Volume Phase Transition Behavior Research Articles

Laccase immobilized in adamantane-modified PEGMA-based microgels: Tuning enzyme activity by beta-cyclodextrin

Intelligent immobilized enzymes can be constructed by designing “smart” carrier materials. In this study, we successfully prepared adamantane-modified PEGMA-based microgel-immobilized laccases (AdM-Lac) by precipitation polymerization in a laccase solution. AdM-Lac-DMCD was obtained by mixing 2,6-di-O-methyl-beta-cyclodextrin (DMCD) and AdM-Lac. By comparison, DLS, AFM, and IR results indicate that AdM-Lac exhibits DMCD-induced volume phase transition behavior. NMR analysis confirms the successful formation of inclusion complexes of DMCDs and adamantyl groups on AdM-Lac. The catalytic tests show that the enzyme activity of AdM-Lac-DMCD at 20 °C (24.09 U/L) is ca.70% higher than AdM-Lac (14.20 U/L). The Vmax value of AdM-Lac-DMCD (1.22 µM min−1) is similar to AdM-Lac (1.24 µM min−1), Whereas the Km value (52 µM) decreases by ca. 69%, even close to free laccase (41 µM), and the Vmax/Km ratio (0.0235 min−1) increases by about 2-fold. These results imply that DMCD initiates the volume swelling of AdM-Lac, resulting in increased enzyme activity and improved kinetic properties. Due to AdM-Lac having better storage stability, we suggest that laccase is stored as AdM-Lac, and applied as AdM-Lac-DMCD. This study successfully achieved the regulation of enzyme activity through the addition of molecules, providing a novel strategy for the design of “smart” carrier materials.

Influence of Buffers, Ionic Strength, and pH on the Volume Phase Transition Behavior of Acrylamide-Based Nanogels.

The use of covalently crosslinked nanogels for applications in biology and medicine is dependent on their properties and characteristics, which often change because of the biological media involved. Understanding the role of salts, ionic strength and pH in altering specific properties is key to progress in this area. We studied the effect of both chemical structure and media environment on the thermoresponsive behavior of nanogels. A small library of methylenebisacrylamide (MBA) crosslinked nanogels were prepared using N-isopropylacrylamide (NIPAM) or N-n-propylacrylamide (NPAM), in combination with functional monomers N-hydroxyethylacrylamide (HEAM) and N-acryloyl-l-proline (APrOH). The thermoresponsive properties of nanogels were evaluated in phosphate buffer, tris-acetate buffer and Ringer HEPES, with varying concentrations and ionic strengths. The presence of ions facilitates the phase separation of nanogels, and this “salting-out” effect strongly depends on the electrolyte concentration as well as the specificity of individual anions, e.g., their positions in the Hofmeister series. A subtle change in the chemical structure of the side chain of the monomer from NIPAM to NPAM leads to a reduction of the volume phase transition temperature (VPTT) value by ~10 °C. The addition of hydrophilic comonomers such as HEAM, on the other hand, causes a ~20 °C shift in VPTT to higher values. The data highlight the significant role played by the chemical structure of the monomers used, with hydrophobicity and rigidity closely interlinked in determining thermoresponsive behavior. Furthermore, the volume phase transition temperature (VPTT) of nanogels copolymerized with ionizable APrOH comonomer can be tailored by changes in the pH of buffer solutions. This temperature-controlled phase transition is driven by intricate interplay involving the entropy of mixing, electrostatic interactions, conformational transitions, and structural rigidity. These results highlight the importance of understanding the physiochemical properties and behavior of covalently crosslinked nanogels in a biological environment prior to their applications in life-science, such as temperature/pH-triggered drug delivery systems.

Naphthalimide-Based Aggregation-Induced Emissive Polymeric Hydrogels for Fluorescent Pattern Switch and Biomimetic Actuators.

