Part 4 of #developmentchallenges. This week I am working on trying to dry a solvent-cast printed construct. The drying goal is to remove as much as possible of the residual solvent without damaging the construct.

The challenge I am facing is not to get it done but to get it done efficiently, repeatably, and prevent contamination. Let me explain the challenge. The solvent needs to be evaporated when you have printed a construct using a polymer dissolved in a solvent. When this happens too fast, bubbles are created. We want to avoid as much bubble creation. This can be done by ensuring the evaporation is done very slowly. Drying at 1 atm in the air using a cooled print bed results in sufficiently slow evaporation and very limited bubble forming. However, doing this in the air stream of the fume hood might contaminate the product with airborne particles. Further, it takes a lot of time, and the process is depending on the environmental temperature, which varies from summer to winter.  So not Efficient, not repeatable (over the year) and not free of potential contamination.

Keeping samples in a vacuum oven is safer and evaporation faster. We are currently experimenting with a very slow vacuum ramp. Keep the sample a long time at slightly reduced pressure (e.g. 900 mbar) before moving to full vacuum. The vacuum oven has a thermoshelf (a shelf that can be heated but not cooled). At the beginning of the process, I keep the shelf at room temperature and only later in the process do I increase it.  You want eventually evaporate as much of the solvent present as possible. The process of removing the solvent residues can be improved with a washing process, but then you introduce a new solvent (ethanol) and water. Working with water in cleanrooms is not preferred due to microorganisms that blossom well in water.

This is a post in a series about our daily #developmentchallenges and #productionchallenges at Vosfox Medical. We perform process development, validations and regular production of medical devices for our customers. Our speciality is low-volume production such as Medical 3D printing. Please visit for general information, Contract Manufacturing for information about sterilization services, or Services for information about sterilization validation.

Source: Bakrani Balani et al. (2021). Processes and materials used for direct writing technologies: A review. Results in Engineering.11.100257.10.1016.


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