Temperature-induced volume change and glucose sensitivity of poly[(N -isopropylacry- lamide)-co -acrylamide-co -(phenylboronic acid)] microgels

Synthesis of multi-responsive poly(NIPA-co-DMAEMA)-PBA hydrogel nanoparticles in aqueous solution for application as glucose-sensitive insulin-releasing nanoparticles

Objectives

This study aimed to present an innovative method for synthesizing pH-thermo-glucose responsive poly(NIPA-co-DMAEMA)-PBA hydrogel nanoparticles via single-step aqueous free radical polymerization.

Methods

The synthesis process involved free radical polymerization in an aqueous solution, and the resulting nanoparticles were characterized for their physical and chemical properties by 1H NMR, Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM). Insulin-loaded poly(NIPA-co-DMAEMA)-PBA hydrogel nanoparticles were prepared and evaluated for their insulin capture and release properties at different pH and temperature, in addition to different glucose concentrations, with the release profile of insulin quantitatively evaluated using the Bradford method.

Results

1H NMR results confirmed successful PBA incorporation, and DLS outcomes consistently indicated a transition to a more hydrophobic state above the Lower Critical Solution Temperature (LCST) of NIPA and DMAEMA. While pH responsiveness exhibited variation, insulin release generally increased with rising pH from acidic to neutral conditions, aligning with the anticipated augmentation of anionic PBA moieties and increased hydrogel hydrophilicity. Increased insulin release in the presence of glucose, particularly for formulations with the lowest mol % PBA, along with a slight increase for the highest mol % PBA formulation when increasing glucose from 1 to 4 mg/mL, supported the potential of this approach for nanoparticle synthesis tailored for glucose-responsive insulin release.

Conclusions

This work successfully demonstrates a novel method for synthesizing responsive hydrogel nanoparticles and underscores their potential for controlled insulin release in response to glucose concentrations. The observed pH-dependent insulin release patterns and the influence of PBA content on responsiveness highlight the versatility and promise of this nanoparticle synthesis approach for applications in glucose-responsive drug delivery systems.

Graphical abstract

Poly(NIPA) nanoparticles containing PBA moieties are normally synthesized in two or more steps in the presence of organic solvents. Here we propose a new method for the synthesis of multiresponsive hydrogel poly(NIPA-co-DMAEMA)-PBA nanoparticles in aqueous medium in a single reaction to provide a fast and effective strategy for the production of glucose-responsive multi-systems in aqueous media from free radical polymerization.

Physicochemical aspects of inorganic nanoparticles stabilized in N-vinyl caprolactam based microgels for various applications

The vinyl caprolactam (VCL) based microgel system has become the center of great attention due to its versatile properties. Copolymerization of VCL with an ionic monomer imparts pH responsive properties into the microgel system in addition to thermo-sensitivity. Stimuli responsive behavior of VCL-based microgels makes them prospective and appealing candidates for practical applications covering the fields of drug delivery, catalysis and optical devices. In the last few years, VCL-based microgels have been used as microreactors and stabilizers for the synthesis and stabilization of inorganic nanoparticles to obtain hybrid microgels. The present review article provides a summary of the present-day progress of fabrication, stabilization, categorization and analysis of VCL-based microgels and their hybrids with different morphologies. The stimuli responsive properties and applications of VCL-based hybrid microgels have been reviewed critically. The remaining problems which need to be addressed have been pointed out for further advancement in this field.

Recent Advances in Phenylboronic Acid-Based Gels with Potential for Self-Regulated Drug Delivery

Glucose-sensitive drug platforms are highly attractive in the field of self-regulated drug delivery. Drug carriers based on boronic acid (BA), especially phenylboronic acid (PBA), have been designed for glucose-sensitive self-regulated insulin delivery. The PBA-functionalized gels have attracted more interest in recent years. The cross-linked three-dimensional (3D) structure endows the glucose-sensitive gels with great physicochemical properties. The PBA-based platforms with cross-linked structures have found promising applications in self-regulated drug delivery systems. This article summarizes some recent attempts at the developments of PBA-mediated glucose-sensitive gels for self-regulated drug delivery. The PBA-based glucose-sensitive gels, including hydrogels, microgels, and nanogels, are expected to significantly promote the development of smart self-regulated drug delivery systems for diabetes therapy.

Fundamentals and applications of acrylamide based microgels and their hybrids: a review

Recent advances in synthesis, characterization and applications of acrylamide based polymer microgels and their hybrids are discussed for further development in this area.

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.

Glucose monitoring using a polymer brush modified polypropylene hollow fiber-based hydraulic flow sensor

Tight regulation of blood glucose levels of diabetic patients requires durable and robust continuous glucose sensing schemes. This manuscript reports the fabrication of ultrathin, phenylboronic acid (PBA) functionalized polymer brushes that swell upon glucose binding and which were integrated as the sensing interface in a new polypropylene hollow fiber (PPHF)-based hydraulic flow glucose sensor prototype. The polymer brushes were prepared via surface-initiated atom transfer radical polymerization of sodium methacrylate followed by postpolymerization modification with 3-aminophenyl boronic acid. In a first series of experiments, the glucose-response of PBA-functionalized poly(methacrylic acid) (PMAA) brushes grafted from planar silicon surfaces was investigated by quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM) experiments. The QCM-D experiments revealed a more or less linear change of the frequency shift for glucose concentrations up to ∼10 mM and demonstrated that glucose binding was completely reversible for up to seven switching cycles. The AFM experiments indicated that glucose binding was accompanied by an increase in the film thickness of the PBA functionalized PMAA brushes. The PBA functionalized PMAA brushes were subsequently grafted from the surface of PPHF membranes. The hydraulic permeability of these porous fibers depends on the thickness and swelling of the PMAA brush coating. PBA functionalized brush-coated PPHFs showed a decrease in flux upon exposure to glucose, which is consistent with swelling of the brush coating. Because they avoid the use of enzymes and do not rely on an electrochemical transduction scheme, these PPHF-based hydraulic flow sensors could represent an interesting alternative class of continuous glucose sensors.

Responsive hydrogels--structurally and dimensionally optimized smart frameworks for applications in catalysis, micro-system technology and material science

Although the technological and scientific importance of functional polymers has been well established over the last few decades, the most recent focus that has attracted much attention has been on stimuli-responsive polymers. This group of materials is of particular interest due to its ability to respond to internal and/or external chemico-physical stimuli, which is often manifested as large macroscopic responses. Aside from scientific challenges of designing stimuli-responsive polymers, the main technological interest lies in their numerous applications ranging from catalysis through microsystem technology and chemomechanical actuators to sensors that have been extensively explored. Since the phase transition phenomenon of hydrogels is theoretically well understood advanced materials based on the predictions can be prepared. Since the volume phase transition of hydrogels is a diffusion-limited process the size of the synthesized hydrogels is an important factor. Consistent downscaling of the gel size will result in fast smart gels with sufficient response times. In order to apply smart gels in microsystems and sensors, new preparation techniques for hydrogels have to be developed. For the up-coming nanotechnology, nano-sized gels as actuating materials would be of great interest.