Reversible Swelling Behavior Research Articles

Green Synthesis of Stable Lignin Nanoparticles with Reversible Swelling Behavior and Enhanced Multifunctional Features

Green Synthesis of Stable Lignin Nanoparticles with Reversible Swelling Behavior and Enhanced Multifunctional Features

Light-Triggered Reversible Swelling of Azobenzene-Containing Block Copolymer Worms via Confined Deformation Prepared by Polymerization-Induced Self-Assembly.

Stimuli-responsive block copolymer nanoparticles (NPs) have received close attention in recent years owing to their tremendous application potential in smart materials. Azobenzene-containing NPs are widely studied due to the advantages of light as a stimulus and fast reversible trans-cis isomerization of azobenzene chromophores. However, the inefficient preparation process and difficult reversible transformation of morphologies limit their development. Herein it is demonstrated that the light-triggered reversible swelling behavior of wormlike NPs with high azobenzene content could be realized via confined deformation. These worms are prepared in large quantities via polymerization-induced self-assembly based on the copolymerization of 11-(4-(4-butylphenylazo)phenoxy)undecyl methacrylate (MAAz) and N-(methacryloxy)succinimide (NMAS) monomers. Upon UV/visible light irradiation, the reversible deformation of worms is achieved when the feed molar ratio of NMAS/MAAz is relatively high or via crosslinking using diamines, which leads to the reduction of the photoisomerization efficiency. The diameter variation of the worms is influenced by the amount and types of crosslinkers. Moreover, the scalability of this strategy is further proved by the fabrication of photo- and reductant-responsive crosslinked worms. It is expected that this study not only provides a new route to affording reversible photoresponsive NPs but also offers a unique insight into the reversible photodeformation mechanism of azobenzene-containing NPs.

Light- and Solvent-Responsive Bilayer Hydrogel Actuators with Reversible Bending Behaviors.

Light-responsive hydrogel systems have gained significant attention due to their unique ability to undergo controlled and reversible swelling behavior in response to light stimuli. Combining light-responsive hydrogels with nonresponsive polymers offers a unique self-folding feature that can be used in soft robotic actuator designs. However, simple formulation of such systems with rapid response time is still a challenging task. Herein, we demonstrate a simple but versatile bilayer polymeric design combining light-responsive spiropyran-polyacrylamide (SP-PAAm) with polyacrylamide (PAAm) hydrogels. The photochromic spiropyran in our polymer design is a closed-ring, hydrophobic compound and turns into an open-ring, hydrophilic merocyanine isomer under light irradiation. The swelling degree of SP-PAAm and PAAm hydrogels was evaluated using LED lights with different wavelengths and solvent media (e.g., water, ethanol, DMF, and DMSO). We observed that SP-PAAm hydrogels reached a swelling ratio of ∼370% with the illumination of the blue LED in the DMF medium. By combining light-responsive SP-PAAm hydrogels with nonresponsive PAAm, a proof-of-concept demonstration was performed to demonstrate the applicability of our fabricated platforms. Although fabricated one-armed bilayer hydrogels possessed self-folding ability with a folding angle of ∼40° in 30 min, the four-armed bilayer platforms demonstrated more efficient and rapid folding behavior and reached a folding angle of ∼75° in ∼15 min. Given their simplicity and efficiency, we believe that such polymeric designs may offer new avenues for the fields of polymeric actuators and soft robotic systems.

Microneedles coated with composites of phenylboronic acid-containing polymer and carbon nanotubes for glucose measurements in interstitial fluids

A microneedle (MN) sensor coated with a sensing composite material was proposed for measuring glucose concentrations in interstitial fluid (ISF). The sensing composite material was prepared by blending a polymer containing glucose-responsive phenylboronic acid (PBA) moieties (i.e., polystyrene-block-poly(acrylic acid-co-acrylamidophenylboronic acid)) with conductive carbon nanotubes (CNTs). The polymer exhibited reversible swelling behavior in response to glucose concentrations, which influenced the distribution of the embedded CNTs, resulting in sensitive variations in electrical percolation, even when coated onto a confined surface of the MN in the sensor. We varied the ratio of PBA moieties and the loading amount of CNTs in the sensing composite material of the MN sensor and tested them in vitro using an ISF-mimicking gel with physiological glucose concentrations to determine the optimal sensitivity conditions. When tested in animal models with varying blood glucose concentrations, the MN sensor coated with the selected sensing material exhibited a strong correlation between the measured electrical currents and blood glucose concentrations, showing accuracy comparable to that of a glucometer in clinical use.

