Droplet size distribution, atomization mechanism and dynamics of dental aerosols.

Since the outbreak of COVID-19 pandemic, maintaining safety in dental operations has challenged health care providers and policy makers. Studies on dental aerosols often focus on bacterial viability or particle size measurements inside dental offices during and after dental procedures, which limits their conclusions to specific cases. Fundamental understanding on atomization mechanism and dynamics of dental aerosols are needed while assessing the risks. Most dental instruments feature a build-in atomizer. Dental aerosols that are produced by ultrasonic or rotary atomization are considered to pose the highest risks. In this work, we aimed to characterize dental aerosols produced by both methods, namely by Mectron PIEZOSURGERY® and KaVo EXPERTtorque™. Droplet size distributions and velocities were measured with a high-speed camera and a rail system. By fitting the data to probability density distributions and using empirical equations to predict droplet sizes, we were able to postulate the main factors that determine droplet sizes. Both dental instruments had wide size distributions including small droplets. Droplet size distribution changed based on operational parameters such as liquid flow rate or air pressure. With a larger fraction of small droplets, rotary atomization poses a higher risk. With the measured velocities reaching up to 5 m s-1, droplets can easily reach the dentist in a few seconds. Small droplets can evaporate completely before reaching the ground and can be suspended in the air for a long time. We suggest that relative humidity in dental offices are adjusted to 50% to prevent fast evaporation while maintaining comfort in the office. This can reduce the risk of disease transmission among patients. We recommend that dentists wear a face shield and N95/FFP2/KN95 masks instead of surgical masks. We believe that this work gives health-care professionals, policy makers and engineers who design dental instruments insights into a safer dental practice.

Acoustic resonance and atomization for gas-liquid systems in microreactors.

It is shown that a liquid slug in gas-liquid segmented flow in microchannels can act as an acoustic resonator to disperse large amounts of small liquid droplets, commonly referred to as atomization, into the gas phase. We investigate the principles of acoustic resonance within a liquid slug through experimental analysis and numerical simulation. A mechanism of atomization in the confined channels and a hypothesis based on high-speed image analysis that links acoustic resonance within a liquid slug with the observed atomization is proposed. The observed phenomenon provides a novel source of confined micro sprays and could be an avenue, amongst others, to overcome mass transfer limitations for gas-liquid processes in flow.

Dawn of a new era in industrial photochemistry: the scale-up of micro- and mesostructured photoreactors.

Photochemical activation routes are gaining the attention of the scientific community since they can offer an alternative to the traditional chemical industry that mainly utilizes thermochemical activation of molecules. Photoreactions are fast and selective, which would potentially reduce the downstream costs significantly if the process is optimized properly. With the transition towards green chemistry, the traditional batch photoreactor operation is becoming abundant in this field. Process intensification efforts led to micro- and mesostructured flow photoreactors. In this work, we are reviewing structured photoreactors by elaborating on the bottleneck of this field: the development of an efficient scale-up strategy. In line with this, micro- and mesostructured bench-scale photoreactors were evaluated based on a new benchmark called photochemical space time yield (mol·day-1·kW-1), which takes into account the energy efficiency of the photoreactors. It was manifested that along with the selection of the photoreactor dimensions and an appropriate light source, optimization of the process conditions, such as the residence time and the concentration of the photoactive molecule is also crucial for an efficient photoreactor operation. In this paper, we are aiming to give a comprehensive understanding for scale-up strategies by benchmarking selected photoreactors and by discussing transport phenomena in several other photoreactors.

An accessible visible-light actinometer for the determination of photon flux and optical pathlength in flow photo microreactors.

Coupling photochemistry with flow microreactors enables novel synthesis strategies with higher efficiencies compared to batch systems. Improving the reproducibility and understanding of the photochemical reaction mechanisms requires quantitative tools such as chemical actinometry. However, the choice of actinometric systems which can be applied in microreactors is limited, due to their short optical pathlength in combination with a large received photon flux. Furthermore, actinometers for the characterization of reactions driven by visible light between 500 and 600 nm (e.g. photosensitized oxidations) are largely missing. In this paper, we propose a new visible-light actinometer which can be applied in flow microreactors between 480 and 620 nm. This actinometric system is based on the photoisomerization reaction of a diarylethene derivative from its closed to the open form. The experimental protocol for actinometric measurements is facile and characterized by excellent reproducibility and we also present an analytical estimation to calculate the photon flux. Furthermore, we propose an experimental methodology to determine the average pathlength in microreactors using actinometric measurements. In the context of a growing research interest on using flow microreactors for photochemical reactions, the proposed visible-light actinometer facilitates the determination of the received photon flux and average pathlength in confined geometries.

Factors affecting sentinel lymph node metastasis in Turkish breast cancer patients: Predictive value of Ki-67 and the size of lymph node.

