Han Lu's research while affiliated with University of Science and Technology of China and other places

Conductive polymer-based hydrogels (CHs) have gained increasing attention as flexible electrode materials for making high-performance flexible supercapacitors (FSCs). However, the amorphous nature of current CHs severely limits their energy density and electrochemical stability, due to the structural damage of amorphous CHs at high operation voltages and during repeated redox reactions. We hypothesized that semi-crystalline CHs that possess more ordered chemical structure and less defects should be more resistant to structural damage. Herein, we report a soft-template synthesis strategy to prepare semi-crystalline CHs by the supramolecular assembly of poly(3,4-ethylenedioxythiophene) (PEDOT) and polyvinyl alcohol (PVA, serving as a soft template) for making FSCs with higher energy density and better electrochemical stability. In a water/DMSO mixture solvent, semi-crystalline PEDOT nanofibers are formed by oxidative polymerization of EDOT monomer, and in-situ assemble with PVA to form PEDOT-PVA supramolecular hydrogel (PPSH) with a regular porous microstructure. Owing to the ordered polymer chain alignments in the compact nanosheets of PPSH, both the energy density (24 Wh kg-1) and electrochemical stability (100% capacitance retention after 15000 charge-discharge cycles) of the PPSH-based FSC operating at 1.4 V are far beyond previously reported amorphous CHs-based FSCs. This soft-template synthesis method provides an effective strategy to prepare semi-crystalline CHs with enhanced electrochemical performance for broad applications.

Electroconductive hydrogels (EHs), combining both the biomimetic features of hydrogels and the electrochemical properties of conductive polymers and carbon‐based materials, have received immense considerations over the past decade. The three‐dimensional porous structure, hydrophilic properties, and regulatable chemical and physical properties of EH resemble the extracellular matrix in tissues, enable EHs a good matrix for cell growth, proliferation, and migration. Different from nonconductive hydrogels, EHs possess high electrical conductivity and electrochemical redox properties, which can be utilized to detect electric signals generated in biological systems, and also to supply electrical stimulation to regulate the activity and function of cells and tissues. Hence, this article provides a summary of the new development of EH for biomedical applications in the decade. We give a brief introduction of the design and synthesis of EHs, as well as current applications of EHs in biomedical fields, including cell culture, tissue engineering, drug delivery and controlled release, biosensors, and implantable bioelectronics. The development trends and challenges of EHs for biomedical applications are also discussed. This article is categorized under: • Implantable Materials and Surgical Technologies > Nanomaterials and Implants • Diagnostic Tools > Biosensing • Therapeutic Approaches and Drug Discovery > Emerging Technologies

Powerful soft actuators that can perform programmable actuations are highly desired for the development of soft robotics. Herein we report a moisture-driven polymer actuator: PPA, which is a composite of poly(3,4-ethylenedioxythiophene)/polyvinyl alcohol/copolymer of acrylic acid and 2-acrylanmido-2-methylpropanesulfonic acid. PPA can not only generate powerful actuation with a contractile stress up to 13 MPa, but also perform programmable helical motions. PPA films with internal stress along the radial directions were prepared by a simple solution casting method. Driven by moisture, rectangular ribbons cut from the same PPA film but with different cutting angles (the oblique angle between the long axis of PPA ribbon and the radial axis of PPA film) can perform direct bending, left-handed or right-handed helical motions, demonstrating the generation of chirality from asymmetric internal stress. By modulating the distribution of internal stress in PPA ribbons, their moving direction and speed are readily prescribed. The powerful and programmable PPA ribbons can be used to make soft devices, such as moisture-responsive switches and transporters. Our strategy of generating and utilizing internal stress in responsive polymers represents a promising platform for fabricating smart soft actuators.

The development of stretchable supercapacitors (SSCs) is heading to compact and robust devices with higher capacitance and simpler preparation process. Herein, a new strategy is reported to prepare a highly stretchable and conductive polypyrrole hydrogel with a unique biphase microstructure (loose phase and dense phase), which is formed by the supramolecular assembly of polypyrrole (PPy), poly(vinyl alcohol), and anionic micelles. The loose phase enables the PPy hydrogel large stretchability (elongation at a break of 500%) and good electrochemical capacitive behavior, while the dense phase enables the PPy hydrogel high tensile strength (2 MPa) and good conductivity (0.8 S cm−1). Without using any substrate, the SSC made of this polypyrrole hydrogel provides an areal capacitance of 950 mF cm−2 at a current density of 1.6 mA cm−2, exceeding most of reported SSCs. This SSC can withstand repeated deformation and retain 81% capacitance after 500 stretching–releasing cycles. Besides, at subzero temperature down to −20 °C, this SSC can still retain its good stretchability and capacitance. The combination of high areal capacitance, good stretchability, and high retention of capacitance under various circumstances enables the polypyrrole hydrogel–based SSC an economical and robust SSC for stretchable electronics. Strong and stretchable conductive polypyrrole hydrogels with a unique spongy biphase microstructure are facilely prepared. Without any substrate, the supercapacitor assembled with this hydrogel as electrode demonstrates high areal capacitance, good stretchability and high retention of capacitance under large deformation and subzero temperature environment, which enable this supercapactor a high‐performance and low‐cost stretchable energy supply for flexible electronics.

High-performance stretchable conductive fibers are desired for the development of stretchable electronic devices. Here we show a simple spinning method to prepare conductive hydrogel fibers with ordered polymer chain alignment that mimics the hierarchically organized structure of spider silk. The as-prepared sodium polyacrylate hydrogel fiber is further coated with a thin layer of polymethyl acrylate to form a core-shell water-resistant MAPAH fiber. Owing to the coexistence and reversible transformation of crystalline and amorphous domains in the fibers, MAPAH fibers exhibit high tensile strength, large stretchability and fast resilience from large strain. MAPAH fiber can serve as a highly stretchable wire with a conductive hydrogel core and an insulating cover. The stretchability and conductivity of the MAPAH fiber are retained at −35 °C, indicating its anti-freezing property. As a prime example of stretchable conductive fibers, MAPAH fibers will shed light on the design of next generation textile-based stretchable electronic devices.