Recently, three-dimensional printing (3DP) technology has been widely adopted in biology and biomedical applications, thanks to its capacity to readily construct complex 3D features. Using hot-melt extrusion 3DP, scaffolds for bone tissue engineering were fabricated using a composite of biodegradable polycaprolactone (PCL) and hydroxyapatite (HA). However, there are hardly any published reports on the application of the fused deposition modeling (FDM) method using feed filaments, which is the most common 3D printing method. In this study, we report on the fabrication and characterization of biocompatible filaments made of polycaprolactone (PCL)/hydroxyapatite (HA), a raw material mainly used for bone scaffolds, using FDM 3D printing. A series of filaments with varying HA content, from 5 to 25 wt.%, were fabricated. The mechanical and electrical properties of the various structures, printed using a commercially available 3D printer, were examined. Specifically, mechanical tensile tests were performed on the 3D-printed filaments and specimens. In addition, the electrical dielectric properties of the 3D-printed structures were investigated. Our method facilitates the fabrication of biocompatible structures using FDM-type 3DP, creating not only bone scaffolds but also testbeds for mimicking bone structure that may be useful in various fields of study.

A flexible piezoelectric composite is composed of a polymer matrix and piezoelectric ceramic fillers to achieve good mechanical flexibility and processability. The overall piezoelectric performance of a composite is largely determined by the piezoelectric filler inside. Thus, different dispersion methods and additives that can promote the dispersion of piezoelectric ceramics and optimal composite structures have been actively investigated. However, relatively few attempts have been made to develop a filler that can effectively contribute to the performance enhancement of piezoelectric devices. In the present work, we introduce the fabrication and performance of the composite piezoelectric devices composed of Li-doped ZnO nanowires (Li: ZnO NWs) grown on the surface of MXene (Ti 3 C 2 ) via the hydrothermal process. Through this approach, a semiconductor−metal hybrid structure is formed, increasing the overall permittivity. Moreover, the Ti 3 C 2 layer can serve as a local ground in the composite so that the ferroelectric phase-transformed Li: ZnO NWs grown on its surface can be more effectively polarized during the poling process. In addition, the NW-covered surface of Ti 3 C 2 prevents the aggregation of metallic Ti 3 C 2 particles, promoting a more uniform electric field distribution during the poling process. As a result, the output performance of the piezoelectric nanogenerator (PENG) fabricated with a Li: ZnO NW/Ti 3 C 2 composite was greatly improved compared to that of the devices fabricated with Li: ZnO NWs without the Ti 3 C 2 platform. Specifically, the Li: ZnO NW/Ti 3 C 2 composite piezoelectric nanogenerator (PENG) demonstrated a twofold higher output power density (∼9 μW/cm 2 ) compared with the values obtained from the PENG devices based on Li: ZnO NWs. The approach introduced in this work can be easily adopted for an effective ferroelectric filler design to improve the output performance of the piezoelectric composite. KEYWORDS: piezoelectric nanogenerator (PENG), zinc oxide (ZnO) nanowires on MXene (Ti 3 C 2 ), hydrothermal growth, composite, phase transition

Flexible and lightweight electromagnetic interference (EMI) shielding materials with excellent EMI shielding performance have attracted significant attention because of their potential applications in various fields. In this study, we reported the fabrication and performance of polyvinylidene fluoride (PVDF) composite nanofiber (NF) EMI shielding materials composed of Fe 3 O 4 nanoparticles (NPs)-embedded PVDF and conductive poly(3,4-ethylenedioxythiophene) (PEDOT) shells. By separating the conductive NF surface, which was prepared using a vapor phase polymerization (VPP) method, from the magnetic nanoparticle region inside the NF, high conductivity of the shell can be maintained and unaffected even when the wt % of Fe 3 O 4 NPs inside the NF is increased. Therefore, the EMI shielding performance can be maximized by simultaneously increasing the conductivity and permeability of the NFs. Fe 3 O 4 NPs embedded in the NF also contributed to increasing permeability and interfacial polarization, boosting multiple reflection and scattering, and absorption of incident EM waves through magnetic and dielectric loss. Additionally, the multi-layered NF structure is suitable to facilitate a multiple reflection mechanism. Consequently, high EMI SE and absolute EMI shielding effectiveness (SSE t ) of 18,760 dB• cm 2 /g were achieved. The EMI shielding material developed in this study can easily be adopted for various applications because of its superb flexibility, hydrophobicity, ultrathin thickness, and robustness.

According to clinical case reports, bacterial co-infection with COVID-19 can significantly increase mortality, with Staphylococcus aureus (S. aureus) being one of the most common pathogens causing complications such as pneumonia. Thus, during the pandemic, research on imparting air filters with antibacterial properties was actively initiated, and several antibacterial agents were investigated. However, air filters with inorganic nanostructures on organic nanofibers (NFs) have not been investigated extensively. This study aimed to demonstrate the efficiency of electropolarized poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) NFs decorated with Li-doped ZnO nanorods (NRs) to improve the filtering ability and antibacterial activity of the ultrathin air filter. The surfactant was loaded onto the ZnOknown for its biocompatibility and low toxicitynanoparticles (NPs) and transferred to the outer surface of the NFs, where Li-doped ZnO NRs were grown. The Li-doped ZnO NR-decorated NF effectively enhanced the physical filtration efficiency and antibacterial properties. Additionally, by exploiting the ferroelectric properties of Li-doped ZnO NRs and PVDF-TrFE NFs, the filter was electropolarized to increase its Coulombic interaction with PMs and S. aureus. As a result, the filter exhibited a 90% PM1.0 removal efficiency and a 99.5% sterilization rate against S. aureus. The method proposed in this study provides an effective route for simultaneously improving the air filter performance and antibacterial activity.

No abstract