Illustration and simulation of RE hexagonal cell deformation under bending moments, and the effect of the re-entrant angle on curvature variation [33]. (a) illustration of the bent RE unit cell with planes along the principal curvature directions. (b) curvature estimation based on Heron's formula. (c) simulation of geometrical change between 60°RE and 120°RE sample under 1 mN load. (d)-(f) effects of internal angle on maximum curvature, minimum curvature and internal angle to the synclastic or anticlastic curvature behavior of samples.