Boronate Ester Bonds Research Articles

Sustainable Polyurethane Networks with High Self‐Healing and Mechanical Properties Based on Dual Dynamic Covalent Bonds

AbstractHydroxy‐terminated polybutadiene (HTPB) based polyurethanes (PU) networks are broadly applied in industry and aviation, however, their nonrecyclability leads to the waste of petroleum. In this work, a series of novel self‐healing, weldable, and recyclable HTPB‐based PU networks with dual reversible covalent bonds are fabricated by one‐pot polycondensation. To shorten the relaxation time, dual reversible covalent bonds (disulfide bonds and boronic ester bonds) are incorporated into the HTPB‐based PU networks. Meanwhile, to promote tensile strength, the rigid isocyanate and cross‐link agent are introduced into the networks. Obtained HTPB‐based PU network structures are characterized by FTIR, Raman, and DMA measurements. Obtained HHMB‐4‐20 network shows the best mechanical properties (tensile strength = 6.97 MPa, elongation at break = 302 %), and the mechanical properties almost can be recovered after welding/reprocessing by hot pressing. To satisfy the demands of industrial sustainability, the synthesis of PU networks with capabilities of reprocessing, self‐healing, and welding is a feasible approach.

Preparation of Copolymer of Dihydroxy Monomer and Acrylamide and Its Solution Properties with Polyphenylboronic Acid Compounds

: The construction of composite flooding system based on dynamic covalent bonds is one of the effective methods to improve the salt and temperature resistance of polymer flooding agents. The polymers used in most composite systems are xanthan gum and guar gum. In this paper, a novel multi-hydroxyl polymer was synthesized, and a new composite system was constructed based on the dynamic boronic ester bonds. Firstly, the multi-hydroxyl polymer P(AM-DPMOH2) was prepared by aqueous solution copolymerization of acrylamide (AM) and a dihydroxy monomer 2,3-dihydroxy-N-(3-methacrylamidopropyl)-N,N-dimethylpropan-1-aminium (DPMOH2), which was obtained by quaternization reaction between 3-chloro-1,2-propanediol and N-(3-dimethylaminopropyl). Then, the composite system was prepared by the P(AM-DPMOH2) solution and polyboronic acid compound (BPEI). The effects of DPMOH2 content in P(AM-DPMOH2), molecular weight of P(AM-DPMOH2), molecular weight of BPEI, phenylboronic acid groups content in BPEI and pH on the formation of thickening composite system were investigated. The results showed that when the content of DPMOH2 in P(AM-DPMOH2) exceeded 40 wt%, viscosity average molecular weight of P(AM-DPMOH2) was higher than 5.0×105 g/mol, the molecular weight of PEI in BPEI was larger than 3000 g/mol, the content of phenylboronic acid groups in BPEI was more than 39.3 %, and pH was in the range of 8–9, the thickening composite system can be formed by P(AM-DPMOH2) and BPEI. In addition, both the temperature and salt resistance of the composite system formed by 3000 mg/L P(AM-DPMOH2) and 2000 mg/L BPEI was much better than that of 3000 mg/L P(AM-DPMOH2). The results of this paper provide a new finding of how to construct a composite flooding system with dynamic covalent bonds.

Polymeric Emissive Materials Based on Dynamic Covalent Bonds.

Dynamic covalent polymers, composed of dynamic covalent bonds (DCBs), have received increasing attention in the last decade due to their adaptive and reversible nature compared with common covalent linked polymers. Incorporating the DCBs into the polymeric material endows it with advanced performance including self-healing, shape memory property, and so forth. However, the emissive ability of such dynamic covalent polymeric materials has been rarely reviewed. Herein, this review has summarized DCBs-based emissive polymeric materials which are classified according to the different types of DCBs, including imine bond, acylhydrazone bond, boronic ester bond, dynamic C-C bond, as well as the reversible bonds based on Diels–Alder reaction and transesterification. The mechanism of chemical reactions and various stimuli-responsive behaviors of DCBs are introduced, followed by typical emissive polymers resulting from these DCBs. By taking advantage of the reversible nature of DCBs under chemical/physical stimuli, the constructed emissive polymeric materials show controllable and switchable emission. Finally, challenges and future trends in this field are briefly discussed in this review.

