Synthesis, characterisation and solution thermal behaviour of a family of poly (N-isopropyl acrylamide-co-N-hydroxymethyl acrylamide) copolymers

Synthesis of gum tragacanth-grafted pentapolymer hydrogels for As(III) exclusion: Roles of microwaves, RSM optimization, and DFT studies

Microwave assisted homogeneous heating, selectivity in radical formation, and the faster polymerization facilitate the synthesis, structures, properties, and the higher branching associated stability of multifunctional multipolymers. Thus, the optimum gum tragacanth (GMTR)-grafted pentapolymer hydrogel/ HG2 was synthesized from three monomers, i.e., cis-butenedioic acid (cBDA), N-hydroxymethylacryalamide (NHMAm), and 2-(methacryloyloxy)ethanol (MAOE), and in situ generated 2-(3-((hydroxymethyl)amino)-3-oxopropoxy)ethyl-2-methylbutanoate (CM1) and 2-hydroxyethyl 3-(N-(hydroxymethyl)-2-methylbutanamido)-2-methylpropanoate (CM2) comonomers through microwave assisted facile polymerization in aqueous medium. Here, twenty-one GMTR-grafted-[cBDA-co-CM1-co-NHMAm-co-CM2-co-MAOE/ HG1] hydrogels were prepared by using variable amounts of synthesis parameters, of which the optimum HG2 was chosen for the scale-up repetitive As(III)-exclusion. RSM was used to measure the optimum power-temperature-time of microwave irradiation. The structures of HG1, HG2, and As(III)-adsorbed HG2/ As(III)-HG2, in situ anchored comonomers, GMTR-grafting, reusability, thermostability, and surface phenomena were comprehended by XPS, NMR, UV-vis, FTIR, TG, XRD, DLS, and SEM analyses; pH_PZC; network parameters; and thermodynamic variables. The geometries, electronic structures, and variable coordinations of As(III) with HG2 were investigated through DFT studies of HG2 and As(OH)₃-HG2. The highest exclusion efficiency of 25 mg HG2 within 5-100 mg L^-1 As(III) and at 298 K was 192.91 mg g^-1, which was significantly higher than that of HG1.

Flow-assembled chitosan membranes in microfluidics: recent advances and applications

The integration of membranes in microfluidic devices has been extensively exploited for various chemical engineering and bioengineering applications over the past few decades. To augment the applicability of membrane-integrated microfluidic platforms for biomedical and tissue engineering studies, a biologically friendly fabrication process with naturally occurring materials is highly desired. The in situ preparation of membranes involving interfacial reactions between parallel laminar flows in microfluidic networks, known as the flow-assembly technique, is one of the most biocompatible approaches. Membranes of many types with flexible geometries have been successfully assembled inside complex microchannels using this facile and versatile flow-assembly approach. Chitosan is a naturally abundant polysaccharide known for its pronounced biocompatibility, biodegradability, good mechanical stability, ease of modification and processing, and film-forming ability under near-physiological conditions. Chitosan membranes assembled by flows in microfluidics are freestanding, robust, semipermeable, and well-aligned in microstructure, and show high affinity to bioactive reagents and biological components (e.g. biomolecules, nanoparticles, or cells) that provide facile biological functionalization of microdevices. Here, we discuss the recent developments and optimizations in the flow-assembly of chitosan membranes and chitosan-based membranes in microfluidics. Furthermore, we recapitulate the applications of the chitosan membrane-integrated microfluidic platforms dedicated to biology, biochemistry, and drug release fields, and envision the future developments of this important platform with versatile functions.

Effect of Hydrophobic Interactions on Lower Critical Solution Temperature for Poly(N-isopropylacrylamide-co-dopamine Methacrylamide) Copolymers

For the preparation of thermoresponsive copolymers, for e.g., tissue engineering scaffolds or drug carriers, a precise control of the synthesis parameters to set the lower critical solution temperature (LCST) is required. However, the correlations between molecular parameters and LCST are partially unknown and, furthermore, LCST is defined as an exact temperature, which oversimplifies the real situation. Here, random N-isopropylacrylamide (NIPAM)/dopamine methacrylamide (DMA) copolymers were prepared under a systematical variation of molecular weight and comonomer amount and their LCST in water studied by calorimetry, turbidimetry, and rheology. Structural information was deduced from observed transitions clarifying the contributions of molecular weight, comonomer content, end-group effect or polymerization degree on LCST, which were then statistically modeled. This proved that the LCST can be predicted through molecular structure and conditions of the solutions. While the hydrophobic DMA lowers the LCST especially the onset, polymerization degree has an important but smaller influence over all the whole LCST range.

