Flexible Nanoconfined Thin Films for Biosensing and Implantable Energy Generation

Sponsored by: NSF ECCS awards.

Cardiovascular disease is the number one killer in the US and worldwide. Consequently, there is an upsurge in the various novel devices to diagnose, monitor, and treat cardiovascular disease. With the emergence of micro-electro mechanical systems (MEMS) based low-power consuming sensors and implants, we have developed three projects relevant to nanomaterials based pressure sensors and power harvesters.

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(1) Nanostructures of PVDF-TrFE (polyvinyledenedifluoride-tetrafluoroethylene), a semi-crystalline polymer with high piezoelectricity, results in significant enhancement of crystallinity and better device performance as sensors, actuators and energy harvesters. Using electrospinning of PVDF to manufacture nanofibers, we demonstrate a new method to pattern high-density, highly aligned nanofibers. To further boost the charge transfer from such a bundle of nanofibers, we fabricated novel core-shell structures. Finally, we developed pressure sensors utilizing these fiber structures for endovascular applications. The sensors were tested in-vitro under simulated physiological conditions. We observed significant improvements using core-shell electrospun fibers (4.5 times gain in signal intensity, 4000µV/mmHg sensitivity) over PVDF nanofibers (280µV/mmHg). The preliminary results showed that core-shell fiber based devices exhibit nearly 40 fold higher sensitivity, compared to the thin film structures demonstrated earlier.

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(2) We demonstrate that nanostructured thin films play a significant role in compact energy harvesting Polyvinylidene fluoride (PVDF) nanogenerators. In this work, we introduced a surface control technique for preparing mesoporous PVDF thin films towards high piezoelectric output. We demonstrated that the morphology of the film could be controlled by varying the solvent evaporation rate. The material crystallinity was experimentally confirmed by X-ray diffraction (XRD) and differential scanning calorimeter (DSC) measurement. The porous PVDF surface significantly increased the compressibility and charge collecting area which contribute to the significant output enhancement. The piezoelectric output increased 100% with the modified mesoporous layer. The charging capacity increased 107% compared with the same thickness solid PVDF film.

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3) Implantable Biofuel Cells (iBFCs) have re-gained attention. iBFCs provide superior advantages over conventional batteries by reducing patient costs for battery replacements, providing ease from sterilization and biocompatibility.We use silicon based nanofabrication to construct. The novel design of the iBFC uses mesoporous (nanoporous) silica as a functional membrane and graphene as the cathode material. By varying the physical properties of the mesoporous silica, we can enhance the effective glucose diffusion. Thereby use of such nanomaterials can lead to the better design of more efficient iBFCs. Further we leverage the advantages of an intra-vascular implant to develop sustainable and effective technology.

As advanced nanomaterials, such as nanoporous silica and graphene processing, are becoming semiconductor clean-room friendly, the future holds great promise for the development of mass-producible, high power-density, ultra-thin biosensors and power generators for biomedical implant applications.