Investigating the temporal dynamics of sub-micron particles and particle-bound transition metals in indoor air of a metropolitan city

The present study portrays an association between particle-bound transition metals and children's health. The indoor air quality of the urban metropolitan city households was monitored for four PM sizes, namely PM1.0-2.5, PM0.50-1.0, PM0.25-0.50 and PM<0.25, in major seasons observed in the city; summer and winter. Further transition/heavy metals, viz. Cr, Cu, Fe, Mn, Ni, Pb and Zn, were analysed in PM1-2.5 samples. In order to evaluate the effect, health risk assessment was performed using mathematical and computational model for assessing dermal exposure and dose estimation (multiple path particle dosimetry model version3.0). The study principally targeted the children aged 2-15 years for the health risk assessment. According to the results, for the largest particle size i.e. PM1.0-2.5 the highest deposition was in the head region (49.1%) followed by pulmonary (43.6%) and tracheobronchial region (7.2%), whereas, for the smallest particle size i.e. PM<0.25 the highest deposition was obtained in the pulmonary region (73.0%) followed by the head (13.6%) and TB region (13.2%). Also, the most imperilled group of children with highest dose accumulation was found to be children aged 8-9 years for all particle sizes. Moreover, the dermal exposure dose as evaluated was found to be preeminent for Ni, Zn and Pb. Besides, seasonal variation gesticulated towards elevated concentrations in winter relative to the summer season. Altogether, the study will provide a conception to the researchers in the fields mounting season-specific guidelines and mitigation approaches. Conclusively, the study commends future work focussing on defining the effects of other chemical components on particles and associated transition metal composition along with proper extenuation of the same.

Scalable production of chitosan sub-micron particles by membrane ionotropic gelation process

Ionotropic gelation (IG) is a highly attractive method for the synthesis of natural water-soluble polymeric nanoparticles (NPs) and sub-micron particles (sMP) due to its relatively simple procedure and the absence of organic solvents. The method involves the electrostatic interaction between two ionic species of opposite charge. Although it is well studied at the laboratory scale, the difficulty to achieve size control in conventional bench-top process is actually a critical aspect of the technology. The aim of this work is to study the membrane dispersion technology in combination with IG as a suitable scalable method for the production of chitosan sub-micron particles (CS-sMPs). The two phases, one containing chitosan (CS) and the other containing sodium tripolyphosphate (TPP), were put in contact using a tubular hydrophobic glass membrane with a pore diameter of 1 μm. TPP (dispersed phase) was permeated through the membrane pores into the lumen side along which the CS solution (the continuous phase) flowed in batch recirculation or continuous single-pass operation mode. The influence of chemical variables (i.e. pH, concentration and mass ratio of polyelectrolyte species, emulsifier) and fluid-dynamic parameters (i.e. polyelectrolyte solution flow rate and their relative mass ratio) was studied to precisely tune the size of CS-Ps.

Formation mechanisms of sub-micron pharmaceutical composite particles derived from far- and near-field Raman microscopy

Surface enhanced Raman spectroscopy (SERS) and confocal Raman microscopy are applied to investigate the structure and the molecular arrangement of sub-micron furosemide and polyvinylpyrrolidone (furosemide/PVP) particles produced by spray flash evaporation (SFE). Morphology, size and crystallinity of furosemide/PVP particles are analyzed by scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). Far-field Raman spectra and confocal far-field Raman maps of furosemide/PVP particles are interpreted based on the far-field Raman spectra of pure furosemide and PVP precursors. Confocal far-field Raman microscopy shows that furosemide/PVP particles feature an intermixture of furosemide and PVP molecules at the sub-micron scale. SERS and surface-enhanced confocal Raman microscopy (SECoRM) are performed on furosemide, PVP and furosemide/PVP composite particles sputtered with silver (40 nm). SERS and SECoRM maps reveal that furosemide/PVP particle surfaces mainly consist of PVP molecules. The combination of surface and bulk sensitive analyses reveal that furosemide/PVP sub-micron particles are formed by the agglomeration of primary furosemide nano-crystals embedded in a thin PVP matrix. Interestingly, both far-field Raman microscopy and SECoRM provide molecular information on a statistically-relevant amount of sub-micron particles in a single microscopic map; this combination is thus an effective and time-saving tool for investigating organic sub-micron composites.

