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Hydrogels are significant hydrophilic materials with 3D polymeric network structures, which have received much attention in recent decades. DNA-based hydrogel materials have been widely used for ti...

The pH-sensitive hydrogels are a unique class of three-dimensional hydrophilic polymers containing ionic pendant groups on their polymeric network. In response to the external pH variation, these materials span the volume of an aqueous/biological solution and swell without dissolution. Nowadays, the pH-sensitive hydrogels have attracted the growing interest of many researchers in various fields of researches such as drug delivery, tissue engineering, soft actuators, etc. which makes the simulation of their behavior crucial for optimum utilization. The essential prerequisite for the simulation of these materials is the swelling theory. In this article, we present a review of the fundamental phenomena in swelling theories of the pH-sensitive hydrogels. We also classify the swelling theories into two groups including the monophasic and multiphasic theories. Then, we briefly examine the most highlighted swelling theories in each group. The experimental data is essential for material parameters estimation as well as verification of the constitutive equations. Thus, we introduce and discuss the most highlighted experiments on the swelling and deswelling behavior of the pH-sensitive hydrogels as well.

Pectin hydrogel is a soft hydrocolloid with multifaceted utilities in the food sector. Substantial knowledge acquired on the gelation mechanisms and structure-function relationship of pectin has led to interesting functions of pectin hydrogel. Food applications of pectin hydrogels can be categorized under four headings: food ingredients/additives, food packaging, bioactive delivery and health management. The cross-linked and tangly three-dimensional structure of pectin gel renders it an ideal choice of wall material for the encapsulation of biomolecules and living cells; as a fat replacer and texturizer. Likewise, pectin hydrogel is an effective satiety inducer due to its ability to swell under the simulated gastric and intestinal conditions without losing its gel structure. Coating or composites of pectin hydrogel with proteins and other polysaccharides augment its functionality as an encapsulant, satiety-inducer and food packaging material. Low-methoxyl pectin gel is an appropriate food ink for 3D printing applications due to its viscoelastic properties, adaptable microstructure and texture properties. This review aims at explaining all the applications of pectin hydrogels, as mentioned above. A comprehensive discussion is presented on the approaches by which pectin hydrogel can be transformed as a resourceful material by controlling its dimensions, state, and rheology. The final sections of this article emphasize the recent research trends in this discipline, such as the development of smart hydrogels, injectable gels, aerogels, xerogels and oleogels from pectin.

Smart hydrogels are of great interest in areas such as drug delivery and sensing. Dendrimer-based hydrogels can exhibit tunable properties due to their structural precision. We prepared hydrogels from self-immolative dendrons. Controlled hydrogel degradation in response to light was demonstrated and the hydrogel properties as a function of dendron generation were compared.

Stimuli-responsive smart hydrogels have garnered considerable interest for their potential in biomedical applications. While widely utilized, little is known about the rheological and mechanical properties of the hydrogels with respect to the type of cross-linker in a systematic manner. In this study, we present a facile synthetic route toward ABA triblock copolymer hydrogels based on poly(ethylene oxide) (PEO). Two classes of hydrogels were prepared by employing the functional allyl glycidyl ether (AGE) monomer during the polymerization followed by the subsequent post-polymerization modification of prepared PAGE

Among modern drug formulations, stimuli-responsive hydrogels also called "smart hydrogels" deserve a special attention. The basic feature of this system is the ability to change their mechanical properties, swelling ability, hydrophilicity, bioactive molecules permeability, etc., influenced by various stimuli, such as temperature, pH, electromagnetic radiation, magnetic field and biological factors. Therefore, stimuli-responsive matrices can be potentially used in tissue engineering, cell cultures and technology of innovative drug delivery systems (DDSs), releasing the active substances under the control of internal or external stimuli. Moreover, smart hydrogels can be used as injectable DDSs, due to gel-sol transition connected with in situ cross-linking process. Innovative smart hydrogel DDSs can be utilized as matrices for targeted therapy, which enhances the effectiveness of tumor chemotherapy and subsequently limits systemic toxicity. External stimulus sensitivity allows remote control over the drug release profile and gel formation. On the other hand, internal factors provide drg accumulation in tumor tissue and reduce the concentration of active drug form in healthy tissue. In this report, we summarise the basic knowledge and chemical strategies for the synthetic smart hydrogel DDSs applied in antitumor therapy.

