Smart Hydrogels Research Articles

This Review Recent Advances in Chitosan and Alginate‐Based Hydrogels for Wound Healing Application

Wound healing is a complicated yet necessary event that takes place in both animals and human beings for the body to repair itself due to injury. Wound healing involves various stages that ensure the restoration of the injured tissue at the end of the process. Wound dressing material acts as a protective extracellular barrier against potential damage to the injury and microbial invasion. Naturally, polysaccharides (chitosan and alginate) have inherent properties that have made them attractive for their usage in wound healing therapy. Alginate and chitosan have been used to develop novel wound healing and smart biomaterials due to various functionalities such as reducing swelling, non-toxic nature, biocompatibility, antimicrobial potential, and maintenance moist environment, ability to absorb wound fluid, and skin regeneration promotion. Functionalization of polysaccharides is one of the many approaches that have been used to modify and enhance the wound healing properties of these biomaterials. Many studies have been done to modify the polysaccharide hydrogels. Some of these are highlighted in this paper. The designing and development of smart hydrogels that react to their environment have recently sparked a significant scientific and pharmaceutical interest. Smart hydrogel development has been the primary focal area for developing highly advanced and sophisticated wound healing therapeutic technologies. This paper seeks to comprehensively shed light on the advancements of functionalized chitosan and alginate-based hydrogels and their applicability in wound healing therapeutics. In addition to this, thus identifying critical drawbacks faced in existing hydrogel systems and how prospective technologies enable digitally controlled bio-platforms coupled with biomaterials to improve wound care. This review hopes to stimulate and encourage researchers to identify future avenues worth investigation.

Re-Entrant Conformation Transition in Hydrogels.

Hydrogels are attractive materials not only for their tremendous applications but also for theoretical studies as they provide macroscopic monitoring of the conformation change of polymer chains. The pioneering theoretical work of Dusek predicting the discontinuous volume phase transition in gels followed by the experimental observation of Tanaka opened up a new area, called smart hydrogels, in the gel science. Many ionic hydrogels exhibit a discontinuous volume phase transition due to the change of the polymer–solvent interaction parameter χ depending on the external stimuli such as temperature, pH, composition of the solvent, etc. The observation of a discontinuous volume phase transition in nonionic hydrogels or organogels is still a challenging task as it requires a polymer–solvent system with a strong polymer concentration dependent χ parameter. Such an observation may open up the use of organogels as smart and hydrophobic soft materials. The re-entrant phenomenon first observed by Tanaka is another characteristic of stimuli responsive hydrogels in which they are frustrated between the swollen and collapsed states in a given solvent mixture. Thus, the hydrogel first collapses and then reswells if an environmental parameter is continuously increased. The re-entrant phenomenon of hydrogels in water–cosolvent mixtures is due to the competitive hydrogen-bonding and hydrophobic interactions leading to flow-in and flow-out of the cosolvent molecules through the hydrogel moving boundary as the composition of the solvent mixture is varied. The experimental results reviewed here show that a re-entrant conformation transition in hydrogels requires a hydrophobically modified hydrophilic network, and a moderate hydrogen-bonding cosolvent having competitive attractions with water and polymer. The re-entrant phenomenon may widen the applications of the hydrogels in mechanochemical transducers, switches, memories, and sensors.

Liquid Stratification and Diffusion‐Induced Anisotropic Hydrogel Actuators with Excellent Thermosensitivity and Programmable Functionality

