Relaxation times in single event electrospraying controlled by nozzle front surface modification.

Single event electrospraying (SEE) is a method for on-demand deposition of femtoliter to picoliter volumes of fluids. To determine the influence of the size of the meniscus on the characteristics of the single event electrospraying process, glass capillaries were used with and without an antiwetting coating comprising a self-assembled 1H,1H,2H,2H-perfluorodecyltrichlorosilane-based monolayer to control the meniscus size. A large difference was found in driving single event electrospraying from a small meniscus compared to what is needed to generate a single event electrospraying from a large meniscus. Furthermore, after studying the different time constants related to the electrical and the hydrodynamic phenomena, we are able to explain the timing limitations of the deposition process from both a small and a large meniscus. The hydrodynamic relaxation time is significantly reduced in the case of the modified capillary, and the timing of SEE, which determines the deposition time, is limited by the resistor-capacitor RC time of the electrical circuit needed to drive the SEE. We have built a model that describes the almost one-dimensional motion of the liquid in the capillary during pulsing. The model has been used to estimate the hydrodynamic relaxation times related to the meniscus-to-cone and cone-to-meniscus transitions during SEE. By confining the meniscus to the inner diameter of the nozzle, we are able to deposit a volume smaller than 5 pL per SEE.

Nano-dispensing by electrospray for biotechnology.

Liquid transport of minute amounts of biomaterials is of paramount importance in many biotechnological applications. One of the challenges is the transport of viscous liquids without heating. Electro hydro dynamic atomization or electrospray is a viable method for the controlled transport of nanoliter volume of viscous liquids as shown for PEG400. Experimental results and the design of a novel spraying configuration, which can be incorporated in an optical microscope, are reported.

Microparticles developed by electrohydrodynamic atomization for the local delivery of anticancer drug to treat C6 glioma in vitro.

This study aims to fabricate biodegradable polymeric particles by electrohydrodynamic atomization (EHDA) for applications in sustained delivery of anticancer drug-paclitaxel to treat C6 glioma in vitro. Controllable morphologies such as spheres, doughnut shapes and corrugated shapes with sizes from several tens of microns to hundred nanometers of particles were observed by scanning electron microscopy (SEM) and field emission electron microscope (FSEM). The differential scanning calorimetry (DSC) study indicated that paclitaxel could be either in an amorphous or disordered-crystalline phase of a molecular dispersion or a solid solution state in the polymer matrix after fabrication. The X-ray photoelectron spectroscopy (XPS) result suggested that some amount of paclitaxel could exist on the surface layer of the microparticles. The encapsulation efficiency was around 80% and more than 30 days in vitro sustained release profile could be achieved. Cell cycling results suggested that paclitaxel after encapsulation by EHDA could keep its biological function and inhibit C6 glioma cells in G2/M phase. The cytotoxicity of paclitaxel-loaded biodegradable microparticles to C6 glioma cells could be higher than Taxol in the long-term in vitro tests evaluated by MTS assay. The drug delivery devices developed by EHDA in this study could be promising for the local drug delivery to treat malignant glioma.

Particle size-dependent total mass deposition in lungs determines inhalation toxicity of cadmium chloride aerosols in rats. Application of a multiple path dosimetry model.

The relative importance of the three particulate matter (PM) size fractions in ambient air, i.e. coarse (2.5-10 microm), fine (0.1-2.5 microm) and ultrafine (<0.1 microm) fractions, on the induction of adverse health effects is still unknown. Moreover, there is no straightforward relationship between ambient concentration levels, exposure (external dose) and the dose delivered to the target site (internal dose). Recently, a human and a rat airway PM deposition model (MPPDep V1.1) have been developed by CIIT Centers for Health Research and the National Institute of Public Health and the Environment (RIVM), based on the work of O.G. Raabe et al. (1977, In: W.H. Walton, editor, Inhaled Particles IV/2; Pergamon, Oxford) and S. Anjilvel and B. Asgharian (1995, Fundam Appl Toxicol 28:41-50). This paper describes studies using cadmium chloride (CdCl(2)) as a model for toxic aerosol particles to (1) investigate the role of particle size in the development of pulmonary effects, and (2) evaluate the MPPDep model, by comparing predicted deposition with measured deposition of CdCl(2)in the respiratory tract. Rats (ten per group) were exposed for a single 4-h period to CdCl(2)particles at various sizes, i.e. 33, 170, 637 and 1495 nm, all at a target concentration of 1 mg/m(3). Immediately after exposure, four of ten rats per group were killed and trachea, lung lobes, heart, liver and kidneys were collected and preserved to determine the amount of CdCl(2) present in each of these organs. CdCl(2)-induced toxicity, as measured by lactate dehydrogenase (LDH), N-acetyl glucosaminidase (NAG) and protein levels in bronchoalveolar lavage fluid, was determined in the remaining six rats per group the day after exposure. Animals exposed to 33 nm particles showed the highest level of respiratory toxicity, followed by animals exposed to 637 nm particles, then to 170 nm particles and finally by those exposed to 1495 nm particles. Pulmonary cadmium levels showed a similar relationship. The results from the present study suggest that the induction of pulmonary toxicity following inhalation exposure to soluble CdCl(2)particles in the range 30-1500 nm depends on the amount of deposited material, which in its turn depends on the initial (aerodynamic) particle size. In addition, the MPPDep model accurately predicted the measured CdCl(2) deposition. Conclusively, for soluble particles the deposited pulmonary mass (dose) of particles is important for toxicity and is dependent of particle size. These findings may have serious impact on the evaluation of the role of various particle sizes in PM10-associated health effects.

The self-preserving size distribution theory. II. Comparison with experimental results for Si and Si3N4 aerosols.

The gas to particle synthesis route is a relatively clean and efficient manner for the production of high-quality ceramic powders. These powders can be subsequently sintered in any wanted shape. The modeling of these production systems is difficult because several mechanisms occur in parallel. From theoretical considerations it can be determined, however, that coagulation and sintering are dominant mechanisms as far as shape and size of the particles are considered. In part I of this article an extensive theoretical analysis was given on the self-preserving size distribution theory for power law particles. In this second part, cumulative particle size distributions of silicon and silicon nitride agglomerates, produced in a laser reactor, were determined from TEM pictures and compared to the distributions calculated from this self-preserving theory for power law particles. The calculated distributions were in fair agreement with the measured results, especially at the high end of the distributions. Calculated and measured particle growth rates were also in fair agreement. Using the self-preserving theory an analysis was made on the distribution of annealed silicon agglomerates, of interest in applications to nanoparticle technology.