Figure: (Left) (A) Scheme of the preparation of a superhydrophilic porous polymer film. (B) Fabrication of the superhydrophobic grid-like pattern on the superhydrophilic surface. (C) Water droplet on the superhydrophobic polymer; SEM images of the same polymer. Scale bars: top left - 10 µm, top right and bottom - 1 µm. (D) The array with microspots filled with alternating water solutions of red and blue dyes. (E) A water droplet on a single superhydrophilic microspot. (F) Fluorescent microscope image showing the array with spots filled with Rhodamine 6G.
(Right) Different cell lines growing on the array (after 2 days). (a) Mouse mammary carcinoma cells with GFP expression vector. (b) Rat mammary carcinoma cells with mCherry expression vector. (c) HEK cells, DAPI stained. (d) Hepa cells with GFP-expression vector. In collaboration with Dr. Urban Liebel.

Florian Geyer and Erica Ueda

Living cells are extremely complex biological systems and a variety of cell assays have been developed to study these systems in vitro. Recently, cell microarrays have emerged as a promising technique that enables cell assays in a highly parallel and miniaturized manner. However, due to the cross-contamination and cell migration problems, the density of most current cell microarrays is still limited.

We discovered a way to overcome those problems using a porous superhydrophilic polymer coated onto a substrate and patterned with superhydrophobic barriers. Cell experiments carried out with several commonly used cell lines discovered that cells preferentially adhere and proliferate on the superhydrophilic microspots and virtually don´t grow on the superhydrophobic barriers. In addition, the narrow superhydrophobic gaps between the spots are highly efficient barriers against cell migration. Because of the extreme difference in wettability between the superhydrophilic and superhydrophobic areas, this method allows us: (1) to significantly reduce the distance between the microspots and (2) to achieve precise control over the size and (3) geometry of the microspots. This allows us to increase the amount of spots on one standard microtiter-sized slide to about 50000, which is enough to accommodate two genome-wide siRNA libraries.

We envision that this technology will enable fabrication of “genome-on-a-chip” cell microarrays and will transform genome-wide and other high-throughput cell screening experiments into a significantly more affordable and convenient biological tool.

References:

1. Superhydrophobic-Superhydrophilic Micropatterning: Towards Genome-on-a-Chip Cell Microarrays
   F. Geyer, E. Ueda, U. Liebel, N. Grau, P.A. Levkin
   Angew. Chem. Int. Ed. (2011), in press
   This paper has been chosen as a “Hot Paper” by the Angewandte Editors for “its importance in a rapidly evolving field of high current interest”.
2. Patent: Superhydrophobic patterning for making living cell microarrays
   F.L. Geyer, U. Liebel, P.A. Levkin,
   EU patent submitted in 2010: EP 10-015-106.7

David Zahner, Erica Ueda, Alexander Efremov

Superhydrophobic surfaces showing extreme water-repellency have been eagerly investigated during the last years. Their possible applications range from self-cleaning surfaces, as seen in nature on lotus leaves, to microcondensation and even droplet manipulation. For many of these uses (super)hydrophilic patterns on superhydrophobic surfaces are required, but only a few examples for creating such patterns have been published.

We have developed a facile method for making superhydrophilic micropatterns on superhydrophobic substrates. The method is based on the preparation of a superhydrophobic porous polymer film by UV-initiated radical polymerization. The porous structure of the polymer film can be modified chemically by means of photografting with different hydrophilic monomers through a photomask. This leads to the formation of sharp superhydrophilic patterns surrounded by a superhydrophobic background. Because of the very large difference in wettability, these superhydrophilic areas behave as microfluidic channels. This method allows us to control precisely the size and geometry of the photografted superhydrophilic features, thickness of the porous polymer films as well as morphology of the porous polymer structure. Therefore we are able to customize microfluidic channels or other superhydrophilic patterns to suit all different kinds of applications.

References:

1. A Facile Approach to Superhydrophilic–Superhydrophobic Patterns in Porous Polymer Films
   D. Zahner, J. Abagat, F. Svec, J.M.J. Frechet, P.A. Levkin
   Adv. Mater. (2011)
   http://dx.doi.org/10.1002/adma.201101203
2. Monolithic Superhydrophobic Polymer Layer with Photopatterned Virtual Channel for the Separation of Peptides Using Two-Dimensional Thin Layer Chromatography-Desorption Electrospray Ionization Mass Spectrometry
   Y. Han, P.A. Levkin, I. Abarientos, H. Liu, F. Svec, J.M.J. Frechet
   Analytical Chemistry, 82 (2010), 2520-2528
3. Porous polymer coatings: a versatile approach to superhydrophobic surfaces
   P.A. Levkin, F. Svec, J.M.J. Fréchet
   Adv. Funct. Mater. 19 (2009), 1993-1998
4. Patent: Superhydrophobic and superhydrophilic materials, surfaces and methods
   P.A. Levkin, F. Svec, J.M.J. Fréchet
   WO/2009/137267; PCT/US2009/041277

Figure: Example of cell patterning

Alexander Efremov

Many biological in vivo processes, such as tissue development and regeneration, wound healing and cell migration, cell differentiation and specialization, etc. are controlled by precise spatial organization of different cell types in the tissue. Incorrect and irregular cell arrangement in tissue leads to loosing of functional capabilities followed by abnormal work, malignancy or death of cells. Thus, the ability to precisely control spatial arrangement of different cell types is crucial for studying cell function in vitro, for investigating cell-cell communication processes or mimicking cell environment in vitro and for tissue engineering.

