Boronate-functionalized hydrogel as a novel biosensing interface for the glycated hemoglobin A1c (HbA1c) based on the competitive binding with signaling glycoprotein

According to recent increases in public healthcare costs associated with diabetes mellitus, the development of new glycemic monitoring techniques based on the biosensing of glycated hemoglobin A1c (HbA_1c), a promising long-term glycemic biomarker, has become a major challenge. In the development of HbA_1c biosensors for point-of-care applications, the selection of an effective biorecognition layer that provides a high reaction yield and specificity toward HbA_1c is regarded as the most significant issue. To address this, we developed a novel HbA_1c biosensing interfacial material by the integration of boronate hydrogel with glass fiber membrane. In the present study, a new boronate-functionalized hydrogel was designed and spatio-selectively photopolymerized on a hydrophilic glass fiber membrane by using N-hydroxyethyl acrylamide, 3-(acrylamido)phenylboronic acid, and bis(N,N'-methylene-bis-acrylamide). Using this approach, the boronic acid group, which specifically recognizes the cis-diol residue of glucose on the HbA_1c molecule, can be three-dimensionally coated on the surface of the glass fiber network with a high density. Because this network structure of boronate hydrogel-grafted fibers enables capillary-driven fluid control, facile HbA_1c biosensing in a lateral flow assay concept could be accomplished. On the proposed HbA_1c biosensing interface, various concentrations of HbA_1c (5-15%) in blood-originated samples were sensitively measured by a colorimetric assay using horseradish peroxidase, a glycoenzyme can generate chromogenic signal after the competitive binding against HbA_1c to the boronic acid residues. Based on the demonstrated advantages of boronate hydrogel-modified membrane including high analytical performance, easy operation, and cost-effectiveness, we expect that the proposed biorecognition interfacial material can be applied not only to point-of-care HbA_1c biosensors, but also to the quantitative analysis of other glycoprotein biomarkers.

Glucose-Sensitive Hydrogel Optical Fibers Functionalized with Phenylboronic Acid

Hydrogel optical fibers are utilized for continuous glucose sensing in real time. The hydrogel fibers consist of poly(acrylamide-co-poly(ethylene glycol) diacrylate) cores functionalized with phenylboronic acid. The complexation of the phenylboronic acid and cis-diol groups of glucose enables reversible changes of the hydrogel fiber diameter. The analyses of light propagation loss allow for quantitative glucose measurements within the physiological range.

Metal- and additive-free photoinduced borylation of haloarenes

Boronic acids and esters have critical roles in the areas of synthetic organic chemistry, molecular sensors, materials science, drug discovery, and catalysis. Many of the current applications of boronic acids and esters require materials with very low levels of transition metal contamination. Most of the current methods for the synthesis of boronic acids, however, require transition metal catalysts and ligands that must be removed via additional purification procedures. This protocol describes a simple, metal- and additive-free method of conversion of haloarenes directly to boronic acids and esters. This photoinduced borylation protocol does not require expensive and toxic metal catalysts or ligands, and it produces innocuous and easy-to-remove by-products. Furthermore, the reaction can be carried out on multigram scales in common-grade solvents without the need for reaction mixtures to be deoxygenated. The setup and purification steps are typically accomplished within 1-3 h. The reactions can be run overnight, and the protocol can be completed within 13-16 h. Two representative procedures that are described in this protocol provide details for preparation of a boronic acid (3-cyanopheylboronic acid) and a boronic ester (1,4-benzenediboronic acid bis(pinacol)ester). We also discuss additional details of the method that will be helpful in the application of the protocol to other haloarene substrates.

Boronic Acid as Glucose-Sensitive Agent Regulates Drug Delivery for Diabetes Treatment

In recent years, glucose-sensitive drug delivery systems have attracted considerable attention in the treatment of diabetes. These systems can regulate payload release by the changes of blood glucose levels continuously and automatically with potential application in self-regulated drug delivery. Boronic acid (BA), especially phenylboronic acid (PBA), as glucose-sensitive agent has been the focus of research in the design of glucose-sensitive platforms. This article reviews the previous attempts at the developments of PBA-based glucose-sensitive drug delivery systems regarding the PBA-functionalized materials and glucose-triggered drug delivery. The obstacles and potential developments of glucose-sensitive drug delivery systems based on PBA for diabetes treatment in the future are also described. The PBA-functionalized platforms that regulate drug delivery induced by glucose are expected to contribute significantly to the design and development of advanced intelligent self-regulated drug delivery systems for treatment of diabetes.

