Temperature, pH, and Glucose Responsive Gels via Simple Mixing of Boroxole- and Glyco-Based Polymers

Fabrication and characteristics of multifunctional hydrogel dressings using dopamine modified hyaluronic acid and phenylboronic acid modified chitosan

The healing of damaged skin is a complex and dynamic process, and the multi-functional hydrogel dressings could promote skin tissue healing. This study, therefore, explored the development of a composite multifunctional hydrogel (HDCP) by incorporating the dopamine modified hyaluronic acid (HA-DA) and phenylboronic acid modified chitosan (CS-PBA) crosslinked using boric acid ester bonds. The integration of HA-DA and CS-PBA could be confirmed using the Fourier transform infrared spectrometer and 1H nuclear magnetic resonance analyses. The fabricated HDCP hydrogels exhibited porous structure, elastic solid behavior, shear-thinning, and adhesion properties. Furthermore, the HDCP hydrogels exhibited antibacterial efficacy against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). Subsequently, the cytocompatibility of the HDCP hydrogels was verified through CCK-8 assay and fluorescent image analysis following co-cultivation with NIH-3T3 cells. This research presents an innovative multifunctional hydrogel that holds promise as a wound dressing for various applications within the realm of wound healing.

The Rise of Boron-Containing Compounds: Advancements in Synthesis, Medicinal Chemistry, and Emerging Pharmacology

Boron-containing compounds (BCC) have emerged as important pharmacophores. To date, five BCC drugs (including boronic acids and boroles) have been approved by the FDA for the treatment of cancer, infections, and atopic dermatitis, while some natural BCC are included in dietary supplements. Boron's Lewis acidity facilitates a mechanism of action via formation of reversible covalent bonds within the active site of target proteins. Boron has also been employed in the development of fluorophores, such as BODIPY for imaging, and in carboranes that are potential neutron capture therapy agents as well as novel agents in diagnostics and therapy. The utility of natural and synthetic BCC has become multifaceted, and the breadth of their applications continues to expand. This review covers the many uses and targets of boron in medicinal chemistry.

Microenvironment responsive nanocomposite hydrogel with NIR photothermal therapy, vascularization and anti-inflammation for diabetic infected wound healing

Bacterial infection, excessive inflammation and damaging blood vessels network are the major factors to delay the healing of diabetic ulcer. At present, most of wound repair materials are passive and can't response to the wound microenvironment, resulting in a low utilization of bioactive substances and hence a poor therapeutic effect. Therefore, it's essential to design an intelligent wound dressing responsive to the wound microenvironment to achieve the release of drugs on-demand on the basis of multifunctionality. In this work, metformin-laden CuPDA NPs composite hydrogel (Met@ CuPDA NPs/HG) was fabricated by dynamic phenylborate bonding of gelatin modified by dopamine (Gel-DA), Cu-loaded polydopamine nanoparticles (CuPDA NPs) with hyaluronic acid modified by phenyl boronate acid (HA-PBA), which possessed good injectability, self-healing, adhesive and DPPH scavenging performance. The slow release of metformin was achieved by the interaction with CuPDA NPs, boric groups (B-N coordination) and the constraint of hydrogel network. Metformin had a pH and glucose responsive release behavior to treat different wound microenvironment intelligently. Moreover, CuPDA NPs endowed the hydrogel excellent photothermal responsiveness to kill bacteria of >95% within 10 min and also the slow release of Cu²⁺ to protect wound from infection for a long time. Met@ CuPDA NPs/HG also recruited cells to a certain direction and promoted vascularization by releasing Cu²⁺. More importantly, Met@CuPDA NPs/HG effectively decreased the inflammation by eliminating ROS and inhibiting the activation of NF-κB pathway. Animal experiments demonstrated that Met@CuPDA NPs/HG significantly promoted wound healing of diabetic SD rats by killing bacteria, inhibiting inflammation, improving angiogenesis and accelerating the deposition of ECM and collagen. Therefore, Met@CuPDA NPs/HG had a great application potential for diabetic wound healing.

