Engineering Biodegradable Polyurethanes with Precisely Controlled Hierarchical Structures to Access Shape Memory Effect and Enhanced Bioactivities.

Biodegradable polymers with shape memory effects (SMEs) offer promising solutions for short-term medical interventions, facilitating minimally invasive procedures and subsequent degradation without requiring secondary surgeries. However, achieving a good balance among desirable SMEs, mechanical performance, degradation rate, and bioactivities remains a significant challenge. To address this issue, we established a strategy to develop a versatile biodegradable polyurethane (PPDO-PLC) with tunable hierarchical structures via precise chain segment control. Initial copolymerization of l-lactide and ε-caprolactone sets a tunable Tg close to body temperature, followed by block copolymerization with poly(p-dioxanone) to form a hard domain. This yields a uniform microphase-separation morphology, ensuring robust SME and facilitating the development of roughly porous surface structures in alkaline environments. Cell experiments indicate that these rough surfaces significantly enhance cellular activities, such as adhesion, proliferation, and osteogenic differentiation. Our approach provides a methodology for balancing biodegradability, SMEs, three-dimensional (3D) printability, and bioactivity in materials through hierarchical structure regulation.

Bioinspired Optical Flexible Cellulose Nanocrystal Films with Strain-Adaptive Structural Coloration.

Recent advances of photonic crystals are driven to mechanical sensors and smart wearable devices; however, for chiral photonic cellulose nanocrystal (CNC) materials, vivid structural coloration and reversible mechanochromism like chameleon skin remain a big challenge. Here, we report a ternary co-assembly and post-UV-irradiation polymerization strategy to develop flexible and elastic CNC composite films, which, notably, have naked-eye-visible brilliant structural colors and stretching-induced color change covering a broad wavelength region at a moderate deformation (like skin). By adjusting the stretching, the film is designed as a smart skin to adapt to surrounding environments for camouflage. This work offers a universal strategy for constructing biomimic optically functional cellulose skins.

Photonic Cellulose Films with Vivid Structural Colors: Fabrication and Selectively Chemical Response.

Recent advances in structural-color cellulose nanocrystal (CNC) materials have been made toward chemical sensing applications; however, such materials lack sufficient color chroma for naked-eye observation, and their selective recognition to given chemicals as well as the corresponding mechanism has rarely been reported. Here, a dopamine-infiltration and post-polymerization approach is proposed to construct vivid structural-color composite films. The chiral nematic structure of CNC enables the structural coloration, while the strong light absorption of the polymeric co-phase, polydopamine (PDA) enhances the color chroma and visibility. By controlling the PDA amount, the composite films can detect organic solvents quantitatively and selectively via visible color changes. From the viewpoint of the compatibility and similitude principle, notably, a critical solubility parameter distance (R0) between PDA and "active" solvents is defined with a three-dimensional Hansen solubility sphere; this well constructs a rule for the sensing selectivity of the chemochromic composite films. The findings pave the foundation for the design of colorimetric sensors with specifically testing objects.

Design and Synthesis of PET-Based Copolyesters with Flame-Retardant and Antidripping Performance.

Poly(ethylene terephthalate) (PET) is a fiber-forming polymer with the largest output and widest usage. Its flame retardation is well-achieved via a mechanism of promoting the melt dripping while ignited. However, the melt dripping leads to secondary damage and an immediate empyrosis during fire. How to address the contradiction between the flame retardation and the melt-dripping behavior of PET via an inherent flame-retardant approach becomes a real challenge. This feature article highlights the design and synthesis of novel PET-based copolyesters with flame-retardant and antidripping performance. Three approaches are used to design these copolyesters: "ionic aggregation," "smart self-cross-linking," and "rearrangement at high temperatures." Some new conceptions are proposed accordingly. The synthesis, structure characterization, and properties of those copolyesters are discussed together with the ongoing challenges and limitations at this frontier.

