Microcontact Printers for Surface Patterning and Nanoimprint Lithography

Microcontact Printing With the GeSiM Polymer Stamps

Whether you decide for an automatic solution or for the entry-level µCP Core, the stamping module is always the same. The clever combination of pneumatic actuation and Z-movement ensures high reproducibility for patterns down to the range of 100 Nanometres.

Layout of µCP4.3 with optional pipetting unit – An automatic benchtop robot

Components of µCP Core – Requires an inverse microscope as well as a UV lamp (Not included)

Our Microcontact Printer for your Individual Research

The particular foot layout of the polymer stamp is always the specific link to your daily research routine. A typical startup incorporates the following steps:

• An application test with your material will be done at GeSiM if necessary. Feel free to contact us.
• Based on your unique print design(s) GeSiM develops one or several silicon master chips.
• Each GeSiM microcontact printer comes with a small casting station to produce copies of the sensitive stamp(s). Thus, your operational costs remain reasonably even when your process requires “fresh” stamps very often. During the design optimization new silicon masters can be ordered at GeSiM.

Basic function of all GeSiM microcontact printers

The footprint of the stamp represents particular patterns down to 100 Nanometres. Both PDMS and PTFE are proven polymers for these stamps. The complete process differs for microcontact printing and NIL (See next tab). Both SU8 and NOA 81 (Norland) are popular resists for 3D imprinting.

When the print head touches down the stamp gets bulged out by air pressure and connects smoothly and without artefacts to the substrate surface. Onboard video microscopes on the automatic printers allow X/Y/Phi alignment of the stamp to existing patterns or markers on your target object.

Fluidic “flow-through” stamps are a special version for applying grains or bead during the microcontact printing process.

Different sizes of PDMS stamps for GeSiM microcontact printers

Optional Tools for Material Handling on µCP4.3 and µCP6.3

All automatic GeSiM microcontact printers come with built-in spinning table and a pneumatic  cartridge dispenser. It allows to create homogeneous resist layers for precise NIL. Our optional tools allow selective coatings and the application of multiple materials on the target:

• Displacement pipet tips as you use it in your daily work flow
• Piezoelectric GeSiM dispensers for managing smallest volumes
• Piezoelectric valves (Third party) for making smallest drops of high-viscous liquids.
• Powder pipets for transfer of micrograms of granular materials.

µCP stamp (Left) and powder pipet above a reservoir (Right)

UV Lamp

The UV lamp for resist hardening is available for all automatic microcontact printers but optionally available for µCP Core.

UV hardening during NIL on µCP4.3

Each GeSiM microcontact printer allows two different applications:

Microcontact Printing

This process transfers a sample liquid called “ink” onto a planar target surface. The PDMS stamp is inked with the sample, subsequently pressed onto the surface, thereby transferring the sample only from the high areas, as in letterpress printing.

Spinning of ink on target

Stamp inking

Drying of Stamp

Stamping

Stamp detached from target

Not just chemicals, also biomolecules, nanoparticles, beads, or cells can be printed. Patterns of proteins like fibronectin or laminin can serve as adhesive substrate to grow cells only on protein-covered areas.

GeSiM printers automatically use up to five stamps with different inks and different patterns for well aligned prints on the same substrate.

NIL – Nanoimprint Lithography

Nanoimprint Lithography (NIL) is a popular approach to make disposable microfluidic devices at low numbers. The GeSiM microcontact printers have to be supplied with a curable photopolymer as well as with the printing substrate.

First, the target surface has to be coated with an appropriated material, e.g. a liquid, UV-hardened, polymer. Then, instead of transferring an ink, the elevated patterns of the PDMS stamp shape their reverse image into a homogeneous layer on the stamp target. µCP6.3 is capable of lining up several prints step-by-step without any spacing in between.

Spinning of photo resist

Stamp alignment/ Drying

Stamping

Stamp detached from target

UV hardening

3D structures can be printed with SU8 photoresist or NOA (Norland). Heights of up to 150 microns are feasible. The aspect ratio height/width depends on the layout but can easily reach (3…5)/1.

After detaching the stamp the printed targets can be sealed by cover lids in order to achieve microfluidic devices.

Selection of Applications Already Done:

• Selective printing of self-assembled monolayers (SAM) by µCP, or microstructuring by NIL, on metal (Cu) and electroplating on the unprotected areas
• Fabrication of silver micro- and nanopatterns by µCP of SAM on glass and electroless metallization
• Direct (nano)imprinting of microfluidic structures into photoresist
• Microcontact printing of extracellular matrix proteins to direct cell adhesion to certain spots (see below…)
• Fine-structuring of surfaces via NIL for cell growth studies (e.g. flat vs. grooved surface)
• Printing of patterned thermoresponsive microgel coatings to study adherent cells (Uhlig et al., 2016)

Micro-Contact-Printing: Fibronectin Patterns for Cell Growing

Human Umbilical Cord Blood Neural Stem Cells (HUCB-NSC) were grown on microcontact printed fibronectin squares for a differentiation study.