Optimized Carbohydrate-Based Nanogel Formulation to Sensitize Hypoxic Tumors

Solid tumors are often poorly vascularized, which impairs oxygen supply and drug delivery to the cells. This often leads to genetic and translational adaptations that promote tumor progression, invasion, metastasis, and resistance to conventional chemo-/radiotherapy and immunotherapy. A hypoxia-directed nanosensitizer formulation of a hypoxia-activated prodrug (HAP) was developed by encapsulating iodoazomycin arabinofuranoside (IAZA), a 2-nitroimidazole nucleoside-based HAP, in a functionally modified carbohydrate-based nanogel, facilitating delivery and accrual selectively in the hypoxic head and neck and prostate cancer cells. Although IAZA has been reported as a clinically validated hypoxia diagnostic agent, recent studies have pointed to its promising hypoxia-selective anti-tumor properties, which make IAZA an excellent candidate for further exploration as a multimodal theranostic of hypoxic tumors. The nanogels are composed of a galactose-based shell with an inner core of thermoresponsive (di(ethylene glycol) methyl ethyl methacrylate) (DEGMA). Optimization of the nanogels led to high IAZA-loading capacity (≅80-88%) and a slow time-controlled release over 50 h. Furthermore, nanoIAZA (encapsulated IAZA) displayed superior in vitro hypoxia-selective cytotoxicity and radiosensitization in comparison to free IAZA in the head and neck (FaDu) and prostate (PC3) cancer cell lines. The acute systemic toxicity profile of the nanogel (NG1) was studied in immunocompromised mice, indicating no signs of toxicity. Additionally, growth inhibition of subcutaneous FaDu xenograft tumors was observed with nanoIAZA, demonstrating that this nanoformulation offers a significant improvement in tumor regression and overall survival compared to the control.

Injectable, Self-Healing and Multiple Responsive Histamine Modified Hyaluronic Acid Hydrogels with Potentialities in Drug Delivery, Antibacterial and Tissue Engineering

Hydrogels are 3D network structures composed of physically or chemically crosslinked, hydrophilic molecules. Compared with conventional hydrogels with static and permanent network structures, injectable and responsive hydrogels generated from dynamic networks, have attracted increasing attention from various disciplines due to their wide-ranging applications in tissue engineering, drug delivery, soft robotics, etc. Herein, an injectable self-healing and multiple-responsive hyaluronic acid (HA)- histamine (His)/metal hydrogel is developed by modifying His onto HA and the subsequent, dynamic coordination between imidazole and metal ions. The pH-responsive and mechanical behaviors exhibited by the HA-His/metal hydrogels are tunable with the kinds and the concentrations of metal ions. The HA-His/Zr⁴⁺ hydrogels demonstrate a moldable capability at a neutral pH and a multi-stimulus-responsive capability when exposed to a weak alkaline environment and hyaluronidase, which inhibits bacterial growth and biofilm formation. Biocompatibilities and accelerated wound healing are demonstrated in vitro and in vivo and are thoroughly investigated and well characterized. The HA-His/Zr⁴⁺ hydrogel has great potential in various biomedical applications, such as pH- and hyaluronidase-responsive sustained release, antibacterial, and implantable materials for tissue engineering.

Self-Healing Hydrogels: Development, Biomedical Applications, and Challenges

Polymeric hydrogels have drawn considerable attention as a biomedical material for their unique mechanical and chemical properties, which are very similar to natural tissues. Among the conventional hydrogel materials, self-healing hydrogels (SHH) are showing their promise in biomedical applications in tissue engineering, wound healing, and drug delivery. Additionally, their responses can be controlled via external stimuli (e.g., pH, temperature, pressure, or radiation). Identifying a suitable combination of viscous and elastic materials, lipophilicity and biocompatibility are crucial challenges in the development of SHH. Furthermore, the trade-off relation between the healing performance and the mechanical toughness also limits their real-time applications. Additionally, short-term and long-term effects of many SHH in the in vivo model are yet to be reported. This review will discuss the mechanism of various SHH, their recent advancements, and their challenges in tissue engineering, wound healing, and drug delivery.

