Property Regulation of Conjugated Oligoelectrolytes with Polyisocyanide to Achieve Efficient Photodynamic Antibacterial Biomimetic Hydrogels

Antibacterial Hydrogels for Wound Dressing Applications: Current Status, Progress, Challenges, and Trends

Bacterial infection treatment for chronic wounds has posed a major medical threat and challenge. Bacteria at the wounded sites can compete with the immune system and subsequently invade live tissues, leading to more severe tissue damage. Therefore, there is an urgent demand for wound dressings with antibacterial and anti-inflammatory properties. Considering the concept of moist healing, hydrogels with a three-dimensional (3D) network structure are widely used as wound dressings due to their excellent hydrophilicity, water retention properties, and biocompatibility. Developing antibacterial hydrogels for the treatment of infected wounds has been receiving extensive attention recently. This article categorizes antibacterial hydrogels according to their materials and antibacterial modes, and introduces the recent findings and progress regarding their status. More importantly, with the development of emerging technologies, new therapies are utilized to prepare antibacterial hydrogels such as nanoenzymes, photothermal therapy (PTT), photodynamic therapy (PDT), metal-organic frameworks (MOFs), and other external stimuli-responsive methods. Therefore, this review also examines their progress, challenges, and future trends as wound dressings. In the following studies, there will still be a focus on antibacterial hydrogels that have a high performance, multi-functions, and intelligence, especially biocompatibility, a high and long-lasting antibacterial property, responsiveness, and on-demand therapeutic ability.

Self-supporting noncovalent Choline Alginate/Tannic acid/Ag antibacterial films for strawberry preservation

Packaging materials with peculiar antibacterial properties can shield off and inhibit microorganism proliferation, thus achieving packaging goals such as fresh-keeping, good hygiene, and biosafety. Especially, antibacterial films made of biocompatible substances have received wide attentions, which could effectively extend the shelf life, enhance food security, and guarantee economic benefits. Herein, a self-supporting hybrid antibacterial film was prepared based on non-covalently linked choline hydroxide (ChOH) and alginic acid (HAlg). Then tannic acid (TA) and silver ions were added to improve the mechanical and antimicrobial properties of this hybrid film. The rich hydroxyl groups from TA not only form multiple hydrogen bonds with ChAlg, but can also in situ reduce silver ions to silver nanoparticles, which were confirmed with various characterizations. In addition, the quantitative antibacterial test proved that the antibacterial rate was significantly improved after adding silver ions, reaching >60 %. In an actual storage test, we found that choline cation (Ch+) captured in antibacterial film by electrostatic interaction could achieve sustained release, i.e. sustainable bacteriostasis, and keep strawberries fresh for 48 h at room temperature. This work offers a new strategy for preparing antibacterial films via non-covalent weak interactions, explored an alternative antibacterial film for food packaging applications.

Supramolecular Switch for the Regulation of Antibacterial Efficacy of Near-Infrared Photosensitizer

The global antibiotic resistance crisis has drawn attention to the development of treatment methods less prone to inducing drug resistance, such as antimicrobial photodynamic therapy (aPDT). However, there is an increasing demand for new photosensitizers capable of efficiently absorbing in the near-infrared (NIR) region, enabling antibacterial treatment in deeper sites. Additionally, advanced strategies need to be developed to avert drug resistance stemming from prolonged exposure. Herein, we have designed a conjugated oligoelectrolyte, namely TTQAd, with a donor-acceptor-donor (D-A-D) backbone, enabling the generation of reactive oxygen species (ROS) under NIR light irradiation, and cationic adamantaneammonium groups on the side chains, enabling the host-guest interaction with curcubit[7]uril (CB7). Due to the amphiphilic nature of TTQAd, it could spontaneously form nanoassemblies in aqueous solution. Upon CB7 treatment, the positive charge of the cationic adamantaneammonium group was largely shielded by CB7, leading to a further aggregation of the nanoassemblies and a reduced antibacterial efficacy of TTQAd. Subsequent treatment with competitor guests enables the release of TTQAd and restores its antibacterial effect. The reversible supramolecular switch for regulating the antibacterial effect offers the potential for the controlled release of active photosensitizers, thereby showing promise in preventing the emergence of drug-resistant bacteria.

