Enhancing Thermal Conductivity of hBN/SiC/PTFE Composites with Low Dielectric Properties via Pulse Vibration Molding.

In order to enhance the thermal conductivity of polytetrafluoroethylene (PTFE)-based composites, while maintaining relatively low dielectric constant and dielectric loss for high-frequency and high-speed applications, hexagonal boron nitride (hBN) and silicon carbide (SiC) compounded fillers are filled into the PTFE matrix. The hBN/SiC/PTFE composites are prepared by pulse vibration molding (PVM), and their subsequent thermal conductivities are comparatively investigated. The PVM process with controlled fluctuation in pressure (1 Hz square wave force, 0-20 MPa, at 150 °C) can reduce the sample porosity and surface defects, improve the orientation of hBN, and increase the thermal conductivity by 44.6% compared with that obtained by compression molding. When hBN:SiC (vol) is 3:1, the in-plane thermal conductivity of the composite with 40 vol% filler content is ≈4.83 W m-1  K-1 , which is 40.3% higher than that of hBN/PTFE. Regarding the dielectric properties, hBN/SiC/PTFE maintains a low dielectric constant of 3.27 and a low dielectric loss of 0.0058. The dielectric constants of hBN/SiC/PTFE ternary composites are predicted by using different prediction models, among which the effective medium theory (EMT), is in good agreement with the experimental results. PVM shows great potential in the large-scale preparation of thermal conductive composites for high-frequency and high-speed applications.

Preparation of the Levo-Tetrahydropalmatine Liposome Gel and Its Transdermal Study.

Purpose: The aim of this study was to develop a liposome gel containing levo-tetrahydropalmatine (l-THP) and evaluate its transdermal properties. Methods: A L16 (43) orthogonal experiment was conducted to optimize the preparation of l-THP liposomes and assess their characterization and stability in a gel. The transdermal features were analyzed through in vivo and in vitro experiments on rats and Strat-M® membrane, respectively. The metabolism of l-THP in liver and skin S9 fractions was also studied. Results: The optimization of the orthogonal experiment revealed that the ideal mass ratio of phosphatidylcholine, cholesterol, and l-THP during preparation was 10:1:3. The resulting liposome exhibited a particle size of 68 nm, a PDI of 0.27, a drug loading of 4.33%, an encapsulation of 18.79%, and a zeta potential of -41.27 mV. Both the l-THP and its liposome-gel formulation were found to be stable for a duration of 45 days at 4 °C and 30 °C. During the in vivo transdermal study, the maximum concentration (Cmax) of l-THP from the liposome gel was 0.16 µg/mL, and the time to reach this maximum concentration (tmax) was 1.2 hours. The relative bioavailability of l-THP in the liposome gel was 233.8% compared to the emulsion. The concentration of l-THP (prepared in PBS) decreased at a rate of 0.0067 µg/mL/min in the liver S9 fraction and 0.0027 µg/mL/min in the skin S9 fraction, however, this difference was not observed when l-THP was encapsulated in liposomes. l-THP passed through the Strat-M® membrane at a rate of 0.0032 mg/cm2/h and 0.002 mg/cm2/h for the emulsion and liposome gel, respectively. Conclusion: The optimal process for the preparation of l-THP liposomes was obtained. Compared to the emulsion, the liposomes provided greater bioavailability when used transdermally. The liposomes also provided greater stability for l-THP during storage.

Persistence of extracrevicular bacterial reservoirs after treatment of aggressive periodontitis.

BACKGROUND: The purpose of this study was to test the hypothesis that periodontal pathogens associated with aggressive periodontitis persist in extracrevicular locations following scaling and root planing, systemic antibiotics, and antimicrobial rinses. METHODS: Eighteen patients with aggressive periodontitis received a clinical examination during which samples of subgingival plaque and buccal epithelial cells were obtained. Treatment consisted of full-mouth root planing, systemic antibiotics, and chlorhexidine rinses. Clinical measurements and sampling were repeated at 3 and 6 months. Quantitative polymerase chain reaction determined the number of Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans), Prevotella intermedia, Porphyromonas gingivalis, Tannerella forsythia (previously T. forsythensis), and Treponema denticola in the plaque. Fluorescence in situ hybridization and confocal microscopy determined the extent of intracellular invasion in epithelial cells. RESULTS: Clinical measurements improved significantly following treatment. All bacterial species except P. gingivalis were significantly reduced in plaque between baseline and 3 months. However, all species showed a trend to repopulate between 3 and 6 months. This increase was statistically significant for log T. denticola counts. All species were detected intracellularly. The percentage of cells infected intracellularly was not affected by therapy. CONCLUSIONS: The 6-month increasing trend in the levels of plaque bacteria suggests that subgingival recolonization was occurring. Because the presence of these species within epithelial cells was not altered after treatment, it is plausible that recolonization may occur from the oral mucosa. Systemic antibiotics and topical chlorhexidine did not reduce the percentage of invaded epithelial cells. These data support the hypothesis that extracrevicular reservoirs of bacteria exist, which might contribute to recurrent or refractory disease in some patients.