N-isopropylacrylamide Hydrogel Research Articles

Succulent-Inspired Implicit Structural Change for Smart "ON/OFF" Switchable and Flexible EMI Shielding Coating.

Modern miniaturized intelligent electronics call for smart switchable and flexible electromagnetic interference (EMI) shielding material for highly precise applications. However, most switchable EMI shielding materials are based on an explicit structural change. Herein, we report a succulent-inspired smart switchable MXene (WR-MXene) coating film realized by inner implicit structural change, which benefits from the insertion of our reversible large-cavity yolk-shell biomicrospheres. The novel switchable yolk-shell biomicrospheres contain a soft N-isopropylacrylamide (PNIPAM) hydrogel core, an "ON/OFF" switchable cavity (over 30% volume fraction), and a porous polydopamine (p-PDA) shell. The yolk-shell biomicrospheres can be obtained by a facile two-step polymerization and a simple drying-dehydration treatment. Because of the "ON/OFF" switchable void space brought by the smart biomicrospheres and conductive framework of MXene, an optimized ultralight and flexible WR-MXene coating film (vWR-coating film) showed both large switchable change (over 60 dB) and extraordinary EMI shielding effectiveness, reaching 95 and over 50 dB in the whole X band (8.2-12.4 GHz). These novel reversible yolk-shell biomicrospheres and the succulent-inspired switchable coating films are promising for smart flexible wearable devices and many advanced multifunctional systems needing dynamic real-time response.

Design of an Anti-HMGB1 Synthetic Antibody for In Vivo Ischemic/Reperfusion Injury Therapy.

High-mobility group box 1 (HMGB1) is a multifunctional protein. Upon injury or infection, HMGB1 is passively released from necrotic and activated dendritic cells and macrophages, where it functions as a cytokine, acting as a ligand for RAGE, a major receptor of innate immunity stimulating inflammation responses including the pathogenesis of cerebral ischemia/reperfusion (I/R) injury. Blocking the HMGB1/RAGE axis offers a therapeutic approach to treating these inflammatory conditions. Here, we describe a synthetic antibody (SA), a copolymer nanoparticle (NP) that binds HMGB1. A lightly cross-linked N-isopropylacrylamide (NIPAm) hydrogel copolymer with nanomolar affinity for HMGB1 was selected from a small library containing trisulfated 3,4,6S-GlcNAc and hydrophobic N-tert-butylacrylamide (TBAm) monomers. Competition binding experiments with heparin established that the dominant interaction between SA and HMGB1 occurs at the heparin-binding domain. In vitro studies established that anti-HMGB1-SA inhibits HMGB1-dependent ICAM-1 expression and ERK phosphorylation of HUVECs, confirming that SA binding to HMGB1 inhibits the proteins' interaction with the RAGE receptor. Using temporary middle cerebral artery occlusion (t-MCAO) model rats, anti-HMGB1-SA was found to accumulate in the ischemic brain by crossing the blood-brain barrier. Significantly, administration of anti-HMGB1-SA to t-MCAO rats dramatically reduced brain damage caused by cerebral ischemia/reperfusion. These results establish that a statistical copolymer, selected from a small library of candidates synthesized using an "informed" selection of functional monomers, can yield a functional synthetic antibody. The knowledge gained from these experiments can facilitate the discovery, design, and development of a new category of drug.

Pearl‐Like Sheen in Soft Capsules: An Unusual Optical Effect that is Reversibly Induced by Temperature

