pH-activated nanoparticles for controlled topical delivery of farnesol to disrupt oral biofilm virulence

Enhanced antibacterial activity of bovine milk exosome-based drug formulation against bacterial pathogens

Milk is not only a source of nutrients, but also contains exosomes (Exo) that can serve as a vehicle for drug delivery. Here, we obtained bovine milk Exo using three efficient methods, demonstrating high quality for commercial production. The optimized Exo displayed a size of 105.2 nm and an entrapment efficiency of 88.4 %. The Exo has been functionalized with a combination therapy comprising isobavachalcone (IS) and polymyxin B (PB), referred to as IP-Exo. The antibacterial efficacy of IP-Exo was significantly enhanced, enabling the elimination of 99 % of multidrug-resistant (MDR) bacterial pathogens in 4 h. Furthermore, scanning electron microscopy images demonstrated that the drug combination led to the complete dismantling of the bacterial structure. IP-Exo showed nearly 100 % microbial inhibition in fresh orange juice and accelerated wound healing in mouse models. Collectively, IP-Exo provides excellent potential for application within the food industry and animal husbandry as a defense against bacterial pathogens.

pH-Responsive Charge Convertible Hyperbranched Poly(ionic liquid) Nanoassembly with High Biocompatibility for Resistance-Free Antimicrobial Applications

As a potential alternative to antibiotics, hyperbranched poly(ionic liquid)s (HPILs) have demonstrated significant potential in combating bacterial biofilms. However, their high cation density poses a high risk of toxicity, greatly limiting their in vivo applications. In this study, we constructed a biocompatible HPIL (HPIL-Glu) from a hyperbranched polyurea core with modified terminals featuring charge-convertible ionic liquids. These ionic liquid moieties consist of an ammonium-based cation and a gluconate (Glu) organic counter. HPIL-Glu could form a homogeneous nanoassembly in water and exhibited a pH-responsive charge conversion property. Under neutral conditions, Glu shielded the positively charged surface, minimizing the toxicity. In a mildly acidic environment, Glu protonation exposes cationic moieties to biofilm eradication. Comprehensive antimicrobial assessments demonstrate that HPIL-Glu effectively kills bacteria and promotes the healing of bacteria-infected chronic wounds. Furthermore, prolonged exposure to HPIL-Glu does not induce antimicrobial resistance.

Oxygen self-sufficient nanodroplet composed of fluorinated polymer for high-efficiently PDT eradicating oral biofilm

Oral biofilm is the leading cause of dental caries, which is difficult to completely eradicate because of the complicated biofilm structure. What's more, the hypoxia environment of biofilm and low water-solubility of conventional photosensitizers severely restrict the therapeutic effect of photodynamic therapy (PDT) for biofilm. Although conventional photosensitizers could be loaded in nanocarriers, it has reduced PDT effect because of aggregation-caused quenching (ACQ) phenomenon. In this study, we fabricated an oxygen self-sufficient nanodroplet (PFC/TPA@FNDs), which was composed of fluorinated-polymer (FP), perfluorocarbons (PFC) and an aggregation-induced emission (AIE) photosensitizer (Triphenylamine, TPA), to eradicate oral bacterial biofilm and whiten tooth. Fluorinated-polymer was synthesized by polymerizing (Dimethylamino)ethyl methacrylate, fluorinated monomer and 1-nonanol monomer. The nanodroplets could be protonated and behave strong positive charge under bacterial biofilm acid environment promoting nanodroplets deeply penetrating biofilm. More importantly, the nanodroplets had extremely high PFC and oxygen loading efficacy because of the hydrophobic affinity between fluorinated-polymer and PFC to relieve the hypoxia environment and enhance PDT effect. Additionally, compared with conventional ACQ photosensitizers loaded system, PFC/TPA@FNDs could behave superior PDT effect to ablate oral bacterial biofilm under light irradiation due to the unique AIE effect. In vivo caries animal model proved the nanodroplets could reduce dental caries area without damaging tooth structure. Ex vivo tooth whitening assay also confirmed the nanodroplets had similar tooth whitening ability compared with commercial tooth whitener H2O2, while did not disrupt the surface microstructure of tooth. This oxygen self-sufficient nanodroplet provides an alternative visual angle for oral biofilm eradication in biomedicine.

Chitosan Phytate Nanoparticles: A Synergistic Strategy for Effective Dental Caries Prevention

Dental caries is a widespread oral disease that poses a significant medical challenge. Traditional caries prevention methods, primarily the application of fluoride, often fall short in effectively destroying biofilms and preventing enamel demineralization, thereby providing limited efficacy in halting the progression of caries over time. To address this issue, we have developed a green and cost-effective synergistic strategy for the prevention of dental caries. By combining natural sodium phytate and chitosan, we have created chitosan-sodium phytate nanoparticles that offer both the antimicrobial properties of chitosan and the enamel demineralization-inhibiting capabilities of sodium phytate. In an ex vivo biofilm model of human teeth, we found that these nanoparticles effectively prevent biofilm buildup and acid damage to the mineralized tissue. Additionally, topical treatment of dental caries in rodent models has shown that these nanoparticles effectively suppress disease progression without negatively impacting oral microbiota diversity or causing harm to the gingival-mucosal tissues, unlike traditional prevention methods.

Polymeric Nanoparticles for Drug Delivery

The recent emergence of nanomedicine has revolutionized the therapeutic landscape and necessitated the creation of more sophisticated drug delivery systems. Polymeric nanoparticles sit at the forefront of numerous promising drug delivery designs, due to their unmatched control over physiochemical properties such as size, shape, architecture, charge, and surface functionality. Furthermore, polymeric nanoparticles have the ability to navigate various biological barriers to precisely target specific sites within the body, encapsulate a diverse range of therapeutic cargo and efficiently release this cargo in response to internal and external stimuli. However, despite these remarkable advantages, the presence of polymeric nanoparticles in wider clinical application is minimal. This review will provide a comprehensive understanding of polymeric nanoparticles as drug delivery vehicles. The biological barriers affecting drug delivery will be outlined first, followed by a comprehensive description of the various nanoparticle designs and preparation methods, beginning with the polymers on which they are based. The review will meticulously explore the current performance of polymeric nanoparticles against a myriad of diseases including cancer, viral and bacterial infections, before finally evaluating the advantages and crucial challenges that will determine their wider clinical potential in the decades to come.

Microenvironment-Driven Fenton Nanoreactor Enabled by Metal-Phenolic Encapsulation of Calcium Peroxide for Effective Control of Dental Caries

Caries are one of the most common oral diseases caused by pathogenic bacterial infections, which are widespread and persistently harmful to human health. Using nanoparticles to invade biofilms and produce reactive oxygen species (ROS) in situ is a promising strategy for killing bacteria and disrupting the structure of biofilms. In this work, a biofilm-targeting Fenton nanoreactor is reported that can generate ROS responsive to the cariogenic microenvironment. The nanoreactor is constructed by metal-phenolic encapsulation of calcium peroxide (CaO2) followed by modification with a biofilm targeting ligand dextran. Within the cariogenic biofilm, the Fenton nanoreactor is activated by an acidic microenvironment to be decomposed into H2O2 and iron ions, triggering a Fenton-like reaction to generate ROS that can eliminate the biofilm by breaking down extracellular polymeric substances (EPS) and killing cariogenic bacteria. Meanwhile, the depletion of excess protons in biofilm leads to a reversal of the cariogenic microenvironment. The Fenton nanoreactor can effectively inhibit the biofilm formation of Streptococcus mutans on ex vivo human teeth and is effective in preventing caries meanwhile maintaining the oral microbial diversity in rat caries infection model. This work provides a novel and efficient modality for acid microenvironment-driven ROS therapy.

