Antimicrobial photodynamic therapy against a dual-species cariogenic biofilm using a ruthenium-loaded resin-based dental material.

BACKGROUND: Streptococcus mutans and Candida albicans are associated with caries recurrence. Therefore, this study evaluated the combination of a Ru(II)-loaded resin-based dental material (RDM) and antimicrobial photodynamic therapy (aPDT) against a dual-species biofilm of S. mutans and C. albicans. METHODS: An aPDT protocol was established evaluating Ru(II)'s photocatalytic activity and antimicrobial potential under blue LED irradiation (440-460 nm, 22.55 mW/cm2) at different energy densities (0.00, 6.25, 20.25, 40.50 J/cm2). This evaluation involved singlet oxygen quantification and determination of minimum inhibitory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC). The biofilm was grown (72 h) on resin disks prepared with Ru(II)-doped RDM (0.00, 0.56, or 1.12 %) and samples were exposed to aPDT or dark conditions. The biofilm was then harvested to analyze cell viability (CFU counts) and formation of soluble and insoluble exopolysaccharides. RESULTS: The photocatalytic activity of Ru(II) was concentration and energy density dependent (p < 0.05), and MIC/MBC values were reduced for the microorganisms after LED irradiation (40.5 J/cm2); therefor, this energy density was chosen for aPDT. Although incorporation of Ru(II) into RDM reduced the biofilm growth compared to Ru(II)-free RDM for both species in dark conditions (p < 0.05), aPDT combined with an Ru(II)-loaded RDM (0.56 or 1.12 %) potentialized CFU reductions (p < 0.05). Conversely, only 1.12 % Ru(II) with LED irradiation showed lower levels of both soluble and insoluble exopolysaccharides compared to Ru(II)-free samples in dark conditions (p < 0.05). CONCLUSIONS: When the Ru(II)-loaded RDM was associated with blue LED, aPDT reduced cell viability and lower soluble and insoluble exopolysaccharides were found in the cariogenic dual-species biofilm.

Exploring the use of a Ruthenium complex incorporated into a methacrylate-based dental material for antimicrobial photodynamic therapy.

OBJECTIVES: To evaluate the effects of a blue light photosensitizer (PS), Ruthenium II complex (Ru), on the chemical, physical, mechanical, and antimicrobial properties of experimental dental resin blends. METHODS: The experimental resin (BisEMA, TEEGDMA, HPMA, ethanol, and photoinitiator) was loaded with Ru at 0.00%, 0.07%, 0.14%, 0.28%, 0.56%, 1.12%, 1.2%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% w/w. Samples were evaluated for the degree of conversion (DC) after 30 and 60 s curing-time (n = 6). Selected formulations (0.00%, 0.28%, 0.56%, 1.12%) were further tested for shear bond strength (SBS) (n = 15); flexural strength (FS) (n = 12); and antimicrobial properties (CFUs), in dark and light conditions. These latter tests were performed on specimens stored for 24-h or 2-month in 37°C water. Water sorption (WS) and solubility (SL) tests were also performed (n = 12). Data were analyzed either by a one- or two-factor general linear model (α = 0.05). RESULTS: Overall, Ru concentration above 1.2% resulted in reduced DC. In SBS results, only the 1.12%Ru resin blend samples had statistically lower values compared to the 0.00%Ru resin blend at 24-h storage (p = 0.004). In addition, no differences in SBS were detected among the experimental groups after 2-month storage in water. Meanwhile, FS increased for all experimental groups under similar aging conditions (p < 0.001). Antimicrobial properties were improved upon inclusion of Ru and application of light (p < 0.001 for both) at 24-h and 2-month storage. Lastly, no detectable changes in WS or SL were observed for the Ru-added resins compared to the 0.00%Ru resin blend. However, the 0.28% Ru blend presented significantly higher WS compared to the 0.56% Ru blend (p = 0.007). CONCLUSIONS: Stable SBS, improved FS, and sustained antimicrobial properties after aging gives significant credence to our approach of adding the Ruthenium II complex into dental adhesive resin blends intended for an aPDT approach.

Photothermal release of an encapsulated therapeutic agent from polymer-wrapped gold nanoparticles.

Visible light is used to generate heat from gold nanoparticles wrapped in an amphiphilic polymer shell and trigger a reverse Diels-Alder reaction of a 'caged' tyrphostin therapeutic agent. The hydrophilic nature of the released agent results in it travelling from the polymer to the bulk medium, while the byproduct of the reaction is trapped in the hydrophobic layer of the nano-assembly.

A dual-mode visual detector for toxic hydrazine.

