A rechargeable calcium-oxygen battery that operates at room temperature.

Calcium-oxygen (Ca-O2) batteries can theoretically afford high capacity by the reduction of O2 to calcium oxide compounds (CaOx) at low cost1-5. Yet, a rechargeable Ca-O2 battery that operates at room temperature has not been achieved because the CaOx/O2 chemistry typically involves inert discharge products and few electrolytes can accommodate both a highly reductive Ca metal anode and O2. Here we report a Ca-O2 battery that is rechargeable for 700 cycles at room temperature. Our battery relies on a highly reversible two-electron redox to form chemically reactive calcium peroxide (CaO2) as the discharge product. Using a durable ionic liquid-based electrolyte, this two-electron reaction is enabled by the facilitated Ca plating-stripping in the Ca metal anode at room temperature and improved CaO2/O2 redox in the air cathode. We show the proposed Ca-O2 battery is stable in air and can be made into flexible fibres that are weaved into textile batteries for next-generation wearable systems.

A dynamically stable self-healable wire based on mechanical-electrical coupling.

The rise in wearable electronics has witnessed the advancement of self-healable wires, which are capable of recovering mechanical and electrical properties upon structural damage. However, their highly fluctuating electrical resistances in the range of hundreds to thousands of ohms under dynamic conditions such as bending, pressing, stretching and tremoring may seriously degrade the precision and continuity of the resulting electronic devices, thus severely hindering their wearable applications. Here, we report a new family of self-healable wires with high strengths and stable electrical conductivities under dynamic conditions, inspired by mechanical-electrical coupling of the myelinated axon in nature. Our self-healable wire based on mechanical-electrical coupling between the structural and conductive components has significantly improved the electrical stability under dynamic scenarios, enabling precise monitoring of human health status and daily activities, even in the case of limb tremors from simulated Parkinson's disease. Our mechanical-electrical coupling strategy opens a new avenue for the development of dynamically stable electrodes and devices toward real-world wearable applications.

A Fiber Sensor for Long-Term Monitoring of Extracellular Potassium Ion Fluctuations in Chronic Neuropsychiatric Diseases.

The extracellular potassium ion concentration in the brain exerts a significant influence on cellular excitability and intercellular communication. Perturbations in the extracellular potassium ion level are closely correlated with various chronic neuropsychiatric disorders including depression. However, a critical gap persists in performing real-time and long-term monitoring of extracellular potassium ions, which is necessary for comprehensive profiling of chronic neuropsychiatric diseases. Here, a fiber potassium ion sensor (FKS) that consists of a soft conductive fiber with a rough surface and a hydrophobic-treated transduction layer interfaced with a potassium ion-selective membrane is found to solve this problem. The FKS demonstrates stable interfaces between its distinct functional layers in an aqueous environment, conferring an exceptional stability of 6 months in vivo, in stark contrast to previous reports with working durations from hours to days. Upon implantation into the mouse brain, the FKS enables effective monitoring of extracellular potassium ion dynamics under diverse physiological states including anesthesia, forced swimming, and tail suspension. Using this FKS, tracking of extracellular potassium ion fluctuations that align with behaviors associated with the progression of depression over months is achieved, demonstrating its usability in studying chronic neuropsychiatric disorders from a new biochemical perspective.

Biomedical polymers: synthesis, properties, and applications.

Biomedical polymers have been extensively developed for promising applications in a lot of biomedical fields, such as therapeutic medicine delivery, disease detection and diagnosis, biosensing, regenerative medicine, and disease treatment. In this review, we summarize the most recent advances in the synthesis and application of biomedical polymers, and discuss the comprehensive understanding of their property-function relationship for corresponding biomedical applications. In particular, a few burgeoning bioactive polymers, such as peptide/biomembrane/microorganism/cell-based biomedical polymers, are also introduced and highlighted as the emerging biomaterials for cancer precision therapy. Furthermore, the foreseeable challenges and outlook of the development of more efficient, healthier and safer biomedical polymers are discussed. We wish this systemic and comprehensive review on highlighting frontier progress of biomedical polymers could inspire and promote new breakthrough in fundamental research and clinical translation.