Due to their hydrophilic, biocompatible and adjustability properties, hydrogels have received a lot of attention. The introduction of nucleic acids has made hydrogels highly stimuli-responsiveness and they have become a new generation of intelligent biomaterials. In this review, the development and utilization of smart nucleic acid hydrogels (NAHs) with a high stimulation responsiveness were elaborated systematically. We discussed NAHs with a high stimuli-responsiveness, including pure NAHs and hybrid NAHs. In particular, four stimulation factors of NAHs were described in details, including pH, ions, small molecular substances, and temperature. The research progress of nucleic acid hydrogels in biomedical applications in recent years is comprehensively discussed. Finally, the opportunities and challenges facing the future development of nucleic acid hydrogels are also discussed.

Peptide-based hydrogels have captivated remarkable attention in recent times and serve as an excellent platform for biomedical applications owing to the impressive amalgamation of unique properties such as biocompatibility, biodegradability, easily tunable hydrophilicity/hydrophobicity, modular incorporation of stimuli sensitivity and other functionalities, adjustable mechanical stiffness/rigidity and close mimicry to biological molecules. Putting all these on the same plate offers smart soft materials that can be used for tissue engineering, drug delivery, 3D bioprinting, wound healing to name a few. A plethora of work has been accomplished and a significant progress has been realized using these peptide-based platforms. However, designing hydrogelators with the desired functionalities and their self-assembled nanostructures is still highly serendipitous in nature and thus a roadmap providing guidelines toward designing and preparing these soft-materials and applying them for a desired goal is a pressing need of the hour. This review aims to provide a concise outline for that purpose and the design principles of peptide-based hydrogels along with their potential for biomedical applications are discussed with the help of selected recent reports.

In this paper, injectable, thermosensitive smart hydrogel local drug delivery systems (LDDSs) releasing the model antitumour drug 5-fluorouracil (5-FU) were developed. The systems were based on biodegradable triblock copolymers synthesized via ring opening polymerization (ROP) of ε-caprolactone (CL) in the presence of poly(ethylene glycol) (PEG) and zirconium(IV) acetylacetonate (Zr(acac)4), as co-initiator and catalyst, respectively. The structure, molecular weight (Mn) and molecular weight distribution (Đ) of the synthesized materials was studied in detail using nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) techniques, the optimal synthesis conditions were determined. The structure corresponded well to the theoretical assumptions. The produced hydrogels demonstrated a sharp sol–gel transition at temperature close to physiological value, forming a stable gel with good mechanical properties at 37 °C. The kinetics and mechanism of in vitro 5-FU release were characterized by zero order, first order, Higuchi and Korsmeyer–Peppas mathematical models. The obtained results indicate good release control, the kinetics were generally defined as first order according to the predominant diffusion mechanism, and the total drug release time was approximately 12 h. The copolymers were considered to be biodegradable and non-toxic, the resulting hydrogels appear to be promising as short-term LDDSs, potentially useful in antitumor therapy.

Hydrogels are polymeric three-dimensional network structures with high water content. Due to their superior biocompatibility and low toxicity, hydrogels play a significant role in the biomedical fields. Hydrogels are categorized by the composition from natural polymers to synthetic polymers. To meet the complicated situation in the biomedical applications, suitable host–guest supramolecular interactions are rationally selected. This review will have an introduction of hydrogel classification based on the formulation molecules, and then a discussion over the rational design of the intelligent hydrogel to the environmental stimuli such as temperature, irradiation, pH, and targeted biomolecules. Further, the applications of rationally designed smart hydrogels in the biomedical field will be presented, such as tissue repair, drug delivery, and cancer therapy. Finally, the perspectives and the challenges of smart hydrogels will be outlined.

Hydrogels have attracted much attention especially due to their biocompatibility and their potential for stimulus responsiveness. By combining hydrogels with aptamers, biological recognition and responsiveness can be added to hydrogels, thereby opening path to advanced applications in biosensing and biomedicine. Within this chapter aptamers will be introduced and their contributions to biological responsiveness of hydrogels will be described. Especially the aptamer-based mechanisms that result in biological responsiveness will be explained and examples for the application of these mechanisms will be given ranging from rather simple sensing approaches to advanced materials for tissue engineering and drug delivery. Since aptamers are not only highly specific bioreceptors, but represent switchable structures that can be easily manipulated using well-known DNA techniques, the combination of aptamers and hydrogels facilitates the rational design of well-programmable and target-responsive smart hydrogels.

