Direct writing of colloidal suspensions onto inclined surfaces: Optimizing dispense volume for homogeneous structures

HYPOTHESIS

A process to fabricate structures on inclined substrates has the potential to yield novel applications for colloidal-based structures. However, for conventional techniques, besides the coffee ring effect (CRE), anisotropic particle deposition along the inclination direction (IE) is expected to occur. We hypothesize that both effects can be inhibited by reducing the dispense volume during printing by direct writing.

EXPERIMENTS

We combined an additive manufacturing technique, namely direct writing, with colloidal assembly (AMCA) for an automated and localized drop-cast of polystyrene and silica suspensions onto inclined surfaces. Herein, we investigated the influence of the substrate tilting angle and the dispense volume on the printing of colloids and the resulting structures' morphology.

FINDINGS

The results demonstrate that a reduction in the dispense volume hinders the CRE and IE for both particles' systems, even though the evaporation mode is different. For polystyrene, the droplets evaporated solely in stick-mode, enabling a "surface capturing effect", while for silica, droplets evaporated in mixed stick-slip mode and a "confinement effect" was observed, which improved uniformity of the deposition. These findings were used to generate a model of the critical droplet radius needed to print homogeneous colloidal-based structures onto inclined substrates.

Low-Voltage Continuous Electrospinning: A Versatile Protocol for Patterning Nano- and Micro-Scaled Fibers for Cell Interface

Nano- and micro-scaled fibers have been incorporated in a number of applications in biofabrication and tissue cultures, providing a cell interfacing structure with extracellular matrix-mimicking topography and adhesion sites, and further supporting localized drug release. Here, we describe the low-voltage electrospinning patterning (LEP) protocol, which allows direct and continuous patterning of sub-micron fibers in a controlled fashion. The processable polymers range from protein (e.g., gelatin) to thermoplastic (e.g., polystyrene) polymers, with flexible selections of collecting substrates. The operation voltage for fiber fabrication can be as low as 50 V, which brings the benefits of reducing costs and mild-processing.

Production of Scaffolds Using Melt Electrospinning Writing and Cell Seeding

Melt electrospinning writing (MEW) is a solvent-free fabrication method for making polymer fiber scaffolds with features which include large surface area, high porosity, and controlled deposition of the fibers. These scaffolds are ideal for tissue engineering applications. Here we describe how to produce scaffolds made from poly(ε-caprolactone) using MEW and the seeding of primary human-derived dermal fibroblasts to create cell-scaffold constructs. The same methodology could be used with any number of cell types and MEW scaffold designs.

Use of permanent marker to deposit a protection layer against FIB damage in TEM specimen preparation

Permanent marker deposition (PMD), which creates permanent writing on an object with a permanent marker, was investigated as a method to deposit a protection layer against focused ion beam damage. PMD is a simple, fast and cheap process. Further, PMD is excellent in filling in narrow and deep trenches, enabling damage-free observation of high aspect ratio structures with atomic resolution in transmission electron microscopy (TEM). The microstructure, composition, gap filling ability and planarization of the PMD layer were studied using dual beam focused ion beam, transmission electron microscopy, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy. It was found that a PMD layer is basically an amorphous carbon structure, and that such a layer should be at least 65 nm thick to protect a surface against 30 keV focused ion beam damage. We suggest that such a PMD layer can be an excellent protection layer to maintain a pristine sample structure against focused ion beam damage during transmission electron microscopy specimen preparation.