Self-evolutionary recycling of flame-retardant polyurethane foam enabled by controllable catalytic cleavage.

Polyurethane (PU) foams, pivotal in modern life, face challenges suh as fire hazards and environmental waste burdens. The current reliance of PU on potentially ecotoxic halogen-/phosphorus-based flame retardants impedes large-scale material recycling. Here, our demonstrated controllable catalytic cracking strategy, using cesium salts, enables self-evolving recycling of flame-retardant PU. The incorporation of cesium citrates facilitates efficient urethane bond cleavage at low temperatures (160 °C), promoting effective recycling, while encouraging pyrolytic rearrangement of isocyanates into char at high temperatures (300 °C) for enhanced PU fire safety. Even in the absence of halogen/phosphorus components, this foam exhibits a substantial increase in ignition time (+258.8%) and a significant reduction in total smoke release (-79%). This flame-retardant foam can be easily recycled into high-quality polyol under mild conditions, 60 °C lower than that for the pure foam. Notably, the trace amounts of cesium gathered in recycled polyols stimulate the regenerated PU to undergo self-evolution, improving both flame-retardancy and mechanical properties. Our controllable catalytic cracking strategy paves the way for the self-evolutionary recycling of high-performance firefighting materials.

Microcage flame retardants with complete recyclability and durability via reversible interfacial locking engineering.

Flame retardants are effective in protecting materials from fire but pose environmental challenges due to limited recyclability. Urgently needed for circular material economy are new flame retardants that are chemically recyclable and durable. Here, we report a new facile and scalable strategy for engineering reversible microcages with infinite chemical recyclability to starting monomers, exceptional durability, and versatile flame retardancy. This is achieved through a highly synergistic hierarchical assembly of easily obtainable phosphoric acid and Cu2+ monomers. By leveraging dynamic reversible assembly networks, microcages can be circularly and infinitely dissociated into starting monomers via eco-friendly pH adjustment. Remarkable recovery rates of 92% for phosphoric acid and 96.2% for Cu2+ monomers are achieved, while the separated virgin matrix undergoes conventional chemical recycling, facilitating reformulation and seamless reintroduction into new supply chains as needed. Notably, when integrated with matrix-like surfaces, microcage clasp matrices tightly engage through in situ formed interfacial locking structures, showcasing outstanding flame-retardant efficiency, prolonged durability in hydrothermal aging, and extensive applicability across diverse polymeric materials such as polyurethane, epoxy resin, and polycarbonate. This study emphasizes a novel, straightforward, and scalable chemical platform, utilizing reversible interfacial locking engineering, for the development of flame retardants that are not only infinitely recyclable but also durable and broadly applicable.

Stable, Bioresponsive, and Macrophage-Evading Polyurethane Micelles Containing an Anionic Tripeptide Chain Extender.

Polymeric nanocarriers have been extensively used in medicinal applications for drug delivery. However, intravenous nanocarriers circulating in the blood will be rapidly cleared from the mononuclear macrophage system. The surface physicochemical characterizations of nanocarriers are the primary factors to determine their fate in vivo, such as evading the reticuloendothelial system, exhibiting long blood circulation times, and accumulating in the targeted site. In this work, we develop a series of polyurethane micelles containing segments of an anionic tripeptide, hydrophilic mPEG, and disulfide bonds. It is found that the long hydrophilic mPEG can shield the micellar surface and have a synergistic effect with the negatively charged tripeptide to minimize macrophage phagocytosis. Meanwhile, the disulfide bond can rapidly respond to the intracellular reduction environment, leading to the acceleration of drug release and improvement of the therapeutic effect. Our results verify that these anionic polyurethane micelles hold great potential in the development of the stealth immune system and controllable intracellular drug transporters.

Albumin-Modified Cationic Nanocarriers To Potentially Create a New Platform for Drug Delivery Systems.