Effects of the flue gas treatment of incinerator plants on sub-micron particle concentrations at the stack

The paper is focused on the emission of sub-micron particles from incinerator plants characterized by different treatment sections. In particular, measurement of particle number concentrations and distributions in different sampling points of the flue-gas treatment sections, and/or over several years, allowed to detect, for the very first time through in-field tests, the effect of the age of the fabric filter bags and of the SCR system on the emission of sub-micron particles. In fact, tests showed that the age of the fabric filter bags can affect the particle number concentrations at the stack: indeed, for older bags higher concentrations at the stack were measured likely due to the filter cleaning process. Concerning the effect of the SCR system, the natural gas combustion performed in the SCR system leads to an increase of sub-micron particle concentrations at the stack with respect to the values measured after the filtration section.

A comparative assessment of continuous production techniques to generate sub-micron size PLGA particles

The clinical and commercial development of polymeric sub-micron size formulations based on poly(lactic-co-glycolic acid) (PLGA) particles is hampered by the challenges related to their good manufacturing practice (GMP)-compliant, scale-up production without affecting the formulation specifications. Continuous process technologies enable large-scale production without changing the process or formulation parameters by increasing the operation time. Here, we explore three well-established process technologies regarding continuity for the large-scale production of sub-micron size PLGA particles developed at the lab scale using a batch method. We demonstrate optimization of critical process and formulation parameters for high-shear mixing, high-pressure homogenization and microfluidics technologies to obtain PLGA particles with a mean diameter of 150-250 nm and a small polydispersity index (PDI, ≤0.2). The most influential parameters on the particle size distribution are discussed for each technique with a critical evaluation of their suitability for GMP production. Although each technique can provide particles in the desired size range, high-shear mixing is found to be particularly promising due to the availability of GMP-ready equipment and large throughput of production. Overall, our results will be of great guidance for establishing continuous process technologies for the GMP-compliant, large-scale production of sub-micron size PLGA particles, facilitating their commercial and clinical development.

Penetration of sub-micron particles into dentinal tubules using ultrasonic cavitation

OBJECTIVES

Functionalised silica sub-micron particles are being investigated as a method of delivering antimicrobials and remineralisation agents into dentinal tubules. However, their methods of application are not optimised, resulting in shallow penetration and aggregation. The aim of this study is to investigate the impact of cavitation occurring around ultrasonic scalers for enhancing particle penetration into dentinal tubules.

METHODS

Dentine slices were prepared from premolar teeth. Silica sub-micron particles were prepared in water or acetone. Cavitation from an ultrasonic scaler (Satelec P5 Newtron, Acteon, France) was applied to dentine slices immersed inside the sub-micron particle solutions. Samples were imaged with scanning electron microscopy (SEM) to assess tubule occlusion and particle penetration.

RESULTS

Qualitative observations of SEM images showed some tubule occlusion. The particles could penetrate inside the tubules up to 60μm when there was no cavitation and up to ∼180μm when there was cavitation.

CONCLUSIONS

The cavitation bubbles produced from an ultrasonic scaler may be used to deliver sub-micron particles into dentine. This method has the potential to deliver such particles deeper into the dentinal tubules.

CLINICAL SIGNIFICANCE

Cavitation from a clinical ultrasonic scaler may enhance penetration of sub-micron particles into dentinal tubules. This can aid in the development of novel methods for delivering therapeutic clinical materials for hypersensitivity relief and treatment of dentinal caries.

Characterization and source identification of sub-micron particles at the HKUST Supersite in Hong Kong

Particle size distribution measurements were conducted continuously at a 30-second interval using the Fast Mobility Particle Sizer (FMPS) in August, September, November and December of 2011 at a coastal background site in Hong Kong. Concurrent measurements of CO, NOx, O3, SO2 and volatile organic compounds (VOCs) were used to determine the causes of high particle number concentration (PNC) events. In all sampling months, PNC were usually higher in the evening, likely resulting from the arrival of upwind air pollutants as wind direction changed in the late afternoon. On the more polluted days, the PNC were usually higher around noon, particularly in August, similar to the diurnal trend of O3. The mode diameter at noon was smaller than in other time periods in all sampling months, further highlighting the role of secondary formation at this urban background site. A prolonged period of pollution episode occurred in late August. High PNC resulted from the arrival of pollution laden air from the PRD region or super regions. In December, new particle formation followed by subsequent growth accounted for most of the polluted days. Overall, meteorology was the most important parameter affecting particle concentrations and formation at this Hong Kong background site.