Experimental Investigation on Reversible Swelling Mechanisms of Lithium-Ion Batteries under a Varying Preload Force

The safety of lithium-ion batteries has to be guaranteed over the complete lifetime considering geometry changes caused by reversible and irreversible swellings and degradation mechanisms. An understanding of the pressure distribution and gradients is necessary to optimize battery modules and avoid local degradation bearing the risk of safety-relevant battery changes. In this study, the pressure distribution of two fresh lithium-ion pouch cells was measured with an initial preload force of 300 or 4000 N. Four identical cells were electrochemically aged with a 300 or 4000 N preload force. The irreversible thickness change was measured during aging. After aging, the reversible swelling behavior was investigated to draw conclusions on how the pressure distribution affected the aging behavior. A novel test setup was developed to measure the local cell thickness without contact and with high precision. The results suggested that the applied preload force affected the pressure distribution and pressure gradients on the cell surface. The pressure gradients were found to affect the locality of the irreversible swelling. Positions suffering from large pressure variations and gradients increased strongly in thickness and were affected in terms of their reversible swelling behavior. In particular, the edges of the investigated cells showed a strong thickness increase caused by pressure peaks.

Light-Triggered Reversible Swelling of Polymeric Spheres via Surfactant-Free RAFT Emulsion Polymerization-Induced Self-Assembly.

Responsive photonic crystals (RPCs) assembled by monodisperse colloidal particles have attracted enormous interest recently due to their tremendous applications in smart devices. Their structural colors can be determined by particle sizes. However, the lack of a reliable way to tune the sizes in situ limits their development. Herein, we present an efficient route to solve this problem through the fabrication of spherical polymeric particles with light-triggered reversible swelling behavior via surfactant-free reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization-induced self-assembly (PISA). Amphiphilic macro-RAFT agents containing azobenzene groups were synthesized and subsequently employed to mediate the polymerization of methyl methacrylate. Uniform submicron spheres were obtained by modulating solid contents and other parameters. Benefiting from the photoisomerization of azobenzene moieties, the particle sizes expanded and contracted upon alternative ultraviolet/visible-light irradiation accordingly. This strategy will be a supplement to the emulsion PISA and especially give aid to the progress of the RPC materials.

Breathable Lignin Nanoparticles as Reversible Gas Swellable Nanoreactors.

The design of stimuli-responsive lignin nanoparticles (LNPs) for advanced applications has hitherto been limited to the preparation of lignin-grafted polymers in which usually the lignin content is low (<25 wt.%) and its role is debatable. Here, the preparation of O2 -responsive LNPs exceeding 75 wt.% in lignin content is shown. Softwood Kraft lignin (SKL) is coprecipitated with a modified SKL fluorinated oleic acid ester (SKL-OlF) to form colloidal stable hybrid LNPs (hy-LNPs). The hy-LNPs with a SKL-OlF content ranging from 10 to 50 wt.% demonstrated a reversible swelling behavior upon O2 /N2 bubbling, increasing their size - ≈35% by volume - and changing their morphology from spherical to core-shell. Exposition of hy-LNPs to O2 bubbling promotes a polarity change on lignin-fluorinated oleic chains, and consequently their migration from the inner part to the surface of the particle, which not only increases the particle size but also endows hy-LNPs with enhanced stability under harsh conditions (pH < 2.5) by the hydration barrier effect. Furthermore, it is also demonstrated that these new stimuli-responsive particles as gas tunable nanoreactors for the synthesis of gold nanoparticles. Combining a straightforward preparation with their enhanced stability and responsiveness to O2 gas these new LNPs pave the way for the next generation of smart lignin-based nanomaterials.

