Reivindicaciones

1. Method for generating and controlling mechanical stiffness and/or complex strain patterns on biological materials (3) comprising the steps of: - providing a magnetic stimulation device (1); - providing a magneto-responsive substrate (2); - culturing biological material (3) in the magneto-responsive substrate (2); - determining the position of magnets (4) of the magnetic stimulation device (1) for obtaining a defined strain pattern on the biological material (3); - placing the magnets (4) in the position determined by means of at least one motor (5) of the magnetic stimulation device (1); - activating a magnetic stimulation device (1) to generate a complex strain pattern in the magneto-responsive substrate (2) and consequently in the biological material (3). 2. Method according to claim 1, wherein the step of determining the position of magnets (4) of the magnetic stimulation device (1) is performed by simulating the magnetic field obtained as a function of the magnets' (4) position, by using finite element simulations or machine learning algorithms fed by a comprehensive experimental characterization of several magneto-active samples. 3. Method according to claim 2, further comprising the steps of characterizing a magneto-mechanical response of the substrate (2) macroscopically, by using a magneto-mechanical rheometer under uniaxial compression and shear deformation modes, and microscopically, by conducting nanoindentation tests at different rate conditions and using said characterization to simulate the strain pattern generated by the magnetic field obtained. 4. Method according to claim 3, wherein in the step of using said characterization to simulate the strain pattern generated: - fixed boundary conditions are imposed, such that the substrate (2) presents a nonlinear mechanical behavior and suffers a variation in apparent material stiffness; or - free boundary conditions are imposed, such that the substrate (2) mechanically deforms. 5. Method according to claim 3, further comprising the steps of determining a new position of magnets (4) of the magnetic stimulation device (1) for obtaining a modified strain pattern on the biological material (3), once the strain pattern generated is obtained for controlling said strain pattern on the fly and moving the magnets (4) of the magnetic stimulation device (1) to the new position determined. 6. Magneto-mechanical stimulation system for generating complex strain patterns in biological materials (3) comprising: - a magneto-responsive substrate (2) comprising a polymeric matrix and a plurality of micron-size magnetic particles configured to hold biological material (3); - a holder (6) for placing the magneto-responsive substrate (2); - a magnetic stimulation device (1) comprising at least one motor (5) and at least two magnets (4) placed on the holder (6) around the magneto-responsive substrate (2) and configured to generate a complex strain pattern on the biological material (3) by generating a magnetic field which acts over the magneto-responsive substrate (2), wherein the at least one motor (5) is connected to the magnets (4) to displace them; - a computing module (7) to determine the position of the magnets (4) for controlling the magnetic field generated; - an imaging module (8) for measuring the shape of the biological material (3) under the magnetic field generated; and - an interface module for imposing magneto-mechanical dynamic conditions on the computing module (7) by using the measurements obtained from the imaging module (8). 7. Stimulation system according to claim 6, wherein the magneto-responsive substrate (2) is a magnetorheological elastomer (MRE). 8. Stimulation system according to claim 6, wherein the polymeric matrix is made of a magneto-active hydrogel or Dowsil CY52-276 (PDMS), and is filled with micron-size magnetic particles of carbonyl iron powder. 9. Stimulation system according to claim 6, wherein the surface in contact with the cultured cellular system is covered with a collagen coating. 10. Stimulation system according to claim 6, wherein the magnetic stimulation device (1) comprises four independently controllable sets of permanent magnets (4) surrounding the substrate (2), with two sets aligned along an axis, forming two axes which lie orthogonal to control the field in each direction, and a rotation mechanism to allow an azimuthal rotation. 11. Stimulation system according to claim 6, wherein the interface module comprises a 3D finite element module or artificial intelligence algorithms for controlling and predicting the deformation patterns transmitted to the cells during the application of the magnetic field. 12. Stimulation system according to claim 6, further comprising a magneto-mechanical rheometer and/or a nanoindentation system to characterize macroscopically and/or microscopically the substrate (2). 13. Stimulation system according to claim 6, wherein the holder (6) and the imaging module (8) are comprised by an incubator (6). 14. A computer program adapted to perform the steps of the method of any of claims 1 to 5 by using the computing module (7) of the stimulation system of any of claims 7 to 13. 15. A computer readable storage medium comprising the computer program of claim 14.