New Strategy to Access Dual-Stimuli-Responsive Triple-Shape-Memory Effect in a Non-overlapping Pattern.

Multistimuli-responsive shape-memory polymers are highly desirable in various applications, and numerous modes have been developed in recent years. However, most of them need to reprogram before they are ready to respond to another stimulus while one is triggered. Here, a new strategy is developed to achieve dual-stimuli-responsive triple-shape memory with non-overlapping effect in one programming cycle. Here, a series of poly(l-lactide)-poly(tetramethylene oxide) glycol copolymers (PLA-PTMEG-A) is prepared by selected dangling photoresponsive anthracene moieties on the crystalline PTMEG backbone. The architectures of the copolymers are well-controlled in order to keep a good balance between the crystallinity of the soft segment and the mobility of the anthracene moieties. Thus, PLA-PTMEG-A's can respond to heat and light with non-overlapping effect. The thermally-induced shape-memory effect (TSME) is realized by the crystallization-melting transition of PTMEG soft segments, while the light-induced shape-memory effect (LSME) is achieved by the reversible photodimerization of anthracene groups. In view of the non-overlapping effect of TSME and LSME in the copolymers, a triple-shape-memory effect triggered by dual-stimuli is realized in one programming and recovery cycle.

Fully biobased and supertough polylactide-based thermoplastic vulcanizates fabricated by peroxide-induced dynamic vulcanization and interfacial compatibilization.

A fully biobased and supertough thermoplastic vulcanizate (TPV) consisting of polylactide (PLA) and a biobased vulcanized unsaturated aliphatic polyester elastomer (UPE) was fabricated via peroxide-induced dynamic vulcanization. Interfacial compatibilization between PLA and UPE took place during dynamic vulcanization, which was confirmed by gel measurement and NMR analysis. After vulcanization, the TPV exhibited a quasi cocontinuous morphology with vulcanized UPE compactly dispersed in PLA matrix, which was different from the pristine PLA/UPE blend, exhibiting typically phase-separated morphology with unvulcanized UPE droplets discretely dispersed in matrix. The TPV showed significantly improved tensile and impact toughness with values up to about 99.3 MJ/m(3) and 586.6 J/m, respectively, compared to those of 3.2 MJ/m(3) and 16.8 J/m for neat PLA, respectively. The toughening mechanisms under tensile and impact tests were investigated and deduced as massive shear yielding of the PLA matrix triggered by internal cavitation of VUPE. The fully biobased supertough PLA vulcanizate could serve as a promising alternative to traditional commodity plastics.

Preparation of core-shell nanofibers with selectively localized CNTs from Shish Kebab-like hierarchical composite micelles.

A novel and facile bottom-up strategy for preparing core-shell nanofibers with selectively localized carbon nanotubes is developed using hierarchical composite micelles of crystalline-coil copolymer and carbon nanotubes as the building blocks. An amphiphilic di-block copolymer of poly (p-dioxanone) (PPDO) and PEG (polyethylene glycol) functionalized with pyrene moieties at the chain ends of PPDO blocks (Py-PPDO-b-PEG) is designed for constructing composite micelles with multiwalled carbon nanotubes (MWCNTs). The self-assembly of Py-PPDO-b-PEG and MWCNTs is co-induced by the crystallization of PPDO blocks and the π-π stacking interactions between pyrene moieties and MWCNTs, resulting in composite micelles with "shish kebab"-like nanostructure. A mixture of composite micelles and polyvinyl alcohol (PVA) water solution is then used as the spinning solution for preparing electrospun nanofibers. The morphologies of the nanofibers with different composition are investigated by SEM and TEM. The results suggest that the MWCNTs selectively localized in the core of the nanofibers of MWCNTs/Py-PPDO-b-PEG/PVA. The alignment and interfusion of composite micelles during the formation of nanofibers may confine the carbon nanotubes in the hydrophobic core region. In contrast, the copolymer without pyrene moieties cannot form composite micelles, thus these nanofibers show selective localization of MWCNTs in the PVA shell region.