Dual Dynamic Covalently Crosslinked Alginate Hydrogels with Tunable Properties and Multiple Stimuli-Responsiveness.

Alginate is a biopolymer that can be crosslinked with calcium ions to fabricate cytocompatible hydrogels. However, using calcium ions to crosslink alginate provides limited properties and functions to alginate hydrogels, restricting their biomedical applications. Here, phenylboronic acid-functionalized polyethyleneimine (PBA-PEI) was developed to introduce two orthogonal dynamic covalent crosslinks in the alginate hydrogels, where PBA-PEI was used to crosslink alginate dialdehyde (ADA) through imine bonds and boronate ester bonds. The grafting degree of PBA in the PEI structure was applied to fine-tune the properties of PBA-PEI/ADA hydrogels, including the rheological property, mechanical strength, swelling behavior, and antibacterial activity. In particular, the highly sensitive boronate ester bonds in the network enabled PBA-PEI/ADA hydrogels to be responsive to several stimuli, such as glucose, fructose, and hydrogen peroxide. Taken together, PBA-PEI/ADA hydrogels with tunable properties and multiple stimuli-responsiveness have been demonstrated as smart biomaterials for advanced biomedical applications.

A Biomarker-Responsive Nanosystem with Colon-Targeted Delivery for Ulcerative Colitis's Detection and Treatment with Optoacoustic/NIR-II Fluorescence Imaging.

Ulcerative colitis (UC) is a prevalent idiopathic inflammatory disease which causes such complications as intestinal perforation, obstruction, and bleeding, and thus deleteriously impacting people's normal work and quality of life. Hence, accurate diagnosis of UC is crucial in terms of planning optimal treatment plan. Herein, a pH/reactive oxygen species (ROS) dual-responsive nanosystem (BM@EP) is developed for UC's detection and therapy. BM@EP is composed of a chromophore-drug dyad and the enteric coating. The chromophore-drug dyad (BOD-XT-DHM) is synthesized by linking the chromophore (BOD-XT-BOH) and a flavonoid drug (dihydromyricetin DHM) through boronate ester bond. The enteric coating includes Eudragit S100 and poly(lactic-co-glycolic acid) (PLGA), the former is commonly employed as a pH-dependent polymer coating excipient so as to attain colon-targeted delivery, and the latter has been widely used as an excipient for the controlled-extended release. After oral administration, BM@EP delivers the dyad (BOD-XT-DHM) into the colon and releases the dyad molecules by being triggered by the alkaline pH in t colon, thereafter upon being stimulated by overexpressed H2 O2 in the inflamed colon, the boronate bond in the dyad is broken down and correspondingly the drug DHM is released for UC therapy, simultaneously the chromophore is released for near-infrared second window (NIR-II) fluorescence and optoacoustic imaging for UC diagnosis and recovery evaluation.

Ultrastretchable, Self-Healable, and Tissue-Adhesive Hydrogel Dressings Involving Nanoscale Tannic Acid/Ferric Ion Complexes for Combating Bacterial Infection and Promoting Wound Healing.

Preventing bacterial infections and accelerating wound closure are essential in the process of wound healing. Current wound dressings lack enough mechanical properties, self-healing ability, and tissue adhesiveness, and the bacterial killing also relies on the use of antibiotic drugs. Herein, a well-designed hybrid hydrogel dressing is constructed by simple copolymerization of acrylamide (AM), 3-acrylamido phenylboronic acid (AAPBA), chitosan (CS), and the nanoscale tannic acid (TA)/ferric ion (Fe3+) complex (TFe). The resulting hydrogel possesses lots of free catechol, phenylboronic acid, amine, and hydroxyl groups and contains many reversible and dynamic bonds such as multiple hydrogen bonds and boronate ester bonds, thereby showing satisfactory mechanical properties, fast self-healing ability, and desirable tissue-adhesive performance. Benefiting from the high photothermal conversion efficiency of the TFe, the hydrogel exhibits satisfactory antibacterial activity against both Gram-positive and Gram-negative bacteria. Moreover, the embedded TFe also endows the hydrogel with good antioxidant activity, anti-inflammatory property, and cell proliferation to promote tissue regeneration. Remarkably, in vivo animal assays reveal that the hybrid hydrogel effectively eliminates biofilm bacteria in the wound sites and accelerates the healing process of infected wounds. Taken together, the developed versatile hydrogels overcome the shortcomings of traditional wound dressings and are expected to become potential antibacterial dressings for future biomedical applications.