AbstractA pearl‐like sheen (i.e., pearlescence) is seen in many natural materials like nacre and in some commercial paints and cosmetics. This phenomenon is attributed to the interaction of light with plate‐like particles in the material. Here, for the first time, pearlescence is demonstrated in soft millimeter‐scale capsules that contain no plate‐like particles. The capsules have a thin (~500 µm) outer shell of N‐isopropylacrylamide (NIPA) hydrogel, which has a lower critical solution temperature (LCST) of 32 °C. When a transparent NIPA‐shelled capsule is heated above this LCST, it turns pearlescent. The effect is reversible, with the transparent state being recovered upon cooling. This is the first example of reversible pearlescence in any solid. Specular reflectance measurements show that the pearlescence of the capsules is comparable to that of natural pearls. Pearlescence is not observed in NIPA hydrogels; it arises only in NIPA‐shelled capsules, and that too only when the shell is thin. Above its LCST, the NIPA shell shrinks and gets stretched, and nanoscale NIPA‐rich domains arise within this shell, which induce the pearlescence. This study sheds fresh insight into the nature of pearlescence, on how it can be tuned, and on how this property can be introduced into various soft materials.

Selective in situ dynamic motion stay and recover under single NIR light in soft actuator by triggered Shape-Memory and phase transition of hydrogel

Inspired by nature, hydrogel actuators are important for designing soft robots and become one of the most essential components of intelligent research. However, classical actuation method, such as Near-Infrared (NIR) light stimulates the actuator to complete the motions then it automatically recovers original state when the light is off, cannot provide continuous in situ dynamic motion stay and recovery under one NIR light. In this study, a novel network-polycaprolactone (Net-PCL)-poly N-isopropylacrylamide (PNIPAM) hydrogel actuator (Net-PCL-Gel) is proposed through a layer-by-layer stacking technology, leading to the co-existence of Net-PCL with photoinduced shape memory capability and PNIPAM hydrogel segments showing de-swelling/swelling phase transition. Owing to the shape memory property of Net-PCL, the Net-PCL-Gel exhibits in situ dynamic bending and recovering stay behavior in response to NIR irradiation with the active force of PNIPAM. Different from the conventional hydrogel system, the Net-PCL-Gel also displayed remarkable decryption performance in information reading and hiding, while retaining excellent accuracy and stability. Due to its simplicity, this strategy shows great potential for the biomimetic operation of soft grippers and multifunctional actuators.

Sustainable Hierarchical-Pored PAAS-PNIPAAm Hydrogel with Core-Shell Structure Tailored for Highly Efficient Atmospheric Water Harvesting.

As an effective way to obtain freshwater resources, atmospheric water harvesting (AWH) technology has been a wide concern of researchers. Therefore, hydrogels gradually become key materials for atmospheric water harvesters due to their high specific surface area and three-dimensional porous structure. Here, we construct a core-shell hydrogel-based atmospheric water harvesting material consisting of a shell sodium polyacrylate (PAAS) hydrogel with an open pore structure and a core thermosensitive poly N-isopropylacrylamide (PNIPAAm) hydrogel with a large pore size. Theoretically, the mutual synergistic hygroscopic effect between the core layer and the shell layer accelerates the capture, transport, and storage of moisture to achieve continuous and high-capacity moisture adsorption. Simultaneously, the integration of polydopamine (PDA) with the hydrogel realizes solar-driven photothermal evaporation. Therefore, the prepared core-shell hydrogel material possesses great advantages in water adsorption capacity and water desorption capacity with an adsorption of 2.76 g g-1 (90% RH) and a desorption of 1.42 kg m-2 h-1. Additionally, the core-shell structure hydrogel collects 1.31 g g-1 day-1 of fresh water in outdoor experiments, which verifies that this core-shell hydrogel with integrated photothermal properties can capture moisture in a wide range of humidity without any external energy consumption, can further sustainably obtain fresh water in remote water-shortage areas.

Osmanthus Fragrans Loaded NIPAAM Hydrogel Promotes Osteogenic Differentiation of MC3T3-E1.

