Jin Kuk Kim

The limited number of materials and mechanical weakness of fused deposition modeling (FDM) parts are deficiencies of FDM technology. The preparation of polymer composites parts with suitable filler is a promising method to improve the properties of the 3D printed parts. However, the agglomerate of filler makes its difficult disperse in the matrix. In this work, graphene nanoplatelets (GnPs) were surface modified with chemical, low-temperature plasma and in situ methods, in order to apply them as fillers for thermoplastic polyurethane (TPU). Following its modification, the surface chemical composition of GnPs was analyzed. Three wt% of surface-modified GnPs were incorporated into TPU to produce FDM filaments using a melting compounding process. Their effects on rheology properties and electrical conductivity on TPU/GnPs composites, as well as the dimensional accuracy and mechanical properties of FDM parts, are compared. The images of sample facture surfaces were examined by scanning electron microscope (SEM) to determine the dispersion of GnPs. Results indicate that chemical treatment of GnPs with zwitterionic surfactant is a good candidate to significantly enhance TPU filaments, when considering the FDM parts demonstrated the highest mechanical properties and lowest dimensional accuracy.

The design and development of intrinsically stretchable all-organic self-powered sensors concurrently perceiving temperature and pressure remain a challenge but deliver an exciting platform to realize environmentally friendly wearable electronics. In this approach, a biomimetic all-organic stretchable energy harvester is designed by a xylitol-added poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS/Xyl) film as a compatible overlay electrode with polyaniline-reinforced one-dimensional aligned poly(vinylidene fluoride) hybrid electroactive soft nanowires. The gradient of elastic modulus between the electrode and the active nanowire component enables the all-organic device to manifest excellent power-generating performance under external temperature fluctuation (∼3 μW/m² under ΔT ∼ 92 K) and mechanical force (∼31 μW/cm² at 30 N). Importantly, the device renders simultaneous energy scavenging of temperature and pressure changes under pressing and stretching conditions (∼20%). The excellent mechanosensitivity (∼100 mV/N), fast response time (∼1 ms), outstanding mechanical and thermal stability, and good temperature resolution <10 K enable the harvester to act as an epidermal sensor, which simultaneously detects and discriminates both subtle pressure and thermal deviations exposed to an epidermis surface. The real-time recording and wireless transferring of physiological signals to a smartphone indicate an effective way to realize remote healthcare monitoring for early intervention.

Inspired by the keratin–elastin composition of human skin, here an artificial skin (alias electronic (e)‐skin) is developed through solvent‐free extrusion based melt mixing of thermoplastic polyurethane (TPU) with the biowaste human hair keratin. Self‐assembled composite film of TPU and keratin (i.e., PUK) shows leg skin equivalent coefficient of friction value of 0.26 ± 0.05, cheek skin equivalent average surface roughness (Ra) of 0.047 ± 0.07 µm, cytoskeletal keratin intermediate filament network like rheological behavior, porous morphology, and skin like positive triboelectric property, when the keratin content is 10 wt%. H‐bonded self‐assembled network and lubricating behavior of cysteine‐rich keratin provide such tribological and rheological behaviors of the PUK. Single electrode triboelectric nanogenerator (STENG) made of PUK containing 10 wt% keratin (i.e., 10% PUK) not only shows clear discrimination between the touch feeling sensations of bare, and glove protected human finger, by producing output voltage of ≈1 and ≈16 V cm⁻², respectively, but it also can discriminate the tactile sensations of different objects viz., aluminum foil, cotton glove, wood, polyimide, and poly(tetrafluoroethylene) by producing different output voltages, resembling that the PUK composite film is well fitted for e‐skin applications.

Inspired by the epidermis–dermis composition of human skin, here we have simply developed a lightweight, robust, flexible, and biocompatible single-electrode triboelectric nanogenerator (S-TENG)-based prototype of bilayer artificial skin, by attaching one induction electrode with unfoamed skin layer of microcellular thermoplastic polyurethane (TPU) foam, which shows high-performance object manipulation [by responding differently toward different objects, viz., aluminum foil, balloon, cotton glove, human finger, glass, rubber glove, artificial leather, polyimide, poly(tetrafluoroethylene) (PTFE), paper, and wood], due to electrification and electrostatic induction during contact with the objects having different chemical functionalities. Comparative foaming behavior of ecofriendly supercritical fluids, viz., CO₂ over N₂ under variable temperatures (e.g., 130 and 150 °C) and constant pressure (15 MPa), have been examined here to pursue the soft and flexible triboelectric TPU foam. The foam derived by CO₂ foaming at 150 °C has been prioritized for development of S-TENG. Foam derived by CO₂ foaming at 130 °C did not respond as well due to the smaller cell size, higher hardness, and thicker skin. Inflexible N₂-derived foam was not considered for S-TENG fabrication. Object manipulation performance has been visualized by principal component analysis (PCA), which shows good discrimination among responses to different objects.