Engineered insulin-polycation complexes for glucose-responsive delivery with high insulin loading

Glucose-responsive insulin delivery systems have the potential to improve quality of life for individuals with diabetes by improving blood sugar control and limiting the risk of hypoglycemia. However, systems with desirable insulin release kinetics and high loading capacities have proven difficult to achieve. Here, we report the development of electrostatic complexes (ECs) comprised of insulin, a polycation, and glucose oxidase (GOx). Under normoglycemic physiological conditions, insulin carries a slight negative charge and forms a stable EC with the polycation. In hyperglycemia, the encapsulated glucose-sensing enzyme GOx converts glucose to gluconic acid and lowers the pH of the microenvironment, causing insulin to adopt a positive charge. Thus, the electrostatic interactions are disrupted, and insulin is released. Using a model polycation, we conducted molecular dynamics simulations to model these interactions, synthesized ECs with > 50% insulin loading capacity, and determined in vitro release kinetics. We further showed that a single dose of ECs can provide a glycemic profile in streptozotocin-induced diabetic mice that mimics healthy mice over a 9 h period with 2 glucose tolerance tests.

Fabrication of Cationic Poly(vinyl alcohol) Films Cross-Linked Using Copolymers Containing Quaternary Ammonium Cations, Benzoxaborole, and Carboxy Groups

Water-insoluble cationic poly(vinyl alcohol) (PVA) films were fabricated using a mixed aqueous solution of PVA and poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC)-co-methacrylic acid (MAAc)-co-5-methacrylamido-1,2-benzoxaborole (MAAmBO)) copolymer (3D). The surface of the PVA film is typically negatively charged, and simple fabrication methods for water-insoluble PVA films with cationic surface charges are required to expand their application fields. METAC, which has a permanent positive charge owing to the presence of a quaternary ammonium cation, was selected as the cationic unit. The MAAc and MAAmBO units were used as two types of cross-linking structures for the thermal cross-linking of the hydroxy and carboxy groups of the MAAc unit (covalent bonding) as well as the diol and benzoxaborole groups of the MAAmBO unit (dynamic covalent bonding). The films were thermally cross-linked at 135 °C for 4 h without the addition of materials. After immersion in surplus water at 80 °C for 3 h, the cross-linked PVA/3D films retained almost 100% of their weights. The ζ-potential of the water-insoluble PVA/3D film was 9.4 ± 0.8 mV. The PVA/3D film was strongly dyed using anionic acid red 1 (AR1) because of its positively charged surface. Interestingly, it could also be slightly dyed using cationic methylene blue (MB) and became transparent (original state) after immersion in water for 2 days. These results suggested that positive and negative charges coexisted in the PVA/3D film, and the surface properties were positively inclined. Moreover, the degree of hemolysis of the PVA/3D films was similar to that of the negative control, which showed high blood compatibility. To our knowledge, this is the first report on the fabrication of water-insoluble cationic PVA films using two types of cross-linking structures containing carboxy and benzoxaborole groups. The cross-linked PVA films were analyzed using Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), and contact angle (CA) and ζ-potential measurement, as well as by determining the mechanical properties, adsorption of charged molecules, and biocompatibility. These readily fabricated water-insoluble PVA films with positive charges can show potential applications in sensors, adsorption systems, and antimicrobial materials.

Multi-responsive, injectable, and self-healing hydrogels based on benzoxaborole–tannic acid complexation

A bio-inspired, multi-responsive, injectable, and self-healing hydrogel was developed via the interaction of tannic acid (TA) and benzoxaborole-based linear copolymers.

Chemoresponsive polymer systems for selective molecular recognition of organic molecules in biological systems

Smart polymer materials that respond to a chemical stimulus are applied for the construction of biomedical devices and purification/separation systems. Small organic molecules are a particular type of stimulus. Their abnormal concentration indisputably indicates certain diseases. They are also hazardous environment contaminants. Polymer materials, which structure is selectively changed in the presence of a defined organic compound are promising in view of regulation of certain biomedical functions, as well as in view of chemical detectors construction. This review summarizes the state of the art in the self-assemblies of amphiphilic copolymers and polymer networks sensitive toward organic species, with an emphasis on the reports from the last decade. We focus on the relationship between the selectivity of introduced receptor moieties responsible for the change of material structure, the overall structure of material and its functionality.