Formulation and Evaluation of Superporus Hydrogel Composite as a Gastro Retentive Drug Delivery for Cefditoren Pivoxil

The purpose of this work was to incorporate superporus hydrogels for cefditoren pivoxil by using polymer like poly acrylic acid aqua cc polymer and composite agent like cross linked sodium carboxy methyl cellulose in the presence of N,N-methylene-bis-Acrylamide as crosslinking agent. Pluronic F-127 as a stabilizer and ammonium per sulfate and tetramethylene diamine as a initiator pair. Poly acrylic acid aqua cc polymer-cross linked sodium carboxy methyl cellulose superporus hydrogels of cefditoren pivoxil were incorporate by gas blowing technique. The reaction of pH on the swelling ratio was decisive. Swelling reversibility research was also achieve. Fourier transform infrared spectroscopy analysis and scanning electron microscopy studies were assume to indicate the drug loaded superporous hydrogels, while dissolution studies were achieve to assess release characteristics. Swelling was hugely depending on the term of crosslinking and the quantity of the polymer existing in formulation. The huge amount of cross-linking agent reduced the swelling ratio. The superporous hydrogels were hugely perceptive to pH of swelling medium, and exhibit reversible swelling and de-swelling behavior during still keep their mechanical stability. Apparent density was reliant on the amount of the superporous hydrogels and reduced with developing crosslink density. Degradation kinetics reveals that poly acrylic acid aqua cc polymer superporous hydrogels had good water holding potential. Drug release was similar to quantity of cross-linking agent. The studies report that poly acrylic acid aqua cc polymer superporous hydrogels can be used as a Gastroretentive drug delivery system in view of their swelling characteristics in acidic pH.

EVALUATION OF SWELLING PROPERTIES OF POLY (ACRYLIC ACID)/Zr-PILLARED K10 SUPERABSORBENT HYDROGEL

Zr- Pillared K10 (Zr-K10) was synthesized by using Montmorillonite K10 clay. Zr- pillared K10 based superabsorbent (Zr-PILC-SA) was synthesized by using Zr- pillared- montmorillonite K10 via graft copolymerization reaction of acrylic acid (AA). After preparation of the films of hydrogels of Zr- pillared K10, swelling studies were performed in distilled water and different pH values at room temperature to investigate swelling behavior of pillared clay based superabsorbent films. It was also obtained that Zr-K10 based superabsorbent was pH dependent and showed a reversible swelling behavior. The swelling behavior of Zr-K10-SA was increasing by decreasing amount of Zr-K10 in the hydrogel. SEM, FTIR and XRD analysis were conducted for further characterization of the Zr-PILC-SA. FTIR analyses lead to ester formation between Zr-K10 and SA. XRD revealed the morphology of the superabsorbent was exfoliated and the layers of clay dispersed on the composite. &#x0D;

Synthesis, characterization and swelling properties of poly (acrylic acid)/Zr-pillared clay superabsorbent composites

Superabsorbents&#x0D; hydrogel were prepared by using Zr pillared- montmorillonite KSF by graft&#x0D; copolymerization reaction of acrylic acid (AA).&amp;nbsp;&#x0D; Swelling behavior of pillared clay based superabsorbent films in&#x0D; distilled water and different pH values were investigated at room temperature.&#x0D; It was also obtained that pillared clay based superabsorbents were pH dependent&#x0D; and showed a reversible swelling behavior. Water absorbency of pillared clay&#x0D; based superabsorbent (PILC-SA) was increased by decreasing pillared clay amount&#x0D; in the network of the superabsorbents. SEM and XRD analysis were conducted for&#x0D; further characterization of the PILC-SA. XRD revealed the basal spacing of the&#x0D; pillared clays before and after in-situ incorporation indicating that the&#x0D; morphology of the superabsorbent was exfoliated and the layers of clay&#x0D; dispersed on the composite.&amp;nbsp;

Physico-chemical characterization of pH-sensitive N-Succinyl chitosan-g-poly (acrylamide-co-acrylic acid) hydrogels and in vitro drug release studies

