Reversible Cross-linking Research Articles

Intrinsically Healable Fabrics

AbstractWearable electronics with healability have been extensively researched recently. To provide wearing comfort, fabrics are often adopted as the base materials. Intrinsic healability, however, is challenging for fabrics because of the inability to retain the fibrous morphologies. Herein, an unprecedented strategy is presented for producing electrospun fabrics that are intrinsically healable by carefully balancing the crystalline structural support and healing ability. Fluorocarbon polymers with different crystallinities are mixed with ionic liquids to form ionogels, which are spun into fabrics using a unique wet electrospinning apparatus. Importantly, the introduction of the crystalline domains prevents the fusion of the electrospun fibers; even after 1 year, no significant morphological change is observed. The nonwoven fabrics are not only stretchable and waterproof but also intrinsically healable. The ion–dipole interactions between the polar copolymers and ionic liquids provide the reversible physical crosslinking essential to the healing capability. When damaged, the fabrics can be overlapped and healed after applying pressure. Moreover, the fabrics demonstrate healability underwater. Healable sensing devices, pressure, and tensile sensors are also designed by printing ion‐conductive gels as electrodes. Both devices show good stability before and after healing. This work demonstrates the first example of intrinsically healable electrospun fabrics, which are promising for fabric‐based wearable electronics and smart clothing.

Dynamic Crosslinked Injectable Mussel-Inspired Hydrogels with Adhesive, Self-Healing, and Biodegradation Properties.

The non-invasive tissue adhesives with strong tissue adhesion and good biocompatibility are ideal for replacing traditional wound treatment methods such as sutures and needles. The self-healing hydrogels based on dynamic reversible crosslinking can recover their structure and function after damage, which is suitable for the application scenario of tissue adhesives. Herein, inspired by mussel adhesive proteins, we propose a facile strategy to achieve an injectable hydrogel (DACS hydrogel) by grafting dopamine (DOPA) onto hyaluronic acid (HA) and mixing it with carboxymethyl chitosan (CMCS) solution. The gelation time and rheological and swelling properties of the hydrogel can be controlled conveniently by adjusting the substitution degree of the catechol group and the concentration of raw materials. More importantly, the hydrogel exhibited rapid and highly efficient self-healing ability and excellent biodegradation and biocompatibility in vitro. Meanwhile, the hydrogel exhibited ~4-fold enhanced wet tissue adhesion strength (21.41 kPa) over the commercial fibrin glue. This kind of HA-based mussel biomimetic self-healing hydrogel is expected to be used as a multifunctional tissue adhesive material.

Reversible imine crosslinking in waterborne self-healing polymer coatings

Waterborne polymer coatings have the potential to address the environmental concerns associated with solvent based systems. To improve their performance without using volatile organic compounds, we propose a new approach based on reconfigurable covalent crosslinking that provides mechanical resistance and self-healing properties. The new waterborne polymer coatings are based on mixtures of aldehyde- and amine-functionalized polymer nanoparticles (PNPs) that take advantage of the reversibility of imine bonds in the presence of water. Different degrees of functional monomer incorporation (10 % to 40 %) allowed us to balance crosslinking and interdiffusion during film formation, to obtain mechanically robust and solvent resistant films. A clear structure-properties relation was assessed by following the formation of water resulting from amine-aldehyde condensation crosslinking, measured by differential scanning calorimetry. The resulting polymer coatings further show self-healing properties at room temperature, triggered with residual amounts of water and featuring high recovery rates of the mechanical properties. Our mechanically robust waterborne polymer coatings based in imine reversible crosslinking, featuring self-healing in mild conditions, offer excellent prospects for application in smart coating materials.

Cyclic Polyphenylene Sulfide as Additive to Improve the Mechanical Properties of Polystyrene-Based Materials

Cyclic polyphenylene sulfide (PPS) is an unavoidable byproduct of the preparation of linear PPS, one of the most important engineering plastics. Turning the waste into treasure is the best way to address byproducts, prevent pollution, and save energy and resources. Cyclic PPS’s potential to be used in supramolecular chemistry was proven as an additive to enhance the mechanical properties of polystyrene (PS)-based materials. After the addition of cyclic PPS, the toughness of poly(styrene-co-ethyl acrylate) (PS-PEA) was approximately 4 times that of PS, and the value of Young’s modulus saw a slight increase. Cyclic PPS was found to form reversible and movable cross-links with PS-PEA and increase the homogeneity of PS-PEA. Thus, the results of this study provide not only a way to make use of cyclic PPS but also an easy and practical method to prepare reinforced PS-based polymers.