Chitosan as a natural polysaccharide have been widely applied in biomedicine due to their outstanding biodegradability, non-toxic, and low-price. As carriers, the multi-functional chitosan hydrogels can be prepared by physical and chemical modification to form smart hydrogels to release cargoes. The smart hydrogels can generate sol-gel phase transition while gaining stimulus from the environment including pH, temperature, photo, and so forth. In recent years, a variety of therapeutic approaches such as gene therapy, chemotherapy, and combined therapy can be achieved by combining chitosan-based hydrogels with therapeutic agents.This review reports the state-of-the-art progress of chitosan-based hydrogel delivery systems and some new technologies and discusses the smart chitosan hydrogels. In addition, the current trends and the future prospects together with the drawbacks of chitosan hydrogels as biomaterials are also discussed.Chitosan as a natural material has been widely studied and reported. Due to its many advantages, the development of chitosan has been applied in all walks of life. However, the application of chitosan hydrogels in disease therapy is limited due to their weak physical and chemical properties in vivo. Thus, it is high likely that chitosan-based hydrogels will contribute to further research and exploration.

Tissue engineering is a promising strategy for the repair and regeneration of damaged tissues or organs. Biomaterials are one of the most important components in tissue engineering. Recently, magnetic hydrogels, which are fabricated using iron oxide-based particles and different types of hydrogel matrices, are becoming more and more attractive in biomedical applications by taking advantage of their biocompatibility, controlled architectures, and smart response to magnetic field remotely. In this literature review, the aim is to summarize the current development of magnetically sensitive smart hydrogels in tissue engineering, which is of great importance but has not yet been comprehensively viewed.

We report a new strategy for fabricating a smart low molecular weight hydrogel based on dynamic covalent chemistry from a bola-type supra-gelator, which was facilely fabricated in situ from two non-assembling building blocks, (3-(2-(4-formylphenoxy) ethyl)-1-methyl imidazolium bromide, MA) and (3,3'-dithiobis (propionohydrazide), DSPDZ), through dynamic acylhydrazone bonding. The obtained low molecular weight hydrogels exhibited redox-responsive and controllable self-healing properties. The role of dynamic covalent bonding in the formation of smart hydrogels is revealed in this study, which provides a simple and bottom-up method for constructing smart low molecular weight hydrogels.

Aims: In the present study, we evaluated the use of egg white proteins in alginate scaffolds and calcium alginate for the formulation of Lactobacillus casei and Lactobacillus acidophilus in the stomach acidic conditions. Material and Methods: after microorganism’s encapsulation in egg white proteins in alginate, survival assays and release in different conditions were evaluated. Scanning electron microscope and Fourier-transform infrared spectroscopy were used for analysis. Results: The results showed the high potential of this type of formulation in protecting the probiotics from stomach acidic conditions that is due to the significant increase in survival of the bacteria. Our study showed that the viability of the L. casei to free L. acidophilus had much less, however, with the encapsulation of the bacteria Egg white proteins in Alginate increased their survival significantly. Specially for the L. casei. Swelling and shrinkage behavior of egg white proteins in alginate capsules in different pH showed that the swelling of the capsule in the distilled water in the neutral terms had more inflation- capacity than similar position in terms of gastric acidity. Conclusions: the use of egg white proteins-Alginate for encapsulation of probiotics enhanced the stability of these microorganisms in simulated gastric environments adverse conditions.

Smart hydrogels have received increasing attention for their great potential for the applications in many fields. Herein, we report a facile approach to prepare a class of dual-responsive hydrogels assembled from synthetic statistical/block thermal-responsive copoly(L-glutamate)s copolymerized with poly(ethylene glycol), which were prepared by ring-opening polymerization (ROP) and post-modification strategy. The incorporation of oligo(ethylene glycol) (OEG) and glutamic acid residues offers the gels with thermal- and pH-responsive properties simultaneously. We have systematically studied the influence of both temperature and pH on the gelation behaviors of these copolymers. It is found that the increase of glutamic acid content and solution pH values can significantly suppress the gelation ability of the samples. Circular dichroism (CD) results show that the α-helix conformation appears to be the dominant secondary conformation. More interestingly, the gelation property of the block copolymer with statistical thermal-responsive copoly(L-glutamate)s shows greater dependence on pH as compared to that with block segments due to the distinct morphology of the self-assemblies. The obtained hydrogels exhibit pH-dependent and thermal-responsive gelation behaviors, which enable them as an ideal smart hydrogel system for biomedical applications.

