Long-term antimicrobial assessment of orthodontic brackets coated with nitrogen-doped titanium dioxide against Streptococcus mutans

Background

The antimicrobial properties of orthodontic wire and brackets with nitrogen-doped titanium dioxide (N-doped TiO2) coating have been studied in the past. However, the evaluation period had been short and limited to 30 days. The aim of the present study was to extend the evaluation period (up to 90 days) of assessing the long-term antimicrobial effects of stainless steel orthodontic brackets coated with nitrogen-doped titanium dioxide (N-doped TiO2).

Methods

A total of 40 stainless steel pre-adjusted premolar brackets were equally divided into two groups; namely the control group (n=20, uncoated brackets) and the experimental group (n=20, coated brackets). RF magnetron sputtering was used to apply a thin film of TiO2 on the bracket surface. The crystalline structure of the thin film was assessed using X-ray diffraction. The antimicrobial property of the brackets against Streptococcus mutans (S. mutans) was evaluated using the survival rate by colony-forming units (CFU) at four intervals: 24 hours (T0), 30 days (T1), 60 days (T2), and 90 days (T3). 2-way ANOVA Repeated Measures was used to compare the effects between the groups over the time.

Results

There was no significant interaction between group and time (p = 0.568). The orthodontic brackets coated with the N-doped TiO2 thin film showed a significant CFU reduction (37.71 ± 5.21, 37.81 ± 5.03, 37.98 ± 5.37, and 37.74 ± 5.21 at T0, T1, T2, and T3, respectively) compared to the uncoated brackets (400.91 ± 14.67, 401.58 ± 14.01, 400.31 ± 14.68, and 402.04 ± 13.98 at T0, T1, T2, and T3, respectively) through visible light (p < 0.001).

Conclusion

N-doped TiO2 coated orthodontic brackets showed strong antimicrobial property against S. mutans over a period of 90 days, which is effective in preventing enamel decalcification during orthodontic therapy.

Notch-Jagged complex structure implicates a catch bond in tuning ligand sensitivity

Notch receptor activation initiates cell fate decisions and is distinctive in its reliance on mechanical force and protein glycosylation. The 2.5-angstrom-resolution crystal structure of the extracellular interacting region of Notch1 complexed with an engineered, high-affinity variant of Jagged1 (Jag1) reveals a binding interface that extends ~120 angstroms along five consecutive domains of each protein. O-Linked fucose modifications on Notch1 epidermal growth factor-like (EGF) domains 8 and 12 engage the EGF3 and C2 domains of Jag1, respectively, and different Notch1 domains are favored in binding to Jag1 than those that bind to the Delta-like 4 ligand. Jag1 undergoes conformational changes upon Notch binding, exhibiting catch bond behavior that prolongs interactions in the range of forces required for Notch activation. This mechanism enables cellular forces to regulate binding, discriminate among Notch ligands, and potentiate Notch signaling.

Integrin Molecular Tension within Motile Focal Adhesions

Forces transmitted by integrins regulate many important cellular functions. Previously, we developed tension gauge tether (TGT) as a molecular force sensor and determined the threshold tension across a single integrin-ligand bond, termed integrin tension, required for initial cell adhesion. Here, we used fluorescently labeled TGTs to study the magnitude and spatial distribution of integrin tension on the cell-substratum interface. We observed two distinct levels of integrin tension. A >54 pN molecular tension is transmitted by clustered integrins in motile focal adhesions (FAs) and such force is generated by actomyosin, whereas the previously reported ∼40 pN integrin tension is transmitted by integrins before FA formation and is independent of actomyosin. We then studied FA motility using a TGT-coated surface as a fluorescent canvas, which records the history of integrin force activity. Our data suggest that the region of the strongest integrin force overlaps with the center of a motile FA within 0.2 μm resolution. We also found that FAs move in pairs and that the asymmetry in the motility of an FA pair is dependent on the initial FA locations on the cell-substratum interface.

Rupture force of cell adhesion ligand tethers modulates biological activities of a cell-laden hydrogel

Recent efforts to design a synthetic extracellular matrix for cell culture, engineering, and therapies greatly contributed to addressing biological roles of types and spatial organization of cell adhesion ligands. It is often suggested that ligand-matrix bond strength is another path to regulate cell adhesion and activities; however tools are lacking. To this end, this study demonstrates that a hydrogel coupled with integrin-binding deoxyribonucleic acid (DNA) tethers with pre-defined rupture forces can modulate cell adhesion, differentiation, and secretion activities due to the changes in the number and, likely, force of cells adhered to a gel. The rupture force of DNA tethers was tuned by altering the spatial arrangement of matrix-binding biotin groups. The DNA tethers were immobilized on a hydrogel of alginate grafted with biotin using avidin. Mesenchymal stem cells showed enhanced adhesion, neural differentiation, and paracrine secretion when cultured on the gel coupled with DNA tethers with higher rupture forces. Such innovative cell-matrix interface engineering would be broadly useful for a series of materials used for fundamental and applied studies on biological cells.