Single versus dual microgel species for forming guest-host microporous annealed particle PEG-MAL hydrogel.

Inter-particle secondary crosslinks allow microporous annealed particle (MAP) hydrogels to be formed. Methods to introduce secondary crosslinking networksin MAP hydrogels include particle jamming, annealing with covalent bonds, and reversible noncovalent interactions. Here, we investigate the effect of two different approaches to secondary crosslinking of polyethylene glycol (PEG) microgels via reversible guest-host interactions. We generated a dual-particle MAP-PEG hydrogel using two species of PEG microgels, one functionalized with the guest molecule, adamantane, and the other with the host molecule, β-cyclodextrin (Inter-MAP-PEG). In a different approach, a mono-particle MAP-PEG hydrogel was generated using one species of microgel functionalized with both guest and host molecules (Intra-MAP-PEG). The Intra-MAP-PEG formed a homogenous distribution due to the single type of microgels used. We then compared the mechanical properties of these two types of MAP-PEG hydrogels and found that Intra-MAP-PEG resulted in significantly softer gels with lower yield stress. We investigated the effect of intra-particle guest-host interactions through titrated weight percentage and the concentration of functional groups added to the hydrogel. We found that there was an ideal concentration of guest-host molecules that enables intra- and inter-particle guest-host interactions with sufficient covalent crosslinking. Based on these studies, Intra-MAP-PEG provides a homogeneous guest-host hydrogel that is shear-thinning with reversible secondary crosslinking.

Bioinspired multifunctional injectable hydrogel for hemostasis and infected wound management.

Routine wound management faces significant challenges including rebleeding and bacterial infection that affect millions of people each year. However, conventional wound dressings (e.g., gauze, bandage) are limited to simply cover the injured surfaces and rarely show special functionality to promote the wound recovery. Currently, injectable hydrogels have been widely designed as multifunctional wound dressings to manage the hemostatic and wound healing process. Nevertheless, the integration of multiple functions through simple composition and easy construction is still difficult and hardly achieved. Herein, we reported a bioinspired multifunctional injectable hydrogel (CQCS@gel) consisted of only two components, catechol-functionalized quaternized chitosan (CQCS) and dibenzaldehyde-terminated poly(ethylene glycol) (DB-PEG2000). The building blocks endowed CQCS@gel with tissue-adhesive, antibacterial, antioxidant, self-healing and pH-responsive properties. Based on the in vivo hemostatic study, quick hemostasis for acute tissue injuries such as liver and carotid wounds was realized owing to the rapid gelation rate and strong tissue-adhesiveness of CQCS@gel. Moreover, CQCS@gel remarkably boosted the chronic recovery process of MRSA-infected cutaneous wounds by promoting collagen deposition, hair follicles regeneration and angiogenesis. Overall, this multifunctional injectable hydrogel shows potentials as a universal wound dressing in clinical applications, enabling both hemostasis and infected wound management. STATEMENT OF SIGNIFICANCE: This is the first report showing the multifunctional injectable hydrogel (CQCS@gel) consisted of catechol-functionalized quaternized chitosan and dibenzaldehyde-terminated poly(ethylene glycol). The incorporation of quaternary ammonium groups imparted the CQCS@gel with outstanding contact-active bacterial killing efficiency and the catechol moieties enhanced its tissue adhesive and antioxidant properties. Moreover, the reversible imine crosslinks endowed the CQCS@gel with self-healing and pH-responsive drug release capabilities. These multiple functions were integrated into a single injectable hydrogel system with easy availability and low cost. In vitro and in vivo results showed that the newly designed hydrogel was biocompatible, realized successful sealing hemostasis under multiple bleeding scenarios and enabled accelerated healing of infected skin wounds.