An Anti-Biofouling Flexible Fiber Biofuel Cell Working in the Brain.

Biofuel cell (BFC) that transfers chemical energy into electricity is a promising candidate as an energy-harvesting device for implantable electronics. However, there still remain major challenges for implantable BFCs, including bulky and rigid device structure mismatching with soft tissues such as the brain, and the power output decreases due to the fouling process in a biological environment. Here, a flexible and anti-biofouling fiber BFC working in the brain chronically is developed. The fiber BFC is based on a carbon nanotube fiber electrode to possess small size and flexibility. A hydrophilic zwitterionic anti-biofouling polydopamine-2-methacryloyloxyethyl phosphorylcholine layer is designed on the surface of fiber BFC to resist the nonspecific protein adsorption in a complex biological environment. After implantation, the fiber BFC can achieve a stable device/tissue interface, along with a negligible immune response. The fiber BFC has first realized power generation in the mouse brain for over a month, exhibiting its promising prospect as an energy-harvesting device in vivo.

Lithium-Metal Anodes Working at 60†mA cm-2 and 60†mAh cm-2 through Nanoscale Lithium-Ion Adsorbing.

Achieving high-current-density and high-area-capacity operation of Li metal anodes offers promising opportunities for high-performing next-generation batteries. However, high-rate Li deposition suffers from undesired Li-ion depletion especially at the electrolyte-anode interface, which compromises achievable capacity and lifetime. Here, electronegative graphene quantum dots are synthesized and assembled into an ultra-thin overlayer capable of efficient Li-ion adsorbing at the nanoscale on Li-metal to fully relieve Li-ion depletion. The protected Li anode achieves long-term reversible Li plating/stripping over 1000 h at both superior current density of 60 mA cm-2 and areal capacity of 60 mAh cm-2 . Implementation of the protected anode allows for the construction of Li-air full battery with both enhanced rate capability and cycling performance.

A fiber-shaped neural probe with alterable elastic moduli for direct implantation and stable electronic-brain interfaces.

Researchers developing implantable neural probes face a dilemma. Rigid neural probes facilitate direct implantation, but the brain tissue suffers from a vulnerable interface and a strong neuroinflammatory response due to mechanical mismatch between the probe and the brain tissue. Flexible neural probes offer stable interfaces and eliminate neuroinflammatory responses but require auxiliary implantation. Here, we have created a new kind of micro fiber-shaped neural probe with alterable elastic moduli before and after implantation. Carbon nanotube fibers and calcium crosslinked sodium alginate functioned as the core electrode and sheath layer, respectively. The response of calcium crosslinked sodium alginate to water will alter the probe elastic moduli from ∼10 GPa to ∼10 kPa post implantation, which is close to the elastic modulus of brain tissue. The micro fiber probes were directly implanted into mouse brains without any additional materials. After implantation, they became soft and offered dynamically adaptable interfaces with a reduced inflammatory response, benefiting long-term monitoring of neuron signals. Continuous four week monitoring of neuron signals was achieved. The simplicity of the strategy makes it suitable for versatile neuron techniques in neuron recording and modulation.

Functionalized helical fibre bundles of carbon nanotubes as electrochemical sensors for long-term in vivo monitoring of multiple disease biomarkers.

Mechanical mismatches between implanted electronics and biological tissues can lead to inaccurate readings and long-term tissue damage. Here, we show that functionalized multi-walled carbon nanotubes twisted into helical fibre bundles that mimic the hierarchical structure of muscle can monitor multiple disease biomarkers in vivo. The flexible fibre bundles are injectable, have a low bending stiffness and display ultralow stress under compression. As proof-of-concept evidence of the sensing capabilities of these fibre bundles, we show that the fibre bundles enable the spatially resolved and real-time monitoring of H2O2 when implanted in tumours in mice, and that they can be integrated with a wireless transmission system on an adhesive skin patch to monitor calcium ions and glucose in the venous blood of cats for 28 d. The versatility of the helical fibre bundles as chemically functionalized electrochemical sensors makes them suitable for multiple sensing applications in biomedicine and healthcare.

