A nucleobase-inspired super adhesive hydrogel with desirable mechanical, tough and fatigue resistant properties based on cytosine and ε-caprolactone

Hydrogen-bonded cytosine-endowed supramolecular polymeric nanogels: Highly efficient cancer cell targeting and enhanced therapeutic efficacy

We demonstrate that cytosine moieties within physically cross-linked supramolecular polymers not only manipulate drug delivery and release, but also confer specific targeting of cancer cells to effectively enhance the safety and efficacy of chemotherapy-and thus hold significant potential as a new perspective for development of drug delivery systems. Herein, we successfully developed physically cross-linked supramolecular polymers (PECH-PEG-Cy) comprised of hydrogen-bonding cytosine pendant groups, hydrophilic poly(ethylene glycol) side chains, and a hydrophobic poly(epichlorohydrin) main chain. The polymers spontaneously self-assemble into a reversibly hydrogen-bonded network structure induced by cytosine and directly form spherical nanogels in aqueous solution. Nanogels with a high hydrogen-bond network density (i.e., a higher content of cytosine moieties) exhibit outstanding long-term structural stability in cell culture substrates containing serum, whereas nanogels with a relatively low hydrogen-bond network density cannot preserve their structural integrity. The nanogels also exhibit numerous unique physicochemical characteristics in aqueous solution, such as a desirable spherical size, high biocompatibility with normal and cancer cells, excellent drug encapsulation capacity, and controlled pH-responsive drug release properties. More importantly, in vitro experiments conclusively indicate the drug-loaded PECH-PEG-Cy nanogels can selectively induce cancer cell-specific apoptosis and cell death via cytosine receptor-mediated endocytosis, without significantly harming normal cells. In contrast, control drug-loaded PECH-PEG nanogels, which lack cytosine moieties in their structure, can only induce cell death in cancer cells through non-specific pathways, which significantly inhibits the induction of apoptosis. This work clearly demonstrates that the cytosine moieties in PECH-PEG-Cy nanogels confer selective affinity for the surface of cancer cells, which enhances their targeted cellular uptake, cytotoxicity, and subsequent induction of programmed cell death in cancer cells.

Natural polymer-based bioadhesives as hemostatic platforms for wound healing

Medical adhesives are advanced but challenging alternatives to wound closure and repair, especially in mitigating uncontrolled hemorrhage. Ideal hemostatic adhesives need to meet good biocompatibility and biodegradability, adequate mechanical strength, and strong tissue adhesion functionality under wet and dynamic conditions. Considering these requirements, natural polymers such as polysaccharide, protein and DNA, attract great attention as candidates for making bioadhesives because of their distinctive physicochemical performances and biological properties. This review systematically summarizes the advances of bioadhesives based on natural polysaccharide, protein and DNA. Various physical and chemical cross-linking strategies have been introduced for adhesive synthesis and their hemostatic applications are introduced from the aspect of versatility. Furthermore, the possible challenges and future opportunities of bioadhesives are discussed, providing insights into the development of high-performance hemostatic materials.

Reactive oxygen species-responsive thymine-conjugated chitosan: Synthesis and evaluation as cryogel

Chitosan (CS) is a biodegradable, biocompatible cationic polysaccharide based natural polymer with antibacterial and anti-inflammatory properties. Hydrogels made from CS have been found their applications in wound healing, tissue regeneration and drug delivery. Although, mucoadhesive properties resulted from the polycationic nature of CS, in hydrogel form amines are engaged in interactions with water leading to decrease in mucoadhesive properties. In case of injury, presence of elevated level of reactive oxygen species (ROS) has inspired many drug delivery platform to conjugate ROS responsive linkers for on demand drug delivery. In this report we have conjugated a reactive oxygen species (ROS) responsive thioketal (TK) linker and nucleobase thymine (Thy) with CS. Cryogel from this doubly functionalized polymer CS-Thy-TK was prepared through crosslinking with sodium alginate. Inosine was loaded on the scaffold and studied for its release under oxidative condition. We anticipated that the presence of thymine shall retain the mucoadhesive nature of the CS-Thy-TK polymer in hydrogel form and when placed at the site of injury, due to the presence of excessive ROS at inflammatory condition, loaded drug shall release due to degradation of the linker. Porous cryogel scaffold was prepared via chemical crosslinking of amine functional group of chitosan with carboxylic acid containing polysaccharide sodium alginate. The cryogel was evaluated for porosity (FE-SEM), rheology, swelling, degradation, mucoadhesive properties and biocompatibility. Resulted scaffold was found to be porous with average pore size of 107 ± 23 μm, biocompatible, hemocompatible and possesses improved mucoadhesive property (mucin binding efficiency of 19.54 %) which was found to be 4 times better as compared to chitosan (4.53 %). The cumulative drug release found to be better in the presence of H₂O₂ (~90 %) when compared to that of PBS alone (~60-70 %)_. Therefore, the modified CS-Thy-TK polymer may hold potential as interesting scaffold in case of conditions associated with elevated ROS level such as injury and tumor.

