Swelling behavior of thermosensitive nanocomposite hydrogels composed of oligo(ethylene glycol) methacrylates and clay

Doped Carbon Quantum Dots Reinforced Hydrogels for Sustained Delivery of Molecular Cargo

Hydrogels have emerged as important soft materials with numerous applications in fields including biomedicine, biomimetic smart materials, and electrochemistry. Because of their outstanding photo-physical properties and prolonged colloidal stability, the serendipitous findings of carbon quantum dots (CQDs) have introduced a new topic of investigation for materials scientists. CQDs confined polymeric hydrogel nanocomposites have emerged as novel materials with integrated properties of the individual constituents, resulting in vital uses in the realm of soft nanomaterials. Immobilizing CQDs within hydrogels has been shown to be a smart tactic for preventing the aggregation-caused quenching effect and also for manipulating the characteristics of hydrogels and introducing new properties. The combination of these two very different types of materials results in not only structural diversity but also significant improvements in many property aspects, leading to novel multifunctional materials. This review covers the synthesis of doped CQDs, different fabrication techniques for nanostructured materials made of CQDs and polymers, as well as their applications in sustained drug delivery. Finally, a brief overview of the present market and future perspectives are discussed.

Poly(N-vinylpyrrolidone)-Laponite XLG Nanocomposite Hydrogels: Characterization, Properties and Comparison with Divinyl Monomer-Crosslinked Hydrogels

The present work investigates, for the first time, the synthesis and properties of some nanocomposite (NC) hydrogels obtained by the aqueous solution free radical polymerization of N-vinylpyrrolidone (NVP) in the presence of Laponite XLG (XLG) as a crosslinker, in comparison with the corresponding hydrogels prepared by using two conventional crosslinking divinyl monomers: N,N'-methylenebisacrylamide (MBA) and tri(ethylene glycol) divinyl ether (DVE). The structure and properties of the hydrogels were studied by FTIR, TEM, XRD, SEM, swelling and rheological and compressive mechanical measurements. The results showed that DVE and XLG are much better crosslinking agents for the synthesis of PNVP hydrogels than MBA, leading to larger gel fractions and more homogeneous network hydrogels. The hydrogels crosslinked by either DVE or XLG displayed comparable viscoelastic and compressive mechanical properties under the experimental conditions employed. The properties of the XLG-crosslinked hydrogels steadily improved as the clay content increased. The addition of XLG as a second crosslinker together with a divinyl monomer strongly enhanced the material properties in comparison with the hydrogels crosslinked by only one of the crosslinkers involved. The FTIR analyses suggested that the crosslinking of the NC hydrogels was the result of two different interactions occurring between the clay platelets and the PNVP chains. Laponite XLG displayed a uniform distribution within the NC hydrogels, the clay being mostly exfoliated. However, a small number of platelet agglomerations were still present. The PNVP hydrogels described here may find applications for water purification and in the biomedical field as drug delivery systems or wound dressings.

Clay-Based Nanocomposite Hydrogels for Biomedical Applications: A Review

In recent decades, new and improved materials have been developed with a significant interest in three-dimensional (3D) scaffolds that can cope with the diverse needs of the expanding biomedical field and promote the required biological response in multiple applications. Due to their biocompatibility, ability to encapsulate and deliver drugs, and capacity to mimic the extracellular matrix (ECM), typical hydrogels have been extensively investigated in the biomedical and biotechnological fields. The major limitations of hydrogels include poor mechanical integrity and limited cell interaction, restricting their broad applicability. To overcome these limitations, an emerging approach, aimed at the generation of hybrid materials with synergistic effects, is focused on incorporating nanoparticles (NPs) within polymeric gels to achieve nanocomposites with tailored functionality and improved properties. This review focuses on the unique contributions of clay nanoparticles, regarding the recent developments of clay-based nanocomposite hydrogels, with an emphasis on biomedical applications.