A pH, glucose, and dopamine triple-responsive, self-healable adhesive hydrogel formed by phenylborate–catechol complexation

A pH, glucose, and dopamine triple-responsive, self-healable and adhesive polyethylene glycol hydrogel was developed via the formation of phenylborate–catechol complexation.

Synthesis of polymer macrogels with rapid and significant response to glucose concentration changes

Polymer macrogels with rapid and significant responses to glucose concentration changes were made of a poly(phenylboronic acid) microgel array tethered chemically to bridging polymers.

G-Quartet hydrogels for effective cell growth applications

Functional G-quartet hydrogels formed from natural guanosine cross linked with benzene-1,4-diboronic acid and Mg²⁺ support cell growth with no visible signs of gel degradation.

A novel transparent luminous hydrogel with self-healing property

A Luminous hydrogel with self-healing properties and biocompatibility was synthesized by a Eu-containing PVA with boric acid as a cross-linking agent.

Improving tumor chemotherapy effect using an injectable self-healing hydrogel as drug carrier

A self-healing hydrogel has been used as the anti-tumor drug carrier to improve the chemotherapy effect.

pH-Responsive polymers

This review summarizes pH-responsive monomers, polymers and their derivative nano- and micro-structures including micelles, cross-linked micelles, microgels and hydrogels.

Functional micelles formed from glucose-, thermo- and pH-triple responsive copolymers for controlled release

Spherical micelles self-assembled from the block copolymer PPBDEMA-b-PDMAEMA presented glucose, thermo- and pH-triple responsive properties.

Mussel-mimetic hydrogels with defined cross-linkers achieved via controlled catechol dimerization exhibiting tough adhesion for wet biological tissues

Mussel-mimetic hydrogels possessing ultrahigh adhesion energy on wet biological tissues via enhancing both the interfacial adhesion and bulk cohesion are fabricated.

High performance boronic acid-containing hydrogel for biocompatible continuous glucose monitoring

Rapid and robust hydrogels are essential in realizing continuous glucose monitoring in diabetes monitoring.

Dynamic covalent polymers

This Highlight presents an overview of the rapidly growing field of dynamic covalent polymers. This class of polymers combines intrinsic reversibility with the robustness of covalent bonds, thus enabling formation of mechanically stable, polymer-based materials that are responsive to external stimuli. It will be discussed how the inherent dynamic nature of the dynamic covalent bonds on the molecular level can be translated to the macroscopic level of the polymer, giving access to a range of applications, such as stimuli-responsive or self-healing materials. A primary distinction will be made based on the type of dynamic covalent bond employed, while a secondary distinction will be based on the consideration whether the dynamic covalent bond is used in the main chain of the polymer or whether it is used to allow side chain modification of the polymer. Emphasis will be on the chemistry of the dynamic covalent bonds present in the polymer, in particular in relation to how the specific (dynamic) features of the bond impart functionality to the polymer material, and to the conditions under which this dynamic behavior is manifested. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3551-3577.

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.

Dynamic Covalent Chemistry-based Sensing: Pyrenyl Derivatives of Phenylboronic Acid for Saccharide and Formaldehyde

We synthesized two specially designed pyrenyl (Py) derivatives of phenylboronic acid, PSNB1 and PSNB2, of which PSNB2 self-assemble to form dynamic aggregate in methanol-water mixture (1:99, v/v) via intermolecular H-bonding and pi-pi stacking. Interestingly, the dynamic aggregate shows smart response to presence of fructose (F) as evidenced by fluorescence color change from green to blue. More interestingly, the fluorescence emission of the resulted PSNB2-F changes from blue to green with the addition of formaldehyde (FA). The reason behind is formation of a PSNB2-F dimer via FA cross-linking. Based upon the reactions as found, sensitive and fast sensing of F and FA in water was realized, of which the experimental DLs could be significantly lower than 10 μM for both analytes, and the response times are less than 1 min. It is believed that not only the materials as created may have the potential to find real-life applications but also the strategy as developed can be adopted to develop other dynamic materials.