The squares were printed using PDMS stamp on a cell repellent, plasma polymerized poly-ethylene-oxide (PEO) like surface using fibronectin solution in an acetate buffer as an ink.

HUCB-NSC cells on micro-contact printed Fibronectin squares – Phase contrast image

Fluorescence Image – Green: β-tubulin-II neuronal marker; Red: GFAP; Blue: Cell nuklei

The cells do not adhere to the PEO coated regions, but are attached to the printed 100 µm fibronectin squares. After the culturing period the cells were fixed and immunostained for glial and neuronal differentiation markers.

Courtesy of EC Joint Research Centre, Nanobiosciences Unit, Ispra, Italy (Dora Mehn)

Nano-Imprint Lithography: Micro Needle Arrays

Vacuum containment on the print head of µCP4.1

Functionalized micro needle arrays gain increasing interest for subcutaneous drug delivery without injection needles. Development of a cost-effective manufacturing technology for controlled drug release is still challenging. Here we present an approach for low-volume manufacturing of micro needle arrays with the GeSiM micro-contact printers. Nano-Imprint-Lithography allows much better spatial resolution than conventional 3D-SLA.

Microneedle arrays with high-aspect ratio are achieved by evacuating the space around the PDMS stamp. GeSiM microcontact printers are available with a containment ring surrounding the stamp. Thus a sealed volume allows evacuation when the stamp touches down on the print target.

Master structure for stamp casting

PDMS print stamp

Final micro needle array

The master structure for multiple stamp casting (left(top) image) was done by 2-photone-lithography using a stiff synthetic material. The µCP4.1 stamp was than made from PDMS Sylgard 184, Dow Chemicals Europe GmbH) as usually (middle). Finally the micro needle array (right (bottom)) consists of a UV-hardened resist (NOA-63, Norland Products Ltd.).

The geometry of the NOA-63 needle array supports usability: The height is 1,200 µm, both bottom diameter and spacing between adjacent needles are 200 µm.

For more details please download the µCP4.1 microneedle array application note.

Nano-Imprint Lithography: Nanoplasmonic Sensor Structure

Surface plasmon resonance (SPR) sensors allow label-free, real-time biomolecule detection with high sensitivity. Classical SPR sensors utilize a gold film on a prism, which cannot be scaled down. To overcome this, a nanostructured gold layer is used to excite plasmons without bulky optics. The nanoplasmonic sensor structure detects diclofenac in wastewater using immobilized diclofenac in the presence of diclofenac antibodies (Steinke et al., 2018) or measures ethanol concentration during fermentation processes with an ethanol-sensitive hydrogel (Kroh et al., 2019).

Central to this method is the reproducible fabrication of nanostructured surfaces by nanoimprint lithography (UV-NIL) using a GeSiM µCP 4.1 and a UV-cross linkable photoresist.

Nanopillar arrays made by UV-NIL on a glass wafer with a GeSiM µCP4.1, SEM image inline

Nano-Imprint Lithography: Picolitre Wells for Cell Biology

Picowells, 25 µm wide, printed by UV-NIL, empty

Picowells filled with cells

In cooperation with M. Deutsch’s lab from Bar-Ilan University and others, picowell arrays have been printed by UV-NIL in UV-curable adhesives such as NOA81 for the activity measurement, e.g. by multiparametric enzymic assays, of individual cells (Deutsch et al., 2010; Afrimzon et al., 2010; Markovitz-Bishitz et al., 2010).

NIL made honeycomb Picowells with single cells

One application was toxicology testing of nanoparticles that the GeSiM Nano-Plotter had spotted into the picowells, another the formation and study of organoids from cancer cells in honeycomb structures (Zurgil et al., 2014), also with electrodes.

Courtesy of Matti Deutsch, Bar-Ilan University

Nano-Imprint Lithography: In Vitro Neurotoxicity Assay Development

Electrodes on the well bottom of a MEA chip, each well 100 x 100 x 50 µm

Scanning electron microscopic image of one well of the microarray (by Cesar Pasqual Garcia)

Primary (rat) neurons grown forming a network in the microwells; Green: β-tubulin-II neuronal marker, Blue: cell nuclei. (by Jakub Nowak)

Microelectrode array chambers (MEA chips) were applied as a support to generate 3D microwell environment for neural cells in electrical activity measurement studies.

The printer with UV illumination and the 24 well stamps were used to generate imprints with 100 µm sized wells and interconnecting channels aligned to the electrodes of the multi-electrode arrays. The matrix of PEG based hydrogel was polymerized by 60 s UV exposition.

Courtesy of EC Joint Research Centre, Nanobiosciences Unit, Ispra, Italy (Dora Mehn)