YOU CAN BUILD A 400-DOLLAR MACHINE THAT MEASURES THE STIFFNESS OF SOFT MATERIALS, A JOB LABS USUALLY BOOK A COMMERCIAL INSTRUMENT FOR
A desktop machine that measures how stiff a gel or rubber is, for about 400 dollars, where commercial indenters cost 10,000 to 100,000 dollars.
by Dylan List, Alan Gardner, Isabella Claure, Joyce Y. Wong, and Keith A. Brown
ScienceOpen-hardware
Built with3D printing
- difficulty
- ●●●●○
- time
- a weekend-plus
- license
- MIT
- repo
- repo FINISHED0 stars
●●●●○ · a weekend-plus · MIT · 0 stars · repo FINISHED
WHAT YOU’LL NEED
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COMPAREE VERDICT
The hardware is deliberately simple: a 269-dollar Genmitsu 3018-PROVer CNC router, a 119-dollar Vernier force sensor, a steel ball indenter, 3D-printed mounts and Python, about 400 dollars in total. The paper's own comparison table lists commercial nanoindenters at 10,000 dollars to 100,000 dollars and AFM nanoindentation at 30,000 dollars to 300,000 dollars. ASMI covers 7 kPa to 67 MPa and runs 96 samples unattended. In the published validation, PDMS measured inside its literature range, and 3D-printed TPU came out within 30 percent of compression tests on an Instron universal testing machine. The single most likely problem is not the build — it is getting reliable contact detection and sample geometry right; sloppy samples give wrong moduli you will not notice until you compare them to literature. If you are in a tissue engineering lab, a soft robotics group, or a materials characterisation facility and you have been putting off indentation because the quotes were absurd, this is the build. If you do not already know why you need an elastic modulus, you do not need this machine.
IN THE REPO
GOOD TO KNOW
- —STL files and Python control code are on GitHub (dlist26/ASMI, archived on Zenodo); the paper lists them under the MIT licence, and the BOM with prices is in the paper.
- —The paper is open access under CC BY 4.0 and includes full build instructions, operating instructions and validation data.
- —The motion platform is a Genmitsu 3018-PROVer semi-assembled CNC router (269 dollars), which is part of the ~400 dollars BOM.
- —The ~400 dollars figure covers the 3018-PROVer CNC router (269 dollars), the Vernier Go Direct Force and Acceleration sensor (119 dollars), a steel ball-bearing indenter, mounting hardware and 3D-printed parts.
- —MIT licence permits commercial use.
- —This is a published, peer-reviewed instrument with repeatability data and a comparison table against commercial systems.
Parts to buy
5 itemsFrom our check of the build. Exact quantities and part numbers are in the creator’s BOM.
Can I build this?
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.Read the HardwareX paper (The paper is open access and contains the full build procedure, calibration protocol, and Python code walkthrough.)
- 2.Download the design files and code from Zenodo (An archived copy of the GitHub repo: the 3D-printable parts (STL) and the Python control scripts, with the software under the MIT licence. The bill of materials with prices is in the paper.)
- 3.Order the Vernier Go Direct Force and Acceleration sensor(About 119 dollars. Get the exact model named in the paper; the code uses its Go Direct library.)
- 4.Print the standoff and assemble the bracket(The STL files are in the GitHub repo (also archived on Zenodo). The steel ball is epoxied to the standoff, the standoff to the sensor, and the printed mount slides into the CNC's spindle holder; centring and vertical alignment matter.)
- 5.Validate the build on a reference material with a known modulus(The paper validates on PDMS (known modulus 1.3–3.0 MPa) and 3D-printed TPU. Repeat a check like this on your own build before trusting your numbers.)
KNOWN ISSUES
- The motion system is a cheap Genmitsu 3018-PROVer CNC router (269 dollars, included in the ~400 dollars BOM) that you convert into the indenter; if you swap in a different mill, expect to rework the G-code and mounts.
- Validate your build before trusting it. The paper checks the instrument on PDMS with a known modulus; do the same with a reference sample, or you will not notice wrong moduli until you compare to literature.
- The design is built around the Vernier Go Direct Force and Acceleration Sensor (about 119 dollars) and its Python library; a different force sensor means rewriting the data-acquisition code.
- The paper's validation is on PDMS and 3D-printed TPU (NinjaFlex, Cheetah). Outside the stated range (below 7 kPa or above 67 MPa) the results are not reliable.
- Sample height must be between 1 and 30 mm. Thinner samples will bottom out, thicker samples will not fit under the sensor.
- The Python code drives the 3018-PROVer with G-code over serial; a different mill or controller means adapting the motion commands and the well-plate coordinates.
Can I use a different force sensor?
Technically yes, but the code reads the sensor through Vernier's Go Direct Python library, so a different sensor means rewriting data acquisition and re-validating against known materials. The Vernier was chosen for its precision and its compatibility with open-source software.
How does this compare to a real nanoindenter?
ASMI measures bulk elastic modulus by pressing a steel ball into the sample and fitting force-displacement curves. A nanoindenter measures local properties at very small scale and covers effectively all materials. ASMI cannot replace a nanoindenter for thin films or surface characterisation; for bulk soft materials between 7 kPa and 67 MPa it gives useful numbers at a small fraction of the cost. In the paper it landed inside the literature range for PDMS and within 30 percent of an Instron compression test on printed TPU.
What if I do not have access to a CNC mill?
You do not need one already: the build starts from a 269-dollar Genmitsu 3018-PROVer semi-assembled CNC router, which is included in the ~400 dollars bill of materials and provides all the motion.
Can I run it on biological tissue?
Possibly, but the paper validates it on PDMS and 3D-printed TPU, not tissue. The 96-well plate format suits high-throughput screens; for soft hydrated samples keep them hydrated, and note the lower limit is about 7 kPa.
How repeatable is it?
The paper repeats measurements on PDMS and on 3D-printed TPU samples and compares them with literature values and with compression tests on an Instron 5965 universal testing machine; the numbers are in its validation tables.
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Discussion1
FROM THE COMPAREE TEAM
The paper names a Hysitron TI-950 TriboIndenter as the closest commercial analog, and validates ASMI on PDMS and printed TPU against an Instron compression test. If you are already running stiffness tests on soft materials, what would convince you to build this instead of booking time on a commercial instrument?
Dylan List, Alan Gardner, Isabella Claure, Joyce Y. Wong, and Keith A. Brown
The ASMI team is at Boston University, spanning Mechanical Engineering, Biomedical Engineering and Physics, with Keith Brown's group leading. They turned a 269-dollar hobby CNC router and a classroom force sensor into an automated indenter and checked it against PDMS reference values and an Instron testing machine.
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- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM26d agoedited
Practical notes from our verification: the design files are on Zenodo, the Python scripts are on GitHub (dlist26/ASMI), and the paper itself is the build manual — it walks through the assembly, the code structure and the measurement workflow step by step. The roughly 400 dollar hardware figure covers the whole rig, including the Genmitsu 3018-PROVer CNC router that moves the sensor (about 269 dollars) and the Vernier Go Direct force sensor (about 119 dollars), so you do not need to own a mill already. The validation is honest and specific: PDMS samples checked against known literature values, and 3D-printed NinjaFlex and Cheetah TPU checked against an Instron 5965 compression test. A short supplementary movie shows the instrument running. If you are in a lab that needs stiffness data on soft materials and equipment quotes have been a blocker, this is one of the clearest open builds we have seen in the indentation space. 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.