Poly(amino acid)-based drug delivery nanoparticles eliminate Methicillin resistant Staphylococcus aureus via tunable release of antibiotic

Bacterial infections threaten public health, and novel therapeutic strategies critically demand to be explored. Herein, poly(amino acid) (PAA)-based drug delivery nanoparticles (NPs) were designed for eliminating Methicillin resistant Staphylococcus aureus (MRSA) via tunable release of antibiotic. Using N-acryloyl amino acids (valine, valine methyl ester, aspartic acid, serine) as monomers, four kinds of amphiphilic PAAs were synthesized via photoinduced electron/energy transfer-reversible addition fragmentation chain-transfer (PET-RAFT) polymerization and were further assembled into nano-sized delivery systems. Their assemble behavior was drove mainly by hydrophobic/hydrophilic interaction, which determined the particle size, efficacy of drug loading and release; but numerous hydrogen bonding (HB) interaction also played an important role in regulating morphologies of the NPs and enriching drug-binding capacity. By changing the HB- and hydrophobic-interaction of the PAAs, the particle sizes (240.7 nm-302.7 nm), the drug loading efficiency (9.57%-19.76%), and the Rifampicin (Rif) release rate (49.6%-69.7%) of the PAA-based NPs could be tunable. Specially, the antimicrobial properties of the Rif-loaded NPs are found to be related to the release of Rif, which was determined by its hydrophobic interaction with hydrophobic blocks and HB interaction with hydrophilic blocks. These studies provide a new outlook for the design of delivery systems for the therapy of bacterial infection.

Physiological adventures in Candida albicans: farnesol and ubiquinones

SUMMARYFarnesol was first identified as a quorum-sensing molecule, which blocked the yeast to hyphal transition in Candida albicans, 22 years ago. However, its interactions with Candida biology are surprisingly complex. Exogenous (secreted or supplied) farnesol can also act as a virulence factor during pathogenesis and as a fungicidal agent triggering apoptosis in other competing fungi. Farnesol synthesis is turned off both during anaerobic growth and in opaque cells. Distinctly different cellular responses are observed as exogenous farnesol levels are increased from 0.1 to 100 µM. Reported changes include altered morphology, stress response, pathogenicity, antibiotic sensitivity/resistance, and even cell lysis. Throughout, there has been a dearth of mechanisms associated with these observations, in part due to the absence of accurate measurement of intracellular farnesol levels (Fi). This obstacle has recently been overcome, and the above phenomena can now be viewed in terms of changing Fi levels and the percentage of farnesol secreted. Critically, two aspects of isoprenoid metabolism present in higher organisms are absent in C. albicans and likely in other yeasts. These are pathways for farnesol salvage (converting farnesol to farnesyl pyrophosphate) and farnesylcysteine cleavage, a necessary step in the turnover of farnesylated proteins. Together, these developments suggest a unifying model, whereby high, threshold levels of Fi regulate which target proteins are farnesylated or the extent to which they are farnesylated. Thus, we suggest that the diversity of cellular responses to farnesol reflects the diversity of the proteins that are or are not farnesylated.

Enhancing near-infrared II photodynamic therapy with nitric oxide for eradicating multidrug-resistant biofilms in deep tissues

Nitric oxide (NO) enhanced photodynamic therapy (PDT) is a promising approach to overcome drug tolerance and resistance to biofilm but is limited by its short excitation wavelengths and low yield of reactive oxygen species (ROS). Herein, we develop a compelling degradable polymer-based near-infrared II (NIR-II, 1000-1700 nm) photosensitizer (PNIR-II), which can maintain 50 % PDT efficacy even under a 2.6 cm tissue barrier. Remarkably, PNIR-II is synthesized by alternately connecting the electron donor thiophene to the electron acceptors diketopyrrolopyrrole (DPP) and boron dipyrromethene (BODIPY), where the intramolecular charge transfer properties can be tuned to increase the intersystem crossover rate and decrease the internal conversion rate, thereby stabilizing the NIR-II photodynamic rather than photothermal effect. For exerting a combination therapy to eradicate multidrug-resistant biofilms, PNIR-II is further assembled into nanoparticles (NPs) with a synthetic glutathione-triggered NO donor polymer. Under 1064 nm laser radiation, NPs precisely release ROS and NO that triggered by over-expressed GSH in the biofilm microenvironment, thereby forming more bactericidal reactive nitrogen species (RNS) in vitro and in vivo in the mice model that orderly destroy biofilm of multidrug-resistant Staphylococcus aureus cultures from clinical patients. It thus provides a new outlook for destroy the biofilm of deep tissues.

pH-responsive polymeric nanomaterials for the treatment of oral biofilm infections

Bacterial and fungal pathogens forming oral biofilms present significant public health challenges due to the failure of antimicrobial drugs. The ability of biofilms to lower pH levels results in dental plaque, leading to gingivitis and cavities. Nanoparticles (NPs) have attracted considerable interest for drug delivery and, thus, as a solution to biofilm-related microbial infections. A novel strategy in this regard involves using pH-responsive polymeric NPs within the acidic microenvironment of oral biofilms. The acidity of the oral biofilm microenvironment is governed by carbohydrate metabolism, accumulation of lactic acid, and extracellular DNA of extracellular polymeric substances by oral biofilm-forming microbial pathogens. This acidity also provides an opportunity to enhance antibacterial activity against biofilm cells using pH-responsive drug delivery approaches. Thus, various polymeric NPs loaded with poorly soluble drugs and responsive to the acidic pH of oral biofilms have been developed. This review focuses on various forms of such polymeric NPs loaded with drugs. The fundamental mechanisms of action of pH-responsive polymeric NPs, their cytological toxicity, and in vivo efficacy testing are thoroughly discussed.

The Evolving Microbiome of Dental Caries

Dental caries is a significant oral and public health problem worldwide, especially in low-income populations. The risk of dental caries increases with frequent intake of dietary carbohydrates, including sugars, leading to increased acidity and disruption of the symbiotic diverse and complex microbial community of health. Excess acid production leads to a dysbiotic shift in the bacterial biofilm composition, demineralization of tooth structure, and cavities. Highly acidic and acid-tolerant species associated with caries include Streptococcus mutans, Lactobacillus, Actinomyces, Bifidobacterium, and Scardovia species. The differences in microbiotas depend on tooth site, extent of carious lesions, and rate of disease progression. Metagenomics and metatranscriptomics not only reveal the structure and genetic potential of the caries-associated microbiome, but, more importantly, capture the genetic makeup of the metabolically active microbiome in lesion sites. Due to its multifactorial nature, caries has been difficult to prevent. The use of topical fluoride has had a significant impact on reducing caries in clinical settings, but the approach is costly; the results are less sustainable for high-caries-risk individuals, especially children. Developing treatment regimens that specifically target S. mutans and other acidogenic bacteria, such as using nanoparticles, show promise in altering the cariogenic microbiome, thereby combatting the disease.

Acid-Responsive Aggregation of Gold Nanoparticles for the Photothermal Treatment of Bacterial Infections

Photothermal therapy (PTT) is considered to be one of the promising methods to combat pathogenic bacteria. However, traditional PTT is prone to generate undesired temperature increase to surrounding normal tissues, which limits the application of PTT. Herein, an acid-responsive PTT system (Au nanoparticles system: AuNPs-S) was constructed based on the photothermal feature of spherical gold nanoparticles (AuNPs) and the low pH of the bacterial infected site. AuNPs-S is composed of two kinds of AuNPs: AuNPs modified with Asp-Asp-Asp-Asp-Asp-Cys (peptide A) were denoted as AuNPs-A; AuNPs modified with 2,3-dimethylmaleic anhydride (DA) grafted Lys-Gly-Gly-Lys-Gly-Gly-Lys-Cys (peptide B) were denoted as AuNPs-B/DA. AuNPs-B/DA with an acid-responsive moiety showed a charge-convertible feature. The negatively charged AuNPs-B/DA became positively charged AuNPs-B at low pH, aggregating with the negatively charged AuNPs-A via an electrostatic interaction, reaching the threshold to the interparticle plasmonic coupling effect among AuNPs, thereby killing bacteria precisely under the irradiation of near-infrared (NIR) light through the elevated temperature at the targeted area. This acid-responsive PTT strategy supplies an excellent mode for combating bacterial infections with no vital damage to normal tissues.

Potential lipid-based strategies of amphotericin B designed for oral administration in clinical application

Amphotericin B (AmB) is regarded as a first-line therapy against life-threatening invasive fungal infections. Due to its poor oral bioavailability, AmB is restricted to intravenous administration in clinical practice. As science continues to move forward, two lipid-based formulations are successfully developed for oral AmB administration, currently undergoing phase I clinical trials. Encouragingly, lipid-AmB conjugates with emulsions also exhibit a better bioavailability, which may be another strategy to design oral AmB formulation in clinical practice. Thus, this review mainly focused on the two lipid-based formulations in clinical trials, and discussed the potential perspectives of AmB-lipid conjugation-loaded nanocochleates and emulsions.

