| Summary: | Novel tough hydrogel materials are required for 3D-printing applications. Here, a series of thermoplastic polyurethanes (TPUs) based on poly(ɛ-caprolactone)-<i>b</i>-poly(ethylene glycol)-<i>b</i>-poly(ɛ-caprolactone) (PCL-<i>b</i>-PEG-<i>b</i>-PCL) triblock copolymers and hexamethylene diisocyanate (HDI) were developed with PEG contents varying between 30 and 70 mol%. These showed excellent mechanical properties not only when dry, but also when hydrated: TPUs prepared from PCL-<i>b</i>-PEG-<i>b</i>-PCL with PEG of Mn 6 kg/mol (PCL<sub>7</sub>-PEG<sub>6</sub>-PCL<sub>7</sub>) took up 122 wt.% upon hydration and had an E-modulus of 52 ± 10 MPa, a tensile strength of 17 ± 2 MPa, and a strain at break of 1553 ± 155% in the hydrated state. They had a fracture energy of 17976 ± 3011 N/mm<sup>2</sup> and a high tearing energy of 72 kJ/m<sup>2</sup>. TPUs prepared using PEG with Mn of 10 kg/mol (PCL<sub>5</sub>-PEG<sub>10</sub>-PCL<sub>5</sub>) took up 534% water and were more flexible. When wet, they had an E-modulus of 7 ± 2 MPa, a tensile strength of 4 ± 1 MPa, and a strain at break of 147 ± 41%. These hydrogels had a fracture energy of 513 ± 267 N/mm<sup>2</sup> and a tearing energy of 16 kJ/m<sup>2</sup>. The latter TPU was first extruded into filaments and then processed into designed porous hydrogel structures by 3D-printing. These hydrogels can be used in 3D printing of tissue engineering scaffolds with high fracture toughness.
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