Calcium gluconate-based flame retardant towards simultaneously high-efficiency fire safety and mechanical enhancement for epoxy resin.

Flame retardants containing biomass receive growing interest in environmental friendliness and sustainability but usually face the low flame-retardant efficiency and deterioration on mechanical property of matrix. Herein, a calcium gluconate-based flame retardant (CG@APP) was chemically prepared using calcium gluconate (CG) and ammonium polyphosphate (APP) via ion exchange reaction, and enabled the excellent fire safety and mechanical enhancement for epoxy resin (EP). The resulted EP composites containing 6 wt% CG@APP (EP/CG@APP6) exhibited V-0 ratings in UL-94 test. Furthermore, with respect to EP/APP6, the peak of heat release rate (pHRR) and peak of smoke production rate (pSPR) of EP/CG@APP6 decreased by 70.5 % and 50.0 %, respectively. The well synergistic flame-retardant mechanism of CG@APP between gaseous and solid phases was revealed to generate denser and more continuous charring residuals, which could do well work on insulation for heat transfer and fuel diffusion. In addition, the shell rich in hydroxyl group and Ca2+ on the surface of CG@APP well enhanced the interface compatibility through the hydrogen bond and coordinated bond, thus the tensile strength, flexural strength and impact strength of EP/CG@APP6 increased by 18.2 %, 4.5 % and 9.1 % compared with pure EP, respectively. This work provided a simple and sustainable way to construct excellent fire-safety composites.

A pH-responsive chitosan-b-poly(p-dioxanone) nanocarrier: formation and efficient antitumor drug delivery.

Increasing attention has recently been paid to the fabrication of drug delivery systems with excellent cell internalization and intracellular drug release properties. In this study, an amphiphilic block copolymer of chitosan was synthesized for the first time, which can self-assemble into micelles in a neutral aqueous solution but partially disassemble in an acidic endosomal/lysosomal environment. The antitumor drug, camptothecin (CPT), was encapsulated in the cores of the micelles for tumor cell therapy. In vitro drug release studies demonstrated that the micelles presented a much faster release of CPT at pH 5.0 than at pH 7.4. Blank micelles were found to be nontoxic in preliminary in vitro cytotoxicity assays. Cell experiments showed that the CPT-loaded micelles could be effectively internalized by Hela cells and accomplished a potent antitumor cell efficacy, indicating that the chitosan-based micelles might be an attractive new platform for efficient intracellular drug delivery.

Toward regulating biodegradation in stages of polyurethane copolymers with bicontinuous microphase separation.

For typical biodegradable polymers, their overall performance almost declines exponentially to the degradation degree, which inevitably leads to a dilemma between the requirements of service life and retention time in the environment (both in vitro and in vivo). It is a great challenge to develop a biodegradable polymeric device with relatively stable performance in service while rapidly degrading out of service. Herein, we demonstrate an effective strategy to control degradation of biodegradable polymers in stages by constructing separated bicontinuous microphases with very different microphase degradation rates. First, polyurethane copolymers (PCL-b-CrP-U) containing two blocks, i.e., semicrystalline poly(ε-caprolactone) (PCL) blocks and amorphous random copolymer blocks (CrP) based on ε-CL and p-dioxanone (PDO), were synthesized. The microscopic morphology of PCL-b-CrP-U is investigated by an alkali-accelerated degradation experiment, which also demonstrates that the chain cleavage-induced crystallization during degradation resulted in a self-reinforcement by forming degradation residues with a scaffold-like morphology. The tensile test shows that PCL-b-CrP-U has excellent mechanical properties (1500% of elongation at break, a tensile strength of about 7.5 MPa, and an elastic modulus of 40.0 MPa). The degradation experiments with artificial pancreatic juice as a working medium reveal that PCL-b-CrP-U samples containing relatively high PDO units exhibit a three-stage degradation, i.e. an induction stage, a steady degradation stage and an accelerated degradation stage. The CrP phase preferentially hydrolyzes to form some microchannels due to its amorphous nature and relatively high hydrophilicity, effectively accelerating the entry of water and enzymes into the inner parts of the sample. Meanwhile, at this stage, those originally amorphous PCL segments gradually crystalize owing to their enhanced chain mobility induced by the chain cleavage, forming a "scaffold"-like structure, which effectively reinforces the sample to resist the damage from external force and therefore guarantees a relatively stable mechanical performance of PCL-b-CrP-U during service. With the further depletion of the CrP phase, the intermediate "scaffold"-like structure is also very beneficial to accelerate the degradation of residues owing to its large specific surface area, which is expected to be beneficial for preventing long-term retention of the implantation devices.