There is an urgent need to find long-acting, natural osteogenesis-promoting drug systems. In this study, first the potential targets and mechanism of osmanthus fragrans (O. fragrans) extract in regulating osteogenic differentiation based on autophagy were analyzed by network pharmacology and molecular docking. Then, osmanthus fragrans was extracted using the ethanol reflux method and an osmanthus fragrans extract loaded Poly N-isopropylacrylamide (OF/NIPAAM) hydrogel was prepared by electron beam radiation. The chemical components of the osmanthus fragrans extract and the microstructure of OF/NIPAAM hydrogels were characterized by ultraviolet-visible spectrophotometry (UV-Vis) and X-ray diffraction (XRD), respectively. Mouse embryonic osteoblast precursor cells MC3T3-E1 were cultured with different concentrations of OF/NIPAAM hydrogel to discover cell proliferation activity by CCK-8 assay. Alkaline phosphatase (ALP) staining and alizarin red staining were used to observe the differentiation and calcification. Through experimental exploration, we found that a total of 11 targets were predicted, which are TP53, CASP3, SIRT1, etc., and osmanthus fragrans had good binding activity to TP53. In vitro, except for proliferation promotion, OF/NIPAAM hydrogel enhanced ALP activity and formation of mineralized nodules of MC3T3-E1 cells at a concentration equal to or less than 62.5 μg/mL (p < 0.05). The addition of autophagy inhibitor 3-methyladenine (3-MA) reduced ALP activity and mineralized nodule formation.

Temperature-controlled bacteria biofilm adhesion and formation for CO/CO2 bioconversion to ethanol by grafting N-isopropylacrylamide@SiC

Biofilm with high biomass density and high gas–liquid mass transfer efficiency is one of the most efficient bacterial culture modes for ethanol fermentation using CO/ CO2 gas. However, it is very difficult and requires a long time for bacteria to form a stable biofilm due to the weak adhesion ability between bacterial cells and the substrate. To synergistically enhance bacterial adhesion during biofilm formation and biofilm detachment after fermentation to reuse the substrate, a substrate surface with controllable properties is expected. Thus, in this study, a temperature responsive substrate was prepared by grafting a thermosensitive hydrogel of N-isopropylacrylamide onto the surface of a silicon carbide (SiC) substrate to accelerate the formation of biofilm. The hydrophobicity of the modified substrate surface changed from 52.6° to 89.4° as the temperature increased from 25 °C to 37 °C (the optimal cell culture temperature). The adhesion free energy between the bacterial biofilm and the substrate changed from −4.11 MJ m−2 to −41.7 MJ m−2, indicating a stronger adsorption capacity. Moreover, the surface zeta potential increased from −7.7 mV to +7.6 mV, forming an electrostatic attraction between the cell (-27 mV) instead of electrostatic repulsion force. All the above making the bacteria easier adhere and forming biofilm faster. Compared with that on the original SiC substrate, the bacterial biofilm-forming rate was increased by 6.2 times, which shortened the stable biofilm-forming time to 4 days. The mean ethanol productivity was 0.54 g/L d-1, 116 % higher than that on the original SiC substrate. Therefore, controlling bacterial adhesion on the temperature responsive substrate was an efficient way to enhance ethanol production by CO/CO2 fermentation.

Thermal and NIR controlled flexible switching devices using a smart conductive composite hydrogel approach

Flexible switching devices with multi-stimulus responsive abilities have shown promising applications as smart materials in the tissue regeneration fields. Herein, a composite hydrogel-based flexible switch system was successfully designed by integrating the nano-sized conductive CNC@PPy (cellulose nanocrystal decorated with polypyrrole (PPy)) and CNC@PDA (cellulose nanocrystal decorated with polydopamine (PDA)) composite particles into the thermal sensitive poly N-isopropyl acrylamide (PNIPAM) hydrogels. The resulting composite hydrogels exhibited enhanced elastic modulus (∼29.5 kPa), superior conductivity (∼1.1 S/m), self-healing, and thermo- and NIR-responsive abilities. Particularly, the incorporated CNC@PDA and CNC@PPy particles within the hydrogel matrix by hydrogen bonds could not only provide a more continuous transporting path for electrons, but also further improve the photothermal conversion efficiency of the composite hydrogel system, in which the temperature increased by 47.6 °C within 10 min under NIR irradiation, and high NIR light-responsive sensitivity with a volume change of 30% within 2 min. Moreover, these composite hydrogels were developed to serve thermo- and NIR light-responsive switchers effectively, which showed excellent stimulus-responsive sensitivities. In all, this work provided a new strategy for designing the multi-stimulus responsive smart hydrogels, which demonstrated excellent potential to serve as remotely controllable switch devices in biomaterials and tissue regeneration.