A Comparison of the Structure and Bonding in the Aliphatic Boronic R-B(OH)2 and Borinic R-BH(OH) acids (R=H; NH2, OH, and F): A Computational Investigation

Boronic acids, R-B(OH)2, play an important role in synthetic, biological, medicinal, and materials chemistry. This investigation compares the structure and bonding surrounding the boron atoms in the simple aliphatic boronic acids, R-B(OH)2 (R = H; NH2, OH, and F) and the analogous borinic acids, R-BH(OH). Geometry optimizations were performed using second-order Møller-Plesset perturbation theory (MP2) with the Dunning-Woon aug-cc-pVTZ, aug-cc-pVQZ and aug-cc-pV5Z basis sets; single-point CCSD(FC)/aug-cc-pVTZ//MP2(FC)/aug-cc-pVTZ level calculations were used to generate a QCI density for Natural Bond Orbital analyses of the bonding. The optimized boron-oxygen bond lengths for the X-B-Ot-H trans-branch of the endo-exo form of the boronic acids and for the X-B-O-H cis-branch of the boronic and borinic acids (X = N, O, and F respectively) decrease as the electronegativity of X increases. The boron-oxygen bond lengths are generally longer in the endo-exo or anti forms of the boronic acids than in the corresponding borinic acids. NBO analyses suggest the boron-oxygen bond in H2BOH is a double bond; the boron-oxygen bonding in the remaining boronic and borinic acids in this study have a significant contribution from dative pπ-pπ bonding. Values for [Formula: see text] for the highly balanced reaction, R-B(OH)2 + R-BH2 → 2 R-BH(OH), suggest that the bonding surrounding the boron atom is stronger in the borinic acid than in the corresponding boronic acid.

Simultaneous detection of platelet-specific antibodies based on a photonic crystal-encoded suspension array

BACKGROUND

The appearance of antibodies to platelets in the blood is an important cause of immune thrombocytopenia (ITP), and platelet glycoprotein (GP)-specific antibody detection may be helpful to diagnose this condition.

METHODS

Photonic crystal microspheres with different distinct reflection spectra were coated with anti-GPIIb, -GPIIIa, -GPIb and -GPIX monoclonal antibodies (MoAbs) to create a photonic crystal-encoded suspension array (PCSA). Fluorescein isothiocyanate-labelled goat anti-human IgG was added to detect human IgG simultaneously. The detection results were analysed by fluorescence microscopy. Parallel MoAb immobilization of platelet antigen (MAIPA) was used as a reference test. Both methods were used to analyse 63 clinical samples including serum from 32 ITP patients and 31 healthy humans.

RESULTS

The PCSA showed greater sensitivity than MAIPA in detecting anti-GPIIb (75.0% vs 31.1%) and GPIIIa (84.4% vs 40.6%) antibodies and similar sensitivity as MAIPA in detecting anti-GPIb (37.5% vs 34.4%) and GPIX (50.0% vs 40.8%) antibodies. The MAIPA and PCSA tests had similar specificity. The PCSA detected higher dilutions of serum containing anti-GPIIIa antibody or anti-GPIIb antibody than did MAIPA. The entire testing process was controlled within 3.5h.

CONCLUSIONS

The PCSA assay described has comparable or better sensitivity and specificity compared to the MAIPA and is more rapid.

Thermoresponsive Polymers and Inverse Opal Hydrogels for the Detection of Diols

Responsive inverse opal hydrogels functionalized by boroxole moieties were synthesized and explored as sensor platforms for various low molar mass as well as polymeric diols and polyols, including saccharides, glycopolymers and catechols, by exploiting the diol induced modulation of their structural color. The underlying thermoresponsive water-soluble copolymers and hydrogels exhibit a coil-to-globule or volume phase transition, respectively, of the LCST-type. They were prepared from oligoethylene oxide methacrylate (macro)monomers and functionalized via copolymerization to bear benzoboroxole moieties. The resulting copolymers represent weak polyacids, which can bind specifically to diols within an appropriate pH window. Due to the resulting modulation of the overall hydrophilicity of the systems and the consequent shift of their phase transition temperature, the usefulness of such systems for indicating the presence of catechols, saccharides, and glycopolymers was studied, exploiting the diol/polyol induced shifts of the soluble polymers' cloud point, or the induced changes of the hydrogels' swelling. In particular, the increased acidity of benzoboroxoles compared to standard phenylboronic acids allowed performing the studies in PBS buffer (phosphate buffered saline) at the physiologically relevant pH of 7.4. The inverse opals constructed of these thermo- and analyte-responsive hydrogels enabled following the binding of specific diols by the induced shift of the optical stop band. Their highly porous structure enabled the facile and specific optical detection of not only low molar mass but also of high molar mass diol/polyol analytes such as glycopolymers. Accordingly, such thermoresponsive inverse opal systems functionalized with recognition units represent attractive and promising platforms for the facile sensing of even rather big analytes by simple optical means, or even by the bare eye.