Since last decade, momentous development has been made in the biomedical field. However, the contribution of polymer hydrogels as drug delivery carrier cannot be ignored. Crosslinking of natural and synthetic polymer has established promising characteristics in stimuli sensitive hydrogels for targeted drug delivery application. In this work, we synthesized N-succinyl chitosan and characterized via Fourier transform infrared (FTIR) spectroscopy, Nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), and differential scanning calorimetry (DSC). Then, we synthesized N-succinyl chitosan-g-Poly (acrylamide-co-acrylic acid) hydrogel via chemical crosslinking of N-succinyl chitosan, acrylamide and acrylic acid. Crosslinking was performed using free radical mechanism. Here, N, N’-methylenebisacrylamide (MBA) and ammonium persulfate (APS) were used as crosslinking agent and initiator, respectively. The hydrogels were synthesized by varying the concentration of monomers, initiator, and crosslinking agent. The chemical interactions in the synthesized hydrogel network were evaluated by FTIR, XRD, and DSC. Field emission scanning electron microscope (FESEM) showed porous morphology of hydrogels. The yield %, gel contents, and gel time were thoroughly examined and excellent results were found. The rheology study was performed to measure the mechanical strength. Moreover, swelling study revealed that hydrogels were highly swellable and depended on the various concentrations of initiator, monomers, and crosslinking agent. The results also showed that pH, type and concentration of salt solutions have strong influence on the swelling properties. Hydrogels expressed reversible swelling behavior in buffer solutions and buffer and salt solutions. Furthermore, theophylline was encapsulated during the synthesis of hydrogel and encapsulation efficiency was found in the range of 59–83%. In addition, theophylline release was observed in buffer solutions of pH 1.2 and pH 7.4. The results revealed the significant effect of pH and hydrogel composition on drug release. The theophylline release was found in the range of 14–24% in buffer solution pH 1.2 and 67–93% in buffer solution pH 7.4. The drug release data showed good fitting to Ritger- Peppas model and release kinetics followed non-Fickian anomalous transport mechanism and relaxation of polymers (case II transport). It was also observed that theophylline maintained its chemical activity after in vitro release. According to the observed facts, synthesized hydrogels can be adapted for their prospective exploitation in targeted drug delivery applications.

Biochemical piezoresistive sensors based on hydrogels for biotechnology and medical applications

Abstract. Many conventional analysis techniques achieve a high-detection sensitivity; however, they are equipment or time expensive due to a multi-step procedure. Sensor concepts, introduced in this work, using piezoresistive pressure sensor chips with integrated analyte-sensitive hydrogels enable inexpensive and robust biochemical sensors, which are miniaturized and in-line capable. For these sensor setups, it is important to optimize current established analyte-sensitive, reversible and biocompatible hydrogels for pH and glucose monitoring of chemical and biochemical processes. Therefore, low-viscous monomer mixtures based on hydroxypropyl methacrylate (HPMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA), tetraethylene glycol dimethacrylate (TEGDMA) and ethylene glycol (EG) were prepared in molar ratios of 70∕30∕01∕20, 60∕40∕01∕20 and 60∕40∕02∕20, respectively. Redox-polymerization of these pre-gel solutions were realized with N,N,N′,N′-tetramethylethylenediamine and ammonium persulfate. The reversible pH-sensitive swelling behavior of hydrogels with compositions were compared. By using the photoinitiator 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone, the free radical photopolymerization could be implemented leading to an increase of the swelling degree (SG). Glucose-sensitive hydrogels were prepared via immobilization of glucose oxidase in HPMA–DMAEMA–TEGDMA–EG hydrogel discs. These showed increasing swelling degrees with higher glucose concentrations in aqueous media and a reversible swelling behavior. The synthesized hydrogels were integrated in different piezoresistive sensors of different designs. The pH-depending course of the output voltage of a dip sensor with photopolymerized 60∕40∕02∕20 hydrogel was studied in detail. Besides the usage of a dip sensor, two implantable, parylene C-coated setups are presented. The implantable sensor with long isolated gold bond wires was proved to be functional even after storage in aqueous media for several days.

