Photonic Hydrogels for Synergistic Visual Bacterial Detection and On-Site Photothermal Disinfection

Recent progress in hydrogels combined with phototherapy for bacterial infection: A review

Phototherapy has become one of the most effective antibacterial methods due to its associated lack of drug resistance and its good antibacterial effect. For the purpose of avoiding the aggregation and premature release of photosensitive/photothermal agents during phototherapy, they can be mixed into three-dimensional hydrogels. The combination of hydrogels and phototherapy combines the merits of both hydrogels and phototherapy, overcomes the disadvantages of traditional antibacterial methodologies, and has broad application prospects. This review presents recent advancements in phototherapeutic antibacterial hydrogels including photodynamic antibacterial hydrogels, photothermal antibacterial hydrogels, photodynamic and photothermal synergistic antibacterial hydrogels, and other synergistic antibacterial hydrogels involving phototherapy.

Theranostic antibacterial hydrogel based on biopolymers cross-linked and doped with phytic acid from rice bran for wound healing

Theranostic antibacterial wound dressing is highly recommended in practical applications. The conventional methods of integrating diagnostic and therapeutic functions have the disadvantages of complicated preparation, mutual interference, inability to effectively broad spectrum antibacterial property, and easy to induce drug-resistant bacteria. Herein, a pH and light-responsive theranostic antibacterial hydrogel is developed by biopolymers polyvinyl alcohol (PVA) and polyaniline (PANI), and cross-linking with phytic acid (PA), which is widely present in rice bran. The biological polymer-based conductive hydrogel enables timely diagnosis and photothermal sterilization in-situ for wound healing. Because PANI is highly sensitive to pH changes in the bacterial microenvironment, the hydrogel can detect bacterial infections at concentrations as low as 103 CFU/mL. Subsequently, PANI absorbs near-infrared light to achieve on-demand exothermic sterilization (under 808 nm irradiation for 20 min, the killing ratios for Staphylococcus aureus and Escherichia coli reached almost 100 %). In addition, the hydrogel can monitor the intensity of joint movement to avoid wound re-tearing sensitively. In vitro cytotoxicity and hemocompatibility experiments and in vivo full-thickness infected wound model indicate that the hydrogel has good biocompatibility, antibacterial ability, and can accelerate the wound healing effectively. This work will promote the development of wearable electronic devices and precision medicine.

Injectable Conductive Hydrogel with Self-Healing, Motion Monitoring, and Bacteria Theranostics for Bioelectronic Wound Dressing

Wounds at joints are difficult to treat and tend to recover more slowly due to the frequent motions. When using traditional hydrogel dressings, they are easy to crack and undergo bacterial infection, difficult to match and monitor the irregular wounds. Integrating multiple functions within a hydrogel dressing to achieve intelligent wound monitoring and healing remains a significant challenge. In this research, a multifunctional hydrogel is developed based on polysaccharide biopolymer, poly(vinyl alcohol), and hydroxylated graphene through dynamic borate ester bonding and supramolecular interaction. The prepared hydrogel not only exhibits rapid self-healing (within 60 s), injectable, conductive and motion monitoring properties, but also realizes in situ bacterial sensing and killing functions. It shows excellent bacterial sensitivity (within 15 min) and killing ability via the changes of electrical signals and photothermal therapy, avoiding the emergence of drug-resistant bacteria. In vivo experiments prove that the hydrogel can promote wound healing effectively. In addition, it displays great electromechanical performance to achieve real-time monitoring and prevent re-tearing of the wound at human joints. The injectable pH-responsive hydrogel with good biocompatibility demonstrates considerable potential as multifunctional bioelectronic dressing for the detection, treatment, management, and healing of infected joint wounds.

Hydrogel-Based Biosensors for Bacterial Infections

Hydrogels are known to have the advantages such as good biodegradability, biocompatibility, and easy functionalization, making them ideal candidates for biosensors. Hydrogel-based biosensors that respond to bacteria-induced microenvironmental changes such as pH, enzymes, antigens, etc., or directly interact with bacterial surface receptors, can be applied for early diagnosis of bacterial infections, providing information for timely treatment while avoiding antibiotic abuse. Furthermore, hydrogel biosensors capable of both bacteria diagnosis and treatment will greatly facilitate the development of point-of-care monitoring of bacterial infections. In this review, the recent advancement of hydrogel-based biosensors for bacterial infection is summarized and discussed. First, the biosensors based on pH-sensitive hydrogels, bacterial-specific secretions-sensitive hydrogels, and hydrogels directly in contact with bacterial surfaces are presented. Next, hydrogel biosensors capable of detecting bacterial infection in the early stage followed by immediate on-demand treatment are discussed. Finally, the challenges and future development of hydrogel biosensors for bacterial infections are proposed.

