Converting an Ender 3 into a Biogel Printer: A Technical Deep Dive

Biogel printing — extruding hydrogels, cell-laden scaffolds, or temperature-responsive polymers through a precision syringe at physiological temperatures — has moved from the exclusive domain of six-figure commercial bioprinters into the reach of well-equipped makers and small research labs. The Creality Ender 3 has become the most common base platform for this conversion, thanks to its rigid steel frame, open firmware, accessible electronics, large build volume, and an enormous community of existing modifications. This guide synthesises the current open-source bioprinter literature to give a clear technical path from stock Ender 3 to functional biogel printer.

The core challenge is not mechanical — syringe pump extruders are well-solved and several peer-reviewed open-source designs exist. The challenge is maintaining precise temperature at 37 °C (physiological temperature) from the reservoir all the way to the nozzle tip, and understanding the specific printing parameters of different biogels. Both require decisions that go well beyond standard FDM printer configuration, and both are covered in detail here.

Before You Start: Two Paths

There are two viable starting points depending on whether you already own an Ender 3.

Path A: Convert an Ender 3

If you have an Ender 3 (any variant — original, Pro, V2, or S1), conversion is the lower-cost and better-documented path. The total modification cost sits at roughly $150–250 USD on top of the printer, and you benefit from a large community, abundant replacement parts, and the ability to revert to standard FDM printing if needed. This is the path the rest of this guide primarily addresses.

Path B: Build a Printess from Scratch

In early 2025, Stanford published the Printess — a fully open-source, purpose-built Direct Ink Writing (DIW) bioprinter at around $250 total cost. All files, assembly instructions, and a full build video are available at printess.org. If you are starting from zero and don't own a 3D printer, Printess is worth comparing directly against the Ender 3 conversion path. Its advantage is that there are no legacy FDM assumptions to work around; its disadvantage is a smaller community and less documentation of specific bioink workflows.

For the rest of this guide, we assume Path A: an Ender 3 conversion.

Syringe Extrusion: Replacing the Hotend

The first major modification is replacing the entire hotend and extruder assembly with a syringe pump. The Ender 3's existing motion system — X, Y, and Z axes — is kept entirely intact. Only what happens at the print head changes.

Why Mechanical, Not Pneumatic

Commercial bioprinters commonly use pneumatic (air-pressure-driven) extrusion because it is mechanically simple. However, pneumatic systems have a fundamental limitation: they cannot perform retraction. Retraction — pulling bioink back into the syringe between moves — is essential for preventing stringing, oozing, and loss of feature resolution in complex geometries. Mechanical stepper-driven syringe pumps support precise displacement control in both directions, making them superior for any print with internal channels, overhangs, or fine features. For a DIY build, mechanical is the correct choice.

The Enderstruder — Recommended Starting Point

The Enderstruder is a peer-reviewed, open-source syringe extruder designed specifically for the Ender series, published in HardwareX under CC-BY-SA 4.0. All CAD files are freely available at OSF (osf.io/9arym). Key specifications:

• Cost: approximately $55 USD including all hardware
• Uses standard 10 mL Becton-Dickinson (BD) syringes at roughly $0.29 per unit — fully disposable, no cleaning required
• 4:1 3D-printed gear ratio, giving 33% more torque than the commonly used Replistruder's 3:1 ratio
• Uses the Ender 3's existing stepper motor — no additional motor purchase needed
• Adds a linear rail to the X-axis for improved carriage stability
• CAD is fully editable; the team included instructions for adapting it to different syringe sizes, including Hamilton glass autoclavable syringes for sterile work
• Comes with Cura profiles tuned for five common biomaterials (including alginate and GelMA)

The Enderstruder is the right starting point for most builds. It is well-documented, cheap, and has been validated in a peer-reviewed context. There is also a community-built Ender 3 V2 conversion kit on Thingiverse (by tcytcytcy) that follows a similar approach and is worth reviewing alongside the official Enderstruder files.