Inflammation-triggered dual release of nitroxide radical and growth factor from heparin mimicking hydrogel-tissue composite as cardiovascular implants for anti-coagulation, endothelialization, anti-inflammation, and anti-calcification

Cardiovascular implants made from heterogeneous tissues (HT) often clinically face premature failures such as thrombosis, inflammation, and calcification. Herein, we report a hydrogel-tissue composite exhibiting inflammation instructive release of multiple components towards preventing coagulation, promoting endothelial growth, and modulating reactive oxygen species (ROS) homeostasis. The hydrogel composed of MMP-responsive segment-crosslinked heparin mimicking polymer was loaded with a nitroxide radical via ROS cleavable boronic ester bonds and vascular endothelial growth factor (VEGF) via electrostatic attraction. Matrix metalloproteinase (MMP), which reportedly showed elevated expression in inflammation response to foreign implant degraded the hydrogel and led to the release of heparin mimicking polymer and VEGF, enhancing its anti-coagulation capacity and accelerating the growth of endothelial cells on it. In addition, the composite could sense oxidation biosignal present in the inflammation environment and subsequently release a ROS scavenger for auto-regulation of ROS balance. Subcutaneous implantation in mice suggested that the composite could steer the immune response toward an anti-inflammation state and subcutaneous implantation in rats suggested an anti-calcification effect of it. The enhanced hemocompatibility and endothelialization effects in vivo were further confirmed by the endovascular implantation of tissues via membrane-covered stent delivery. The current findings demonstrate that the incorporation of functional hydrogel into the tissue sophistically exploiting host response for controlled release of multiple active cargos is a feasible approach to boost the anticoagulant, endothelialization, anti-inflammatory, and anti-calcification functions of HT-based cardiovascular implants.

Recyclable, self-healing itaconic acid-based polyurethane networks with dynamic boronic ester bonds for recoverable adhesion application

Currently, synthesis of biobased polyurethane (PU) networks with recyclability, self-healing, as well as robust mechanical and adhesion properties still remain a challenge. Herein, a series of robust itaconic acid-based polyurethane networks (IAPU) with dynamic boronic ester bonds are fabricated and fully characterized by FTIR and DMA. All the obtained IAPU networks display high thermostability with an initial decomposition temperature around ∼270 °C. The activation energy and typology transition temperature of the IAPU-80 are 71.9 kJ mol−1 and -25.8 °C, respectively. The IAPU-80 shows low relaxation times from 169 to 125 s at moderate temperature from 60 to 65 °C, respectively, as well as excellent mechanical properties (tensile strength = 15.6 MPa, elongation at break = 70.4%, toughness = 12.6 MJ m−3). The IAPU-80 possess outstanding scratch self-healing ability (scratch disappear after heating at 120 °C for 10 min) and reprocessability (without distinct decrement of the tensile strength after twice recycling). Remarkably, the IAPU-80 bonded wood sample exhibits a high recoverable adhesion strength (∼8.2 MPa), after reused for three times. Therefore, the self-healing and malleable IAPUs with recoverable adhesion performance are obtained by incorporating dynamic boronic ester bonds into itaconic acid-based polyurethane networks. Present work describes a green and facile way to prepare sustainable PU networks with multiple functionalities for wide applications.

