Glucose-responsive micelles from self-assembly of poly(ethylene glycol)-b-poly(acrylic acid-co-acrylamidophenylboronic acid) and the controlled release of insulin

Fabrication of Biobased Polyelectrolyte Capsules and Their Application for Glucose-Triggered Insulin Delivery

To enhance the glucose sensitivity and self-regulated release of insulin, biobased capsules with glucose-responsive and competitive properties were fabricated based on poly(γ-glutamic acid) (γ-PGA) and chitosan oligosaccharide (CS) polyelectrolytes. First, poly(γ-glutamic acid)-g-3-aminophenylboronic acid) (γ-PGA-g-APBA) and galactosylated chitosan oligosaccharide (GC) were synthesized by grafting APBA and lactobionic acid (LA) to γ-PGA and CS, respectively. The (γ-PGA-g-APBA/GC)5 capsules were then prepared by layer-by-layer (LBL) assembly of γ-PGA-g-APBA and GC via electrostatic interaction. The size and morphology of the particles and capsules were investigated by DLS, SEM, and TEM. The size of the (γ-PGA-g-APBA/GC)5 capsules increased with increasing glucose concentration due to the swelling of the capsules. The capsules could be dissociated at high glucose concentration due to the breaking of the cross-linking bonds between APBA and LA by the competitive reaction of APBA with glucose. The encapsulated insulin was able to undergo self-regulated release from the capsules depending on the glucose level and APBA composition. The amount of insulin release increased with incubation in higher glucose concentration and decreased with higher APBA composition. Moreover, the on-off regulation of insulin release from the (γ-PGA-g-APBA/GC)5 capsules could be triggered with a synchronizing and variation of the external glucose concentration, whereas the capsules without the LA functional groups did not show the on-off regulated release. Furthermore, the (γ-PGA-g-APBA/GC)5 capsules are biocompatible. These (γ-PGA-g-APBA/GC)5 with good stability, glucose response, and controlled insulin delivery are expected to be used for future applications to glucose-triggered insulin delivery.

Well-defined degradable brush-coil block copolymers for intelligent release of insulin at physiological pH

To achieve an intelligent insulin delivery system with minimal long-term side effect, a kind of brush polymer was synthesized through poly[(2-phenylborate esters-1,3-dioxane-5-ethyl)methylacrylate] grafting from the backbone poly(ε-caprolactone).

Synthesis of a phenylboronic acid-functionalized thermosensitive block copolymer and its application in separation and purification of vicinal-diol-containing compounds

Phenylboronic acid-functionalized PEO₂₀PPO₆₀PEO₂₀ was synthesized and used to separate ortho-hydroxyl compounds as the collector in an aqueous two-phase flotation system.

Preparation of glucose responsive polyelectrolyte capsules with shell crosslinking via the layer-by-layer technique and sustained release of insulin

(Alg/CS-g-CPBA_m)_n capsules were fabricated to study the effect of the capsule structure on the glucose sensitivity and sustained release of insulin.

Nanotheranostics: Congo Red/Rutin-MNPs with Enhanced Magnetic Resonance Imaging and H2O2-Responsive Therapy of Alzheimer's Disease in APPswe/PS1dE9 Transgenic Mice

As nanotheranostics, Congo red/Rutin-MNPs combine the abilities of diagnosis and treatment of Alzheimer's disease (AD). The biocompatible nanotheranostics system based on iron oxide magnetic nanoparticles, with ultrasmall size and excellent magnetic properties, can specifically detect amyloid plaques by magnetic resonance imaging, realize targeted delivery of AD therapeutic agents, achieve drug controlled release by H2O2 response, and prevent oxidative stress.

Block versus Random Amphiphilic Glycopolymer Nanopaticles as Glucose-Responsive Vehicles

To explore the effect of polymer structure on their self-assembled aggregates and their unique characteristics, this study was devoted to developing a series of amphiphilic block and random phenylboronic acid-based glycopolymers by RAFT polymerization. The amphiphilic glycopolymers were successfully self-assembled into spherically shaped nanoparticles with narrow size distribution in aqueous solution. For block and random copolymers with similar monomer compositions, block copolymer nanoparticles exhibited a more regular transmittance change with the increasing glucose level, while a more evident variation of size and quicker decreasing tendency in I/I0 behavior in different glucose media were observed for random copolymer nanoparticles. Cell viability of all the polymer nanoparticles investigated by MTT assay was higher than 80%, indicating that both block and random copolymers had good cytocompatibility. Insulin could be encapsulated into both nanoparticles, and insulin release rate for random glycopolymer was slightly quicker than that for the block ones. We speculate that different chain conformations between block and random glycopolymers play an important role in self-assembled nanoaggregates and underlying glucose-sensitive behavior.

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.