Boronic acid and diol-containing polymers: how to choose the correct couple to form "strong" hydrogels at physiological pH

Dynamic covalent hydrogels crosslinked by boronate ester bonds are promising materials for biomedical applications. However, little is known about the impact of the crosslink structure on the mechanical behaviour of the resulting network. Herein, we provide a mechanistic study on boronate ester crosslinking upon mixing hyaluronic acid (HA) backbones modified, on the one hand, with two different arylboronic acids, and on the other hand, with three different saccharide units. Combining rheology, NMR and computational analysis, we demonstrate that carefully selecting the arylboronic-polyol couple allows for tuning the thermodynamics and molecular exchange kinetics of the boronate ester bond, thereby controlling the rheological properties of the gel. In particular, we report the formation of "strong" gels (i.e. featuring slow relaxation dynamics) through the formation of original complex structures (tridentate or bidentate complexes). These findings offer new prospects for the rational design of hydrogel scaffolds with tailored mechanical response.

Hypoxia and temperature dual-stimuli-responsive random copolymers: facile synthesis, self-assembly and controlled release of drug

The micelles self-assembled from P(NIPAM-co-AA-co-NIA) copolymers presented hypoxia and temperature dual-stimuli-responsive properties and a controlled release of drug was achieved using them.

Preparation of cross-linked poly(vinyl alcohol) films from copolymers with benzoxaborole and carboxylic acid groups, and their degradability in an oxidizing environment

Functionalized PVA films were prepared from copolymers with benzoxaborole and carboxyl groups.

Injectable dual cross-linked adhesive hyaluronic acid multifunctional hydrogel scaffolds for potential applications in cartilage repair

A double crosslinked hydrogels was designed and prepared by combining the Diels–Alder click reaction and possessed good mechanical strength, injectability and adhesion.

Self-crosslinking smart hydrogels through direct complexation between benzoxaborole derivatives and diols from hyaluronic acid

By tailoring the structure of benzoxaborole (BOR), self-crosslinking hydrogels based on hyaluronic acid (HA) modified with BOR derivatives are obtained for the first time through the direct BOR-HA diol complexation at physiological pH.

Dynamic-Covalent Hydrogel with NIR-Triggered Drug Delivery for Localized Chemo-Photothermal Combination Therapy

Near-infrared (NIR) light-responsive, injectable hydrogels are among the most promising drug delivery systems for localized anticancer therapy owing to its minimally invasive administration and remote-controlled manner. However, most currently reported NIR-responsive hydrogels were usually generated through physical mixing of thermosensitive polymers and photothermal conversion agents. In this study, a novel type of dynamic-covalent hydrogel (GelPV-DOX-DBNP) with NIR light-triggered drug release behavior was rationally designed for chemo-photothermal combination treatment of tumors. Concretely, this NIR-responsive hydrogel was formed by specific benzoxaborole-carbohydrate interactions between benzoxaborole (BOB)-modified hyaluronic acid (BOB-HA) and fructose-based glycopolymer (PolyFru), where photosensitizer perylene diimide zwitterionic polymer (PDS), reductant ascorbic acid (Vc), anticancer drug doxorubicin (DOX) as well as photothermal nanoparticles (DB-NPs) were encapsulated, simultaneously. Upon 660 nm light irradiation, both PDS and Vc within the designed hydrogel can convert oxygen into hydrogen peroxide, which could make hydrogel be degraded through the breakage of dynamic covalent bonds based on benzoxaborole-carbohydrate interactions, leading to NIR light-activatable release of DOX and DB-NPs from GelPV-DOX-DBNP. Furthermore, the released DB-NPs can convert 915 nm light irradiation into heat, enabling the application of GelPV-DOX-DBNP as a NIR-responsive drug delivery platform for both chemotherapy and photothermal therapy (PTT). In vivo results prove that GelPV-DOX-DBNP exhibited a markedly enhanced chemo-photothermal synergistic therapy for 4T1 tumor model mice, compared to chemotherapy alone or PTT. This work presents a new strategy to construct NIR light-responsive hydrogel as one alternative drug delivery system for anticancer applications.

