For the Buchmann Institute for Molecular Bio-Sciences at the Goethe University in Frankfurt, Boston Micro Fabrication (BMF) was able to successfully produce test titer plates for the thermoforming of microscopy slides using the new 3D printing process of projection micro-stereolithography (PµSL).

The Buchmann Institute for Molecular Life Sciences is dedicated to understanding macromolecular complexes, in particular the molecular mechanisms that underlie cell functions. In the research group on Physical Biology, Dr. Francesco Pampaloni, a full-time scientist and Principal Investigator (PI) at the institute, conducts research projects with PhD students that require microscopic observations of larger cell cultures and tissues, including optical sections.

Examining Cell Cultures

For these microscopic examinations, positive microforms are regularly required in order to produce slides with specially shaped wells for the examination of cell cultures, vessels and bioreactors. “The exact positioning of the cells and cell clusters plays a major role”, reports Dr. Pampaloni. “The objects should center themselves in pyramids, tetrahedra or hemispheres so that they can be found and observed more easily under the microscope.” The shapes for this are developed using computer-aided design software (CAD) and combined in various arrangements.

They are then used for vacuum thermoforming. Here a thermoplastic plate is drawn onto the convex shape with the help of vacuum pressure. With this approach, very thin plates or foils made of fluorinated ethylene propylene (FEP) can be brought into the required shapes of microtiter plates. They have depressions with prismatic, pyramidal or hemispherical shapes. “With this we promote the formation of spheroids with high density,” says Dr. Pampaloni. “The diameter of these cellular spheroids, which are cultivated in the microwells, is around 100-200 µm each.” The ultra-thin FEP films, which are applied to the microforms in a vacuum, make it easier to analyze the cell cultures using light microscopy, a common analysis technique.

3D printing for positive microforms

With vacuum thermoforming, the quality of the end product depends heavily on the shape properties such as surface details and smoothness. Mold materials with the right thermal and mechanical properties are also required to ensure quality and consistency. Dr. Pampaloni had tried various methods of microfabrication but was not satisfied with the results.

In principle, 3D printing with SLA technology is suitable for the production of positive forms and offers a quick route from conception through design to production. However, the application also required the realization of small, complex shapes with high resolution. In addition, high-performance materials are needed to support a consistently high quality of the results with the FEP film. “With the existing SLA technology 3D printers, we were not able to produce such small features with high resolution and accuracy,” reports Dr. Pamploni. In spring 2020 he discovered the new projection micro-stereolithography (PµSL) process from Boston Micro Fabrication (BMF).

BMF’s PµSL technology achieves a resolution of 2µm ~ 10µm and a tolerance of +/- 5µm ~ 25µm. In addition, 3D printers with PµSL work at a higher speed than other methods of microfabrication. The 3D printers of the microArch series from BMF are the first commercially available microfabrication devices based on PµSL technology.

Production of test parts

Using STL files that Dr. Pampaloni made available, BMF printed the desired test series of eight microforms with a layer resolution of 8µm. In projection micro stereolithography, components are produced in layers using a photochemical process. A photosensitive, liquid resin is irradiated with UV light, so that polymer crosslinking and solidification take place. To show or hide certain areas of a layer, the STL file is broken down into a series of 2D images known as digital masks. Each layer has a mask, the layers are built up one after the other until the entire 3D structure is completed. To produce the individual layers, the cutting data is sent to a microArch 3D printing system. There, PµSL enables continuous exposure of the layers, which speeds up processing. BMF’s open material system includes technical and medical polymers that allow the 3D printing of consistently high-quality parts such as microforms. The test parts were delivered within three weeks.

Further projects planned

“We have extensively tested the BMF parts for their suitability as positive molds for the thermoforming of micro-wells,” Dr. Pamapolini explains. “The BMF micro molds have a superior resolution and surface finish compared to others we tried, so they worked very well indeed for thermoforming of the micro features required for cell culture.”

Soon a larger mold will be 3D printed to be used to make 96-well plates. The quality of the 3D printed parts was perfect for vacuum deep drawing with FEP film. In particular, the smoothness and the details that were achieved through the use of PµSL technology far exceeded the 25µm to 50µm resolution of standard SLA printers. The thermal and mechanical properties of the 3D printed material from BMF also ensured the quality and consistency of the end product.

“The service from BMF was very open and helpful, our expectations for tolerance and precision were met and the parts were delivered on time,” says Dr. Pampaloni. “We look forward to further projects.”

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