Glucose- and pH-responsive nanogated ensemble based on polymeric network capped mesoporous silica

In this paper, a glucose and pH-responsive release system based on polymeric network capped mesoporous silica nanoparticles (MSN) has been presented. The poly(acrylic acid) (PAA) brush on MSN was obtained through the surface-initiated atom transfer radical polymerization (SI-ATRP) of t-butyl acrylate and the subsequent hydrolysis of the ester bond. Then the PAA was glycosylated with glucosamine to obtain P(AA-AGA). To block the pore of silica, the P(AA-AGA) chains were cross-linked through the formation of boronate esters between 4,4-(ethylenedicarbamoyl)phenylboronic acid (EPBA) and the hydroxyl groups of P(AA-AGA). The boronate esters disassociated in the presence of glucose or in acidic conditions, which lead to opening of the mesoporous channels and the release of loaded guest molecules. The rate of release could be tuned by varying the pH or the concentration of glucose in the environment. The combination of two stimuli exhibited an obvious enhanced release capacity in mild acidic conditions (pH 6.0).

Recent advances in nanotechnology for diabetes treatment

Nanotechnology in diabetes research has facilitated the development of novel glucose measurement and insulin delivery modalities which hold the potential to dramatically improve quality of life for diabetics. Recent progress in the field of diabetes research at its interface with nanotechnology is our focus. In particular, we examine glucose sensors with nanoscale components including metal nanoparticles and carbon nanostructures. The addition of nanoscale components commonly increases glucose sensor sensitivity, temporal response, and can lead to sensors which facilitate continuous in vivo glucose monitoring. Additionally, we survey nanoscale approaches to 'closed-loop' insulin delivery strategies which automatically release insulin in response to fluctuating blood glucose levels (BGLs). 'Closing the loop' between BGL measurements and insulin administration by removing the requirement of patient action holds the potential to dramatically improve the health and quality of life of diabetics. Advantages and limitations of current strategies, as well as future opportunities and challenges are also discussed.

Competitive binding-accelerated insulin release from a polypeptide nanogel for potential therapy of diabetes

A novel core cross-linked glycopolypeptide nanogel was prepared for glucose-triggered insulin delivery.

Hydrogel-coated enzyme electrodes formed by GOx-mediated polymerization for glucose detecting

This communication reports the mild fabrication of a hydrogel-coated enzyme electrode for glucose detecting with high sensitivity (35.19 μA mM⁻¹ cm⁻²) and robust stability.

Polypeptide-based "smart" micelles for dual-drug delivery: a combination study of experiments and simulations

A dual-drug-loaded micelle is designed and constructed from a mixture of poly(propylene oxide)-b-poly(γ-benzyl-l-glutamate)-b-poly(ethylene glycol) (PPO-b-PBLG-b-PEG) triblock terpolymers and two model drugs, doxorubicin (DOX) and naproxen (Nap). In the micelles, the DOX is chemically linked to the PBLG backbones through an acid-cleavable hydrazone bond, whereas the Nap is physically encapsulated in the cores. The drug loading and releasing behaviors of the dual-drug-loaded micelles as well as single drug-loaded micelles (DOX-conjugated or Nap-loaded micelles) are studied. The structures of micelles are characterized by means of microscopies and dynamic light scattering, and further examined by dissipative particle dynamics (DPD) simulations. It is revealed that the micelles possess a core-shell-corona structure in which the PPO/Nap, PBLG/DOX, and PEG aggregate to form the core, shell, and corona, respectively. In vitro studies reveal that the release of DOX and Nap is pH- and thermosensitive. Such drug releasing behaviors are also examined by DPD simulations, and more information regarding the mechanism is obtained. In addition, the bio-related properties such as cellular uptake of the micelles and biocompatibility of the deliveries are evaluated. The results show that the dual-drug-loaded micelles are biocompatible at normal physiological conditions and retain the anti-cancer efficiency.

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.

Synthesis of Copolymers from Phenylboronic Acid-Installed Cyclic Carbonates

Organoboron polymers play important roles in biomedical applications. An ample number of monomers bearing boronic acid derivatives have been synthesized, particularly focusing on controlled free radical polymerization methods. Organoboron polymers synthesized by ring-opening polymerization (ROP) routes are far less explored. We report on the ROP of boronic acid-installed cyclic carbonates, catalyzed by DBU from a poly(ethylene glycol) macroinitiator. Controlled polymerization proceeded to relatively high conversions (∼70%) with low polydispersity. Deprotection of the copolymer to generate the boronic acid pendant group was readily achieved by displacement of the protecting group with free diboronic acid. The resulting amphiphilic copolymers self-assembled in water into spherical nanoparticles or vesicles, depending on hydrophilic/hydrophobic ratio. We envision these functional carbonates finding direct applications for core stabilization of biodegradable amphiphilic assemblies or in drug and protein encapsulation.