Cationic nanocarriers have emerged as promising nanoparticle systems for the effective delivery of nucleic acid and anticancer drugs to cancer cells. A positive charge is desirable for promoting cell internalization, whereas it also causes some adverse effects, such as toxicity and rapid clearance by mononuclear phagocytic systems. Herein, a new strategy of modifying cationic polymer micelles with albumin forming a protein corona to improve the surface physiochemical properties is reported. The corona with a monolayer or a multilayer was constructed depending on the albumin concentration, and the proteins would denature in different degrees due to the interaction with the surface of cationic micelles. It is demonstrated that multilayer albumin corona is beneficial to prevent macrophage uptake, increase accumulation in tumor tissues, and reduce toxic side effects to normal tissues. Our work provides a promising method to modify the cationic nanoplatform by optimizing the biosecurity and bioavailability for potential application in drug delivery.

Macrophage Polarization in Response to Varying Pore Sizes of 3D Polyurethane Scaffolds.

Activated macrophages dominate the progression of foreign-body response (FBR) and may be in a bimodal state, which determines the fate of biomaterials postimplantation. The purpose of this study was to investigate the phenotypic profile of macrophages polarized by waterborne biodegradable polyurethane (WBPU) scaffolds with different pore diameters (PU8, PU12, and PU16) both in vitro and in vivo. The results demonstrated that WBPU scaffolds with smaller pore sizes promoted the polarization of RAW 264.7 cells towards an M1 phenotypic profile at the early stage (24 and 48 h of in vitro cultivation), indicating a pro-inflammatory response. After being implanted subcutaneously, however, the WBPU scaffolds recruited more macrophages over time and polarized them towards an M2 phenotype on Day 3 and 14, presenting an anti-inflammatory response and tissue repair. When the internal pores were filled up (on Day 30 of implantation), the interaction between the scaffolds and macrophages decreased, indicating an endpoint of tissue repair. In general, WBPU scaffolds with tunable internal pore sizes have potential application prospects in the field of tissue engineering.

Understanding the effect of alkyl chains of gemini cations on the physicochemical and cellular properties of polyurethane micelles.

Cationic gemini quaternary ammonium (GQA) has been used as a cell internalization promoter to improve the permeability of the cell membrane and enhance the cellular uptake. However, the effect of the alkyl chain length on the cellular properties of nanocarriers has not been elucidated yet. In this study, we developed a series of polyurethane micelles containing GQAs with various alkyl chain lengths. The alteration of the gemini alkyl chain length was found to change the distribution of GQA surfactants in the micellar structure and affect the surface charge exposure, stability, and the protein absorption properties of nanocarriers. Moreover, we also clarified the role of the alkyl chain length in tumor cell internalization and macrophage uptake of polyurethane micelles. This work provides a new understanding on the effect of the GQA alkyl chain length on the physicochemical and biological properties of nanomedicines, and offers guidance on the rational design of effective drug delivery systems where the issue of functional group exposure at the micellar surface should be considered.

Surface Distribution and Biophysicochemical Properties of Polymeric Micelles Bearing Gemini Cationic and Hydrophilic Groups.

Polymeric micelles containing cationic gemini quaternary ammonium (GQA) groups have shown enhanced cellular uptake and efficient drug delivery, while the incorporation of poly(ethylene glycol) (PEG) corona can potentially reduce the absorption of cationic carriers by opsonic proteins and subsequent uptake by mononuclear phagocytic system (MPS). To understand the interactions of GQA and PEG groups and their effects on the biophysicochemical characteristics of nanocarriers, a series of polyurethane micelles containing GQA and different molecular weights of PEG were prepared and carefully characterized. It was found that the GQA and PEG groups are unevenly distributed on the micellar surface to form two kinds of hydrophilic domains. As a result, the particle surface with some defects cannot be completely shielded by the PEG corona. Despite this, the longer PEG chains with a brush conformation provide superior stabilization and steric repulsion against the absorption of proteins and, thus, can reduce the cytotoxicity, protein absorption, and MPS uptake of micelles to some extent. This study provides a new understanding on the interactions between PEG chains and cationic groups and a guideline for the design and fabrication of safe and effective drug delivery systems.