A Vitrimer Acts as a Compatibilizer for Polyethylene and Polypropylene Blends.

Polymer compatibilization plays a critical role in achieving polymer blends with favorable mechanical properties and enabling efficient recycling of mixed plastic wastes. Nonetheless, traditional compatibilization methods often require tailored designs based on the specific chemical compositions of the blends. In this study, we propose a new approach for compatibilizing polymer blends using a dynamically crosslinked polymer network, known as vitrimers. By adding a relatively small amount (1-5 w/w%) of a vitrimer made of siloxane-crosslinked high-density polyethylene (HDPE), we successfully compatibilized unmodified HDPE and isotactic polypropylene (iPP). The vitrimer-compatibilized blend exhibited enhanced elongation at break (120 %) and smaller iPP domain sizes (0.4 µm) compared to the control blend (22 % elongation at break, 0.9 µm iPP droplet size). Moreover, the vitrimer-compatibilized blend showed significantly improved microphase stability during annealing at 180 °C. This straightforward method shows promise for applications across various polymer blend systems.

Sugar-Fueled Dissipative Living Materials.

Dissipative behaviors in biology are fuel-driven processes controlled by living cells, and they shape the structural and functional complexities in biological materials. This concept has inspired the development of various forms of synthetic dissipative materials controlled by time-dependent consumption of chemical or physical fuels, such as reactive chemical species, light, and electricity. To date, synthetic living materials featuring dissipative behaviors directly controlled by the fuel consumption of their constituent cells is unprecedented. In this paper, we report a chemical fuel-driven dissipative behavior of living materials comprising Staphylococcus epidermidis and telechelic block copolymers. The macroscopic phase transition is controlled by d-glucose which serves a dual role of a competitive disassembling agent and a biological fuel source for living cells. Our work is a significant step toward constructing a synthetic dissipative living system and provides a new tool and knowledge to design emergent living materials.

Waste-Free Fully Electrically Fueled Dissipative Self-Assembly System.

The importance and prevalence of energy-fueled active materials in living systems have inspired the design of synthetic active materials using various fuels. However, several major limitations of current designs remain to be addressed, such as the accumulation of chemical wastes during the process, unsustainable active behavior, and the lack of precise spatiotemporal control. Here, we demonstrate a fully electrically fueled (e-fueled) active self-assembly material that can overcome the aforementioned limitations. Using an electrochemical setup with dual electrocatalysts, the anodic oxidation of one electrocatalyst (ferrocyanide, [Fe(CN)6]4-) creates a positive fuel to activate the self-assembly, while simultaneously, the cathodic reduction of the other electrocatalyst (methyl viologen, [MV]2+) generates a negative fuel triggering fiber disassembly. Due to the fully catalytic nature for the reaction networks, this fully e-fueled active material system does not generate any chemical waste, can sustain active behavior for an extended period when the electrical potential is maintained, and provides spatiotemporal control.

Super-Aerophilic Biomimetic Cactus for Underwater Dispersed Microbubble Capture, Self-Transport, Coalescence, and Energy Harvesting.

Human ocean activities are inseparable from the supply of energy. The energy contained in the gas-phase components dispersed in seawater is a potential universal energy source for eupelagic or deep-sea equipment. However, the low energy density of bubbles dispersed in water introduces severe challenges to the potential energy harvesting of gas-phase components. Here, a super-aerophilic biomimetic cactus is developed for underwater dispersive microbubble capture and energy harvesting. The bubbles captured by the super-aerophilic biomimetic cactus spines, driven by the surface tension and liquid pressure, undergo automatic transport, coalescence, accumulation, and concentrated release. The formerly unavailable low-density dispersive surface free energy of the bubbles is converted into high-density concentrated gas buoyancy potential energy, thereby providing an energy source for underwater in situ electricity generation. Experiments show a continuous process of microbubble capture by the biomimetic cactus and demonstrate a 22.76-times increase in output power and a 3.56-times enhancement in electrical energy production compared with a conventional bubble energy harvesting device. The output energy density is 3.64 times that of the existing bubble energy generator. This work provides a novel approach for dispersive gas-phase potential energy harvesting in seawater, opening up promising prospects for wide-area in situ energy supply in underwater environments.