The Replistruder 4 — For Higher Resolution

If print resolution is the priority — for example, printing collagen or fibrin scaffolds with patent channels under 500 µm — the Replistruder 4 from the Feinberg/Shiwarski lab at Carnegie Mellon is the better choice. At $141, it uses precision off-the-shelf linear motion components (rather than purely 3D-printed gears) combined with 2.5 mL Hamilton gastight syringes. Published performance benchmarks demonstrate individual filaments as fine as 3.35 nL and patent channels down to 300 µm width when printing collagen type I. The Replistruder is also optimised for retraction dynamics during FRESH bioprinting (covered below). The trade-off is a more involved build and a narrower syringe (the 2.5 mL Hamilton gastight is considerably more expensive than disposable BD syringes).

The Temperature Problem

Maintaining 37 °C is harder than it appears on a stock Ender 3. Understanding why requires looking at two separate problems: the firmware control problem and the thermal gradient problem. Both must be solved.

Why Naive Approaches Fail

The Ender 3's stock hotend controller is calibrated for 180–280 °C. At 37 °C, several things go wrong with a naive setup: the stock NTC 100K thermistor's resistance-to-temperature curve is poorly characterised at near-ambient temperatures; the PID controller has almost no thermal headroom to overshoot-and-correct when your target is only 12–15 °C above ambient room temperature; and the stock Creality mainboard (8-bit on the original Ender 3) introduces additional limitations. Simply sending M104 S37 will not produce stable or accurate results.

The Thermal Gradient Problem — A Critical Detail

Even if you achieve stable temperature at the syringe barrel, 2024 research on heated printhead design revealed a severe thermal gradient along a standard luer-lock needle. In a measured real-world configuration, a barrel held at 36 °C produced a temperature of only 26 °C at the needle hub and 17–18 °C at the needle tip — a loss of nearly 20 °C across a few centimetres of exposed metal. For temperature-sensitive bioinks like alginate-gelatin composites, GelMA, or Pluronic F-127, this gradient is enough to completely change the material's rheology at the point of extrusion and cause clogging or inconsistent filament diameter.

The solutions the literature identifies are: (1) extend insulation down the full length of the needle, not just around the barrel; (2) use the shortest, widest-bore needle that your feature resolution allows; (3) enclose the entire printhead in a heated chamber so the needle is not exposed to ambient air; or (4) heat the support bath or build plate to 37 °C to compensate at the deposition end. Option 1 is the most accessible for a DIY build — a 3D-printed TPU collar extending from barrel to needle hub, filled with a foam insert, makes a significant difference.

The Right Sensing and Heating Hardware

For sensing, the standard NTC 100K thermistor used in FDM printing is not the right tool for this temperature range. A PT100 or PT1000 RTD (Resistance Temperature Detector) is significantly more accurate at near-body temperatures and is linear in its response, making PID calibration far more reliable. PT100/PT1000 modules are inexpensive (around $10–15 USD) and widely available. For heating, a 12 V silicone resistive heater pad or tape wrapped around the syringe barrel provides even, distributed heat along the gel column — important because a point heat source creates local thermal gradients that can denature proteins or affect gelation.

Environmental Considerations

A 2020 paper published a full open-source temperature and humidity PID controller specifically for a bioprinter atmospheric enclosure, finding that ambient humidity and temperature variations significantly affect print reproducibility — not just the printhead temperature. If the build environment varies significantly from day to day, or if printing with live cells, a simple acrylic enclosure with temperature monitoring is worth the investment.

Firmware: Marlin or Klipper?

The Ender 3 ships with a Creality-branded build of Marlin. For a bioprinter conversion, you have two choices.

Klipper — Recommended

Klipper running on a Raspberry Pi is the strongly recommended firmware for this application. Its advantages for a bioprinter conversion are substantial: configuration lives in a human-readable printer.cfg file that can be modified without recompiling or reflashing the microcontroller; custom heater zones can be defined with non-standard thermistor types (including PT100 via MAX31865 amplifier); PID calibration is done at runtime via a single G-code command; and the configuration for a syringe extruder (rotation_distance, gear_ratio, max_extrude_only_distance) is straightforward to set and adjust in text. Klipper also has an active community of bioprinting-adjacent users, and several published bioprinter conversion projects document their full Klipper configs.