Temperature‐responsive Hydrogels Synthesized from Photo‐Polymerizable Poloxamer Macromers for Topical Skin Moisturizing

Temperature‐responsive hydrogels were fabricated by the photo‐polymerization of bis‐acryloyl poloxamer tri‐block copolymers, and their temperature‐responsive behavior and physiological effect on skin were investigated. For this, poloxamer macromers were prepared by end‐capping both terminal hydroxyl groups of poloxamer tri‐block copolymers with acrylates. They were then photo‐polymerized to generate polymeric hydrogels with structural integrity that allowed excellent stability against dilution in an aqueous environment. The resulting hydrogels exhibited dramatic reversible swelling behavior upon changes in temperature. A demonstration experiment, in which the hydrogels were applied topically to the skin, showed that they shrank rapidly as a result of the increase in temperature, owing to the contact with the skin surface, highlighting their effectiveness for instantaneously moisturizing the skin.

Dual Stimuli-Responsive Phenylboronic Acid-Containing Framboidal Nanoparticles by One-Step Aqueous Dispersion Polymerization

Phenylboronic acid-containing nanomaterials have found applications in various fields including biomedical engineering due to their unique stimuli-responsive characteristics. Contrary to the many reports on spherical nanoparticles, we are interested in nanostructures with different morphology which could potentially exhibit additional morphology-related effects. Here, phenylboronic acid-containing nanoparticles (PBANPs) in the size range of 80–250 nm in diameter were synthesized via aqueous dispersion polymerization of N-acryloyl-3-aminophenylboronic acid (PBAAM) using methoxy poly(ethylene glycol) acrylamide (PEGAM) as a polymerizable dispersant and N,N′-methylenebis(acrylamide) (MBAM) as a cross-linker. Microscopic analysis revealed that PBANPs were clusters, composed of smaller primary nanoparticles of ∼20 nm in diameter, possessing a framboidal morphology. The size of the PBANPs was significantly affected by the concentrations of PBAAM and PEGAM. Furthermore, PBANPs showed reversible swelling behavior...

Beta-cyclodextrin-based molecular-recognizable smart microcapsules for controlled release

Novel molecular-recognizable smart microcapsules for controlled release are successfully fabricated in two steps. Firstly, monodispersed poly(N-isopropylacrylamide-co-acrylic acid) microcapsules are prepared via microfluidic emulsion template synthesis; and then, β-cyclodextrin groups are introduced onto the microcapsules by a condensation reaction. The results of Fourier transform infrared spectrometry confirm that β-cyclodextrin moieties are successfully immobilized onto microcapsules by the condensation reaction between carboxylic groups of acrylic acid components on the microcapsules and amino groups of modified β-cyclodextrin monomers. The resultant poly(N-isopropylacrylamide-co-acrylic acid/aminated β-cyclodextrin) (PNA-ECD) microcapsules show a narrow size distribution. The volume phase transition temperature of prepared PNA-ECD microcapsules exhibits a positive shift in the solution containing model guest molecules 2-naphthalenesulfonic acid (NS). Upon recognizing the guest molecules NS, the PNA-ECD microcapsules show an isothermal and reversible molecular-recognizable swelling behavior. Moreover, the release rate of model drug molecules Fluorescein isothiocyanate-labeled dextran loaded in the microcapsules dramatically increases upon recognizing NS molecules. The results provide valuable guidance for the design and fabrication of monodispersed molecular-recognizable microcapsules for controlled release.

A Non‐ionic Thermophilic Hydrogel with Positive Thermosensitivity in Water and Electrolyte Solution

The first example of a chemically crosslinked synthetic non‐ionic hydrogel showing reversible positive swelling behavior in pure water as well as electrolyte solution is highlighted. Homopolymeric hydrogels are synthesized from N‐acryloylglycinamide with N,N′‐methylenbis(acrylamide) as a chemical crosslinker via free radical polymerization in dimethyl sulfoxide (DMSO). The swelling‐ratio dependency of the hydrogels upon temperature as well as on the amounts of crosslinker from 1 to 4.8 mol% is studied. With 1 mol% crosslinker, the hydrogel is able to take up over three times water of its weight at 37 °C in pure water and phosphate‐buffered saline. All the samples show almost 100% of reversibility for at least 6 d up to 37 °C irrespective of the amount of the crosslinker, making them promising candidates for biomedical applications. The sample with a higher amount of crosslinker, i.e., 4.8 mol% is even stable for over 6 d at 70 °C. image

