Applied Sciences

Background: Orthodontic appliances introduce new surfaces into the oral cavity that can modulate biofilm formation and potentially increase the risk of white spot lesions. Material-dependent differences in surface roughness, wettability and geometry may influence early colonization by Streptococcus mutans, a key cariogenic pathogen. Objectives: To compare early adhesion and biofilm formation of Streptococcus mutans on five commonly used orthodontic materials: stainless-steel (SS) and nickel–titanium (NiTi) archwires, metallic and ceramic brackets, polymethyl methacrylate (PMMA) acrylic resin. Materials and Methods: Standardized specimens were prepared, polished when applicable, sterilized, and conditioned in artificial saliva. The tested materials included SS and NiTi archwires (3M Unitek, Monrovia, CA, USA), metallic and ceramic brackets (Ormco, Orange, CA, USA), and PMMA acrylic resin (GC Corporation, Tokyo, Japan). Early adhesion (CFU), biofilm biomass (crystal violet), and metabolic activity (XTT) were quantified after incubation with S. mutans. Surface roughness (Ra) and contact angle were measured, and correlations with microbiological endpoints were assessed. Results: A clear material-dependent gradient was observed. Stainless steel showed the lowest early adhesion and biofilm formation (5.20 ± 0.28 log₁₀ CFU·cm⁻²; CV OD₅₉₀ = 0.60 ± 0.14), followed by NiTi, metallic brackets, and ceramic brackets, while PMMA exhibited the highest bacterial load and biofilm biomass (6.09 ± 0.32 log₁₀ CFU·cm⁻²; CV OD₅₉₀ = 1.10 ± 0.17). Overall differences between materials were statistically significant (p < 0.0001). Surface roughness and contact angle positively correlated with bacterial colonization. Conclusions: Early S. mutans colonization is strongly influenced by orthodontic material properties, with smoother and less hydrophobic surfaces showing reduced biofilm formation. PMMA and bracket structures may pose higher cariogenic risk during treatment. These findings support the development of surface-engineered or biofilm-resilient orthodontic materials.

Wet flue gas desulfurization (WFGD) is a widely used process for controlling SO₂ emissions in coal-fired power plants. However, the slow dissolution kinetics of limestone (CaCO₃) and the poor dewatering properties of gypsum crystals significantly limit the performance of this process. In this study, the effects of adding adipic acid, an organic acid, at different concentrations (0, 500, 1000, and 1500 ppm) to limestone slurry in the WFGD process were investigated. SO₂ removal performance, limestone consumption, and gypsum quality were evaluated. SO₂ removal efficiency remained unaffected by the addition of adipic acid. The addition of adipic acid reduced limestone consumption by 6.89%, 8.35%, and 9.92% in WFGD, respectively. The moisture content of gypsum decreased from 22.4% to 9.2%. The results revealed that adipic acid accelerates limestone dissolution via a ligand-assisted proton-transfer mechanism and improves the overall efficiency of the WFGD process by controlling gypsum crystallization. The physical quality and structure of gypsum obtained from the WFGD were evaluated by Scanning Electron Microscopy (SEM). Adipic acid led to the development of larger, smoother, and potato-like morphologies in the gypsum crystals and improved dewatering performance. This study demonstrates that using adipic acid in WFGD processes is a significant improvement strategy that enhances process efficiency by accelerating limestone dissolution and controlling gypsum crystallization. Adipic acid addition is an effective optimization strategy for full-scale industrial WFGD systems.

The endogenous security paradigm has emerged to address the limitations of traditional cybersecurity, which relies on reactive “patching” and struggles against unknown threats, APTs, and supply chain attacks. Centered on the principle that “structure determines security”, it diverges from detection-based approaches by employing systems theory and cybernetics to architect closed-loop systems with “heterogeneous execution, multimodal adjudication, and dynamic scheduling”. This is realized through intrinsic architectural constructs such as dynamism, heterogeneity, and redundancy. Theoretically, it transforms deterministic component-level attacks into probabilistic system-level events, thereby shifting the security foundation from a “cognitive contest” to an “entropy-driven confrontation”. This paper provides a comprehensive review of this paradigm. We begin by elucidating its philosophical foundations and core axioms, focusing on the Dynamic Heterogeneous Redundancy (DHR) model, which converts attacks on specific vulnerabilities into probabilistic events under the core assumption of independent heterogeneous execution entities. Next, we trace the architectural evolution from early mimic defense prototypes to a universal framework, analyzing key developments including expanded heterogeneity dimensions, intelligence-driven dynamic policies, and enhanced adjudication mechanisms. We then explore essential enabling technologies and their integration with cutting-edge trends such as artificial intelligence, 6G, and cloud-native computing. Through case studies of the 5G core network and intelligent connected vehicles, the engineering feasibility of the endogenous security paradigm has been validated, with quantifiable security gains demonstrated. In a live-network pilot of the endogenous security micro-segmentation system for the 5G core, resource consumption (CPU/memory usage) of network function virtual machines remained below 3% under steady-state service loads. The system concurrently maintained microsecond-level forwarding performance and achieved carrier-grade core service availability of 99.999%. These results demonstrate that the endogenous security mechanism delivers high-level structural security with an acceptable performance cost. The paper also critically summarizes current theoretical, engineering, and ecosystem challenges, while outlining future research directions such as “Endogenous Security as a Service” and convergence with quantum-safe technologies.