Precise Control of Dissipative Self-assembly by Light and Electricity.

Nature-inspired synthetic dissipative self-assemblies have attracted much attention recently. However, it remains a major challenge to achieve precise control over dissipative supramolecular assembly structures and functions of self-contained systems. Here we combine light and electricity as two clean, and spatiotemporally addressable fuels to provide precise control over the morphology for dissipative self-assembly of a perylene bisimide glycine (PBIg) building block in a self-contained solution. In this design, electrochemical oxidation provides the positive fuel to activate PBIg self-assembly while photoreduction supplies the negative fuel to deactivate the system for disassembly. Through programming the two counteracting fuels, we demonstrated the control of PBIg self-assembly into a variety of assembly morphologies in a self-contained system. In addition, by exerting light and electrical dual fuels simultaneously, we could create an active homeostasis exhibiting dynamic instability, leading to morphological change to asymmetric assemblies with curvatures. Such precise control over self-assembly of self-contained systems may find future applications in programming complex active materials as well as formulating pharmaceutical reagents with desired morphologies.

Facile Synthesis of Multifunctional Bioreducible Polymers for mRNA Delivery.

Bioreducible polymeric mRNA carriers are an emerging family of vectors for gene delivery and vaccine development. A few bioreducible systems have been generated through aqueous-phase ring-opening polymerization of lipoic acid derivatives, however this methodology limits hydrophobic group incorporation and functionality into resulting polymers. Herein, a poly(active ester)disulfide polymer is synthesized that can undergo facile aminolysis with amine-containing substrates under stoichiometric control and mild reaction conditions to yield a library of multifunctional polydisulfide polymers. Functionalized polydisulfide polymer species form stable mRNA-polymer nanoparticles for intracellular delivery of mRNAs in vitro. Alkyl-functionalized polydisulfide-RNA nanoparticles demonstrate rapid cellular uptake and excellent biodegradability when delivering EGFP and OVA mRNAs to cells in vitro. This streamlined polydisulfide synthesis provides a new facile methodology for accessing multifunctional bioreducible polymers as biomaterials for RNA delivery and other applications.

Passive Automatic Switch Relying on Laplace Pressure for Efficient Underwater Low-Gas-Flux Bubble Energy Harvesting.

The buoyancy potential energy contained in bubbles released by subsea geological and biological activities represents a possible in situ energy source for underwater sensing and detection equipment. However, the low gas flux of the bubble seepages that exist widely on the seabed introduces severe challenges. Herein, a passive automatic switch relying on Laplace pressure is proposed for efficient energy harvesting from low-gas-flux bubbles. This switch has no moving mechanical parts; it uses the Laplace-pressure difference across a curved gas-liquid interface in a biconical channel as an invisible "microvalve". If there is mechanical equilibrium between the Laplace-pressure difference and the liquid-pressure difference, the microvalve will remain closed and prevent the release of bubbles as they continue to accumulate. After the accumulated gas reaches a threshold value, the microvalve will open automatically, and the gas will be released rapidly, relying on the positive feedback of interface mechanics. Using this device, the gas buoyancy potential energy entering the energy harvesting system per unit time can be increased by a factor of more than 30. Compared with a traditional bubble energy harvesting system without a switch, this system achieves a 19.55-fold increase in output power and a 5.16-fold enhancement in electrical energy production. The potential energy of ultralow flow rate bubbles (as low as 3.97 mL/min) is effectively collected. This work provides a new design philosophy for passive automatic-switching control of gas-liquid two-phase fluids, presenting an effective approach for harvesting of buoyancy potential energy from low-gas-flux bubble seepages. This opens a promising avenue for in situ energy supply for subsea scientific observation networks.

Electrically Fueled Active Supramolecular Materials.

