An open-source 3D printing system enabling in-situ freeze-thaw processing of hydrogels

Hydrogels are widely used in tissue engineering and scaffold fabrication due to their excellent biocompatibility, while 3D printing excels at creating complex architectures. Among various techniques, low-temperature extrusion-based 3D printing has shown promise for hydrogel scaffold fabrication, as rapid solidification under controlled cooling can improve shape retention during deposition. However, commercial low-temperature DIW systems are often expensive, closed-source, and difficult to customize. Moreover, most require a two-step post-processing workflow involving external freeze-thaw cycles, which can damage structures through mechanical disturbance and temperature gradients, increasing contamination risk. To address these issues, we developed a low-cost, open-source low-temperature 3D printing platform by modifying a commercial FDM printer with custom hardware and upgraded software. It maintains stable - 30 °C ± 1 °C and supports in-situ freezing and freeze-thaw processing. Using a Poly(vinyl alcohol)-lignosulfonate sodium-TEMPO-oxidized cellulose nanofibrils (PVA-LS-TOCNF) hydrogel as the model ink, we achieved stable printing of various patterns and mechanical test specimens, with tensile properties comparable to those from ex-situ freeze-thaw methods. Overall, this platform significantly lowers barriers to low-temperature hydrogel 3D printing and improves accessibility.