Fast, strong, and reversible adhesives with dynamic covalent bonds for potential use in wound dressing

Adhesives typically fall into two categories: those that have high but irreversible adhesion strength due to the formation of covalent bonds at the interface and are slow to deploy, and others that are fast to deploy and the adhesion is reversible but weak in strength due to formation of noncovalent bonds. Synergizing the advantages from both categories remains challenging but pivotal for the development of the next generation of wound dressing adhesives. Here, we report a fast and reversible adhesive consisting of dynamic boronic ester covalent bonds, formed between poly(vinyl alcohol) (PVA) and boric acid (BA) for potential use as a wound dressing adhesive. Mechanical testing shows that the adhesive film has strength in shear of 61 N/cm2 and transcutaneous adhesive strength of 511 N/cm2, generated within 2 min of application. Yet the film can be effortlessly debonded when exposed to excess water. The mechanical properties of PVA/BA adhesives are tunable by varying the cross-linking density. Within seconds of activation by water, the surface boronic ester bonds in the PVA/BA film undergo fast debonding and instant softening, leading to conformal contact with the adherends and reformation of the boronic ester bonds at the interface. Meanwhile, the bulk film remains dehydrated to offer efficient load transmission, which is important to achieve strong adhesion without delamination at the interface. Whether the substrate surface is smooth (e.g., glass) or rough (e.g., hairy mouse skin), PVA/BA adhesives demonstrate superior adhesion compared to the most widely used topical skin adhesive in clinical medicine, Dermabond.

Self-activatable carbon nanotube@ruthenium-catechol coordination complex for hydrogen evolution reaction

We report a simple metal ion-catechol coordination strategy to coat ruthenium-catechol polymer complex (TAC-Ru) on the surface of carbon nanotubes (CNT) to form a core–shell structure (abbreviated as CNT@TAC-Ru). This is achieved by firstly polymerizing catechol and boronic acid monomers on the surface of CNT to form a boronate ester polymer (BP) shell. Then, Ru3+ is used to etch the BP shell, and cleave the dynamic boronate ester bond, leading to the formation of a CNT@ruthenium-catechol coordination complex based on the coordinative efficiency of the catechol group. The electrocatalytic property of the CNT@TAC-Ru composite can be activated through electrochemical cycling treatment. The as-activated CNT@TAC-Ru exhibits evidently improved hydrogen evolution reaction (HER) performance with an overpotential of 10 mV in 1.0 M KOH at a current density of 10 mA cm−2 , which is better than that of commercial Pt/C (32 mV). And the long-term stability is also desirable. This work provides a pyrolysis-free method to form metal-polymer-carbon composite with high HER performance under the alkaline condition.

Boronic ester bonds crosslinked vitrimer elastomers with mechanical robustness, shape memory, self-healing and recyclability properties

Permanently cross-linked networks confer chemical and mechanical stability to cross-linked elastomers, making their recycling a serious environmental issue. Recyclable covalently crosslinked elastomers have recently been developed by building covalently adaptive networks in elastomers. Here, we demonstrate a simple and general strategy to construct covalent adaptable networks with mechanical robustness, self-healing, shape memory, and recyclability. The dynamic boronic ester linkage between silica and epoxidized natural rubber endows the material with high stretchability and high tensile strength. The boronic ester bond exchange enables the cross-linked network to achieve self-healing, remodeling, and shape memory through network structural rearrangement. The materials can be recovered by hot pressing or dissolution, and the structure of the sample recovered by dissolution remains basically unchanged. Furthermore, a self-healing flexible electronic device can be fabricated by spraying conductive graphite on the surface of these elastomers. Considering that this interfacial boronic ester bond cross-linking can be easily achieved between different commercial epoxy polymers and hydroxyl-rich nanoparticles, we believe that this work has great potential in the development of rubber-based vitrimer elastomers and flexible wearable devices.

Preparation of ROS-responsive drug-loaded hydrogels applied in wound dressings using supercritical solvent impregnation

Drug-loaded hydrogels with wound environment stimuli-responsive property can significantly promote wound healing and are widely applied in dressings. Two natural polymers, i.e. sodium alginate and sodium hyaluronate, were modified by 3-aminophenylboric acid and then cross-linked with polyvinyl alcohol to prepare ROS responsive hydrogels. Doxycycline hydrochloride was loaded onto hydrogels using supercritical solvent impregnation (SSI) technology, and the effects of immersion time, pressure and temperature on drug loading capacity (DLC) were investigated. DLC firstly increased and then decreased with the elevation of supercritical CO2 pressure, and maximum value was up to 11 mg/g at 15 MPa and 50 °C. In the in vitro drug release study, doxycycline hydrochloride was controllably released from hydrogels for 10 h via the sensitivity of boronate ester bonds to ROS. This work expands the application of SSI in wound dressing, which provides a new approach for the design of composite hydrogel formulations with uniform drug distribution.

