Polymer Pen Lithography with Lipids for Large-Area Gradient Patterns

Abstract

Gradient patterns comprising bioactive compounds over comparably (in regard to a cell size) large areas are key for many applications in the biomedical sector, in particular, for cell screening assays, guidance, and migration experiments. Polymer pen lithography (PPL) as an inherent highly parallel and large area technique has a great potential to serve in the fabrication of such patterns. We present strategies for the printing of functional phospholipid patterns via PPL that provide tunable feature size and feature density gradients over surface areas of several square millimeters. By controlling the printing parameters, two transfer modes can be achieved. Each of these modes leads to different feature morphologies. By increasing the force applied to the elastomeric pens, which increases the tip-surface contact area and boosts the ink delivery rate, a switch between a dip-pen nanolithography (DPN) and a microcontact printing (μCP) transfer mode can be induced. A careful inking procedure ensuring a homogeneous and not-too-high ink-load on the PPL stamp ensures a membrane-spreading dominated transfer mode, which, used in combination with smooth and hydrophilic substrates, generates features with constant height, independently of the applied force of the pens. Ultimately, this allows us to obtain a gradient of feature sizes over a mm substrate, all having the same height on the order of that of a biological cellular membrane. These strategies allow the construction of membrane structures by direct transfer of the lipid mixture to the substrate, without requiring previous substrate functionalization, in contrast to other molecular inks, where structure is directly determined by the printing process itself. The patterns are demonstrated to be viable for subsequent protein binding, therefore adding to a flexible feature library when gradients of protein presentation are desired.

Development of Dip‐Pen Nanolithography (DPN) and Its Derivatives

“…This feature‐size dependence on force enabled by the compression of the polymeric tips is a distinguishing controllable parameter that is not realized in a classical DPN (Figure E). Utilizing this force‐dependent property, PPL can pattern combinatorial library of features from nanoscale to microscale over large areas by simply tilting the tip array . In recent years, Chen et al used PPL to create combinatorial libraries consisting of every combination of metallic elements (Au, Ag,Co, Cu, and Ni) through polymer nanoreactor‐mediated synthesis .…”

“…Utilizing this force-dependent property, PPL can pattern combinatorial library of features from nanoscale to microscale over large areas by simply tilting the tip array. [109,110] In recent years, Chen et al used PPL to create combinatorial libraries consisting of every combination of metallic elements (Au, Ag,Co, Cu, and Ni) through polymer nanoreactor-mediated synthesis. [111][112][113] Furthermore, the large area elastomeric tip array significantly increases the amount of ink adsorbed and enables multiple printing tasks without re-inking.…”

Printing ZnO Inks: From Principles to Devices

“…to the support by tilting has been demonstrated to be a powerful way to print gradient patterns of molecules [74]. A summary of the different printing methodologies reported in this review can be found in Table 1, which specifically lists ink properties, such as viscosity and surface tension, printing resolution, and process characteristics (speed, resolution range, typical thicknesses, etc.).…”

“…It combines DPN and microcontact printing (µCP) features, by using an array of soft elastomeric tips (~10 6 pyramid-shaped tips), that can be brought into contact with the solid support and optically leveled for uniform patterning. Additionally, the possibility to control the relative position of the tip array with respect to the support by tilting has been demonstrated to be a powerful way to print gradient patterns of molecules [74]. A summary of the different printing methodologies reported in this review can be found in Table 1, which specifically lists ink properties, such as viscosity and surface tension, printing resolution, and process characteristics (speed, resolution range, typical thicknesses, etc.).…”

Evaluation of Microfluidic Ceiling Designs for the Capture of Circulating Tumor Cells on a Microarray Platform

“…The microarray within the microfluidic channel was printed via polymer pen lithography (PPL) . This technique combines aspects of microcontact printing and dip‐pen nanolithography (DPN) in a hybrid way and allows large area (several cm²) patterning, especially for sensitive, bioactive molecules in gradients and in a multiplexed fashion . This allows also easy integration into microfluidic systems as we demonstrated for the above‐mentioned application of CTC capture and mast cell screening, recently.…”