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In Langmuir : the ACS journal of surfaces and colloids

In recent years, flexible and sensitive pressure sensors are of extensive interest in healthcare monitoring, artificial intelligence and national security. In this context, we report the synthetic procedure of a 3D metal-organic framework (MOF) comprising with cadmium (Cd) metals as nodes and isoniazid (INH) moieties as organic linkers (CdI2-INH=CMe2) for designing self-polarized ferroelectret based highly mechano-sensitive skin sensor. The as synthesized MOF preferentially nucleate stable piezoelectric β-phase in poly(vinylidene fluoride) (PVDF) and also give rise to a porous ferroelectret composite film. Benefiting from the porous structure of 3D MOF, composite ferroelectret film based ultra-sensitive pressure sensor (mechano-sensitivity of 8.52 V/kPa within 1kPa of pressure range) as well as high throughput (e.g., power density of 32 W/cm2) mechanical energy harvester (MEH) has been designed. Simulation based finite element method (FEM) analysis indicating that geometrical stress confinement effect within the inter-pore region of the ferroelectret structure synergistically influences the mechano-electrical property of the MEH. In addition, 143 pC/N (~ 4.5 times higher than commercial piezoelectric PVDF film) of piezoelectric charge coefficient (d33) magnitude and superior response time (tr~8 ms) of this composite ferroelectret film enable to detect different physiological signals such as coughing, pronunciation, gulping behaviour makes it a promising candidate for early intervention of healthcare which may play a significant role in accurate alert of influenza and chronic obstructive pulmonary disease (COPD) related symptoms. In addition, MEH enables to track the subtle pressure change in wrist pulse that indicates its usefulness of effective mechano-sensitivity. Since the cardiovascular signal is one of the vital parameter that can determine the on-going physiological conditions, thus the wireless transmission of the detected wrist pulse signal has been demonstrated. All these features coupled with wireless data transmission indicate the promising application of MOF assisted composite ferroelectret film in non-invasive real time remote heath care monitoring.

Roy Krittish, Jana Srikanta, Ghosh Sujoy Kumar, Mahanty Biswajit, Mallick Zinnia, Sarkar Subrata, Sinha Chittaranjan, Mandal Dipankar