Novel photoresist enables 3D printing of smallest porous structures
Researchers of the cluster of excellence 3D matter made to order expand possibilities of two-photon microprinting

Date:
September 16, 2020
Source:
Karlsruher Institut fu"r Technologie (KIT)
Summary:
Researchers have developed a photoresist for two-photon
microprinting. It has now been used for the first time to produce
three-dimensional polymer microstructures with cavities in the
nano range. The scientists report how porosity can be controlled
during printing and how this affects light scattering properties
of the microstructures.



FULL STORY ========================================================================== Researchers of Karlsruhe Institute of Technology (KIT) and Heidelberg University have developed a photoresist for two-photon microprinting. It
has now been used for the first time to produce three-dimensional polymer microstructures with cavities in the nano range. In Advanced Materials,
the scientists involved in the joint Cluster of Excellence 3D Matter
Made to Order report how porosity can be controlled during printing and
how this affects light scattering properties of the microstructures.


========================================================================== Photoresists are printing inks used to print smallest microstructures in
three dimensions by so-called two-photon lithography. During printing,
a laser beam is moved in all spatial directions through the initially
liquid photoresist.

The photoresist hardens in the focal point of the laser beam only. Little
by little, complex microstructures can be built in this way. In a second
step, a solvent is used to remove those areas that were not exposed
to radiation.

Complex polymer architectures in the micrometer and nanometer ranges
remain.

Two-photon polymerization -- or two-photon microprinting based on this
process -- has been studied extensively for some years now, in particular
as regards the production of microoptics, so-called metamaterials, and microscaffolds for experiments with single biological cells. To expand
the spectrum of applications, new printable materials are required. This
is the point of departure of the scientists involved in the Cluster
of Excellence 3D Matter Made to Order (3DMM2O) of KIT and Heidelberg University. "With the help of conventional photoresists, it was possible
to print transparent, glassy polymers only," says Frederik Mayer,
physicist of KIT and main author of the study. "Our new photoresist
for the first time enables printing of 3D microstructures from porous
nanofoam. This polymer foam has cavities of 30 to 100 nm in size, which
are filled with air." From Transparent to White "There has never been
a photoresist for 3D laser microprinting, with which "white" material
can be printed," Frederik Mayer points out. As in a porous eggshell,
the many small air holes in the porous nanoarchitectures make them
appear white. Mixing white particles into a conventional photoresist
would not have this effect, because the photoresist must be transparent
for the (red) laser beam during printing. "Our photoresist," Mayer says,
"is transparent prior to printing, but the printed objects are white and
have a high reflectivity." The researchers from Karlsruhe and Heidelberg demonstrated this by printing an Ulbricht ball (an optical component)
as fine as a hair.

Another factor that opens up new applications is the extremely large
internal surface area of the porous material. It might be useful for
filtration processes on smallest space, highly water-repellent coatings,
or the cultivation of biological cells.

The collaboration of three of the nine research thrusts of the Cluster
of Excellence revealed the uses for which the novel photoresist is suited
and how it can be applied in the best possible way. By means of electron microscopy scans and optical experiments, researchers showed how the
cavities are distributed in printed structures and how their formation
can be controlled by varying the printing parameters and in particular
the intensity of the laser pulses. Work in the cluster of excellence
was carried out by materials scientists from Heidelberg University as
well as chemists and physicists from KIT.


========================================================================== Story Source: Materials provided by
Karlsruher_Institut_fu"r_Technologie_(KIT). Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Frederik Mayer, Daniel Ryklin, Irene Wacker, Ronald Curticean,
Martin
Čalkovsky', Andreas Niemeyer, Zheqin Dong, Pavel A. Levkin,
Dagmar Gerthsen, Rasmus R. Schro"der, Martin Wegener. 3D
Two‐Photon Microprinting of Nanoporous Architectures. Advanced
Materials, 2020; 32 (32): 2002044 DOI: 10.1002/adma.202002044 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200916113500.htm

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