Bacterial biofilms cause persistent infectious diseases and create tremendous obstacles to anti-infection treatment. [5,6] Epidemiological evidence has shown that biofilm formation poses a risk of chronic infection for clinical treatments, particularly in implant patients [7,8] such as cardiovascular grafts, fracture treatment, and orthodontic treatment. [9,10] If the biofilm infection is not cured in time, the long-term use of antibiotics to treat chronic infection may further aggravate the negative impact of antibiotics on the human body.The particular structure and components of the biofilm hinder the penetration efficiency of drugs and reduce the therapeutic effect of antibiotics, causing the hazard of bacterial biofilms. [11] In addition, some drug-resistant bacteria that inhabit the biofilms could secrete hydrolases (e.g., β-lactamases) to degrade antibiotics, making antibiotics ineffective. [12] In biofilms, the matrix, which accounts for most of the dry mass, possesses diverse functions such as the external digestive system, recycling center, gene pool, and nutrient source. [13,14] Biofilm organisms produce extracellular polymeric substances (EPS), primarily comprising exopolysaccharides, proteins, lipids, and extracellular DNA (eDNA), varying according to the environmental conditions. [15,16] EPS protects the organism from drying, oxidization, charged biocides, antibiotics, metal cations, and the host's immune defenses. [13,17,18] Additionally, EPS limits the diffusion of nutrients, creating a nutrient-deficient environment, further resulting in the slow metabolism of bacteria within the biofilm, making the bacteria less sensitive to antibiotics. [19] First, obstruction of the biofilm matrix results in extremely poor antibiotic and nutrient permeability. The aggregation of cations, such as Ca 2+ and Mg 2+ , in biofilms, promotes crosslinking between polymeric polysaccharide molecules, increasing both the viscosity and binding forces of the biofilm matrix. [20] The hydrophilic-hydrophobic properties of EPS also influence the drug penetration effect, which is related to the hydration state of EPS. [21,22] Furthermore, EPS helps immobilize bacterioplankton. The embedded bacteria in the biofilm show intense interconnections and produce stronger intercellular signal communication, a process called quorum sensing (QS). [23] Benefitting from QS, a relatively Bacterial biofilm-related infectious diseases severely influence human health. Under typical situations, pathogens can colonize inert or biological surfaces and form biofilms. Biofilms are functional aggregates that coat bacteria with extracellular polymeric substances (EPS). The main reason for the failure of biofilm infection treatment is the low permeability and enrichment of therapeutic agents within the biofilm, which results from the particular features of biofilm matrix barriers such as negatively charged biofilm components and highly viscous compact EPS structures. Hence, developing novel therapeutic strategies with enhanced biofilm penetrability is...

The hydrogel aggregates in a state that is halfway between solid and liquid. [2] The solid character of the hydrogel ensures it maintains a certain shape and volume under particular circumstances, while the liquid behavior enables the solute in the hydrogel to permeate or penetrate. Ascribed to the attractive and special structure, the hydrogel is featured with high water content, high deformability, high structural similarity to biological tissues, and adjustable mechanical properties, promising wide potential functionalized applications in the fields of biomaterials, tissue engineering, biosensors, implanted electronics, etc. [1,3,4] By adopting particular elements or functional groups into the polymer matrix, abundant chemical and physical interactions (hydrogen bond, [5][6][7] metal coordination bond, [8][9][10] ionic bond, [11][12][13] host-guest interaction, [14][15][16] etc.) are formed, resulting in unique functionalized capabilities.However, with more diversified human activities, additional requirements for flexible materials are prompted to satisfy the applicability of flexible wearable devices in a variety of circumstances. Typically, when wearable devices are utilized in high humidity or even underwater, the stability of the polymer matrix is critical to maintaining accurate and sensitive intelligent perception. The hydrogel absorbs water and expands, causing distinct mechanical properties and deterioration. In addition, a hydration overlay will be generated on the hydrogel surface to prevent the creation of the molecular bridge between the hydrogel and the substrate interface, weakening the interaction effect and conformality. As a result, the universality of the hydrogels is strictly restricted in high humidity. Over the past few decades, a lot of efforts have gone into the preparation, modification, and application of underwater hydrogels, and a variety of underwater hydrogels have been created with featured and unique characteristics. To date, the review [17][18][19][20][21][22] articles solving the problem of underwater application of hydrogels have mostly focused on two aspects: one is to improve the underwater stability of the hydrogel, and the other is to strengthen the interaction in the hydrogel and substrate interface. The water swelling ratio of most known adhesive hydrogels is excessively high, resulting in a considerably enlarged and brittle hydrogel network in the water environment. [17,18] Therefore, the anti-swelling property of hydrogel is also critical to realizing tough underwater adhesion. Herein, we first briefly introduced the crucial design principles of underwater Wearable devices, biomaterials, and tissue engineering have all gained from the development of flexible materials. Hydrogels are made up of the polymer matrix in an amount of water and are now being explored extensively. Ascribed to their high hydrophilicity, conventional hydrogels are difficult to deal with high humidity, being easily swell and even decompose. The utilization of hydrogel underwater is influenced by...