Totally dynamically cross-linked dual-network conductive hydrogel with superb and rapid self-healing ability for motion detection sensors

To overcome the status quo of fragile network and single function in the single-network hydrogel, this work designed and fabricated a dual-network O-CMCS (O-carboxymethyl chitosan)/PVA (polyvinyl alcohol) PBOC conductive hydrogel based on two kinds of totally dynamic reversible cross-linking networks. The PBOC conductive hydrogel combined a flexible O-PT (oxidized pectin)/O-CMCS network with a rigid PVA-borax network, and CNTs (carbon nanotubes) were introduced to improve its toughness and conductivity. Its structural characteristics were investigated through Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray diffractometer (XRD), nuclear magnetic resonance (NMR) and other techniques. Its superb and rapid self-healing property was confirmed through dynamic rheological tests, and its electrical property was studied through an electrochemical workstation. The co-existence of the dual networks endowed the PBOC conductive hydrogel with excellent stretchable property (821% of the maximum elongation at break), and it could quickly self-heal within 60 s after being cut due to the intense interaction of totally reversible multiple dynamic bonding. Notably, the PBOC conductive hydrogel strain sensor exhibited high strain sensitivity with GF (gauge factor) of 8.44 at 800% strain and could accurately detect all kinds of human motions (e.g. finger bending, wrist bending and elbow bending, etc.), confirming its tremendous application potential in the field of wearable sensor devices.

Adaptive Magnetoactive Soft Composites for Modular and Reconfigurable Actuators

AbstractMagnetoactive soft materials, typically composed of magnetic particles dispersed in a soft polymer matrix, are finding many applications in soft robotics due to their reversible and remote shape transformations under magnetic fields. To achieve complex shape transformations, anisotropic, and heterogeneous magnetization profiles must be programmed in the material. However, once programmed and assembled, magnetic soft actuators cannot be easily reconfigured, repurposed, or repaired, which limits their application, their durability, and versatility in their design. Here, magnetoactive soft composites are developed from squid‐derived biopolymers and NdFeB microparticles with tunable ferromagnetic and thermomechanical properties. By leveraging reversible crosslinking nanostructures in the biopolymer matrix, a healing‐assisted assembly process is developed that allows for on‐demand reconfiguration and magnetic reprogramming of magnetoactive composites. This concept in multi‐material modular actuators is demonstrated with programmable deformation modes, self‐healing properties to recover their function after mechanical damage, and shape‐memory behavior to lock in their preferred configuration and un‐actuated catch states. These dynamic magnetic soft composites can enable the modular design and assembly of new types of magnetic actuators, not only eliminating device vulnerabilities through healing and repair but also by providing adaptive mechanisms to reconfigure their function on demand.

Reconfigurable and Reprocessable Thermadapt Stress‐Free Two‐Way Shape Memory Polymers Based on a Dual Crosslinking Network with Outstanding Mechanical Properties

The reconfigurable and reprocessable thermadapt two‐way shape memory polymers (2W‐SMPs) are highly desirable for many advanced biomimetic applications, but the preparation of these polymers with economical raw materials and convenient approaches still remains a challenge. In this work, thermadapt 2W‐SMPs based on a dual crosslinking network are synthesized by linking polyethylene glycol with hydroxylated modified SBS via dynamic covalent bonds. Benefiting from the synergistic effect of combining a dynamic covalent network and a physical cross‐linking network, the thermadapt 2W‐SMPs exhibit a good balance of mechanical properties and favorable two‐way shape memory effect (2W‐SME) with the reversible actuation strain of 11.9%. The 2W‐SMPs can be reprocessed and transformed into complex 3D shapes after multiple folding processes due to the dynamic covalent exchange as well as the reversible physical crosslinking, and the obtained new samples still exhibit good 2W‐SMEs. Furthermore, the transition temperature of 2W‐SMPs is designed to be close to human body temperature, and it is manufactured into a biomimetic mimosa actuator that can undergo shape changes through finger contact and cooling. This work provides a new idea for the development of thermadapt 2W‐SMPs, and the obtained materials show great potential applications in intelligent actuators.

