantum yields, which decrease upon saccharide addition.

Multilayered Thin Films from Boronic Acid-Functional Poly(amido amine)s

PURPOSE

To investigate the properties of phenylboronic acid-functional poly(amido amine) polymers (BA-PAA) in forming multilayered thin films with poly(vinyl alcohol) (PVA) and chondroitin sulfate (ChS), and to evaluate their compatibility with COS-7 cells.

METHODS

Copolymers of phenylboronic acid-functional poly(amido amine)s, differing in the content of primary amine (DAB-BA-PAA) or alcohol (ABOL-BA-PAA) side groups, were synthesized and applied in the formation of multilayers with PVA and ChS. Biocompatibility of the resulting films was evaluated through cell culture experiments with COS-7 cells grown on the films.

RESULTS

PVA-based multilayers were thin, reaching ~100 nm at 10 bilayers, whereas ChS-based multilayers were thick, reaching ~600 nm at the same number of bilayers. All of the multilayers are stable under physiological conditions in vitro and are responsive to reducing agents, owing to the presence of disulfide bonds in the polymers. PVA-based films were demonstrated to be responsive to glucose at physiological pH at the investigated glucose concentrations (10-100 mM). The multilayered films displayed biocompatibility in cell culture experiments, promoting attachment and proliferation of COS-7 cells.

CONCLUSIONS

Responsive thin films based on boronic acid functional poly(amido amine)s are promising biocompatible materials for biomedical applications, such as drug releasing surfaces on stents or implants. Graphical Abstract Layer-by-Layer Assembly.

Sugar-Responsive Pseudopolyrotaxane Composed of Phenylboronic Acid-Modified Polyethylene Glycol and γ-Cyclodextrin

We have designed a sugar-responsive pseudopolyrotaxane (PPRX) by combining phenylboronic acid-modified polyethylene glycol (PBA–PEG) and γ-cyclodextrin. Phenylboronic acid (PBA) was used as a sugar-recognition motif in the PPRX because PBA reacts with a diol portion of the sugar molecule and forms a cyclic ester. When D-fructose or D-glucose was added to a suspension of PPRX, PPRX disintegrated, depending on the concentration of the sugars. Interestingly, catechol does not show a response although catechol has a high affinity for PBA. We analyzed the response mechanism of PPRX by considering equilibria.

Stimuli-responsive microgel-based etalons for optical sensing

Responsive polymers have found numerous applications over the years. This review highlights their use as components of photonic materials, with emphasis on responsive polymer-based etalons. The use of these materials for sensing and biosensing is detailed.

Switchable glucose-responsive volume phase transition behavior of poly(phenylboronic acid) microgels

We report a poly(phenylboronic acid) microgel that can display switchable glucose-responsive volume phase transition behavior with temperature as a trigger.

Glucose-responsive hydrogels based on dynamic covalent chemistry and inclusion complexation

A novel glucose-responsive hydrogel system based on dynamic covalent chemistry and inclusion complexation was described. Hydrogels are formed by simply mixing the solutions of three components: poly(ethylene oxide)-b-poly vinyl alcohol (PEO-b-PVA) diblock polymer, α-cyclodextrin (α-CD) and phenylboronic acid (PBA)-terminated PEO crosslinker. Dynamic covalent bonds between PVA and PBA provide sugar-responsive crosslinking, and the inclusion complexation between PEO and α-CD can promote hydrogel formation and enhance hydrogel stability. The ratios of the three components have a remarkable effect on the gelation time and the mechanical properties of the final gels. In rheological measurements, the hydrogels are demonstrated to possess solid-like behaviour and good structural recovery ability after yielding. The sugar-responsiveness of the hydrogels was examined by protein loading and release experiments, and the results indicate that this property is also dependent on the compositions of the gels; at a proper component ratio, a new glucose-responsive hydrogel system operating at physiological pH can be obtained. The combination of good biocompatibility of the three components and the easy preparation of hydrogels with tunable glucose-responsiveness may enable an alternative design of hydrogel systems that finds potential applications in biomedical and pharmaceutical fields, such as treatment of diabetes.

Phenylboronate-diol crosslinked glycopolymeric nanocarriers for insulin delivery at physiological pH

Research into polymers with glucose-sensitivity in physiological conditions has expanded recently due to their therapeutic potential in diabetes. Herein, to explore the glucose-responsive properties of a new polymer under physiological conditions, we synthesized an amphiphilic block glycopolymer based on phenylboronic acid and a carbohydrate, which was named poly(d-gluconamidoethyl methacrylate-block-3-acrylamidophenylboronic acid) (p(AAPBA-b-GAMA)). Based on the cross-linking between the diol groups of the carbohydrates and phenylboronic acid, the glycopolymers self-assembled to form nanoparticles (NPs). The glucose-sensitivity was revealed by the swelling behavior of the NPs at different glucose concentrations and was found to be dependent on the glucose level. The morphology of the NPs revealed by transmission electron microscopy showed that the NPs were spherical in shape with good dispersity. The cell viability of the NPs investigated by MTT assay was more than 90%, indicating that the glycopolymers had good cytocompatibility. Insulin could be loaded onto the glycopolymer NPs with high efficiency (up to 10%), and insulin release increased with enhancement of the glucose level in the medium. Such a glucose-responsive glycopolymer is an excellent candidate that holds great potential in the treatment of diabetes.

Synthesis and volume phase transition of concanavalin A-based glucose-responsive nanogels

A glucose-responsive nanogel that can undergo reversible and rapid volume phase transitions is made of ConA interpenetrated in a poly(NIPAM) network.