Advancing biofilm management through nanoformulation strategies: a review of dosage forms and administration routes

Biofilms are complex microbial communities formed by the attachment of bacteria or fungi to surfaces encased in a self-produced polymeric matrix. These biofilms are highly resistant to conventional antimicrobial therapies. The resistance mechanisms exhibited by biofilms include low antibiotic absorption, sluggish replication, adaptive stress response, and the formation of dormant-like phenotypes. The eradication of biofilms requires alternative strategies and approaches. Nanotechnological drug delivery systems allow excellent control over the drug chemistry, surface area, particle size, particle shape, and composition of nanostructures. Nanoformulations can enhance the efficacy of antimicrobial agents by improving their bioavailability, stability, and targeted delivery to the site of infection that helps biofilm eradication more effectively. In addition to nanoformulations, the route of administration and choice of dosage forms play a crucial role in treating biofilm infections. Systemic administration of antibiotics is effective in controlling systemic infection and sepsis associated with biofilms. Alternative routes of administration, such as inhalation, vaginal, ocular, or dermal, have been explored to target biofilm infections in specific organs. This review primarily examines the utilisation of nanoformulations in various administration routes for biofilm management. It also provides an overview of biofilms, current approaches, and the drawbacks associated with conventional methods.

Theranostic gold-in-gold cage nanoparticles enable photothermal ablation and photoacoustic imaging in biofilm-associated infection models

Biofilms are structured communities of microbial cells embedded in a self-produced matrix of extracellular polymeric substances. Biofilms are associated with many health issues in humans, including chronic wound infections and tooth decay. Current antimicrobials are often incapable of disrupting the polymeric biofilm matrix and reaching the bacteria within. Alternative approaches are needed. Here, we described a complex structure of a dextran-coated gold-in-gold cage nanoparticle that enabled photoacoustic and photothermal properties for biofilm detection and treatment. Activation of these nanoparticles with a near infrared laser could selectively detect and kill biofilm bacteria with precise spatial control and in a short timeframe. We observed a strong biocidal effect against both Streptococcus mutans and Staphylococcus aureus biofilms in mouse models of oral plaque and wound infections, respectively. These effects were over 100 times greater than those seen with chlorhexidine, a conventional antimicrobial agent. Moreover, this approach did not adversely affect surrounding tissues. We concluded that photothermal ablation using theranostic nanoparticles is a rapid, precise, and nontoxic method to detect and treat biofilm-associated infections.

Applications of quaternary ammonium compounds in the prevention and treatment of oral diseases: State-of-the-art and future directions

OBJECTIVES

The aim of this review is to comprehensively summarize the state-of-the-art developments of quaternary ammonium compounds (QACs) in the prevention and treatment of oral diseases. By discussing the structural diversity and the potential killing mechanism, we try to offer some insights for the future research of QACs.

DATA, SOURCES & STUDY SELECTION

A literature search was conducted in electronic databases (Web of Science, PubMed, Medline, and Scopus). Publications that involved the applications of QACs, especially those related to the prevention and treatment of oral diseases, are included.

RESULTS

We have reviewed the relevant research on QACs over the past two decades. The research results indicate that the current applications are mainly focused on dental material modification and direct pharmacological interventions. Concurrently, challenges such as potential risks to normal tissues and impediments in drug resistance and microbial persistence present certain application constraints. The latest studies have encompassed the exploration of smart materials and nanoparticle formulations.

CONCLUSIONS

The killing mechanism may possess a threshold related to charge density. However, the exact process remains enigmatic. The structural diversity and the exploration of intelligent materials and nanoparticle formulations provide directions in development of novel QACs.

CLINICAL SIGNIFICANCE

The intricate oral anatomy, combined with the multifaceted oral microbiome, necessitates specialized materials for the targeted prevention and treatment of oral pathologies. QACs represent a cohort of compounds distinguished by potent anti-infective and anti-tumor attributes. Innovations in intelligent materials and nanoparticle formulations amplify their potential in significantly advancing the prevention and therapeutic interventions for oral diseases.

Progress on the pathological tissue microenvironment barrier-modulated nanomedicine

Imbalance in the tissue microenvironment is the main obstacle to drug delivery and distribution in the human body. Before penetrating the pathological tissue microenvironment to the target site, therapeutic agents are usually accompanied by three consumption steps: the first step is tissue physical barriers for prevention of their penetration, the second step is inactivation of them by biological molecules, and the third step is a cytoprotective mechanism for preventing them from functioning on specific subcellular organelles. However, recent studies in drug-hindering mainly focus on normal physiological rather than pathological microenvironment, and the repair of damaged physiological barriers is also rarely discussed. Actually, both the modulation of pathological barriers and the repair of damaged physiological barriers are essential in the disease treatment and the homeostasis maintenance. In this review, we present an overview describing the latest advances in the generality of these pathological barriers and barrier-modulated nanomedicine. Overall, this review holds considerable significance for guiding the design of nanomedicine to increase drug efficacy in the future.

Research progress of nanoparticle targeting delivery systems in bacterial infections

Bacterial infection is a huge threat to the health of human beings and animals. The abuse of antibiotics have led to the occurrence of bacterial multidrug resistance, which have become a difficult problem in the treatment of clinical infections. Given the outstanding advantages of nanodrug delivery systems in cancer treatment, many scholars have begun to pay attention to their application in bacterial infections. However, due to the similarity of the microenvironment between bacterial infection lesions and cancer sites, the targeting and accuracy of traditional microenvironment-responsive nanocarriers are questionable. Therefore, finding new specific targets has become a new development direction of nanocarriers in bacterial prevention and treatment. This article reviews the infectious microenvironment induced by bacteria and a series of virulence factors of common pathogenic bacteria and their physiological functions, which may be used as potential targets to improve the targeting accuracy of nanocarriers in lesions.

Antibacterial mechanism of areca nut essential oils against Streptococcus mutans by targeting the biofilm and the cell membrane

Introduction

Dental caries is one of the most common and costly biofilm-dependent oral diseases in the world. Streptococcus mutans is the major cariogenic pathogen of dental caries. S. mutans synthesizes extracellular polysaccharides by autologous glucosyltransferases, which then promotes bacterial adhesion and cariogenic biofilm formation. The S. mutans biofilm is the principal target for caries treatment. This study was designed to explore the antibacterial activity and mechanisms of areca nut essential oil (ANEO) against S. mutans.

Methods

The ANEOs were separated by negative pressure hydro-distillation. The Kirby-Bauer method and broth microdilution method were carried out to evaluate the antibacterial activity of different ANEOs. The antibacterial mechanism was revealed by crystal violet staining, XTT reduction, microbial adhesion to hydrocarbon test, extracellular polysaccharide production assay, glucosyltransferase activity assay, lactate dehydrogenase leaking, propidium iodide staining and scanning electron microscopy (SEM). The cytotoxicity of ANEOs was determine by MTT assay.

Results

The ANEOs separated at different temperatures exhibited different levels of antibacterial activity against S. mutans, and the ANEO separated at 70°C showed the most prominent bacteriostatic activity. Anti-biofilm experiments showed that the ANEOs attenuated the adhesion ability of S. mutans by decreasing the surface hydrophobicity of the bacteria, prevented S. mutans biofilm formation by inhibiting glucosyltransferase activity, reducing extracellular polysaccharide synthesis, and reducing the total biofilm biomass and activity. SEM further demonstrated the destructive effects of the ANEOs on the S. mutans biofilm. Cell membrane-related experiments indicated that the ANEOs destroyed the integrity of the cell membrane, resulting in the leakage of lactic dehydrogenase and nucleic acids. SEM imaging of S. mutans cell showed the disruption of the cellular morphology by the ANEOs. The cytotoxicity assay suggested that ANEO was non-toxic towards normal oral epithelial cells.

