Mallet finger is a common athletic injury, and the current treatment involves fixing the injured finger by a splint
or orthosis. 3D printing technology offers an innovative way to customize patient-specific finger orthosis that fits
the individual anthropometrics. However, the existing printed materials cannot combine the high stiffness and
toughness to construct an ideal finger orthosis. Herein, we report a new chain extender carrying one amide and
one urea group in the side chain, and utilize it to extend polyurethane prepolymer to fabricate a highly stiff and
tough thermoplastic polyurethane (TPU). Strong and mobile H-bonds in the side chain promote the formation of
multiphase-separated structure in the TPU network, thus endowing this TPU with high Young’s modulus (213.0
± 3.7 MPa) and high toughness (47.8 ± 1.9 MJ m􀀀 3). Due to the dynamic H-bonds in the polymer network, this
TPU exhibits an excellent 3D printing ability, and can be used to print finger orthosis by fused deposition
modeling technology at an elevated temperature. The printed finger orthosis can be attached with a wireless
pulse oximeter by virtue of TPU adhesiveness, thus monitoring vital physiological signals on the injured index
finger that can be well fixed by the stiff orthosis.