Wound microenvironment self-adaptive hydrogel with efficient angiogenesis for promoting diabetic wound healing.

Neovascularization is critical to improve the diabetic microenvironment, deliver abundant nutrients to the wound and promote wound closure. However, the excess of oxidative stress impedes the healing process. Herein, a self-adaptive multifunctional hydrogel with self-healing property and injectability is fabricated through a boronic ester-based reaction between the phenylboronic acid groups of the 3-carboxyl-4-fluorophenylboronic acid -grafted quaternized chitosan and the hydroxyl groups of the polyvinyl alcohol, in which pro-angiogenic drug of desferrioxamine (DFO) is loaded in the form of gelatin microspheres (DFO@G). The boronic ester bonds of the hydrogel can self-adaptively react with hyperglycemic and hydrogen peroxide to alleviate oxidative stress and release DFO@G in the early phase of wound healing. A sustained release of DFO is then realized by responding to overexpressed matrix metalloproteinases. In a full-thickness diabetic wound model, the DFO@G loaded hydrogel accelerates angiogenesis by upregulating expression of hypoxia-inducible factor-1 and angiogenic growth factors, resulting in collagen deposition and rapid wound closure. This multifunctional hydrogel can not only self-adaptively change the microenvironment to a pro-healing state by decreasing oxidative stress, but also respond to matrix metalloproteinases to release DFO. The self-adaptive multifunctional hydrogel has a potential for treating diabetic wounds.

An injectable mitochondria-targeted nanodrug loaded-hydrogel for restoring mitochondrial function and hierarchically attenuating oxidative stress to reduce myocardial ischemia-reperfusion injury

Timely reperfusion is the common treatment for myocardial infarction. However, ischemia-reperfusion (I/R) therapy can lead to oxidative stress and mitochondrial dysfunction that further aggravate myocardial injury, and no effective therapy is currently available for alleviating myocardial I/R injury. Herein, we engineer a mitochondria-targeted Szeto-Schiller (SS31) peptide modified-amphiphilic polymer (PTPS) that self-assembles into nanomicelles (PTPSCs) for loading cyclosporine A (CsA). The PTPSCs are then encapsulated into a pH/ROS dual responsive injectable hydrogel crosslinked with reversible imine and boronic ester bonds. The loaded PTPSCs are controllably delivered from the hydrogel matrix in response to the low pH and high ROS microenvironment of the I/R heart, thus realizing reconstruction of mitochondrial function and unprecedented hierarchical attenuation of oxidative stress. The boronic ester in the hydrogel consumes the ROS in cardiac microenvironment, and the mitochondria-targeted delivery of CsA is revealed to inhibit mitochondria-mediated apoptosis signaling pathway to prevent cardiomyocyte apoptosis, meanwhile attenuating the mitochondrial ROS output to reduce the level of cytosolic ROS. Additionally, SS31 can also serve as an antioxidant to consume ROS in the mitochondria. In rat model of myocardial I/R injury with administration of this injectable hydrogel, the targeted release of PTPSCs efficiently restores mitochondrial and cardiac function.

Dental plaque-inspired versatile nanosystem for caries prevention and tooth restoration

