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BUILD THE ROBOT THAT TESTS HOW MUCH CREAM GETS THROUGH YOUR SKIN

The standard test for whether a drug crosses skin runs for one to three days and needs sampling around the clock — Otto does the overnight sampling instead.

by Keng Wooi Ng, Liam Archbold, Wing Man Lau

FULL CAD BOM FIRMWARE DOCS

ScienceAutomation

Built with3D printing

difficulty
●●●●○
time
a weekend-plus
license
CC BY 4.0 (two parts GPL-3.0 and GPL-2.0)
repo
repo FINISHED0 stars

WHAT YOU’LL NEED

1
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COMPAREE VERDICT

Otto automates the Franz diffusion cell test, the standard laboratory method for measuring how a formulation crosses a membrane such as skin. Experiments last 24 to 72 hours, and someone has to draw a sample and refill the receptor fluid at fixed intervals around the clock. Otto does that job on a Creality Ender-3 Pro gantry retrofitted with printed parts, electronics and off-the-shelf consumables, and the modifications to the printer are reversible. Total hardware cost is under 500 British pounds; the paper names the Vision Microette, System 913 and Phoenix RDS as the commercial alternatives and calls them costly, and they need proprietary cells. The build is for people who already run Franz cell tests and want to stop doing the overnight sampling themselves. The single hardest part is that this is not a hobbyist project: you need Franz diffusion cells, an understanding of the test protocol, and comfort adapting lab equipment. The BOM lists specific syringe types, tubing sizes and electronics; the control app is a single HTML file you open in a browser that generates the G-code, which is simpler than it sounds but still assumes you can troubleshoot hardware. If you are in a lab that runs permeation studies, this will save you nights.

GOOD TO KNOW

  • —FreeCAD sources, printable 3mf files, and a parts list are in the Mendeley dataset.
  • —OttoMate control application is a single HTML file — you open it in a browser, no install.
  • —BOM lists the Ender-3 Pro at 157.79 GBP; other parts are syringes, tubing, electronics and fasteners.
  • —Most files are CC BY 4.0, but two individual part files carry GPL-3.0 and GPL-2.0.
  • —The paper is HardwareX DOI 10.1016/j.ohx.2025.e00735; a separate validation study is in the Journal of Pharmaceutical Sciences.
  • —This is lab automation, not a consumer device — you need Franz diffusion cells to retrofit it to.

Parts to buy

8 items

From our check of the build. Exact quantities and part numbers are in the creator’s BOM.

  • Creality Ender-3 Pro (157.79 GBPFind
  • Three 12 V peristaltic pumpsFind
  • Silicone and PVC tubing with Luer fittingsFind
  • Syringes and needlesFind
  • Limit switchFind
  • 24 V to 12 V buck converterFind
  • Autosampler vial racksFind
  • PETG filament and M3 fastenersFind

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Can I build this?

PrintSampling module, dispenser, refill mechanism and gantry adaptations — printable 3mf files provided
BuyCreality Ender-3 Pro (157.79 GBP in the BOM), three 12 V peristaltic pumps, check valves, silicone and PVC tubing with Luer fittings, syringes and needles, a limit switch, a 24 V to 12 V buck converter, autosampler vial racks, PETG filament and M3 fasteners — full parts list in the paper
ToolsSoldering iron, hex keys, basic hand tools; a browser for OttoMate; Franz diffusion cells to retrofit
SkillsMechanical assembly, basic electronics, familiarity with Franz cell protocols — this is lab automation, not a first build
TimeAssembly over a weekend, then calibration and validation time that depends on your cell setup
CostUnder 500 GBP total hardware; the Ender-3 Pro is 158 pounds, the rest is consumables and electronics
SafetyNone beyond ordinary lab and electronics care — no mains voltage modification, no hazardous chemistry in the build itself.

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

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Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the HardwareX paper (The full build context, BOM and protocol are in the paper — start there to decide if this fits your setup.)
  2. 2.Download the dataset from Mendeley Data(DOI 10.17632/cvc9vxjgn9.2, version 2 — contains FreeCAD sources, 3mf files, parts list, OttoMate app and videos.)
  3. 3.Check the BOM against your cells(The machine retrofits to generic Franz cells, but syringe and tubing sizes depend on your cell geometry.)
  4. 4.Print the parts and assemble the gantry modifications(3mf files are ready to slice; version 2 also adds the plunger-lock CAD source and a printable parts list.)

KNOWN ISSUES

  • This is lab automation for people who already run Franz cell tests — if you do not own Franz diffusion cells or run permeation studies, the project has no application.
  • Two individual part files carry GPL-3.0 and GPL-2.0 rather than CC BY 4.0 — the rest of the project is CC BY, but those two parts restrict how you can share derivatives.
  • The BOM lists specific syringe types and tubing sizes that match the team's Franz cells — you may need different consumables depending on your cell design.
  • The control app is a single HTML file that runs in a browser, which is simpler than a full install but still requires you to connect and troubleshoot the electronics.
  • Version 1 of the dataset was missing the FreeCAD source for the refiller plunger lock — version 2 added it, so download version 2 if you plan to modify parts.
  • Commercial automated Franz cell systems are costly and need the manufacturer's own cells, so the real comparison is Otto plus your existing cells against replacing your whole setup.

Do I need to build an Ender-3 Pro from scratch?

No — the BOM lists a complete Ender-3 Pro at 157.79 GBP, and you retrofit it with printed parts and electronics rather than modifying the base printer.

Will this work with my Franz cells?

The paper says it retrofits to generic Franz cells, but syringe and tubing sizes depend on your cell geometry — check the BOM against your setup before ordering parts.

Is the control software complicated?

OttoMate is a single HTML file you open in a browser — simpler than installing an app, but you still need to connect the electronics and understand the sampling protocol.

What is the catch with the GPL parts?

Two individual part files carry GPL-3.0 and GPL-2.0 rather than CC BY 4.0 — the rest is open, but those two restrict how you share modified versions of those specific parts.

How much does a commercial alternative cost?

The paper names the Vision Microette, System 913 and Phoenix RDS as the closest commercial analogues and calls them costly; it gives no prices. They also need the maker's own Franz cells, while Otto retrofits to cells you already have, for under 500 British pounds.

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Discussion1

FROM THE COMPAREE TEAM

The BOM lists the Ender-3 Pro at 157.79 pounds, and the total hardware cost is under 500 — how does that compare to what your lab spends on overnight sampling labour?

CompareeTEAM1mo agoedited

Practical notes from our verification: the hardware files are on Mendeley Data (DOI 10.17632/cvc9vxjgn9.2), not GitHub, and version 2 is the one to download — version 1 was missing the plunger lock part. The one piece with a live GitHub repository is OttoMate, the browser-based G-code generator that programs the gantry. There is no official YouTube channel; the three videos in the dataset show the machine running but are not walkthroughs. The gantry is a converted Ender 3 Pro, and the paper notes the modifications are reversible. The single biggest decision is whether you already run Franz cell tests — if you do not, this project has no purpose, and if you do, the overnight sampling labour is the real number to compare against. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.

Keng Wooi Ng, Liam Archbold, Wing Man Lau

Keng Wooi Ng, Liam Archbold and Wing Man Lau are at the School of Pharmacy, Newcastle University. They built Otto to stop doing overnight sampling themselves, published it in HardwareX, and released a separate validation study in the Journal of Pharmaceutical Sciences.

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