  The propagation of matter waves in curved geometry is relevant for electrons
in nano-wires, solid-state physics structures and atomtronics. Curvature
effects are usually addressed within the adiabatic limit and treated via an
effective potential acting on the manifold to which the particles are strongly
confined. However, the strength of the confinements that can be achieved
experimentally are in practice limited, and the adiabatic approximation
framework often appears too restrictive for the realistic design of relevant
propagation structures. Here, we explore the design of 2D sharply bent
wave-guides for the propagation of matter waves beyond the adiabatic regime.
The bend design, which enables the connection of guide components rotated by an
arbitrary angle and of arbitrary curvatures, rests on an exact
inverse-engineering technique. The resolution of the full 2D Schr\"odinger
equation in curved geometry shows that our method yields reflectionless guides
with a transverse stability improved by several orders of magnitude when
compared to circular guides of similar size.
