Abstract
This paper presents flexible pressure sensors based on free-standing and biodegradable glycine–chitosan piezoelectric films. Fabricated by the self-assembly of biological molecules of glycine within a water-based chitosan solution, the piezoelectric films consist of a stable spherulite structure of β-glycine (size varying from a few millimeters to 1 cm) embedded in an amorphous chitosan polymer. The polymorphic phase of glycine crystals in chitosan, evaluated by X-ray diffraction, confirms formation of a pure ferroelectric phase of glycine (β-phase). Our results show that a simple solvent-casting method can be used to prepare a biodegradable β-glycine/chitosan-based piezoelectric film with sensitivity (∼2.82 ± 0.2 mV kPa–1) comparable to those of nondegradable commercial piezoelectric materials. The measured capacitance of the β-glycine/chitosan film is in the range from 0.26 to 0.12 nF at a frequency range from 100 Hz to 1 MHz, and its dielectric constant and loss factor are 7.7 and 0.18, respectively, in the high impedance range under ambient conditions. The results suggest that the glycine–chitosan composite is a promising new biobased piezoelectric material for biodegradable sensors for applications in wearable biomedical diagnostics.
Highlights
With the advent of wearable systems for health monitoring, there is a tremendous need for the development of biodegradable self-powered devices to monitor the physiological state.[1,2] To this end, piezoelectric materials are appealing as they can generate electrical charges under mechanical stress and can be used for force/pressuresensing applications.[3]
We observed that the substrate did not have any effect on the film properties, and the film grown on different substrates with the same concentration of glycine had a similar morphology
For a higher ratio of glycine:chitosan (2.7:1), thick fibrillar crystalline regions of glycine are observed in amorphous regions of chitosan, and they are randomly oriented in the film (Figure. 2e)
Summary
With the advent of wearable systems for health monitoring, there is a tremendous need for the development of biodegradable self-powered devices to monitor the physiological state.[1,2] To this end, piezoelectric materials are appealing as they can generate electrical charges under mechanical stress and can be used for force/pressuresensing applications.[3]. Most of the research far has focused on stabilization of the polymorphs with techniques such as crystal growth in nanoscale crystallization chambers,[18,19] on patterned substrate,[20] or on Pt-coated Si substrates.[21] In all of these reported methods, the β-crystals were micro/nanoscale and/or are usually in a mixture with the other phases of glycine In another recent work, piezoelectricity/ferroelectricity on selfassembled microislands of β-glycine on the Si substrate has been reported.[22] the reported microcrystals were quite stable and grown on the same crystallographic direction, it is difficult to use them for any device fabrication due to their small size and stability while in contact with the rigid silicon substrate. The flexible biodegradable piezoelectric films were used as functional materials in the piezoelectric sensors, and their sensitivity was measured under dynamic pressure (5−60 kPa)
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