Hybrid Microgels Research Articles

Efficient and continuous chemical conversion in a thin membrane comprising three-dimensional network trapping Ag nanoparticles

In this work, we report a novel and highly efficient catalytic membrane (PES/PNM-Ag) comprising well-dispersed silver nanoparticles (NPs). The membrane can be straightforwardly constructed via dynamic loading expansible hybrid microgels PNM-Ag into a commercially-available poly(ether sulfone) (PES) membrane with asymmetric structure. Characterization results of PNM-Ag and PES/PNM-Ag indicate that a nanoscale three-dimensional network embedded with Ag NPs was developed in membrane pores by swollen microgels. The flat-sheet membrane reactor assembled with PES/PNM-Ag can efficiently and continuously catalyze the reduction of 4-nitrophenol (apparent reaction rate constant reaching 1.12 s−1) and showed good stability. The improved catalytic activity was attributed to fully accessible surface of Ag NPs as well as the unique structure of the membrane, in which the reactant was restricted to flow through immobilized catalyst. Present strategy hints to design other noble metal NPs loaded catalytic membranes for efficient conversion of nitro-aromatic pollutants.

Rheology Applied to Microgels: Brief (Revision of the) State of the Art.

The ability of polymer microgels to rapidly respond to external stimuli is of great interest in sensors, lubricants, and biomedical applications, among others. In most of their uses, microgels are subjected to shear, deformation, and compression forces or a combination of them, leading to variations in their rheological properties. This review article mainly refers to the rheology of microgels, from the hard sphere versus soft particles’ model. It clearly describes the scaling theories and fractal structure formation, in particular, the Shih et al. and Wu and Morbidelli models as a tool to determine the interactions among microgel particles and, thus, the viscoelastic properties. Additionally, the most recent advances on the characterization of microgels’ single-particle interactions are also described. The review starts with the definition of microgels, and a brief introduction addresses the preparation and applications of microgels and hybrid microgels.

Engineering hybrid microgels as particulate emulsifiers for reversible Pickering emulsions.

Thermo-responsive microgels are unique stabilizers for stimuli-sensitive Pickering emulsions that can be switched between the state of emulsification and demulsification by changing the temperature. However, directly temperature-triggering the phase inversion of microgel-stabilized emulsions remains a great challenge. Here, a hybrid poly(N-isopropylacrylamide)-based microgel has now been successfully fabricated with tunable wettability from hydrophilicity to hydrophobicity in a controlled manner. Engineered microgels are synthesized from an inverse emulsion stabilized with hydrophobic silica nanoparticles, and the swelling-induced feature can make the resultant microgel behave like either hydrophilic or hydrophobic colloids. Remarkably, the phase inversion of such microgel-stabilized Pickering emulsions can be in situ regulated by temperature change. Moreover, the engineered microgels were capable of stabilizing water-in-oil Pickering emulsions and encapsulation of enzymes for interfacial bio-catalysis, as well as rapid cargo release triggered by phase inversion.

Near-Infrared-Light-Modulated Lubricating Coating Enabled by Photothermal Microgels.

As a micro-/nano-sized hydrogel, polymeric microgel not only has three-dimensional (3D) molecular networks but also displays the small-size effect, which has been widely used in various fields, such as drug nanocarrier, photonic crystal, functional coating, and aqueous lubrication. In this work, a photothermal lubricating coating was prepared using polymeric/inorganic hybrid microgels and its surficial friction was deliberately modulated by the remote irradiation of near-infrared (NIR) light. Specifically, a photothermal hybrid microgel, Fe3O4@poly(N-isopropylacrylamide-co-polyacrylic acid) (Fe3O4@PNA), was first fabricated and then sprayed onto poly(ethyleneimine) (PEI)-modified substrate to form a lubricating microgel coating. At room temperature, this microgel coating was hydrophilic and achieved good hydration lubrication with relatively low friction. After the introduction of NIR light, the photothermal microgel coating converted light energy into heat energy for increasing its own temperature rapidly. Due to the thermosensitive PNA shell, the wettability of the coating was transformed to hydrophobicity above the lower critical solution temperature (LCST), resulting in a remarkable increase in friction. In other words, the surficial friction of this microgel coating could be reversibly modulated using NIR light. This work expands the application scope of microgels in the field of aqueous lubrication and introduces the functional microgels into making the smart lubricating coating for the first time. This basic research in the field of friction control may provide an efficient strategy for the design of interfacial sensing, controlled transmission, and intelligent manipulator.

