Photothermal-modulated reversible volume transition of wireless hydrogels embedded with redox-responsive carbon dots

Emerging trends in CDs@hydrogels composites: from materials to applications

Carbon dots (CDs) are nanoscale carbon materials with unique optical properties and biocompatibility. Their applications are limited by their tendency to aggregate or oxidize in aqueous environments. Turning weakness to strengths, CDs can be incorporated with hydrogels, which are three-dimensional networks of crosslinked polymers that can retain large amounts of water. Hydrogels can provide a stable and tunable matrix for CDs, enhancing their fluorescence, stability, and functionality. CDs@hydrogels, known for their ease of synthesis, strong binding capabilities, and rich surface functional groups, have emerged as promising composite materials. In this review, recent advances in the synthesis and characterization of CDs@hydrogels, composite materials composed of CDs and various types of natural or synthetic hydrogels, are summarized. The potential applications of CDs@hydrogels in fluorescence sensing, adsorption, drug delivery, antibacterial activity, flexible electronics, and energy storage are also highlighted. The current challenges and future prospects of CDs@hydrogels systems for the novel functional materials are discussed.

Tailoring the Swelling-Shrinkable Behavior of Hydrogels for Biomedical Applications

Hydrogels with tailor-made swelling-shrinkable properties have aroused considerable interest in numerous biomedical domains. For example, as swelling is a key issue for blood and wound extrudates absorption, the transference of nutrients and metabolites, as well as drug diffusion and release, hydrogels with high swelling capacity have been widely applicated in full-thickness skin wound healing and tissue regeneration, and drug delivery. Nevertheless, in the fields of tissue adhesives and internal soft-tissue wound healing, and bioelectronics, non-swelling hydrogels play very important functions owing to their stable macroscopic dimension and physical performance in physiological environment. Moreover, the negative swelling behavior (i.e., shrinkage) of hydrogels can be exploited to drive noninvasive wound closure, and achieve resolution enhancement of hydrogel scaffolds. In addition, it can help push out the entrapped drugs, thus promote drug release. However, there still has not been a general review of the constructions and biomedical applications of hydrogels from the viewpoint of swelling-shrinkable properties. Therefore, this review summarizes the tactics employed so far in tailoring the swelling-shrinkable properties of hydrogels and their biomedical applications. And a relatively comprehensive understanding of the current progress and future challenge of the hydrogels with different swelling-shrinkable features is provided for potential clinical translations.

Carbon Dot-Based Hydrogels: Preparations, Properties, and Applications

Hydrogels have extremely high moisture content, which makes it very soft and excellently biocompatible. They have become an important soft material and have a wide range of applications in various fields such as biomedicine, bionic smart material, and electrochemistry. Carbon dot (CD)-based hydrogels are based on carbon dots (CDs) and auxiliary substances, forming a gel material with comprehensive properties of individual components. CDs embedding in hydrogels could not only solve their aggregation-caused quenching (ACQ) effect, but also manipulate the properties of hydrogels and even bring some novel properties, achieving a win-win situation. In this review, the preparation methods, formation mechanism, and properties of CD-based hydrogels, and their applications in biomedicine, sensing, adsorption, energy storage, and catalysis -are summarized. Finally, a brief discussion on future research directions of CD-based hydrogels will be given.

Synthesis and Processing of Dynamic Covalently Crosslinked Polydextran/Carbon Dot Nanocomposite Hydrogels with Tailorable Microstructures and Properties

Using functionalized nanoparticles to crosslink hydrophilic polymers is a growing theme of directly constructing nanocomposite (NC) hydrogels. Employing dynamic covalent chemistry at the nanoparticle-polymer interface is particularly attractive due to the spontaneous formation and reversible manner of dynamic covalent bonds. However, the structure and property modulation of the dynamic covalently crosslinked NC hydrogels has not been thoroughly discussed. Here, we fabricated NC hydrogels by using amine-functionalized carbon dots (CDs) to crosslink polydextran aldehyde (PDA) polymers through imine bond formation. The role of PDA with different oxidation degrees (i.e., PDA10, PDA30, and PDA50) in affecting the microstructures and properties of PDA@CD hydrogels was systematically investigated, showing that the PDA50@CD hydrogel presented the densest structure and the highest mechanical strength among the three PDA@CD hydrogels. The pH-responsiveness, 3D printing, electrospinning, and biocompatibility of PDA@CD hydrogels were also demonstrated, showing the great promise of using PDA@CD hydrogels for applications in biomedicine and biofabrication.

Programmed Stimuli-Responsive Carbon Dot-Nanogel Hybrids for Imaging-Guided Enhanced Tumor Phototherapy

For harmonizing the contradiction of nanotheranostic agents between enhanced tumor accumulation and penetration, efficient cell internalization and fast elimination are key tactics for promoting their clinical applications. Herein, programmed stimuli-responsive poly(N-isopropylacrylamide)-carbon dot (PNIPAM-CD) hybrid nanogels are designed to address the abovementioned conflicts. The enlarged particle size of PNIPAM-CDs enables one to effectively improve their accumulation at tumor sites. Once the hybrid nanogels are docked in tumors and exposed to deep-red-light (660 nm) irradiation, heat and reactive oxygen species (ROS) are generated from the CDs, consequently activating photothermal therapy (PTT) and photodynamic therapy (PDT) effects and meanwhile inducing partial degradation of PNIPAM-CDs for deep tissue penetration. Further, enhanced cellular internalization of the functional components can be achieved owing to the pH-responsive charge reversal and temperature-dependent hydrophilic/hydrophobic conversion characteristics of PNIPAM-CDs. Finally, the overexpressed glutathione (GSH) in tumor cells would trigger further cleavage of the partially degraded hybrid nanogels, which is beneficial for their rapid clearance from the body. This work not only proposed a novel strategy to fabricate nanotheranostic agents using just a single functional component (i.e., the versatile CDs) to simplify the preparation process but also achieved effective delivery of agents into tumor cells by overcoming the multiple biological barriers to enhance therapeutic efficacy and decrease side effects.

Injectable Nanocomposite Hydrogels for Cancer Therapy

Hydrogel is a kind of 3D polymer network with strong swelling ability in water and appropriate mechanical and biological properties, which make it feasible to maintain bioactive substances and has promising applications in the fields of biomaterials, soft machines, and artificial tissues. Unfortunately, traditional hydrogels prepared by chemical crosslinking have poor mechanical properties and limited functions, which limit their further application. In recent years, with the continuous development of nanoparticle research, more and more studies have combined nanoparticles with hydrogels to make up for the shortcomings of traditional hydrogels. In this article, the types and functions of hydrogels and nanomaterials are introduced first, as well as the functions and applications of injectable nanocomposite hydrogels (INHs), then the latest progress of INHs for cancer treatment is reviewed, some existing problems are summarized, and the application prospect of NHs is prospected.