Kewen Li

Hierarchical alginate biopolymer papers produced via lanthanide ion coordination

Inspired by the heterogeneous architectures of biological composites, mimicking the hierarchical structure of nacre is a powerful strategy to construct high-performance materials. This paper presents a lightweight and nacre-like hierarchical paper which was fabricated via lanthanide ion coordination. Sodium alginate (SA) biopolymers and lanthanide ions (Nd3+, Gd3+, Ce3+ and Yb3+) were used as ideal building blocks and connection points, respectively. SA biopolymers and lanthanide ions rapidly self-assembled into an aligned hydrogel. The synthesized hydrogel was subsequently dried to form layered alginate-based papers. The formation mechanism of the layered paper was investigated and demonstrated that lanthanide ion coordination can produce the hierarchical structure. The as-prepared layered SA–Nd(III) nanopaper exhibited a high strength of 124.2 ± 5.2 MPa, toughness of 8.2 ± 0.4 MJ m−3, and Youngs modulus of 5.2 ± 0.2 GPa, as well as excellent resistance to solvents. Owing to their outstanding mechanical properties and easy and fast fabrication, the layered SA–Nd(III) papers demonstrated a potential application in the fields of biomaterials. This new strategy based on lanthanide ion coordination, can also be used to construct integrated, high-performance, and biopolymer materials.

Lanthanide ions-induced formation of hierarchical and transparent polysaccharide hybrid films

Nacre-like hybrid films based on N-succinyl chitosan (NSC), sodium alginate (SA) and lanthanide ions were fabricated via coordination interactions. In this work, the binary building blocks (NSC and SA) were self-assembled into aligned hydrogel films by coordination with lanthanide ions, and hierarchical NSC-SA hybrid films were obtained upon drying. Two species of lanthanide ions (Gd3+ and Yb3+) were used to fabricate the hierarchical NSC-SA hybrid films. The as-prepared NSC-SA hybrid films exhibit high tensile strength and stability. The tensile strength and toughness of as-prepared hybrid films reach 122.10MPa and 3.89MJm-3, respectively. Meanwhile, the well-aligned lamellar microstructures also exhibit a good light transmittance. The highest light transmittance reaches 92% for NSC-SA hybrid films at 760nm. This fabrication method for hierarchical NSC-SA hybrid films is innovative due to the utilization of rare earth coordination bonding, and can serve as the basic strategy for the construction of high-performance composites in the near future.

Preparation of well-defined fibrous hydrogels via electrospinning and in situ “click chemistry”

In this work, well-defined PEG-based fibrous hydrogels (FHs) were successfully prepared via electrospinning and in situ copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction. Initially, the linear functional PEG derivatives with pendant alkynyl groups (PEGn(CCH))m and with azido moieties (PEGn(N3))m were synthesized via epoxide-amine chain-extension reaction between poly(ethylene glycol) diglycidyl ether (PEGDGE) and propargylamine/1-azido-3-aminopropane. Subsequently, the PEG-based FHs were fabricated from the blends of poly(ethylene oxide) (PEO) and the functional PEG derivatives via electrospinning and in situ CuAAC reaction using the encapsulated copper nanoparticles as the catalyst. The blends of PEO and the functional PEG derivatives were also utilized to prepare the microscopic hydrogels (MHs). The properties of the FHs and MHs were investigated by scanning electron microscopy (SEM) observation, swelling ratios, differential scanning calorimetry (DSC) and in vitro degradation. The copper nanoparticles-encapsulated FHs and MHs were further used to catalyze the CuAAC reaction in a small molecule model. The reusability of the FHs for the CuAAC reaction was also studied.

A Conductive Self-Healing Double Network Hydrogel with Toughness and Force Sensitivity

Mechanically tough and electrically conductive self-healing hydrogels may have broad applications in wearable electronics, health-monitoring systems, and smart robotics in the following years. Herein, a new design strategy is proposed to synthesize a dual physical cross-linked polyethylene glycol/poly(acrylic acid) (PEG/PAA) double network hydrogel, consisting of ferric ion cross-linked linear chain extensions of PEG (2,6-pyridinedicarbonyl moieties incorporated into the PEG backbone, PEG-H2 pdca) as the first physical network and a PAA-Fe3+ gel as the second physical network. Metal-ion coordination and the double network structure enable the double network hydrogel to withstand up to 0.4 MPa tensile stress and 1560 % elongation at breakage; the healing efficiency reaches 96.8 % in 12 h. In addition, due to dynamic ion transfer in the network, the resulting hydrogels exhibit controllable conductivity (0.0026-0.0061 S cm-1 ) and stretching sensitivity. These functional self-healing hydrogels have potential applications in electronic skin. It is envisioned that this strategy can also be employed to prepare other high-performance, multifunctional polymers.