In this work, a set of well-defined linear triblock copolymers and star block copolymers (3 and 4-arms) with semi-crystalline blocks consisting of poly(ethylene oxide) (PEO) and poly(ε-caprolactone) (PCL), synthesized by combining ring-opening polymerization and organic catalyst switch strategy, were studied as thermosensitive gel-forming biomaterials for applications in 3D extrusion printing. The hydrogels derived from linear copolymers underwent a temperature-dependent sol–gel–sol transition, behaving as a flowing sol at room temperature and transforming into a non-flowing gel upon heating. On the other hand, the hydrogels derived from 4-arm star block copolymers experienced a gel-sol transition and did not flow at room temperature. This behavior allowed them to be used as 3D printing inks at room temperature. 3D printing results revealed that the semi-crystalline hydrogels of the 4-arm star block copolymers could not only be extruded and printed with high shape fidelity, but they also exhibited a favorable dissolution profile for their use as sacrificial biomaterial inks. Additionally, we thoroughly investigated the crystalline organization of the PCL and the PEO blocks within the hydrogels through comparison with the results obtained in bulk. The results demonstrated evident structural ordering in the hydrogels associated with the crystallization of the PCL blocks. Unexpectedly, DSC results combined with SAXS experiments revealed the presence of PEO block crystals within the 30 % w/v hydrogels from 4-arm star block copolymers, in addition to the PCL block crystals. Hence, remarkable double crystalline hydrogels have been obtained for the first time.

This research was financially supported by the projects PID2020- 113045GB-C21 and PID2020-113045GB-C22 funded by MCIN/ AEI /10.13039/501100011033 and by the Basque Government through grant IT1503-22. M.I.P. acknowledges funding through an FPI contract (PRE2018-086104) to develop a PhD thesis. The support of the ALBA (2022086944 and 2022086957 proposals) synchrotron facility is gratefully acknowledged. R.H. is a member of the CSIC Interdisciplinary Thematic Platform (PTI+) Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy+ (PTI-SusPlast+) and the PTI CSIC FAB3D. The authors would also like to thank Alejandro Hernandez-Sosa for assistance regarding 3D printing experiments. P.Z., V.L., and N.H. gratefully acknowledge the support of the King Abdullah University of Science and Technology (KAUST).