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Rechargeable aqueous zinc-ion batteries (RAZIBs) have some inherent advantages such as intrinsic safety, low-cost and theoretically high energy density, making them a current topic of interest. However, the phenomenon of zinc (Zn) dendrite growth at the anode results in the instability of RAZIBs and limits their real-world application. Herein, by employing a high strength hydrogel polymer electrolyte, the growth of dendritic Zn crystals is effectively eliminated through the mechanical suppression effect, resulting in a stable Zn anode that demonstrates dendrite-free plating/stripping with a long lifespan. Even under a high current density of 5 mA cm(-2), the Zn||Zn symmetric cell is shown to have a cyclic lifetime of longer than 1000 hours. Moreover, the stable cyclic performance of the Zn anode spawns a Zn||MnO2 battery with high capacity (4.8-1.9 mA h cm(-2)) and long lifetime (500 cycles at 9.2 mA cm(-2), 1C), which can meet the practical demands for portable devices. This work shows that high strength polymer gel electrolytes with internal energy dissipation mechanisms can overcome previous challenges that prevented practical utilization of RAZIBs. Together with the outstanding cyclic properties of the high capacity Zn||MnO2 batteries, this work provides a new pathway toward designing high energy density RAZIBs.

Biological tissues usually have complex superstructures and elaborated functionalities. However, creating superstructures in soft and wet hydrogels is challenging because of the absence of effective approaches to control the molecular orientation. Here we introduce a method to create superstructures in photonic hydrogels comprising lamellar bilayers intercalated in the cross-linked polymer network. The orientation of lamellar bilayers in the photonic gel, which are sensitive to shear, is modulated by applying a gradient shear field on the precursor solution using a customized rheometer. The difference in orientation of lamellar bilayers leads to swelling mismatch in the radial direction, endowing the disk-shape hydrogel with a macroscopic flower-like shape with a central dome and an edge petal, along with a bright photonic color. By characterization of the swelling anisotropy of the radial profile, the shear rate required for the unidirectional orientation of lamellar bilayers was extracted. Moreover, a delayed polymerization experiment was designed to measure the lifetime of aligned lamellar bilayers, which reveals the domain size of lamellar bilayers in the precursor solution. Furthermore, we also demonstrated that the hydrogel flowers could fade and rebloom reversibly in response to external stimuli. This work presents a strategy to develop superstructures in hydrogels and sheds light on designing biomimetic materials with intricately architectural superstructure.

The high water content of hydrogels makes them important as synthetic biomaterials, and tuning the mechanical properties of hydrogels to match those of natural tissues without changing chemistry is usually difficult. In this study, we have developed a series of hydrogels with varied stiffness, strength, and toughness based on a combination of poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS), a strong acidic polyelectrolyte, and poly-N-(carboxymethyl)-N,N-dimethyl-2-(methacryloyloxy) ethanaminium) (PCDME), a polyzwitterion with a weak acidic moiety. We demonstrate that modifying the true molar ratio, R, of PCDME to PAMPS results in four unique categories of hydrogels with different swelling ratios and Young’s moduli. When R < 1, a negatively charged polyelectrolyte gel (PE) is formed; when 1 < R < 3, a tough and viscoelastic polyelectrolyte complex gel (PEC) is formed; when 3 < R < 6.5, a conventional, elastic interpenetrating network gel (IPN) is formed; and when R > 6.5, a tough and stiff double-network gel (DN) is formed. Both the PEC and DN gels exhibit high toughness and fracture stress, up to 1.8 and 1.5 MPa, respectively. Importantly, the PEC gels exhibit strong recovery properties along with high toughness, distinguishing them from DN gels. Without requiring a change in chemistry, we can tune the mechanical response of hydrogels over a wide spectrum, making this a useful system of soft and hydrated iomaterials.

Polyampholyte hydrogels (PA gels) are drawing great attention for their excellent mechanical properties including self-healing, high toughness, and fatigue resistance. These mechanical performances are found to be attributed to the hierarchical structure of the PA gels, consisting of reversible ionic bonds at the 1 nm scale, permanent polymer network at the 10 nm scale, and icontinuous phase network at the 100 nm scale. In this work, we systematically studied the phase network formation of these gels aiming to answer the following three questions: (1) how the phase separation occurs? (2) what determines the phase structure? and (3) is this structure in thermodynamic equilibrium or not? Our results show that the phase separation occurs during dialysis of counterions from the gels and it is driven by the Coulombic and hydrophobic interactions. The phase size d0 and the number of aggregated chains in a unit cell of the phase structure n scale with the molecular weight of the partial chain between permanent effective cross-linking Meff as d0 ∼ Meff and n ∼ Meff 2, respectively. A chemical cross-linker and topological entanglement suppress phase separation, while hydrophobic interaction favors phase separation. An intrinsic correlation between the polymer density difference (Δρ) between two phases and d0 is observed (Δρ ∼ d02) as a result of the competition between the driving force to induce phase separation and the resistance to suppress the phase separation. The phase-separated structure is metastable, which is locally trapped by strong intermolecular interactions.

Candidate materials towards soft tissue engineering require anti-fouling materials that are biocompatible, protein anti-fouling, and mechanically flexible. Conventional hydrogels having more than 70 wt% water are available to design with these criteria in mind. However, some of hydrogels are difficulty to apply hydrogels in internal body organs, because some undesirable proteins absorption on their surfaces. Previously, due to the lack of an effective method in observing the true charge densities of hydrogels,the reason why electrostatic interactions dominate protein absorption behavior is still unclear. In this work, we adopt the microelectrode technique (MET) to study the electrical potential of hydrogels that having negative, positive and neutral potentials,and demonstrate the protein absorption behavior on those hydrogels. The results show that the MET is an effective method to obtain the surface charge densities of various hydrogels. Furthermore, the amount of proteins absorbed to the gel is quantified by the charge density of hydrogels. These results indicate that the electrostatic absorption was quantitatively dominated by a combination of the charge density of hydrogels and the overall charges of proteins. With the knowledge obtained in this work, the effect of surface charges in a hydrogel on protein absorption could be well understood, and this result could be prospective to promote the application of hydrogel in tissue engineering.