A SERS-signalled, CRISPR/Cas-powered bioassay for amplification-free and anti-interference detection of SARS-CoV-2 in foods and environmental samples using a single tube-in-tube vessel

The pandemic of COVID-19 creates an imperative need for sensitive and portable detection of SARS-CoV-2. We devised a SERS-read, CRISPR/Cas-powered nanobioassay, termed as OVER-SARS-CoV-2 (One-Vessel Enhanced RNA test on SARS-CoV-2), which enabled supersensitive, ultrafast, accurate and portable detection of SARS-CoV-2 in a single vessel in an amplification-free and anti-interference manner. The SERS nanoprobes were constructed by conjugating gold nanoparticles with Raman reporting molecular and single-stranded DNA (ssDNA) probes, whose aggregation-to-dispersion changes can be finely tuned by target-activated Cas12a though trans-cleavage of linker ssDNA. As such, the nucleic acid signals could be dexterously converted and amplified to SERS signals. By customizing an ingenious vessel, the steps of RNA reverse transcription, Cas12a trans-cleavage and SERS nanoprobes crosslinking can be integrated into a single and disposal vessel. It was proved that our proposed nanobioassay was able to detect SARS-CoV-2 as low as 200 copies/mL without any pre-amplification within 45 min. In addition, the proposed nanobioassay was confirmed by clinical swab samples and challenged for SARS-CoV-2 detection in simulated complex environmental and food samples. This work enriches the arsenal of CRISPR-based diagnostics (CRISPR-Dx) and provides a novel and robust platform for SARS-CoV-2 decentralized detection, which can be put into practice in the near future.

Multifunctional Starch-Based Sensor with Non-Covalent Network to Achieve "3R" Circulation.

With the consumption of disposable electronic devices increasing, it is meaningful but also a big challenge to develop reusable and sustainable materials to replace traditional single-use sensors. Herein, a clever strategy for constructing a multifunctional sensor with 3R circulation (renewable, reusable, pollution-reducing biodegradable) is presented, in which silver nanoparticles (AgNPs) with multiple interactions are introduced into a reversible non-covalent cross-linking network composed of biocompatible and degradable carboxymethyl starch (CMS) and polyvinyl alcohol (PVA) to simultaneously obtain high mechanical conductivity and long-term antibacterial properties by a one-pot method. Surprisingly, the assembled sensor shows high sensitivity (gauge factor up to 4.02), high conductivity (0.1753 S m-1 ), low detection limit (0.5%), long-term antibacterial ability (more than 7 days), and stable sensing performance. Thus, the CMS/PVA/AgNPs sensor can not only accurately monitor a series of human behavior, but also identify handwriting recognition from different people. More importantly, the abandoned starch-based sensor can form a 3R circulation. Especially, the fully renewable film still shows excellent mechanical performance, achieving reusable without sacrificing its original function. Therefore, this work provides a new horizon for multifunctional starch-based materials as sustainable substrates for replacing traditional single-use sensors.

Elastin-like protein hydrogels with controllable stress relaxation rate and stiffness modulate endothelial cell function.

Mechanical cues from the extracellular matrix (ECM) regulate vascular endothelial cell (EC) morphology and function. Since naturally derived ECMs are viscoelastic, cells respond to viscoelastic matrices that exhibit stress relaxation, in which a cell-applied force results in matrix remodeling. To decouple the effects of stress relaxation rate from substrate stiffness on EC behavior, we engineered elastin-like protein (ELP) hydrogels in which dynamic covalent chemistry (DCC) was used to crosslink hydrazine-modified ELP (ELP-HYD) and aldehyde/benzaldehyde-modified polyethylene glycol (PEG-ALD/PEG-BZA). The reversible DCC crosslinks in ELP-PEG hydrogels create a matrix with independently tunable stiffness and stress relaxation rate. By formulating fast-relaxing or slow-relaxing hydrogels with a range of stiffness (500-3300 Pa), we examined the effect of these mechanical properties on EC spreading, proliferation, vascular sprouting, and vascularization. The results show that both stress relaxation rate and stiffness modulate endothelial spreading on two-dimensional substrates, on which ECs exhibited greater cell spreading on fast-relaxing hydrogels up through 3 days, compared with slow-relaxing hydrogels at the same stiffness. In three-dimensional hydrogels encapsulating ECs and fibroblasts in coculture, the fast-relaxing, low-stiffness hydrogels produced the widest vascular sprouts, a measure of vessel maturity. This finding was validated in a murine subcutaneous implantation model, in which the fast-relaxing, low-stiffness hydrogel produced significantly more vascularization compared with the slow-relaxing, low-stiffness hydrogel. Together, these results suggest that both stress relaxation rate and stiffness modulate endothelial behavior, and that the fast-relaxing, low-stiffness hydrogels supported the highest capillary density in vivo.