Fuel-driven dissipative self-assemblies play essential roles in living systems, contributing both to their complex, dynamic structures and emergent functions. Several dissipative supramolecular materials have been created using chemicals or light as fuel. However, electrical energy, one of the most common energy sources, has remained unexplored for such purposes. Here, we demonstrate a new platform for creating active supramolecular materials using electrically fueled dissipative self-assembly. Through an electrochemical redox reaction network, a transient and highly active supramolecular assembly is achieved with rapid kinetics, directionality, and precise spatiotemporal control. As electronic signals are the default information carriers in modern technology, the described approach offers a potential opportunity to integrate active materials into electronic devices for bioelectronic applications.

Multifunctional Dendronized Polypeptides for Controlled Adjuvanticity.

Vaccination has been playing an important role in treating both infectious and cancerous diseases. Nevertheless, many diseases still lack proper vaccines due to the difficulty to generate sufficient amounts of antigen-specific antibodies or T cells. Adjuvants provide an important route to improve and direct immune responses. However, there are few adjuvants approved clinically and many of them lack the clear structure/adjuvanticity relationship. Here, we synthesized and evaluated a series of dendronized polypeptides (denpols) functionalized with varying tryptophan/histidine (W/H) molar ratios of 0/100, 25/75, 50/50, 75/25, and 100/0 as tunable synthetic adjuvants. The denpols showed structure-dependent inflammasome activation in THP1 monocytic cells and structure-related activation and antigen cross-presentation in vitro in bone marrow-derived dendritic cells. We used the denpols with bacterial pathogen Coxiella burnetii antigens in vivo, which showed both high and tunable adjuvating activities, as demonstrated by the antigen-specific antibody and T cell responses. The denpols are easy to make and scalable, biodegradable, and have highly adjustable chemical structures. Taken together, denpols show great potential as a new and versatile adjuvant platform that allows us to adjust adjuvanticity based on structure-activity correlation with the aim to fine-tune the immune response, thus advancing vaccine development.

Multivalent Peptide-Functionalized Bioreducible Polymers for Cellular Delivery of Various RNAs.

RNA-based therapeutics have garnered tremendous attention due to their potential to revolutionize protein replacement therapies, immunotherapy, and treatment of genetic disorders. The lack of safe and efficient RNA delivery methods has significantly hindered the clinical translation and widespread application of RNA-based therapeutics. With differing sizes and structures of therapeutic RNA molecules, a critical challenge of the field is to develop RNA delivery systems that accommodate these variations while retaining high biocompatibility and efficacy. In this study, we developed a series of multivalent peptide-functionalized bioreducible polymers (MPBP) as a safe and efficient delivery vehicle derived from a core polymer backbone for various RNA species. The facile synthesis of MPBPs from a single polymer backbone provides access to numerous polymers with diverse architectures that enable cellular delivery of different RNA cargos. Postfunctionalization with multifunctional peptides enables strong RNA complexation, enhanced cellular uptake, and facilitates endosomal escape of cargo. The high delivery efficiency and low cytotoxicity for various RNA-MPBP nanoparticles in multiple cell lines demonstrates that the MPBP approach is a novel promising vector strategy for future RNA delivery systems.

Direct Silyl Ether Metathesis for Vitrimers with Exceptional Thermal Stability.

Vitrimers are a new class of polymeric materials that simultaneously offer the desired physical properties of thermosets and malleability/reprocessability of thermoplastics. Despite significant progress being made in the field of vitrimers, there exists a critical need for the development of robust dynamic covalent chemistries for the production of strong and thermally stable vitrimers. In this work, we discovered a new silyl ether metathesis reaction and used it for the preparation of vitrimers with exceptional thermal stability. In small-molecule model studies, we observed that silyl ether motifs directly exchange under anhydrous conditions catalyzed by a Brønsted or Lewis acid catalyst. For initial vitrimer demonstration, a commodity polymer, poly(ethylene-co-vinyl alcohol) (PEOH), was silylated with trimethylsilyl (TMS) groups followed by cross-linking with a bis-silyl ether cross-linker. The resulting thermoset showed exceptional thermal stability while maintaining malleability/reprocessability at elevated temperatures. The vitrimer properties such as recyclability and stress relaxation at various temperatures were carefully investigated. The material was reprocessable at 150 °C while also exhibiting good creep resistance at temperatures below its melting transition (Tm). This work demonstrates the silyl ether metathesis reaction as a new, robust dynamic covalent chemistry to introduce plasticity, reprocessability, and recyclability to thermosets.