Phosphonium-Substituted Conjugated Polyelectrolytes Display Efficient Visible-Light-Induced Antibacterial Activity

We report the light-activated antibacterial activity of a new class of phosphonium (R-PMe3+)-substituted conjugated polyelectrolytes (CPEs). These polyelectrolytes feature a poly(phenylene ethynylene) (PPE) conjugated backbone substituted with side groups with the structure -O-(CH2)nPMe3+, where n = 3 or 6. The length of the side groups has an effect on the hydrophobic character of the CPEs and their propensity to interact with bacterial membranes. In a separate study, these phosphonium-substituted PPE CPEs were demonstrated to photosensitize singlet oxygen (1O2) and reactive oxygen species, a key factor for the photoinduced inactivation of bacteria. In this study, in vitro antibacterial assays against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus were performed by employing the series of polyelectrolytes under both dark and illumination conditions. In general, the phosphonium-substituted CPEs displayed profound light-activated biocidal activity, with >99% colony forming unit (CFU) reduction after 15 min of light exposure (16 mW cm-2) at a ≤20 μM CPE concentration. Strong biocidal activity was also observed in the dark for a CPE concentration of 20 μM against S. aureus; however, higher concentrations (200 μM) were needed to enable dark inactivation of E. coli. The dark activity is ascribed to bacterial membrane disruption by the CPEs, supported by a correlation of dark biocidal activity with the chain length of the side groups. The light-activated biocidal activity is associated with the ability of the CPEs to sensitize ROS, which is cytotoxic to the microorganisms. Serial dilution bacterial plating experiments revealed that the series of CPEs was able to induce a >5-log kill versus E. coli with 15 min of exposure to a blue LED source (16 mW cm-2).

Hyaluronic acid-based injectable nanocomposite hydrogels with photo-thermal antibacterial properties for infected chronic diabetic wound healing

A hydrogel wound dressing with a single functionality fails to meet the requirements for successful clinical treatment of chronic diabetic wounds that generally possess complicated microenvironments. A multifunctional hydrogel is thus highly desirable for improved clinical treatment. For this purpose, we reported herein construction of an injectable nanocomposite hydrogel with self-healing and photo-thermal properties as an antibacterial adhesive via dynamic Michael addition reaction and electrostatic interactions among three building moieties, i.e., catechol and thiol-modified hyaluronic acid (HA-CA and HA-SH), poly(hexamethylene guanidine) (PHMG), and black phosphorus nanosheets (BPs). An optimized hydrogel formulation eliminated over 99.99 % of bacteria (E. coli and S. aureus) and exhibited a free radical scavenging capability >70 % as well as photo-thermal properties in addition to viscoelastic characteristics, degradation properties in vitro, good adhesion and self-adaptation capacity. Wound healing experiments in vivo further confirmed the better performance of the developed hydrogels than that of a commercially available dressing (Tegaderm™) in promoting the healing of infected chronic wounds by preventing wound infection, decreasing inflammation, supporting collagen deposition, facilitating angiogenesis, and improving granulation tissues formation in the wound sites. Overall, the HA-based injectable composite hydrogels developed herein represent promising multifunctional wound dressings for infected diabetic wound repair.

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.

Constructing a self-healing injectable SABA/Borax/PDA@AgNPs hydrogel for synergistic low-temperature photothermal antibacterial therapy

Infections caused by bacteria are one of the biggest challenges humans face around the world. Photothermal therapy (PTT) has been regarded as a promising strategy in combating pathogenic infection, however the high temperatures (55-65 °C) required during a single PTT process can induce injury to healthy tissues nearby. Combination therapy could overcome this problem by reducing the photothermal temperature. Here, we developed a self-healing and injectable hydrogel to realize low-temperature PTT (LT-PTT, ≤45 °C) for antisepsis with high-efficiency. The hybrid hydrogel is prepared by incorporating borax into a mixture of 3-aminophenylboronic acid grafted sodium alginate and nano-silver decorated polydopamine nanoparticles. Our results showed that the SABA/Borax/PDA@AgNPs hydrogel possesses satisfactory mechanical properties and self-healing capacity, and as a result, it can repair itself after being damaged mechanically, retaining its integrality and recovering its initial functionalities. Furthermore, through utilizing the photothermal property of polydopamine nanoparticles and broad-spectrum antibacterial activity of nano-silver, the hybrid hydrogel achieves excellent LT-PTT for sterilization both in vitro as well as in an in vivo mice skin wound model with no distinct injury to normal tissues. Overall, our prepared hydrogel is expected to be an excellent candidate for treating bacterial infections.