Multiresponsive and Self-Healing Hydrogel via Formation of Polymer-Nanogel Interfacial Dynamic Benzoxaborole Esters at Physiological pH

Nanocomposite hydrogels with multiresponsiveness and self-healing property are attracting extensive interest due to their enhanced performance for a wide range of applications. In this work, we have successfully developed novel hydrogels based on interfacial polymer-nanogel benzoxaborolate cross-linking at physiological pH. Temperature-sensitive nanogels (NG-Gal) containing galactose residues on the nanosurface were prepared and subsequently used as macro-cross-linkers to form a hydrogel network through formation of dynamic adducts with benzoxaborole groups of a hydrophilic copolymer poly(DMA-st-MAABO). Benefiting from the low pK_a value of benzoxaborole (∼7.2), hydrogels can be constructed rapidly at physiological pH, which is of great significance for biomedical applications. Changing the molar ratio between benzoxaborole and galactose was found to alter the mechanical properties of hydrogels as confirmed by rheological measurements. The dynamic nature of benzoxaborole esters endowed the hydrogel with moldability and self-healing ability after disruption. Moreover, the hydrogel showed multiresponsiveness toward pH, sugar, adenosine triphosphate (ATP), hydrogen peroxide (H₂O₂), and temperature. Therefore, the novel nanocomposite hydrogel we demonstrated here exhibits great potential for biomedical applications such as tissue engineering and controlled drug delivery.

Biopolymer monolith for protein purification

Porous glycopolymers, "glycomonoliths", were prepared by radical polymerization based on polymerization-induced phase separation with an acrylamide derivative of α-mannose, acrylamide and cross-linker in order to investigate protein adsorption and separation. The porous structure was induced by a porogenic alcohol. The pore diameter and surface area were controlled by the type of alcohol. The protein adsorption was measured in both batch and continuous flow systems. The glycomonoliths showed specific interaction with the sugar recognition protein of concanavalin A, and non-specific interaction to other proteins was negligible. The amount of protein adsorption to the materials was determined by the sugar density and the composition of the glycomonoliths. Fundamental knowledge regarding the glycomonoliths for protein separation was obtained.

Tunable Hydrogen Release from Amine-Boranes via their Insertion into Functional Polystyrenes

Polystyrene-g-boramine random copolymers are dihydrogen reservoirs with tunable dehydrogenation temperatures, which can be adjusted by selecting the boramine content in the copolymers. They display a unique dihydrogen thermal release profile, which is a direct consequence of the insertion of the amine-boranes in a polymeric scaffold, and not from a direct modification of the electronics or sterics of the amine-borane function. Finally, the mixture of polystyrene-g-boramines with conventional NH₃ -BH₃ (borazane) allows for a direct access to organic/inorganic hybrid dihydrogen reservoirs with a maximal H₂ loading of 8 wt %. These exhibit a dehydrogenation temperature lower than that of either the borazane or the polystyrene-g-boramines taken separately.

Biologically Inspired and Chemically Derived Methods for Glucose-Responsive Insulin Therapy

The controlled delivery of therapeutics in a manner responsive to physiological indicators has promise in realizing new therapeutic approaches to combat disease. This approach is especially relevant in the context of diabetes. Natural fluctuations in blood glucose seen in the healthy state, complete with peaks and troughs, are poorly regulated as a result of detrimental production or ineffective signaling of the insulin hormone. While several manifestations of diabetes are treated with regularly administered exogenous insulin, the present standard of care results in suboptimal glycemic management that poorly recreates natural hormone control, leading to long-term instability and a significantly increased risk for secondary health complications. New synthetic technologies that make insulin available only when needed, and at the exact dose required, have been explored under the broad vision of realizing a "fully synthetic pancreas." Yet, many challenges remain to realizing a technology that is appropriately responsive, safe, and well integrated into a manageable routine. Herein, many of the approaches explored thus far to sense physiological blood glucose and elicit response through the release of therapeutic insulin are summarized. The approaches point to a new, autonomous approach to managing diabetes with biomimetic therapy.