In Situ Intercalation of Bismuth into 3D Reduced Graphene Oxide Scaffolds for High Capacity and Long Cycle-Life Energy Storage.

Metal anodes, such as zinc and bismuth have been regarded as ideal materials for aqueous batteries due to high gravimetrical capacity, high abundance, low toxicity, and intrinsic safety. However, their translation into practical applications are hindered by the low mass loading (≈1 mg cm-2 ) of active materials. Here, the multiscale integrated structural engineering of 3D scaffold and active material, i.e., bismuth is in situ intercalated in reduced graphene oxide (rGO) wall of network, are reported. Tailoring the rapid charge transport on rGO 3D network and facile access to nano- and microscale bismuth, the rGO/Bi hybrid anode shows high utilization efficiency of 91.4% at effective high load density of ≈40 mg cm-2 , high areal capacity of 3.51 mAh cm-2 at the current density of 2 mA cm-2 and high reversibility of >10 000 cycles. The resulting Ni-Bi full battery exhibits high areal capacity of 3.13 mAh cm-2 at the current density of 2 mA cm-2 , far outperforming the other counterpart batteries. It represents a general and efficient strategy in enhancing the battery performance by designing hierarchically networked structure.

Stabilizing Lithium into Cross-Stacked Nanotube Sheets with an Ultra-High Specific Capacity for Lithium Oxygen Batteries.

Although lithium-oxygen batteries possess a high theoretical energy density and are considered as promising candidates for next-generation power systems, the enhancement of safety and cycling efficiency of the lithium anodes while maintaining the high energy storage capability remains difficult. Here, we overcome this challenge by cross-stacking aligned carbon nanotubes into porous networks for ultrahigh-capacity lithium anodes to achieve high-performance lithium-oxygen batteries. The novel anode shows a reversible specific capacity of 3656 mAh g-1 , approaching the theoretical capacity of 3861 mAh g-1 of pure lithium. When this anode is employed in lithium-oxygen full batteries, the cycling stability is significantly enhanced, owing to the dendrite-free morphology and stabilized solid-electrolyte interface. This work presents a new pathway to high performance lithium-oxygen batteries towards practical applications by designing cross-stacked and aligned structures for one-dimensional conducting nanomaterials.

Root-soil structure inspired hydrogel microspheres with high dimensional stability and anion-exchange capacity.

Ion exchange materials show great advantages in water purification, food industry, pharmaceutical industry, etc. However, the ion exchange capacities of ion exchange materials, especially for anion-exchange materials, at present are still relatively low. Hydrogels own abundant functional groups and show high hydrophilicity, and thus are recognized as high-potential ion exchange materials, but may deform and even crush in use due to their low mechanical strength and unavoidable swelling behavior. In this study, inspired by the root-soil structure, novel poly(methacryloxyethyltrimethyl ammonium chloride) composite hydrogel microspheres with ultrahigh ion exchange capacity (more than 3.8 meuqiv/g), low swelling ratio (less than 1.5 g/g under pH = 7), and ultrahigh mechanical strength (more than 28.1 MPa) were prepared. The microspheres showed efficient adsorption for anionic dyes (1491 mg/g for methyl orange, 1693 mg/g for Congo red, and 204.7 mg/g for amaranth, respectively) and great adsorption for bilirubin (131.6 mg/g). Taken together, the hydrogel microspheres were qualified as stable and high-efficiency ion exchange materials. More importantly, the root-soil structure opens up avenues for enhancing the dimensional stability of functional hydrogels.

A Real-Time Wearable UV-Radiation Monitor based on a High-Performance p-CuZnS/n-TiO2 Photodetector.