Traditional intravenous chemotherapy is relative to many systemic side effects, including myelosuppression, liver or kidney dysfunction, and neurotoxicity. As an alternative method, the injectable hydrogel can efficiently avoid these problems by releasing drugs topically at the tumor site. With advantages of localized drug toxicity in the tumor site, proper injectable hydrogel as the drug delivery system has become a research hotspot. Based on different types and stages of cancer, a variety of hydrogel drug delivery systems were developed, including thermosensitive, pH-sensitive, photosensitive, and dual-sensitive hydrogel. In this review, the latest developments of these hydrogels and related drug delivery systems were summarized. In summary, our increasing knowledge of injectable hydrogel for localized cancer therapy ensures us that it is a more durable and effective approach than traditional chemotherapy. Smart release system reacting to different stimuli at different time according to the micro-environment changes in the tumor site is a promising tendency for further studies.

Hydrogels prepared from natural polymers have received immense considerations over the past decade due to their safe nature, biocompatibility, hydrophilic properties, and biodegradable nature. More recently, when treated with electroactive materials, these hydrogels were endowed with high electrical conductivity, electrochemical redox properties, and electromechanical properties; consequently, forming a smart hydrogel. The biological properties of these smart hydrogels, classified as electroconductive hydrogels, can be combined with electronics. Thus, they are considered as good candidates for some potential uses, which include bioconductors, biosensors, electro-stimulated drug delivery systems, as well as neuron-, muscle-, and skin-tissue engineering. However, there is lacking comprehensive information on the current state of these electroconductive hydrogels which complicates our understanding of this new type of biomaterials as well as their potential applications. Hence, this review provides a summary on the current development of electroconductive natural polymer-based hydrogels (ENPHs). We have introduced various types of ENPHs, with a brief description of their advantages and shortcomings. In addition, emerging technologies regarding their synthesis developed during the past decade are discussed. Finally, two attractive potential applications of ENPHs, cell culture and biomedical devices, are reviewed, along with their current challenges.

A facile polymer-assisted method achieves simultaneous exfoliation and noncovalent functionalization of MoSe2 nanosheets. The nanosheet dispersion can further assemble into a novel "smart" nanocomposite hydrogel, whose dual-responsive (photo- and thermoresponsive) behavior is reversible and can be controllably tailored by varying the distribution of hydrophilic and hydrophobic groups in the polymer.

Development of polymer-based smart materials, which can autonomously alter their physical and/or chemical properties when exposed to external stimuli, is a thriving research frontier in contemporary advanced functional materials science. Poly(N-isopropylacrylamide) (PNIPAM)-based smart hydrogels are known to exhibit distinct thermo-responsive properties near a lower critical solution temperature (LCST), which have found diverse promising applications such as smart coating, drug delivery, tissue regeneration, and artificial muscles. In this review, we provide an up-to-date account on the recent developments in advanced functional PNIPAM-based smart hydrogels and their emerging technological applications in the fields of smart actuators, photonic crystals, smart windows and novel biomedical applications. The fundamental design and synthetic strategies of PNIPAM-based smart hydrogels are discussed. Their unique properties, underlying mechanisms and potential applications in different fields are highlighted. Finally, this review provides a brief conclusion and enumerates the challenges and opportunities in this rising area of research and development involving these intriguing polymer-based advanced smart systems rooted in chemistry and materials science. It is expected that this review would provide significant insights for the development of reconfigurable and programmable advanced smart materials with numerous possibilities, prompting the rapid advancement of this highly interdisciplinary area, which encompasses materials science, polymer science, synthetic chemistry, device engineering, physics, biology, nanoscience and nanotechnology.

The advances in the field of biomaterials have led to several studies on alternative biocompatible devices and to their development focusing on their properties, benefits, limitations, and utilization of alternative resources. Due to their advantages like biocompatibility, biodegradability, and low costs, polysaccharides have been widely used in the development of hydrogels. Among the polysaccharides, which are studied on hydrogel preparations, chitosan (pure or combined with natural/synthetic polymers) have been widely investigated for use in biomedical field, especially due to its biocompatibility and non-toxicity. Thus, the chitosan-based hydrogels play a crucial role in the development of new biomaterials. Many crosslinking (or polymerization) approaches have been developed to convert chitosan into smart hydrogels, with the aim of obtaining new drug delivery devices. Such hydrogels can also undergo changes in their physical-chemical properties in response to environmental changes such as pH, ionic strength, temperature, magnetic field, and so forth. In view of potential applications of chitosan-based hydrogels, this chapter focuses on the most recent progress made with respect to preparation, properties, and their salient accomplishments in drug delivery.