Shape Memory Polyester Scaffold Promotes Bone Defect Repair through Enhanced Osteogenic Ability and Mechanical Stability.

Bone tissue engineering involving scaffolds is recognized as the ideal approach for bone defect repair. However, scaffold materials exhibit several limitations, such as low bioactivity, less osseointegration, and poor processability, for developing bone tissue engineering. Herein, a bioactive and shape memory bone scaffold was fabricated using the biodegradable polyester copolymer's four-dimensional fused deposition modeling. The poly(ε-caprolactone) segment with a transition temperature near body temperature was selected as the molecular switch to realize the shape memory effect. Another copolymer segment, i.e., poly(propylene fumarate), was introduced for post-cross-linking and improving the regulation effect of the resulting bioadaptable scaffold on osteogenesis. To mimic the porous structures and mechanical properties of the native spongy bone, the pore size of the printed scaffold was set as ∼300 µm, and a comparable compression modulus was achieved after photo-cross-linking. Compared with the pristine poly(ε-caprolactone), the scaffold made from fumarate-functionalized copolymer considerably enhanced the adhesion and osteogenic differentiation of MC3T3-E1 cells in vitro. In vivo experiments indicated that the bioactive shape memory scaffold could quickly adapt to the defect geometry during implantation via shape change, and bone regeneration at the defect site was remarkably promoted, providing a promising strategy to treat bone defects in the clinic, substantial bone defects with irregular geometry.

4D Printing of Biocompatible Scaffolds via In Situ Photo-crosslinking from Shape Memory Copolyesters.

The complexity of surgical treatments for large-area soft tissue injuries makes placing large implants into injury sites challenging. Aliphatic polyesters are often used for scaffold preparation in tissue engineering owing to their excellent biodegradability and biocompatibility. Scaffolds with shape-memory effect (SME) can also avoid large-volume trauma during the implantation. However, the complexity and diversity of diseases require more adaptable and precise processing methods. Four-dimensional (4D) printing, a booming smart material additive manufacturing technology, provides a new opportunity for developing shape memory scaffolds. With the aim of personalized or patient-adaptable soft tissues such as blood vessels, we developed a feasible strategy for fabricating scaffolds with fine architectures using 4D printing crosslinkable shape memory linear copolyesters using fused deposition modeling (FDM). To overcome the weak bonding strength of each printed layer during FDM, a catalyst-free photo-crosslinkable functional group derived from biocompatible cinnamic acid was embedded into the linear copolyesters as in situ crosslinking points during FDM printing. Under ultraviolet-assisted irradiation, the resulting 4D scaffold models demonstrated excellent SME, desirable mechanical performance, and good stability in a water environment owing to the chemical bonding between each layer. Moreover, the excellent biocompatibility of the scaffold was evaluated in vitro and in vivo. The developed composite scaffolds could be used for minimally invasive soft tissue repair.

A cellulose nanocrystal templating approach to synthesize size-controlled gold nanoparticles with high catalytic activity.

