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Arranging the Particles: Step Changing Chemical Measurement Technology

Periodic Reporting for period 3 - PrintPack (Arranging the Particles: Step Changing Chemical Measurement Technology)

Reporting period: 2019-10-01 to 2021-03-31

The PRINTPACK project aims at developing a fabrication method to produce perfectly ordered 3D-materials composed of 3D-networks of spherical (functionalized) microparticles. One key application for this novel type of meta-materials is liquid chromatography (LC. In the past decades, the progress in LC has basically been following Moore’s law over the last decade, will soon come to a halt. LC is the current state-of-the-art chemical separation method to measure the composition of complex mixtures. Driven by the ever-growing complexity of the samples in e.g. environmental and biomedical research, LC is constantly pushed to higher efficiencies. Using highly optimized and monodisperse spherical particles, randomly packed in high pressure columns, the progress in LC has up till now been realized by reducing the particle size and concomitantly increasing the pressure. With pressure already up at 1500 bar, groundbreaking progress is still badly needed, e.g. to fully unravel the complex reaction networks in human cells.

For this purpose, it is proposed to leave the randomly packed bed paradigm and move to structures wherein the 1 to 5 micrometer particles currently used in LC are arranged in perfectly ordered and open-structured geometries. This is now possible, as the latest advances in nano-manufacturing and positioning allow proposing and developing an inventive high-throughput particle assembly and deposition strategy. The produced structures will be used to pursue the disruptive gain margin (order of factor 100 in separation speed) that can be expected based on general chromatography theory.

Testing this groundbreaking new generation of LC columns together with world-leading bio-analytical scientists will illustrate their potential in making new discoveries in biology and life sciences. The new nano-assembly strategies might also be pushed to other applications, such as photonic crystals.
On the theoretical side, correlations for the dependency of the dispersion coefficient and the local Sherwood number as a function of the Peclet number have been established. These calculations will define a new yardstick for the chromatographic performance of perfectly ordered structures. This work has been published in the Journal of Chromatography.

We also discovered a new mode hydrodynamic dispersion regime in ordered flow-through media. This regime is characterized by the fact that the exponent for the velocity-dependence of the axial dispersion coefficient does not increase monotonically with the Peclet-number (Pe), but instead goes through a transition where the exponent decreases with Pe over a range of intermediate Pe-values. In addition, we could also build a model explaining this unexpected phenomenon by combining the existing finite parallel zone model with a physically sound closure model to represent how the species transport in a series of finite parallel zones is coupled. This work has been published in two papers in the Journal of Chromatography.
Concerning the core goal of the project, i.e. developing a rapid large-scale method to produce ordered sphere arrays, an important breakthrough was realized by generating stable particles clouds using an electrostatic cell as a means to present the particles to the vacuum-driven assembly membranes. Because of the stable and less dense nature of the generated particle cloud compared to the initially used pressure-shock method, this approach allows for much more uniform and reproducible printing results. A second important factor contributing to obtaining flawless layers was the development of a micromachining method to produce membranes pores with a sloped inlet so as to minimize the area of flat surface between adjacent pores and more automatically guide the particles towards their resting position. In addition, we also developed three suitable methods to remove excess particles, one using a liquid jet, one using an air jet and one using a brushing device. All three methods produced comparable results. The initial results towards the realization of the ordered arrays using the liquid-phase have been submitted to Langmuir.

A major breakthrough has been realized by developing a method to uniformly fill an array of circular pockets with single particles. This was a key step towards the realization of the structures as shown in Fig. 2b and Fig. 4 (left) of part B2 of the application. Designs are not disclosed in public for IP protection reasons. Up to date, we have now demonstrated that we can also fill structures that can be used in a flow-through mode and that can be directly connected to inlet and outlet capillaries, thus opening the road to do actual liquid phase chromatography separations.

As an unexpected result, we discovered a new method for the directed particle segregation & self-assembly of silica particles by rubbing-induced tribo-electrification on patterned surfaces (pattern of fluorocarbon coated patches). Our key finding is the fact that silica particles are tribo-charged due to the rubbing process and therefore stick on the fluorocarbon coating, while they are repelled from the silicon regions in between the fluorocarbon patches because of the opposite charge. During the rubbing, a monolayer of particles is on the fluorocarbon surfaces, thus creating an ordered array of self-assembled particle collections. Using Kelvin Probe Force Microscopy (KPFM), we could show that the rubbing process induces electric charge on the FC coated surface and particles. This work was published in Langmuir.

Another unexpected result is the fact that we demonstrated the possibility to transport particles at a high frequency through a membrane with straight running, micromachined through-pores that are only 50% wider than the particles (15m wide, 40m long), just by using vacuum force as the flow driver. This finding, implying the particles can flow through these ultra-low aspect ratio micro-pores in a one-by-one mode without any disturbance or hindrance (also clogging at the inlet is very minimal and does not disturb functioning of the sieve filter), might offer new possibilities for particle sieving and shape selection (e.g. rods versus spheres).
With our improved particle presentation methods (electrostatic particle cloud generation) we can now fill 2D-array of 1 by 1mm with 99.7% accuracy using the proposed vacuum-driven assembly approach envisioned in the project proposal. In the next step towards the actual printing of structures, current efforts are now focusing on the transfer of the assembled layers onto a flat surface. Concerning the latter, success rates (order of 95%) still need to be improved before we can make the step to subsequent depositions and the actual 3D-printing.

With the newly developed to produce particle-filled micro-groove networks, ready to be tested under flow conditions, we are on the verge of produce the first ordered chromatographic packed bed column. Given the expected superior separation efficiency and flow resistance characteristics, it is believed this concept will revolutionize the way chromatographic separations are being conducted.
2-Ordered sphere packing obtained using the developed of vacuum-driven particle assembly technology
Computational fluid dynamics simulations of the flow fields in a stacked sing vacuum chamber
Ordered sphere packing obtained using the developed of vacuum-driven particle assembly technology
Large-areas ordered sphere packing with variable pattern (100x100 array)
Computational fluid dynamics simulations of the air flow fields in a moving particle feeder
Large-area ordered sphere packing obtained using vacuum-driven particle assembly (100x100 array)
Large-area ordered sphere array transferred onto flat surface coated with sticky top layer