Smart hydrogel actuators with programmable anisotropic structures present fascinating prospects considering their distinctive shape transformation and controllable environmental responsiveness under external stimuli. However, the design of anisotropic hydrogels with simple and universal fabrication and programmable functionality is challenging for their valuable applications in smart actuators and soft robots. Herein, a simple, green, and devisable strategy is proposed to construct a heterogeneous porous hydrogel system by the different liquid diffusion (such as amyl alcohol, water, and ethanol) into a monomeric precursor solution of thermosensitive hydrogels. The well‐defined micro/nanoporous gradient and patterned structures related to selective liquid stratification and interfacial diffusion favor the fast response and accurate programmable deformation of hydrogels under temperature stimuli. Inspiringly, this simple diffusion‐driven tactic can be perfectly applicable for different responsive hydrogels with programmable multifunctionality by adding functional nanomaterials into the diffusible liquid. This green, general, and facile diffusion‐driven strategy provides significant guidance for fabricating environmentally responsive hydrogels with tailorable functionality for their multipurpose applications in drug delivery, bioengineering, smart actuators, and soft robots.

Control of Glucose‐Induced Degradation and Cargo Release in Multi‐Responsive Polymer Hydrogels

AbstractOn‐demand cargo/drug release from hydrogel under physiological conditions is a significant challenge for advanced therapeutics. Specifically, smart hydrogels capable of the glucose‐responsive release of anti‐diabetic drugs are of current research thurst. Despite the recent developments, there is a need for more glucose‐sensing hydrogel that retain the properties in a wide‐range of pH environments. Herein, a facile and generalized fabrication strategy of multiple stimuli (pH, glucose, and hydrogen peroxide)‐responsive hydrogels is reported. Poly(vinyl alcohol) (PVA) is crosslinked with three bis‐boronic acid molecules‐ benzene‐1,4‐diboronic acid (1,4‐BDBA), 4,4′‐biphenyldiboronic acid (4,4′‐BPDBA), tetrahydroxydiboron(THDB) in ambient conditions to produce hydrogels with water content > 80% and suitable for (macro)molecular cargo incorporation in the matrix. Extensive analytical studies suggest that hydrogels derived from 1,4‐BDBA and 4,4′‐BPDBA show degradation under the stimuli mentioned earlier, but THDB crosslinked hydrogel does not degrade under pH or glucose environment. This unusual property allows the incorporation of glucose oxidase (GOx) in the hydrogel matrix that imparts the glucose responsiveness for THDB crosslinked hydrogel. Finally, the glucose‐specific release of (macro)molecular cargo/drugs is demonstrated in a glucose oxidase containing PVA/THDB hydrogel in the physiological milieu. The hydrogel developed herein will open up new ways to develop glucose‐specific smart‐matrix for the on‐demand delivery of drugs.

Cellulose-Based Hydrogels as Smart, Green and Controllable Nitrogenous Fertilizers Releasing Agents

Abstract A smart, green, and controllable-release hydrogel based on cellulose was prepared to avoid the problem of soil fertilizer abuse. A field-emission scanning electron microscope (FE-SEM) demonstrated a wrinkled, rough, lamellar structure with long microtubes. The effect of the cross-linker concentration, epichlorohydrin (ECH), on the physical and mechanical properties in addition to swelling and urea-release kinetics was thoroughly studied. A relatively high swelling ratio, urea entrapment, and proper flexibility were obtained for an ECH concentration of 3.33 %. The swelling kinetics of hydrogel was found to be a second-order process. The maximum swelling value and the initial swelling rate were dependent on cross-linker concentration. The hydrogel exhibited a dehydration shrinkage in saline solution. A significantly high urea release of 6.61 % at 3.33 ECH concentrations was estimated. The urea-release mechanism matches well with the Fickian model. Accordingly, the prepared hydrogel is potential as a smart, green, and controllable-release fertilizer for applications in agriculture and horticulture.

Analyzing the Effects of Silica Nanospheres on the Sol-Gel Transition Profile of Thermosensitive Hydrogels.