Hydroxyl-Rich PGMA-Based Cationic Glycopolymers for Intracellular siRNA Delivery: Biocompatibility and Effect of Sugar Decoration Degree

The ErbB family of proteins, structurally related to the epidermal growth factor receptor (EGFR), is found to be overexpressed in many cancers such as gliomas, a lung and cervical carcinomas. Gene therapy allows to modify the expression of genes like ErbB and has been a promising strategy to target oncogenes and tumor suppressor genes. In the current work, novel hydroxyl-rich poly(glycidyl methacrylate) (PGMA)-based cationic glycopolymers were designed for intracellular small interfering RNA (siRNA) delivery to silence the EGFR gene. The cationic polymers with different sugar decoration degrees (0, 9, and 33%) were synthesized by ring-opening reaction of PGMA with ethanolamine and a lactobionic acid-derived aminosaccharide (Lac-NH₂). Specific EGFR knockdown of the protein tyrosine kinase ErbB-overexpressing HeLa cells was achieved using these hydroxyl-rich polycation/siRNA complexes. Higher sugar content improved the biocompatibility of the polymers, but it also seems to decrease the EGFR knockdown capability, which should mainly be related to the surface charge of polyplexes. An optimum balance was observed with PGEL-1 (9% sugar content) formulation, achieving ∼52% knockdown efficiency as well as high cell viability. Considering the specific recognition between galactose residues and asialoglycoprotein receptor in hepatocytes, our novel PGMA-based cationic glycopolymers exhibited promising future to serve as a safe and targeting gene delivery vector to hepatoma cell line like HepG2.

Programming Stimuli-Responsive Behavior into Biomaterials

Stimuli-responsive materials undergo triggered changes when presented with specific environmental cues. These dynamic systems can leverage biological signals found locally within the body as well as exogenous cues administered with spatiotemporal control, providing powerful opportunities in next-generation diagnostics and personalized medicine. Here, we review the synthetic and strategic advances used to impart diverse responsiveness to a wide variety of biomaterials. Categorizing systems on the basis of material type, number of inputs, and response mechanism, we examine past and ongoing efforts toward endowing biomaterials with customizable sensitivity. We draw an analogy to computer science, whereby a stimuli-responsive biomaterial transduces a set of inputs into a functional output as governed by a user-specified logical operator. We discuss Boolean and non-Boolean operations, as well as the various chemical and physical modes of signal transduction. Finally, we examine current limitations and promising directions in the ongoing development of programmable stimuli-responsive biomaterials.

Synthesis and Evaluation of Thermoresponsive Boron-Containing Poly(N-isopropylacrylamide) Diblock Copolymers for Self-Assembling Nanomicellar Boron Carriers

Development of new boron nanocarriers has been a crucial issue to be solved for advancing boron neutron capture therapy (BNCT) as an effective radiation treatment for cancers. The present study aimed to create a novel double-thermoresponsive boron-containing diblock copolymer based on poly(N-isopropylacrylamide) [poly(NIPAAm)], which exhibits two-step phase transitions (morphological transitions) at the temperature region below human body temperature. The boronated diblock copolymer considerably concentrates boron atoms into the water-dispersible (i.e., intravenous-administration possible) nanomicelles self-assembled by the first phase transition, and furthermore the properly controlled size and hydrophobicity of the second phase-transitioned nanoparticles are expected to make a significant contribution to the selective delivery and long-term retention of boron atoms into tumor tissues. Here we present the detailed synthesis of the strategic NIPAAm-based diblock copolymer with 3-acrylamidophenylboronic acid (PBA), i.e., poly(NIPAAm-block-NIPAAm-co-PBA), through a reversible addition-fragmentation chain transfer polymerization. Furthermore, the stepwise phase transition behavior of the obtained boronic-acid diblock copolymers was characterized in detail by temperature-variable ¹H and 11B-nuclear magnetic resonance spectroscopy. The phase-transition-induced molecular structural changes, including the structural compositions and sizes of nanomicelles and nanoparticles, are also discussed here.

Rational Design of Self-Healing Tough Hydrogels: A Mini Review

Hydrogels are three-dimensional cross-linked polymer networks which can absorb and retain large amount of water. As representative soft materials with tunable chemical, physical and biological properties, hydrogels with different functions have been developed and utilized in a broad range of applications, from tissue engineering to soft robotics. However, conventional hydrogels usually suffer from weak mechanical properties and they are easily deformed or damaged when they are subjected to mechanical forces. The accumulation of the damage may lead to the permanent structural change and the loss of the functional properties of the hydrogels. Therefore, it is important to develop mechanically robust hydrogels with autonomous self-healing property in order to extend their lifespan for various applications. In this mini review, we focus on the discussion about the appropriate molecular design of the hydrogel network for achieving self-healing and excellent mechanical properties, respectively as well as the corresponding self-healing and toughening mechanisms. We conclude with perspectives on the remaining challenges in the field as well as the recommendations for future development.

