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. 2023 Jul 7;9(7):554.
doi: 10.3390/gels9070554.

On-Demand Free Radical Release by Laser Irradiation for Photothermal-Thermodynamic Biofilm Inactivation and Tooth Whitening

Affiliations

On-Demand Free Radical Release by Laser Irradiation for Photothermal-Thermodynamic Biofilm Inactivation and Tooth Whitening

Qi Zhang et al. Gels. .

Abstract

Dental diseases associated with biofilm infections and tooth staining affect billions of people worldwide. In this study, we combine photothermal agents (MoS2@BSA nanosheets, MB NSs), a thermolysis free-radical initiator (AIPH), and carbomer gel to develop laser-responsive hydrogel (MBA-CB Gel) for biofilm inactivating and tooth whitening. Under a physiological temperature without laser irradiation, MB NSs can eliminate free radicals generated from the slow decomposition of AIPH due to their antioxidative activity, thereby avoiding potential side effects. A cytotoxicity study indicates that MB NSs can protect mammalian cells from the free radicals released from AIPH without laser irradiation. Upon exposure to laser irradiation, MB NSs promote the rapid decomposition of AIPH to release free radicals by photothermal effect, suggesting their on-demand release ability of free radicals. In vitro experimental results show that the bacteria inactivation efficiency is 99.91% (3.01 log units) for planktonic Streptococcus mutans (S. mutans) and 99.98% (3.83 log units) for planktonic methicillin-resistant Staphylococcus aureus (MRSA) by the mixed solution of MB NSs and AIPH (MBA solution) under 808 nm laser irradiation (1.0 W/cm2, 5 min). For S. mutans biofilms, an MBA solution can inactivate 99.97% (3.63 log units) of the bacteria under similar laser irradiation conditions. Moreover, MBA-CB Gel can whiten an indigo carmine-stained tooth under laser irradiation after 60 min of laser treatment, and the color difference (ΔE) in the teeth of the MBA-CB Gel treatment group was 10.9 times that of the control group. This study demonstrates the potential of MBA-CB Gel as a promising platform for biofilm inactivation and tooth whitening. It is worth noting that, since this study only used stained models of extracted teeth, the research results may not fully reflect the actual clinic situation. Future clinical research needs to further validate these findings.

Keywords: bacterial biofilm; controllable free radical release; photothermal-thermodynamic therapy; tooth whitening; transition-metal dichalcogenides.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
(a) Preparation of carbomer gels containing MB NSs and AIPH (MBA-CB Gel). (b) On-demand release of alkyl free radicals from AIPH by MB NSs with laser on/off. (c) Applications of MBA-CB Gel for biofilm inactivation and tooth whitening.
Figure 1
Figure 1
Characterization of MB NSs. Transmission electron microscopy (TEM) images of MoS2 NSs (a), and MB NSs (b). (c) X-ray photoelectron spectroscopy (XPS) spectra of MoS2 NSs and MB NSs. (d) X-ray diffraction (XRD) patterns of MoS2 NSs and MB NSs. (e) Fourier transform infrared spectroscopy (FT-IR) spectra of MoS2 NSs, BSA, and MB NSs. (f) Photothermal heating curves of MB NSs aqueous dispersions at various concentrations under 808 nm laser irradiation (1.0 W/cm2).
Figure 2
Figure 2
The stability of AIPH at various temperatures and the degradation effect of various dyes by AIPH. (ac) Ultraviolet-visible (UV-Vis) absorption spectra of AIPH aqueous solutions incubated at 25 °C (a), 37 °C (b), and 55 °C (c) for different times. (d) The absorbance of AIPH aqueous solutions at 363 nm at different temperatures for different times (n = 3). (e,f) Ultraviolet-visible near-infrared (UV-Vis-NIR) absorption spectra and photographs (inset) of indigo carmine (e) and methyl orange (f) under various incubation conditions.
Figure 3
Figure 3
The regulatory capability of MB NSs on free radical release. (a) The UV-Vis-NIR absorption spectra of MB NSs aqueous solutions after incubation with AIPH at 37 °C (inset: photographs of MB NSs and MB NSs + AIPH). TEM images of MB NSs after being incubated for 6 h at 37 °C without (b) and with AIPH (c). (d) XPS spectra of MB NSs after 6 h incubation at 37 °C with and without AIPH. (e) Temperature evolution curves of MB NSs aqueous dispersions with varying AIPH concentrations. (f) NIR light-triggered degradation of indigo carmine (50 μg/mL) by MB NSs mixed with AIPH (MB NSs 40 μg/mL, AIPH 60 μg/mL). Irradiation conditions were kept constant (808 nm, 1.0 W/cm2, 5 min) across all experimental groups.
Figure 4
Figure 4
Treatment of planktonic MRSA and S. mutans. (a) Photographs of MRSA colonies formed on Luria–Bertani (LB) agar plates and the corresponding numbers of MRSA (b) after various treatments. (c) Photographs of S. mutans colonies formed on Brain Heart Infusion Broth (BHI) agar plates and the corresponding numbers of S. mutans (d) after various treatments (n = 3 biologically independent samples; mean ± SD). All experimental groups were subjected to identical irradiation conditions (808 nm, 1.0 W/cm2, 5 min). Statistical significance was analyzed via one-way ANOVA with a Tukey post hoc test.
Figure 5
Figure 5
Treatment of S. mutans biofilms. (a) Photographs of S. mutans colonies formed on BHI agar plates and the corresponding numbers of S. mutans (b) from the biofilm after various treatments (n = 3 biologically independent samples, mean ± SD). (c) SEM images of S. mutans after various treatments. All experimental groups were subjected to an identical irradiation condition (808 nm, 1.0 W/cm2, 5 min). The scale bar is 3 μm. Statistical significance was analyzed via one-way ANOVA with a Tukey post hoc test.
Figure 6
Figure 6
Images of carbomer gels with different components. (a) The gel formation under different AIPH feeding concentrations (samples (16): 0.12, 0.24, 0.48, 0.96, 2.5, and 5.0 mg/mL) when the final concentration of carbomer was 0.5%. (b) The gel formation under different AIPH feeding concentrations (samples (16): 0.12, 0.24, 0.48, 0.96, 2.5, and 5.0 mg/mL) when the final concentration of carbomer is 1.0%. (c) The gel formation under different MB NSs feeding concentrations (samples (14): 0, 50, 100, and 150 μg/mL) when the carbomer concentration was 1.0% and AIPH concentration was 2.5 mg/mL.
Figure 7
Figure 7
Characterization of MBA-CB Gel. (a) SEM images and pictures (inset) of carbomer gel (CB Gel) and (b) carbomer composite gel encapsulating MB NSs and AIPH (MBA-CB Gel). (c) XPS spectra of CB Gel and MBA-CB Gel. (d) FT-IR spectra of MB NSs, AIPH, CB Gel, and MBA-CB Gel. (e) Infrared thermal images and (f) corresponding temperature increase curves of MBA-CB Gel with different MB NSs contents (0, 50, 100, 150 μg/mL). Irradiation conditions were kept constant (808 nm, 1.0 W/cm2, 5 min) across all experimental groups.
Figure 8
Figure 8
Tooth whitening by AIPH-CB Gel, MB-CB Gel, and MBA-CB Gel. (a) Photographs of indigo carmine-stained teeth after treatment with various CB gels under laser irradiation at different time points. Tooth whitening performance was evaluated using variations in luminance L (b), color value of the red-green axis a (c), color value of the blue-yellow axis b (d), and color difference ΔE (e) calculated from (a). Statistical significance was analyzed via one-way ANOVA with a Tukey post hoc test.

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