Well-defined amphiphilic triblock poly(sodium methacrylate)-polystyrene-poly(sodium methacrylate) (PMAA-b-PS-b-PMAA) copolymers characterized by a different length of either the hydrophilic or the hydrophobic block have been synthesized by ATRP. In solution the micelle-like aggregates consist of a collapsed PS core surrounded by stretched charged PMAA chains. The micelles are kinetically ‘frozen’ and as a consequence the triblock copolymers do not show a significant surface activity. The hydrophilic block length has a major influence on the rheology, the shortest PMAA blocks yielding the strongest gels (at the same total weight concentration). The hydrophobic block length has only a minor influence until a certain threshold, below which the hydrophobic interactions are too weak resulting in weak gels. A mathematical model is used to describe the micelle radius and the results were in good agreement with the experimentally found radius in transmission electron microscopy. The influences of the ionic strength, pH and temperature on the rheology has also been investigated, showing the potential of these polymers as smart hydrogels. The change in conformation of the hydrophilic corona from the collapsed state to the stretched state by changing the pH was quantified with zeta-potential measurements. To the best of our knowledge, this is the first systematic investigation of this kind of triblock copolymers in terms of their rheological behavior in water.

The physiological milieu of healthy skin is slightly acidic, with a pH value between 4 and 6, whereas for skin with chronic or infected wounds, the pH value is above 7.3. As testing pH value is an effective way to monitor the status of wounds, a novel smart hydrogel wound patch incorporating modified pH indicator dyes was developed in this study. Phenol red (PR), the dye molecule, was successfully modified with methacrylate (MA) to allow a copolymerization with the alginate/polyacrylamide (PAAm) hydrogel matrix. This covalent attachment prevented the dye from leaching out of the matrix. The prepared pH-responsive hydrogel patch exhibited a porous internal structure, excellent mechanical property, and high swelling ratio, as well as an appropriate water vapour transmission rate. Mechanical responses of alginate/P(AAm-MAPR) hydrogel patches under different calcium and water contents were also investigated to consider the case of exudate accumulation into hydrogels. Results showed that increased calcium amount and reduced water content significantly improved the Young's modulus and elongation at break of the hydrogels. These characteristics indicated the suitability of hydrogels as wound dressing materials. When pH increased, the color of the hydrogel patches underwent a transition from yellow (pH 5, 6 and 7) to orange (7.4 and 8), and finally to red (pH 9). This range of color change matches the clinically-meaningful pH range of chronic or infected wounds. Therefore, our developed hydrogels could be applied as promising wound dressing materials to monitor the wound healing process by a simple colorimetric display, thus providing a desirable substrate for printed electronics for smart wound dressing.

During the past few decades, thiomers have attracted interest as responsive-polymers in the design of smart hydrogels, due to thiol reactivity to physical stimuli (i.e., pH, oxygen, UV/Vis irradiation). However, thiomer potentialities have been limited by their low thiolation degree and lack of multi-responsiveness to physical cues. In this work, a new class of thiomers with tailored thiolation degree and sensitivity to multiple physical stimuli was developed. To this aim, a polyurethane (33,000 Da) was synthesised from Poloxamer® 407, 1,6-diisocyanatohexane and N-Boc diethanolamine. Secondary amino groups were exposed through Boc-removal (yield 80%, assessed by 1H NMR) giving up to 4.5 × 1020 ± 1.8 × 1019 –NH units/gpolymer (Orange II Sodium Salt colorimetric assay) without polymer chemical degradation. Polymer thermo-responsiveness was proved by the increase in micelle hydrodynamic diameter upon system heating up to 45 °C and through estimated critical micellar temperatures. Thioglycolic acid grafting to exposed amines via carbodiimide chemistry was optimised to give up to 1.73 × 1019 thiols/gpolymer (Ellman's method), while minimising disulphide bond formation. Finally, the best storage conditions against oxidation were investigated by quantifying free thiols at different time points.