Solar radiation, especially ultraviolet (UV) light, is a major hazard for most skin-related cancers. The growing needs for wearable health monitoring systems call for a high-performance real-time UV sensor to prevent skin diseases caused by excess UV exposure. To this end, here a novel self-powered p-CuZnS/n-TiO2 UV photodetector (PD) with high performance is successfully developed (responsivity of 2.54 mA W-1 at 0 V toward 300 nm). Moreover, by effectively replacing the Ti foil with a thin Ti wire for the anodization process, the conventional planar rigid device is artfully turned into a fiber-shaped flexible and wearable one. The fiber-shaped device shows an outstanding responsivity of 640 A W-1 , external quantum efficiency of 2.3 × 105 %, and photocurrent of ≈4 mA at 3 V, exceeding those of most current UV PDs. Its ultrahigh photocurrent enables it to be easily integrated with commercial electronics to function as a real-time monitor system. Thus, the first real-time wearable UV radiation sensor that reads out ambient UV power density and transmits data to smart phones via wifi is demonstrated. This work not only presents a promising wearable health monitor, but also provides a general strategy for designing and fabricating smart wearable electronic devices.

Design of Carrageenan-Based Heparin-Mimetic Gel Beads as Self-Anticoagulant Hemoperfusion Adsorbents.

The currently used hemoperfusion adsorbents such as activated carbon and ion-exchange resin show dissatisfactory hemocompatibility, and a large dose of injected heparin leads to the increasing cost and the risk of systematic bleeding. Natural polysaccharide adsorbents commonly have good biocompatibility, but their application is restricted by the poor mechanical strength and low content of functional groups. Herein, we developed an efficient, self-anticoagulant and blood compatible hemoperfusion adsorbent by imitating the structure and functional groups of heparin. Carrageenan and poly(acrylic acid) (PAA) cross-linked networks were built up by the combination of phase inversion of carrageenan and post-cross-linking of AA, and the formed dual-network structure endowed the beads with improved mechanical properties and controlled swelling ratios. The beads exhibited low protein adsorption amounts, low hemolysis ratios, low cytotoxicity, and suppressed complement activation and contact activation levels. Especially, the activated partial thromboplastin time, prothrombin time, and thrombin time of the gel beads were prolonged over 13, 18, and 4 times than those of the control. The self-anticoagulant and biocompatible beads showed good adsorption capacities toward exogenous toxins (560.34 mg/g for heavy metal ions) and endogenous toxins (14.83 mg/g for creatinine, 228.16 mg/g for bilirubin, and 18.15 mg/g for low density lipoprotein (LDL)), thus, highlighting their potential usage for safe and efficient blood purification.

Co-deposition towards mussel-inspired antifouling and antibacterial membranes by using zwitterionic polymers and silver nanoparticles.

Bacterial attachment and the subsequent colonization on the surfaces of bio-materials usually result in biofilm formation, and thus lead to implant failure, inflammation and so on. Herein, a novel mussel-inspired antibacterial and antifouling membrane was designed via co-deposition of polydopamine (PDA) and a zwitterionic polymer, followed by incorporating bactericidal silver nanoparticles (Ag NPs). Polyethyleneimine-graft-sulfobetaine methacrylate (PEI-SBMA) was firstly co-deposited onto a polyethersulfone (PES) membrane surface via crosslinking with PDA to construct an antifouling surface. Then, Ag NPs were in situ synthesized on the membrane surface without adding any external reducing agents. Elemental and morphological surface analyses confirmed the successful co-deposition of PEI-SBMA onto the PES surface and the successful reduction of silver ions by the PDA layer. In addition, the PEI-SBMA could significantly reduce Ag NP aggregation, and the modified surface exhibited sustained bactericidal activity and effective inhibition of bacterial adhesion. This demonstrated that the proposed approach was straightforward to fabricate mussel-inspired antifouling and antibacterial membranes, which showed great potential to be used in biomedical fields.