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In depth characterization of bio-mimetic lipid membrane structures generated by dip-pen nanolithography

Final Report Summary - DPNLIPIDMEMBRANES (In depth characterization of bio-mimetic lipid membrane structures generated by dip-pen nanolithography)

Final Report(3) - Publishable Summary
results, conclusions and socioeconomic impact of the project

The objective of the project is to analyze in lipid membrane generation and structuration with Dip-Pen Nanolithography (DPN) in order to provide key information allowing the design and tailored fabrication of bio-mimetic structures to be used in biological and bio-medical studies.

The structure (area, height and volume) of lipid membranes created by DPN is controlled by the ink flow rate and the surface energy. The first depends on the ink physicochemical properties (e.g. viscosity) as well as on the experiment parameters. The dependence with the latter, including dwell time and relative humidity, is in agreement with a diffusive Fickian transport character of the lipids. The influence of the experiment parameters magnitude on the features’ geometric characteristics follows an analytical expression. Up to our knowledge, this is the first model that accounts for the lipid transport in DPN. By using this model, it can be shown that at any humidity the dependence of the area spread with the dwell time shows two diffusion regimes: at short dwell times growth is controlled by meniscus diffusion while at long ones surface diffusion governs the process. The critical point for switch of regime depends on the humidity.
Feature shape is controlled by the substrate surface energy. As the lipids are a diffusive ink, their transport to the surface from the tip delivery depends on the concentration at the meniscus/substrate and then, transport itself depends on the surface spreading characteristics.
Highly hydrophobic surfaces promote lipid rearrangement in the wetting monolayers, which spread over surfaces following different kinetics, as compared with the spreading over hydrophilic surfaces. Surfaces with a strong interaction with the lipids promote fast spreading of the ink as it is delivered by the tip, generating features with larger surface. The spreading dynamics of this system are governed by short-range forces.
Thanks to the diffusive character of the lipids, one can generate structures with different aspect ratios by changing either their viscosity (lipids admixtures) or the writing technique (e.g. line writing at different conditions). However, and due to the liquid character of the lipids, aspect ratios are limited due to the internal membrane diffusivity.

The project led to 6 publications in highly esteemed peer-reviewed journals, and a book chapter, especially publication of the ink transfer model as “A diffusive ink transport model for lipid dip-pen nanolithography” by A. Urtizberea and M. Hirtz, Nanoscale 7, 15618 (2015), highlighted as back cover issue 38.
More updated information can be found at the group web page https://www.int.kit.edu/fuchs.php

L-DPN sees rising interest as a tool for combinational arraying and screening in biological/biomedical systems as well as a tool for sensor and device functionalization. A key role for a broader application and future commercialization of the technique is a thorough understanding of all processes involved in the generation of the structures and details on the organization of the bio-mimetic membranes generated in L-DPN. The knowledge gathered by the scientists in this EU project has provided key information for further optimization and prospective design of new applications of this technique in mentioned areas.