Periodic Reporting for period 4 - INCANA (Insect-inspired capillary nanostamping)
Reporting period: 2020-03-01 to 2021-08-31
Prior to digitalization, stamping was ubiquitous in everyday life – examples include the application of postmarks and seals or the validation of tickets for public transport. Stamping has also emerged as a versatile technique to micropattern substrates in materials science, in nanotechnology and microtechnology as well as in industrial production processes because stamping enables simultaneous patterning of large substrate areas. Therefore, stamping is a “parallel” micropatterning method – in contrast to serial patterning approaches like inkjet printing, which involve pixel-by-pixel writing. Stamping may involve embossing or lithographic deposition of ink. In the latter case, stamping is referred to additive. Up to now, parallel additive substrate patterning by ink deposition has typically been carried out using solid elastomeric stamps with topographically micropatterned contact surfaces. Ink is adsorbed onto the outer stamp surfaces. The quality of the deposited patterns deteriorates already after a few successive stamp-substrate contacts because of ink depletion. The unsolved problem of ink replenishment impedes the upscaling of stamping-based parallel additive substrate patterning. Moreover, only limited amounts of ink can be deposited onto counterpart substrates by classical stamping methods, and the possibilities to stamp environmentally friendly aqueous inks are limited also.
Project “Insect-inspired capillary nanostamping” (INCANA) exploits a bioinspired approach to overcome the drawbacks of state-of-the-art parallel additive stamping. Insect feet adhere to vertical walls and ceilings by contact formation via a large number of hairy contact elements. The insects deploy secretions for adhesion management through channels in their hairy contact elements to the contact interfaces. After detachment of the insect feet, arrays of secretion droplets remain on the counterpart surface. Artificial stamps mimicking insect feet, which are penetrated by spongy-porous pore systems enabling ink supply to the contact surfaces anytime during stamping, may overcome the drawbacks of state-of-the-art microcontact printing. However, only limited efforts to prepare such porous stamps had been reported prior to the start of project INCANA. In the course of project INCANA, porous capillary stamps with topographically micropatterned contact surfaces consisting, for example, of polymers, resins, silica glass and metals were designed. Using these porous stamps, insect-inspired capillary nanostamping was developed for the parallel and additive high-throughput deposition of a broad range of aqueous and nonaqueous inks. Capillary nanostamping can be carried out manually under ambient conditions or continuously in automated devices. Since ink can be supplied anytime during stamping, no interruptions for ink replenishment are required, and real additive patterning of counterpart substrates by deposition of three-dimensional ink structures is possible. Capillary nanostamping may yield functionalized substrates for optics, electronics, sensing, bioanalytics, clinical diagnostics, lab-on-chip configurations or tissue engineering. Wettability, self-cleaning properties and adhesive properties may be tailored in this way.
Project “Insect-inspired capillary nanostamping” (INCANA) exploits a bioinspired approach to overcome the drawbacks of state-of-the-art parallel additive stamping. Insect feet adhere to vertical walls and ceilings by contact formation via a large number of hairy contact elements. The insects deploy secretions for adhesion management through channels in their hairy contact elements to the contact interfaces. After detachment of the insect feet, arrays of secretion droplets remain on the counterpart surface. Artificial stamps mimicking insect feet, which are penetrated by spongy-porous pore systems enabling ink supply to the contact surfaces anytime during stamping, may overcome the drawbacks of state-of-the-art microcontact printing. However, only limited efforts to prepare such porous stamps had been reported prior to the start of project INCANA. In the course of project INCANA, porous capillary stamps with topographically micropatterned contact surfaces consisting, for example, of polymers, resins, silica glass and metals were designed. Using these porous stamps, insect-inspired capillary nanostamping was developed for the parallel and additive high-throughput deposition of a broad range of aqueous and nonaqueous inks. Capillary nanostamping can be carried out manually under ambient conditions or continuously in automated devices. Since ink can be supplied anytime during stamping, no interruptions for ink replenishment are required, and real additive patterning of counterpart substrates by deposition of three-dimensional ink structures is possible. Capillary nanostamping may yield functionalized substrates for optics, electronics, sensing, bioanalytics, clinical diagnostics, lab-on-chip configurations or tissue engineering. Wettability, self-cleaning properties and adhesive properties may be tailored in this way.
Preparation procedures for porous capillary stamps consisting of polymers, resins, silica glass and metals were established, which combine pore formation with topographic micropatterning of the stamps’ contact surfaces by replication molding. The pore systems of the capillary stamps can be backfilled with ink anytime during ongoing stamping operations so that continuous stamping operations without interruptions for ink replenishment are possible. Even without backfilling several 100 successive stamp-substrate contacts are possible without deterioration of the quality of the stamped patterns. Capillary stamping with porous stamps can be performed under ambient conditions – either manually or by the use of simple mechanical appliances. However, we also designed porous composite stamps that can be mounted on commercially available stamping machines, which were so far operated with solid elastomeric stamps not enabling ink replenishment. As exemplary micropatterns, dot arrays and holey films were realized. Some porous capillary stamps are also suitable for a second mode of parallel additive substrate patterning: decal transfer microlithography involving the lithographic transfer of parts of the stamps to counterpart substrates. Under moderate contact pressures, ink-filled capillary stamps are used for capillary stamping. Under high contact pressures, empty capillary stamps are used for decal transfer microlithography. Capillary stamping or decal transfer microlithography with porous stamps was used to realize preconcentration sensors, catalytic substrates, the stamping of fullerene and nanodiamond nanoparticles, as well as the stamping of drug nanoparticles and their transfer to aqueous suspensions. Capillary stamping of thin micropatterned layers of lithium niobate, a functional material sometimes referred to the new silicon, may replace in some cases tedious layer transfer procedures by ion slicing. We also exploited capillary stamping to generate topographically patterned silicon surfaces for persistent and scratch-resistant identity labels or quick response codes. Patterns generated by capillary stamping were biofunctionalized to generate substrates for nanobioanalytics and the sensing of cellular interactions with subcellular micron-scale resolution.
Parallel additive substrate micropatterning by state-of-the-art microcontact printing with solid elastomeric stamps suffers from ink depletion after a few stamp-substrate contacts. Thus, the quality of the deposited patterns successively deteriorates. Project INCANA systematically explored porous stamps to overcome this problem. Using the porous stamps devised in project INCANA, an indefinite number of successive stamping steps can, in principle, be carried out without loss of the quality of the deposited patterns, since ink can be supplied to the stamps’ contact surfaces anytime through the stamps’ pore systems. The continuous ink supply through the stamps’ pore systems allows simultaneous and parallel additive deposition of inks on large substrate areas. So far, real additive substrate manufacturing has typically been carried out by serial pixel-by-pixel printing. Ongoing efforts deal with high-temperature capillary stamping of polymer melts to deposit polymers without the use of organic solvents. Moreover, capillary stamping will be exploited to create substrates for nanobioanalytics and for the monitoring of cellular interactions with spatial resolutions on submicron length scales. Submicron spatial resolution is important because the related length scales are characteristic of a variety of biomolecular submicroscopic organizations in living cells including membrane microcompartments, membrane-less organelles or protein phase separations that play crucial roles for cell signaling and metabolism. Future activities will thus focus on the customization of substrates functionalized by capillary stamping for biological and medical applications.