The insertion of nanoparticles into smart hydrogels can diversify their functionalities by a synergistic combination of the components properties within the hydrogels. While these hybrid systems are attractive to the biomaterials field, careful design and control of their properties are required since the new interactions between the polymer and the nanoparticles can result in changes or the loss of hydrogels stimuli response. In order to understand the physicochemical aspects of the thermoresponsive systems, nanocomposites of poly(N-vinylcaprolactam) (PNVCL) and silica nanoparticles with different sizes and concentrations were synthesized. The UV-vis and DLS techniques showed that the PNVCL has a sharp phase transition at 34 °C, while the nanocomposites have a diffuse transition. The nanocomposites showed an initial coil-globule transition before the phase transition takes place. This was identified by the evolution of the hydrodynamic diameter of the nanocomposite globules before the cloud point temperature (Tcp), which remained constant for PNVCL. This new transition profile can be described by two stages in which microscopic volume transitions occur first, followed by the macroscopic transition that forms the hydrogel. These results show that the proposed nanocomposites can be designed to have tunable stimuli response to smaller temperature variations with the formation of intermediate globule states.

Wound healing applications of creams and "smart" hydrogels.

Although superficial wounds are often easy to treat for healthy individuals, there are some more severe types of wounds (burns, ulcers, diabetic wounds, etc.) that are a challenge for clinicians. A good therapeutic result is based on the delivery of a treatment at the right time, for the right patient. Our goal was to sum up useful knowledge regarding wound healing and wound treatments, based on creams and hydrogels with various active ingredients. We concluded that both preparations have application in preventing infections and promoting healing, but their efficacy is clearly conditioned by the type, depth, severity of the wound and patient profile. However, due to their superior versatility and capability of maintaining the integrity and functionality of the active ingredient, as well as it is controlled release at site, hydrogels are more suited for incorporating different active ingredients. New wound healing devices can combine smart hydrogel dressings with physical therapies to deliver a more efficient treatment to patients if the indications are appropriate.

Stimulation Modulates Adhesion and Mechanics of Hydrogel Adhesives.

The ability to modulate the adhesion of soft materials on-demand is desired for broad applications ranging from tissue repair to soft robotics. Research effort has been focused on the chemistry and architecture of interfaces, leaving the mechanics of soft adhesives overlooked. Stimuli-responsive mechanisms of smart hydrogels could be leveraged for achieving stimuli-responsive hydrogel adhesives that respond mechanically to external stimuli. Such stimuli-responsive hydrogel adhesives involve complex chemomechanical coupling and interfacial fracture phenomena, calling for mechanistic understanding to enable rational design. Here, we combine experimental, computational, and analytical approaches to study a thermo-responsive hydrogel adhesive. Experimentally, we show that the adhesion and mechanical properties of a stimuli-responsive hydrogel adhesive are both enhanced by the application of a stimulus. Our analysis further reveals that the enhanced adhesion stems from the increased fracture energy of the bulk hydrogel and the insignificant residual stress on the adhesive-tissue interface. This study presents a framework for designing stimuli-responsive hydrogel adhesives based on the modulation of bulk properties and sheds light on the development of smart adhesives with tunable mechanics.