Improved Cooling Performance of Hydrogel Wound Dressings via Integrating Thermal Conductivity and Heat Storage Capacity for Burn Therapy

Burn injury has become a crucial public health issue worldwide. It is necessary to explore new methods to reduce heat damage and improve healing efficiency during burn injury treatment. In this study, a kind of hydrogel combining heat storage capacity and thermal conductivity was fabricated via a one-pot method for burn therapy. The novel hydrogel was easily prepared by in situ cross-linking polymerization, using poly(ethylene glycol) (PEG) derivatives, oligo(ethylene glycol) methacrylate and 2-(2-methoxyethoxy) ethyl methacrylate, as thermally responsive base materials and hydroxylated multiwall carbon nanotubes (CNT-OH) as thermally conductive fillers. By dispersing CNT-OH, a thermally conductive network was formed in the hydrogel, leading to an increase in the thermal conductivity. The cooling performance, thermal conductivity, heat storage property, swelling performance, rheological and mechanical properties, biocompatibility, in vivo cooling effect, and wound healing properties of the prepared hydrogel were systematically investigated. The hydrogel consisted of thermally responsive PEG derivatives, and CNT-OH performed a function of rapid heat absorption, further reduced thermal damage, and promoted wound healing. The improved cooling performance of the hydrogel was ascribed to the improved thermal conductivity, enhanced heat storage capacity, and good adhesive ability. Thus, the hydrogel has great potential to be practically applied in burn therapy, laser treatment, cooling fabrics, heat-protective clothing, and other emergency scenarios.

Ligament-Inspired Tough and Anisotropic Fibrous Gel Belt with Programed Shape Deformations via Dynamic Stretching

Nature provides perpetual inspiration for exploring anisotropic materials to implement complex functions and motions like biological organisms. In particular, fibrous hydrogel-based anisotropic aggregates have attracted tremendous interest as fantastic materials for development into artificial ligaments or muscles. Such aggregates combine the structural anisotropy and macroscopic flexibility of fiber materials, with the intelligence, softness, and wetness of hydrogel materials. However, controlled fabrication of such hydrogels with aligned microstructures, even in a macroscopic level, remains a challenge. Here, a facile and general strategy was proposed to develop ligament-inspired multistructural (mono/bilayer) gel belts via dynamic stretching of multistrand pregels, accompanied by the simultaneous assembly of hydrogel fibers. The resultant gel belts evolved into anisotropic and aligned micro- and macrostructures, exhibiting high elastic moduli (0.01-23.5 MPa) and unique anisotropic swelling behaviors. Through further physical and chemical structure design, bioinspired multiple fibrous gel-based actuators were developed to achieve anisotropic, relatively fast (within 60 s), and delicate macroscopic shape deformations. This work provides a great platform for the design and construction of next-generation soft materials for biomimetic tissues.

Equilibrium Swelling of Biocompatible Thermo-Responsive Copolymer Gels

Biomedical applications of thermo-responsive (TR) hydrogels require these materials to be biocompatible, non-cytotoxic, and non-immunogenic. Due to serious concerns regarding potential toxicity of poly(N-isopropylacrylamide) (PNIPAm), design of alternative homo- and copolymer gels with controllable swelling properties has recently become a hot topic. This study focuses on equilibrium swelling of five potential candidates to replace PNIPAm in biomedical and biotechnological applications: poly(N-vinylcaprolactam), poly(vinyl methyl ether), poly(N,N-dimethyl amino ethyl methacrylate), and two families of poly(2-oxazoline)s, and poly(oligo(ethylene glycol) methacrylates). To evaluate their water uptake properties and to compare them with those of substituted acrylamide gels, a unified model is developed for equilibrium swelling of TR copolymer gels with various types of swelling diagrams. Depending on the strength of hydrophobic interactions (high, intermediate, and low), the (co)polymers under consideration are split into three groups that reveal different responses at and above the volume phase transition temperature.

Self-healing and toughness cellulose nanocrystals nanocomposite hydrogels for strain-sensitive wearable flexible sensor

Recently, self-healing and high mechanical strength hydrogels have aroused much research due to their potential future in strain-sensitive flexible sensors. In this manuscript, we successfully designed self-healing and toughness cellulose nanocrystals (CNCs) nanocomposite hydrogels by grafted polypyrrole (PPy) on the surface of CNCs to enhance electrical conductivity. The obtained nanocomposite hydrogels exhibit outstanding self-healing and mechanical behaviors, and the optimal mechanical strength, toughness and self-healing efficiency can be up to 5.7 MPa, 810% and 89.6%, respectively. Using these functional nanocomposite hydrogels, strain-sensitive wearable flexible sensors were designed to monitor finger joint motions, bending of knee, and even the slight pulse beating. Surprisingly, the flexible sensors could evidently perceive body motions from large movements (knee bending) to tiny signals (pulse beating). In addition, it exhibited excellent durability after repeated cycles. This method of prepared self-healing nanocomposite hydrogels will have a potential prospect in the design of biomedical, biosensors, and flexible electronic devices.

