(I-325) The Enderstruder: An accessible open-source syringe extruder compatible with Ender series 3D printers

3D bioprinting has revolutionized tissue engineering, offering tremendous potential for organ replacement, drug screening, and disease modeling [1]. However, the widespread adoption of bioprinting technology is hindered by the high cost of commercial bioprinters, which can range from tens to hundreds of thousands of dollars, and an expanding ecosystem of subscriptions and proprietary software. Researchers have developed alternative low-cost, open-source DIY syringe extruders that convert conventional thermoplastic 3D printers into bioprinters [2]. In this study, we present our novel open-source syringe extruder, the Enderstuder, tailored specifically for the popular Ender (Creality^TM) series 3D printers. The Enderstuder uses a standard 10 mL BD syringe, positions the stepper motor at the gantry level, enhances x-axis stability with a linear rail, and includes the original stepper motor. These design modifications significantly reduce costs and simplify the assembly process. We provide comprehensive documentation, including detailed build instructions, calibration protocols, and print profiles, to facilitate the seamless assembly, operation, and validation of the Enderstuder. Furthermore, we have developed open-source Ultimaker Cura^TM print profiles that enable the printing of common biomaterial inks. We used these print profiles to reproduce published test calibration shapes and lattices. Our results indicate that the Enderstuder can replicate the printability results reported in existing literature for these high-viscosity biomaterial inks under ambient conditions. By offering an affordable and adaptable bioprinting solution, the Enderstuder holds promise for fostering innovation in tissue engineering and biomedical research.

The Enderstruder consists of four primary components: a 3D-printed core, a 3D-printed syringe carriage, a stock motor, and an inexpensive 10 mL BD syringe (Figure 1A). The core connects the mounted extruder to the printer's x-axis gantry, ensures system rigidity, and prevents needle deflection when extruding viscous biomaterial inks at room temperature. It can be easily attached to the rail carriage and motor using M3 screws, incorporates slots for cylindrical linear rails, and features slits for the toothed belt, facilitating translation along the x-gantry. The NEMA-17 stepper motor, included with most Ender machines, drives a threaded rod connected to a 3D-printed herringbone gear system with a 5:1 ratio. The syringe carriage acts as a sturdy link between the syringe and the core, efficiently transmitting the torque generated by the geared system. We used Pronterface software to calibrate the stepper motor esteps and the slicing software Ultimaker Cura^TM to create print profiles. Printability assessments were conducted using ImageJ, specifically focusing on analyzing the circularity value of pores in log pile lattices in the calibration prints. The performance of the Enderstruder with different materials, including fluid 4% w/v alginate, ionically cross-linked 3.5% w/v alginate, 40% w/v Pluronic F-127, 10% w/v GelMA, and Nivea crème, was assessed using lattice, filament uniformity, and filament fusion tests. The calibration patterns were imaged on a stereo microscope and subsequently analyzed with ImageJ.

We produced an Enderstruder prototype that is low-cost, open-source, and accessible to a broad audience. Comparing our design with the only other reported open-source syringe extruder adapted for Ender series machines [3], we incorporated a linear rail instead of a rolling carriage to ensure smoother movement, reduce ringing artifacts, and enhance stability despite the stepper motor's increased weight [4]. Our design also replaced the clay gun extruder with a cost-effective and widely available syringe and retained the original stepper motor, significantly reducing overall costs. To ensure user-friendly implementation, we refined and simplified the build instructions through multiple trials involving students with minimal 3D printing experience. Unlike the conventional "guess-and-test" approach or AI algorithms for creating slicing profiles, we adopted an iterative methodology to determine optimal wall, top/bottom layer, and infill flow rates for known and novel materials. Demonstrating the efficacy of this approach, we assessed the printability of five biomaterial inks (Figure 1B). Fluid alginate was too fluid to stabilize visible pores; however,  cross-linked alginate, Pluronic F-127, GelMA, and Nivea crème attained printability scores of 1.299, 1.170, 1.333, and 1.039. Our findings showcased a high degree of filament uniformity for all tested biomaterial inks, with variations in line width within a tolerable range of 110 microns. Additionally, the Enderstruder exhibited remarkable capability in printing complex designs with extended printing times and retraction, exemplified by the successful printing of the "Benchy" calibration model (Figure 1C). To further enhance our design, we aim to implement temperature control, incorporate an onboard cross-linking mechanism, and devise a more compact form factor. Moreover, a detailed COMSOL analysis will observe and mitigate shear stress on printed materials, thereby enhancing cell viability. Subsequently, we intend to produce a comprehensive open-source publication, sharing our curated protocols and instructions and depositing our data to OSF (Open Science Framework). By presenting the Enderstruder and its iterative development process, this study contributes to the growing repository of open-source bioprinting solutions, fostering greater accessibility and affordability for researchers in tissue engineering and beyond.

The authors thank Kristie Cheng, Noor Nazeer, and Gabriela Nicole Hislop Gomez for synthesizing and loading the biomaterial inks and FRESH support baths. The authors also acknowledge the contributions of Katie Rosenkrantz and Andrew Vergote for their prior work on estep calibration and developing the suspension bath protocol for the lab, respectively.

Funding: This work was supported by the Robert A. Welch Foundation (AF-0005), the Sam Taylor Foundation, and a generous gift to Southwestern University from Bob and Annie Graham.

[1] Sun, Wei, et al. "The bioprinting roadmap." Biofabrication 12.2 (2020)

[2] Garciamendez-Mijares, Carlos Ezio, et al. "State-of-art affordable bioprinters: A guide for the DIY community." Applied Physics Reviews 8.3 (2021)

[3] Chimene, et al. “Designing cost-effective open-source multihead 3D bioprinters”. GEN Biotechnology 1.4 (2022)

[4] Demircan and Özçelik. “Development of affordable 3D food printer with an exchangeable syringe-pump mechanism”. HardwareX e00430 (2023).