Micromechanical Resonators for Ultrasound-Based Sensors

The current field of biomedical sensor platforms is substantial, and ever more creative approaches are envisioned and realized. Herein, we showcase a new platform technology for continuous biomedical analyte sensing that relies on the resonance absorption of ultrasound waves in microfabricated smart hydrogel structures (see Figure 1). Smart hydrogels can be tailored to be biocompatible and respond to many different analytes to undergo a volume-phase transition in response to changing levels of these biomarkers. [1,2] In addition, smart hydrogels can be designed to be biodegradable by basing them on compositions that include poly(ethylene glycol), poly(methyl methacrylate), or hyaluronic acid.Employing smart hydrogel structures as mechanical resonators and probing them using ultrasound [3,4] can provide an implantable sensor platform that is minimally invasive and free of transcutaneous wires. This approach makes use of the fact that hydrogel structures exhibit a resonant oscillation at certain ultrasound frequencies by strongly absorbing mechanical energy. As they swell or contract in response to the presence or absence of the target analyte, their resonance frequencies change, leading to a modification of their ultrasound absorption spectrum. Measuring this allows for the reconstruction of analyte concentration changes. In addition to that, tailoring the resonance frequency of the hydrogel resonator structures to different frequency ranges allows for multiplexing. We successfully demonstrate the use of this platform technology using glucose as a target metabolic marker in vitro and in a rat model (see Figure 2).Florian Solzbacher declares financial interest in Blackrock Microsystems LLC and Sentiomed, Inc. Jules Magda declares financial interest in Applied Biosensors LLC.[1] Buenger, F. Topuz, and J. Groll, “Hydrogels in sensing applications,” Prog. Polym. Sci., vol. 37, no. 12, pp. 1678–1719, 2012.[2] A. Peppas, J. Z. Hilt, A. Khademhosseini, and R. Langer, “Hydrogels in biology and medicine: From molecular principles to bionanotechnology,” Adv. Mater., vol. 18, no. 11, pp. 1345–1360, Jun. 2006.[3] Carovac, F. Smajlovic, and D. Junuzovic, “Application of Ultrasound in Medicine,” Acta Inform. Medica, vol. 19, no. 3, p. 168, 2011.[4] Troïani, J. R. Dion, and D. H. Burns, “Ultrasonic quantification using smart hydrogel sensors,” Talanta, vol. 83, no. 5, pp. 1371–1375, 2011. Figure 1

A self-healing smart photonic crystal hydrogel sensor for glucose and related saccharides.

A self-healing smart PhC hydrogel sensor that combines the optical property of photonic crystal and the dynamic regeneration property of boronate ester bond has been prepared for determination ofglucose and related saccharidesusing Debye diffraction ring detection. The boronate ester bond formed through phenylboronic acid and dopamine endows the hydrogel network self-healing ability, and the tensile stress of the healing hydrogel can recover to 94.4%; this excellent self-healing property can effectively improve the reliability and lifetime of thehydrogel. Dueto the high bonding capacity between 1,2- and 1,3-diol and phenylboronic acid, the hydrogel sensor has a good recognition ability for glucose and related saccharides. The reaction between the monosaccharides and the phenylboronic acid group makes the sensor swell and the diameter of the Debye diffraction ring decrease. The sensor shows good reuse and responsive ability for saccharides; the RSD of the recoverability assays is 4.3%. Thedetermination range of the sensor to glucose is 0.5 to 12mM. The sensor also has good response to glucose in urine, exhibiting potential application value in thepreliminary screening of diabetes. Although the sensor has poor selectivity for specific monosaccharides, the process of measuring the Debye ring makes the determination no longer rely on expensive and complicated equipment and greatly simplifies the determining process and reduces the cost of determination, which shows a broad application prospect. The boronate ester bond formed through phenylboronic acid and dopamine results in the self-healing property of hydrogel network, which can effectively improve the reliability and lifetime of hydrogel. And due to the high bonding capacity between 1,2- and 1,3-diol and phenylboronic acid, the smart hydrogel sensor has a good recognition ability for glucose and related saccharides. The reaction between the monosaccharides and the phenylboronic acid group breaks the original boronate ester bond; this will lead to a decrease in cross-linking density of the PhC hydrogel sensor and further makes the sensor swell and the diameter of the Debye diffraction ring decrease.

Smart Hydrogel Bilayers Prepared by Irradiation.

Environment-responsive hydrogel actuators have attracted tremendous attention due to their intriguing properties. Gamma radiation has been considered as a green cross-linking process for hydrogel synthesis, as toxic cross-linking agents and initiators were not required. In this work, chitosan/agar/P(N-isopropyl acrylamide-co-acrylamide) (CS/agar/P(NIPAM-co-AM)) and CS/agar/Montmorillonite (MMT)/PNIPAM temperature-sensitive hydrogel bilayers were synthesized via gamma radiation at room temperature. The mechanical properties and temperature sensitivity of hydrogels under different agar content and irradiation doses were explored. The enhancement of the mechanical properties of the composite hydrogel can be attributed to the presence of agar and MMT. Due to the different temperature sensitivities provided by the two layers of hydrogel, they can move autonomously and act as a flexible gripper as the temperature changes. Thanks to the antibacterial properties of the hydrogel, their storage time and service life may be improved. The as prepared hydrogel bilayers have potential applications in control devices, soft robots, artificial muscles and other fields.

