Sonodynamic action of chlorin e6 on Staphylococcus aureus and Escherichia coli

External Stimuli-Responsive Strategies for Surface Modification of Orthopedic Implants: Killing Bacteria and Enhancing Osteogenesis

Bacterial infection and insufficient osteogenic activity are the main causes of orthopedic implant failure. Conventional surface modification methods are difficult to meet the requirements for long-term implant placement. In order to better regulate the function of implant surfaces, especially to improve both the antibacterial and osteogenic activity, external stimuli-responsive (ESR) strategies have been employed for the surface modification of orthopedic implants. External stimuli act as "smart switches" to regulate the surface interactions with bacteria and cells. The balance between antibacterial and osteogenic capabilities of implant surfaces can be achieved through these specific ESR manifestations, including temperature changes, reactive oxygen species production, controlled release of bioactive molecules, controlled release of functional ions, etc. This Review summarizes the recent progress on different ESR strategies (based on light, ultrasound, electric, and magnetic fields) that can effectively balance antibacterial performance and osteogenic capability of orthopedic implants. Furthermore, the current limitations and challenges of ESR strategies for surface modification of orthopedic implants as well as future development direction are also discussed.

Sonodynamic inactivation of gram-negative and gram-positive bacteria in the presence of phenothiazine compounds toluidine blue and azurin A

BACKGROUND

Sonodynamic antimicrobial chemotherapy (SACT) is an effective antimicrobial treatment that can avoid the production of drug-resistant bacteria. Design and development of new high-efficiency sonosensitizers play a key role in the practical application of SACT.

METHODS

The bacteriostatic effects of two phenothiazine compounds, toluidine blue (TB) and azure A (AA) combined with ultrasonic (US) on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were studied, and the sonodynamic antibacterial activities of TB and AA were compared. The reactive oxygen species (ROS) and the types of ROS produced in the sonodynamic system were detected and the sonodynamic mechanisms of TB and AA were proposed.

RESULTS

The sonodynamic bacteriostasis mediated by TB and AA increased with the increasing concentration of sonosensitizer, the extension of sonication time and the increase of reaction temperature. The production of ROS was the main reason that TB and AA had excellent sonodynamic antibacterial performance. Singlet oxygen (1O2) and hydroxyl radical (•OH) were the main ROS types in the sonodynamic antibacterial system. The ROS produced by the combined action of AA and US was higher than that of TB.

CONCLUSION

Both TB and AA displayed excellent sonodynamic antibacterial activities. Moreover, AA had a higher sonodynamic activity than TB. The electron donation effect and steric hindrance effect of the methyl group of phenothiazine parent nucleus of TB might be the cause of the decrease of its sonodynamic activity. These results would provide a valuable reference for the further study of phenothiazines sonosensitizers and their clinical application in SACT.

Enhanced cavitation dose and reactive oxygen species production in microbubble-mediated sonodynamic therapy for inhibition of Escherichia coli and biofilm

Sonodynamic therapy (SDT) is an emerging antibacterial therapy. This work selected hematoporphyrin monomethyl ether (HMME) as the sonosensitizer, and studied the enhanced inhibition effect of Escherichia coli and biofilm by microbubble-mediated cavitation in SDT. Firstly, the influence of microbubble-mediated cavitation effect on different concentrations of HMME (10 µg/ml, 30 µg/ml, 50 µg/ml) was studied. Using 1,3-diphenylisobenzofuran (DPBF) as an indicator, the effect of microbubble-mediated cavitation on the production of reactive oxygen species (ROS) was studied by absorption spectroscopy. Secondly, using agar medium, laser confocal microscopy and scanning electron microscopy, the effect of microbubble-mediated cavitation on the activity and morphology of bacteria was studied. Finally, the inhibitory effect of cavitation combined with SDT on biofilm was evaluated by laser confocal microscopy. The research results indicate that: (1) Microbubble-mediated ultrasound cavitation can significantly increase cavitation intensity and production of ROS. (2) Microbubble-mediated acoustic cavitation can alter the morphological structure of bacteria. (3) It can significantly enhance the inhibition of SDT on the activity of Escherichia coli and its biofilm. Compared with the control group, the addition of microbubbles resulted in an increase in the number of dead bacteria by 61.7 %, 71.6 %, and 76.2 %, respectively. The fluorescence intensity of the biofilm decreased by 27.1 %, 80.3 %, and 98.2 %, respectively. On the basis of adding microbubbles to ensure antibacterial and biofilm inhibition effects, this work studied the influence of cavitation effect in SDT on bacterial structure, providing a foundation for further revealing the intrinsic mechanism of SDT.