Hydrazine (N2H4) is one of the commonly used chemical reagents in numerous industries and applications but its toxicity to humans poses a need to develop simple visual detection methods. Herein, we demonstrate a novel dual-mode system to detect and simultaneously consume hydrazine in vapour and solution by using a small photoresponsive molecule that has altered optical response (both colourimetric and fluorescent) after reacting with hydrazine.

The Interaction of Urinary Components with Biomaterials in the Urinary Tract: Ureteral Stent Discoloration.

Purpose: Ureteral stents are fraught with complications. Not much is known regarding what causes these issues. Studies suggested that discoloration of indwelling stents changes surface characteristics to promote stent-associated complications. Occasional stent discoloration has been observed; however, underlying mechanisms and potential material changes are unknown. In this study, we identify a potential mechanism for stent discoloration and characterize potential changes in stent surface characteristics and their impact on encrustation and bacterial colonization. Materials and Methods: Twenty Polaris Ultra and 20 Percuflex Plus stents (same polymer material) with varying degrees of discoloration were collected from Japanese and Canadian patients. Surface characterization using scanning electron microscopy and Fourier transmission infrared spectroscopy was conducted. Encrustation of variably discolored stents was assessed via atomic absorption spectroscopy and bacterial adhesion to discolored and control stents via colony-forming unit counts. Results: Bismuth subcarbonate was found in control stents, and discoloration was induced via incubation in 1% sodium sulfide and increasing concentrations of hydrochloric acid (HCl) to produce hydrogen sulfide (H2S). Discoloration of either patient-derived stents or in vitro discolored stents did not result in significant changes in stent material or increased rates of encrustation or bacterial adhesion. Conclusions: Ureteral stent discoloration may be triggered by sulfur containing urinary components reacting with bismuth subcarbonate in the stent material, rather than the surface deposition of unusual crystals as previously proposed. Stent discoloration does not result in increased levels of encrustation or bacterial adhesion. Given this, stent discoloration appears to be cosmetic and has no effect on the functionality of the indwelling stent.

Probing the Microenvironments in a Polymer-Wrapped Core-Shell Nanoassembly Using Pyrene Chromophores.

The local environments within an amphiphilic polymer shell wrapped around lanthanide-doped upconverting nanoparticles were probed using steady-state and time-resolved fluorescence spectroscopy techniques. Emission lifetime measurements of pyrene chromophores trapped within the polymer shell reveal that there are at least two environments, where the organic pyrene molecules are encapsulated in hydrophobic environments that have lower polarity than in water. The migration of pyrene chromophores from their initial location to another location was also observed, demonstrating that the polymeric shell provides both hydrophobicity and mobility for entrapped molecules. These results offer insight into what outcomes can be expected when chemical reactions are carried out in these nanoassemblies, especially if they are to be used as nanoreactors for synthesis or delivery vehicles for therapeutics.

Visible-Light-Triggered Activation of a Protein Kinase Inhibitor.

A photoresponsive small molecule undergoes a ring-opening reaction when exposed to visible light and becomes an active inhibitor of the enzyme protein kinase C. This "turning on" of enzyme inhibition with light puts control into the hands of the user, creating the opportunity to regulate when and where enzyme catalysis takes place.

Using low-energy near infrared light and upconverting nanoparticles to trigger photoreactions within supramolecular assemblies.

This overview highlights how the high-energy ultraviolet or visible light required to drive photochemical reactions can be overcome by integrating the chromophores into supramolecular structures containing upconverting nanoparticles with trivalent lanthanide dopants (such as Tm(3+) and Er(3+)). These nanoparticles are particularly interesting systems because they absorb multiple photons of near infrared light and convert them into higher-energy light which is emitted in the ultraviolet and visible regions of the electromagnetic spectrum. The upconverting nanoparticles effectively act as nanoscopic 'light bulbs', and in this way, less damaging near infrared light can be used to trigger photochemical reactions for use in imaging and small molecule release. Several examples of how this phenomenon is being used in photochemistry will be presented with the focus being on self-assembled supramolecular systems, some of which are being used in cells and small animals.

A 'Plug and Play' Method to Create Water-dispersible Nanoassemblies Containing an Amphiphilic Polymer, Organic Dyes and Upconverting Nanoparticles.