Synthesis of pH responsive, photocrosslinked gelatin-based hydrogel system for control release of ceftriaxone

Stimuli-responsive or smart nanocarriers are emerging class of materials used for drug delivery and tissue engineering applications. The objective of this study was to develop environment friendly, economic and smart gelatin based hydrogel for controlled delivery of ceftriaxone. Gelatin was modified with furfuryl amine and converted to hydrogel via photo oxidation reaction, initiated with visible light in the presence of crosslinking agent (eosin Y and riboflavin) to enhance the mechanical properties and increase structural integrity of the hydrogel. The conjugated gelatin-furfuryl amine (GFA) was characterized by 1H NMR and FTIR techniques. An antimicrobial drug (ceftriaxone) was encapsulated in hydrogels systems (HG-E and HG-R) and its encapsulation efficiency was found as 88 % and 74 %, respectively. The in-vitro swelling property and release profile of the drug reveals that the behavior of hydrogel was pH dependent for both the hydrogels systems. Antibacterial study performed on HG-R hydrogel system via disc diffusion method revealed a greater zone of inhibition for Staphylococcus aureus. Findings of the presented work revealed the formation of an excellent, smart hydrogel system using Eosin-Y as cross-linker having greater encapsulation efficiency that can potentially be used for drug delivery application of ceftriaxone to enhance its therapeutic effects.

Robust and rapid responsive organic-inorganic hybrid bilayer hydrogel actuators with silicon nanoparticles as the cross-linker

Hydrogel actuators belong to a type of smart soft materials which can take place anisotropic thrust and/or displacement under various environmental stimuli including thermal, light, pH, humidity etc. Robust strength and rapid response are of critical importance to high-performance hydrogel actuators. Here we report the syntheses and investigations of mechanical properties for series novel organic-inorganic hydrogels by using vinyl functionalized silicon nanoparticles (SiNPs) as the cross-linker. The doped SiNPs significantly enhance the mechanical strength of polyacrylamide (PAAm) hydrogels. Furthermore, the SiNPs composite poly-N-isopropylacrylamide (PNIPAm) hydrogels exhibit rapid response in deswelling and swelling behaviours. The excellent mechanical and responsive properties are attributed to the enhanced rigidity via SiNPs doping into the hydrogel network and the improved water diffusion through mPEG branch chains on the surface of nanoparticles, respectively. As a proof of concept, a bilayer PNIPAm@PAAm hydrogel actuator is facilely synthesized via an in-situ polymerization process. This composite hydrogel actuator shows extremely fast response rate of directional bending in hot water, about 6 times faster than the control without doping of SiNPs. This work demonstrates that these SiNPs composite hydrogels provide enhanced mechanical and responsive performances and may expand the future applications in smart hydrogel materials.

Synergistic and receptor-mediated targeting of arthritic joints via intra-articular injectable smart hydrogels containing leflunomide-loaded lipid nanocarriers.