Discussion

This study displayed that ANEOs exerted antibacterial activity against S. mutans primarily by affecting the biofilm and disrupting the integrity of the cell membrane. ANEOs has the potential to be developed as an antibacterial agent for preventing dental caries. Additionally, a new method for the separation of essential oil components is presented.

pH-Responsive Biomaterials for the Treatment of Dental Caries-A Focussed and Critical Review

Dental caries is a common and costly multifactorial biofilm disease caused by cariogenic bacteria that ferment carbohydrates to lactic acid, demineralizing the inorganic component of teeth. Therefore, low pH (pH 4.5) is a characteristic signal of the localised carious environment, compared to a healthy oral pH range (6.8 to 7.4). The development of pH-responsive delivery systems that release antibacterial agents in response to low pH has gained attention as a targeted therapy for dental caries. Release is triggered by high levels of acidogenic species and their reduction may select for the establishment of health-associated biofilm communities. Moreover, drug efficacy can be amplified by the modification of the delivery system to target adhesion to the plaque biofilm to extend the retention time of antimicrobial agents in the oral cavity. In this review, recent developments of different pH-responsive nanocarriers and their biofilm targeting mechanisms are discussed. This review critically discusses the current state of the art and innovations in the development and use of smart delivery materials for dental caries treatment. The authors' views for the future of the field are also presented.

Hydrogel-Encapsulated Biofilm Inhibitors Abrogate the Cariogenic Activity of Streptococcus mutans

We designed and synthesized analogues of a previously identified biofilm inhibitor IIIC5 to improve solubility, retain inhibitory activities, and to facilitate encapsulation into pH-responsive hydrogel microparticles. The optimized lead compound HA5 showed improved solubility of 120.09 μg/mL, inhibited Streptococcus mutans biofilm with an IC50 value of 6.42 μM, and did not affect the growth of oral commensal species up to a 15-fold higher concentration. The cocrystal structure of HA5 with GtfB catalytic domain determined at 2.35 Å resolution revealed its active site interactions. The ability of HA5 to inhibit S. mutans Gtfs and to reduce glucan production has been demonstrated. The hydrogel-encapsulated biofilm inhibitor (HEBI), generated by encapsulating HA5 in hydrogel, selectively inhibited S. mutans biofilms like HA5. Treatment of S. mutans-infected rats with HA5 or HEBI resulted in a significant reduction in buccal, sulcal, and proximal dental caries compared to untreated, infected rats.

Smart Dental Materials Intelligently Responding to Oral pH to Combat Caries: A Literature Review

Smart dental materials are designed to intelligently respond to physiological changes and local environmental stimuli to protect the teeth and promote oral health. Dental plaque, or biofilms, can substantially reduce the local pH, causing demineralization that can then progress to tooth caries. Progress has been made recently in developing smart dental materials that possess antibacterial and remineralizing capabilities in response to local oral pH in order to suppress caries, promote mineralization, and protect tooth structures. This article reviews cutting-edge research on smart dental materials, their novel microstructural and chemical designs, physical and biological properties, antibiofilm and remineralizing capabilities, and mechanisms of being smart to respond to pH. In addition, this article discusses exciting and new developments, methods to further improve the smart materials, and potential clinical applications.

Combating Bacterial Biofilms: Current and Emerging Antibiofilm Strategies for Treating Persistent Infections

Biofilms are intricate multicellular structures created by microorganisms on living (biotic) or nonliving (abiotic) surfaces. Medically, biofilms often lead to persistent infections, increased antibiotic resistance, and recurrence of infections. In this review, we highlighted the clinical problem associated with biofilm infections and focused on current and emerging antibiofilm strategies. These strategies are often directed at disrupting quorum sensing, which is crucial for biofilm formation, preventing bacterial adhesion to surfaces, impeding bacterial aggregation in viscous mucus layers, degrading the extracellular polymeric matrix, and developing nanoparticle-based antimicrobial drug complexes which target persistent cells within the biofilm core. It is important to acknowledge, however, that the use of antibiofilm agents faces obstacles, such as limited effectiveness in vivo, potential cytotoxicity to host cells, and propensity to elicit resistance in targeted biofilm-forming microbes. Emerging next generation antibiofilm strategies, which rely on multipronged approaches, were highlighted, and these benefit from current advances in nanotechnology, synthetic biology, and antimicrobial drug discovery. The assessment of current antibiofilm mitigation approaches, as presented here, could guide future initiatives toward innovative antibiofilm therapeutic strategies. Enhancing the efficacy and specificity of some emerging antibiofilm strategies via careful investigations, under conditions that closely mimic biofilm characteristics within the human body, could bridge the gap between laboratory research and practical application.

Smart dental materials for antimicrobial applications

Smart biomaterials can sense and react to physiological or external environmental stimuli (e.g., mechanical, chemical, electrical, or magnetic signals). The last decades have seen exponential growth in the use and development of smart dental biomaterials for antimicrobial applications in dentistry. These biomaterial systems offer improved efficacy and controllable bio-functionalities to prevent infections and extend the longevity of dental devices. This review article presents the current state-of-the-art of design, evaluation, advantages, and limitations of bioactive and stimuli-responsive and autonomous dental materials for antimicrobial applications. First, the importance and classification of smart biomaterials are discussed. Second, the categories of bioresponsive antibacterial dental materials are systematically itemized based on different stimuli, including pH, enzymes, light, magnetic field, and vibrations. For each category, their antimicrobial mechanism, applications, and examples are discussed. Finally, we examined the limitations and obstacles required to develop clinically relevant applications of these appealing technologies.

Theranostic gold in a gold cage nanoparticle for photothermal ablation and photoacoustic imaging of skin and oral infections

Biofilms are structured communities of microbial cells embedded in a self-produced matrix of extracellular polymeric substances. Biofilms are associated with many health issues in humans, including chronic wound infections and tooth decay. Current antimicrobials are often incapable of disrupting the polymeric biofilm matrix and reaching the bacteria within. Alternative approaches are needed. Here, we describe a unique structure of dextran coated gold in a gold cage nanoparticle that enables photoacoustic and photothermal properties for biofilm detection and treatment. Activation of these nanoparticles with a near infrared laser can selectively detect and kill biofilm bacteria with precise spatial control and in a short timeframe. We observe a strong biocidal effect against both Streptococcus mutans and Staphylococcus aureus biofilms in mouse models of oral plaque and wound infections respectively. These effects were over 100 times greater than that seen with chlorhexidine, a conventional antimicrobial agent. Moreover, this approach did not adversely affect surrounding tissues. We conclude that photothermal ablation using theranostic nanoparticles is a rapid, precise, and non-toxic method to detect and treat biofilm-associated infections.

Novel bioactive dental restorations to inhibit secondary caries in enamel and dentin under oral biofilms

OBJECTIVE

To provide the first review on cutting-edge research on the development of new bioactive restorations to inhibit secondary caries in enamel and dentin under biofilms. State-of-the-art bioactive and therapeutic materials design, structure-property relationships, performance and efficacies in oral biofilm models.

DATA, SOURCES AND STUDY SELECTION

Researches on development and assessment new secondary caries inhibition restorations via in vitro and in vivo biofilm-based secondary caries models were included. The search of articles was carried out in Web of Science, PubMed, Medline and Scopus.

CONCLUSIONS

Based on the found articles, novel bioactive materials are divided into different categories according to their remineralization and antibacterial biofunctions. In vitro and in vivo biofilm-based secondary caries models are effective way of evaluating the materials efficacies. However, new intelligent and pH-responsive materials were still urgent need. And the materials evaluation should be performed via more clinical relevant biofilm-based secondary caries models.

CLINICAL SIGNIFICANCE

Secondary caries is a primary reason for dental restoration failures. Biofilms produce acids, causing demineralization and secondary caries. To inhibit dental caries and improve the health and quality of life for millions of people, it is necessary to summarize the present state of technologies and new advances in dental biomaterials for preventing secondary caries and protecting tooth structures against oral biofilm attacks. In addition, suggestions for future studies are provided.

