The Microfluidics Core Facility at Heidelberg University successfully uses the 3D printing technology of projection micro-stereolithography (PµSL) from Boston Micro Fabrication (BMF). Sophisticated research projects are supported with microparts such as microwells, various microfluidic devices and “organs-on-a-chip”.
In 2022, the Institute for Molecular Systems Engineering and Advanced Materials (IMSEAM) was established at Heidelberg University, the oldest university in Germany, founded in 1386. The mission of the IMSEAM is to create new materials, methods and technologies from synthetic and natural building blocks at the molecular level, considering complete systems from molecule to function. Four research groups and two junior research groups are currently working at IMSEAM on basic principles and applications for materials development, organic electronics, environmental technology and medicine. IMSEAM also offers core facilities in the field of device fabrication and characterization (IMSEAM core Facility), soft (bio) materials characterization and microfluidics for other university groups.
Scientific Facility for Microfabrication and Microfluidics
Microfluidics is an emerging field and is finding use in various disciplines. Starting from understanding flow mechanisms, to the generation of synthetic cells with droplet-based microfluidics, continuous flow microfluidics to complex organ-on-a-chip models. The Microfluidics Core Facility (µFlu CF) aims to provide this valuable tool to every interested research group at the University. For example, researchers are supported with contributions to project design, the production of microfluidic chips and the implementation of experiments in biosafety laboratories. “In May 2022, we began procuring the first instruments for the production and analysis of microfluidic chips,” reports Dr. Sadaf Pashapour, project manager of the Core Facility. Traditionally, photolithography is used to create a master wafer on a photoresist-coated silicon wafer. A maskless aligner that can produce 2D geometries with 1 to 200 µm in height was procured for this purpose. In addition, the height of the generated structure must be measured with an interference profilometer. The difference in height between the silicon wafer and the exposed photoresist lies within a measuring range of 1 µm to 2-3 mm. “In addition to this process, however, we also wanted to be able to produce 3D geometries,” says Dr. Pashapour. “That’s why we looked around for a suitable 3D printer.”
Decision in favor of PµSL technology
After extensive market research, a typical design was selected and sent to four or five suppliers. “For us, the challenge is to print narrow channels with the smoothest possible walls so that there is no turbulence later on”, Dr. Pashapour explains. “Only BMF was able to produce the sample part perfectly.” The company has developed projection micro stereolithography (PμSL) to achieve the right resolution, accuracy and precision for micro production. As a form of stereolithography (SLA), it requires a digital light processing engine (DLP), precision optics, high-precision motion control and associated software. As with SLA, components are broken down into layers and projected onto liquid, photosensitive resin using a light source. Polymer cross-linking and solidification takes place at the exposed areas. With PμSL technology, an ultraviolet (UV) flash of light causes the rapid photopolymerization of an entire resin layer. Continuous exposure is used to ensure faster processing. Based on this technology, BMF offers 3D printing platforms with different resolutions: The top model microArch S230 achieves an optical resolution of 2µm with a layer thickness of 5µm to 20µm. “For budget reasons, however, we opted for a microArch S140, a desktop model with 10µm resolution,” says Dr. Pashapour. “This incredible device produces very good results.”
Installation and introduction
The microArch S140 offers sufficient build space of 94 x 52 x 45 millimeters. The platform is material-open – not only the materials offered by BMF can be used, but also suitable products from third-party suppliers. In contrast to other manufacturers, BMF also allows extensive intervention in the printing parameters so that users can achieve the desired results under optimal conditions. After the installation, BMF offered a comprehensive introduction: “The introduction was carried out step by step for a whole week and the entire theory behind the device was explained very well, so we really understand all functions of the printer,” says Dr. Pashapour happily. “When I wanted to print my first projects, I received support in a messenger group. They responded really quickly there.” The microArch S140 has now been working around the clock since September 2023 – except for a Christmas break. Since then, Dr. Pashapour has had to change the membrane once and received an online course.
Best results at the cutting edge of research
In the meantime, word of the new possibilities of the Microfluidics Core Facility has spread beyond the campus. Around 20 researchers have already worked on projects here right through to the finished chip. Collaborations now exist with the Technical University of Munich, the Leibnitz Institute in Saarbrücken and as far away as Chile. The printer works day and night all week. “I operate the printer alone so that I can assign priorities correctly,” says Dr. Pashapour. “While the printer is running, I can prepare new projects, rework components or pursue my other tasks.”
The ability to print directly onto a glass substrate with the yellow resin is particularly valuable. “The better view allows us to better analyze the microfluidic processes,” says Dr. Pashapour. “However, we would like to have software support for the micron-precise alignment of the glass plate on the build plate – we now use calipers for this.” Various other projects, from cubes with 150µm cavities to 3D-printed micro-wells with a diameter and depth of 80µm and a spacing of 20µm to 100µm fine grids for cell-induced deformations, have been successfully completed. “The S140 meets our requirements for accuracy and precision every time – the surfaces become just as smooth as we need them to be,” says Dr. Pashapour. In addition to solid resin, she would also like to use elastic materials, for example for a synthetic lung as an “organ on a chip”. At first, one design was too complex for the 3D printer. “We have sent it to the support team at BMF,” explains Dr. Pashapour. “Maybe the 100 micrometer struts can be realized with the 2µm printer.”