Clustering Small Dendrimers into Nanoaggregates for Efficient DNA and siRNA Delivery with Minimal Toxicity

Cationic dendrimers are widely used as nonviral gene vectors, however, current gene materials based on dendrimers are either little effective or too toxic on the transfected cells. Here, a facile strategy is presented to prepare high efficient dendrimers with low transfection toxicity. Small dendrimers with 2 nm are clustered into nanoaggregates (≈100 nm) via phenylboronic acid modification and the self-assembled materials enable efficient DNA and siRNA delivery on several cell lines. The clustered nanostructures can disassemble into small dendrimers in acidic conditions thus exerting significantly less toxicity on the transfected cells. Further structure-function relationship studies reveal that both the phenyl group and boronic acid group play essential roles in the self-assembly and gene delivery processes. The transfection efficacy of phenylboronic acid-modified dendrimers can be down-regulated by blocking the boronic acid groups on dendrimers with diols or degrading the groups with hydrogen peroxide. This study provides a facile strategy in the development of efficient and biocompatible gene vectors based on low molecular weight polymers and clearly demonstrates the structure-function relationship of phenylboronic acid-modified polymers in gene delivery.

Scalable, Metal- and Additive-Free, Photoinduced Borylation of Haloarenes and Quaternary Arylammonium Salts

We report herein a simple, metal- and additive-free, photoinduced borylation of haloarenes, including electron-rich fluoroarenes, as well as arylammonium salts directly to boronic acids. This borylation method has a broad scope and functional group tolerance. We show that it can be further extended to boronic esters and carried out on gram scale as well as under flow conditions.

Synthesis and characterization of responsive poly(anionic liquid) microgels

Responsive poly(anionic liquid) microgels are synthesized by polymerization of tetrabutylphosphonium 4-styrenesulfonate, which can be further functionalized to harness catalytic properties.

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.

Mussel-inspired multifunctional supramolecular hydrogels with self-healing, shape memory and adhesive properties

A novel multifunctional supramolecular hydrogel with self-healing, shape memory and adhesive properties is successfully developed on the basis of dynamic phenylboronic acid (PBA)–catechol interactions.

Graphene oxide-based boronate polymer brushes via surface initiated atom transfer radical polymerization for the selective enrichment of glycoproteins

A facile and efficient method was developed to synthesize boronic acid polymer brushes immobilized on magnetic graphene oxide for the selective enrichment of glycoproteins from complex biological samples via surface initiated atom transfer radical polymerization (SI-ATRP).

Boronic acid functionalized magnetic nanoparticles synthesized by atom transfer radical polymerization and their application for selective enrichment of glycoproteins

A facile and efficient approach to synthesize boronate affinity ligand-functionalized magnetic nanoparticles for specific enrichment of glycoproteins via surface-initiated atom transfer radical polymerization (SI-ATRP) has been developed.

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.

Boronate affinity materials for separation and molecular recognition: structure, properties and applications

Boronate affinity materials, as unique sorbents, have emerged as important media for the selective separation and molecular recognition of cis-diol-containing compounds. With the introduction of boronic acid functionality, boronate affinity materials exhibit several significant advantages, including broad-spectrum selectivity, reversible covalent binding, pH-controlled capture/release, fast association/desorption kinetics, and good compatibility with mass spectrometry. Because cis-diol-containing biomolecules, including nucleosides, saccharides, glycans, glycoproteins and so on, are the important targets in current research frontiers such as metabolomics, glycomics and proteomics, boronate affinity materials have gained rapid development and found increasing applications in the last decade. In this review, we critically survey recent advances in boronate affinity materials. We focus on fundamental considerations as well as important progress and new boronate affinity materials reported in the last decade. We particularly discuss on the effects of the structure of boronate ligands and supporting materials on the properties of boronate affinity materials, such as binding pH, affinity, selectivity, binding capacity, tolerance for interference and so on. A variety of promising applications, including affinity separation, proteomics, metabolomics, disease diagnostics and aptamer selection, are introduced with main emphasis on how boronate affinity materials can solve the issues in the applications and what merits boronate affinity materials can provide.