Intra-articular drug delivery represents a tempting strategy for local treatment of rheumatoid arthritis. Targeting drugs to inflamed joints bypasses systemic-related side effects. Albeit, rapid drug clearance and short joint residence limit intra-articular administration. Herein, injectable smart hydrogels comprising free/nanoencapsulated leflunomide (LEF) were developed. Nanostructured lipid carriers (NLCs), 200-300nm, were coated with either chondroitin sulfate (CHS), hyaluronic acid (HA), or chitosan (CS) to provide joint targetability. Coated NLCs were incorporated in either hyaluronic/pluronic (HP) or chitosan/β-glycerophosphate (CS/βGP) hydrogels. Optimized systems ensured convenient gelation time (14-100s), injectability (5-15s), formulation-dependent mechanical strength, and extended LEF release up to 51days. In vivo intra-articular injection in induced arthritis rat model revealed that rats treated with HA-coated NLCs showed the fastest recovery. Histopathological examination demonstrated perfect joint healing in case of HA-coated LEF-NLCs in CS/βGP thermogel manifested as minor erosion of subchondral bone, improved intensity of extracellular matrix, cartilage thickness, and chondrocyte number. Both HA- and CHS-coated NLCs reduced TNF-α level 4-5-fold relative to positive control. The feat would be achieved via active targeting to CD44 receptors overexpressed in the articular tissue, limiting chondrocyte apoptosis together with innate synergistic targetability by promoting chondrocyte proliferation and neovascularization, inhibiting the production of pro-inflammatory cytokines, thus enhancing cartilaginous tissue repair.

Rationally designed protein cross-linked hydrogel for bone regeneration via synergistic release of magnesium and zinc ions

The development of recombinant protein cross-linked injectable hydrogels with good mechanical strength and effective drug loading capacity for bone regeneration is extremely attractive and rarely reported. Here, we report the fabrication of a smart hydrogel delivery system by incorporating a rationally designed T4 lysozyme mutant (T4M) to mediate the localized delivery and synergistic release of Mg2+ and Zn2+ for bone repair. Apart from its intrinsic antibacterial properties, T4M bears abundant free amine groups on its surface to function as effective covalent crosslinkers to strengthen the hydrogel network as well as exhibits specific binding affinity to multivalent cations such as Zn2+. Moreover, the integrin receptor-binding Arg-Gly-Asp (RGD) sequence was introduced onto the C-terminus of T4 lysozyme to improve its cellular affinity and further facilitate rapid tissue regeneration. The final composite hydrogel displays excellent injectability, improved mechanical properties, antibacterial activity, and unique bioactivities. The effective loading of Mg2+/Zn2+ in the hydrogels could mediate the sequential and sustained release of Mg2+ and Zn2+, thereby resulting in synergistic enhancement on bone regeneration through modulation of the MAPK signaling pathway. We believe that the strategy proposed in this paper opens up a new route for developing protein cross-linked smart delivery systems for tissue regeneration.

An integrated liquid crystal sensing device assisted by the surfactant-embedded smart hydrogel

The abnormal levels of trypsin in biological fluids can cause some acute illnesses, such as acute pancreatitis, cystic fibrosis and malnutrition. In this paper, we report the development of an integrated liquid crystal (LC) sensing device for simple, rapid and sensitive detection of trypsin assisted by the surfactant-embedded smart hydrogel. The gelatin hydrogel mixed with CTAB is added into the side channel of the LC sensing device. In the presence of trypsin, the gelatin hydrogel is decomposed, which triggers instant release of CTAB into the aqueous solution. The CTAB molecules are then captured by the LCs and form CTAB monolayers at the aqueous/LC interface, which leads to change of the LC images from the bright to the dark appearance under the crossed polarizers. The integrated LC sensing device has a remarkable detection limit of 3.4 × 10−5 mg/mL. It is successfully employed to single-step detection of trypsin in human serum within 30 min. The integrated LC sensing device with use of the surfactant-embedded hydrogel takes advantages of single-step detection, high portability, remarkable sensitivity and fast response time, which provides a new perspective to facilitate development of user-friendly LC-based sensors.

Thermosensitive Chitosan-β-Glycerophosphate Hydrogels as Targeted Drug Delivery Systems: An Overview on Preparation and Their Applications.

