Living Machines 2024: Positional accuracy characterization of converted 3D bioprinters via a low-cost camera-based system (Supplementary Materials)
Creators: name: Sun, Anika
name: Williamson, Avery
name: Ashraf, Syed Faaz
name: Feinberg, Adam
name: Webster-Wood, Victoria
Publisher: name: Zenodo
Year: 2024

description: Supplementary Materials from "Positional accuracy characterization of converted 3D bioprinters via a low-cost camera-based system" including references with original datasets, current experimental datasets, and presentation materials. 

Extrusion 3D bioprinting is a widely used technique for creating biohybrid robots. Many affordable FDM 3D printers on the market can serve as a base for conversion into low-cost bioprinters, widening access to bioprinting for research. In bioprinting, positional accuracy and geometric fidelity of final parts are crucial, with most bioprinters using extrusion needles from 20-30G. Previous work has shown bioprinters can have uniaxial position errors up to 35µm after correction, yielding structures with geometric fidelity error up to 18%. These measurements are often made with a dial indicator or by assessing a final printed part. However, assessing inaccuracies by gauging the final part can obscure the error’s source due to the effects of the bioink, support bath, environment, post-processing, and printer limitations. In addition, dial indicators can not easily measure inaccuracies at the extrusion needle tip due to needle curvature and size. Accessible, low cost methods are needed to measure inaccuracies in the base printer directly to improve outcomes as new labs adopt these systems.

 In this pilot study, we assessed the position error at the needle tip on a CoreXY-based system from E3D with a custom Replistruder printhead. To track needle motion, we built a system that recorded the needle tip’s location at 720p and 110 frames per second. This system uses a Raspberry Pi, camera (Raspberry Pi HQ Camera CS), and short focal-length lens (Arducam 50 degree 1/2.3” M12). For preliminary testing, measurements were taken as the printer executed hexagonal and circular paths to collect single and multi-motor engagement motion data. Position data was extracted from videos using Physlets Tracker. Mean squared distance relative to the commanded path and standard deviation of position at each frame were used to assess position accuracy and variance.  

 The maximum mean squared distance error was 36.1±10.5µm, with a standard deviation of position at each frame of 85.1µm across runs. This is less than the needle’s 160µm internal diameter. Furthermore, qualitative assessment of the videos indicates peak deviations occur during single motor activation or sudden velocity changes. Finally, the mean squared distance errors approach the camera's pixel resolution of ~28.8µm. 

While additional testing is needed, the errors measured with our < $150 camera system on the E3D-based printer with Replistruder printheads are similar to previously observed values collected on other bioprinters. The measurement system presented in this work provides a low-cost solution for assessing positioning error at the needle tip on customized bioprinters to inform subsequent part design.