Emerging micro- and nanotechnology based synthetic approaches for insulin delivery

Insulin is essential for type 1 and advanced type 2 diabetics to maintain blood glucose levels and prolong lives. The traditional administration requires frequent subcutaneous insulin injections that are associated with poor patient compliance, including pain, local tissue necrosis, infection, and nerve damage. Taking advantage of emerging micro- and nanotechnologies, numerous alternative strategies integrated with chemical approaches for insulin delivery have been investigated. This review outlines recent developments in the controlled delivery of insulin, including oral, nasal, pulmonary, transdermal, subcutaneous and closed-loop insulin delivery. Perspectives from new materials, formulations and devices at the micro- or nano-scales are specifically surveyed. Advantages and limitations of current delivery methods, as well as future opportunities and challenges are also discussed.

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.

Fluorescent boronic acid polymer grafted on silica particles for affinity separation of saccharides

Boronic acid affinity gels are important for effective separation of biological active cis-diols, and are finding applications both in biotech industry and in biomedical research areas. To increase the efficacy of boronate affinity separation, it is interesting to introduce repeating boronic acid units in flexible polymer chains attached on solid materials. In this work, we synthesize polymer brushes containing boronic acid repeating units on silica gels using surface-initiated atom transfer radical polymerization (ATRP). A fluorescent boronic acid monomer is first prepared from an azide-tagged fluorogenic boronic acid and an alkyne-containing acrylate by Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction (the CuAAC click chemistry). The boronic acid monomer is then grafted to the surface of silica gel modified with an ATRP initiator. The obtained composite material contains boronic acid polymer brushes on surface and shows favorable saccharide binding capability under physiological pH conditions, and displays interesting fluorescence intensity change upon binding fructose and glucose. In addition to saccharide binding, the flexible polymer brushes on silica also enable fast separation of a model glycoprotein based on selective boronate affinity interaction. The synthetic approach and the composite functional material developed in this work should open new opportunities for high efficiency detection, separation, and analysis of not only simple saccharides, but also glycopeptides and large glycoproteins.

Complex Micelles with Glucose-Responsive Shells for Self-Regulated Release of Glibenclamide

Complex micelles with a hydrophobic poly(ϵ-caprolactone) (PCL) core and a mixed P(Asp-co-AspPBA)/PEG shell were prepared through co-assembly of two block copolymers PCL-b- P(Asp-co-AspPBA) and PEG-b-PCL in basic aqueous solutions. The P(Asp-co-AspPBA) chains (Asp = aspartic acid; AspPBA = aspartamidophenylboronic acid) collapsed and formed a shell layer around the PCL core at neutral pH while the soluble PEG chains stabilised the micelles. The collapsed P(Asp-co-AspPBA) polymer becomes soluble under higher glucose concentration and collapses onto the PCL core reversibly at lower glucose concentration. Self-regulated release of glibenclamide from the complex micelles was achieved based on the reversible change of P(Asp-co-AspPBA) chain mobility in response to the change of glucose concentration. As a result, polymeric micelles with glucose-responsive on-off switches were successfully developed.

Direct and indirect core–shell inversion of block copolymer micelles

A novel block copolymer PNIPAm-b-PBOB is reported where denaturation of PNIPAm and PBOB is switched by independent, controllable stimuli. Core–shell inversion may be realized via different pathways, indirect and direct, by adjusting the program of imposing the stimuli.

Stimuli-responsive nanocarriers for drug delivery

Spurred by recent progress in materials chemistry and drug delivery, stimuli-responsive devices that deliver a drug in spatial-, temporal- and dosage-controlled fashions have become possible. Implementation of such devices requires the use of biocompatible materials that are susceptible to a specific physical incitement or that, in response to a specific stimulus, undergo a protonation, a hydrolytic cleavage or a (supra)molecular conformational change. In this Review, we discuss recent advances in the design of nanoscale stimuli-responsive systems that are able to control drug biodistribution in response to specific stimuli, either exogenous (variations in temperature, magnetic field, ultrasound intensity, light or electric pulses) or endogenous (changes in pH, enzyme concentration or redox gradients).