Dental caries is one of the most prevalent human diseases resulting from tooth demineralization caused by acid production of bacteria plaque. It remains challenges for current practice to specifically identify, intervene and interrupt the development of caries while restoring defects. In this study, inspired by natural dental plaque, a stimuli-responsive multidrug delivery system (PMs@NaF-SAP) has been developed to prevent tooth decay and promote enamel restoration. Classic spherical core-shell structures of micelles dual-loaded with antibacterial and restorative agents are self-assembled into bacteria-responsive multidrug delivery system based on the pH-cleavable boronate ester bond, followed by conjugation with salivary-acquired peptide (SAP) to endow the nanoparticle with strong adhesion to tooth enamel. The constructed PMs@NaF-SAP specifically adheres to tooth, identifies cariogenic conditions and intelligently releases drugs at acidic pH, thereby providing antibacterial adhesion and cariogenic biofilm resistance, and restoring the microarchitecture and mechanical properties of demineralized teeth. Topical treatment with PMs@NaF-SAP effectively diminishes the onset and severity of caries without impacting oral microbiota diversity or surrounding mucosal tissues. These findings demonstrate this novel nanotherapy has potential as a promising biomedical application for caries prevention and tooth defect restoration while resisting biofilm-associated diseases in a controlled manner activated by pathological bacteria.

Super Stretchable, Self‐Healing, Adhesive Ionic Conductive Hydrogels Based on Tailor‐Made Ionic Liquid for High‐Performance Strain Sensors

AbstractIonic conductive hydrogels (ICHs) integrate the conductive performance and soft nature of tissue‐like materials to imitate the features of human skin with mechanical and sensory traits; thus, they are considered promising substitutes for conventional rigid metallic conductors when fabricating human‐motion sensors. However, the simultaneous incorporation of excellent stretchability, toughness, ionic conductivity, self‐healing, and adhesion via a simple method remains a grand challenge. Herein, a novel ICH platform is proposed by designing a phenylboronic acid‐ionic liquid (PBA‐IL) with multiple roles that simultaneously realize the highly mechanical, electrical, and versatile properties. This elaborately designed semi‐interpenetrating network ICH is fabricated via a facile one‐step approach by introducing cellulose nanofibrils (CNFs) into the PBA‐IL/acrylamide cross‐linked network. Ingeniously, the dynamic boronic ester bonds and physical interactions (hydrogen bonds and electrostatic interactions) of the cross‐linked network endow these hydrogels with remarkable stretchability (1810 ± 38%), toughness (2.65 ± 0.03 MJ m−3), self‐healing property (92 ± 2% efficiency), adhesiveness, and transparency. Moreover, the construction of this material shows that CNFs can synergistically enhance mechanical performance and conductivity. The wide working strain range (≈1000%) and high sensitivity (GF = 8.36) make this ICH a promising candidate for constructing the next generation of gel‐based strain sensor platforms.

Reprocessable Polybenzoxazine Thermosets with High Tgs and Mechanical Strength Retentions Using Boronic Ester Bonds as Crosslinkages.

In order to obtain reprocessable polybenzoxazine thermosets with high heat resistance and mechanical strength retentions, network structures without irreversible parts were constructed via crosslinking benzoxazine oligomers using boronic ester cross-linkers. Firstly, the benzoxazine monomer containing carbon–carbon double bonds was synthesized via the Mannich reaction. After thermal ring-opening polymerization, the benzoxazine oligomer containing carbon–carbon double bonds (OBZ) was yielded. Through the thiol-ene click reaction of the OBZ and dithiol cross-linker bearing boronic ester bonds, the polybenzoxazine thermosets using boronic ester bonds as crosslinkages (OBZ-BDB) were successfully synthesized. The structures of OBZ and OBZ-BDB were characterized by SEC, 1H NMR, and FT-IR measurements. Reprocessing experiments showed that OBZ-BDB has remarkable reprocessability. The retention rates of the tensile strengths through three generations of reprocessing were 98%, 95%, and 84%, respectively. Meanwhile, OBZ-BDB cross-linked by boronic ester bonds had brilliant thermal properties. The Tg of the original OBZ-BDB was 224 °C. With the increase of the reprocessing generations, the Tgs basically remained unchanged.

Mapping hierarchical networks of poly(vinyl alcohol)/cellulose nanofiber composite hydrogels via viscoelastic probes

Discriminating the roles of different networks in the multiply cross-linked hydrogels is vital to optimize their overall performance. Poly(vinyl alcohol)/cellulose nanofiber composite hydrogels were used as template for the study. Three types of characteristic networks, including chemical network cross-linked with boronic ester bonds, physical network cross-linked with microcrystallites, and coexistence of these two networks, were constructed in the system, and the viscoelastic responses were used to detect the characteristic relaxation behavior of those networks. The physical network is more sensitive to stress-induced deformation, whereas the chemical network more sensitive to strain-induced one. The former has lower level of viscous dissipation and higher level of elastic storage as compared to the latter, and dominates linear viscoelasticity of hydrogels as the two networks coexist. Their synergistic effect can be well defined by the scaling behavior of hysteretic work. This work proposes an interesting method of probing networks in the multiply cross-linked hydrogels.

