Hydrogel Extrusion Troubleshooting Guide

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Every bioink requires specific conditions and printing parameters for an optimal extrusion. Despite differences between materials, problems with correct deposition often stem from the same reasons. Follow our general hydrogel extrusion troubleshooting guide to deal with the most common issues regarding biomaterial extrusion.

extrusion troubleshooting

Hydrogel doesn’t extrude at all.

  • Check if the extruder is pressurized. In the Allevi Bioprint Online Software, go to the Extruders section and check the current pressure reading. 
  • Set the correct pressure and extruder temperature for your hydrogel. Make sure that the correct needle is attached. You can find the right settings in our Bioprinting Parameters Cheat Sheet.
  • Make sure that the air compressor is properly connected. The printer can manage excess pressure from the source, but it cannot compensate for insufficient input. If your extruder cannot reach the target pressure due to inadequate supply, your printer will stop active pressure control and turn on a red error light.
  • Click and hold the Extrude button in the Software under Pressure settings to test the extrusion. 
  • Make sure that the nozzle is not clogged. You can try increasing the pressure slightly and holding the Extrude button for a few seconds. If this doesn’t clear the nozzle use a fresh one. In the case of Hyperelastic Bone, you can follow our Cleaning Protocol.
  • Make sure that you insert the rubber stopper into the syringe barrel. Printing without the rubber stopper may displace the material on the walls of the syringe preventing it from extruding. 
  • If you have problems extruding a biomaterial that is not listed in our Bioprinting Parameters Cheat Sheet, follow general Printer Parameter Optimization and the Guide to Picking Your Needle

Hydrogel over-extrudes.

  • Decrease the pressure and test it with the Extrude button in the Software under Pressure settings.
  • Use a longer needle or a nozzle with a larger gauge size. Follow our Guide to Picking Your Needle for more detailed instructions. 
  • Increase the printing speed. Faster extrusion movement can compensate for a too-high material deposition rate. 
  • If you have problems extruding a biomaterial that is not listed in our Bioprinting Parameters Cheat Sheet, follow general Printer Parameter Optimization

Extrusion is uneven.

  • Check if the extruder is pressurized. In the Allevi Bioprint Online Software go to the Extruders section and check the current pressure reading. 
  • Set the correct pressure and extruder temperature for your hydrogel. Make sure that the correct needle is attached. You can find the right settings in our Bioprinting Parameters Cheat Sheet
  • Make sure that the air compressor is supplying more air pressure to the printer than you are requesting at the extruder! The printer can manage excess pressure from the source, but it cannot compensate for insufficient input. If your extruder cannot reach the target pressure due to inadequate supply, your printer will stop active pressure control and turn on a red error light.
  • Click and hold the Extrude button in the Software under Pressure settings to test the extrusion. 
  • Make sure that the nozzle is not clogged. You can try increasing the pressure slightly and holding the  Extrude button for a few seconds. If this doesn’t clear the nozzle use a fresh one. In the case of Hyperelastic Bone, you can follow our Cleaning Protocol
  • Make sure that you insert the rubber stopper into the syringe barrel. Printing without the rubber stopper may displace the material on the walls of the syringe preventing it from extrusion. 
  • Check if there are any bubbles in the hydrogel. Air trapped in the material may cause uneven extrusion. Remove the bubbles and try printing again.
  • If you have problems extruding a biomaterial that is not listed in our Bioprinting Parameters Cheat Sheet, follow general Printer Parameter Optimization and the Guide to Picking Your Needle.

Hydrogel stops extruding during the printing.

  • Make sure that you didn’t run out of the hydrogel in the syringe.
  • Check if the extruder is pressurized. In the Allevi Bioprint Online Software go to the Extruders section and check the current pressure reading.
  • Make sure that the air compressor is always on during the printing and that it is supplying more air pressure to the printer than you are requesting at the extruder.
  • Check if the needle is not clogged. Click and hold the Extrude button in the Software under Pressure settings. If nothing comes out, increase the pressure slightly and test Extrusion again. Sometimes immersing the needle in PBS helps to remove the clot.  
  • Replace the needle with a fresh one. 
  • If the clogging issue is persistent, try a nozzle with a smaller gauge size. You can read more about that in our Guide to Picking Your Needle
  • In the case of photocurable hydrogels, UV/Blue light might be crosslinking the material in the needle before it is extruded. Make sure that you use an opaque nozzle to protect the hydrogel from the exposure to the light prematurely.

Hydrogel doesn’t support its shape.

  • Hydrogels with low viscosity are difficult to pattern due to spreading on the build surface after deposition. You can try one of the following solutions:
    • Increase the percentage of your hydrogel if possible. Some hydrogels display better mechanical properties in higher concentrations. 
    • Apply FRESH bioprinting method to provide support and crosslinking during printing low viscosity materials. 
    • If applicable, use coaxial bioprinting to provide quick crosslinking upon deposition of the material. 
    • Apply sacrificial materials as a mechanical support for your target biomaterial while it is crosslinking. Use for example Pluronic or Carbohydrate Glass
    • Mix your hydrogel with another one to provide means for quick crosslinking. For example, mixing low viscosity sodium alginate with GelMA results in an interpenetrated polymer network that can be rapidly crosslinked using light with a subsequent ionic crosslinking of sodium alginate. 

Hydrogel doesn’t adhere to the print surface.

The first printed layer is uneven.

  • Set the correct pressure and extruder temperature for your hydrogel. Make sure that the correct needle is attached. You can find the right settings in our Bioprinting Parameters Cheat Sheet
  • Check the gap between the needle and your printing surface. If the needle is too close it will limit the extrusion. If the distance is too big, the material won’t reach the surface and may start curling on the needle or create drops. This distance can be modified by changing the layer height setting in the Current Print settings in the software.
  • Make sure there is no z-offset set in your gcode. This may override your z-height calibration settings. 
  • If the first layer looks uneven, it might mean that your surface is not flat. Even small differences can result in sub-optimal results. Make sure you are using dishes or well plates with a flat bottom. In general – bigger Petri dishes tend to be concave. Becuase of this, we recommend using smaller dishes, well plates, or glass surfaces such as microscope glass slides. 

The reproducibility of printed line geometry is poor.

  • Always use a fresh needle. If you are using a reusable nozzle make sure it’s clean and not damaged. 
  • Confirm that the pressure is stable. In the Allevi Bioprint Online Software go to the Extruders section and check the current pressure reading. 
  • Always load the same volume of the hydrogel into the printing syringe. Loading different volumes may result in variance between prints.  

If you still have problems printing your material contact our Allevi Support Team at [email protected]

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