Water-Triggered Stiffening of Shape-Memory Polyurethanes Composed of Hard Backbone Dangling PEG Soft Segments

Hydrogen Bonding Competition Mediated Phase Separation with Abnormal Moisture-Induced Stiffness Boosting

Moisture usually deteriorates polymers' mechanical performance owing to its plasticizing effect, causing side effects in their practical load-bearing applications. Herein, a simple binary ionogel consisting of an amphiphilic polymer network and a hydrophobic ionic liquid (IL) is developed with remarkable stiffening effect after moisture absorption, demonstrating a complete contrast to water-induced softening effect of most polymer materials. Such a moisture-induced stiffening behavior is induced by phase separation after hydration of this binary ionogel. Specifically, it is revealed that hydrogen (H)-bonding structures play a dominant role in the humidity-responsive behavior of the ionogel, where water will preferentially interact with polymer chains through H-bonding and break the polymer-IL H-bonds, thus leading to phase separation structures with modulus boosting. This work may provide a facile and effective molecular engineering route to construct mechanically adaptive polymers with water-induced dramatic stiffening for diverse applications.

Pearl-Inspired Intelligent Marine Hetero Nanocomposite Coating Based on "Brick&Mortar" Strategy: Anticorrosion Durability and Switchable Antifouling

Corrosion activities and biofouling pose significant challenges for marine facilities, resulting in substantial economic losses. Inspired by the "brick&mortar" structure of pearls, a novel nanocomposite coating (Pun-HJTx) with long-lasting anticorrosion and intelligent antifouling modes is fabricated by integrating a compatible MoS2/MXene heterostructure as the "brick" into a polyurea-modified PDMS (Pun) acting as "mortar." Notably, the presence of multiple hydrogen bonds within the coating effectively reduces the pinholes resulted from solution volatilizing. In the dark, where fouling adhesion and microbial corrosion activities are weakened, the MoS2/MXene plays a role in contact bactericidal action. Conversely, during daylight when fouling adhesion and microbial corrosion activities intensify, the coating releases reactive oxygen species (such as hydroxyl radicals and superoxide ions) to counteract fouling adhesion. Additionally, the coating exhibits multisource self-healing performance under heated or exposed to light (maximum self-healing rate can reach 99.46%) and proves efficient self-cleaning performance and adhesion strength (>2.0 Mpa), making it highly suitable for various practical marine applications. Furthermore, the outstanding performance of the Pun-HJT1 is maintained for ≈180 days in real-world marine conditions, which proving its practicality and feasibility in real shallow sea environments.

Bioinspired Injectable Polyurethane Underwater Adhesive with Fast Bonding and Hemostatic Properties

Underwater adhesives with injectable, organic solvent-free, strong, fast adhesion, and hemostatic properties have become an urgent need in biomedical field. Herein, a novel polyurethane underwater adhesive (PUWA) inspired by mussels is developed utilizing the rapid post-cure reaction of isocyanate esterification without organic solvents. The PUWA is created through the injectable two component curing process of component A (biocompatible polyurethane prepolymer) and component B (dopamine modified lysine derivatives: chain extender-LDA and crosslinker-L3DA). The two-component adhesive cures quickly and firmly underwater, with an impressive bonding strength of 40 kPa on pork skin and excellent burst pressure of 394 mmHg. Moreover, the PUWA exhibits robust adhesion strength in hostile environments with acid, alkali and saline solutions. Combined with excellent biocompatibility and hemostatic performance, the PUWA demonstrates effectively sealing wounds and promoting healing. With the ability to bond diverse substrates rapidly and strongly, the PUWA holds significant potential for application in both biomedical and industrial fields.