Dual-responsive antibiotic and baicalein co-delivery nanoparticles with enhanced synergistic antibacterial activity

Globally, due to the rapid development of bacterial resistance, bacterial infections lead to significant mortality and morbidity which require efficient strategies to eradicate these infections. Herein, we prepared a dual-responsive synergistic drug delivery nanoparticle carrier (NPS@Bai/Cip), which responds to sub-acid bacterial microenvironments and targets phosphatase or phospholipase at infection sites. Nanoparticles surfaces were positively (10.0 mV) charged under acidic conditions, leading to good bacterial adhesion and enhanced drug accumulation. NPS@Bai/Cip showed good antibacterial and anti-biofilm activity against drug-resistant Pseudomonas aeruginosa. NPS@Bai/Cip could inhibit the biofilm formation via affecting the swimming, swarming, and twitching motilities of P. aeruginosa. NPS@Bai/Cip was used to treat drug-resistance P. aeruginosa-induced infection in rats by improving wound healing and reducing inflammatory responses. Thus, NPS@Bai/Cip functioned as an antibacterial and antibiofilm agent with good potential for treating bacteria-induced infections.

Targeted pH-responsive chitosan nanogels with Tanshinone IIA for enhancing the antibacterial/anti-biofilm efficacy

Persistent bacterial infection caused by biofilms is one of the most serious problems that threatened human health. The development of antibacterial agents remains a challenge to penetrate biofilm and effectively treat the underlying bacterial infection. In the current study, chitosan-based nanogels were developed for encapsulating the Tanshinone IIA (TA) to enhance the antibacterial and anti-biofilm efficacy against Streptococcus mutans (S. mutans). The as-prepared nanogels (TA@CS) displayed excellent encapsulation efficiency (91.41 ± 0.11 %), uniform particle sizes (393.97 ± 13.92 nm), and enhanced positive potential (42.27 ± 1.25 mV). After being coated with CS, the stability of TA under light and other harsh environments was greatly improved. In addition, TA@CS displayed pH responsiveness, allowing it to selectively release more TA in acidic conditions. Furthermore, the positively charged TA@CS were equipped to target negatively charged biofilm surfaces and efficiently penetrate through biofilm barriers, making it promising for remarkable anti-biofilm activity. More importantly, when TA was encapsulated into CS nanogels, the antibacterial activity of TA was enhanced at least 4-fold. Meanwhile, TA@CS inhibited 72 % of biofilm formation at 500 μg/mL. The results demonstrated that the nanogels constituted CS and TA had antibacterial/anti-biofilm properties with synergistic enhanced effects, which will benefit pharmaceutical, food, and other fields.

Promoting lacunar bone regeneration with an injectable hydrogel adaptive to the microenvironment

Injectable hydrogel is suitable for the repair of lacunar bone deficiency. This study fabricated an injectable, self-adaptive silk fibroin/mesoporous bioglass/sodium alginate (SMS) composite hydrogel system. With controllable and adjustable physical and chemical properties, the SMS hydrogel could be easily optimized adaptively to different clinical applications. The SMS hydrogel effectively showed great injectability and shapeability, allowing defect filling with no gap. Moreover, the SMS hydrogel displayed self-adaptability in mechanical reinforcement and degradation, responsive to the concentration of Ca²⁺ and inflammatory-like pH value in the microenvironment of bone deficiency, respectively. In vitro biological studies indicated that SMS hydrogel could promote osteogenic differentiation of bone marrow mesenchymal stem cells by activation of the MAPK signaling pathway. The SMS hydrogel also could improve migration and tube formation of human umbilical vein endothelial cells. Investigations of the crosstalk between osteoblasts and macrophages confirmed that SMS hydrogel could regulate macrophage polarization from M1 to M2, which could create a specific favorable environment to induce new bone formation and angiogenesis. Meanwhile, SMS hydrogel was proved to be antibacterial, especially for gram-negative bacteria. Furthermore, in vivo study indicated that SMS could be easily applied for maxillary sinus elevation, inducing sufficient new bone formation. Thus, it is convincing that SMS hydrogel could be potent in a simple, minimally invasive and efficient treatment for the repair of lacunar bone deficiency.

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Mesoporous bioglass was used as the crosslinking agent and in-situ porogen to form a porous injectable hydrogel.

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The composite hydrogel had suitable injectability and self-adaptability for lacunar bone regeneration.

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The composite hydrogel can simultaneously regulate macrophage polarization and osteogenic differentiation.

Recent nanotechnology-based strategies for interfering with the life cycle of bacterial biofilms

Biofilm formation plays an important role in the resistance development in bacteria to conventional antibiotics. Different properties of the bacterial strains within biofilms compared with their planktonic states and the protective effect of extracellular polymeric substances contribute to the insusceptibility of bacterial cells to conventional antimicrobials. Although great effort has been devoted to developing novel antibiotics or synthetic antibacterial compounds, their efficiency is overshadowed by the growth of drug resistance. Developments in nanotechnology have brought various feasible strategies to combat biofilms by interfering with the biofilm life cycle. In this review, recent nanotechnology-based strategies for interfering with the biofilm life cycle according to the requirements of different stages are summarized. Additionally, the importance of strategies that modulate the bacterial biofilm microenvironment is also illustrated with specific examples. Lastly, we discussed the remaining challenges and future perspectives on nanotechnology-based strategies for the treatment of bacterial infection.

Exploring Possible Ways to Enhance the Potential and Use of Natural Products through Nanotechnology in the Battle against Biofilms of Foodborne Bacterial Pathogens

Biofilms enable pathogenic bacteria to survive in unfavorable environments. As biofilm-forming pathogens can cause rapid food spoilage and recurrent infections in humans, especially their presence in the food industry is problematic. Using chemical disinfectants in the food industry to prevent biofilm formation raises serious health concerns. Further, the ability of biofilm-forming bacterial pathogens to tolerate disinfection procedures questions the traditional treatment methods. Thus, there is a dire need for alternative treatment options targeting bacterial pathogens, especially biofilms. As clean-label products without carcinogenic and hazardous potential, natural compounds with growth and biofilm-inhibiting and biofilm-eradicating potentials have gained popularity as natural preservatives in the food industry. However, the use of these natural preservatives in the food industry is restricted by their poor availability, stability during food processing and storage. Also there is a lack of standardization, and unattractive organoleptic qualities. Nanotechnology is one way to get around these limitations and as well as the use of underutilized bioactives. The use of nanotechnology has several advantages including traversing the biofilm matrix, targeted drug delivery, controlled release, and enhanced bioavailability, bioactivity, and stability. The nanoparticles used in fabricating or encapsulating natural products are considered as an appealing antibiofilm strategy since the nanoparticles enhance the activity of the natural products against biofilms of foodborne bacterial pathogens. Hence, this literature review is intended to provide a comprehensive analysis of the current methods in nanotechnology used for natural products delivery (biofabrication, encapsulation, and nanoemulsion) and also discuss the different promising strategies employed in the recent and past to enhance the inhibition and eradication of foodborne bacterial biofilms.

Engineered organic nanoparticles to combat biofilms

Biofilms are colonies of microorganisms that are embedded in autocrine extracellular polymeric substances (EPS), imparting antibiotic resistance and recalcitrant bacterial infection. Nanoparticles (NPs) can enhance the biofilm inhibition and eradication of delivered antibiotics. This is mainly because of enhanced EPS penetration and a high local drug concentration. As we discuss here, novel strategies are being developed to further enhance the antibiofilm capacity of NPs, including size optimization, surface modification, stimuli-triggered release, and combined strategies. Thus, NPs represent an effective and promising approach to combat biofilms.

Smart delivery systems for microbial biofilm therapy: Dissecting design, drug release and toxicological features

Bacterial biofilms are highly protected surface attached communities of bacteria that typically cause chronic infections. To address their recalcitrance to antibiotics and minimise side effects of current therapies, smart drug carriers are being explored as promising platforms for antimicrobials. Herein, we briefly summarize recent efforts and considerations that have been applied in the design of these smart carriers. We guide readers on a journey on how they can leverage the inherent biofilm microenvironment, external stimuli, or combine both types of stimuli in a predictable manner. The specific carrier features that are responsible for their 'on-demand' properties are detailed and their impact on antibiofilm property are further discussed. Moreover, an analysis on the impact of such features on drug release profiles is provided. Since nanotechnology represents a significant slice of the drug delivery pie, some insights on the potential toxicity are also depicted. We hope that this review inspires researchers to use their knowledge and creativity to design responsive systems that can eradicate biofilm infections.