Phenylboronic acid-functionalized polymeric micelles with a HepG2 cell targetability

Phenylboronic acid-functionalized amphiphilic block copolymer Pluronic-PMCC-BA was synthesized via ring-opening polymerization of 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MBC) with fumaric acid as a catalyst followed by the deprotection of carboxyl groups by catalyzed hydrogenation and the condensation of 3-aminophenylboronic acid with the copolymer side groups. Pluronic-PMCC-BA can form stable micelle solution by self-assembly in water. The phenylboronic acid groups are located at the shell of micelle as proved by (1)H NMR. The diameter of drug-free micelles is approximate 60 nm. Nano-spheres with narrow size distribution could be observed in the TEM image. MTT assay results show that Pluronic-PMCC-BA exhibits slight cytotoxicity when the polymer concentration is higher than 25 μg mL(-1). The toxicities of DOX@Pluronic-PMCC and DOX@Pluronic-PMCC-BA to COS7, HeLa, and HepG2 cell lines are similar with those of free DOX. Interestingly, phenylboronic acid groups located at the surface of Pluronic-PMCC-BA micelles can recognize HepG2 cells and promote the drug uptake of the cells, which are observed by confocal laser scanning microscopy (CLSM). The results imply that Pluronic-PMCC-BA would be a promising material for targeted drug delivery to the cancer cells.

Self-assembly and chemical processing of block copolymers: a roadmap towards a diverse array of block copolymer nanostructures

Block copolymers can yield a diverse array of nanostructures. Their assembly structures are influenced by their inherent structures, and the wide variety of structures that can be prepared especially becomes apparent when one considers the number of routes available to prepare block copolymer assemblies. Some examples include self-assembly, directed assembly, coupling, as well as hierarchical assembly, which can yield assemblies having even higher structural order. These assembly routes can also be complemented by processing techniques such as selective crosslinking and etching, the former technique leading to permanent structures, the latter towards sculpted and the combination of the two towards permanent sculpted structures. The combination of these pathways provides extremely versatile routes towards an exciting variety of architectures. This review will attempt to highlight destinations reached by LIU Guojun and coworkers following these pathways.

Carbohydrate biomarker recognition using synthetic lectin mimics

Carbohydrate biomarkers play very important roles in a wide range of biological and pathological processes. Compounds that can specifically recognize a carbohydrate biomarker are useful for targeted delivery of imaging agents and for development of new diagnostics. Furthermore, such compounds could also be candidates for the development of therapeutic agents. A tremendous amount of active work on synthetic lectin mimics has been reported in recent years. Amongst all the synthetic lectins, boronic-acid-based lectins (boronolectins) have shown great promise. Along this line, four classes of boronolectins including peptide-, nucleic-acid-, polymer-, and small-molecule-based ones are discussed with a focus on the design principles and recent advances. We hope that by presenting the potentials of this field, this review will stimulate more research in this area.

pH- and glucose-sensitive glycopolymer nanoparticles based on phenylboronic acid for triggered release of insulin

Amphiphilic poly(acrylic acid-co-acrylamidophenylboronic acid)-block-poly(2-acryloxyethyl galactose)-block-poly(acrylic acid-co-acrylamidophenylboronic acid) (((PAA-co-PAAPBA)-b-)₂PAEG) copolymer was fabricated: The poly(2-acryloyloxyethyl pentaacetylgalactoside) (PAEAcG) with narrow molecular weight distributions (Mw/Mn≤1.22) was prepared by atom transfer radical polymerization (ATRP) using dibromo-p-xylene (DBX) as initiator. Then the well-defined triblock copolymer poly(t-butyl acrylate)-b-poly(2-acryloyloxyethyl pentaacetylgalactoside)-b-poly(t-butyl acrylate) (PtBA-b-PAEAcG-b-PtBA) was synthesized by ATRP of tBA using PAEAcG homopolymer with dibromo end groups as macroinitiator. After hydrolysis of t-butyl acrylate block, amide linkage and deacetylation, the final copolymer ((PAA-co-PAAPBA)-b-)₂PAEG was obtained. Because of characteristics of three different segments, amphiphilic ((PAA-co-PAAPBA)-b-)₂PAEG can self-assemble into pH- and glucose-responsive nanoparticles studied by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Furthermore, the in vitro release profiles of insulin also revealed obvious pH- and glucose-sensitivity of the nanoparticles. The analysis of cell viability suggested that the copolymer nanoparticles had good cytocompatibility.

Non inflammatory boronate based glucose-responsive insulin delivery systems

Boronic acids, known to bind diols, were screened to identify non-inflammatory cross-linkers for the preparation of glucose sensitive and insulin releasing agglomerates of liposomes (Agglomerated Vesicle Technology-AVT). This was done in order to select a suitable replacement for the previously used cross-linker, ConcanavalinA (ConA), a lectin known to have both toxic and inflammatory effects in vivo. Lead-compounds were selected from screens that involved testing for inflammatory potential, cytotoxicity and glucose-binding. These were then conjugated to insulin-encapsulating nanoparticles and agglomerated via sugar-boronate ester linkages to form AVTs. In vitro, the particles demonstrated triggered release of insulin upon exposure to physiologically relevant concentrations of glucose (10 mmoles/L–40 mmoles/L). The agglomerates were also shown to be responsive to multiple spikes in glucose levels over several hours, releasing insulin at a rate defined by the concentration of the glucose trigger.