Anisotropic Microgels Show Their Soft Side.

Anisotropic, submicrometer-sized particles are versatile systems providing interesting features in creating ordering in two-dimensional systems. Combining hard ellipsoids with a soft shell further enhances the opportunities to trigger and control order and alignment. In this work, we report rich 2D phase behavior and show how softness affects the ordering of anisotropic particles at fluid oil-water interfaces. Three different core-shell systems were synthesized such that they have the same elliptical hematite-silica core but differ with respect to thickness and stiffness of the soft microgel shell. Compression isotherms, the shape of individual core-shell microgels, and their 2D order at a decane-water interface are investigated by means of the Langmuir-Blodgett technique combined with ex-situ atomic force microscopy (AFM) imaging as well as dissipative particle dynamics (DPD) simulations. We show how the softness, size, and anisotropy of the microgel shell affect the side-to-side vs tip-to-tip ordering of anisotropic hybrid microgels as well as the alignment with respect to the direction of compression in the Langmuir trough. A large, soft microgel shell leads to an ordered structure with tip-to-tip alignment directed perpendicular to the direction of compression. In contrast, a thin and harder microgel shell leads to side-to-side ordering orientated parallel to the compression direction. In addition, the thin and harder microgel shell induces clustering of the microgels in the dilute state, indicating the presence of strong capillary interactions. Our findings highlight the relevance of softness for the complex ordering of anisotropic hybrid microgels at interfaces.

Zirconium nanoparticles-poly (N-isopropylacrylamide-methacrylic acid) hybrid microgels decorated graphene sheets for catalytic reduction of organic pollutants

First approach towards fabrication of zirconium-microgels@graphene is developed in this work. Hybrid microgels are loaded onto graphene sheets to boost the electron relay among pollutants and borohydride ions. For this purpose, poly(N-isopropylacrylamide-co-methacrylic acid) p(NIPAM-MAA) microgel is synthesized through precipitation polymerization method. Zirconium nanoparticle is fabricated inside microgels through in-situ reduction of zirconium ions then hybrid microgels are decorated onto graphene. Zr-p(NIPAM-MAA)@graphene composite is used as catalyst for reduction of following organic pollutants: Congo red, 4-nitrophenol, Safranine, methylene orange, methylene blue, 4-nitroanisole, 2,4 dinitrophenol and 4-nitrobenzoic acid. Values of apparent rate constant, percentage reduction and reduction time are calculated and compared.

Synthesis of bimetallic nanoparticles loaded on to PNIPAM hybrid microgel and their catalytic activity

This study was designed to preparecarboxyl-functionalized poly (N-isopropylacrylamide) PNIPAM microgels having excellent catalytic properties.Recently, researchers are trying to fabricate cost effective and efficient hybrid catalytic materials for the synthesis of nitrogenous compounds along with enhanced optical properties. For the same motive, synthesis of carboxyl-functionalized PNIPAM microgels was performed by using polymerization of soap-free emulsion of N-isopropyl acrylamide, which is NIPAM along with acrylic acid (AA). The thiol group was introduced through the imide bond mediated by carbodiimide, between carboxyl-functionalized microgels through carboxyl group and aminoethanethiol (AET). Copper, Palladium and Cu/Pd nanoparticles were incorporated successfully into thiol-functionalized PNIPAM microgels through metals thiol linkage. The synthesized microgels and hybrid encompassing metallic nanoparticles were characterized in detail by using Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron (XPS) and Fourier transformed infrared spectroscopy for structural interpretation. The thermal properties of the pure and hybrid microgels were inspected by TG analysis. The prepared nanocomposites PNIPAM-Cu, PNIPAM-Pd and PNIPAM-Cu/Pd exhibited decent catalytic properties for the degradation of 4-Nitrophenol and methylene blue, but the bimetallic Cu/Pd have remarkable catalytic properties. The catalytic reaction followed pseudo-first-order reaction with rate constants 0.223 min−1, 0.173 min−1 for 4-Nitrophenol and methylene blue in that order. In this study,we were able to establish that Cu/Pd hybrid is an efficient catalyst for 4-Nitrophenol and methylene blue as compared to its atomic analogue.