Advances in Gelatin Bioinks to Optimize Bioprinted Cell Functions.

Gelatin is a widely utilized bioprinting biomaterial due to its cell-adhesive and enzymatically cleavable properties, which improve cell adhesion and growth. Gelatin is often covalently cross-linked to stabilize bioprinted structures, yet the covalently cross-linked matrix is unable to recapitulate the dynamic microenvironment of the natural extracellular matrix (ECM), thereby limiting the functions of bioprinted cells. To some extent, a double network bioink can provide a more ECM-mimetic, bioprinted niche for cell growth. More recently, gelatin matrices are being designed using reversible cross-linking methods that can emulate the dynamic mechanical properties of the ECM. This review analyzes the progress in developing gelatin bioink formulations for 3D cell culture, and critically analyzes the bioprinting and cross-linking techniques, with a focus on strategies to optimize the functions of bioprinted cells. This review discusses new cross-linking chemistries that recapitulate the viscoelastic, stress-relaxing microenvironment of the ECM, and enable advanced cell functions, yet are less explored in engineering the gelatin bioink. Finally, this work presents the perspective on the areas of future research and argues that the next generation of gelatin bioinks should be designed by considering cell-matrix interactions, and bioprinted constructs should be validated against currently established 3D cell culture standards to achieve improved therapeutic outcomes.

Strain-Stiffening Hydrogels with Dynamic, Secondary Cross-Linking.

Hydrogels are water-swollen, typically soft networks useful as biomaterials and in other fields of biotechnology. Hydrogel networks capable of sensing and responding to external perturbations, such as light, temperature, pH, or force, are useful across a wide range of applications requiring on-demand cross-linking or dynamic changes. Thus far, although mechanophores have been described as strain-sensitive reactive groups, embedding this type of force-responsiveness into hydrogels is unproven. Here, we synthesized multifunctional polymers that combine a hydrophilic zwitterion with permanently cross-linking alkenes, and dynamically cross-linking disulfides. From these polymers, we created hydrogels that contain irreversible and strong thiol-ene cross-links and reversible disulfide cross-links, and they stiffened in response to strain, increasing hundreds of kPa in modulus under compression. We examined variations in polymer composition and used a constitutive model to determine how to balance the number of thiol-ene vs disulfide cross-links to create maximally force-responsive networks. These strain-stiffening hydrogels represent potential biomaterials that benefit from the mechanoresponsive behavior needed for emerging applications in areas such as tissue engineering.

Multifunctional Bioinspired Bredigite-Modified Adhesive for Bone Fracture Healing

Despite recent advances in bone adhesives applied for full median sternotomy, the regeneration of bone defects has remained challenging since the healing process is hampered by poor adhesiveness, limited bioactivity, and lack of antibacterial functions. Bioinspired adhesives by marine organisms provide a novel concept to circumvent these problems. Herein, a dual cross-link strategy is employed in designing a multifaceted bioinspired adhesive consisting of a catechol amine-functionalized hyperbranched polymer (polydopamine-co-acrylate, PDA), bredigite (BR) nanoparticles, and Fe3+ ions. The hybrid adhesives exhibit strong adhesion to various substrates such as poly(methyl methacrylate), glass, bone, and skin tissues through synergy between irreversible covalent and reversible noncovalent cross-linking, depending on the BR content. Noticeably, the adhesion strength of hybrid adhesives containing 2 wt % BR nanoparticles to bone tissues is 2.3 ± 0.8 MPa, which is about 3 times higher than that of pure PDA adhesives. We also demonstrate that these hybrid adhesives not only are bioactive and accelerate in vitro bone-like apatite formation but also exhibit antibacterial properties against Staphylococcus aureus, depending on the BR concentration. Furthermore, the superior cellular responses in contact with hybrid adhesives, including improved human osteosarcoma MG63 cell spreading and osteogenic differentiation, are achieved owing to the appropriate ion release and flexibility of the cross-linked double-network adhesive. In summary, multifunctional hybrid PDA/BR adhesives with appreciable osteoconductive, mechanical, and antibacterial properties represent the potential applications for median sternotomy surgery as a bone tissue adhesive.