The ever-increasing developments in pharmaceutical formulations have led to the widespread use of biodegradable polymers in various forms and configurations. In particular, interpenetrating network (IPN) and semi-IPN polymer structures that are capable of releasing drugs in a controlled manner have gained much wider importance in recent years.Recently, IPNs and semi-IPNs have emerged as innovative materials of choice in controlled release (CR) of drugs as the release from these systems depends on pH of the media and temperature in addition to the nature of the system. These networks can be prepared as smart hydrogels following chemical or physical crosslinking methods to show remarkable drug release patterns compared to single polymer systems.A large number of IPNs and semi-IPNs have been reported in the literature. The present review is focused on the preparation methods and their CR properties with reference to anticancer, anti-asthmatic, antibiotic, anti-inflammatory, anti-tuberculosis and antihypertensive drugs, as majority of these drugs have been reported to be the ideal choices for using IPNs and semi-IPNs.

The ability of hydrophilic chain segments in polymer networks to strongly interact with water allows the volumetric expansion of the material and formation of a hydrogel. When polymer chain segments undergo reversible hydration depending on environmental conditions, smart hydrogels can be realized, which are able to shrink/swell and thus alter their volume on demand. In contrast, implementing the capacity of hydrogels to switch their shape rather than volume demands more sophisticated chemical approaches and structural concepts. In this Account, the principles of hydrogel network design, incorporation of molecular switches, and hydrogel microstructures are summarized that enable a spatially directed actuation of hydrogels by a shape-memory effect (SME) without major volume alteration. The SME involves an elastic deformation (programming) of samples, which are temporarily fixed by reversible covalent or physical cross-links resulting in a temporary shape. The material can reverse to the original shape when these molecular switches are affected by application of a suitable stimulus. Hydrophobic shape-memory polymers (SMPs), which are established with complex functions including multiple or reversible shape-switching, may provide inspiration for the molecular architecture of shape-memory hydrogels (SMHs), but cannot be identically copied in the world of hydrophilic soft materials. For instance, fixation of the temporary shape requires cross-links to be formed also in an aqueous environment, which may not be realized, for example, by crystalline domains from the hydrophilic main chains as these may dissolve in presence of water. Accordingly, dual-shape hydrogels have evolved, where, for example, hydrophobic crystallizable side chains have been linked into hydrophilic polymer networks to act as temperature-sensitive temporary cross-links. By incorporating a second type of such side chains, triple-shape hydrogels can be realized. Considering the typically given light permeability of hydrogels and the fully hydrated state with easy permeation by small molecules, other types of stimuli like light, pH, or ions can be employed that may not be easily used in hydrophobic SMPs. In some cases, those molecular switches can respond to more than one stimulus, thus increasing the number of opportunities to induce actuation of these synthetic hydrogels. Beyond this, biopolymer-based hydrogels can be equipped with a shape switching function when facilitating, for example, triple helix formation in proteins or ionic interactions in polysaccharides. Eventually, microstructured SMHs such as hybrid or porous structures can combine the shape-switching function with an improved performance by helping to overcome frequent shortcomings of hydrogels such as low mechanical strength or volume change upon temporary cross-link cleavage. Specifically, shape switching without major volume alteration is possible in porous SMHs by decoupling small volume changes of pore walls on the microscale and the macroscopic sample size. Furthermore, oligomeric rather than short aliphatic side chains as molecular switches allow stabilization of the sample volumes. Based on those structural principles and switching functionalities, SMHs have already entered into applications as soft actuators and are considered, for example, for cell manipulation in biomedicine. In the context of those applications, switching kinetics, switching forces, and reversibility of switching are aspects to be further explored.

Smart hydrogels that respond to magnetic fields have attracted increasing interest in recent years. This is as a result of their numerous potential applications such as tunable delivery vehicles, magnetic resonance imaging contrast agents, hyperthermal therapy agents, etc. In this review, we summarize the methods for preparing magnetic hydrogels. Then we give an overview of magnetic hydrogels with various applications. Finally, the current limitations in the preparation and application of magnetic hydrogels are discussed and perspectives will be proposed for the next generation of hydrogels. © 2016 Society of Chemical Industry

Marine mussels secrete adhesive proteins that enable these organisms to bind tenaciously to surfaces in a wet, saline, and turbulent environment. One of the unique structural features of these adhesive proteins is the presence of DOPA, an amino acid consisting of an adhesive catechol side chain. This chapter reviews the reversible and irreversible chemistries of catechol and various methods in creating catechol-functionalized polymeric materials. Finally, recent applications of these biomimetic polymers in designing tissue adhesives, antifouling coatings, delivery vehicles for therapeutic drugs and cells, and smart hydrogels and adhesives are reviewed.

