Thermoset polymers are known for their superior thermomechanical properties, but the chemical crosslinking typically leads to intractability. This is reflected in the great differences between thermoset and thermoplastic shape-memory polymers; the former exhibit a robust shape memory but are not capable of redefining the permanent shape. Contrary to current knowledge, we reveal here that a classical thermoset shape-memory polyurethane is readily capable of permanent reshaping (plasticity) after a topological network rearrangement that is induced by transcarbamoylation. By employing the Jianzhi technique (also known as kirigami), unexpected shape-shifting versatility was observed for this otherwise classical material. As the essential carbamate moiety in polyurethanes is one of the most common polymer building units, we anticipate that our finding will have significant benefits beyond shape shifting.

Peripheral neuromodulation has been widely used throughout clinical practices and basic neuroscience research. However, the mechanical and geometrical mismatches at current electrode-nerve interfaces and complicated surgical implantation often induce irreversible neural damage, such as axonal degradation. Here, compatible with traditional 2D planar processing, we propose a 3D twining electrode by integrating stretchable mesh serpentine wires onto a flexible shape memory substrate, which has permanent shape reconfigurability (from 2D to 3D), distinct elastic modulus controllability (from ~100 MPa to ~300 kPa), and shape memory recoverability at body temperature. Similar to the climbing process of twining plants, the temporarily flattened 2D stiff twining electrode can naturally self-climb onto nerves driven by 37°C normal saline and form 3D flexible neural interfaces with minimal constraint on the deforming nerves. In vivo animal experiments, including right vagus nerve stimulation for reducing the heart rate and action potential recording of the sciatic nerve, demonstrate the potential clinical utility.

Thermoset shape memory polymer (SMP) with dynamic covalent bonds in the network is a new class of SMPs for which the permanent shape can be reconfigured via topological rearrangement (plasticity). Catalyzed transcarbamoylation has recently been established as an effective exchange reaction for plasticity in cross-linked polyurethane networks. However, ensuring the plasticity severely constrains the network design which adversely affects the ability to tune other classical shape memory properties for practical applications. Facing this new challenge, we design an amorphous polyurethane system for which the cross-linking density can be adjusted in a wide range. We discovered that the use of an aromatic diisocyanate in the synthesis of the polyurethanes facilitates achieving plasticity without requiring any catalyst. The overall network design leads to tunable recovery stress and shape memory transition temperatures without sacrificing the plasticity. The versatility of our polyurethane SMP is further reflected in its triple-shape memory performance. We anticipate that our tunable polyurethanes will benefit a variety of potential SMP device applications.