Migrating an Ender 3 to Klipper requires a Raspberry Pi (any model with USB), a micro-SD card, and approximately two hours. The SKR Mini E3 v3 is the recommended mainboard upgrade — it is 32-bit, widely supported by Klipper, and costs around $30 USD. The stock Ender 3 8-bit board can run Klipper but with limitations on thermal table accuracy at low temperatures.

The key Klipper configuration for the syringe heater zone:

printer.cfg (relevant excerpt)
[extruder]
step_pin: ...
dir_pin: ...
enable_pin: ...
# Calibrate rotation_distance empirically for your syringe diameter
rotation_distance: 1.2
gear_ratio: 4:1
microsteps: 16
heater_pin: PC8          # spare heater output
sensor_type: PT1000      # or PT100 via MAX31865 module
sensor_pin: PA0
min_temp: 0
max_temp: 60
# After PID_CALIBRATE HEATER=extruder TARGET=37:
control: pid
pid_Kp: ...
pid_Ki: ...
pid_Kd: ...

Run PID_CALIBRATE HEATER=extruder TARGET=37 and allow at least 40 minutes for the syringe's thermal mass to reach steady state before saving the PID values. The low target temperature means the controller will be operating very close to ambient, so thermal stability of the surrounding environment matters more than it does for hotend printing.

Marlin — Viable But More Work

If staying with Marlin, you will need to recompile the firmware with a custom thermistor table calibrated for your PT100 or PT1000 sensor, and run M303 E0 S37 for PID autotune. The stock 8-bit board can produce acceptable results at 37 °C, but upgrading to a 32-bit board (SKR Mini E3, BTT E3 Turbo) is recommended for reliability. The syringe extruder steps/mm will need substantial recalculation from the stock FDM value — use the formula: steps/mm = (motor steps × microstepping × gear ratio) / (π × syringe plunger diameter × plunger travel per revolution).

The FRESH Technique: Printing Soft Gels Without Collapse

Many biologically relevant hydrogels — collagen type I, fibrin, Matrigel, soft GelMA formulations — are far too weak to support their own weight during printing. Extruding them into air produces collapsed, deformed structures. The FRESH (Freeform Reversible Embedding of Suspended Hydrogels) technique, developed by Feinberg's group at Carnegie Mellon, solves this elegantly.

In FRESH printing, you fill the build container with a gelatin microparticle slurry bath before printing begins. The slurry behaves as a Bingham plastic: it is rigid at low shear stress (holding extruded filaments in place immediately after deposition) but flows like a viscous fluid under higher shear (allowing the needle to move through it freely). After printing, the entire assembly is warmed to 37 °C, which melts the gelatin slurry while leaving the printed construct intact — the gelatin rinses away, revealing the freestanding 3D structure.

For alginate printing with FRESH, Duquesne University published a student-accessible protocol: print into a gelatin slurry support bath (CaCl₂ can be dissolved directly in the gelatin to enable ionic crosslinking of alginate in situ), then warm to release the construct. This approach allows printing of complex internal geometries — branched channels, hollow tubes, and multi-layer cell-laden constructs — that would be impossible with direct-deposition printing into air.

A 2025 Scientific Reports paper also demonstrated a DIY coaxial bioprinter (built on a modified FDM printer) that extends FRESH to core-shell extrusion, enabling fabrication of hollow filaments and vascularised tissue analogues. The coaxial nozzle requires a custom-machined or precision-printed concentric needle assembly, which is a further modification beyond the base Enderstruder build.

For a first build, FRESH is optional — it is only required if you plan to print low-viscosity hydrogels that collapse in air. Alginate at 2–4% w/v, Pluronic F-127 at 20–40% w/v, and high-concentration GelMA (>10% w/v) are all printable without a support bath.

Bioink Properties and Printing Parameters

Each class of biogel has different crosslinking chemistry, temperature requirements, and practical constraints for DIY printing. This section covers the four most commonly used materials.

Sodium Alginate

Alginate is the most accessible starting bioink: inexpensive, non-toxic, and crosslinks ionically (no UV, no heat required) when it encounters calcium ions (CaCl₂). Typical formulation is 2–4% w/v sodium alginate dissolved in PBS or cell culture medium. Printability is good without a support bath at these concentrations. The key limitation is poor long-term mechanical stability and limited cell-matrix interaction — alginate doesn't naturally present cell-adhesion motifs, which matters if long-term cell culture is the goal. For initial calibration of the bioprinter, alginate is an excellent choice precisely because its crosslinking does not require additional hardware (no UV LEDs, no heated stage).