Toward Self-Healing Hydrogels Using One-Pot Thiol-Ene Click and Borax-Diol Chemistry

Intrinsic self-healing soft materials such as hydrogels are especially promising for a variety of medical applications. Multistep preparation of starting functional polymer precursors and the expensive stock materials such as tetra-polyethylene glycol are one of the factors that limit the wider use of self-healing hydrogels. Herein, we reported a facile one-pot approach to prepare PEG based self-healing hydrogels from inexpensive commercially available components: polyethylene glycol diacrylate and dithiothreitol. For the first time, borax was used as the catalyst for a thiol-ene Michael-type polyaddition of PEG gels. Borax as the catalyst is quite efficient, allowing rapid gelation (from 40 s to 2 min) under ambient conditions and at room temperature. Essentially, as one catalyst, borax induces the formation of two classes of bonds, covalent thioether and transient boronate ester bonds, were formed at the same time. The storage modulus of the afforded PEG gel (87.5% water) reached up to 10⁴ Pa, making the mechanical performance comparable with permanently cross-linked PEG gels. Additionally, the dynamic nature of the boronate ester linkages imparts the gel with self-healing properties, and the obtained gels can be healed within 30 min without external stimulus. Further, the transparent hydrogel is pH and thermal responsive. We believe that the manifold impacts of borax can open a new route to prepare hydrogels with intriguing properties, which find potential application as gel sealant, biosensors, or regenerative medicines.

Responsive inverse opal hydrogels for the sensing of macromolecules

Dual responsive inverse opal hydrogels were designed as autonomous sensor systems for (bio)macromolecules, exploiting the analyte-induced modulation of the opal's structural color. The systems that are based on oligo(ethylene glycol) macromonomers additionally incorporate comonomers with various recognition units. They combine a coil-to-globule collapse transition of the LCST type with sensitivity of the transition temperature toward molecular recognition processes. This enables the specific detection of macromolecular analytes, such as glycopolymers and proteins, by simple optical methods. While the inverse opal structure assists the effective diffusion even of large analytes into the photonic crystal, the stimulus responsiveness gives rise to strong shifts of the optical Bragg peak of more than 100 nm upon analyte binding at a given temperature. The systems' design provides a versatile platform for the development of easy-to-use, fast, and low-cost sensors for pathogens.

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.

Glucose-responsive polymer vesicles templated by α-CD/PEG inclusion complex

Polymeric nanoparticles with glucose-responsiveness are of great interest in developing a self-regulated drug delivery system. In this work, glucose-responsive polymer vesicles were fabricated based on the complexation between a glucosamine (GA)-containing block copolymer PEG45-b-P(Asp-co-AspGA) and a phenylboronic acid (PBA)-containing block copolymer PEG114-b-P(Asp-co-AspPBA) with α-CD/PEG45 inclusion complex as the sacrificial template. The obtained polymer vesicles composed of cross-linked P(Asp-co-AspGA)/P(Asp-co-AspPBA) layer as wall and PEG chains as both inner and outer coronas. The vesicular morphology was observed by transmission electron microscopy (TEM), and the glucose-responsiveness was investigated by monitoring the variations of hydrodynamic diameter (Dh) and light scattering intensity (LSI) in the polymer vesicle solution with glucose using dynamic light scattering (DLS). Vancomycin as a model drug was encapsulated in the polymer vesicles and sugar-triggered drug release was carried out. This kind of polymer vesicle may be a promising candidate for glucose-responsive drug delivery.

Nanoscaled boron-containing delivery systems and therapeutic agents for cancer treatment

Significant efforts have recently been made to develop nanoscaled boron-containing delivery systems for improving drug delivery in cancer therapy. On one hand, borate ester chemistry has shown importance in ligand-mediated tumor targeting owing to the recognition ability of boronic acid to polyol residues in cell membranes. In particular, the phenylboronic acid-functionalized nanocarriers for specific targeting to sialic acid groups which are overexpressed on tumor cells have made great achievements. On the other hand, nanoscaled boron neutron capture therapy agents show growing potential in efficiently transporting boron to tumor. The current review outlines the recent developments in the application of borate ester chemistry in tumor targeting by nanoparticles, then summarizes recent work on the development of boron-based nanomaterials as boron neutron capture therapy agents.

Swelling-induced surface instability patterns guided by pre-introduced structures

Swelling-induced, spontaneously generated surface instability patterns in substrate-attached hydrogel films can be harnessed for advanced applications, however, methods to control their formation and morphology are missing. Here we propose that their generation may be guided by intentionally pre-introduced line structures. While uniform gel films produce irregular polygonal instability patterns, instability patterns generated in pre-patterned films with hexagonal line structures are regular hexagons with long-range order. The pre-introduced line structures act as defects in the generation of the surface instability patterns, which determine the position of the creases, regulate their rearrangement and determine their final morphology. The contrast between the pre-introduced structures and the surrounding area should be high enough for the pre-introduced structures to act as defects. Only when the characteristic wavelength of the pre-introduced pattern matches with the one of the gel film, perfect hexagonal patterns can be obtained. The gel films with uniform topographic features may find various advanced applications.