Synthesis of a New Drug Delivery System Based on Alginate via Graft Copolymerization

The present work focused on the design of drug delivery system (DDS) based on a pH-sensitive hydrogel. The hydrogels were prepared via graft copolymerization of acrylonitrile (AN) monomer was directly grafted onto alginate using ammonium persulfate (APS) as an initiator and sodium hydroxide (NaOH) as a crosslinking agent under an inert atmosphere. Porous structure of hydrogel was essential in this system to yield a large surface area so that Metronidazole release could be facilitated. Due to the reversible swelling behavior of the hydrogels, the synthesized networks can sense the environmental pH change and achieve an oscillatory release pattern. The concentration of released Metronidazole loaded was monitored at 278 nm on the UV spectrophotometer.

Preparation and characterization of pH-controlled-release intelligent corrosion inhibitor

A pH-controlled-release intelligent corrosion inhibitor is designed, which performs long-term inhibition capability in the solution. The pH-sensitive hydrogel was prepared via grafting the mixtures of acrylic acid (AA) and 2-hydroxy ethyl methacrylate (HEMA) onto potato starch backbones. Increasing pH generally produced an increased swelling of the hydrogel which peaked at pH 8.0. The hydrogel also showed a fast and reversible swelling behavior when alternately immersed in pH 1.0 and 8.0 solutions. A corrosion inhibitor, 1 H-Benzotriazole (BTA), was loaded into the hydrogels and the cumulative release capabilities were studied at different pH. From the electrochemical measurement and scanning electron microscopy (SEM) analysis, the intelligent corrosion inhibitor exhibited an improved long-term inhibition ability on aluminum alloy due to the controlled-release behaviors.

Synthesis of Polyvinyl Alcohol/Maleic Acid Hydrogels by Electron Beam Irradiation for Dye Uptake

Novel polyelectrolyte hydrogels based on maleic acid (MA) and polyvinyl alcohol (PVA) were prepared in the presence of electron beams irradiation as initiator and crosslinker. PVA was used as a template for the polymerization of MA in an aqueous solution. The effect of pH on swelling behavior of the hydrogels was examined. In particular, a reversible swelling behavior between acidic and alkaline solutions was investigated. The structure, thermal properties and morphologies of PVA/MA hydrogels were characterized by FTIR, DSC and SEM, respectively. The swelling ratios of gels increased with the increase MA content, pH values, but decreased with enhanced irradiation dose. PVA/MA has been utilized as an adsorbent for the removal of two textile dyes, Reactive red SH.B and Ismative violet 2R, as model dyes from aqueous solution. Factors affecting dye sorption were extensively investigated. The adsorption capacity for dyes increased with the increase of initial dye concentration, contact time, pH, temperature and MA content in the hydrogels. The equilibrium adsorption data were modeled using Langmuir and Freundlich adsorption isotherms. The results revealed that the adsorption of dyes onto PVA/MA hydrogel fit very well with Langmuir isotherm model.

Interpenetrating polymer networks templated on bicontinuous microemulsions containing silicone oil, methacrylic acid, and hydroxyethyl methacrylate

Polydimethylsiloxane-poly(methacrylic acid—hydroxyethyl methacrylate) interpenetrating polymer networks (PDMS-P(MAA–HEMA) IPN) were formulated and polymerized simultaneously from bicontinuous microemulsion templates. Microemulsions containing reactive silicone oils and MAA/HEMA in aqueous solution were stabilized with silicone surfactants, and were then reacted at 50 °C for 3 h under an N2 atmosphere. The formation of bicontinuous morphology was confirmed by laser scanning confocal microscopy, reversible swelling behavior, differential scanning calorimetry, texture analysis, and permeability to vitamin B12 in aqueous solution. Incorporating polymerizable surfactants into the microemulsion aided in stabilizing the initial microemulsion structure during polymerization, yielding a more uniform IPN morphology with domain sizes of <200 nm at equilibrium swelling. The process developed here demonstrates a simple, single-step polymerization approach to forming IPNs from low viscosity microemulsion templates, and could potentially be extended to a variety of hydrophilic and hydrophobic monomers.