Design and fabrication of piezoelectric cardiac patches with auxetic geometry for myocardial repair

Myocardial infarction (MI) is a major contributor to global mortality, impairing heart function by inducing extensive loss of cardiomyocytes and isolation of the remaining cells within a fibrotic scar tissue. Among emerging regenerative pathways, cardiac patches represent a promising approach for myocardial regeneration, as studies have demonstrated their capacity to support cellular regeneration by providing mechanical reinforcement or facilitating electrical conductivity. However, many existing designs fail to integrate both functionalities, which are essential for optimal cardiac tissue repair. Piezoelectric materials are particularly suited for this purpose, due to their ability to generate electrical fields in response to mechanical actuation, and the potential to adapt to match the anisotropic motion of the cardiac chambers. This research project aims to achieve the integration of both an auxetic patch geometry and piezoelectric functionality in a cardiac patch with tuneable properties, with the dual goal of establishing a pipeline for comparing auxetic designs and laying the groundwork towards the integration of piezoelectric properties. Medical-grade polycaprolactone (PCL) patches were fabricated via melt electrowriting (MEW) to determine how printing and geometric parameters affect mechanical properties, assessed through monotonic tensile testing. Specifically, patches with varying layer counts and mesh sizes were compared using Young’s modulus and Poisson’s ratio as key metrics. A custom MATLAB application was developed to extract the Poisson’s ratio of the meshes from videos acquired during mechanical testing. As both the number of layers and mesh size had an impact on the Young’s modulus, the mechanical performance of different auxetic geometries (lozenge truss, arrowhead and missing rib) was finally evaluated by testing patches of the same dimensions and layer count. Piezoelectricity was introduced by coating the patches with polyvinylidene fluoride (PVDF) or polyvinylidene fluoride - hexafluoropropylene (PVDF-HFP) using a dip coating technique. Both coated and uncoated patches were subjected to cyclic and monotonic uniaxial testing, as well as scanning electron microscopy (SEM). Imaging before and after stretching assessed the stability of the coating, which persisted up to 40% strain. Piezoelectric properties were characterized using Fourier-transform infrared spectroscopy (FTIR), confirming the presence of the piezoelectric β phase in the PVDF. To assess cytocompatibility of the materials, indirect MTT assays were performed on human induced pluripotent stem cell (iPSC) - derived fibroblasts and primary human macrophages. In conclusion, this project offers valuable insight into the fabrication and mechanical characterization of melt electrowritten auxetic patches, while establishing a foundation for the integration of piezoelectric functionality. These findings provide a framework for advancing multifunctional cardiac patches in future regenerative applications.