Substituted naphthalimide (NI) moieties are highly versatile and newly recognized aggregation-induced emission (AIE) building blocks for many potentially useful smart molecules, polymers, and nanoparticles. However, the introduction of NI fluorophore into cross-linked polymeric networks to prepare AIE-active hydrogels still remains underdeveloped. Herein, a novel naphthalimide-based aggregation-induced emissive polymeric hydrogel is reported, followed by its proof-of-concept applications as fluorescence pattern switch and biomimetic actuator. The hydrogel, bearing semi-interpenetrating polymer networks, is synthesized starting from N-isopropylacrylamide, hydroxyethyl methacrylate, and a newly designed NI monomer (4-phenoxy-N-allyl-1,8-naphthalimide, PhAN). Rational molecular design for AIE-active PhAN monomer lies in modification of the NI core with rigid and bulky phenoxy group to break its planarity to produce desirable propeller-shaped molecular conformation. The as-prepared hydrogel is proved to be a aggregation-induced blue-light-emitting hydrogel. It also shows volume phase transition behavior and is endowed with thermally responsive synergistic emission and transmittance change, thus enabling simultaneous regulation of two optical properties merely by one single stimulus. These useful advantages further encourage fabrication of several proto-type fluorescence pattern switching and biomimetic actuating devices. This study may not only enlarge the list of fluorescent hydrogels but also serve as a novel smart optical platform for potential anticounterfeiting, sensing, displaying, or actuating applications.

Observation of Unusual Thermoresponsive Volume Phase Transition Behavior of Cubic Poly(N-isopropylacrylamide) Microgels.

Here, we report the observation of an unusual thermoresponsive volume phase transition behavior of cubic poly(N-isopropylacrylamide) (PNIPAM) microgels. Cubic PNIPAM microgels with a mean edge size of 125 ± 41 nm were synthesized via electrochemical-initiated radical polymerization with a photovoltaic cell as power supply. In turbidity and laser light scattering studies on dilute aqueous dispersions of these cubic microgels, both the light attenuation and hydrodynamic radius variations with temperature reveal an additional transition at about 25.0 °C, besides the widely reported volume phase transition at the PNIPAM LCST that is typically found for (quasi-)spherical microgels. This unusual thermoresponsive volume phase transition behavior of the cubic microgels can be elucidated by using a core-corona model, with the contribution from each part varying at different temperatures. The finding is also checked by thermal analysis.

Facile fabrication of spherical photonic crystals microspheres with angle-independent fluorescent functionality

In this work, we report a facile way to fabricate fluorescent spherical photonic crystals (SPCs) microspheres for the first time. The SPCs microspheres immobilizing Photonic Bandgap (PBG) structure into a hydrogel framework, which can be used to uptake nanosized CdTe NCs particles based on their reversible volume phase transition behavior. Moreover, the resultant SPCs microspheres can not only monitor surrounding humidity, but also exhibit well integration of fluorescence and PBG color in a single structure. More interestingly, the photoluminescence (PL) spectra of fluorescent SPCs microspheres are angle-independent on the curved surface which would open a novel insight into the fabrication of multifunctional optical devices based on PBG and PL functionalities.

Synthesis, Characterization and Drug Loading of Multiresponsive p[NIPAm-co-PEGMA] (core)/p[NIPAm-co-AAc] (Shell) Nanogels with Monodisperse Size Distributions.

We report the synthesis and properties of temperature- and pH-responsive p([NIPAm-co-PEGMA] (core)/[NIPAm-co-AAc] (shell)) nanogels with narrow size distributions, tunable sizes and increased drug loading efficiencies. The core-shell nanogels were synthesized using an optimized two-stage seeded polymerization methodology. The core-shell nanogels show a narrow size distribution and controllable physico-chemical properties. The hydrodynamic sizes, charge distributions, temperature-induced volume phase transition behaviors, pH-responsive behaviors and drug loading capabilities of the core-shell nanogels were investigated using transmission electron microscopy, zeta potential measurements, dynamic light scattering and UV-Vis spectroscopy. The size of the core-shell nanogels was controlled by polymerizing NIPAm with crosslinker poly(ethylene glycol) dimethacrylate (PEGDMA) of different molecular weights (Mn-200, 400, 550 and 750 g/mol) during the core synthesis. It was found that the swelling/deswelling kinetics of the nanogels was sharp and reversible; with its volume phase transition temperature in the range of 40–42 °C. Furthermore, the nanogels loaded with l-3,4-dihydroxyphenylalanine (L-DOPA), using a modified breathing-in mechanism, showed high loading and encapsulation efficiencies, providing potential possibilities of such nanogels for biomedical applications.

Synthesis and characterization of CO2-sensitive temperature-responsive catalytic poly(ionic liquid) microgels

A class of poly(ionic liquid) microgels exhibiting CO2-switchable temperature-responsive volume phase transition behavior have been synthesized and used for CO2 fixation.