A Three-Armed Polymer with Tunable Self-Assembly and Self-Healing Properties Based on Benzene-1,3,5-tricarboxamide and Metal-Ligand Interactions.

The dynamic nature of supramolecules makes them useful in the fields of smart devices. The combination of multiple dynamic interactions in one material may bring some enhanced properties in mechanical property, self-healing property, or recyclability. Thus, it is significantly meaningful to design new materials with multi-dynamic bonds and clarify their bonding mechanisms. Here, a novel three-armed polymer based on benzene-1,3,5-tricarboxamide (BTA) is developed and the polymer could be further complexed by metal ions to form dynamic zinc-imidazole interactions. In this system, BTA is located in the center, and the ligand-functionalized monomer is copolymerized with n-butyl acrylate to form three chains. This is the first time BTA is introduced to a self-healing system to endow the polymer with assembly and self-healing properties. The composition, chemical structure, assembly behavior, mechanical properties, and self-healing properties of the polymer are investigated. It is revealed that the assembly behavior of the polymer depends on the BTA contents and time. The mechanical property can be easily tuned by ligand/metal ratio and is significantly adjusted by the polymer chain length and environment humidity. Long polymer chains not only contribute to good mechanical property but also promote the self-healing process due to the effective physical entanglement.

Recyclable, Strong, and Highly Malleable Thermosets Based on Boroxine Networks.

Traditional thermoset materials have favorable material properties but are unable to reprocess and are difficult to recycle. Small molecule boroxines have been shown to undergo a reversible exchange reaction. Herein we employ boroxine as dynamic cross-links to construct a novel type of thermoset material that is strong, highly malleable, and recyclable. The synthesis and dynamic mechanical properties of boroxine networks are described. Upon heating in water the material can be recycled back to its monomer. With a multitude of tunable variables, we anticipate this system to be a platform for the development of a range of new dynamic materials.

Silyl Ether as a Robust and Thermally Stable Dynamic Covalent Motif for Malleable Polymer Design.

Here we introduce silyl ether linkage as a novel dynamic covalent motif for dynamic material design. Through introduction of a neighboring amino moiety, we show that the silyl ether exchange rate can be accelerated by almost three orders of magnitude. By incorporating such silyl ether linkages into covalently cross-linked polymer networks, we demonstrate dynamic covalent network polymers displaying both malleability and reprocessability. The malleability of the networks is studied by monitoring stress relaxation at varying temperature, and their topology freezing temperatures are determined. The tunable dynamic properties coupled with the high thermal stability and reprocessability of silyl ether-based networks open doors to many potential applications for this family of materials.

Large Continuous Mechanical Gradient Formation via Metal-Ligand Interactions.

Mechanical gradients are often employed in nature to prevent biological materials from damage by creating a smooth transition from strong to weak that dissipates large forces. Synthetic mimics of these natural structures are highly desired to improve distribution of stresses at interfaces and reduce contact deformation in manmade materials. Current synthetic gradient materials commonly suffer from non-continuous transitions, relatively small gradients in mechanical properties, and difficult syntheses. Inspired by the polychaete worm jaw, we report a novel approach to generate stiffness gradients in polymeric materials via incorporation of dynamic monodentate metal-ligand crosslinks. Through spatial control of metal ion content, we created a continuous mechanical gradient that spans over a 200-fold difference in stiffness, approaching the mechanical contrast observed in biological gradient materials.

Control of hierarchical polymer mechanics with bioinspired metal-coordination dynamics.