Conjugated polymer nanoparticles as sonosensitizers in sono-inactivation of a broad spectrum of pathogens

Sonodynamic inactivation (SDI) of pathogens has an important advantage when compared to optical excitation-based protocols due to the deeper penetration of ultrasound (US) excitation in biological media or animal tissue. Sonosensitizers (SS) are compounds or systems that upon US stimulation in the therapeutic window (frequency = 0.8-3 MHz and intensity < 3 W/cm2) can induce damage to vital components of pathogenic microorganisms. Herein, we report the synthesis and application of conjugated polymer nanoparticles (CPNs) as an efficient SS in SDI of methicillin-resistant Staphylococcus aureus (MRSA), Klebsiella pneumoniae and Candida tropicalis. A frequent problem in the design and testing of new SS for SDI is the lack of proper sonoreactor characterization which leads to reproducibility concerns. To address this issue, we performed dosimetry experiments in our setup. This enables the validation of our results by other researchers and facilitates meaningful comparisons with different SDI systems in future studies. On a different note, it is generally accepted that the mechanisms of action underlying SS-mediated SDI involve the production of reactive oxygen species (ROS). In an attempt to establish the nature of the cytotoxic species involved in our CPNs-based SDI protocol, we demonstrated that singlet oxygen (1O2) does not play a major role in the observed sonoinduced killing effect. SDI experiments in planktonic cultures of optimally growing pathogens using CPNs result in a germicide effect on the studied pathogenic microorganisms. The implementation of SDI protocols using CPNs was further tested in mature biofilms of a MRSA resulting in ∼40 % reduction of biomass and ∼70 % reduction of cellular viability. Overall, these results highlight the unique and unexplored capacity of CPNs to act as sonosensitizers opening new possibilities in the design and application of novel inactivation protocols against morbific microbes.

Combinations of Photodynamic Therapy with Other Minimally Invasive Therapeutic Technologies against Cancer and Microbial Infections

The rapid rise in research and development following the discovery of photodynamic therapy to establish novel photosensitizers and overcome the limitations of the technology soon after its clinical translation has given rise to a few significant milestones. These include several novel generations of photosensitizers, the widening of the scope of applications, leveraging of the offerings of nanotechnology for greater efficacy, selectivity for the disease over host tissue and cells, the advent of combination therapies with other similarly minimally invasive therapeutic technologies, the use of stimulus-responsive delivery and disease targeting, and greater penetration depth of the activation energy. Brought together, all these milestones have contributed to the significant enhancement of what is still arguably a novel technology. Yet the major applications of photodynamic therapy still remain firmly located in neoplasms, from where most of the new innovations appear to launch to other areas, such as microbial, fungal, viral, acne, wet age-related macular degeneration, atherosclerosis, psoriasis, environmental sanitization, pest control, and dermatology. Three main value propositions of combinations of photodynamic therapy include the synergistic and additive enhancement of efficacy, the relatively low emergence of resistance and its rapid development as a targeted and high-precision therapy. Combinations with established methods such as chemotherapy and radiotherapy and demonstrated applications in mop-up surgery promise to enhance these top three clinical tools. From published in vitro and preclinical studies, clinical trials and applications, and postclinical case studies, seven combinations with photodynamic therapy have become prominent research interests because they are potentially easily applied, showing enhanced efficacy, and are rapidly translating to the clinic. These include combinations with chemotherapy, photothermal therapy, magnetic hyperthermia, cold plasma therapy, sonodynamic therapy, immunotherapy, and radiotherapy. Photochemical internalization is a critical mechanism for some combinations.

Synthesis and Sonodynamic Antibacterial Activity Evaluation of Three Novel Fluoroquinolone Compounds

OBJECTIVE

Three ciprofloxacin derivatives (CPDs) were synthesized. Also, their sonodynamic antibacterial activities and possible mechanism under ultrasound (US) irradiation were preliminarily investigated.

METHODS

Staphylococcus aureus and Escherichia coli were selected as the research objects. The sonodynamic antibacterial effects of three CPDs and their structure-effective relationship were explored by the inhibition rate. The reactive oxygen species (ROS) produced under US irradiation were detected by oxidative extraction spectrophotometry and used to analyze the sonodynamic antibacterial mechanism of three CPDs.

