  Maxwell lattice metamaterials possess a rich phase space with distinct
topological states featuring mechanically polarized edge behaviors and strongly
asymmetric acoustic responses. Until now, demonstrations of non-trivial
topological behaviors from Maxwell lattices have been limited to either
monoliths with locked configurations or reconfigurable mechanical linkages.
This work introduces a transformable topological mechanical metamaterial (TTMM)
made from a shape memory polymer and based on a generalized kagome lattice. It
is capable of reversibly exploring topologically distinct phases of the
non-trivial phase space via a kinematic strategy that converts sparse
mechanical inputs at free edge pairs into a biaxial, global transformation that
switches its topological state. Thanks to the shape memory effect, all
configurations are stable even in the absence of confinement or a continuous
mechanical input. Topologically-protected mechanical behaviors, while robust
against structural (with broken hinges) or conformational defects (up to ~55%
mis-rotations), are shown to be vulnerable to the adverse effects of stored
elastic energy from prior transformations (up to a ~70% reduction in edge
stiffness ratios, depending on hinge width). Interestingly, we show that shape
memory polymer's intrinsic phase transitions that modulate chain mobility can
effectively shield a dynamic metamaterial's topological response (with a 100%
recovery) from its own kinematic stress history, an effect we refer to as
"stress caching".