Today, with the advances in technology and science, more advanced drug delivery formulations are required. One of these new systems is an intelligent hydrogel. These systems are affected by the environment or conditions that become a gel, stay in the circumstance for a certain period, and slowly release the drug. As an advantage, only a lower dose of the drug is required, and it provides less toxicity and minor damage to other tissues. Hydrogels are of different types, including temperature-sensitive, pH-sensitive, ion change-sensitive, and magnetic field-sensitive. In this study, we investigated a kind of temperature-sensitive smart hydrogel, which has a liquid form at room temperature and becomes gel with increasing temperature. Chitosan-β-glycerophosphate hydrogels have been researched and used in many studies. This study investigates the various factors that influence the gelation mechanism, such as gel formation rates, temperature, pH, time, and gel specificity. Hydrogels are used in many drug delivery systems and diseases, including nasal drug delivery, vaginal drug delivery, wound healing, peritoneal adhesion, ophthalmic drug delivery, tissue engineering, and peptide and protein delivery. Overall, the chitosan-β-glycerophosphate hydrogel is a suitable drug carrier for a wide range of drugs. It shows little toxicity to the body, is biodegradable, and is compatible with other organs. This system can be used in different conditions and different medication ways, such as oral, nasal, and injection.

Chronic Diabetic Wound Treatment: Green Tea Derivative Driven Smart Hydrogels with Desired Functions for Chronic Diabetic Wound Treatment (Adv. Funct. Mater. 18/2021)

In article number 2009442, Ang Li, Yilong Cheng, and co-workers develop a facile dressing strategy via one-pot radical copolymerization of acrylamide and the complex formed through a boronate ester bond by 3-acrylamido phenylboronic acid and green tea derivative epigallocatechin-3-gallate. The resulting hydrogels exhibit good mechanical strength, adequate tissue adhesiveness, fast self-healing capability, easy dressing change, and multiple therapeutic effects, all of which provide a promising and practical method for effective diabetic chronic wound management.

Multistimuli-Responsive Lanthanide-Containing Smart Luminescent Hydrogel Actuator.

Stimuli-responsive hydrogels are flourishing; however, a multiresponsive luminescent hydrogel actuator in which the stimuli do not interfere with each other is still difficult to produce. Here, a smart luminescent bilayer hydrogel actuator with shape memory and reversible luminescence switch behaviors under the co-stimulation of pH and heating is reported. Under alkaline condition, chitosan-containing layer generates physical microcrystals to fix the temporary shape of the actuator while lanthanide emits bright luminescence. Upon acid treatment, the actuator recovers to its original shape and the luminescence is quenched since the "antenna effect" between organic ligand and lanthanide ions is disrupted. It is to be noticed that this multiresponsive cycle can be repeated several times without interfering each other. This work is expected to have potential application prospects in the fields of biomimetic soft robots, sensors, and camouflage.

Free Radical Polymerization of Gold Nanoclusters and Hydrogels for Cell Capture and Light-Controlled Release.

Gold nanocluster (AuNC) decorated hydrogels have attracted considerable attention as versatile biomaterials. To date AuNCs and hydrogels have mainly been mixed as independent components. Here, we report the use of AuNCs as reactive monomers in the polymerization of hydrogels. We used a free radical polymerization to copolymerize AuNCs with acrylamide and N-acryloyl glycinamide to prepare stimuli-responsive smart hydrogels. Multiple C═C bonds were decorated on the surface of the AuNCs as active sites for polymerization. These C═C bonds not only protected the structure of the AuNCs from oxidation by free radicals during polymerization but also covalently connected the AuNCs with the polymer chains. This structure ensured good photothermal performance of the AuNCs while preserving the thermoresponsive hydrogen bonds of polymers. Moreover, the copolymerized AuNCs acted as cross-linkers, which improved the mechanical properties of the hydrogels. These smart hydrogels had good stability, efficient photothermal conversion, and a sensitive thermoresponsive. We examined their potential for capture of MDA-MB-231 cells with hyaluronic acid as target molecules. The captured cells were released under 660 nm irradiation. This process of targeted capture and light-controlled remote release could be repeatedly applied. These results suggest that systems based on AuNCs copolymerized with hydrogels have great potential for biomedical applications.