Targeting Cariogenic Streptococcus mutans in Oral Biofilms with Charge-Switching Smart Antimicrobial Polymers

Cariogenic biofilms produce strong acidic microenvironments, which is the primary cause of dental caries. Streptococcus mutans is a dominant species in cariogenic biofilms. Herein, we report a pH-responsive, charge-switching smart copolymer to selectively target and eradicate bacteria in cariogenic biofilms. To that end, the copolymer is designed to be activated in an acidic environment. The smart copolymer, Poly-1A, consists of ternary compositions of monomers with a cationic ethyl ammonium group, a carboxylic group, and a hydrophobic group in the side chains. The net charge of Poly-1A was charge neutral at neutral pH, but it switched to be cationic because the acidic carboxylate side chains were protonated and became neutral; however, the ammonium groups remained positive. Poly-1A with a net positive charge bound to the anionic surface of oral bacteria by electrostatic interactions and disrupted the bacterial membranes, causing bacterial death. Poly-1A reduced the cell viability of planktonic and biofilm S. mutans at pH 4.5, while it was not bactericidal at pH 7.4. Poly-1A did not reduce the cell viability of human gingival fibroblasts and periodontal ligament stem cells for a 1 h incubation.

Advanced materials and technologies for oral diseases

Oral disease, as a class of diseases with very high morbidity, brings great physical and mental damage to people worldwide. The increasing burden and strain on individuals and society make oral diseases an urgent global health problem. Since the treatment of almost all oral diseases relies on materials, the rapid development of advanced materials and technologies has also promoted innovations in the treatment methods and strategies of oral diseases. In this review, we systematically summarized the application strategies in advanced materials and technologies for oral diseases according to the etiology of the diseases and the comparison of new and old materials. Finally, the challenges and directions of future development for advanced materials and technologies in the treatment of oral diseases were refined. This review will guide the fundamental research and clinical translation of oral diseases for practitioners of oral medicine.

pH-activated antibiofilm strategies for controlling dental caries

Dental biofilms are highly assembled microbial communities surrounded by an extracellular matrix, which protects the resident microbes. The microbes, including commensal bacteria and opportunistic pathogens, coexist with each other to maintain relative balance under healthy conditions. However, under hostile conditions such as sugar intake and poor oral care, biofilms can generate excessive acids. Prolonged low pH in biofilm increases proportions of acidogenic and aciduric microbes, which breaks the ecological equilibrium and finally causes dental caries. Given the complexity of oral microenvironment, controlling the acidic biofilms using antimicrobials that are activated at low pH could be a desirable approach to control dental caries. Therefore, recent researches have focused on designing novel kinds of pH-activated strategies, including pH-responsive antimicrobial agents and pH-sensitive drug delivery systems. These agents exert antibacterial properties only under low pH conditions, so they are able to disrupt acidic biofilms without breaking the neutral microenvironment and biodiversity in the mouth. The mechanisms of low pH activation are mainly based on protonation and deprotonation reactions, acids labile linkages, and H⁺-triggered reactive oxygen species production. This review summarized pH-activated antibiofilm strategies to control dental caries, concentrating on their effect, mechanisms of action, and biocompatibility, as well as the limitation of current research and the prospects for future study.

Drug delivery approaches for enhanced antibiofilm therapy

Biofilms have attracted increasing attention in recent years. Many bacterial infections are associated with biofilm formation. A bacterial biofilm is an aggregated membrane-like substance that is composed of a large number of bacteria and their secreted extracellular polymeric substances. The traditional antibiofilm approaches, such as chemotherapy based on antibiotics, are often ineffective in eradicating biofilms owing to the limited diffusion ability of antibiotics within biofilms and inactivation of antibiotics by biofilms. Moreover, a larger dosage of antibiotics could be effective, but leads to an increased tolerance. Smart drug delivery systems that deliver antibiotics into the biofilm interior is a promising strategy to meet this challenge. In this review, we focus on the methods to improve drug delivery efficiency for enhanced chemotherapy of biofilms. Furthermore, we have summarized chemical approaches for enhanced drug delivery, such as chemical shields, charge reversal, and dual corona enhanced delivery strategies; these methods focus on physicochemical biofilm properties and specific biofilm features. Afterwards, physical approaches are discussed, such as magnetism-mediated drug delivery, electricity-mediated drug delivery, ultrasound-mediated drug delivery, and shock wave-mediated drug delivery. Finally, a perspective on the development of next-generation antibiofilm drug delivery systems is given.

GSH-depleting and H2O2-self-supplying hybrid nanozymes for intensive catalytic antibacterial therapy by photothermal-augmented co-catalysis

Nanozyme-based chemodynamic therapy (CDT) has shown tremendous potential in the treatment of bacterial infections. However, the CDT antibacterial efficacy is severely limited by the catalytic activity of nanozymes or the infection microenvironments such as insufficient hydrogen peroxide (H₂O₂) and overexpressed glutathione (GSH). Herein, a versatile hybrid nanozyme (MoS₂/CuO₂) is rationally constructed by simply decorating ultrasmall CuO₂ nanodots onto lamellar MoS₂ platelets of hydrangea-like MoS₂ nanocarrier via a covalent Cu-S bond. The MoS₂/CuO₂ nanozyme exhibits the peroxidase-mimic activity for catalytically converting H₂O₂ produced by acid-triggered decomposition of the decorated CuO₂ into hydroxyl radical (•OH). Meanwhile, the MoS₂/CuO₂ can consume GSH overexpressed in the infection sites via redox reaction mediated by polyvalent transition metal ions (Cu²⁺ and Mo⁶⁺) for enhanced CDT. More importantly, MoS₂ support can promote the conversion of Cu²⁺ to Cu⁺ by a co-catalytic reaction based on the Mo⁴⁺/Mo⁶⁺ redox couples, and provide photonic hyperthermia (PTT) to augment the peroxidase-mimic activity. The developed MoS₂/CuO₂ nanozymes possesses a desirable catalytic property, as well as a remarkably improved antibacterial efficiency both in vitro and in vivo. Taken together, this study proposes a synergetic multiple enhancement strategy to successfully construct the versatile hybrid nanozymes for intensive in vivo PTT/CDT dual-mode anti-infective therapy. STATEMENT OF SIGNIFICANCE: Chemodynamic therapy (CDT) has shown great potentialities in the treatment of bacterial infections, while its therapeutic efficiency is severely limited by the infection microenvironments such as insufficient hydrogen peroxide (H₂O₂) and overexpressed glutathione (GSH). Here, we rationally construct a hybrid nanozyme (MoS₂/CuO₂) with peroxidase-like activity that can enhance CDT by regulating local microenvironments, that is, simultaneously self-supplying H₂O₂ and consuming GSH. Importantly, MoS₂ support can promote the conversion of Cu²⁺ to Cu⁺ by the Mo⁴⁺/Mo⁶⁺ redox couples, and provide photonic hyperthermia (PTT) to augment the peroxidase-mimic activity. The developed MoS₂/CuO₂ shows desirable PTT/CDT dual-mode antibacterial efficacy both in vitro and in vivo. This study proposes a versatile hybrid nanozyme with multiple enhancement effects for intensive in vivo anti-infective therapy.

Antimicrobial properties of nanoparticles in biofilms

Biofilm is a structure in the shape of a surface adherent composed of a microbe’s community and plays a crucial role in stimulating the infection. Due to the Biofilm’s complex structure compared with the individual microbe, it occasionally develops recalcitrant to the host immune system, which may lead to antibiotic resistance. The National Institutes of Health has reported that more than 80% of bacterial infections are caused by biofilm formation. Removing biofilm-mediated infections is an immense challenge that should involve various strategies that may induce sensitive and effective antibiofilm therapy. In the last decade, nanoparticle NPs application has been employed as one of the strategies that have grown great stimulus to target antibiofilm treatment due to their unique properties. Nanobiotechnology holds promise for the future because it has various antimicrobial properties in biofilms and promising new drug delivery methods that stand out from conventional antibiotics. Studying the interaction between the Biofilm and the nanoparticles can deliver additional insights regarding the mechanism of biofilm regulation. This review article will define synthetic nanoparticle NPs, their medical applications, and their potential use against a broad range of microbial biofilms in the coming years. The motivation of the current review is to focus on NPs materials’ properties and applications and their use as antimicrobial agents to fight resistant infections, which can locally terminate bacteria without being toxic to the surrounding tissue and share its role in improving human health in the future. Keywords: Biofilms, antimicrobial, nanoparticles, bio-nanotechnology, drug resistance.