RESULTS

Research indicated that three CPDs, named compound 1 (C1), compound 2 (C2) and compound 3 (C3), separately all had strong sonodynamic antibacterial activities. In addition, C3 had the strongest effect relative to the other CPDs. The study also found that CPDs' concentration, US irradiation time, US solution temperature and US medium could disturb their sonodynamic antimicrobial effects. Moreover, ¹O₂ and ·OH were the main types of ROS produced by C1 and C3; the ROS produced by C2 included ¹O₂, among other types.

CONCLUSION

Results showed that all three CPDs could be activated to produce ROS after US irradiation. Among them, C3 displayed the highest ROS production and the utmost activity, which may be related to the introduction of the electron-giving group at the C-3 position of the quinoline backbone.

Ultrasonic interfacial crosslinking of TiO2-based nanocomposite hydrogels through thiol-norbornene reactions for sonodynamic antibacterial treatment

Nanocomposite (NC) hydrogels used for sonodynamic therapy (SDT) face challenges such as lacking interfacial interactions between the polymers and nanomaterials as well as presenting uneven dispersion of nanomaterials in the hydrogel network, reducing their mechanical properties and treatment efficiency. Here, we demonstrate a promising approach of co-engineering nanomaterials and interfacial crosslinking to expand the materials construction and biomedical applications of NC hydrogels in SDT. In this work, mesoporous silica-coated titanium dioxide nanoparticles with thiolated surface functionalization (TiO₂@MS-SH) are utilized as crosslinkers to react with norbornene-functionalized dextran (Nor-Dex) through ultrasound-triggered thiol-norbornene reactions, forming TiO₂@MS-SH/Nor-Dex NC hydrogels. The TiO₂@MS-SH nanoparticles act not only as multivalent crosslinkers to improve the mechanical properties of hydrogels under ultrasound irradiation but also as reactive oxygen species (ROS) generators to allow the use of TiO₂@MS-SH/Nor-Dex NC hydrogels in SDT applications. Particularly, the TiO₂@MS-SH/Nor-Dex NC hydrogels present tailorable microstructures, properties, and sonodynamic killing of bacteria through the modulation of the ultrasound frequency. Taken together, a versatile TiO₂-based NC hydrogel platform prepared under ultrasonic interfacial crosslinking reactions is developed for advancing the applications in SDT.

Synthesis of Ciprofloxacin-capped Gold Nanoparticles Conjugates with Enhanced Sonodynamic Antimicrobial Activity in vitro

The purpose of this article is to discuss whether gold nanoparticles (GNPs) play an auxo-action on ciprofloxacin (CIP)-mediated sonodynamic antimicrobial chemotherapy (SACT) in vitro. The measuring criterion of SACT, bactericidal efficiency, was measured by plate colony-counting methods. According to research findings, the duration of ultrasound (US) exposure, solution temperature and CIP:GNPs concentration were all critical influencing factors of SACT. Furthermore, scanning electron microscopy revealed that the group of CIP:GNPs combined with US showed the most severe damaged effect on Escherichia coli and Staphylococcus aureus, resulting in the loss of their typical microbial morphology and the disclosure of contents. Therefore, the above experimental results confirmed initially that GNPs could enhance the bacteriostasis of CIP-mediated SACT. And the intracellular reactive oxygen species (ROS) detection assays proved that this acceleration might be connected to the ROS generated through the ultrasonic mechanics. In conclusion, GNPs would be regarded as a promising auxiliary material for SACT, since they are both used to be the medication carriers and sonosensitizer accelerants.

Recent developments of sonodynamic therapy in antibacterial application

The rapid emergence of pathogenic bacteria poses a serious threat to global health. Notably, traditional antibiotic therapies suffer from the risk of strengthening bacterial drug resistance. Sonodynamic therapy (SDT) combining sonosensitizers and low-intensity ultrasound (US) has broadened the way towards treating drug-resistant bacteria. The allure of this therapy emerges from the capacity to focus the US energy on bacterial infection sites buried deep in tissues, locally activating the sonosensitizers to produce cytotoxic reactive oxygen species (ROS) with the ability to induce bacterial death. The past decade has witnessed the rapid development of antibacterial SDT owing to their excellent penetration, favorable biocompatibility and specific targeting ability. This review summarizes available sonosensitizers for antibacterial SDT, and digs into innovative biotechnologies to improve SDT efficiency, such as enhancing the targeting ability of sonosensitizers, image-guided assisted SDT, improvement of hypoxia and combination of SDT with other therapies. Finally, we conclude with the present challenges and provide insights into the future research of antibacterial SDT.