Simultaneous Release of Aflibercept and Dexamethasone from an Ocular Drug Delivery System

Purpose Intravitreal injections of anti-vascular endothelial growth factors (anti-VEGF) are the current standard of care for patients with choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD). There is a growing subset of patients that does not respond to anti-VEGF monotherapy treatment. Some patients, however, do respond to combination therapy of corticosteroids and anti-VEGF. This treatment requires monthly/bimonthly injections of anti-VEGF and semi-annual injections of corticosteroid. A drug delivery system (DDS) that simultaneously releases multiple drugs could benefit these patients by reducing the number of injections. The purpose of this study was to characterize the simultaneous release of aflibercept and dexamethasone from a biodegradable microparticle- and nanoparticle-hydrogel DDS. Methods Dexamethasone-loaded nanoparticles and aflibercept-loaded microparticles were created using modified single- and double-emulsion techniques, respectively. Then, microparticles and nanoparticles were embedded into a thermoresponsive, biodegradable poly(ethylene glycol)-co-(L-lactic acid) diacrylate (PEG-PLLA-DA)-N-isopropylacrylamide (NIPAAm) hydrogel DDS. Drug release studies and characterization of DDS were conducted with varying doses of microparticles and nanoparticles. Results The combination aflibercept-loaded microparticle- and dexamethasone-loaded nanoparticle- hydrogel (Combo-DDS) achieved a total release time of 224 days. Small decreases were seen in swelling ratio and equilibrium water content for Combo-DDS compared to monotherapy aflibercept-loaded microparticle-hydrogel DDS (AFL-DDS) and monotherapy dexamethasone-loaded nanoparticle-hydrogel DDS (DEX-DDS). Bioactivity of aflibercept was maintained in Combo-DDS compared to AFL-DDS. Conclusions The Combo-DDS was able to extend and control the release of both aflibercept and dexamethasone simultaneously from a single DDS. This may eliminate the need for separate dosing regiments of anti-VEGF and corticosteroids for wet AMD patients.

Intelligent hydrogel with both redox and thermo-response based on cellulose nanofiber for controlled drug delivery

The purpose of this study is to develop a hydrogel with temperature and redox response to control drug delivery. However, the strength of temperature sensitive N-isopropylacrylamide (NIPAM) hydrogel is weak. Therefore, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose nanofiber (CNF) is introduced to improve this problem. The compressive strength of hydrogels increased by 360% after CNF addition. Meanwhile, N,N′-bis(acryloyl)cystamine (BACy) is introduced into the hydrogels as a cross-linker, imparting redox responsive properties to the hydrogels. Tumor therapeutic drugs are used as model drugs for in vitro release studies. The drug release rate of hydrogel is regulated by temperature and reducing environment. The maximum cumulative release rate of doxorubicin (DOX) is 39.56%, and the Berberine (BBR) is 99.50% after 60 h. The swelling and transparency of hydrogels showed dramatic changes in the range of 30–40 °C. Cytotoxicity experiments demonstrated that the hydrogel had almost no cytotoxicity.

Highly Robust Interfacially Polymerized PA Layer on Thermally Responsive Semi-IPN Hydrogel: Toward On-Demand Tuning of Porosity and Surface Charge.