General Semi-Solid Freeze Casting for Uniform Large-Scale Isotropic Porous Scaffolds: An Application for Extensive Oral Mucosal Reconstruction

Ice-templated porous biomaterials possess transformative potential in regenerative medicine; yet, scaling up ice-templating processes for broader applications-owing to inconsistent pore formation-remains challenging. This study reports an innovative semi-solid freeze-casting technique that draws inspiration from semi-solid metal processing (SSMP) combined with ice cream-production routines. This versatile approach allows for the large-scale assembly of various materials, from polymers to inorganic particles, into isotropic 3D scaffolds featuring uniformly equiaxed pores throughout the centimeter scale. Through (cryo-)electron microscopy, X-ray tomography, and finite element modeling, the structural evolution of ice grains/pores is elucidated, demonstrating how the method increases the initial ice nucleus density by pre-fabricating a semi-frozen slurry, which facilitates a transition from columnar to equiaxed grain structures. For a practical demonstration, as-prepared scaffolds are integrated into a bilayer tissue patch using biodegradable waterborne polyurethane (WPU) for large-scale oral mucosal reconstruction in minipigs. Systematic analyses, including histology and RNA sequencing, prove that the patch modulates the healing process toward near-scarless mucosal remodeling via innate and adaptive immunomodulation and activation of pro-healing genes converging on matrix synthesis and epithelialization. This study not only advances the field of ice-templating fabrication but sets a promising precedent for scaffold-based large-scale tissue regeneration.

Bicontinuous vitrimer heterogels with wide-span switchable stiffness-gated iontronic coordination

Currently, it remains challenging to balance intrinsic stiffness with programmability in most vitrimers. Simultaneously, coordinating materials with gel-like iontronic properties for intrinsic ion transmission while maintaining vitrimer programmable features remains underexplored. Here, we introduce a phase-engineering strategy to fabricate bicontinuous vitrimer heterogel (VHG) materials. Such VHGs exhibited high mechanical strength, with an elastic modulus of up to 116 MPa, a high strain performance exceeding 1000%, and a switchable stiffness ratio surpassing 5 × 103. Moreover, highly programmable reprocessing and shape memory morphing were realized owing to the ion liquid-enhanced VHG network reconfiguration. Derived from the ion transmission pathway in the ILgel, which responded to the wide-span switchable mechanics, the VHG iontronics had a unique bidirectional stiffness-gated piezoresistivity, coordinating both positive and negative piezoresistive properties. Our findings indicate that the VHG system can act as a foundational material in various promising applications, including smart sensors, soft machines, and bioelectronics.

Fracture-Resistant Stretchable Materials: An Overview from Methodology to Applications

Stretchable materials, such as gels and elastomers, are attractive materials in diverse applications. Their versatile fabrication platforms enable the creation of materials with various physiochemical properties and geometries. However, the mechanical performance of traditional stretchable materials is often hindered by the deficiencies in their energy dissipation system, leading to lower fracture resistance and impeding their broader range of applications. Therefore, the synthesis of fracture-resistant stretchable materials has attracted great interest. This review comprehensively summarizes key design considerations for constructing fracture-resistant stretchable materials, examines their synthesis strategies to achieve elevated fracture energy, and highlights recent advancements in their potential applications.

Ultrastable, Superrobust, and Recyclable Supramolecular Polymer Networks

Supramolecular polymer networks (SPNs), crosslinked by noncovalent bonds, have emerged as reorganizable and recyclable polymeric materials with unique functionality. However, poor stability is an imperative challenge faced by SPNs, because SPNs are susceptible to heat, water, and/or solvents due to the dynamic and reversible nature of noncovalent bonds. Herein, the design of a noncovalent cooperative network (NCoN) to simultaneously stabilize and reinforce SPNs is reported, resulting in an ultrastable, superrobust, and recyclable SPN. The NCoN is constructed by multiplying the H-bonding sites and tuning the conformation/geometry of the H-bonding segment to optimize the multivalence cooperativity of H-bonds. The rationally designed H-bonding segment with high conformational compliance favors the formation of tightly packed H-bond arrays comprising higher-density and stronger H-bonds. Consequently, the H-bonded crosslinks in the NCoN display a covalent crosslinking effect but retain on-demand dynamics and reversibility. The resultant ultrastable SPN not only displays remarkable resistance to heat up to 120 °C, water soaking, and a broad spectrum of solvents, but also possesses a superhigh true stress at break (1.1 GPa) and an ultrahigh toughness (406 MJ m-3 ). Despite the covalent-network-like stability, the SPN is recyclable through activating its reversibility in a high-polarity solvent heated to a threshold temperature.