Advanced templating methods have shown precise regulation of the micro/nanostructures of inorganic catalysts. Here, on the basis of controlled self-assembly and micro-structures of cellulose nanocrystals (CNCs), a new bio-mass-mediated templating approach is proposed to control the growth of gold nanoparticles (Au NPs). The catalytic performance of the as-prepared Au NPs was evaluated using p-nitrophenol as a model pollutant. TEM, POM, zeta-potential, and rheological measurements were conducted to investigate the structure and catalytic activity of the nano-materials. By regulating the chiral nematic liquid crystal texture formed by the self-assembly of CNCs, the size of Au NPs could be adjusted at the nanoscale dimension, from 1.38 ± 0.38 nm to 4.25 ± 1.24 nm. Depending on the Au size, a high catalytic effect, namely, 98.0% conversion rate, was obtained within 30 min. The conversion rate was maintained at 97.0% even after 3-run cyclic application. Such findings demonstrate the potential of using CNCs as a bio-template to control the growth of nanomaterials.

Thermoformable and transparent one-component nanocomposites based on surface grafted cellulose nanofiber.

One-component nanocomposites based on poly(methyl methacrylate)(PMMA) and polystyrene (PS) grafted cellulose nanofiber (CNF) with high polymer graft percentage were fabricated. At relative ambient conditions, less active vinyl monomer, MMA, and styrene were grafted from CNF via surface-initiated Cu(0)-mediated reversible deactivation radical polymerizations (RDRP), and PMMA/PS grafted CNFs could reach a graft percentage as high as 7550 % and 3530 %, respectively. The one-component composite films were manufactured by simple hot-pressing subsequentially. Optical transparency, thermal stability, and glass transition temperature of one-component nanocomposites were enhanced dramatically in contrast with the bicomponent nanocomposite. The uniform fracture surface confirmed the uniform dispersity by morphological observation. Mechanical tests indicated that break elongation and tensile strength ascended notably, and tensile modulus slightly descended as the graft percentage increased for PS and PMMA grafted CNF one-component composite. It was concluded that for glassy graft chains, obtaining one-component nanocomposites with high enough graft chain length was essential to achieve moderated mechanical performance without compromising optical properties and thermal manufacturing ability.

Recyclable, malleable and intrinsically flame-retardant epoxy resin with catalytic transesterification.

Flame retardancy and recyclability are two important issues in the research field of thermosets, particularly for epoxy resin (EP) with the biggest market share. It is of great importance, but rarely achievable, to integrate these properties simultaneously into EP. Herein, we report a facile way to prepare intrinsically flame-retardant epoxy vitrimers combining rapid recycling and multiple shape memory effects by introducing dynamic ester-linkages with catalytic transesterification activity into the crosslinking networks of EP. The flame-retardant epoxy vitrimers exhibited high Tg (∼110.7 °C), desirable thermal stability and excellent flame retardancy with UL-94 V-0 rating, and high LOI of ∼34%. Also, the value of the peak heat release rate (PHRR) and the total heat release (THR) showed 63% and 32% reduction, respectively. Meanwhile, flame-retardant epoxy vitrimers showed high malleability that could be reprocessed in 15 min at 200 °C without sacrificing the mechanical properties and flame retardancy. Moreover, the dynamic transesterification network allowed flame-retardant EP to access multiple shape memory effect. The design of flame-retardant epoxy vitrimers provide a prime example to foster the cyclic utilization of flame-retardant thermosetting polymers.

Cellulose nanocrystal and ß-cyclodextrin chiral nematic composite films as selective sensor for methanol discrimination.