Preparation and characterization of resorcinol-dialdehyde starch-formaldehyde copolycondensation resin adhesive

A resorcinol-dialdehyde starch-formaldehyde (RDSF) copolycondensation resin adhesive was prepared by substituting high reactive dialdehyde starch for a portion of formaldehyde in the formulation. Fourier transforms infrared spectrometer (FTIR) analysis results confirmed that the copolycondensation reaction of the dialdehyde starch with resorcinol and formaldehyde was successful. The curing property, thermal stability, permeability and crystal structure of the RDSF adhesive were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscope (SEM), X-ray diffraction (XRD). The solids content, viscosity, curing time, bonding strength were also obtained. The results showed that the RDSF adhesive had a higher solids content, moderate viscosity, shorter curing time and better bond strength than a standard resorcinol-starch-formaldehyde (RSF) adhesive. It was found that dialdehyde starch could accelerate the curing rate, while decreasing the curing temperature and heat release during the curing process of RDSF. The dense cross-linked structure of the dialdehyde starch and resorcinol-formaldehyde (RF) system produced improved thermal stability. SEM results showed that the RDSF adhesive formed a thin and continuous adhesive layer on the surface of a poplar board, and filled the pores of the wood, which improved the bond strength. The crystal structure of the RDSF was not altered by addition of the starch, and the physicochemical properties of the adhesive were similar to those of a normal resorcinol-formaldehyde resin.

Anomalous diffusion in thermoresponsive polymer-clay composite hydrogels probed by wide-field fluorescence microscopy

Thermoresponsive materials exhibit an enormous potential for tissue engineering, separation systems, and drug delivery. We investigated the diffusion of laponite clay nanoparticles, which serve as physical cross-linkers to achieve improved material properties in poly(N-isopropylacrylamide) (PNIPAM)-clay composite hydrogels close to the gel point. The networks are formed through physical interactions between PNIPAM chains and clay nanoparticles after these two components are mixed. In contrast to previous studies, a covalent labeling strategy was chosen to minimize the amount of free dyes in solution. Single-particle tracking of the labeled clay nanoparticles showed that their diffusion is anomalous at all temperatures used in this study, reflecting the viscoelastic behavior as a cross-linker. Stepwise heating from 24 to 38 °C resulted in a slight increase of the diffusion coefficient and the anomality parameter α up to the volume phase transition temperature of ca. 31 °C, which was followed by a significant drop of both parameters, reflecting strongly hindered motion of the collapsed nanoparticle aggregates.

In situ fabrication of a temperature- and ethanol-responsive smart membrane in a microchip

Here we report a simple and versatile strategy for the in situ fabrication of nanogel-containing smart membranes in microchannels of microchips. The fabrication approach is demonstrated by the in situ formation of a chitosan membrane containing poly(N-isopropylacrylamide) (PNIPAM) nanogels in a microchannel of a microchip. The PNIPAM nanogels, that allow temperature- and ethanol-responsive swelling-shrinking volume transitions, serve as smart nanovalves for controlling the diffusional permeability of solutes across the membrane. Such self-regulation of the membrane permeability is investigated by using fluorescein isothiocyanate (FITC) as a tracer molecule. This approach provides a promising strategy for the in situ fabrication of versatile nanogel-containing smart membranes within microchips via simply changing the functional nanogels for developing micro-scale detectors, sensors, separators and controlled release systems.

Calix[4]arene-click-cyclodextrin and supramolecular structures with watersoluble NIPAAM-copolymers bearing adamantyl units: "Rings on ring on chain"

We describe the calixarene-cyclodextrin-coupling via click reaction starting from 5,11,17,23-tetra-tert-butyl-25,27-dipropargylether-26,28-hydroxy-calix[4]arene (calix[4]arene-dipropargylether) (2) onto 6I-azido-6I-deoxycyclomaltoheptaose (3) under microwave assisted conditions. The coupling was proven by MALDI-TOF mass spectrometry, ¹H NMR and IR-spectroscopy. The pH dependent supramolecular complex formation with poly(NIPAAM) bearing attached adamantyl units was investigated by dynamic light scattering (DLS) and turbidity measurements.