4D printed hydrogel scaffold with swelling-stiffening properties and programmable deformation for minimally invasive implantation

The power of three-dimensional printing in designing personalized scaffolds with precise dimensions and properties is well-known. However, minimally invasive implantation of complex scaffolds is still challenging. Here, we develop amphiphilic dynamic thermoset polyurethanes catering for multi-material four-dimensional printing to fabricate supportive scaffolds with body temperature-triggered shape memory and water-triggered programmable deformation. Shape memory effect enables the two-dimensional printed pattern to be fixed into temporary one-dimensional shape, facilitating transcatheter delivery. Upon implantation, the body temperature triggers shape recovery of the one-dimensional shape to its original two-dimensional pattern. After swelling, the hydrated pattern undergoes programmable morphing into the desired three-dimensional structure because of swelling mismatch. The structure exhibits unusual soft-to-stiff transition due to the water-driven microphase separation formed between hydrophilic and hydrophobic chain segments. The integration of shape memory, programmable deformability, and swelling-stiffening properties makes the developed dynamic thermoset polyurethanes promising supportive void-filling scaffold materials for minimally invasive implantation.

Novel Heterogeneous Hydrogel with Dual-Responsive Shape Programmability and Good Biocompatibility

Shape memory polymers (SMPs) responsive to various external stimuli can realize a complex shape transformation process and have attracted extensive attention. However, integrating multiple stimulus-responsive mechanisms in one material often requires a complex molecular design and synthesis procedure. In this work, we designed a novel dual-responsive heterogeneous hydrogel (PU-PAM/Alg/PDA), which was manufactured through in situ free radical polymerization of acrylamide (AM) in the presence of alginate (Alg) and polydopamine (PDA) in a porous polycaprolactone-based polyurethane foam (PU-foam). The PU-PAM/Alg/PDA hydrogel could achieve thermal responsiveness through melting-crystallization transformation of polycaprolactone (PCL), while the metallo-supramolecular interactions between Alg and Fe3+ could provide ion responsiveness for this hydrogel. This dual-programmable feature endowed the heterogeneous hydrogel with a complex shape-morphing behavior and also a reconfiguration ability for the permanent shape. Meanwhile, the strong hydrogen bondings between PDA and polyurethane chains enhanced the interfacial adhesions, resulting in the structural integrity and excellent mechanical property of PU-PAM/Alg/PDA. The in vitro and in vivo tests revealed the good biocompatibility of the heterogeneous hydrogel, and the potential of the heterogeneous hydrogel as an esophageal stent was evaluated in vitro as conceptual proof.

Chondrocyte-laden gelatin/sodium alginate hydrogel integrating 3D printed PU scaffold for auricular cartilage reconstruction

Clinically, modified autologous rib cartilage grafts and commercial implants are commonly used for intraoperative repair of auricular cartilage defects caused by injuries. However, scaffold implantation is often accompanied by various complications including absorption and collapse, resulting in undesirable clinical outcomes. Three-dimensional printed auricular cartilage scaffolds have the advantage of individual design and biofunctionality, which attracted tremendous attention in this field. In this study, to better simulate the mechanical properties of auricular cartilage, we tested PU treated by ultrasonication and high temperature for 30 min (PU-30) or 60 min (PU-60). The results indicated that the compression modulus of PU-30 was 2.21-2.48 MPa, which similar to that of natural auricular cartilage (2.22-7.23 MPa) and was chosen for subsequent experiments. And the pores of treated PU were filled with a gelatin/sodium alginate hydrogel loaded with chondrocytes. In vivo analysis using a rabbit model confirmed that implanted PU-30 scaffold filled with chondrocytes contained hydrogel successfully integrated with normal auricular cartilage, and that new cartilage was generated at the scaffold-tissue interface by histological examination. These findings illustrate that this engineered scaffold represents a potential strategy for repair of ear cartilage damage in clinical.