ECM-Inspired Hydrogels with ADSCs Encapsulation for Rheumatoid Arthritis Treatment.

Due to their intrinsic anti-inflammatory and immunomodulatory properties, adipose-derived stem cells (ADSCs) are explored as a promising alternative in treating rheumatoid arthritis (RA). To address the poor survival and function loss of directly injected stem cells, efforts in this area are focus on the generation of efficient cell delivery vehicles. Herein, a novel extracellular matrix (ECM)-inspired injectable hydrogel for ADSCs encapsulation and RA treatment is proposed. The hydrogel with dendritic polylysine and polysaccharide components is formed through the reversible Schiff base crosslinking. It possesses self-healing capability, superior mechanical properties, minimal toxicity, and immunomodulatory ability. When encapsulated with ADSCs, the hydrogel could recover chronic inflammation by directly reversing the dominant macrophage phenotype from M1 to M2 and inhibiting the migration of fibroblast-like synoviocytes. Through a collagen-induced arthritis rat model, the tremendous therapeutic outcomes of this ADSCs-laden hydrogel, including inflammation attenuation, cartilage protection, and bone mineral density promotion are demonstrated. These results make the ECM-inspired hydrogel laden with ADSCs an ideal candidate for treating RA and other autoimmune disorders.

Mechanistic Investigation of the Androgen Receptor DNA-Binding Domain and Modulation via Direct Interactions with DNA Abasic Sites: Understanding the Mechanisms Involved in Castration-Resistant Prostate Cancer.

The androgen receptor (AR) is an important drug target in prostate cancer and a driver of castration-resistant prostate cancer (CRPC). A significant challenge in designing effective drugs lies in targeting constitutively active AR variants and, most importantly, nearly all AR variants lacking the ligand-binding domain (LBD). Recent findings show that an AR's constitutive activity may occur in the presence of somatic DNA mutations within non-coding regions, but the role of these mutations remains elusive. The discovery of new drugs targeting CRPC is hampered by the limited molecular understanding of how AR binds mutated DNA sequences, frequently observed in prostate cancer, and how mutations within the protein and DNA regulate AR-DNA interactions. Using atomistic molecular dynamics (MD) simulations and quantum mechanical calculations, we focused our efforts on (i) rationalising the role of several activating DBD mutations linked to prostate cancer, and (ii) DBD interactions in the presence of abasic DNA lesions, which frequently occur in CRPC. Our results elucidate the role of mutations within DBD through their modulation of the intrinsic dynamics of the DBD-DNA ternary complex. Furthermore, our results indicate that the DNA apurinic lesions occurring in the androgen-responsive element (ARE) enhance direct AR-DNA interactions and stabilise the DBD homodimerisation interface. Moreover, our results strongly suggest that those abasic lesions may form reversible covalent crosslinks between DNA and lysine residues of an AR via a Schiff base. In addition to providing an atomistic model explaining how protein mutations within the AR DNA-binding domain affect AR dimerisation and AR-DNA interactions, our findings provide insight into how somatic mutations occurring in DNA non-coding regions may activate ARs. These mutations are frequently observed in prostate cancer and may contribute to disease progression by enhancing direct AR-DNA interactions.