The role of unique spatial structure in the volume phase transition behavior of poly(N-isopropylacrylamide)-based interpenetrating polymer network microgels including a thermosensitive poly(ionic liquid).

Well-defined poly(N-isopropylacrylamide)/poly(tributylhexylphosphonium 3-sulfopropylmethacrylate) (PNIPAM/P[P4,4,4,6][MC3S]) interpenetrating polymer network (IPN) microgels were synthesized by two-step precipitation polymerization, and the thermally induced phase transition mechanism of IPN microgels was investigated using dynamic light scattering (DLS), temperature-dependent IR spectroscopy together with the perturbation correlation moving window (PCMW) technique and two dimensional correlation spectroscopy (2Dcos). For comparison, PNIPAM/P[P4,4,4,6][MC3S] polymer mixture was also studied to reveal the influence of the complex spatial network of IPN on the thermoresponsive behavior. Due to the strong hydrophilic feature of P[P4,4,4,6][MC3S] and the special IPN structure, PNIPAM and P[P4,4,4,6][MC3S] moieties exhibited different phase transition tendencies during heating. In detail, the dehydration behavior of the PNIPAM part seemed gradual and continuous, whereas that of ester C[double bond, length as m-dash]O in the P[P4,4,4,6][MC3S] part became sharp. The two components dehydrated independently and successively in the polymer mixture without any mutual interaction. The collapse of the P[P4,4,4,6][MC3S] network at the second transition stage increased the amount of intramolecular hydrogen bonding (amide C[double bond, length as m-dash]OD-N) in the PNIPAM moiety. Additionally, the electrostatic interaction in the P[P4,4,4,6][MC3S] network played a non-ignorable role in enhancing the swelling property of PNIPAM/P[P4,4,4,6][MC3S] IPN microgels.

Fabrication of Active Surfaces with Metastable Microgel Layers Formed during Breath Figure Templating.

Patterned porous surfaces with responsive functionalities are fabricated by a thermoresponsive microgel-assisted breath figure (BF) process. When water droplets submerge into a polystyrene (PS) solution during formation of a porous surface by the bottom-up BF process, poly(N-isopropylacrylamide)-co-acrylic acid (PNIPAm-co-AA) microgels dispersed in the solution spontaneously assemble at the water-organic interfaces like "Pickering emulsions", reinforced by capillary flow. The conformal layer of PNIPAm-co-AA microgels lining the pores appears in images from a scanning electron microscope (SEM) either as a smooth surface layer (L) or as an array of domelike protrusions (D), depending on the conditions at which the sample was dried for SEM. The change between L and D morphology correlates with the volume phase transition behavior of the microgels freely suspended: drying at a temperature below the volume phase transition temperature (VPTT) gives L, and the D morphology is formed by drying at a temperature greater than the VPTT of PNIPAm-co-AA microgels. The morphological transition is shown to accompany a significant change in surface contact angle (CA) relative to a corresponding pore layer made of PS, with L having a CA that is reduced by 85° relative to PS, while the decrease is only 22° for D. Porous structures with morphologically responsive surfaces could find application in biocatalysis or tissue engineering, for example, with functional enzymes sequestered when microgels are collaped and accessible when the microgels are swollen.

The structure and volume phase transition behavior of poly(N-vinylcaprolactam)-based hybrid microgels containing carbon nanodots.

In this paper, we investigated the internal structure and the volume phase transition (VPT) behavior of poly(N-vinylcaprolactam-co-vinylimidazole)/polymerizable carbon nanodot (P(VCL-co-VIM)/PCND) microgels with different amounts of PCNDs. Our study shows that compared to the pure P(VCL-co-VIM) microgel, the hybrid microgels undergo a two-step VPT as the temperature increases and a core-shell(-corona) structure of the hybrid microgels is formed by copolymerization with PCNDs. A change in the amount of PCNDs has effects on both of the volume phase transition temperature and internal structure of microgels. Moreover, based on FT-IR in combination with perturbation correlation moving window (PCMW) and two-dimensional correlation spectral (2Dcos) analyses, the difference in VPT behavior between the shell and the core (corona) structure of the hybrid microgels at the molecular level is elucidated. The core/shell of the hybrid microgels fixed with hydrophilic PCNDs has a higher transition temperature during heating and a more compact structure due to the additional crosslinkers PCNDs.

