Myocardial infarction (MI) is responsible for millions of deaths every year worldwide. Biomaterials and regenerative therapies may have the capacity to treat this disease. Conjugated polymers are of particular interest for treating MIs, primarily for their potential ability to improve signal transduction and reduce arrhythmias that occur in the insulating fibrotic tissue that forms following an MI. However, such materials need further optimisation to be applicable as a cardiac patch. Herein the need for improved mechanical properties, particularly the magnitude and anisotropy of effective stiffness, is addressed by the auxetic micropatterning of a cardiac patch. Auxetic materials are those with a negative Poisson's ratio, they expand laterally when stretched longitudinally and have the potential to enhance biomaterial conformability. High precision micropatterning into a chitosan-polyaniline composite was achieved through excimer laser microablation. This produces a repeating, re-entrant honeycomb design with scalable feature sizes (20 to 480 µm). Tensile tests show that the magnitude (E: 140 ± 40 kPa to 2.8 ± 0.5 MPa) and anisotropic ratio of the effective stiffnesses (EY/EX: 0.8 to 5.6) can be tuned to match the values of the native heart by modifying pattern dimensions. These auxetic cardiac patches display conductivity (10-2 S/cm) and cytocompatibility. Consequently, ex vivo studies found that the auxetic cardiac patches had no detrimental effect on the electrophysiology of both healthy and MI native rat heart tissue. In addition, a biomechanical rig was designed and built to enable a novel ex vivo technique, which has shown that patterning the patches improves their conformability to native heart tissue movements. Most notably, the work in this thesis describes a versatile and sophisticated method to control and tune the mechanical properties of a biomaterial, whilst maintaining the bulk properties of the material. This in turn could lead to improved biomaterial design for treating MIs.