Crosslinked polymer encapsulated palladium nanoparticles for catalytic reduction and Suzuki reactions in aqueous medium

Acrylamide and N-isopropylacrylamide were copolymerized in the presence of a N,N-methylenebisacrylamide crosslinker to obtain poly(N-isopropylacrylamide-co-acrylamide) [P(NA)] polymer colloidal particles. Pd nano crystals with diameter of 4–8 nm were loaded into the [P(NA)] microgels by reduction of [PdCl4]-2 within dispersion of polymer microgels. The Pd NPs-loaded hybrid microgels were analysed by TEM, STEM, EDX and XRD. The catalytic ability of the Pd-[P(NA)] system was investigated towards reductive transformation of nitroarenes into corresponding aryl amines and Suzuki coupling transformation in a green solvent, H2O. The progress of catalytic reaction was examined by thin layer chromatography (TLC). Different reactants were effectively converted into their corresponding products with great to fabulous yields (extending from 75 to 97%) under gentle reaction conditions. The Pd-[P(NA)] catalyst is stable for long time and can be utilized numerous times without any notable loss in its catalytic action.

Recyclable polymer microgel stabilized rhodium nanoparticles for reductive degradation of para-nitrophenol

Abstract The purpose of present work is to fabricate rhodium nanoparticles in Poly(N-isopropylmethacrylamide-acrylic acid) [p(NMAA)] microgel system. Synthesized polymer [p(NMAA)] microgels and rhodium nanoparticles loaded [Rh-p(NMAA)] microgels were analyzed by FTIR (Fourier Transform Infra-red) spectroscopy, XRD (X-ray Diffraction) analysis and UV/Vis (Ultraviolet–Visible) spectroscopy. Catalytic reductive conversion of P-nitrophenol (P-Nph) into P-aminophenol (P-Aph) via Rh-p(NMAA) was used to evaluate the catalytic activity of the hybrid microgel [Rh-p(NMAA)]. Kinetic study of catalytic reductive conversion of P-Nph was explored by considering various reaction parameters. It was found that the value of first order observed rate constant (k obs) was varied from 0.019 to 0.206 min−1 with change in concentration of sodium borohydride (SBH) from 3 to 14 mM at given temperature. However, further increment in concentration of SBH from 14 to 17 mM, reduced the value of k obs from 0.206 to 0.156 min−1. The similar dependence of k obs on concentration of P-Nph was observed at specific concentration of SBH and Rh-p(NMAA) at constant temperature. Kinetic study reveals that conversion of P-Nph to P-Aph takes place on the surface of rhodium nanoparticles (RhNPs) by adopting different reactions intermediates and obeys the Langmuir-Hinshelwood mechanism. Reduction efficiency of recycled Rh-p(NMAA) catalytic system was also measured and no significant reduction in the percentage catalytic activity was obtained up to four cycles for P-Nph conversion into P-Aph.

Poly(styrene@N-isopropylmethacrylamide-co-methacrylic acid)@Ag hybrid particles with excellent catalytic potential

Poly(styrene-N‐isopropylmethacrylamide‐methacrylic acid) [P(SNM)CS] colloidal particles were synthesized by two-step precipitation polymerization in aqueous system. Silver ions loaded into P(SNM)CS network were reduced by using NaBH4 as a reductant to obtain the aqueous dispersion of Ag-P(SNM)CS hybrid particles. Various techniques including transmission electron microscopy (TEM), dynamic light scattering (DLS), UV–Visible (UV–Vis), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) were used to characterize P(SNM)CS and Ag-P(SNM)CS systems. Silver nanoparticles have excellent stability in P(SNM)CS system even on their storage for months. Reduction of 4-nitrophenol (4Nph) was chosen as an exemplary reaction to examine the catalytic ability of newly synthesized Ag-P(SNM)CS hybrid microgels under different reaction conditions. Reaction progress was inspected by spectrophotometric method. The value of observed rate constant (kobs) was measured as a dependent of contents of Ag-P(SNM)CS, reductant and substrate using pseudo first order kinetic modeling to explore mechanism of catalysis by Ag-P(SNM)CS.