Designing Composite Stimuli-Responsive Hydrogels for Wound Healing Applications: The State-of-the-Art and Recent Discoveries

Effective wound treatment has become one of the most important challenges for healthcare as it continues to be one of the leading causes of death worldwide. Therefore, wound care technologies significantly evolved in order to provide a holistic approach based on various designs of functional wound dressings. Among them, hydrogels have been widely used for wound treatment due to their biocompatibility and similarity to the extracellular matrix. The hydrogel formula offers the control of an optimal wound moisture level due to its ability to absorb excess fluid from the wound or release moisture as needed. Additionally, hydrogels can be successfully integrated with a plethora of biologically active components (e.g., nanoparticles, pharmaceuticals, natural extracts, peptides), thus enhancing the performance of resulting composite hydrogels in wound healing applications. In this review, the-state-of-the-art discoveries related to stimuli-responsive hydrogel-based dressings have been summarized, taking into account their antimicrobial, anti-inflammatory, antioxidant, and hemostatic properties, as well as other effects (e.g., re-epithelialization, vascularization, and restoration of the tissue) resulting from their use.

Stimulus-responsive nonclose-packed photonic crystals: fabrications and applications

Stimulus-responsive photonic crystals (PCs) possessing unconventional nonclosely packed structures have received growing attention due to their unique capability of mimicking the active structural colors of natural organisms (for example, chameleons' mechanochromic properties). However, there is rarely any systematic review regarding the progress of nonclose-packed photonic crystals (NPCs), involving their fabrication, working mechanisms, and applications. Herein, a comprehensive review of the fundamental principles and practical fabrication strategies of one/two/three-dimensional NPCs is summarized from the perspective of designing nonclose-packed structures. Subsequently, responsive NPCs with exciting functions and working mechanisms are sorted and delineated according to their diverse responses to physical (force, temperature, magnetic, and electric fields), chemical (ions, pH, vapors, and solvents), and biological (glucose, organophosphate, creatinine, and bacteria) stimuli. We then systematically introduced and discussed the applications of NPCs in sensors, printing, anticounterfeiting, display, optical devices, etc. Finally, the current challenges and development prospects for NPCs are presented. This review not only concludes the design principle for NPCs but also provides a significant basis for the exploration of next-generation NPCs.

Near-IR-Regulated Composite Hydrogel with Real-Time Infection Monitoring and a Combined Antibacterial Effect for Efficient Wound Management

Chronic wounds induced by bacterial infection have seriously affected the health of people in the world. So, it is meaningful to develop a novel strategy with real-time infection monitoring and excellent antibacterial performance for enhancing wound management. Herein, we constructed a composite hydrogel by loading the pH indicator bromothymol blue (BTB) and gold nanocages containing 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (Au NCs@AIPH) into a polyacrylamide-co-poly(acrylic anhydride-modified oxidized sodium alginate) (PAM-co-PAOSA) hydrogel. In vitro and in vivo experimental results demonstrated that the composite hydrogel could effectively detect bacteria and diagnose the infection status of a wound in real time by showing visible color changes. In addition, the composite hydrogel containing Au NCs@AIPH possessed an excellent photothermal effect under near-IR (NIR) laser irradiation. The photothermal effect further activated AIPH to generate toxic free radicals to form combined antibacterial therapy for accelerating wound healing. Moreover, the composite hydrogel showed great biocompatibility. Therefore, the multifunctional hydrogel provided a novel wound management strategy for bacterial infection diagnosis and combined therapy in an infected wound.

A K+-sensitive photonic crystal hydrogel sensor for efficient visual monitoring of hyperkalemia/hypokalemia

Potassium ions (K⁺) play crucial roles in many biological processes. Abnormal K⁺ levels in the body are usually associated with physiological disorders or diseases, and thus, developing K⁺-sensitive sensors/devices is of great importance for disease diagnosis and health monitoring. Herein, we report a K⁺-sensitive photonic crystal hydrogel (PCH) sensor with bright structural colors for efficient monitoring of serum potassium. This PCH sensor consists of a poly(acrylamide-co-N-isopropylacrylamide-co-benzo-15-crown-5-acrylamide) (PANBC) smart hydrogel with embedded Fe₃O₄ colloidal photonic crystals (CPCs), which could strongly diffract visible light and endow the hydrogel with brilliant structural colors. The rich 15-crown-5 (15C5) units appended on the polymer backbone could selectively bind K⁺ ions to form stable 2 : 1 [15C5]₂/K⁺ supramolecular complexes. These bis-bidentate complexes served as physical crosslinkers to crosslink the hydrogel and contracted its volume, and thus reduced the lattice spacing of Fe₃O₄ CPCs and blue-shifted the light diffraction, and finally reported on the K⁺ concentrations by a color change of the PCH. Our fabricated PCH sensor possessed high K⁺ selectivity and pH- and thermo-sensitive response performances to K⁺. Most interestingly, the K⁺-responding PANBC PCH sensor could be conveniently regenerated via simple alternate flushing with hot/cold water due to the excellent thermosensitivity of the introduced PNIPAM moieties into the hydrogel. Such a PCH sensor provides a simple, low-cost and efficient strategy for visualized monitoring of hyperkalemia/hypokalemia, which will significantly promote the development of biosensors.

