Applications of Nanoparticle Technology

Session Chair:

• Christine Hrenya, University of Colorado at Boulder

Schedule:

Silicon Nanocrystals for Biological Imaging

Brian Korgel, The University of Texas at Austin

Silicon nanocrystals fluoresce with size-tunable color in the red-to-near infrared spectral range and are biocompatible, making them well-suited for in vivo biological imaging.  There are however challenges facing their use in biological applications.  Their band-edge absorption is relatively weak, leading to a large apparent Stokes shift between optical excitation and emission.  To induce strong red light absorption while retaining the fluorescence properties of Si nanocrystals (i.e., red to NIR emission with long microsecond lifetimes), Si nanocrystals can be modified with molecular antenna with strong red absorption and charge transfer to the emitting nanocrystals.  Si nanocrystals are also susceptible to oxidation and photoluminescence quenching in water, which has required ligand passivation chemistry utilizing bifunctional alkenes with ester or carboxylate terminal functional groups.  Hydrophobic Si nanocrystals can also be dispersed in aqueous media using lipids and other surfactants.   For specific targeting of molecular recognition groups on cells, the nanocrystals can be modified with either nucleic acids or peptides.

Capillary Torque on a Rolling Particle in the Presence of a Thin Liquid Film

Jeffrey Marshall, The University of Vermont

A spherical particle rolling on a flat surface in the presence of a thin liquid film experiences a capillary torque that resists the rolling motion. A theory is presented for small values of the capillary number, in which the capillary torque is shown to be caused by two complementary mechanisms. The first mechanism results from the rearward shift of the liquid bridge in the presence of particle rolling, which causes the line of action of the low pressure region within the liquid bridge to shift behind the particle centroid. The second mechanism results from the contact angle asymmetry on the surface tension forces on the advancing and receding sides of the rolling particle. An experiment is described in which we measure the different parameters appearing in the expressions for both types of capillary torque. Using this experimental data, we show that the capillary torque varies with capillary number in accordance with a power law. When combined with a standard expression for viscous torque on a rolling particle, the capillary torque expressions are found to yield predictions for particle terminal velocity that are in good agreement with experimental data for a particle rolling down an inclined surface.    

Modeling and Validation of the Cohesion Reduction of Fine Powders via Surface Modification

Rajesh Dave, New Jersey Institute of Technology

Flow and handling of fine powders is a topic of great interest to industry. High cohesion relative to their weight of fine powders leads to problems such as, agglomeration, poor flowability, electrostatic charging and low bulk density. In this talk, powders of interest to pharmaceutical industry are considered where poor flow problems lead to downstream problems such as poor content uniformity and marginal improvement in dissolution rate of fine API powders. To encounter these problems, nano-particle dry coating is shown to be a more rigorous approach. Surface modified pharmaceutical powders are produced using several devices, both based on batch and scalable continuous operation. Results illustrate the improvement in flow, fluidization, dispersion, lack of agglomeration, bulk density, and electrostatic tendency, all leading to potentially significant cost benefits in industrial processing, handling, storage and transportation. In order to understand the cause of cohesion reduction, contact modeling based on our multi-asperity advanced models where the influence of material properties, surface area coverage and spatial and size distribution of guest particles is presented. Models are qualitatively validated by bulk and particle scale experimental results, including detailed surface energy measurements that explain cohesion of pharmaceutical powders based on two major tuning parameters, surface roughness and surface energy. Issues of linking particle to bulk scale are discussed along with selected results from Discrete Element Modeling of cohesive powders.

Engineered Particle Systems for Inhaled Drug Delivery

Benjamin Maynor, Liquidia Technologies

Particle properties such as size, shape, and density play a critical role in determining the performance of inhaled medicines. Here, we will highlight progress in the field of “engineered particles” for pulmonary delivery and highlight the use of a particle molding technique called PRINT® (Particle Replication in Non-wetting Templates) (Liquidia Technologies, Inc). PRINT molding produces precisely controlled particles on the micron and nanometer scale for drug delivery. Unlike other particle generation technologies, the PRINT molding technique simultaneously enables precise control over particle size, shape, and chemical composition.  Examples from the application of the PRINT technology and other “engineered particle” generation approaches towards advancing the field of pulmonary medicine will be described here, including improvement of particle dispersion, dissolution enhancement of poorly soluble compounds, and control of cellular interactions.