Membrane-intercalating conjugated oligoelectrolytes

By acting as effective biomimetics of the lipid bilayers, membrane-intercalating conjugated oligoelectrolytes (MICOEs) can spontaneously insert themselves into both synthetic lipid bilayers and biological membranes. The modular and intentional molecular design of MICOEs enable a range of applications, such as bioproduction, biocatalysis, biosensing, and therapeutics. This tutorial review provides a structural evolution of MICOEs, which originated from the broader class of conjugated molecules, and analyses the drivers behind this evolutionary process. Various representative applications of MICOEs, accompanied by insights into their molecular design principles, will be reviewed separately. Perspectives on the current challenges and opportunities in research on MICOEs will be discussed at the end of the review to highlight their potential as unconventional and value-added materials for biological systems.

Photodynamic Antimicrobial Therapy Based on Conjugated Polymers

Pathogenic microorganisms have been a serious threat to human life and have become a public health problem of global concern. However, in the actual treatment there is a lack of efficient antimicrobial strategies which do not easily develop drug resistance; this can lead to inaccurate drug treatment that worsens the infection and even threatens life. With the emergence of a variety of drug-resistant bacteria and fungi, photodynamic therapy has gradually become one of the most promising treatment methods for drug-resistant bacteria infection; this is because it is controllable, non-invasive, and not prone to cause the development of drug resistance. Organic conjugated polymers that possess high fluorescence intensity, a large molar extinction coefficient, excellent light stability, an adjustable energy band, easy modification, good biocompatibility, and the ability to photosensitize oxygen to produce reactive oxygen species have been widely used in the fields of solar cells, highly sensitive detection systems, biological imaging, and anti-cancer and anti-microbial treatment. Photodynamic therapy is non-invasive and has high temporal and spatial resolution and is a highly effective antimicrobial treatment that does not easily induce drug resistance; it has also stimulated the scientific research enthusiasm of researchers and has become a research hotspot in the antimicrobial field. In this review, the photodynamic antibacterial applications of conjugated polymers with different structure types are summarized, and their development directions are considered.

Hydrogels for Antitumor and Antibacterial Therapy

As a highly absorbent and hydrophobic material with a three-dimensional network structure, hydrogels are widely used in biomedical fields for their excellent biocompatibility, low immunogenicity, adjustable physicochemical properties, ability to encapsulate a variety of drugs, controllability, and degradability. Hydrogels can be used not only for wound dressings and tissue repair, but also as drug carriers for the treatment of tumors. As multifunctional hydrogels are the focus for many researchers, this review focuses on hydrogels for antitumor therapy, hydrogels for antibacterial therapy, and hydrogels for co-use in tumor therapy and bacterial infection. We highlighted the advantages and representative applications of hydrogels in these fields and also outlined the shortages and future orientations of this useful tool, which might give inspirations for future studies.

Dual-Light-Triggered In Situ Structure and Function Regulation of Injectable Hydrogels for High-Efficient Anti-Infective Wound Therapy

Most injectable hydrogels used in biomedical engineering have unsatisfactory and untunable mechanical properties, making it difficult to match them with the mechanical strengths of different tissues and organs, which can cause a series of adverse consequences such as immune rejection and soft tissue contusion. In this contribution, dopamine-modified hyaluronic acid (HA-DA) is developed as the backbone for an injectable hydrogel using a catechol-Fe³⁺ coordination crosslinking strategy. Due to dynamic physical crosslinking, the hydrogel can be easily injected through a single syringe. Into the hydrogel, black phosphorous nanosheets loaded with a Zr-based porphyrinic metal-organic framework (PCN@BP) are introduced that could generate reactive oxygen species (ROS) under 660 nm laser irradiation, this promotes the oxidative coupling of dopamine in the presence of the ROS, introducing in situ chemical crosslinking into the hydrogel. A physical/chemical double-crosslinked hydrogel is obtained, effectively improving the hydrogel's mechanical properties, which are tuned in situ by adjusting the irradiation time to match the mechanical modulus of different biological tissues. Combining the excellent photothermal properties and photodynamic performance of the PCN@BP nanosheets yields effective sterilization under mild conditions (below 50 °C, low ROS production). The results show that this hydrogel is an excellent multifunctional wound dressing.