Programmable Nanostructures Based on Framework-DNA for Applications in Biosensing

DNA has been actively utilized as bricks to construct exquisite nanostructures due to their unparalleled programmability. Particularly, nanostructures based on framework DNA (F-DNA) with controllable size, tailorable functionality, and precise addressability hold excellent promise for molecular biology studies and versatile tools for biosensor applications. In this review, we provide an overview of the current development of F-DNA-enabled biosensors. Firstly, we summarize the design and working principle of F-DNA-based nanodevices. Then, recent advances in their use in different kinds of target sensing with effectiveness have been exhibited. Finally, we envision potential perspectives on the future opportunities and challenges of biosensing platforms.

NIR regulated upconversion nanoparticles@metal-organic framework composite hydrogel dressing with catalase-like performance and enhanced antibacterial efficacy for accelerating wound healing

Developing a hydrogel dressing with excellent antibacterial efficacy for accelerating wound healing is high desirable in clinical applications. In this work, NIR regulated metal-organic framework composite hydrogel dressing was constructed for enhanced antibacterial efficacy and accelerated wound healing via the compounding between hydrogel and UCNPs@ZrMOF-Pt nanoparticles. The visible light emitted from upconvertion nanoparticles (UCNPs) activated porphyrin based metal-organic framework (MOF) in composite hydrogel to generate ¹O₂ for photodynamic antibacterial therapy under NIR laser irradiation. Moreover, the UCNPs@ZrMOF-Pt in composite hydrogel with catalase-like performance could effectively convert the high concentration H₂O₂ in wound to abundant O₂, which relieved the hypoxic in infected wound. Thus, the photodynamic antibacterial efficacy was remarkably enhanced, leading to accelerate the wound healing. This work presented a novel strategy for high efficient antibacterial therapy and accelerated wound healing.

Photothermal Hydrogels for Promoting Infected Wound Healing

Photothermal therapies (PTT), with spatiotemporally controllable antibacterial capabilities without inducing resistance, have shown encouraging prospects in the field of infected wound treatments. As an important platform for PTT, photothermal hydrogels exhibit attractive advantages in the field of infected wound treatment due to their excellent biochemical properties and have been intensively explored in recent years. This review summarizes the progress of the photothermal hydrogels for promoting infected wound healing. Three major elements of photothermal hydrogels, i.e., photothermal materials, hydrogel matrix, and construction methods, are introduced. Furthermore, different strategies of photothermal hydrogels in the treatment of infected wounds are summarized. Finally, the challenges and prospects in the clinical treatment of photothermal hydrogels are discussed.

When Iodine Meets Starch: On-Demand Generation of Photothermal Hydrogels for Mild-Temperature Photothermal-Chemo Disinfection

As an emerging antibacterial strategy, photothermal disinfection attracts increasing attention due to its advantages of high efficacy, wide pertinence, and non-drug resistance. However, the unavoidable shielding of observation by photothermal components and the possible damage to normal tissue caused by hyperthermia restrict its applications. Herein, we propose a composite hydrogel with the ability of on-demand generation of photothermal components and mild-temperature photothermal disinfection by elegantly tuning the binding and release of iodine and starch. The composite hydrogel is obtained by blending iodine-adsorbed pH-responsive ZIF-8 nanoparticles (NPs) with a starch-based hydrogel matrix. Through a convenient pH response, the composite hydrogel leverages the triple functions of iodine, which serves as a disinfectant and reacts with starch to generate a photothermal agent and color indicator, allowing photothermal-chemotherapy combined disinfection on demand. In vitro antibacterial experiments show that the composite hydrogel can respond to the acidification of the microenvironment caused by bacterial metabolism and produce corresponding color changes, realizing naked-eye observation. Meanwhile, under the combined treatment of heating/I2/Zn2+, the composite hydrogel can completely kill Escherichia coli and Staphylococcus aureus at a mild temperature of ∼41 °C. This study represents a breakthrough in on-demand generation of photothermal hydrogels for mild-temperature photothermal disinfection.

Novel Trends in Hydrogel Development for Biomedical Applications: A Review

Nowadays, there are still numerous challenges for well-known biomedical applications, such as tissue engineering (TE), wound healing and controlled drug delivery, which must be faced and solved. Hydrogels have been proposed as excellent candidates for these applications, as they have promising properties for the mentioned applications, including biocompatibility, biodegradability, great absorption capacity and tunable mechanical properties. However, depending on the material or the manufacturing method, the resulting hydrogel may not be up to the specific task for which it is designed, thus there are different approaches proposed to enhance hydrogel performance for the requirements of the application in question. The main purpose of this review article was to summarize the most recent trends of hydrogel technology, going through the most used polymeric materials and the most popular hydrogel synthesis methods in recent years, including different strategies of enhancing hydrogels’ properties, such as cross-linking and the manufacture of composite hydrogels. In addition, the secondary objective of this review was to briefly discuss other novel applications of hydrogels that have been proposed in the past few years which have drawn a lot of attention.