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To perceive the human body's multienvironmental mobility, intelligent flexible electronic equipment with an underwater motion monitoring function has potential research value in the field of intelligent detection. Hydrogels are widely used in the field of flexible electronics for their unique three-dimensional polymer networks. Due to the instinctive hydrophilicity of hydrogels, the swelling of hydrogels underwater and the formation of hydration coating on the surface become the primary obstacles to underwater applications. Herein, a hydrogel sensor that can achieve underwater utilization was prepared through copolymerization between hydrophobic and hydrophilic polymer monomers. The synergistic impact of electrostatic interaction, metal coordination, and hydrogen bonding ensured the hydrogel's remarkable underwater adhesive ability to a variety of substrates. The hydrophobic micelles and self-hydrophobization process induced from ultrasonic dispersion in the polymer matrix gave an outstanding hydrophobic performance (water contact angle of 130.4°) and antiswelling property (swelling ratio of 26% after 72 h of immersion), presenting unprecedented underwater adaptability. The above-mentioned hydrogel could be assembled into a flexible hydrogel sensor with satisfactory sensitivity (gauge factor of 0.44), ultrafast response rate (106 ms), and excellent cyclic stability, demonstrating accurate monitoring of complex human motions in water and air.

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ideal ionic conductors for flexible electronics because of their high stretchability, transparency, and excellent ionic conductivity. [2] However, ascribed to the introduction of hydrophilic groups, the hydrogel swelling is unavoidable and has become the major technical bottleneck of underwater sensing. Many efforts have been made to address the issue of hydrogel swelling, such as solvent exchange, [3] multiple crosslinking, [4] and supramolecular strategy. [5] For instance, Cui et al. [6] established a type of hydrogels enabled a process of self-hydrophobization produced by Fe 3+ that endow the hydrogels excellent underwater adhesion and stability. Zhao et al. [7] constructed double network hydrogel consisting of poly (acrylamideco-acrylic acid) and sodium alginate with extremely high crosslinking density, which exhibited excellent swelling-resistance underwater. Although these specially created anti-swelling hydrogels can be submerged in water for a period of time, it is still extremely difficult to prevent the ion dispersion due to the concentration gradient, which will severely depress or even completely eliminate their conducting and sensing capacities.Moreover, for consistent and steady signals, the sensor must be securely adhered to the target substrates with a high signalto-noise ratio when utilized underwater. However, achieving strong underwater adhesion remains a challenge for commercial electrodes. [8] The adhesion strength of the substrate will be greatly decreased or even eliminated because water molecules will create a hydration layer on its surface, preventing direct Creating flexible materials that can work underwater has the potential to broaden applications to aquatic and marine environments. Hydrogels have long been thought to be excellent ionic conductors for wearable electronics, because of their high stretchability, transparency, and excellent ionic conductivity. However, due to the huge differences between the underwater and air environments, the previously reported soft materials can rarely satisfy the critical needs of adhesive, underwater stability, and steady conductivity. Herein, an ionogel is proposed with abundant physical and chemical crosslinked, involving ion-dipole, electrostatic, and hydrogen bonding interactions, to achieve excellent mechanical strength, resilience, and underwater stability. The ionogel with long-lasting underwater adherence and durability is further assembled into a high sensitivity, fast response, and excellent durability underwater wearable sensor. The ionogel sensor demonstrated high precision in various human motion detection and Morse code is used to transmit information both in the air and underwater. In addition, the tough underwater adhesion and the distinct discrepancy in electrical properties in different concentration solutions enable the ionogel sensor to adhere to the surface of marine animals and monitor the water quality in their habitats. It is identified that the designed ionogel possesses great promise in wearable devices and soft ionotronics.

Photoacoustic (PA) imaging is an emerging biomedical imaging technique with the features of non‐invasiveness and non‐ionization. It takes advantage of the photothermal effect of PA probes to convert absorbed photon energy into heat and subsequent transient thermoelastic tissue expansion for ultrasonic waves for PA images. Thus, PA imaging exhibits the combined superiority of high‐contrast optical imaging and deep tissue penetration of acoustic imaging, which furnishes high‐resolution and high‐contrast tissue images. Stimuli‐responsive organic PA agents in the near‐infrared (NIR) biological window have attracted increasing attention because of their low biological toxicity and response characteristics. This review focuses on the recent research progress of stimuli‐responsive organic NIR probes for PA imaging, including the temperature response, pH response, redox response, metal ion response, and enzyme response. And the stimuli‐responsive mechanisms are highlighted in detail. Moreover, their perspectives and challenges are discussed. It will be of great help for the further development of organic NIR PA probes with stimuli‐response.

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