Hydroxyl-Terminated Polybutadiene-Based Polyurethane with Self-Healing and Reprocessing Capabilities.

Hydroxyl-terminated polybutadiene (HTPB)-based polyurethane (PU) networks play indispensable roles in a variety of applications; however, they cannot be reprocessed, resulting in environmental problems and unsustainable industrial development. In this work, recyclable HTPB-based PU vitrimer (HTPB-PUV) networks are fabricated by introduction of a cross-linker 2,2′-(1,4-phenylene)-bis[4-mercaptan-1,3,2-dioxaborolane] (BDB) with dynamic boronic ester bonds into the network. Meanwhile, the BDB can stabilize the HTPB unit in the network by elimination of double bonds. The novel HTPB-PUV networks are constructed by a thiol-ene “click” reaction and an addition reaction between HTPB and cross-linker BDB and isocyanates (HDI). The dynamic HTPB-PUV networks are characterized by dynamic mechanical analysis (DMA) and Fourier transform infrared (FTIR). The obtained dynamic HTPB-PUV networks possess superior thermostability. Moreover, due to the presence of dynamic boronic ester bonds, the HTPB-PUV network topologies can be altered, contributing to the reprocessing, self-healing, and welding abilities of the final polymer. Through a hot press, the pulverized sample can be reprocessed for several cycles, and mechanical properties of the reprocessed samples are similar to those of the pristine one, with the tensile strength being even higher. The self-healed sample exhibits almost complete recovery from scratch after the healing treatment at 130 °C for 3 h. Moreover, a welding efficiency of 120% was achieved.

Dopamine Assisted Self-Cleaning, Antifouling, and Antibacterial Coating via Dynamic Covalent Interactions.

The rapid accumulation of dead bacteria or protein on a bactericidal surface can reduce the effectiveness of the modified surface and alter its biocidal activity by shielding the surface biocide functional groups, promoting microbial attachment and subsequent biofilm formation. Thus, the alteration of biocidal activity due to biofilm formation can cause serious trouble including severe infection or implant or medical device failure leading to death. Therefore, developing a smart self-cleaning surface is of great interest. Ideally, such a surface can not only kill the attached microbials but also release the dead cells and foulants from the surface under a particular incitement on demand. In this project, a sugar-responsive self-cleaning coating has been developed by forming covalent boronic ester bonds between catechol groups from polydopamine and a benzoxaborole pendant from zwitterionic and cationic polymers. To incorporate antifouling properties and enhance the biocompatibility of the coating, bioinspired zwitterionic compound 2-methacryloyloxyethyl phosphorylcholine (MPC) was chosen and benzoxaborole pendant containing zwitterionic polymer poly(MPC-st-MAABO) (MAABO: 5-methacrylamido-1,2-benzoxaborole) was synthesized. Additionally to impart antibacterial properties to the surface, a quaternary ammonium containing cationic polymer poly(2-(methacryloyloxy)ethyl trimethylammonium (META)-st-MAABO)) was synthesized. These synthesized polymers were covalently grafted to a polydopamine (PDA) coated surface by forming a strong cyclic boronic ester complex with a catechol group of the PDA layer endowing the surface with bacteria contact-killing properties and capturing specific protein. After the addition of cis-diol containing competitive molecules, i.e., saccharides/sugars, this boronic ester complex with a catechol group of PDA was replaced and the attached polymer layer was cleaved from the surface, resulting in the release of both absorbed protein and live/killed bacteria electrostatically attached to the polymer layer. This dynamic self-cleaning surface can be a promising material for biomedical applications avoiding the gathering of dead cells and debris that are typically encountered on a traditional biocidal surface.