Gated thermoelectric sensation by nanochannels grafted with thermally responsive polymers

We report that conical PET nanochannels grafted with thermally responsive polymers can mimic the thermosensation of protein channels in living organisms, showing an adjustable gated potential rather than current response to an ambient temperature stimulus, which is more consistent with real biochannels.

Hydrogel-clay Nanocomposites as Carriers for Controlled Release

The present review aims to summarize the research efforts undertaken in the last few years in the development and testing of hydrogel-clay nanocomposites proposed as carriers for controlled release of diverse drugs. Their advantages, disadvantages and different compositions of polymers/biopolymers with diverse types of clays, as well as their interactions are discussed. Illustrative examples of studies regarding hydrogel-clay nanocomposites are detailed in order to underline the progressive researches on hydrogel-clay-drug pharmaceutical formulations able to respond to a series of demands for the most diverse applications. Brief descriptions of the different techniques used for the characterization of the obtained complex hybrid materials such as: swelling, TGA, DSC, FTIR, XRD, mechanical, SEM, TEM and biology tests, are also included. Enlightened by the presented data, we can suppose that hydrogel-clay nanocomposites will still be a challenging subject of global assiduous researches. We can dare to dream to an efficient drug delivery platform for the treatment of multiple affection concomitantly, these being undoubtedly like "a tree of life" bearing different kinds of fruits and leaves proper for human healing.

Conductive Self-Healing Nanocomposite Hydrogel Skin Sensors with Antifreezing and Thermoresponsive Properties

With growing interest in flexible and wearable devices, the demand for nature-inspired soft smart materials, especially intelligent hydrogels with multiple perceptions toward external strain and temperatures to mimic the human skin, is on the rise. However, simultaneous achievement of intelligent hydrogels with skin-compatible performances, including good transparency, appropriate mechanical properties, autonomous self-healing ability, multiple mechanical/thermoresponsiveness, and retaining flexibility at subzero temperatures, is still challenging and thus limits their application as skinlike devices. Here, conductive nanocomposite hydrogels (NC gels) were delicately designed and prepared via gelation of oligo(ethylene glycol) methacrylate (OEGMA)-based monomers in a glycerol-water cosolvent, where inorganic clay served as the physical cross-linker and provided conductive ions. The resultant NC gels exhibited good conductivity (∼3.32 × 10^-4 S cm^-1, akin to biological muscle tissue) and an autonomously self-healing capacity (healing efficiency reached 84.8%). Additionally, such NC gels displayed excellent flexibility and responded well to multiple strain/temperature external stimuli and subtle human motions in a wide temperature range (from -20 to 45 °C). These distinguished properties would endow such NC gels significant applications in fields of biosensors, human-machine interfaces, and soft robotics.

Tuning Physical Crosslinks in Hybrid Hydrogels for Network Structure Analysis and Mechanical Reinforcement

Hydrogels with high mechanical strength are needed for a variety of industrial applications. Here, a series of hydrogels was prepared by introducing hybrid particles as hydrophobic association points to toughen the hydrogels. These toughened hydrogels were able to transfer an external mechanical force via the reorganization of the crosslinking networks. They exhibited an extraordinary mechanical performance, which was the result of the coordination between hydrophobic segments and hybrid particles. Herein, the connection between the dissipated energy of the inner distribution structure (on a small scale) and the mechanical properties (on a large scale) was conducted. Specifically, we inspected hydrogels of latex particles (LPs) with different chain lengths (C4, C12, C18) and studied their inner structural parameters, namely, the relationship between the density and molecular weight of crosslinking points to the mechanical strength and energy dissipation. Favorable traits of the hydrogels included compact internal structures that were basically free from defects and external structures with puncture resistance, high toughness, etc. Based on the experimental results that agreed with the theoretical results, this study provides a profound understanding of the internal structure of hydrogels, and it offers a new idea for the design of high-strength hybrid hydrogels.

Laponite®: A key nanoplatform for biomedical applications?

Laponite® is a synthetic smectite clay that already has many important technological applications, which go beyond the conventional uses of clays in pharmaceutics and cosmetics. In biomedical applications, particularly in nanomedicine, this material holds great potential. Laponite® is a 2-dimensional (2D) nanomaterial composed of disk-shaped nanoscale crystals that have a high aspect ratio. These disks can strongly interact with many types of chemical entities (from small molecules or ions, to natural or synthetic polymers, to different inorganic nanoparticles) and are also easily functionalized and readily degraded in the physiological environment giving rise to non-toxic and even bioactive products. This review will highlight the potential of Laponite® as a nanomaterial in the fields of drug delivery, bioimaging, tissue engineering and regenerative medicine. New concepts, as well as novel innovative materials that stand out from the usual ones due to the unique properties of Laponite®, will also be presented and discussed.

