Micro-arranged ZnO particles and conductive fillers in PCL composites for enhanced piezoelectric and dielectric properties in bone tissue engineering applications

Piezoelectric polymers are promising for replicating bone tissue's piezoelectric properties. Typically, non-piezoelectric biopolymers are combined with piezoelectric particles, but this yields low piezoelectric output. We addressed this by aligning piezoelectric zinc oxide (ZnO) micro-rods in 3D-printed polycaprolactone (PCL) scaffolds and adding conductive particles like thermally reduced graphene oxide (TrGO). Our findings revealed that controlled particle alignment in PCL/ZnO composites significantly enhanced dielectric properties. TrGO further improved these properties by creating conductive pathways and micro-capacitor networks by apparent polarization due to electron displacement, promoting Maxwell-Wagner-Sillars effect. This design strategy significantly increased dielectric and piezoelectric performance, achieving values akin to bone tissue. TrGO also boosted the piezoelectric response, with maximum voltage generation of 696 ± 52 and 142 ± 9 mV during direct contact mechanical pressure by a linear actuator and remote mechanical pressure induced by ultrasound waves, respectively. The 3D-printed composites demonstrated bioactivity for MC3T3-E1, enhanced ALP activity, improved cell adhesion, migration, and extracellular matrix formation under remote ultrasound stimulation, underscoring the potential of these novel ternary composites for bone tissue engineering.