Adaptable Fast Relaxing Boronate-Based Hydrogels for Probing Cell-Matrix Interactions

Hydrogels with tunable viscoelasticity hold promise as materials that can recapitulate many dynamic mechanical properties found in native tissues. Here, covalent adaptable boronate bonds are exploited to prepare hydrogels that exhibit fast relaxation, with relaxation time constants on the order of seconds or less, but are stable for long-term cell culture and are cytocompatible for 3D cell encapsulation. Using human mesenchymal stem cells (hMSC) as a model, the fast relaxation matrix mechanics are found to promote cell-matrix interactions, leading to spreading and an increase in nuclear volume, and induce yes-associated protein/PDZ binding domain nuclear localization at longer times. All of these effects are exclusively based on the hMSCs' ability to physically remodel their surrounding microenvironment. Given the increasingly recognized importance of viscoelasticity in controlling cell function and fate, it is expected that the synthetic strategies and material platform presented should provide a useful system to study mechanotransduction on and within viscoelastic environments and explore many questions related to matrix biology.

Bioinspired Self-Healing Hydrogel Based on Benzoxaborole-Catechol Dynamic Covalent Chemistry for 3D Cell Encapsulation

Boronic ester, one typical example of dynamic covalent bonds, has presented great potential to prepare self-healing hydrogels. However, most of currently reported hydrogels based on boronic esters are formed at pH > 8, which impeded their further use in physiological conditions. In this study, we designed two kinds of zwitterionic copolymers with benzoxaborole and catechol pendant groups, respectively. Owing to the lower pK_a value of benzoxaborole (7.2), gelation can happen easily at pH 7.4 PBS after mixing these two copolymers due to efficient formation of benzoxaborole-catechol complexations. The resulting hydrogels exhibited excellent self-healing property as well as dual pH/sugar responsiveness due to the dynamic nature of boronic ester. Moreover, benefiting from the cell membrane bioinspired 2-methacryloyloxyethyl phosphorylcholine (MPC)-based polymeric matrix, the hydrogel was further investigated for 3D cell encapsulation. The combination of biocompatible zwitterionic polymers with dynamic benzoxaborole-catechol complexation makes the hydrogels a promising platform for diverse potential bioapplications like drug delivery and tissue engineering.

Fabrication of Polymer-Protein Hybrids

Rapid developments in organic chemistry and polymer chemistry promote the synthesis of polymer-protein hybrids with different structures and biofunctionalities. In this feature article, recent progress achieved in the synthesis of polymer-protein conjugates, protein-nanoparticle core-shell structures, and polymer-protein nanogels/hydrogels is briefly reviewed. The polymer-protein conjugates can be synthesized by the "grafting-to" or the "grafting-from" approach. In this article, different coupling reactions and polymerization methods used in the synthesis of bioconjugates are reviewed. Protein molecules can be immobilized on the surfaces of nanoparticles by covalent or noncovalent linkages. The specific interactions and chemical reactions employed in the synthesis of core-shell structures are discussed. Finally, a general introduction to the synthesis of environmentally responsive polymer-protein nanogels/hydrogels by chemical cross-linking reactions or molecular recognition is provided.

Synthesis of hydrogel-bearing phenylboronic acid moieties and their applications in glucose sensing and insulin delivery

In past few years, phenylboronic acids (PBAs) have attracted researcher's attention due to their unique responsiveness towards diol-containing molecules such as glucose.