Incorporation of Dual-Stimuli Responsive Microgels in Nanofibrous Membranes for Cancer Treatment by Magnetic Hyperthermia.

The delivery of multiple anti-cancer agents holds great promise for better treatments. The present work focuses on developing multifunctional materials for simultaneous and local combinatory treatment: Chemotherapy and hyperthermia. We first produced hybrid microgels (MG), synthesized by surfactant-free emulsion polymerization, consisting of Poly (N-isopropyl acrylamide) (PNIPAAm), chitosan (40 wt.%), and iron oxide nanoparticles (NPs) (5 wt.%) as the inorganic component. PNIPAAm MGs with a hydrodynamic diameter of about 1 μm (in their swollen state) were successfully synthesized. With the incorporation of chitosan and NPs in PNIPAAm MG, a decrease in MG diameter and swelling capacity was observed, without affecting their thermosensitivity. We then sought to produce biocompatible and mechanically robust membranes containing these dual-responsive MG. To achieve this, MG were incorporated in poly (vinyl pyrrolidone) (PVP) fibers through colloidal electrospinning. The presence of NPs in MG decreases the membrane swelling ratio from 10 to values between 6 and 7, and increases the material stiffness, raising its Young modulus from 20 to 35 MPa. Furthermore, magnetic hyperthermia assay shows that PVP-MG-NP composites perform better than any other formulation, with a temperature variation of about 1 °C. The present work demonstrates the potential of using multifunctional colloidal membranes for magnetic hyperthermia and may in the future be used as an alternative treatment for cancer.

Stimuli-responsive microgels with fluorescent and SERS activities for water and temperature sensing

Design and application of stimulus-responsive microgels is still in its infancy but is an exhilarating topic in controllable sensing device. Here, we have fabricated a dual-responsive platform capable of both sensitive on-spot fluorescence analysis and reliable surface-enhanced Raman scattering (SERS) quantification of water and temperature by in-situ encapsulating 4,4′-dimercaptoazobenzene (DMAB), meso-formyl-1,3,5,7-tetramethyl pyrromethene fluoroborate (FPF) probe and Ag nanoparticles (AgNPs) into polyvinyl alcohol (PVA) microgels. The smart microgels exhibit ultra-sensitive (detection limit 10−4% v/v) and reversible response towards water due to the liner relationship between network volume and SERS performance of the microgels. Furthermore, the presence of water triggers the conversion of FPF to aldehyde hydrate, facilitating visual assay of trace water in matrix samples through the enhanced fluorescence signals. Interestingly, the SERS signals can be precisely tuned by the thermo-sensitive microgels substrate, thus achieving the temperature monitoring from 32 to 50 °C. The microgels-based sensor has fast-response (2 min), excellent stability, and enables accurate and reliable response of water in organic solvent and pharmaceutical products. As a smart and flexible sensor, the hybrid microgels will facilitate the field of POC analysis, as well as molecular recognition in the future.

Synthesis of a thermoresponsive crosslinked MEO2MA polymer coating on microclusters of iron oxide nanoparticles

Encapsulation of magnetic nanoparticles (MNPs) of iron (II, III) oxide (Fe3O4) with a thermopolymeric shell of a crosslinked poly(2-(2-methoxyethoxy)ethyl methacrylate) P(MEO2MA) is successfully developed. Magnetic aggregates of large size, around 150–200 nm are obtained during the functionalization of the iron oxide NPs with vinyl groups by using 3-butenoic acid in the presence of a water soluble azo-initiator and a surfactant, at 70 °C. These polymerizable groups provide a covalent attachment of the P(MEO2MA) shell on the surface of the MNPs while a crosslinked network is achieved by including tetraethylene glycol dimethacrylate in the precipitation polymerization synthesis. Temperature control is used to modulate the swelling-to-collapse transition volume until a maximum of around 21:1 ratio between the expanded: shrunk states (from 364 to 144 nm in diameter) between 9 and 49 °C. The hybrid Fe3O4@P(MEO2MA) microgel exhibits a lower critical solution temperature of 21.9 °C below the corresponding value for P(MEO2MA) (bulk, 26 °C). The MEO2MA coating performance in the hybrid microgel is characterized by dynamic light scattering and transmission electron microscopy. The content of preformed MNPs [up to 30.2 (wt%) vs. microgel] was established by thermogravimetric analysis while magnetic properties by vibrating sample magnetometry.