In conventional polymer materials, mechanical performance is traditionally engineered via material structure, using motifs such as polymer molecular weight, polymer branching, or block copolymer design. Here, by means of a model system of 4-arm poly(ethylene glycol) hydrogels crosslinked with multiple, kinetically distinct dynamic metal-ligand coordinate complexes, we show that polymer materials with decoupled spatial structure and mechanical performance can be designed. By tuning the relative concentration of two types of metal-ligand crosslinks, we demonstrate control over the material's mechanical hierarchy of energy-dissipating modes under dynamic mechanical loading, and therefore the ability to engineer a priori the viscoelastic properties of these materials by controlling the types of crosslinks rather than by modifying the polymer itself. This strategy to decouple material mechanics from structure is general and may inform the design of soft materials for use in complex mechanical environments. Three examples that demonstrate this are provided.

Fluorocarbon Modified Low-Molecular-Weight Polyethylenimine for siRNA Delivery.

We report the synthesis and study of fluorocarbon (FC) modified polyethylenimine (PEI) for the purpose of siRNA delivery. Low-molecular-weight PEI (Mn = 600) was functionalized with fluorocarbon epoxides of varying length. All FC-modified samples with greater than 2.0 equiv of FC epoxide per PEI induced potent gene silencing in vitro. Compared to hydrocarbon (HC) analogues, the FC vectors showed greater general silencing efficacy, higher cell uptake, and reduced association with serum components. Collectively, the data suggest that modification of polyamines with FCs is a promising approach for the discovery of novel vectors for siRNA delivery.

Focused Library Approach to Discover Discrete Dipeptide Bolaamphiphiles for siRNA Delivery.

In this study, we report a new dipeptide functionalization strategy for developing new dendritic bolaamphiphile vectors for efficient siRNA transfection. A focused library of dipeptides was constructed using four amino acids: l-arginine, l-histidine, l-lysine, and l-tryptophan. The dipeptides were coupled to two dendritic bolaamphiphile scaffolds that we developed previously, allowing us to quickly access a focused library of discrete vectors with multivalent dendritic dipeptide functionalities. The resulting discrete bolaamphiphiles were screened for siRNA delivery in vitro in HEK-293 and HeLa cells. Bolaamphiphiles functionalized with dipeptides containing Lys or Arg and either His or Trp were the most effective for in vitro siRNA delivery. Necessary cationic charge to ensure efficient siRNA binding are provided by Arg and Lys residues, whereas endosomal escape is provided through pH responsive buffering of His or membrane interactions of Trp. The most effective vectors (F10 HR/RH) exhibited greater than 75% gene silencing in multiple cell lines and exhibited serum stability.

Enhanced Glassy State Mechanical Properties of Polymer Nanocomposites via Supramolecular Interactions.

It is now well accepted that the addition of nanoparticles (NPs) can strongly affect the thermomechanical properties of the polymers into which they are incorporated. In the solid (glassy) state, previous work has implied that optimal mechanical properties are achieved when the NPs are well dispersed in the matrix and when there is strong interfacial binding between the grafted NPs and the polymer matrix. Here we provide strong evidence supporting the importance of intermolecular interactions through the use of NPs grafted with polymers that can hydrogen bond with the matrix, yielding to significant improvements in the measured mechanical properties. Our finding thus supports the previously implied central role of strong interfacial binding in optimizing the mechanical properties of polymer nanocomposites.

Enhancing mechanical performance of a covalent self-healing material by sacrificial noncovalent bonds.

Polymers that repair themselves after mechanical damage can significantly improve their durability and safety. A major goal in the field of self-healing materials is to combine robust mechanical and efficient healing properties. Here, we show that incorporation of sacrificial bonds into a self-repairable network dramatically improves the overall mechanical properties. Specifically, we use simple secondary amide side chains to create dynamic energy dissipative hydrogen bonds in a covalently cross-linked polymer network, which can self-heal via olefin cross-metathesis. We envision that this straightforward sacrificial bonding strategy can be employed to improve mechanical properties in a variety of self-healing systems.