In this protocol, we first describe a procedure to synthesize lanthanide doped upconverting nanoparticles (UCNPs). We then demonstrate how to generate amphiphilic polymers in situ, and describe a protocol to encapsulate the prepared UCNPs and different organic dye molecules (porphyrins and diarylethenes) using polymer shells to form stable water-dispersible nanoassemblies. The nanoassembly samples containing both the UCNPs and the diarylethene organic dyes have interesting photochemical and photophysical properties. Upon 365 nm UV irradiation, the diarylethene group undergoes a visual color change. When the samples are irradiated with visible light of another specific wavelength, the color fades and the samples return to the initial colorless state. The samples also emit visible light from the UCNPs upon irradiation with 980 nm near-infrared light. The emission intensity of the samples can be tuned through alternate irradiation with UV and visible light. Modulation of fluorescence can be performed for many cycles without observable degradation of the samples. This versatile encapsulation procedure allows for the transfer of hydrophobic molecules and nanoparticles from an organic solvent to an aqueous medium. The polymer helps to maintain a lipid-like microenvironment for the organic molecules to aid in preservation of their photochemical behavior in water. Thus this method is ideal to prepare water-dispersible photoresponsive systems. The use of near-infrared light to activate upconverting nanoparticles allows for lower energy light to be used to activate photoreactions instead of more harmful ultraviolet light.

Two-colour fluorescent imaging in organisms using self-assembled nano-systems of upconverting nanoparticles and molecular switches.

The water-insolubility of a potentially versatile photoresponsive 'turn-on' fluorescence probe was overcome by incorporating it into a nano-assembly containing an upconverting nanoparticle wrapped in an amphiphilic polymer. The appeal of the nano-system is not only in the ability to turn "on" and "off" the fluorescence from the organic chromophore using UV and visible light, it is in the fact that the nanoparticle acts as a static probe because it emits red and green light when excited by near infrared light, which is not effected by UV and visible light. This dual-functioning emission behaviour was demonstrated in live organisms.

From slow to fast--the user controls the rate of the release of molecules from masked forms using a photoswitch and different types of light.

Exposure to UV light generates a ring-closed isomer of a diarylethene, which undergoes very slow bond breaking and release even after the light is turned off. The rate of release is increased by exposing the isomer to UV and/or visible light.

Two colors of light are needed to break bonds and release small molecules from the surface of SiO2-Au core-shell nanoparticles.

The photothermal effect is not able to break bonds and release small molecules from the surface of SiO2-Au core-shell nanoparticles unless the nanosystem is first exposed to visible light. Only after this light triggers the ring-opening reaction of dithienylethene chromophores attached to the surface of the nanoparticles can the heat generated by the NIR light induce reverse Diels-Alder reactions.

Controlling a polymer adhesive using light and a molecular switch.

A thermally remendable polymer was synthesized by the Diels-Alder reaction between dithienylfuran and maleimide monomers to generate a photoresponsive diarylethene. UV light (312 nm) and visible light (>435 nm) "gate" the reversibility of the Diels-Alder reaction and turn the self-healing properties of the polymer "off" and "on", respectively. After exposure to UV light, the strength of the polymer as an adhesive is enhanced. Visible light weakens the adhesive.

A UV-blocking polymer shell prevents one-photon photoreactions while allowing multi-photon processes in encapsulated upconverting nanoparticles.

Sun block for nanoparticles: Unintentional photorelease triggered by UV light is a problem in photodynamic therapy. Encapsulating upconverting nanoparticles containing photoswitches in a UV-blocking amphiphilic polymer shuts down the one-photon process and only allows two-photon-driven photochemistry. Thus, UV light is blocked while NIR light can reach the nanoparticle core and trigger photorelease.

Photothermal release of singlet oxygen from gold nanoparticles.

Anthracene endoperoxide ligands anchored to the surfaces of gold nanoparticles undergo bond breaking and release singlet oxygen when the nanoparticles convert 532 nm laser light to heat localized near their surfaces.

Near infrared light triggered release of biomacromolecules from hydrogels loaded with upconversion nanoparticles.

Using a photosensitive hybrid hydrogel loaded with upconversion nanoparticles (UCNPs), we show that continuous-wave near-infrared (NIR) light (980 nm) can be used to induce the gel-sol transition and release large, inactive biomacromolecules (protein and enzyme) entrapped in the hydrogel into aqueous solution "on demand", where their bioactivity is recovered. This study is a new demonstration and development in harnessing the unique multiphoton effect of UCNPs for photosensitive materials of biomedical interest.

Multimodal fluorescence modulation using molecular photoswitches and upconverting nanoparticles.

The intensity and colour of the light emitted from upconverting nanoparticles is controlled by the state of photoresponsive dithienylethene ligands decorated onto the surface of the nanoparticles. By selectively activating one or both ligands in a mixed, 3-component system, a multimodal read-out of the emitted light is achieved.

Using light and a molecular switch to 'lock' and 'unlock' the Diels-Alder reaction.

Light is used to 'gate' the Diels-Alder reaction using a photoresponsive dithienylfuran backbone and turn the reversibility of the Diels-Alder reaction 'off' and 'on' at 100 °C. These features make the reported system an excellent candidate for developing the next generation of self-healing polymers and photothermal drug delivery vehicles.