Interactions of Glycopolymers with Assemblies of Peptide Amphiphiles via Dynamic Covalent Bonding

In this work, peptide amphiphile (PA) with benzoboroxole (BOB) group at the hydrophilic end was prepared and assembled into fibers (PAA) with BOB group on the fiber surface. Then glycopolymer with mannopyranoside as pendent group interacted with the PAA via dynamic covalent bond between sugar and BOB. By combining the results from 2D ¹H NMR spectroscopy, the exact binding mode of mannopyranoside pendent group and BOB, i.e., mannopyranoside participated by its diol on 2,3-position instead of that on 4,6-position, which was clearly observed on the fiber surface. The success in determining this binding mode in macroscopic material was due to the high density of BOB on PAA and the multivalent effect between the multiple BOB moieties on fiber surface and repeating mannopyranoside groups of the glycopolymer.

Effective and Specific Gene Silencing of Epidermal Growth Factor Receptors Mediated by Conjugated Oxaborole and Galactose-Based Polymers

Oxaborole-based polymers are stimuli-responsive materials that can reversibly interact with diols at pH values higher than their pK_a. The strong binding of the oxaborole with cis-hydroxyl groups allow rapid cross-linking of the polymer chains. In this study, we exploited this phenomenon to develop a novel delivery system for the complexation, protection, and delivery of epidermal growth factor receptors (EGFR) siRNA (small interfering RNA). Galactose and oxaborole polymers were first synthesized by the reversible addition-fragmentation chain transfer (RAFT) process, and they were found to show a robust interaction with each other via the oxaborole-diol effect, which allowed the formation of stable polyplexes with siRNA. Although complexes were successfully formed between the neutral galactose and oxaborole-based polymers, these complexes were insufficient in the protection of the siRNA. Therefore, cationic glycopolymers and oxaborole polymers were investigated showing superior complexation with siRNA and exhibiting effective gene silencing in HeLa (cervical) cancer cells, while showing low toxicity. Gene silencing of up to 60% was achieved with these new complexes in the presence and absence of serum. The excellent stability of the complexes under physiological conditions and the observed low cytotoxicity 48 h post-transfection demonstrated the high potential of this new system for gene silencing therapy application in clinics.

Rapid and Highly Sensitive Detection of Dopamine Using Conjugated Oxaborole-Based Polymer and Glycopolymer Systems

A conjugated polymer interface consisting of an oxaborole containing polymer and a glycopolymer was used for achieving very high selectivity in dopamine (DA) detection. The optimum binding affinity between the polymers promotes the selectivity to DA through a displacement mechanism while remaining unaffected by other structurally related analogs and saccharide derivatives. Real-time detection of DA with very high selectivity and sensitivity has been demonstrated by immobilizing the polymer conjugates on surface plasmon resonance (SPR) and microcantilever (MCL) sensor platforms. Using the conjugated polymer sensing layer, the SPR biosensor was capable of detecting DA in the concentration range of 1 × 10^-9 to 1 × 10^-4 mol L^-1, whereas the MCL sensor showed a limit of detection (LOD) of 5 × 10^-11 mol L^-1. We find that the sensing mechanism is based on DA-induced reversible swelling of the conjugated polymer layer and this allows regeneration and reuse of the sensor multiple times. Also, we conclude that SPR is a suitable sensor platform for DA in-line detection at clinical level considering the detection time and stability, whereas MCL can achieve a much lower LOD.

Organocatalytic, enantioselective synthesis of benzoxaboroles via Wittig/oxa-Michael reaction Cascade of α-formyl boronic acids

An unprecedented enantioselective synthesis of 3-substituted benzoxaboroles has been developed. An in situ generated ortho-boronic acid containing chalcone provides the chiral benzoxaboroles via an asymmetric oxa-Michael addition of hydroxyl group attached to the boronic acid triggered by the cinchona alkaloid based chiral amino-squaramide catalysts. In general, good yields with good to excellent enantioselectivities (up to 99%) were obtained. The resulting benzoxaboroles were converted to the corresponding chiral β-hydroxy ketones without affecting the enantioselectivity.

Borinic Acid Polymer: Simplified Synthesis and Enzymatic Biofuel Cell Application

A simplified one-pot and less harmful method has been introduced for the synthesis of borinic acid monomer. The corresponding borinic acid polymer (PBA) has been prepared by reversible addition-fragmentation chain transfer polymerization. Property investigations confirm the characteristics of PBA as a new type of "smart material" in the field of thermo-responsive polymer. The potential application of PBA in the field of enzymatic biofuel cell has been illustrated with a wide open circuit potential of 0.92 V.