Application of sonodynamic technology and sonosensitizers in food sterilization: a review of developments, trends and challenges

Food safety and food waste have always been hot topics of discussion in recent years. However, the infection of human pathogenic bacteria and the waste of food resources caused by microbial-contaminated food remains common. Although traditional sterilization technology has been very mature, it causes changes in food flavor and excessive energy consumption to a certain extent. Moreover, the widespread bacterial resistance has also sounded a warning for researchers and finding a new alternative to antibiotics is urgently needed. The application of sonodynamic sterilization technology in medical treatment has aroused the interest of researchers. It provides ideas for new food sterilization technology. As a new non-thermal sterilization technology, sonodynamic sterilization technology has strong penetration, safety, less residue and by-products, and will less change the quality of the food itself. Therefore, sonodynamic sterilization technology has great potential applied in food sterilization technology. This review describes the concept of sonodynamic sterilization technology, the sterilization mechanism of sonodynamic sterilization and the inactivation mechanism of various pathogens, the classification and application of sonosensitizers, and the ultrasonic technology in sonodynamic sterilization in the application over the recent years. It provides a scientific reference for the application of sonodynamic sterilization technology in the field of food sterilization.

Excited state and reactive oxygen species against cancer and pathogens: a review on sonodynamic and sono-photodynamic therapy

Photodynamic and sonodynamic therapy are therapies having great potential in the treatment of bacterial infections and cancer. Their background is associated with photo- and sonosensitizers - substances that can be excited when exposed to light or ultrasound. These sensitizers belong to a variety of compounds groups, including porphyrins, porphyrazines, and phthalocyanines. Releasing the energy when returning to the ground state can occur in the manner of transferring it to oxygen molecules, leading to reactive oxygen species able to disrupt membranes of bacterial and cancer cells, leaving the organism's cells unaffected. In recent years, the number of reports on numerous sensitizers being effective has been constantly growing. Therefore, the development of this field may prove beneficial for dealing with cancer and microbes. This review describes the development of photodynamic and sonodynamic therapy, as well as their combination, with emphasize on sonodynamic therapy and its potential in the treatment of cancer and bacterial infections.

Recent advances in metal-organic framework-based materials for anti-staphylococcus aureus infection

The rapid spread of staphylococcus aureus (S. aureus) causes an increased morbidity and mortality, as well as great economic losses in the world. Anti-S. aureus infection becomes a major challenge for clinicians and nursing professionals to address drug resistance. Hence, it is urgent to explore high efficiency, low toxicity, and environmental-friendly methods against S. aureus. Metal-organic frameworks (MOFs) represent great potential in treating S. aureus infection due to the unique features of MOFs including tunable chemical constitute, open crystalline structure, and high specific surface area. Especially, these properties endow MOF-based materials outstanding antibacterial effect, which can be mainly attributed to the continuously released active components and the exerted catalytic activity to fight bacterial infection. Herein, the structural characteristics of MOFs and evaluation method of antimicrobial activity are briefly summarized. Then we systematically give an overview on their recent progress on antibacterial mechanisms, metal ion sustained-release system, controlled delivery system, catalytic system, and energy conversion system based on MOF materials. Finally, suggestions and direction for future research to develop and mechanism understand MOF-based materials are discussed in antibacterial application.

The promise of low-intensity ultrasound: A review on sonosensitizers and sonocatalysts by ultrasonic activation for bacterial killing

Antimicrobial resistance has become one of the main public health issues in modern society. Ultrasonicantimicrobial treatment (UAT) is expected to solve the problem of antimicrobial resistance since ultrasonic treatment does not cause drug resistance during inactivation. However, the ultrasonic application is hindered due to the high energy cost. To cast more lights on the ultrasound in tandem with catalysts as a superior strategy for bacterial inactivation, the present review focuses on the UAT with the assistant of continuous development of organic sonosensitizer and inorganic sonocatalyst. With the application of these nanomaterials, the ultrasonic parameters changed from low-frequency and high-power ultrasound to high-frequency and low-power ultrasound. The review also presents the composition of sonosensitizers/sonocatalysts including organic and inorganic nanoparticles and discusses the ultrasonic activation mechanisms triggered by these catalysts. Based on the synergistic effect of ultrasound and catalysts, we discuss the importance of extracellular oxidation and intracellular oxidation in the process of bacterial inactivation. Overall, UAT combined with catalysts appears to be an effective treatment strategy that can be successfully applied in the field of medicine, environmental treatment, and food industry.