We have developed a method that allows us to position different cell types on a surface to form precise geometrical patterns (see Figure). Our new method enables patterning of different cell types in close proximity and is very flexible in terms of pattern geometry. More than two cell types can be patterned simultaneously and the technique is not limited to mammalian cells.

Currently, we are working in collaboration with research groups of Dr. Scholpp (KIT) and Prof. Weber (Freiburg Uni) to exploit our method for investigating naturally occurring cell-cell communication processes.

Figure. Encapsulation of cells in arrays of microdroplets and hydrogel
micropads.

Erica Ueda, Florian Geyer, Victoria Nedashkivska

High-throughput (HT) screening of live cells is an immensely important and growing task in areas ranging from studies of gene functions using RNA  interference and the search for new drug candidates to screenings of new gene delivery systems and the identification of factors controlling stem cell differentiation. During the last decade, cell microarrays – a miniaturized method for HT cell screening– have been developed. Droplet microfluidics-based cell culture platforms are actively progressing and are able to address some issues of other systems. However, depending on the chip design, up to 90% of the droplets may not be trapped in a microfluidic static droplet array, so precious samples could be lost. In addition, managing thousands of droplets in a  microfluidic device can lead to complicated chip designs and many components, as well as long channels with high resistance to flow that can require higher pressures than the material can handle.

We show a facile one-step method for creating thousands of isolated  microdroplets with defined geometry and volume. The extreme wettability contrast of superhydrophilic spots on a superhydrophobic background allows spontaneous separation of an aqueous solution, leading to the formation of high-density arrays of completely separated microdroplets. This rapid and facile droplet formation does not require manual pipetting or a liquid handling device. Bioactive molecules, nonadherent cells, or microorganisms can be trapped
in the fully isolated microdroplets.

Figure: SEM images of porous polymer films with different surface topographies

Behavior of cells and bacteria at the interfaces, biocompatibility of materials, antifouling and antibacterial effects depend on specific surface properties, such as surface chemistry, surface morphology, porosity and elasticity, as well as on their combinations. The performance of existing biomedical devices, implants and cell culture dishes depends on the understanding of cell-surface interactions.

We work on the development of surfaces with gradients of different biologically relevant properties. The surfaces are then used to screen, in a combinatorial way, the effects different surfaces have on cell behavior. Our goal is to understand better how cells interact with surfaces and also to develop methods to effectively control and direct behavior of cells. The cells studies are performed in collaboration with Dr. Irina Nazarenko.

Figures.(A) Schematic representation of switching from superhydrophobicity to superhydrophilicity by applying an “ink” containing a phospholipid. (B) Schematic representation of creating superhydrophilic-superhydrophobic patterns with contact printer and patterning of one or more compounds on the superhydrophilic-superhydrophobic pattern. C) Top: image of a water droplet on the superhydrophobic part of  the patterned surface and water droplets filling the superhydrophilic spots. Bottom: lipid array printed with a 10 mg/mL POPG in ethanol solution. The hydrophilic lipid spots were then filled using a 0.1 mg/ml Rhodamine 6G in water solution. 

Junsheng Li, Erica Ueda, Asritha Nallapaneni and Linxian  Li

In this project, we demonstrated a new simple method for creating superhydrophilic micropatterns on a superhydrophobic surface. The method is based on printing an “ink” – an ethanol solution of a lipid – onto a porous superhydrophobic surface and is compatible with different printing techniques, e.g. microcontact or ink-jet printing. The lipid-coated microspots became hydrophilic (Fig. A) and can be easily filled with an aqueous solution by dipping or wetting the surface. (Fig. B, C) Since the lipid layer can also incorporate different bioactive molecules, transmembrane proteins, or other functional lipids, we envision that this facile procedure for creating superhydrophilic patterns combined with contemporary printing technology will lead to numerous applications.

 
References:

1. Printable Superhydrophilic−Superhydrophobic Micropatterns Based on Supported Lipid Layers.Junsheng S. Li, Erica Ueda, Asritha Nallapaneni, Linxian X. Li, and Pavel A. Levkin
Langmuir (2012)
http://pubs.acs.org/doi/abs/10.1021/la3010932
2. A Facile Approach to Superhydrophilic–Superhydrophobic Patterns in Porous Polymer Films
D.Zahner, J. Abagat, F. Svec, J.M.J. Frechet, P.A. Levkin 
Adv. Mater. (2011)
http://dx.doi.org/10.1002/adma.201101203
3. Porous polymer coatings: a versatile approach to superhydrophobic surfaces
P.A. Levkin, F. Svec, J.M.J. Fréchet
Adv. Funct. Mater. 19 (2009), 1993-1998