In Situ Growth of Functional Hydrogel Coatings by a Reactive Polyurethane for Biomedical Devices

Surface modification of thermoplastic polyurethane (TPU) could significantly enhance its suitability for biomedical devices and public health products. Nevertheless, customized modification of polyurethane surfaces with robust interfacial bonding and diverse functions via a simple method remains an enormous challenge. Herein, a novel thermoplastic polyurethane with a photoinitiated benzophenone unit (BPTPU) is designed and synthesized, which can directly grow functional hydrogel coating on polyurethane (PU) in situ by initiating polymerization of diverse monomers under ultraviolet irradiation, without the involvement of organic solvent. The resulting coating not only exhibits tissue-like softness, controllable thickness, lubrication, and robust adhesion strength but also provides customized functions (i.e., antifouling, stimuli-responsive, antibacterial, and fluorescence emission) to the original passive polymer substrates. Importantly, BPTPU can be blended with commercial TPU to produce the BPTPU-based tube by an extruder. Only a trace amount of BPTPU can endow the tube with good photoinitiated capacity. As a proof of concept, the hydrophilic hydrogel-coated BPTPU is shown to mitigate foreign body response in vivo and prevent thrombus formation in rat blood circulation without anticoagulants in vitro. This work offers a new strategy to guide the design of functional polyurethane, an elastomer-hydrogel composite, and holds great prospects for clinical translation.

Autonomous underwater adhesion driven by water-induced interfacial rearrangement

Underwater adhesives receive extensive attention due to their wide applications in marine explorations and various related industries. However, current adhesives still suffer from excessive water absorption and lack of spontaneity. Herein, we report an autonomous underwater adhesive based on poly(2-hydroxyethyl methacrylate-co-benzyl methacrylate) amphiphilic polymeric matrix swollen by hydrophobic imidazolium ionic liquid. The as-prepared adhesive is tough and flexible, showing little to none instantaneous underwater adhesion onto the PET substrate, whereas its adhesion energy on the substrate can grow more than 5 times to 458 J·m-2 after 24 hours. More importantly, this process is entirely spontaneous, without any external pressing force. Our comprehensive studies based on experimental characterizations and molecular dynamic simulations confirm that such autonomous adhesion process is driven by water-induced rearrangement of the functional groups. It is believed that such material can provide insights into the development of next-generation smart adhesives.

Polypropylene composite mesh modified by polyurethane gel with ROS scavenging and anti-inflammatory effects for pelvic floor repair

Development of an inflammation modulating polypropylene (PP) mesh in pelvic floor repair is an urgent clinical need. This is because PP mesh for pelvic floor repair can cause a series of complications related to foreign body reactions (FBR) in postoperative period. Therefore, we successfully prepared PP composite mesh that can scavenge reactive oxygen species (ROS) and inhibit inflammation to moderate FBR by a simple method. First, a pregel layer was formed on PP mesh by dip coating. Among them, polyurethane with polythioketal (PTK) is an excellent ROS scavenger, and dopamine methacrylamide (DMA) improves the stability of the coating and synergistically scavenges ROS. Then, a composite mesh (optimal PU50-PP) was obtained by photopolymerization. The results showed that the polyurethane gel layer was able to scavenge more than 90% of free radicals and about 75% of intracellular ROS. In vitro, PU50-PP mesh significantly scavenged ROS and resisted macrophage adhesion. After implantation in the posterior vaginal wall of rats, PU50-PP eliminated 53% of ROS, inhibited inflammation (decreased IL-6, increased IL-10), and dramatically reduced collagen deposition by about 64%, compared to PP mesh. Thus, the composite PP mesh with ROS scavenging and anti-inflammatory properties provides a promising approach for mitigating FBR.

