Recent Advances in Organic Piezoelectric Biomaterials for Energy and Biomedical Applications

Abstract

The past decade has witnessed significant advances in medically implantable and wearable devices technologies as a promising personal healthcare platform. Organic piezoelectric biomaterials have attracted widespread attention as the functional materials in the biomedical devices due to their advantages of excellent biocompatibility and environmental friendliness. Biomedical devices featuring the biocompatible piezoelectric materials involve energy harvesting devices, sensors, and scaffolds for cell and tissue engineering. This paper offers a comprehensive review of the principles, properties, and applications of organic piezoelectric biomaterials. How to tackle issues relating to the better integration of the organic piezoelectric biomaterials into the biomedical devices is discussed. Further developments in biocompatible piezoelectric materials can spark a new age in the field of biomedical technologies.

Keywords: biomaterials; biomedical applications; energy applications; organic materials; piezoelectric materials.

Figure 1

Piezoelectricity in the organic piezoelectric biomaterials. (a) Molecular origin of the piezoelectric effect in collagen. Reproduced with permission from [20]. Copyright American Chemical Society, 2016. (b) Schematic illustration of piezoelectric M13 bacteriophage. Reproduced with permission from [27]. Copyright The Royal Society of Chemistry, 2015. (c) Unit cell of β-glycine crystal has two molecules, where two molecular dipole moments form the net dipole moment along the z-axis. Reproduced with permission from [40]. Copyright Nature Publishing Group, 2019. (d) Unit cell and molecular packing of diphenylalanine. Reproduced with permission from [44]. Copyright Wiley–VCH, 2001. (e) Structures of non-piezoelectric (α-phase) and piezoelectric (β-phase) poly(vinylidene fluoride) (PVDF). Reproduced with permission from [2]. Copyright Wiley–VCH, 2018. (f) Molecular structure of poly(L-lactic acid) (PLLA) chain. Reproduced with permission from [2]. Copyright Wiley–VCH, 2018.

Figure 2

Applications of organic piezoelectric biomaterials in energy harvesting. (a) Schematic of sustainable energy harvesting and battery-free humidity sensor using biocompatible collagen nanofibrils. The collagen nanofibrils deposited on cotton cloth serve as a humidity sensor by measuring current signal at a fixed bias voltage. In order to demonstrate the self-powered sensing system, the energy harvester comprising collagen nanofibrils film sandwiched between Al electrodes is parallelly connected to the humidity sensor. Reproduced with permission from [77]. Copyright American Chemical Society, 2018. (b–d) Vertical self-assembly of polarized M13 bacteriophage nanostructure for energy harvesting. Reproduced with permission from [28]. Copyright American Chemical Society, 2019. (b) 3D-atomic force microscope (AFM) topography image of vertically aligned M13 bacteriophages. (c) Piezoresponse force microscope amplitude image corresponding to the 3D–AFM topography image. (d) The direction of polarization of the vertically aligned M13 bacteriophage with specific binding between the 6H tag on phage tail and the Ni-nitrilotriacetic acid (NTA) substrate. (e,f) Insole pedometer with piezoelectric energy harvester. Reproduced with permission from [85]. Copyright IEEE, 2012. (e) Schematics of the proposed insole pedometer. The pieces of PVDF sheet are used for the piezoelectric energy harvester as well as the pulse generator to detect steps in which each PVDF piece was rolled to increase the total area. The organic circuits are integrated with PVDF pieces to count the number of steps. (f) Photograph of the prototype insole pedometer.

Figure 3

Applications of organic piezoelectric biomaterials in sensors. (a–c) Flexible piezoelectric nanogenerator in a wearable, self-powered active sensor for healthcare monitoring. Reproduced with permission from [89]. Copyright IOP Publishing, 2017. (a) Photographs of the flexible piezoelectric nanogenerator. (b) hand gesture sensing. (c) human voice recording. (d,e) Electronic skins for discriminating static/dynamic pressure stimuli. Reproduced with permission from [91]. Copyright The American Association for the Advancement of Science, 2015. (d) Schematic illustration of flexible and multimodal ferroelectric e-skin. (e) The waveform and short-time Fourier transform (STFT) signals of the sound source, readout signals from the interlocked e-skin, and microphone.

Figure 4

Applications of organic piezoelectric biomaterials in cell and tissue regenerations. (a) Representative gross images and histological images of scaffolds after 28 days undergoing chondrogenesis in dynamic conditions. As-spun PVDF–TrFE (left), annealed PVDF–TrFE (middle) and polycaprolactone (right) scaffolds. Reproduced with permission from [98]. Copyright Elsevier, 2017. (b–d) Ultrasound-mediated piezoelectric differentiation of neuron-like PC12 cells on PVDF membranes. Reproduced with permission from [100]. Copyright Nature Publishing Group, 2017. (b) Schematic of ultrasound stimulation of the piezoelectric β-PVDF membrane. (c) Comparison images of PC12 cells cultured under mechanical stimuli on PVDF substrate and neuronal growth factor stimuli. (d) Comparison of average neurite length of PC12 cells.