• Print temperature: 21–25 °C (room temperature) or 37 °C — alginate is not strongly temperature-sensitive in this range
• Crosslinking: CaCl₂ bath post-print, or CaCl₂ dissolved in FRESH support bath for in situ crosslinking
• Target concentration for printability + cell viability: 2–4% w/v

GelMA (Gelatin Methacryloyl)

GelMA is one of the most widely used bioinks in academic research due to its excellent cell compatibility, tuneable mechanical properties, and ability to mimic the extracellular matrix. It is a modified gelatin that crosslinks under UV light (365 nm wavelength) in the presence of a photoinitiator (typically LAP or Irgacure 2959). This makes it more demanding than alginate from a hardware perspective — a 365 nm UV LED module must be mounted to the printer for post-extrusion crosslinking.

GelMA is also thermally sensitive: it gels on cooling (below ~30 °C) and liquefies on warming. For extrusion, the syringe should be maintained at 37 °C to keep the material fluid enough to extrude, then rapid UV crosslinking at the print surface locks the deposited filament in place before the next layer. At 11–15% w/v, cell viability through the print process has been demonstrated above 75% in published work.

• Print temperature: 37 °C in syringe (critical — lower temps will clog the needle)
• Crosslinking: 365 nm UV, 30–60 seconds per layer depending on intensity
• Photoinitiator: 0.1–0.5% w/v LAP or Irgacure 2959 in PBS
• Target concentration: 10–15% w/v for printability with cells; higher concentrations are stiffer but more printable
• Hardware addition needed: 365 nm UV LED array, mounted to the gantry or on a separate articulating arm

Pluronic F-127

Pluronic F-127 is a temperature-responsive amphiphilic block copolymer with an important and counterintuitive property: it is liquid when cold and gels when warm. At concentrations of 20–40% w/v, F-127 solutions are liquid at 4 °C and gel at room temperature or body temperature. This makes it an excellent material for calibration and for use as a sacrificial template — print an F-127 scaffold, embed it in a surrounding matrix, then cool the entire construct to 4 °C to liquefy and flush the Pluronic, leaving behind hollow channels (a common technique for fabricating vasculature-like structures).

• Print temperature: 37 °C build plate (for instant gelation on deposition) — the syringe should be kept cold or at room temperature to prevent gelation before extrusion
• Removal: cool construct to 4 °C; F-127 liquefies and can be rinsed out
• Not suitable for long-term cell culture by itself — primarily a sacrificial/template material
• Preparation: autoclave 40% F-127 stock at 4 °C; mix with any additives cold; load into syringe cold and allow to equilibrate

Collagen Type I

Collagen is the gold standard for cell-compatible bioinks but the most technically demanding to print. It is liquid at 4 °C and gels slowly at 37 °C via a self-assembly mechanism (not chemical crosslinking). Its low viscosity means it requires a FRESH support bath to print any structure more complex than a flat slab. For high-resolution collagen printing, the Replistruder 4 is the preferred extruder — the Feinberg lab demonstrated 3.35 nL filaments and 300 µm patent channels in type I collagen using FRESH, which represents the current DIY state of the art. Collagen is also expensive (commercial preparations from Corning or Advanced BioMatrix run $80–200 per 10 mL) and requires cold-chain handling throughout.

Sterility, Enclosure, and UV Crosslinking

Sterility Strategy

If printing with live cells, sterility is non-negotiable. There are two practical approaches for a lab or maker setting. The first and simplest is to place the entire printer inside a biosafety cabinet (BSC) during the print run. This requires a BSC with sufficient internal clearance (most Class II BSCs can accommodate the Ender 3's footprint with the enclosure removed), and it means the printer must be cleaned and UV-decontaminated before each use. The second approach is to build a custom acrylic enclosure around the printer with UV LED sterilisation panels (420 nm is effective for surface decontamination) and HEPA-filtered positive-pressure air. Research-grade commercial bioprinters use exactly this approach — the CELLINK and Allevi machines use UV LED arrays with automated sterilisation cycles. Constructing a DIY version of this is achievable at relatively low cost using off-the-shelf acrylic sheet, an 80 mm HEPA fan module, and UV LED strips.

