Vitrimeric Polylactide by Two-step Alcoholysis and Transesterification during Reactive Processing for Enhanced Melt Strength.

Because of its rather low melt strength, polylactide (PLA) has yet to fulfill its promise as advanced biobased and biodegradable foams to replace fossil-based polymer foams. In this work, PLA vitrimers were prepared by two-step reactive processing from commercial PLA thermoplastics, glycerol, and diphenylmethane diisocyanate (MDI) using Zn(II)-catalyzed addition and transesterification chemistry. The transesterification reaction of PLA and glycerol occurs with zinc acetate as the catalyst, and chain scission will take place due to the alcoholysis of the PLA chains by the free hydroxyl groups from the glycerol. Long-chain PLA with hydroxyl groups can be obtained and then cross-linked with MDI. Rheological analysis shows that the formed cross-linked network can significantly improve melt strength and promote strain hardening under extensional flow. PLA vitrimers still maintain the ability of thermoplastic processing via extrusion and compression. The enhanced melt strength and the rearrangement of network topology facilitate the foaming processing. An expansion ratio as large as 49.2-fold and microcellular foam with a uniform cell morphology can be obtained for PLA vitrimers with a gel fraction of 51.8% through a supercritical carbon dioxide foaming technique. This work provides a new way with the scale-up possibility to enhance the melt strength of PLA, and the broadened range of PLA applicability brought by PLA vitrimers is truly valuable in terms of the realization of a sustainable society.

Phase change mediated mechanically transformative dynamic gel for intelligent control of versatile devices.

Traditional devices, including conventional rigid electronics and machines, as well as emerging wearable electronics and soft robotics, almost all have a single mechanical state for particular service purposes. Nonetheless, dynamic materials with interchangeable mechanical states, which enable more diverse and versatile applications, are urgently necessary for intelligent and adaptive application cases in the future electronic and robot fields. Here, we report a gel-like material composed of a crosslinking polymer network impregnated with a phase changing molten liquid, which undergoes an exceptional stiffness transition in response to a thermal stimulus. Vice versa, the material switches from a soft gel state to a rigid solid state with a dramatic stiffness change of 105 times (601 MPa versus 4.5 kPa) benefiting from the liquid-solid phase change of the crystalline polymer once cooled. Such reversibility of the phase and mechanical transition upon thermal stimuli enables the dynamic gel mechanical transformation, demonstrating potential applications in an adhesive thermal interface gasket (TIG) to facilitate thermal transport, a high-temperature warning sensor and an intelligent gripper. Overall, this dynamic gel with a tunable stiffness change paves a new way to design and fabricate adaptive smart materials toward intelligent control of versatile devices.

Redox-Mediated Artificial Non-Enzymatic Antioxidant MXene Nanoplatforms for Acute Kidney Injury Alleviation.

Acute kidney injury (AKI), as a common oxidative stress-related renal disease, causes high mortality in clinics annually, and many other clinical diseases, including the pandemic COVID-19, have a high potential to cause AKI, yet only rehydration, renal dialysis, and other supportive therapies are available for AKI in the clinics. Nanotechnology-mediated antioxidant therapy represents a promising therapeutic strategy for AKI treatment. However, current enzyme-mimicking nanoantioxidants show poor biocompatibility and biodegradability, as well as non-specific ROS level regulation, further potentially causing deleterious adverse effects. Herein, the authors report a novel non-enzymatic antioxidant strategy based on ultrathin Ti3 C2 -PVP nanosheets (TPNS) with excellent biocompatibility and great chemical reactivity toward multiple ROS for AKI treatment. These TPNS nanosheets exhibit enzyme/ROS-triggered biodegradability and broad-spectrum ROS scavenging ability through the readily occurring redox reaction between Ti3 C2 and various ROS, as verified by theoretical calculations. Furthermore, both in vivo and in vitro experiments demonstrate that TPNS can serve as efficient antioxidant platforms to scavenge the overexpressed ROS and subsequently suppress oxidative stress-induced inflammatory response through inhibition of NF-κB signal pathway for AKI treatment. This study highlights a new type of therapeutic agent, that is, the redox-mediated non-enzymatic antioxidant MXene nanoplatforms in treatment of AKI and other ROS-associated diseases.

Orthogonal test design for optimization of the extraction of flavonid from the Fructus Gardeniae.

OBJECTIVE: It is imperative to provide some consistent experimental results for the extraction of flavonid from Fructus Gardeniae. METHODS: The key extraction parameters that influenced the yield of flavonid from Fructus Gardeniae were optimized by employing an orthogonal experiment [L(9)(3)(4)], including the ratio of buffer solution (Na(2)B(4)O(7)·10H(2)O) to raw material, concentration of Fructus Gardeniae in extracting solution, extraction time and pH of buffer solution. An UV/Vis detector was used to perform the qualitative and quantitative analyses of the extracted flavonid with the using of the standard sample. RESULTS: The maximum extraction yield of the crude extract was 5.0533 (mg/g) after 20 min when the mass ratio of Na(2)B(4)O(7)·10H(2)O to raw material was 0.4%, the concentration of Fructus Gardeniae in the extraction solution was 1/12 (g/mL), and pH of buffer solution was 4.5. The positive reactions to the Molish and HCl-Mg tests suggested that the extracted compound was flavonoid, and FTIR measurements also identified the presence of flavonoid in the extracts. CONCLUSION: This work is expected to provide a basis for further research, development, and utilization of Fructus gardenia in flavonid extraction.

Investigation on reliability and scalability of an FBG-based hierarchical AOFSN.

The reliability and scalability of large-scale based optical fiber sensor networks (AOFSN) are considered in this paper. The AOFSN network consists of three-level hierarchical sensor network architectures. The first two levels consist of active interrogation and remote nodes (RNs) and the third level, called the sensor subnet (SSN), consists of passive Fiber Bragg Gratings (FBGs) and a few switches. The switch architectures in the RN and various SSNs to improve the reliability and scalability of AOFSN are studied. Two SSNs with a regular topology are proposed to support simple routing and scalability in AOFSN: square-based sensor cells (SSC) and pentagon-based sensor cells (PSC). The reliability and scalability are evaluated in terms of the available sensing coverage in the case of one or multiple link failures.