Superfast and Reversible Thermoresponse of Poly( N-isopropylacrylamide) Hydrogels Grafted on Macroporous Poly(vinyl alcohol) Formaldehyde Sponges

Poly( N-isopropylacrylamide) (PNIPAAm), a typical thermoresponsive polymer, exhibits potential application in smart materials. However, bulk PNIPAAm hydrogel monoliths undergo slow volume phase transition at least tens of minutes to hours as determined by the shape and size of polymers due to the formation of the skin layer. In this regard, novel macroporous sponges with rapid thermoresponse are prepared via grafting polymerization of N-isopropylacrylamide (NIPAAm) onto the macroporous poly(vinyl alcohol) formaldehyde (PVF) network as confirmed by attenuated total reflection-infrared (ATR IR) and ¹H NMR spectra. As prepared PVF- g-PNIPAAm sponges display interconnected open-cell structures, and their average pore sizes and porosities are ∼90 μm and >85%, respectively. The equilibrium swelling ratio of PVF- g-PNIPAAm sponges varies from 11 to 50 with temperature. The volume phase transition temperature is at 30-34 °C, as detected in the DSC curves of swollen samples. These features indicate that the existence of the original PVF network exerts almost no influence on the PNIPAAm temperature responsibility. As prepared samples can reach the swelling equilibrium in less than 80 s, and their rapid swelling kinetics can be fitted using the pseudo-first-order rate kinetic equation. Notably, the samples also display rapid deswelling rate in less than 40 s at relative high temperature (48 °C), thereby indicating a superfast responsive behavior to temperature change. The PVF- g-PNIPAAm sponges exhibit rapid and reversible thermoresponse in repeatable swelling-deswelling cycles, which can satisfy the need of special smart materials. In particular, combined with iodine solution (i.e., PVF- g-PNIPAAm/I₂), these sponges can serve as a novel temperature indicator and exhibit excellent antibacterial performances.

3D shape change of multi-responsive hydrogels based on a light-programmed gradient in volume phase transition

We present a new type of anisotropic oligo(ethylene glycol) methacrylate hydrogel with multi-responsive and programmable 3D deformation behaviour.

Antimicrobial colloidal hydrogels assembled by graphene oxide and thermo-sensitive nanogels for cell encapsulation

Hydrogels are promising 3D materials that have demonstrated increasing applications in the encapsulation and delivery of drugs and cells. Herein we report an injectable colloidal hydrogel that directly assembled by graphene oxide (GO) and thermo-sensitive nanogels (tNG). The pH dependent hydrogen bonding interactions between the carboxyl and oxethyl groups induce the reversible assembly of GO and nanogels. The hydrogel is mouldable and can be shaped into different macroscopic objects, and the mechanical strengths are tunable with pH and temperature adjustment. The hybrid hydrogel by its own possesses high antibacterial activity, and demonstrates responsive drug release behaviour and high viability of 3D encapsulated cells. We expect this hybrid colloidal hydrogel can serve as an interesting scaffold for active cargo delivery and cell culture.

What determines the volume transition temperature of UCST acrylamide–acrylonitrile hydrogels?

The positive thermosensitivity of a hydrogel composed of acrylamide and acrylonitrile was investigated, and the parameters that determine the hydrogel's volume transition temperature were identified.

Composites of Polymer Hydrogels and Nanoparticulate Systems for Biomedical and Pharmaceutical Applications

Due to their unique structures and properties, three-dimensional hydrogels and nanostructured particles have been widely studied and shown a very high potential for medical, therapeutic and diagnostic applications. However, hydrogels and nanoparticulate systems have respective disadvantages that limit their widespread applications. Recently, the incorporation of nanostructured fillers into hydrogels has been developed as an innovative means for the creation of novel materials with diverse functionality in order to meet new challenges. In this review, the fundamentals of hydrogels and nanoparticles (NPs) were briefly discussed, and then we comprehensively summarized recent advances in the design, synthesis, functionalization and application of nanocomposite hydrogels with enhanced mechanical, biological and physicochemical properties. Moreover, the current challenges and future opportunities for the use of these promising materials in the biomedical sector, especially the nanocomposite hydrogels produced from hydrogels and polymeric NPs, are discussed.