Regardless of which approach you take, all 3D-printed plastic components that contact the bioink should either be disposable (PLA parts can be treated as single-use if printed fresh for each experiment) or autoclavable. The Enderstruder documentation specifically mentions Hamilton glass autoclavable syringes as a supported alternative to disposable BD syringes for this reason.

UV Crosslinking Module for GelMA

If GelMA is on the roadmap, a 365 nm UV LED module needs to be integrated into the build. The simplest implementation is a commercially available 365 nm UV LED array (available from electronics distributors for $15–30 USD) mounted on a 3D-printed bracket attached to the Ender 3's Z-axis uprights or X-carriage. It should be wired to a spare output pin on the mainboard (Klipper can control it as a fan output), allowing layer-by-layer UV crosslinking to be triggered from G-code. The LED should be positioned 20–40 mm above the build plate, with a measured irradiance of at least 5 mW/cm² at the print surface for effective GelMA crosslinking. Lower-intensity sources require proportionally longer exposure times.

Recommended Build and Bill of Materials

Based on the full literature review, here is the most practical and cost-effective build for a first biogel printer conversion.

Bill of Materials

• Creality Ender 3 V2 or S1 — $200–280 (or use an existing printer)
• Enderstruder kit components — ~$55: 3D-printed housing (print yourself), NEMA 17 motor (often spare from printer), 10 mL BD syringes ($0.29 ea), M3 hardware, 300 mm linear rail MGN9H
• SKR Mini E3 v3 mainboard — $30 (recommended upgrade; stock 8-bit board is workable but limited)
• Raspberry Pi 4 (2 GB) + microSD — $50
• PT1000 temperature sensor + MAX31865 amplifier — $12
• 12 V silicone heater tape (5 W, 10 cm) — $8
• TPU filament for insulating collar (50 g) — $5
• SSR (Solid State Relay) for heater control — $8
• Optional — 365 nm UV LED array (for GelMA) — $20
• Optional — acrylic sheet for enclosure, HEPA fan, UV LED strips — $60
• Total: ~$240–390 USD depending on options, not counting an existing Ender 3

Build Sequence

The two steps highlighted in the roadmap (thermal system assembly and PID calibration) are where the majority of time and iteration happens. Budget at least a full day for the thermal system and another half-day for Klipper configuration and PID tuning before attempting a first print.

First Print Recommendation

Start with Pluronic F-127 at 25% w/v for initial calibration — it requires no crosslinking chemistry, no UV hardware, and its thermal response (liquid in syringe at room temperature, instant gelation on a 37 °C build plate) makes it extremely easy to verify that the temperature system is working correctly. A simple grid or lattice structure is the ideal first print geometry. Once you can produce consistent, uniform filaments with no oozing between moves and good layer adhesion, move on to alginate and then to your target bioink.

Key References

The following peer-reviewed sources were the primary basis for this guide. All are open-access or available via institutional access.

• Enderstruder — HardwareX 2024 (doi:10.1016/j.ohx.2024.e00004)
• Replistruder 4 — HardwareX 2021 (doi:10.1016/j.ohx.2020.e00079)
• Printess (Stanford) — bioRxiv / 3Dnatives, February 2025
• Ender 3 V2 bioprinter conversion — PMC / HardwareX 2022 (PMC9041258)
• FRESH bioprinting — Science Advances 2015 (doi:10.1126/sciadv.1500758)
• Optimising printhead thermal design — Micromachines 2024 (PMC11356115)
• Temperature and humidity PID for bioprinter enclosure — Micromachines 2020 (PMC7698131)
• GelMA bioink printability + cell viability — Polymers 2024 (PMC11124935)
• Pluronic F-127 bioprinting protocol — Allevi/Cellink open protocol library
• DIY coaxial bioprinter for soft hydrogels — Scientific Reports 2025 (doi:10.1038/s41598-025-06478-9)