Due to the serious threat of methanol to human health, the convenient, quick and specific detection of methanol is of great importance. Therefore, in this study, a biomass-derived chiral nematic composite film is fabricated by the co-evaporation of cellulose nanocrystals (CNC) and water-soluble polymer of ß-cyclodextrin (PCD). The freestanding iridescent CNC-PCD film shows distinguishing structural colors of red and yellow green for methanol and ethanol respectively, realizing the identification of the two homologous alcohols by naked eyes. Besides, the quick, reversible and quantitative colorimetric sensing of the CNC-PCD film to methanol is verified. As its structural color and maximum reflection wavelength redshift to the greatest extent for methanol than other alcohols, the CNC-PCD film exhibits the specificity and selectivity for methanol detection in both single and mixed solvents. Such less-consumed and easy-to-handle CNC-PCD film may be useful as a colorimetric sensor to detect or discriminate methanol in some industrial products.

Exploiting valuable supramolecular materials from waste plastics.

A new family of supramolecular materials is exploited from waste thermosets via a one-step retrosynthetic approach, which exhibits distinguished adhesion properties in dry/wet environments, good corrosion resistance and dynamic reversibility. This work opens up a wide design space for supramolecular materials with excellent performances and proposes a new strategy for efficient utilization of hybrid degraded products.

Multicycling of Epoxy Thermoset Through a Two-Step Strategy of Alcoholysis and Hydrolysis using a Self-Separating Catalysis System.

Plastic has now become a contradiction between civilization and pollution that human society has to resolve. The recycling of thermosetting plastics in waste plastics is a huge challenge since they are difficult to remold like thermoplastic plastics due to their high crosslinking density. Here, a new strategy was developed to achieve multicycling of anhydride-cured epoxy thermosets. The process consisted of mild and high-efficiency alcoholysis catalyzed by potassium phosphate/low-boiling alcohol system, and subsequent fast hydrolysis to obtain degradation products rich of carboxyl groups. The degradation products were reused as curing agent to prepare new anhydride-cured epoxy thermosets without sacrifice of high strength and stability. Moreover, the new epoxy thermosets could still be repeatedly recycled using the same protocol. The insolubility of potassium phosphate in ethanol at room temperature made the separation and reuse of the catalyst more convenient. The use of low-boiling alcohol not only allowed high-efficiency degradation but also enabled easy separation from the degradation products. The excellent degradation performance was attributed to the improved swelling of the thermoset and the increased solubility of potassium phosphate induced by small amounts of water in the alcohol. This research provides a recycling method that can reintegrate thermoset waste plastics into remodeling ones under the background of circular economy.

Multifunctional Materials from Aerobic Degradation of Epoxy Thermoset via Phosphotungstic Acid-Involved Activation and Bonding.

The growing scale of production of wind turbines represents a big challenge for chemical recycling of amine-cured epoxy resin (EP) to achieve high-efficiency degradation and high-value utilization of degradation products. Here, H2 O2 /phosphotungstic acid (HPW) catalytic oxidation system is demonstrated to completely degrade EP thermoset with the solid recovery rate of 96% at a reaction temperature of 80 °C for 4 h. Owing to protonation and bonding effect of HPW to the amine groups, the degradation products had a weight-average molecular weight of 4285 with narrow molecular weight distribution. They were used as dye adsorption blend films and supramolecular adhesives based on hydrogen bonding and coordination bonding respectively. The work demonstrates a feasible and promising method to recover the EP thermoset into high-performance materials.

Biodegradable soy protein isolate-based materials: a review.

Recently, there is an increasing interest of using bio-based polymers instead of conventional petroleum-based polymers to fabricate biodegradable materials. Soy protein isolate (SPI), a protein with reproducible resource, good biocompatibility, biodegradability, and processability, has a significant potential in the food industry, agriculture, bioscience, and biotechnology. Up to now, several technologies have been applied to prepare SPI-based materials with equivalent or superior physical and mechanical properties compared with petroleum-based materials. The aim of this review is focused on discussion of the advantages and limitations of native SPI as well as the bulk and surface modification strategies for SPI. Moreover, some applications of SPI-based materials, especially for food preservation and packaging technology, were discussed.