Preparation, Characterization, and Staphylococcus aureus Biofilm Elimination Effect of Baicalein-Loaded β-Cyclodextrin-Grafted Chitosan Nanoparticles

BACKGROUND AND PURPOSE

Infections caused by Staphylococcus aureus (S. aureus) colonization in medical implants are resistant to antibiotics due to the formation of bacterial biofilm internal. Baicalein (BA) has been confirmed as an inhibitor of bacterial biofilm with less pronounced effects owing to its poor solubility and absorption. Studies have found that β-cyclodextrin-grafted chitosan (CD-CS) can improve drug efficiency as a drug carrier. Therefore, this research aims to prepare BA-loaded CD-CS nanoparticles (CD-CS-BA-NPs) for S. aureus biofilm elimination enhancement.

METHODS

CD-CS-BA-NPs were prepared via the ultrasonic method. The NPs were characterized using the X-ray diffraction (XRD), Thermo gravimetric analyzer (TGA), Transmission electron microscopy (TEM) and Malvern Instrument. The minimum inhibitory concentration (MIC) of the NPs were investigated. The biofilm models in vivo and in vitro were constructed to assess the S. aureus biofilm elimination ability of the NPs. The Confocal laser method (CLSM) and the Live/Dead kit were employed to explore the mechanism of the NPs in promoting biofilm elimination.

RESULTS

CD-CS-BA-NPs have an average particle size of 424.5 ± 5.16 nm, a PDI of 0.2 ± 0.02, and a Zeta potential of 46.13 ± 1.62 mV. TEM images revealed that the NPs were spherical with uniform distribution. XRD and TGA analysis verified the formation and the thermal stability of the NPs. The NPs with a MIC of 12.5 ug/mL exhibited a better elimination effect on S. aureus biofilm both in vivo and in vitro. The mechanism study demonstrated that the NPs may permeate into the biofilm more easily, thereby improving the biofilm elimination effect of BA.

CONCLUSION

CD-CS-BA-NPs were successfully prepared with enhanced elimination of S. aureus biofilm, which may serve as a reference for future development of anti-biofilm agents.

Self-Assembly Anchored Cationic Copolymer Interfaces for Applying the Control of Counterion-Induced Bacteria Killing/Release Procedure

In recent years, daily hygiene and disease control issues have received increasing attention, especially the raging epidemics caused by the spread of deadly viruses. The construction of the interface of new polymer materials is focused on, which can provide a cyclic operation process for the killing and releasing of bacteria, and perform repeated regeneration, which is of great significance for the development of advanced medical biomaterials. In order to explore the basic physical phenomena of bacterial attachment and detachment on the polymer material interface by different amine groups, this study plans to synthesize four different butyl methacrylate (BMA)-based cationic copolymers with primary, ternary, and quaternary amine groups, and compare their effects on bactericidal efficiency. Since BMA can generate strong hydrophobic interactions with the benzene ring structure, this study used a polystyrene substrate to realize a self-assembled cationic copolymer interface for controlling the counterion-induced bacterial killing/release process. Furthermore, negatively charged ions are introduced to induce changes in the hydration capability of water molecules and control the subsequent bacterial detachment function. In this study, possible directions to answer and clarify the above concepts are proposed, and there is a basic reference principle that can lead to research work in macromolecular bioscience fields.

Advanced Drug Delivery Platforms for the Treatment of Oral Pathogens

The oral cavity is a complex ecosystem accommodating various microorganisms (e.g., bacteria and fungi). Various factors, such as diet change and poor oral hygiene, can change the composition of oral microbiota, resulting in the dysbiosis of the oral micro-environment and the emergence of pathogenic microorganisms, and consequently, oral infectious diseases. Systemic administration is frequently used for drug delivery in the treatment of diseases and is associated with the problems, such as drug resistance and dysbiosis. To overcome these challenges, oral drug delivery systems (DDS) have received considerable attention. In this literature review, the related articles are identified, and their findings, in terms of current therapeutic challenges and the applications of DDSs, especially nanoscopic DDSs, for the treatment of oral infectious diseases are highlighted. DDSs are also discussed in terms of structures and therapeutic agents (e.g., antibiotics, antifungals, antiviral, and ions) that they deliver. In addition, strategies (e.g., theranostics, hydrogel, microparticle, strips/fibers, and pH-sensitive nanoparticles), which can improve the treatment outcome of these diseases, are highlighted.

Effects of Photodynamic Therapy on Streptococcus mutans and Enamel Remineralization of Multifunctional TiO2-HAP Composite Nanomaterials

BACKGROUND

As photosensitizer and photocatalyst, titanium dioxide (TiO₂) can produce a photodynamic reaction for antibacterial treatment. This study aims to explore a Titanium dioxide/nano-hydroxyapatite (TiO₂-HAP) composite combined with the dental curing lamp (385-515 nm) in clinical which could inhibit the dental plaque biofilm formed by Streptococcus mutans (S. mutans) and promote the enamel surface remineralization simultaneously.

METHODS

X-ray Diffraction (XRD) and high resolution transmission electron microscope (HRTEM) were used to detect the characterization of TiO₂-HAP composite nanomaterials. Photodynamic properties of TiO₂-HAP were detected by Diffuse reflectance spectrum (DRS) and fluorescence spectroscopy. Bacterial growth was measured by reading the absorbance of bacterial cultures and confocal microscope was used to observe the biofilm removal ability of nanomaterials. The ability of TiO₂-HAP to promote enamel remineralization was measured by Scanning electron microscope (SEM).

RESULTS

The OD 600 of S. mutans was 0.76 in the control group and 0.13 in group of TiO₂-HAP with exposure to light-emitting diode (LED) (150 mW/cm²) for 5 min, suggesting its sustained antibacterial potency and inhibition of the metabolic activity of dental plaque microcosm biofilm. Also, the release of calcium and phosphorus ions in TiO₂-HAP can promote enamel mineralization simultaneously. After 15 days of remineralization, the Ca/P ratio of demineralized enamel surface increased from 1.28 to 1.67, which was similar to that of normal enamel.

CONCLUSIONS

The TiO₂-HAP exhibit a promising anti-bacterial activity and remineralization capacity which can prevent the occurrence of caries to the greatest extent and promote the biomimetic mineralization of dental tissues.

Farnesol delivery via polymeric nanoparticle carriers inhibits cariogenic cross-kingdom biofilms and prevents enamel demineralization

Streptococcus mutans and Candida albicans are frequently detected together in the plaque from patients with early childhood caries (ECC) and synergistically interact to form a cariogenic cross-kingdom biofilm. However, this biofilm is difficult to control. Thus, to achieve maximal efficacy within the complex biofilm microenvironment, nanoparticle carriers have shown increased interest in treating oral biofilms in recent years. Here, we assessed the anti-biofilm efficacy of farnesol (Far), a hydrophobic antibacterial drug and repressor of Candida filamentous forms, against cross-kingdom biofilms employing drug delivery via polymeric nanoparticle carriers (NPCs). We also evaluated the effect of the strategy on teeth enamel demineralization. The farnesol-loaded NPCs (NPC+Far) resulted in a 2-log CFU/mL reduction of S. mutans and C. albicans (hydroxyapatite disc biofilm model). High-resolution confocal images further confirmed a significant reduction in exopolysaccharides, smaller microcolonies of S. mutans, and no hyphal form of C. albicans after treatment with NPC+Far on human tooth enamel (HT) slabs, altering the biofilm 3D structure. Furthermore, NPC+Far treatment was highly effective in preventing enamel demineralization on HT, reducing lesion depth (79% reduction) and mineral loss (85% reduction) versus vehicle PBS-treated HT, while NPC or Far alone had no differences with the PBS. The drug delivery via polymeric NPCs has the potential for targeting bacterial-fungal biofilms associated with a prevalent and costly pediatric oral disease, such as ECC.