Hydrogel composites with skin layer that allows fast and selective rejection of molecules possess high potential for numerous applications, including sample preconcentration for point-of-use detection and analysis. The stimuli-responsive hydrogels are particularly promising due to facile regenerability. However, poor adhesion of the skin layer due to swelling-degree difference during continuous swelling/deswelling of the hydrogel hinders its further development. In this work, a polyamide skin layer with strong adhesion was fabricated via gel-liquid interfacial polymerization (GLIP) of branched polyethyleneimine (PEI) with trimesoyl chloride (TMC) on a cross-linked N-isopropyl acrylamide hydrogel network containing dispersed poly sodium acrylate (PSA), while the traditional m-phenylenediamine (MPD)-TMC polyamide layer readily delaminates. We investigated the mechanistic design principle, which not only resulted in strong anchoring of the polyamide layer to the hydrogel surface but also enabled manipulation of the surface morphology, porosity, and surface charge by tailoring interfacial reaction conditions. The polyamide/hydrogel composite was able to withstand 100 cycles of swelling/deswelling without any delamination or a significant decrease in its rejection performance of the model dye, i.e., methylene blue. Regeneration can be done by deswelling the swollen beads at 60 °C, which also releases any loosely bound molecules together with absorbed water. This work provides insights into the development of a physically and chemically robust skin layer on various types of hydrogels for applications such as preconcentration, antifouling-coating, selective compound extraction, etc.

Personalized and Programmable Microneedle Dressing for Promoting Wound Healing.

Microneedle (MN) dressings, with the ability of transdermal drug delivery, have played an essential role in the field of wound healing. However, patients may still feel uncomfortable when sensitive unhealing wounds are pieced by strong needles. Here, inspired by the structure of mosquito mouthparts, which possess a fixation part and a liquid-transferring part, we present a novel MN wound dressing with superfine needle tips, personalized pattern design, programmable needle length, and multiple mechanical strengths for intelligent and painless drug delivery. By simply stretching the silicone rubber (Ecoflex) molds before engraving, superfine MNs can be formed in the restored molds. Meanwhile, by utilizing intelligent image recognition, precise treatment for irregular wounds is achieved. Notably, combined with temperature-responsive N-isopropylacrylamide (NIPAM) hydrogel and inverse opal (IO) photonic crystals (PCs), a controllable drug release system has been achieved on MN dressings. Moreover, the performance of the MN dressing in facilitating wound recovery has been demonstrated by full-thickness skin wounds of a mouse model. These results indicate that novel personalized and programmable MN wound dressings are of considerable value in the field of wound management.

Ethanol fermentation using macroporous monolithic hydrogels as yeast cell scaffolds

Ethanol fermentation with a hybrid system containing free and immobilized yeast cells on a macroporous monolithic hydrogel scaffold was investigated. Cell immobilization was achieved using N-isopropylacrylamide (NIPA) and methoxy triethyleneglycol acrylate (MTGA) hydrogels having macroporous monolithic structures containing interconnected micrometer-sized macropores. The immobilized cells grow within the hydrogel and can exit through the macropores into the fermentation medium, and thus a hybrid bioreactor consisting of free and immobilized yeast cells is constructed. The transformation of d-glucose to ethanol using Saccharomyces cerevisiae in batch and continuous fermentation processes was examined. Ethanol was successfully fermented using the macroporous hydrogels, whereas the conventional nonporous NIPA hydrogel does not effectively act as a cell scaffold. In continuous fermentation, the hybrid system containing both free yeast cells and those immobilized in the macroporous MTGA hydrogel showed higher ethanol productivity than the control system containing only free cells. Crucially, the macroporous hydrogel allowed the stable growth of immobilized yeast cells, resulting in a high cell density in the reactor. The hybrid system under steady-state fermentation had free and immobilized cell densities of 1.72 kg-free-cell/m3 and 29 kg-immobilized-cell/m3-gel, respectively, and the ethanol productivities 0.421 kg-ethanol/(kg-free-cell·h) and 0.128 kg-ethanol/(kg-immobilized-cell·h), respectively.

