The contingent circumstance for the return to mathematics concerns one of the last challenges in engineering sciences: we mean the effort to design metamaterials (or architectured materials). Actually such a challenge can be formulated as follows: to find a way for building a material whose behaviour is specified a priori via some specific demands. We are talking about: materials on demand. How can we characterise the peculiar behaviour of a specifically demanded material? Simply by specifying the equations that must govern the behaviour of such a material. In other words: if the synthesis of metamaterials consists in finding the way to construct fabrics whose global behaviour is tailored for a specific application or requirement, we specify such requirement or behaviour by means of the governing equations which we impose to be valid to describe the desired material. Therefore the old problem of synthesis of electronic circuits for obtaining analogic computers finds a renewed life in a slightly different context. It can be reformulated as follows: Given the governing equations one has to find the microstructure that describe them macroscopically. The parallel development of 3D printing technologies made this endeavour realizable also in practice. Some theoretical, experimental and numerical results will be presented: they show how the "ancient" theory of generalized continua finds new, beautiful and promising applications. In particular the exotic behaviour of pantographic structures is described and analyses.