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Institute for Microsensors, -actuators and -systems

2-Photon Polymerization of Fluidic 3D Microstructures

Polymerisation Nanoscribe
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2PP structures in microfluidic channels. a) Sieve-like filter structures for particles and cells with openings of a few micron. b) Microfluidic mixer which swaps the inner flow streams using a screw-like structure. c) Electrostatically actuated microvalve supported by conical springs with a length of about 1 mm and a cross-section of 10 µm x 5 µm. d) Flow sensor with optoelectronic readout: depending on the drag force the massive part of the 2PP structure bends into a focused light beam and scatters the light. e) Cell trap with movable flap: a cell in front of the inner flap of the rotor increases the attacked area and, thus, the drag force. Therefore, a holding structure breaks and the second flap closes the trap behind the cell.

Summary:

With the technology of direct laser writing using two-photon polymerization we can realize complex three-dimensional sub‑micron structures in photopolymer resists. The increased writing speed of modern equipment allows wafer-level processing. In this work we aim to design and fabricate novel microfluidic structures that can be written directly into microchannels to integrate fluidic functionality such as filters, mixers, valves, flow sensors as well as movable and optofluidic elements.

 

Project Description:

In standard lithography 1-photon absorption is used to excite molecules by UV light along the complete path of light. Making use of 2-photon absorption instead, only the molecules within the focal point of a laser beam are excited. 3D laser lithography using 2-photon polymerization is based on the process of exciting light-sensitive molecules by simultaneous absorption of two photons with lower energy (wavelength of about 780 nm). With femtosecond lasers this nonlinear process can be implemented in such a way that the photon density is sufficiently high for the simultaneous absorption only in the focal point of the laser beam. By guiding the focal point through the photo-sensitive resist, three-dimensional structures with sub-micron resolution are written point-by-point. This technology covers structure sizes from the nanoscale to the mesoscale and thus, bridges the gap between 3D-printing and planar microfabrication.

 

In this project we focus on exploring the fabrication and integration of three-dimensional micron elements in a fluidic microchannel or chamber, as well as writing small microfluidic systems directly as one part. First examples include sieve-like filter structures for particles and cells with openings of a few micron (a) as well as microfluidic swapper mixers based on rearranging a laminar two-phase flow into a flow with multiple interfaces by repeatedly 3D swapping inlet and outlet locations (b).

 

Further work addresses the fabrication of movable components. Those either include flexible springs or rotate freely. As spring-based systems we realized a movable lens, a microfluidic valve (c) and a flow sensor with an optical readout for instance (d). Freely rotating elements can be used as flaps e. g. to close a cell trap (e). Here, we also investigate electrostatic and magnetic actuation mechanisms.

 

Contact:

Prof. Dr.-Ing. M. Vellekoop 
IMSAS, NW1, Raum O2140
Tel.: +49 421 218 62604
E-mail: contact

 

For this work we have procured a Nanoscribe Photonic Professional GT in 2017, partially funded by the German Research Foundation (DFG) under the major instrumentation funding program (GZ: INST 144/395-1 FUGG).

 

Selected Publications:

Gehlken W, Reede S, and Vellekoop MJ, “Implementation of Fragile Holding Structures for Rotating Elements in the Printing Process of 2-Photon-Polymerization”, Proc. MikroSystemTechnik Kongress 2021, pp. 178-181.

Oellers M, Lucklum F, Vellekoop MJ, “On-chip mixing of liquids with swap structures written by two-photon polymerization”, Microfluid Nanofluid (2020) 24: 4.

M. Oellers, F. Bunge, F. Lucklum, P.P. Vinayaka, C. Habben, M. Kirsch, S. van den Driesche, and M. J. Vellekoop, “Microfluidic swap structure to enhance on-chip liquid mixing”, IEEE SENSORS (2017). DOI:10.1109/ICSENS.2017.8234445

S. Reede, I. Eichhorn, M. Oellers, A. Schander, M. J. Vellekoop, “Two-Photon Polymerized Flow Sensor Integrated in a Microfluidic Channel with Optoelectronic Readout”, Proc. IEEE Sensors Conf. (2020).

S. Reede, M. J. Vellekoop, H. Müller-Landau, N. Matscheko, U. Rant, F. Lucklum. A5.3 Single Cell Immobilization at High Flow Rates Using 2PP-Traps in a Microfluidic Channel. SMSI 2020-Sensors and Instrumentation, 81-82, 2020.

 

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Updated by: L.Reichel
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