Microfluidic production of degradable thermoresponsive poly(N-isopropylacrylamide)-based microgels.

Highly monodisperse and hydrolytically degradable thermoresponsive microgels on the tens-to-hundreds of micron size scale have been fabricated based on simultaneous on-chip mixing and emulsification of aldehyde and hydrazide-functionalized poly(N-isopropylacrylamide) precursor polymers. The microfluidic chip can run for extended periods without upstream gelation and can produce monodisperse (<10% particle size variability) microgels on the size range of ∼30-90 μm, with size tunable according to the flow rate of the oil continuous phase. Fluorescence analysis indicates a uniform distribution of each reactive pre-polymer inside the microgels while micromechanical testing suggests that smaller microfluidic-produced microgels exhibit significantly higher compressive moduli compared to bulk hydrogels of the same composition, an effect we attribute to improved mixing (and thus crosslinking) of the precursor polymer solutions within the microfluidic device. The microgels retain the reversible volume phase transition behavior of conventional microgels but can be hydrolytically degraded back into their oligomeric precursor polymer fragments, offering potential for microgel clearance following use in vivo.

Influence of Charged Groups on the Structure of Microgel and Volume Phase Transition by Dielectric Analysis

The thermally sensitive charged poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAM-co-MAA)) spherical microgel was prepared and their temperature-dependent volume phase transition behavior was systematically studied by analyzing the dielectric spectroscopy theoretically over a frequency range from 40 Hz to 110 MHz. It was found that the dielectric relaxation of the charged P(NIPAM-co-MAA) microgel drastically changed between 30 and 35 °C, and was significantly different from that of neutral PNIPAM microgels recently published in Soft Matter. The relaxation mechanism was speculated and the relaxation parameters were fitted after successfully eliminating the electrode polarization at low-frequency. On the basis of this, the differences in the structure, swelling ability and dehydration dynamics between charged P(NIPAM-co-MAA) and neutral PNIPAM microgels were compared. Although both of the two microgels showed the same changing trend around the volume phase transition temperature (VPTT), VPTT of charg...

Autonomous Chemical Oscillator Circuit Based on Bidirectional Chemical‐Microfluidic Coupling

Autonomous Chemical Oscillator Circuit Based on Bidirectional Chemical‐Microfluidic Coupling

Visualizing phase transition behavior of dilute stimuli responsive polymer solutions via Mueller matrix polarimetry.

Probing volume phase transition behavior of superdiluted polymer solutions both micro- and macroscopically still persists as an outstanding challenge. In this regard, we have explored 4 × 4 spectral Mueller matrix measurement and its inverse analysis for excavating the microarchitectural facts about stimuli responsiveness of "smart" polymers. Phase separation behavior of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) and pH responsive poly(N,N-(dimethylamino)ethyl methacrylate) (PDMAEMA) and their copolymers were analyzed in terms of Mueller matrix derived polarization parameters, namely, depolarization (Δ), diattenuation (d), and linear retardance (δ). The Δ, d, and δ parameters provided useful information on both macro- and microstructural alterations during the phase separation. Additionally, the two step action ((i) breakage of polymer-water hydrogen bonding and (ii) polymer-polymer aggregation) at the molecular microenvironment during the cloud point generation was successfully probed via these parameters. It is demonstrated that, in comparison to the present techniques available for assessing the hydrophobic-hydrophilic switch over of simple stimuli-responsive polymers, Mueller matrix polarimetry offers an important advantage requiring a few hundred times dilute polymer solution (0.01 mg/mL, 1.1-1.4 μM) at a low-volume format.

The Phase Transition Model for Heat-Shrinkable Thermo-Sensitive Hydrogels Based on Interaction Energy

AbstractA biphase mixture continuum mechanics model is derived for neutral heat-shrinkable thermo-sensitive hydrogels in this paper. The mixing free energy of the special mixture is recalculated based on the partition function of Bose system, and it evaluates the contribution of the hydrophilic, hydrophobic interaction and hydrogen bonding to the volume phase transition behaviors. The ideas of the Flory lattice theory and the UNIFAC group contribution method are employed to get the expression of the mixing free energy. Then we deduce a particular model by combining this mixing free energy with the conservation laws equations and constitutive relations of both phases to predict the volume transition behaviors of these special hydrogels.