The deposition and imaging of silica sub-micron particles in dentine

OBJECTIVES

Sub-micron particles may assist in the delivery of compounds into dentine tubules. The surface interactions of the particles with dentine may prevent them from entering the tubules. The aim of this study is to investigate whether silica particles, treated with surfactants improves dentine tubules occlusion using both artificial and human tooth models

METHODS

Spherical silica particles (size 130-810nm) bearing an encapsulated ruthenium luminescent complex were coated with the following surfactants: Zonyl(®) FSA, Triton(®) X-100 and Tween20(®). The particles were prepared as 0.004% w/v and 0.04% w/v solutions with deionized water and were applied to the surface of; (1) in vitro model of PET ThinCert™ cell culture inserts; (2) 0.1mm thick sections of human molar teeth.

RESULTS

Scanning electron and confocal fluorescence microscopy images show that particles without any coating and with TritonX-100 coating had the highest aggregation. Particles with Tween-20 are less aggregated on the surface and show inclusion in the tubules. Particles coated with fluorosurfactant Zonyl show a preference for aggregation at the tubule. With the ThinCert™ membranes high aggregation within the artificial tubules was increased by particle concentration.

CONCLUSIONS

The use of silica sub-micron particles on hard dental tissues is dependent on the modification of the surface chemistry of both the particle and the dentine and the employment of the fluorοsurfactant may improve tubule occlusion. The use of ThinCerts™ membrane is useful in vitro model to mimic dentinal tubules and observe the ability of particles to occlude small channels.

CLINICAL SIGNIFICANCE

The use of silica sub-micron particles on hard dentine tissues is dependent on the modification of the surface coating of the particles. This may influence how particles are incorporated in potential delivery vehicles applied to the dentine surface with the employment of a fluorosurfactant showing promise.

Effect of sonication conditions: solvent, time, temperature and reactor type on the preparation of micron sized vermiculite particles

The effects of temperature, time, solvent and sonication conditions under air and Argon are described for the preparation of micron and sub-micron sized vermiculite particles in a double-jacketed Rosett-type or cylindrical reactor. The resulting materials were characterized via X-ray powder diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared (FTIR) Spectroscopy, BET surface area analysis, chemical analysis (elemental analysis), Thermogravimetry analysis (TGA) and Laser Granulometry. The sonicated vermiculites displayed modified particle morphologies and reduced sizes (observed by scanning electron microscopy and laser granulometry). Under the conditions used in this work, sub-micron sized particles were obtained after 5h of sonication, whereas longer times promoted aggregation again. Laser granulometry data revealed also that the smallest particles were obtained at high temperature while it is generally accepted that the mechanical effects of ultrasound are optimum at low temperatures according to physical/chemical properties of the used solvent. X-ray diffraction results indicated a reduction of the crystallite size along the basal direction [001]; but structural changes were not observed. Sonication at different conditions also led to surface modifications of the vermiculite particles brought out by BET surface measurements and Infrared Spectroscopy. The results indicated clearly that the efficiency of ultrasound irradiation was significantly affected by different parameters such as temperature, solvent, type of gas and reactor type.

Preparation of sub-micron nitrocellulose particles for improved combustion behavior

A novel method to prepare sub-micron nitrocellulose particles with spherical shape is demonstrated. The morphology of the nitrocellulose can be controlled by the solvent and the growth temperature. Using dimethylformamide (DMF) at a growth temperature is 5°C, reproducibly yielded spherical nitrocellulose particles. The final diameter of the prepared nitrocellulose particles can be further tuned by concentration. The smallest particles in this study were found to have diameters of 500nm at a concentration of 5-10mg/ml with 2 micron spheres formed at 30mg/ml. Furthermore, the thermal properties and the burn rates of the prepared materials are studied by differential scanning calorimetry and digital high-speed photography, respectively. In comparison to the bulk nitrocellulose material, the sub-micron nitrocellulose particles have lower decomposition activation energy, a 350% increase in burn rate, and a more complete combustion.