Polymer-matrix stabilized metal nanoparticles: Synthesis, characterizations and insight into molecular interactions between metal ions, atoms and polymer moieties

Handling nanoparticles on a mesoscale order enhances the functionality of nanoparticles for high-end technological applications such as photonics, catalysis, biomedical applications, etc. In this context, polymer-metal hybrids have shown very popularity among material scientists in recent years where a suitable polymer matrix can be effectively used to stabilize nanoparticles through different mechanisms. The current paper deals with the synthesis of different types of hybrid particles of gold (Au), silver (Ag) and iron (Fe) using micron size carboxylic group functionalized Poly(N-isopropyl acrylamide) (PNIPAM) stimuli-responsive cross-linked microgels as micro-reactor in an in-situ approach. Transmission electron microscope (TEM) directly confirms the successful loading of metal nanoparticles within microgels and all the hybrid microgels have a narrow size distribution. Dynamic light scattering (DLS) measurement in the solution state shows that the swollen size of microgel-metal hybrid is comparatively smaller than that of pure microgels. UV-VIS spectroscopy strongly reveals the presence of plasmon peaks at 520 and 405 nm in case of gold and silver microgel hybrids respectively. In case of microgel-iron hybrids, the particles nicely respond to the applied magnetic field exerted by an external magnet and the effect is also reversible when the magnet is removed. Finally, to understand the type of molecular interaction that is responsible in holding the nanoparticles within the polymer matrices of microgels, we have carried out molecular docking between different metal ions (Au3+, Ag+, Fe2+) and atoms of gold, silver and iron (Au0, Ag0, Fe0) with the functional moieties (NIPAM monomer and carboxylate ion, COO−) of the polymer. Molecular docking studies with different types of interaction potentials (Van der Waals, hydrophobic, solvation, torsional and electrostatic) suggest that the electrostatic attraction dominates over all other potentials between positive metal ions and negative carboxylate ion (COO−) giving rise to the net binding energy of −9.28, −5.7, −1.46 kcal/mol for Fe2+, Au3+, and Ag+ respectively.

Preparation and functionalization of zinc oxide nanoparticles with polymer microgels for potential catalytic applications

The preparation, functionalization and catalytic application of ZnO nanoparticles have been systematically carried out. In the first step, the virgin ZnO nanoparticles were prepared from Zn(CH3COO)2·2H2O solution in an alcoholic medium using the liquid precipitation approach. To form a new type of (zinc oxide)-(chitosan)-poly(N-isopropylacrylamide-acrylic acid), abbreviated as [ZnO-CS-P(NIPAAm-AA)], hybrid polymer microgels; ZnO particles were loaded to the chitosan based polymer microgels. Both the pure and hybrid ZnO materials, so obtained, were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), UV–visible spectroscopy and dynamic light scattering (DLS). For the hybridization purpose, the CS-P(NIPAAm-AA) polymeric gels were prepared by free-radical polymerization. Physicochemical behavior of these hybrid microgels was found responsive to external stimuli such as temperature and pH. In order to trace the hydrodynamic size of the ZnO, microgel, and ZnO-microgel hybrid system, DLS were also performed. From the overall results, the formation of ZnO nanoparticles with an average particle size of ≈ 35-42 nm having some irregularity in structure was confirmed. Likewise, SEM results show that pure CS-P(NIPAAm-AA) microgel particles are spheroid in shape with a smooth surface while the ZnO-CS-P(NIPAAm-AA) hybrid microgel particles look somewhat rough and having irregularity in their overall shape/structure. The fine particles of virgin ZnO and their hybrid with microgel was used for the catalytic reduction of 4-nitrophenol into 4-aminophenol and the results of both materials were compared. In addition, the kinetics of this catalytic reduction has also been summarized. The factors those influence the reduction rate of 4-nitrophenol in the presence of inorganic-organic hybrid materials have also been discussed and it was also found that the ZnO-microgel hybrid samples acted as a better catalytic agent compared to the ZnO or microgel alone.