Switchable glucose-responsive volume phase transition behavior of poly(phenylboronic acid) microgels

We report a poly(phenylboronic acid) microgel that can display switchable glucose-responsive volume phase transition behavior with temperature as a trigger.

Core-shell-shell and hollow double-shell microgels with advanced temperature responsiveness.

Unique doubly temperature-responsive hollow microgels are presented. These consist of two concentric thermoresponsive polymer shells made of poly(N-isopropylacrylamide) (PNIPAM) and poly(N-isopropylmethacrylamide) (PNIPMAM), respectively. The hollow particles are derived from silica-PNIPAM-PNIPMAM core-shell-shell (CSS) particles by dissolution of the silica core. Light scattering measurements reveal the twofold volume phase transition behavior that occur in the PNIPAM and PNIPMAM regions of the CSS and the respective hollow particles. In the presence of the silica core, i.e., in case of the CSS particles, the swelling of the inner shell is tremendously restricted by the core. However, after the core is dissolved, the transition of the inner shell from the swollen to the collapsed state is highly pronounced. This versatile approach allows preparing hollow particles with individually tunable properties on the particle inside and outside for various applications as multifunctional smart materials.

The effect of added gold nanoparticles on the volume phase transition behavior for PVCL-based microgels

The volume phase transition (VPT) behavior of poly(N-vinylcaprolactam-co-4-vinylpyridine) P(VCL-co-4VP) microgels and their hybrid counterparts containing Au nanoparticles (AuNPs) is explored and compared by FTIR measurements in combination with the perturbation correlation moving window (PCMW) technique and two-dimensional correlation spectroscopy (2Dcos) analysis. It is demonstrated that the incorporation of AuNPs inside the microgels cause a slight dehydration effect on the microgels in the swollen state and an increase of the VPT temperature. Moreover, the interaction between CO and AuNPs can be confirmed by combining the conventional IR and 2Dcos analysis. It is with the help of the additional cross-links between AuNPs and the polymer chains (CO and pyridine groups) in the microgel network and the tendency of AuNPs to aggregate that the hybrid microgels exhibit a much greater dehydration during the VPT, as compared with the nonhybrid ones.

Graphene@Poly(phenylboronic acid)s Microgels with Selectively Glucose-Responsive Volume Phase Transition Behavior at a Physiological pH

The selective response to glucose is possible by using a poly(phenylboronic acid) microgel under a rational design. Such a microgel is made of graphene covalently immobilized in a microgel of poly(4-vinylphenylboronic acid) cross-linked with N,N′-methylenebis(acrylamide). Unlike the microgels reported in previous arts that would undergo volume phase transition in response to both glucose and other monosaccharides, the proposed microgels shrink upon adding glucose, whereas keep unchanged in the size upon adding other monosaccharides (with fructose, galactose, and mannose as models). Although the polysaccharides/glycoproteins (with dextran and Ribonuclease B as models) that contain many glycosyl residues can slightly absorb on the microgel surface and lead to a small impact on glucose-response, it can be addressed by further coating the microgel as a core with a thin nonglucose-responsive poly(N-isopropylacrylamide) gel shell. This selectively glucose-responsive volume phase transition behavior enables “tur...

The unusual volume phase transition behavior of the poly(N-isopropylacrylamide)–poly(2-hydroxyethyl methacrylate) interpenetrating polymer network microgel: different roles in different stages

Dynamic thermal phase transition behavior of a well-defined poly(N-isopropylacrylamide)–poly(2-hydroxyethyl methacrylate) (PNIPAM–PHEMA) interpenetrating polymer network (IPN) microgel in D2O synthesized by two-step precipitation polymerization was studied by means of IR spectroscopy in combination with the perturbation correlation moving window (PCMW) technique and two-dimensional correlation spectroscopy (2Dcos) analysis. Due to the hydrophobic and non-thermo-responsive properties of PHEMA and the special IPN structure, the IPN microgel exhibited an unusual thermally induced collapse process. The introduction of PHEMA would lower the volume phase transition temperature (VPTT) and the volume phase transition degree. 2Dcos was finally employed to discern the sequence order of all the group motion during heating and cooling processes. PHEMA plays different roles in different stages during the volume phase transition. Additionally, as PHEMA exhibits only a slight response to temperature, it would provide the PNIPAM–PHEMA IPN microgel with good reversibility.