A novel and facile assembly strategy has been successfully developed to construct smart nanocomposite (NC) hydrogels with inhomogeneous structures using nanoclay-cross-linked stimuli-responsive hydrogel subunits as building blocks via rearranged hydrogen bonding between polymers and clay nanosheets. The assembled thermoresponsive poly(N-isopropylacrylamide-co-acrylamide) (poly(NIPAM-co-AM)) hydrogels with various inhomogeneous structures exhibit excellent mechanical properties due to plenty of new hydrogen bonding interactions created at the interface for locking the NC hydrogel subunits, which are strong enough to tolerate external forces such as high levels of elongations and multicycles of swelling/deswelling operations. The proposed approach is featured with flexibility and designability to build assembled hydrogels with diverse architectures for achieving various responsive deformations, which are highly promising for stimuli-responsive manipulation such as actuation, encapsulation, and cargo transportation. Our assembly strategy creates new opportunities for further developing mechanically strong hydrogel systems with complex architectures that composed of diverse internal structures, multistimuli-responsive properties, and controllable shape deformation behaviors in the soft robots and actuators fields.

Smart hydrogels are promising materials for actuators and sensors, as they can respond to small changes in their environment with a large property change. Hydrogels can respond to a variety of stimuli, for example temperature, pH, metal ions, etc. In this article, the synthesis and characterization of polyampholyte hydrogels based on open chain ligands showing pH and metal ion sensitivity are described. Copolymer and terpolymer gels using different mixtures of monomers i.e., N-[2-(dimethylaminoethyl)acrylamide] (DMAEAAm), N,N-dimethylacrylamide (DMAAm), acrylic acid (AA) and 2-acrylamido-2-methyl-1-propanesulphonic acid (AMPS), have been synthesized. The effect of copolymer composition, i.e., the ratio and amount of ionic monomers and the degree of crosslinking on the swelling characteristics, was evaluated as a function of pH. On this basis, metal ion sensitivity measurements were performed at selected pH values. The metal ion sensitivity was measured by varying the concentration of Cu2+, Zn2+ and Ag+ ions under acidic pH conditions.

This article deals with the modification of medicinally important psyllium polysaccharide with acrylamide through radiation crosslinked polymerisation for the design of double potential hydrogels meant for slow release of insulin. Here the double potential is due to the inherent blood sugar lowering ability of psyllium and release of insulin in controlled manner from the drug loaded hydrogels. Synthesis of hydrogels and their characterisation by scanning electron micrography (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and swelling studies have been discussed. The release dynamics of model drug insulin from the hydrogels has been studied for the evaluation of the release mechanism. The release of the drug from the hydrogels occurred through non-Fickian diffusion mechanism. Cet article traite de la modification du psyllium polysaccharide d'une importance therapeutique avec l'acrylamide par la reticulation sous rayonnement pour la conception d'hydrogels a potentiel double pour la liberation lente de l'insuline. Ici, le potentiel double est du a la capacite inherente de baisse de la glycemie du psyllium et la liberation de l'insuline de maniere controlee des hydrogels charges de medicament. On a discute de la synthese des hydrogels et leur caracterization par MEB, FTIR, analyse thermo-gravimetrique et etudes de gonflement. La dynamique de liberation de l'insuline (medicament modele) des hydrogels a ete etudiee pour l'evaluation du mecanisme de liberation. La liberation du medicament des hydrogels s'est produite par le biais d'un mecanisme de diffusion non-Fickien.

Smart hydrogels, random copolymers composed of poly(acrylic acid) and poly(vinyl sulfonic acid), were prepared. The swelling ratios at various temperatures and pHs, the deswelling water ratio under an electric field, and the free water and bound water contents of the hydrogels were measured. The hydrogels exhibited very high swelling ratios, in the range of 8200%–18 000%, at 37 °C, and showed temperature- and pH-dependent swelling behaviour. The deswelling water ratio of the hydrogel sample CO1 showed a weight reduction of about 80% under a 5 V applied voltage. The free water contents in hydrogel samples CO1, CO2 and CO3 were 47.71%, 40.92% and 37.27% respectively in pure water.