Stimuli‐responsive hybrid microgels for controlled drug delivery: Sorafenib as a model drug

AbstractMicrogels (MGs) are synthetic colloidal hydrogel particles made of three dimensional polymer networks. Their chemical composition is crucial for their use as intelligent drug release systems operated by temperature control. Herein, several MGs using N‐isopropylacrylamide (Nipam)/N‐isopropylmethacrylamide (Nipmam), chitosan and acrylic/methacrylic acid have been synthesized by free radical polymerization reactions (NC MGs) and the effects of surfactants and different reaction times on size and swelling properties have been investigated. MGs have been identified and characterized by dynamic light scattering and atomic force microscopy, and finally used to optimize the encapsulation protocol of the hydrophobic drug sorafenib. The drug delivery system here described has encapsulation efficiency of 40% and releases 10% of the entrapped drug over about 16 h after the temperature is raised above the volume phase transition temperature. Data suggest that MGs with optimized composition may act as properly instructed entities able to trap and release biomolecules following external stimuli.

Magnetic microgels and nanogels: Physical mechanisms and biomedical applications.

Soft micro‐ and nanostructures have been extensively developed for biomedical applications. The main focus has been on multifunctional composite materials that combine the advantages of hydrogels and colloidal particles. Magnetic microgels and nanogels can be realized by hybridizing stimuli‐sensitive gels and magnetic nanoparticles. They are of particular interest since they can be controlled in a wide range of biological environments by using magnetic fields. In this review, we elucidate physical principles underlying the design of magnetic microgels and nanogels for biomedical applications. Particularly, this article provides a comprehensive and conceptual overview on the correlative structural design and physical functionality of the magnetic gel systems under the concept of colloidal biodevices. To this end, we begin with an overview of physicochemical mechanisms related to stimuli‐responsive hydrogels and transport phenomena and summarize the magnetic properties of inorganic nanoparticles. On the basis of the engineering principles, we categorize and summarize recent advances in magnetic hybrid microgels and nanogels, with emphasis on the biomedical applications of these materials. Potential applications of these hybrid microgels and nanogels in anticancer treatment, protein therapeutics, gene therapy, bioseparation, biocatalysis, and regenerative medicine are highlighted. Finally, current challenges and future opportunities in the design of smart colloidal biodevices are discussed.

Hybrid microgels produced via droplet microfluidics for sustainable delivery of hydrophobic and hydrophilic model nanocarriers.

Drug delivery for treatment of chronic diseases relies on the effective delivery of payload materials into the target cells in a long-term release. In this context, the present study investigated hybrid microgels as platforms to carry nanoparticles to drug delivery. Hybrid microgels were produced with silk fibroin (SF) and chondroitin sulfate (CS), and alginate (ALG) by droplet microfluidics. ALG/SF, ALG/CS, and ALG/CS/SF microgels, ranging from 70-90μm, were tested to encapsulate two model nanoparticles, polystyrene latex beads in pristine form (NPs) and NPs coated with bovine serum albumin (NPs-BSA) to simulate hydrophobic and hydrophilic nanocarriers, respectively. IR spectroscopy and fluorescence microscopy analysis confirmed the presence of SF and CS within ALG-based microgels revealing marked differences in their morphology and physicochemical properties. The release profiles of model nanoparticles revealed to be dependent on microgels composition and physicochemical properties. These findings show that SF ternary hybrid microgels facilitated the entrapment of hydrophobic nanocarriers with encapsulation efficiency (EE) from 83 to 98% keeping a better sustainable profile release than nonhybrid ALG microgels. Besides, CS improved the carriage of NPs-BSA (EE=85%) and their profile release. The results highlight the versatility and tunable properties of these biobased microgels, being a good strategy to be used as an efficient platform in using macro and nanoencapsulated systems for drug delivery.

