Otto (Franz Diffusion Cell Autosampler) Printable Parts

Not your typical hobbyist project.

Otto is a DIY autosampler robot for Franz diffusion cells (FDCs). FDCs are a laboratory apparatus used to evaluate drug absorption across the skin and other biological membranes. FDCs are usually operated manually. This autosampler automates that operation, including sample extraction and buffer refills. It uses the Creality Ender 3 Pro 3D printer as the gantry. These 3D-printable parts are modifications to the base printer to turn it into the FDC autosampler robot. Details of usage are described in the scientific paper below (see References).

File formats

3D Manufacturing Format (.3mf) and editable CAD (.fcstd) files are provided. 

• Slice the .3mf files in a slicer of your choice (PrusaSlicer recommended)

• Edit the .fcstd files in FreeCAD

Other files

• Z limit switch bracket for Otto (GPL-3.0)

• Tubing organisers: Scale PTFE-clip-R4.stl from MMU3 printable parts to 75% (GPL-2.0)

Printer settings

I printed the parts on my Prusa MK3.5 and Prusa MINI+. The parts were printed in PETG, 0.4 mm nozzle, 0.20 mm layer height, 15% gyroid infill, unless otherwise stated. The sampler-pusher was printed at 100% infill.

References

• Ng KW, Archbold L, Lau WM. Building Otto: An open-source Franz diffusion cell autosampler for automating in vitro skin permeation studies. HardwareX, 2026;25:e00735. https://doi.org/10.1016/j.ohx.2025.e00735

• Ng KW. Design files for Otto, the Franz diffusion cell autosampling robot. Mendeley Data, 2025. https://doi.org/10.17632/cvc9vxjgn9

• Chan HKY, Archbold L, Lau WM, Ng KW. Validating Otto: a Franz diffusion cell autosampler to automate in vitro permeation studies, Journal of Pharmaceutical Sciences, 2025:103837.