Sustainable castor oil-based vitrimers: Towards new materials with reprocessability, self-healing, degradable and UV-blocking characteristics

Vitrimers with reversible cross-links are emerging promising sustainable materials with reprocessability and recyclability. Here, castor oil-based epoxy resin (EMCO) with epoxy group and carbon-carbon double bonds was prepared through a two-step process and then cured with itaconic acid (IA) through epoxy-acid ring-opening reaction and free radical polymerization to fabricate fully bio-based epoxy vitrimers containing reversible transesterification bond. The thermal-mechanical properties, reprocessability, repairability, and recyclability could be balanced by varying the molar ratio of EMCO to IA. When the carboxyl group/epoxy group molar ratio reached 1.0, the EMCO-IA1.0 vitrimer exhibited the highest tensile strength of 14.39 MPa and Tg of 52.95 °C. Moreover, the vitrimer can be effectively remodeled (2 h at 180 °C) to prepare films and self-healing thanks to a rapid and mild stress relaxation process (2.56 min at 110 °C) and low activation energy (60.94 kJ·mol−1). More significantly, EMCO-IA vitrimer could be degraded in ethanol solution and recycled to prepare films and also exhibited excellent UV blocking ability. Overall, the EMCO-IA vitrimer can achieve a highly efficient closed-loop recycling without significantly sacrificing the mechanical properties, which can extend the service life and facilitate the sustainable development of the castor oil-based polymeric material.

Preparation of reversible cross-linked amphiphilic polymeric micelles with pH-responsive behavior for smart drug delivery.

A new type of reversible cross-linked and pH-responsive polymeric micelle (PM), poly[polyethylene glycol methacrylate-co-2-(acetoacetoxy)ethyl methacrylate]-b-poly [2-(dimethylamino)ethyl methacrylate] [P(PEGMA-co-AEMA)-b-PDMAEMA], was synthesized for targeted delivery of curcumin. After reversible cross-linking of the micellar shell, the PMs with a typical core-shell structure exhibited excellent stability against extensive dilution and good reversibility of pH-responsiveness in solutions with different pH values. P(PEGMA9-co-AEMA6)-b-PDMAEMA10 has the lowest critical micelle concentration (CMC) value (0.0041 mg mL-1), the highest loading capacity (13.86%) and entrapment efficiency (97.03%). A slow sustained drug release at pH 7.4 with 12.36% in 108 h, while a fast release (42.36%) was observed at pH 5.0. Furthermore, a dissipative particle dynamics (DPD) simulation method was employed to investigate the self-assembly process and pH-responsive behavior of PMs. The optimal drug-carrier ratio (2%) and fraction of water (92%) were confirmed by analyzing the drug distribution and morphology of micelles during the self-assembly process of the block copolymer. The simulation results were consistent with experimental results, indicating DPD simulation shows potential to study the structure properties of reversible cross-linked micelles. The present findings provide a new method for the development of SDDS with good structural stability and controlled drug release properties.

Enhancement of the mechanical properties of organic-inorganic hybrid elastomers by introducing movable and reversible crosslinks.

Organic-inorganic materials have been widely utilized in various fields as multifunctional materials. Poly(dimethyl siloxane) (PDMS), a typical inorganic polymer, has industrially appealing functions, such as transparency, biocompatibility, and gas permeability; however, it has poor mechanical properties. We incorporated organic-inorganic hybrid elastomers (PDMS-γCD-AAl⊃P(EA-HEMA) (x)) with movable crosslinks, and we utilized hydrogen bonds as reversible crosslinks. The organic polymer poly ethyl acrylate-r-hydroxy ethyl methacrylate (P(EA-HEMA)) penetrated the cavity of triacetylated γ-cyclodextrin (γCD), which was introduced into the side chains of PDMS, and it compounded with PDMS at the nanoscale. Structural studies involving visual and X-ray scattering measurements revealed that movable crosslinks improved the compatibility levels of PDMS and acrylate copolymers. However, macroscopic phase separation occurred when the number of reversible crosslinks increased. Furthermore, studies on the mobility levels of acrylate copolymers and movable crosslinks indicated that the relaxation behaviour of PDMS-γCD-AAl⊃P(EA-HEMA) (x) changed with changing numbers of reversible crosslinks. Introducing reversible crosslinks improved the Young's modulus and toughness values. The movable and reversible crosslinks between the organic and inorganic polymers contributed to the high elongation properties. The design of PDMS-γCD-AAl⊃P(EA-HEMA) (x) incorporated cooperatively movable and reversible crosslinks to achieve high compatibility of immiscible polymers and to control the mechanical properties.