Synthesis of dual pH‐ and temperature‐sensitive poly(N‐isopropylacrylamide‐co‐acrylic acid)/sewage sludge ash hydrogel with the simultaneously high performance of swelling and deswelling

AbstractAn advanced dual pH‐ and temperature‐sensitive hydrogel (NASH2.5) was optimally synthesized through modification of N‐isopropylacrylamide (NIPAM) hydrogel with introducing 5 mol% acrylic acid (AA) and 2.5 wt% sewage sludge ash (SSA). The swelling kinetic results showed that NASH2.5 exhibited both high equilibrium swelling ratio and swelling rate, which was attributed to the higher porous structure as shown in scanning electron microscope, and the more hydrogen bonding formed inside of the hydrogel as investigated in Fourier transform infrared spectrometer. In addition, its curve was better fitted to the pseudo‐second‐order model, indicating that the water absorption process was dominated by chemisorption through forming the hydrogen bonding among the water molecules and carboxyl/silanol groups of the hydrogel. Compared with the pure NIPAM hydrogel, the water transport mechanism switched from Case I diffusion to Case II diffusion by introduction of AA and further SSA. Furthermore, through the results of the deswelling kinetics in pH value change (from 9 to 4 and 2, respectively), temperature value change (from 25 to 40, 50, and 60°C, respectively), and dual pH and temperature values changes, NASH2.5 not only presented a high pH sensitivity, but also showed high sensitive to temperature by achieving high water recovery ratio in rapid dehydrated rate. Therefore, the dual stimuli‐sensitive hydrogel with the simultaneously high performance of swelling and deswelling would provide a suitable alternative for specific applications such as pollutant adsorption.

Thermally Tunable Acoustic Beam Splitter Based on Poly(vinyl alcohol) Poly(N-isopropylacrylamide) Hydrogel.

In this study, we demonstrated a thermally tunable acoustic beam splitter using a poly(vinyl alcohol) poly(N-isopropylacrylamide) hydrogel (PVA-pNIPAM). The nature of PVA-pNIPAM hydrogel offers exceptional temperature-dependent physical properties due to its phase transition around its lower critical solution temperature. The acoustic impedance of the hydrogel can be tuned below, above, or matched to that of water by changing the environmental temperature. An acoustic wave propagating in water can be split into transmitted and reflected components by the PVA-pNIPAM hydrogel slab on varying its angle of incidence. The intensity ratio between the reflected and the transmitted componence can be adjusted by tuning the temperature of the medium. The acoustic beam can be entirely reflected at a temperature corresponding to the matched impedance between hydrogel and water. The beam-splitting behavior was observed for acoustic waves from both a monochromatic wave and broadband pulse source. In addition, the phase of beam split pulses can be reversed by selecting the hydrogel’s operating temperature.

NIR-responsive structural color hydrogel microchannel for self-regulating microfluidic system

Intelligent microfluidic devices with the capacities to flexibly adjusting the flow rate and flow direction have attracted increasing interest in recent years. Here, we present a responsive structural color hydrogel microchannel with the advanced functions of controllable fluid manipulating and visualized state-feedback by employing photothermal responsive graphene-doped N-isopropylacrylamide (NIPAM) hydrogel to negatively replicate the tubular colloidal crystal array templates. Because of the characteristics of graphene and NIPAM hydrogel, the obtained hydrogel microchannel exhibited a light-controlled reversible shrinking behavior and a corresponding structural color shift. It was demonstrated that when this intelligent microchannel was integrated into microfluidics, it presented a dynamically adjustable inner diameter and provided an intuitive visual state-feedback. In addition, the asymmetric irradiation of near-infrared (NIR) laser could induce a bending behavior of the hydrogel microchannel, enabling a visualized sample flow-switching process. These features indicated that the customized responsive microchannels possessed great potentials in constructing self-regulating micropumps and supporting oriented sensing analysis .

