The trade-off between processability and functional responses presents significant challenges for incorporating piezoelectric materials as potential 3D printable feedstock. Structural compliance and electromechanical coupling sensitivity have been tightly coupled: high piezoelectric responsiveness comes at the cost of low compliance. Here, the formulation and design strategy are presented for a class of a 3D printable, wearable piezoelectric nanocomposite that approaches the upper bound of piezoelectric charge constants while maintaining high compliance. An effective electromechanical interphase model is introduced to elucidate the effects of interfacial functionalization between the highly concentrated perovskite nanoparticulate inclusions (exceeding 74 wt%) and light-sensitive monomer matrix, shedding light on the significant enhancement of piezoelectric coefficients. It is shown that, through theoretical calculation and experimental validations, maximizing the functionalization level approaches the theoretical upper bound of the piezoelectric constant d 33 at any given loading concentration. Based on these findings, their applicability is demonstrated by designing and 3D printing piezoelectric materials that simultaneously achieve high electromechanical sensitivity and structural functionality, as highly sensitive wearables that detect low pressure air (<50 Pa) coming from different directions, as well as wireless, self-sensing sporting gloves for simultaneous impact absorption and punching force mapping.barium titanate (BTO) [5] are the most frequently used piezoelectric ceramic materials for transducer applications. Direct 3D printing of piezoelectric-polymer composites offers a promising solution to fabricating complex piezoelectrics beyond conventional ceramic processing methods which require extensive, time-consuming sintering, may have residual porosity, and have brittle responses. However, due to the functionality-processability tradeoff, the resulting piezoelectric response of the printed nanocomposite is over two ordersof-magnitude lower than pure ceramic. [6] Increasing particle concentration leads to agglomeration, [7] high viscosity, [8] and significant light absorption, [9] making it difficult to manufacture fully complex microarchitectures or free form-factors. Additionally, the incompatibilities between high stiffness nanoparticle and low stiffness polymer, resulting in poor interfacial adhesion, [10] reduce stress transfer efficiency from the polymer matrix to the piezoelectric inclusions, and suppress the functional performance. Increasing the matrix stiffness was previously shown to be key to enhancing piezoelectric response, [11] but it remains unclear if highly-responsive flexible piezoelectric materials are possible.Recent studies have explored surface functionalization of a low concentration of BTO nanoparticles (below 2 vol%, i.e., 10 wt%) to covalently bind them to the polymer matrix, and have demonstrated appreciable enhancement of the piezoelectric coefficient 3D Printed Nanocomposi...
