Highly piezoelectric biocompatible and soft composite fibers

Abstract

We report the fabrication of highly piezoelectric biocompatible soft fibers containing barium titanate ferroelectric ceramic particles dispersed in electrospun poly lactic acid (PLA). These fibers form mats that have two orders of magnitude larger piezoelectric constant per weight than single crystal barium titanate films. We propose that the observed apparent piezoelectricity results from the electrospinning induced polar alignment of the ferroelectric particles that pole the fibers similar to ferroelectret polymer foams that are poled by corona discharge. Due to the biocompatibility of PLA that encases the ferroelectric particles, these mats can be used in biological applications such as bio-sensors, artificial muscles, and energy harvesting devices.Piezoelectricity (a linear coupling between electric and mechanical signals) was discovered in non centro-symmetric crystals by the Curie brothers in 1880. 1 Since then piezoelectricity has been observed in ceramics, 2 certain synthetic 3 and biological polymers, 4,5 and ferroelectric liquid crystals. 6,7 Today piezoelectric materials are used in ultrasonic and hydroacoustic devices, 8 for frequency standards, 9 and in electromechanical actuators and sensors. 10 Recently certain cellular polymers internally charged by corona discharge (ferroelectrets) have been found to behave like soft sensitive piezoelectrics. 11 In addition to the corona charges in the voids in these foams, they usually also have to be inflated further with high pressure gas. 12 As a result, these ferroelectrets have long-term stability issues. 13 Here, we demonstrate high converse piezoelectric response of fiber mats composed of ferroelectric barium titanate (BT) nanoparticles dispersed in polylactic acid (PLA) and show that the effective piezoelectric constant per weight is two orders of magnitude larger than that of single crystal BT and of pure piezoelectric ceramic fibers. We propose that this unexpected super-piezoelectricity is due to the electrospinning-induced polar alignment of the particles, and the large surface area of the fibers, similar to ferroelectrets, however without the need of corona discharge and inflation processes.Electrospun fibers are formed by drawing a solution through a high electric field gradient generated between a nozzle and a collection plate 14-17 by electric fields of about 1-2 kV/cm, which is smaller than the breakdown field of 3 kV/cm of dry air. This produces very thin fibers with diameters ranging from hundreds of nanometers to several microns. Previously fibers of ferroelectric polymers, such as polyvinylidene fluoride (PVDF), have been electrospun and studied for electro-mechanical energy conversion applications. [18][19][20][21] Several examples of ferroelectric ceramic nanofibers have been fabricated using a sol-gel in the electrospinning process. [22][23][24] While the direct piezoelectric responses of ceramic fibers were demonstrated, 25,26 they are brittle. This problem was recently addressed by electrospinning of multi-material piezoelectric polymer...

Advances in Piezoelectric Polymer Composites for Energy Harvesting Applications: A Systematic Review

“…PLA‐based polymers are becoming a popular candidate for energy harvesting applications owing to their higher piezoelectric properties. The carbonyl groups present in PLA structure induces polarity and it shows a d 14 value of 10 pC N −1 without additional poling step in its crystalline structure …”

“…In 2012, Morvan et al . developed a biocompatible fiber composite by dispersing BaTiO 3 ceramic particles in PLA.…”

Cooperativity in the Enhanced Piezoelectric Response of Polymer Nanowires

“…Also, finite deformations would likely introduce quantitative but not qualitative changes to the observed effects. Examples of other piezoelectric fibers whose response can be enhanced by cooperative effects in arrays include those made of liquid crystalline polymers such as poly(γ-benzyl α- l -glutamate),25 biomaterials like β-glycine,26 and composites with ceramic particles 27. A variety of fields may be envisaged, where these findings can find application during device design and realization, including vibration sensing, power sources,28 and especially self-powered and wearable electronics,29 smart textiles and stick-on biomedical patches for health monitoring 30…”

Fillers in advanced nanocomposites for energy harvesting

“…Here, the presence of PLA in the form of fibers and embedded BaTiO 3 ceramic particles exhibit a piezoelectric constant per weight that is 2 orders of magnitude larger than those of crystal BaTiO 3 films (Morvan et al, 2012). Here, the presence of PLA in the form of fibers and embedded BaTiO 3 ceramic particles exhibit a piezoelectric constant per weight that is 2 orders of magnitude larger than those of crystal BaTiO 3 films (Morvan et al, 2012).…”

“…In the case of fillers used in nanocomposites for energy harvesting, PZT or BaTiO 3 (Morvan et al, 2012) are primarily utilized because of their optimal piezoelectric properties. Such nanocomposites provide enhanced energyharvesting performance in comparison to both individual materials.…”