Modeling swelling behavior of hydrogels in aqueous organic solvents

Hydrogel, a three-dimensional elastic structure of cross-linked polymer chains, swells or deswells when immersed in aqueous organic solutions. The swelling of hydrogels depends on temperature, solvent composition, and hydrogel structure as the thermodynamic driving forces for hydrogel swelling are due to solvent – hydrogel interactions and expansion of elastic network. In this work, polymer Nonrandom Two-Liquid activity coefficient model is used to account for the solvent – hydrogel interactions and a semi-empirical expression for rubber elasticity is used to describe the expansion of elastic network. The model successfully correlates data for both swelling and equilibrium phase compositions for n-isopropyl acrylamide hydrogels in water – ethanol, water – acetone, water – n-butanol, and water – methyl isobutyl ketone mixed solvents.

Thermally Tunable Dynamic and Static Elastic Properties of Hydrogel Due to Volumetric Phase Transition.

The temperature dependence of the mechanical properties of polyvinyl alcohol-based poly n-isopropyl acrylamide (PVA-PNIPAm) hydrogel was studied from the static and dynamic bulk modulus of the material. The effect of the temperature-induced volumetric phase transition on Young’s Modulus, Poisson’s ratio, and the density of PVA-PNIPAm was experimentally measured and compared with a non-thermo-responsive Alginate hydrogel as a reference. An increase in the temperature from 27.5 to 32 °C results in the conventional temperature-dependent de-swelling of the PVA-PNIPAm hydrogel volume of up to 70% at the lower critical solution temperature (LCST). However, with the increase in temperature, the PVA-PNIPAm hydrogel showed a drastic increase in Young’s Modulus and density of PVA-PNIPAm and a corresponding decrease in the Poisson’s ratio and the static bulk modulus around the LCST temperature. The dynamic bulk modulus of the PVA-PNIPAm hydrogel is highly frequency-dependent before the LCST and highly temperature-sensitive after the LCST. The dynamic elastic properties of the thermo-responsive PVA-PNIPAm hydrogel were compared and observed to be significantly different from the thermally insensitive Alginate hydrogel.

A multiphysics model of photo-sensitive hydrogels in response to light-thermo-pH-salt coupled stimuli for biomedical applications

This paper aims to unveil the fundamental response mechanism of photo-sensitive hydrogels subject to light-thermo-pH-salt coupled stimuli, for their potential biomedical uses such as cell scaffolds and extracellular matrices, where biological activity largely depends on internal electrochemical changes. To mimic the microenvironment of biomolecules or cells, we focus on a spirobenzopyran-modified N-isopropylacrylamide hydrogel incorporating acrylic acid as a proton generator and develop a multiphysics model to characterize its behaviour within aqueous solution in response to light intensity, temperature, buffer pH, and salt concentration. The model allows for concurrent chemical reactions, ionic diffusion, electrostatic effects and large mechanical deformation, as well as interaction with the solution domain. Validation was performed by comparison with the published experimental results and showed good agreement. It is demonstrated by the simulation results that the photo-sensitive hydrogel exhibits a varied sensitivity to the external stimuli if incorporated with different molar ratios of acrylic acid. The electrical and pH response characteristics of the hydrogel, especially those in neutral solution, may inspire some potential biomedical applications, such as photo-controlled drug release and cell growth.

Programmable Reversible Shape Transformation of Hydrogels Based on Transient Structural Anisotropy.

Stimuli-responsive shape-transforming hydrogels have shown great potential toward various engineering applications including soft robotics and microfluidics. Despite significant progress in designing hydrogels with ever more sophisticated shape-morphing behaviors, an ultimate goal yet to be fulfilled is programmable reversible shape transformation. It is reported here that transient structural anisotropy can be programmed into copolymer hydrogels of N-isopropylacrylamide and stearyl acrylate. Structural anisotropy arises from the deformed hydrophobic domains of the stearyl groups after thermomechanical programming, which serves as a template for the reversible globule-to-coil transition of the poly(N-isopropylacrylamide) chains. The structural anisotropy is transient and can be erased upon cooling. This allows repeated programming for reversible shape transformation, an unknown feature for the current hydrogels. The programmable reversible transformation is expected to greatly extend the technical scope for hydrogel-based devices.