Effects of a Novel, Intelligent, pH-Responsive Resin Adhesive on Cariogenic Biofilms In Vitro

Background: Secondary caries often result in a high failure rate of resin composite restoration. Herein, we studied the dodecylmethylaminoethyl methacrylate−modified resin adhesive (DMAEM@RA) to investigate its pH-responsive antimicrobial effect on Streptococcus mutans and Candida albicans dual-species biofilms and on secondary caries. Methods: Firstly, the pH-responsive antimicrobial experiments including colony-forming units, scanning electron microscopy and exopoly-saccharide staining were measured. Secondly, lactic acid measurement and transverse microradiography analysis were performed to determine the preventive effect of DMAEM@RA on secondary caries. Lastly, quantitative real-time PCR was applied to investigate the antimicrobial effect of DMAEM@RA on cariogenic virulence genes. Results: DMAEM@RA significantly inhibited the growth, EPS, and acid production of Streptococcus mutans and Candida albicans dual-species biofilms under acidic environments (p < 0.05). Moreover, at pH 5 and 5.5, DMAEM@RA remarkably decreased the mineral loss and lesion depth of tooth hard tissue (p < 0.05) and down-regulated the expression of cariogenic genes, virulence-associated genes, and pH-regulated genes of dual-species biofilms (p < 0.05). Conclusions: DMAEM@RA played an antibiofilm role on Streptococcus mutans and Candida albicans dual-species biofilms, prevented the demineralization process, and attenuated cariogenic virulence in a pH-dependent manner.

Strategies for dispersion of cariogenic biofilms: applications and mechanisms

Bacteria residing within biofilms are more resistant to drugs than planktonic bacteria. They can thus play a significant role in the onset of chronic infections. Dispersion of biofilms is a promising avenue for the treatment of biofilm-associated diseases, such as dental caries. In this review, we summarize strategies for dispersion of cariogenic biofilms, including biofilm environment, signaling pathways, biological therapies, and nanovehicle-based adjuvant strategies. The mechanisms behind these strategies have been discussed from the components of oral biofilm. In the future, these strategies may provide great opportunities for the clinical treatment of dental diseases. Graphical Abstract.

Self-locomotive, antimicrobial microrobot (SLAM) swarm for enhanced biofilm elimination

Biofilm is a major cause of infections and infrastructure deterioration, largely due to molecular diffusion restrictions that hamper the antimicrobial activity of traditional antibiotics and disinfectants. Here, we present a self-locomotive, antimicrobial microrobot (SLAM) swarm that can penetrate, fracture, and detach biofilm and, in turn, nullify bacterial resistance to antibiotics. The SLAM is assembled by loading a controlled mass of manganese oxide nanosheets on diatoms with the polydopamine binder. In hydrogen peroxide solution, SLAMs produce oxygen bubbles that generate thrust to penetrate the rigid and dense Pseudomonas aeruginosa biofilm and self-assemble into a swarm that repeatedly surrounds, expands, and bursts oxygen bubbles. The resulting cavities continue to deform and fracture extracellular polymeric substances from microgrooved silicone substrates and wounded skin explants while decreasing the number of viable bacterial cells. Additionally, SLAM allows irrigating water or antibiotics to access the residual biofilm better, thus enhancing the synergistic efficacy in killing up to 99.9% of bacterial cells.

Distinct Agents Induce Streptococcus mutans Cells with Altered Biofilm Formation Capacity

Dental caries is a multifactorial biofilm- and sugar-dependent disease. This study investigated the influence of different agents on the induction of surviving Streptococcus mutans cells after successive treatment cycles and characterized the biofilms formed by these cells recovered posttreatment. The agents (with their main targets listed in parentheses) were compound 1771 (lipoteichoic acids), 4′ hydroxychalcone (exopolysaccharides), myricetin (exopolysaccharides), tt-farnesol (cytoplasmatic membrane), sodium fluoride (enolase—glycolysis), chlorhexidine (antimicrobial), and vehicle. Recovered cells from biofilms were generated from exposure to each agent during 10 cycles of consecutive treatments (modeled on a polystyrene plate bottom). The recovered cell counting was different for each agent. The recovered cells from each group were grown as biofilms on saliva-coated hydroxyapatite discs (culture medium with sucrose/starch). In S. mutans biofilms formed by cells recovered from biofilms previously exposed to compound 1771, 4′ hydroxychalcone, or myricetin, cells presented higher expression of the 16S rRNA, gyrA (DNA replication and transcription), gtfB (insoluble exopolysaccharides), and eno (enolase—glycolysis) genes and lower quantities of insoluble dry weight and insoluble exopolysaccharides than those derived from other agents. These findings were confirmed by the smaller biovolume of bacteria and/or exopolysaccharides and the biofilm distribution (coverage area). Moreover, preexposure to chlorhexidine increased exopolysaccharide production. Therefore, agents with different targets induce cells with distinct biofilm formation capacities, which is critical for developing formulations for biofilm control.

IMPORTANCE This article addresses the effect of distinct agents with distinct targets in the bacterial cell (cytoplasmatic membrane and glycolysis), the cell’s extracellular synthesis of exopolysaccharides that are important for cariogenic extracellular matrix construction and biofilm buildup in the generation of cells that persisted after treatment, and how these cells form biofilms in vitro. For example, if preexposure to an agent augments the production of virulence determinants, such as exopolysaccharides, its clinical value may be inadequate. Modification of biofilm formation capacity after exposure to agents is critical for the development of formulations for biofilm control to prevent caries, a ubiquitous disease associated with biofilm and diet.

Antibacterial, Antibiofilm, and Antiviral Farnesol-Containing Nanoparticles Prevent Staphylococcus aureus from Drug Resistance Development

Multidrug antimicrobial resistance is a constantly growing health care issue associated with increased mortality and morbidity, and huge financial burden. Bacteria frequently form biofilm communities responsible for numerous persistent infections resistant to conventional antibiotics. Herein, novel nanoparticles (NPs) loaded with the natural bactericide farnesol (FSL NPs) are generated using high-intensity ultrasound. The nanoformulation of farnesol improved its antibacterial properties and demonstrated complete eradication of Staphylococcus aureus within less than 3 h, without inducing resistance development, and was able to 100% inhibit the establishment of a drug-resistant S. aureus biofilm. These antibiotic-free nano-antimicrobials also reduced the mature biofilm at a very low concentration of the active agent. In addition to the outstanding antibacterial properties, the engineered nano-entities demonstrated strong antiviral properties and inhibited the spike proteins of SARS-CoV-2 by up to 83%. The novel FSL NPs did not cause skin tissue irritation and did not induce the secretion of anti-inflammatory cytokines in a 3D skin tissue model. These results support the potential of these bio-based nano-actives to replace the existing antibiotics and they may be used for the development of topical pharmaceutic products for controlling microbial skin infections, without inducing resistance development.

Topical Application of 4'-Hydroxychalcone in Combination with tt-Farnesol Is Effective against Candida albicans and Streptococcus mutans Biofilms

Candida albicans and Streptococcus mutans interaction in the presence of dietary sucrose yields a complex biofilm with an organized and structured extracellular matrix that increases the tolerance to environmental stress, including antimicrobials. Both species are found in severe early childhood caries lesions. Thus, compounds 4'-hydroxychalcone (C135) (flavonoid intermediate metabolites), tt-farnesol (Far) (terpenoid), and sodium fluoride (F) were tested either isolated or combined as topical treatments (5 min twice daily) against C. albicans and S. mutans dual-species biofilms grown on saliva-coated hydroxyapatite discs. The biofilms were evaluated for gene expression, microbial population, biochemical components, and three-dimensional (3D) structural organization via confocal microscopy and scanning electron microscopy (SEM). The cytotoxicity of formulations was tested on the keratinocyte monolayer. C135 + Far + F promoted lower gene expression of fungal genes associated with β-glucan synthesis (BGL2, FKS1) and remodeling (XOG1, PHR1, PHR2), oxidative stress (SOD1), and drug tolerance (CDR1, ERG11) and higher expression of bacterial nox1 (oxidative and acidic stress tolerance). C135 + Far yielded less insoluble exopolysaccharides, biomass, and proteins (insoluble portion) and lower expression of BGL2, ERG11, SOD1, and PHR2. C135 + F, C135 + Far + F, and C135 rendered lower biomass, thickness, and coverage percentage (confocal microscopy). C135 + Far and C135 + Far + F maintained C. albicans as yeast morphology (SEM). Therefore, the formulations with C135 affected fungal and bacterial targets but exerted a more pronounced effect against fungal cells.