Sonodynamic antimicrobial chemotherapy: An emerging alternative strategy for microbial inactivation

Sonodynamic antimicrobial chemotherapy (SACT), which relies on a combination of low-intensity ultrasound and chemotherapeutic agents termed sonosensitizers, has been explored as a promising alternative for microbial inactivation. Such treatment has superior penetration ability, high target specificity, and can overcome resistance conferred by the local microenvironment. Taken of these advantages, SACT has been endowed with an extensive application prospect in the past decade and attracted more and more attention. This review focusses on the current understanding of the mechanism of SACT, the interaction of sonodynamic action on different microbes, the factors affecting the efficacy of SACT, discusses the findings of recent works on SACT, and explores further prospects for SACT. Thus, a better understanding of sonodynamic killing facilitates the scientific community and industry personnel to establish a novel strategy to combat microbial burden.

Bacteria-Responsive Nanoliposomes as Smart Sonotheranostics for Multidrug Resistant Bacterial Infections

Rapid emergence of multidrug resistant (MDR) "superbugs" poses a severe threat to global health. Notably, undeveloped diagnosis and concomitant treatment failure remain highly challenging. Herein, we report a sonotheranostic strategy to achieve bacteria-specific labeling and visualized sonodynamic therapy (SDT). Using maltohexaose-decorated cholesterol and bacteria-responsive lipid compositions, a smart nanoliposomes platform (MLP18) was developed for precise delivery of purpurin 18, a potent sonosensitizer proved in this study. Taking advantage of the bacteria-specific maltodextrin transport pathway, the prepared MLP18 can specifically target the bacterial infection site and accurately distinguish the foci from sterile inflammation or cancer with a highly selective fluorescence/photoacoustic signal on the bacteria-infected site of mice. Moreover, the bacteria-responsive feature of MLP18 activated an efficient release and internalization of high concentration sonosensitizer into bacterial cells, resulting in effective sonodynamic elimination of MDR bacteria. In situ MRI monitoring visualized such potent sonodynamic activity and indicated that MLP18-mediated SDT could successfully eradicate inflammation and abscess from mice with bacterial myositis. In view of the above advantages, the developed nanoliposomes may serve as a promising sonotheranostic platform against MDR bacteria in the areas of healthcare.

Sonodynamic inactivation of Gram-positive and Gram-negative bacteria using a Rose Bengal-antimicrobial peptide conjugate

Combating antimicrobial resistance is one of the most serious public health challenges facing society today. The development of new antibiotics or alternative techniques that can help combat antimicrobial resistance is being prioritised by many governments and stakeholders across the globe. Antimicrobial photodynamic therapy is one such technique that has received considerable attention but is limited by the inability of light to penetrate through human tissue, reducing its effectiveness when used to treat deep-seated infections. The related technique sonodynamic therapy (SDT) has the potential to overcome this limitation given the ability of low-intensity ultrasound to penetrate human tissue. In this study, a Rose Bengal-antimicrobial peptide conjugate was prepared for use in antimicrobial SDT (ASDT). When Staphylococcus aureus and Pseudomonas aeruginosa planktonic cultures were treated with the conjugate and subsequently exposed to ultrasound, 5 log and 7 log reductions, respectively, in bacterial numbers were observed. The conjugate also displayed improved uptake by bacterial cells compared with a mammalian cell line (P ≤ 0.01), whilst pre-treatment of a P. aeruginosa biofilm with ultrasound resulted in a 2.6-fold improvement in sensitiser diffusion (P ≤ 0.01). A preliminary in vivo experiment involving ASDT treatment of P. aeruginosa-infected wounds in mice demonstrated that ultrasound irradiation of conjugate-treated wounds affects a substantial reduction in bacterial burden. Combined, the results obtained from this study highlight ASDT as a targeted broad-spectrum novel modality with potential for the treatment of deep-seated bacterial infections.