OBJECTIVES: We aimed to analyze the factors that affect the axillary lymph node involvement in Turkish breast cancer patients with clinically non-palpable axillary lymph node. BACKGROUND: Sentinel lymph node biopsy is the gold standard technique to evaluate the axillary lymph node status that directly influences the prognosis and the treatment options in breast cancer. METHODS: Breast cancer patients without axillary lymph node involvement in clinic examination were enrolled the study. Patients were categorized into the two groups according to existence of axillary lymph node metastasis or not. Demographic, histopathological and clinical data of patients were revealed retrospectively. RESULTS: One-hundred and eighty-seven patients were analyzed and 101 of patients fulfilled the criteria and were included the study. Metastatic lymph node was detected in 38 (37.6 %) patients (Group 1), and was negative in 63 (62.4 %) patients (Group 2). Sentinel lymph node metastasis were statistically significant higher in patients with Ki-67 ≥ 14 % than patients with Ki-67 < 14 % (51.9 % vs 22.4 %; p < 0.01). Likewise, the mean size of the sentinel lymph node was statistically significant higher in Group 1 compared to Group 2 (p < 0.01). CONCLUSION: Ki-67 proliferation index and sentinel lymph node size may provide a higher prediction about the sentinel lymph node involvement in patients with clinically negative axillary lymph nodes (Tab. 3, Fig. 1, Ref. 31).

Hyperbilirubinemia as a predictive factor in acute appendicitis.

PURPOSE: Our aim was to establish the role of hyperbilirubinemia as a predictive parameter for the prediction of either acute, or gangrenous/perforated appendicitis as well as to compare other parameters in a similar role. METHODS: Medical files of the patients who underwent appendectomies between September 2013 and September 2014 were evaluated. Age, gender, preoperative white blood cell count (WBC), neutrophil count (NEU), neutrophil percentage (NEU%), C-reactive protein (CRP), total/direct/indirect bilirubin levels, and the postoperative histopathological findings were recorded. The Fisher's exact, Pearson's χ (2), ANOVA, and Kruskal-Wallis tests while logistic regression for multivariate analysis was performed. p < 0.05 was accepted as statistically significant. RESULTS: The study group of 162 patients consisted of 97 (60 %) men and 65 (40 %) women with a median age of 36 (18-90). Histopathological examinations revealed normal appendix in 21 (13 %) patients, non-complicated acute appendicitis in 100 (62 %), and appendiceal gangrene/perforation in 41 (25 %) patients. WBC, NEU, NEU%, and CRP levels were significantly higher in cases of acute and gangrenous/perforated appendicitis (p < 0.01). Total and direct bilirubin levels were also significantly elevated in patients with acute and gangrenous/perforated appendicitis (p < 0.01). According to multivariate analysis, elevated CRP levels were associated with 14 times, elevated total bilirubin levels were associated with five times, and elevated direct bilirubin levels were associated with 36 times greater risk for appendiceal gangrene/perforation (p < 0.01, p < 0.05, p < 0.01, respectively). CONCLUSIONS: Hyperbilirubinemia, especially with elevated direct bilirubin levels, may be considered as an important marker for the prediction of appendiceal gangrene/perforation.

Separation of human immunoglobulin G subclasses on a protein A monolith column.

Monolithic columns have attracted significant attention for the purification of large biomolecules. In the present study, a step gradient elution method was evaluated for the separation of human immunoglobulin G (hIgG) into its subclasses on CIM (convective interaction media) r-protein A (recombinant protein A) monolithic column. hIgG was loaded onto the column and bound protein was eluted with a pH gradient. The subclass content of the eluted fractions was analyzed by enzyme-linked immunosorbent assay (ELISA). Results showed that separation of IgG3 from the other three subclasses can be successfully achieved with high selectivity (100%) and throughput on monolithic media. It was also revealed that enriched fractions of IgG1 and IgG2 could be obtained from purified hIgG in a 28min long chromatographic run. Three fractions with high IgG1 content (89.1%, 94.3% and 88.8%) were recovered. Furthermore, IgG2 was enriched to 64% successfully. A rapid step gradient elution scheme without any additives in buffers was proven to obtain enriched preparations of the two important subclasses with high throughput. The separation time can be reduced even more by increasing the flow rate without any loss in selectivity, which will be beneficial in industrial scale applications.

Continuous flow photo-Fenton treatment of ciprofloxacin in aqueous solutions using homogeneous and magnetically recoverable catalysts.

The degradation of ciprofloxacin was studied in aqueous solutions by using a continuous flow homogeneous photo-Fenton process under simulated solar light. The effect of different operating conditions on the degradation of ciprofloxacin was investigated by changing the hydrogen peroxide (0-2.50 mM) and iron(II) sulphate (0-10 mg Fe L(-1)) concentrations, as well as the pH (2.8-10), irradiance (0-750 W m(-2)) and residence time (0.13-3.4 min) of the process. As expected, the highest catalytic activity in steady state conditions was achieved at acidic pH (2.8), namely 85 % of ciprofloxacin conversion, when maintaining the other variables constant (i.e. 2.0 mg L(-1) of iron(II), 2.50 mM of hydrogen peroxide, 1.8 min of residence time and 500 W m(-2) of irradiance). Additionally, magnetite magnetic nanoparticles (ca. 20 nm of average particle size) were synthesized, characterized and tested as a possible catalyst for this reaction. In this case, the highest catalytic activity was achieved at natural pH, namely a 55 % average conversion of ciprofloxacin in 1.8 min of residence time and under 500 W m(-2). Some of the photocatalytic activity was attributed to Fe(2+) leaching from the magnetic nanoparticles to the solution.