Molecular architecture regulation for the design of instant and robust underwater adhesives

Development of underwater adhesives with instant and robust adhesion to diverse substrates remains challenging. A strategy taking the structural advantage of phenylalanine derivative, N-acryloyl phenylalanine (APA), is proposed to facilely prepare a series of underwater polymeric glue-type adhesives (UPGAs) through one-pot radical polymerization with commonly used hydrophilic vinyl monomers. The adjacent phenyl and carboxyl groups in APA realize the synergy between interfacial interactions and cohesion strength, by which the UPGAs could achieve instant (~5 seconds) and robust wet tissue adhesion strength (173 kilopascal). The polymers with varied hydrophobicity and substitutional groups as well as carboxyl and phenyl groups in separated components are designed to investigate the underwater adhesion mechanism. The universality of APA for the construction of UPGAs is also verified by the copolymerization with different hydrophilic monomers, and the applications of the UPGAs have been validated in diverse hemorrhage models and distinct substrates. Our work may give a promising solution to design potent underwater adhesives.

Sustainable Approach for the Synthesis of a Semicrystalline Polymer with a Reversible Shape-Memory Effect

Shape-memory polymers (SMPs) have demonstrated potential for use in automotive, biomedical, and aerospace industries. However, ensuring the sustainability of these materials remains a challenge. Herein, a sustainable approach to synthesize a semicrystalline polymer using biomass-derivable precursors via catalyst-free polyesterification is presented. The synthesized biodegradable polymer, poly(1,8-octanediol-co-1,12-dodecanedioate-co-citrate) (PODDC), exhibits excellent shape-memory properties, as evidenced by good shape fixity and shape recovery ratios of 98%, along with a large reversible actuation strain of 28%. Without the use of a catalyst, the mild polymerization enables the reconfiguration of the partially cured two-dimensional (2D) film to a three-dimensional (3D) geometric form in the middle process. This study appears to be a step forward in developing sustainable SMPs and a simple way for constructing a 3D structure of a permanent shape.

Hydration Activates Dual-Confined Shape-Memory Effects of Cold-Reprogrammable Photonic Crystals

Shape-memory photonic crystals (SMPCs) transform the nanoscale deformation of copolymers into structural color through an undifferentiated response to stimuli; however, activatable selective responses are extremely rare. Herein, activatable dual confined shape-memory effects (CSMEs) derived from the remodeling of the interchain hydrogen bonds (H-bonds) in cold-programmable SMPCs are revealed. The first level is the water-triggered reconstruction of interchain H-bonds, which can activate/lock the collapsed skeleton, showing shape recovery/retention in response to ethanol vapor. The second level is the pressure-induced reorganization of interchain H-bonds that results in the recovered skeleton being locked even when exposed to ethanol vapor or water, while the background porous structure can switch between collapse and recovery. Dual CSMEs result from the Laplace pressure difference and the binding effect of interchain H-bonds in the skeleton according to insights of swelling, in situ deformation tracking, multidimensional infrared spectra, and water wetting/evaporation simulations. The signal interference, source code extraction, and color enhancement of structurally colored patterns can be implemented using CSMEs. This work opens up a new method for fabricating activatable responsive structural color and contributes to the expansion of nanophotonic technology in water printing, erasable watermarks, signal amplifiers, and information coding.

Bilayer Actuator with Overload Protection on the Basis of Semicrystalline Polyurethane

Response to external stimuli plays a significant role in the environmental adaptation of living matters and intelligent devices. Most stimulus-response systems in nature can respond to appropriate stimuli, and inhibit the response under excessive stimuli, such as excessive heat or water, which can be called overload protection. However, even though various responsive materials have been developed for different stimuli, most of them are not protective against the overload stimuli. In this work, a bilayer actuator based on semicrystalline polyurethane is designed, which can respond differently to proper stimuli and excessive stimuli, i.e., water. This actuator can bend gradually under the proper stimulation of water, but will straighten and even bend reversely with excessive stimulation. The mechanism behind the reversible and adjustable actuator with overload protection is investigated both experimentally and theoretically, and the competition between dynamic factors and thermodynamic stability in the swelling process is considered the main cause.

Shape memory polyurethane potentially used for vascular stents with water-induced stiffening and improved hemocompatibility

We designed a shape memory polyurethane potentially used for vascular stents with water-induced stiffening in vivo and improved hemocompatibility.