Silver nanoparticles stabilized in polymer hydrogels for catalytic degradation of azo dyes

Fabrication of poly-(N-isopropylmethacrylamide-co-methacrylic acid) [p(NMA)] microgels to be utilized as microreactors to synthesize stable Ag nanoparticles for catalytic reductive degradation of dyes has been addressed in this work. Both p(NMA) microgel and Ag-p(NMA) hybrid microgel systems have been analyzed by Fourier transform infra-red and Dynamic light scattering, Ultraviolet–Visible spectroscopy, X-ray diffraction and Transmission electron microscopy. Catalytic activity of Ag-p(NMA) towards reductive degradation of Congo Red (CR), Methyl Orange (MO) and Alizarin Yellow (AY) was investigated under different operating conditions. Spectrophotometry was employed to check the progress of reaction while the rate constant (kapp) value of degradation reaction was determined under various conditions to optimize reaction parameters for rapid and economical degradation of these dyes. An increase in kapp value was observed by increasing feed content of dye up to a certain value that decreases again by further increment in dye concentration which reflects that catalysis follows Langmuir–Hinshelwood mechanism. A gradual increase in the kapp value was also observed with increasing quantity of hybrid microgel used as a catalyst. By comparing kapp values of degradation of aforementioned dyes, it was found that Ag-p(NMA) hybrid microgel gives better activity for MO dye degradation in comparison to catalytic degradation of CR and AY.

Engineering the cellular mechanical microenvironment to regulate stem cell chondrogenesis: Insights from a microgel model

Biophysical cues (especially mechanical cues) embedded in cellular microenvironments show a critical impact on stem cell fate. Despite the capability of traditional hydrogels to mimic the feature of extracellular matrix (ECM) and tune their physicochemical properties via diverse approaches, their relatively large size not only induces biased results, but also hinders high-throughput screening and analysis. In this paper, a microgel model is proposed to recapitulate the role of 3D mechanical microenvironment on stem cell behaviors especially chondrogenesis in vitro. The small diameter of microgels brings the high surface area to volume ratio and then the enlarged diffusion area and shortened diffusion distance of soluble molecules, leading to uniform distribution of nutrients and negligible biochemical gradient inside microgels. To construct ECM-like microenvironment with tunable mechanical strength, three gelatin/hyaluronic acid hybrid microgels with low, medium and high crosslinking densities, i.e., Gel-HA(L), Gel-HA(M) and Gel-HA(H), are fabricated in microfluidic devices by Michael addition reaction between thiolated gelatin (Gel-SH) and ethylsulfated hyaluronic acid (HA-VS) with different substitution degrees of vinyl sulfone groups. Our results show that mouse bone marrow mesenchymal stem cell (BMSC) proliferation, distribution and chondrogenesis are all closely dependent on mechanical microenvironments in microgels. Noteworthily, BMSCs show a clear trend of differentiating into hyaline cartilage in Gel-HA(L) and fibrocartilage in Gel-HA(M) and Gel-HA(H). Whole transcriptome RNA sequencing reveals that mechanical microenvironment of microgels affects BMSC differentiation via TGF-β/Smad signaling pathway, Hippo signaling pathway and Integrin/YAP/TAZ signaling pathway. We believe this microgel model provides a new way to further explore the interaction between cells and 3D microenvironment. Statement of SignificanceIn recent years, hydrogels have been frequently used to construct 3D microenvironment for cells. However, their relatively large size not only brings biased experimental results, but also limits high-throughput screening and analysis. Herein we propose a gelatin/hyaluronic acid microgel model to explore the effects of 3D cellular mechanical microenvironment (biophysical cues) on BMSC behaviors especially chondrogenesis, which can minimize the interference of biochemical gradients. Our results reveal that BMSC differentiation into either hyaline cartilage or fibrocartilage can be regulated via tailoring the mechanical properties of microgels. Whole transcriptome RNA sequencing proves that “TGF-β/Smad signaling pathway”, “Hippo signaling pathway” and “Integrins/YAP/ TAZ signaling pathway” are activated or inhibited in this process.