2015 AIChE Annual Meeting Proceedings
(350f) Mass Transfer through Hollow Metallic Microneedles
Authors
Unicellular plant cells such as microalgae is potential photosynthetic bio-factory that can replace fossil-fuel industry. However, the lack of tools for delivering genes into these organisms for genetic mutation is a major impediment in making this technology cost-competitive. The goal of our group is to accelerate the efforts in microalgae genetics by engineering a highly efficient gene delivery device. This device consists of an array of microneedles (MNs) loaded with genetic materials, onto which microalgae are centrifugally driven and impaled. Similar MN-based approaches have been demonstrated with various combinations of mammalian cells and cargoes. 1-3 In our recent work, we reported the first example of applying this technology to wild-type microalgae with hard cell walls.4An array of solid MNs were shown to withstand the impact of cell impalement, and the cells were viable after impalement. We also demonstrated that the cells expressed the genes coated onto the MNs.
Hollow MNs offer an additional advantage over solid MNs due to the capability for temporal and quantitative control over the transport of target molecules. In this talk, we will focus on the fabrication and characterization of the h-MN array, and quantitative analysis on mass transport through the h-MNs using numerical (COMSOL®) simulation. A multiphysics model that uses the Nernst-Planck equation, Poisson equation and Navier-Stokes equation is applied to combine the effect diffusion, migration and electroosmosis in conically shaped channels.5The talk will focus on the effects of the three parameters that are easily controlled experimentally: electric field (∂ϕ(x)⁄∂x), concentration gradient (∂C(x)⁄∂x), and zeta potential (ζ) within the h-MN.
The MN arrays are fabricated by template synthesis. Here, a template membrane prepared in-house is coated with a thin film of Ni using electrochemical deposition. The thickness of the deposition is controlled by the duration of the deposition. After deposition, the template membrane is removed to expose the MN array. The external dimensions of the Ni MNs are ~7 um, ~1 um and ~0.1 um for their height, base and tip diameters, respectively. These dimensions are comparable to what we had previously used for microalgae impalement.4Scanning electron microscopy images and measurements of ion transport through the hollow Ni MNs consistently show that the prepared MNs are hollow, and longer electrodeposition time decreases the lumen diameter. Experimental results on mass transfer through the hollow microneedles using a gene surrogate (gold nanoparticles that are comparable to the size of DNA plasmids) will also be discussed in detail, and compared with the results from the numerical simulation.
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