Bioinspired gelatin based sticky hydrogel for diverse surfaces in burn wound care

Proper burn wound management considers patient’s compliance and provides an environment to accelerate wound closure. Sticky hydrogels are conducive to wound management. They can act as a preventive infection patch with controlled drug delivery and diverse surface adherence. A hypothesis-driven investigation explores a bioinspired polydopamine property in a gelatin-based hydrogel (GbH) where polyvinyl alcohol and starch function as hydrogel backbone. The GbH displayed promising physical properties with O–H group rich surface. The GbH was sticky onto dry surfaces (glass, plastic and aluminium) and wet surfaces (pork and chicken). The GbH demonstrated mathematical kinetics for a transdermal formulation, and the in vitro and in vivo toxicity of the GbH on test models confirmed the models’ healthy growth and biocompatibility. The quercetin-loaded GbH showed 45–50% wound contraction on day 4 for second-degree burn wounds in rat models that were equivalent to the silver sulfadiazine treatment group. The estimates for tensile strength, biochemicals, connective tissue markers and NF-κB were restored on day 21 in the GbH treated healed wounds to imitate the normal level of the skin. The bioinspired GbH promotes efficient wound healing of second-degree burn wounds in rat models, indicating its pre-clinical applicability.

Antifreezing and Nondrying Sensors of Ionic Hydrogels with a Double-Layer Structure for Highly Sensitive Motion Monitoring

Freezing and dehydration together with interfacial failure are capable of causing the functional reduction of hydrogels for sensing applications. Herein, we develop a multifunctional bilayer that consists of a mussel-inspired adhesive layer and a functionally ionic layer that is composed of sodium p-styrene sulfonate (SSS) and an ionic liquid of [BMIM]Cl. The adhesive layer enables the strong adhesion of the bilayer to the surface of the skin. The introduction of ionic elements of SSS-[BMIM]Cl not only provides the bilayer with sensing adaptability in a wide temperature range of -25 to 75 °C, but also endows it with elastic, stretchable, self-healing, and conductive features. These mechanical properties are utilized to assemble a wearable sensor that has unprecedented sensitivity and reusability in monitoring human motions, including stretching, pulsing, frowning, and speaking. It is thus expected that the concept in this work would provide a promising route to design soft sensing devices that can work in a wide temperature range.

Quadruple Hydrogen Bond-Containing A-AB-A Triblock Copolymers: Probing the Influence of Hydrogen Bonding in the Central Block

This work reveals the influence of pendant hydrogen bonding strength and distribution on self-assembly and the resulting thermomechanical properties of A-AB-A triblock copolymers. Reversible addition-fragmentation chain transfer polymerization afforded a library of A-AB-A acrylic triblock copolymers, wherein the A unit contained cytosine acrylate (CyA) or post-functionalized ureido cytosine acrylate (UCyA) and the B unit consisted of n-butyl acrylate (nBA). Differential scanning calorimetry revealed two glass transition temperatures, suggesting microphase-separation in the A-AB-A triblock copolymers. Thermomechanical and morphological analysis revealed the effects of hydrogen bonding distribution and strength on the self-assembly and microphase-separated morphology. Dynamic mechanical analysis showed multiple tan delta (δ) transitions that correlated to chain relaxation and hydrogen bonding dissociation, further confirming the microphase-separated structure. In addition, UCyA triblock copolymers possessed an extended modulus plateau versus temperature compared to the CyA analogs due to the stronger association of quadruple hydrogen bonding. CyA triblock copolymers exhibited a cylindrical microphase-separated morphology according to small-angle X-ray scattering. In contrast, UCyA triblock copolymers lacked long-range ordering due to hydrogen bonding induced phase mixing. The incorporation of UCyA into the soft central block resulted in improved tensile strength, extensibility, and toughness compared to the AB random copolymer and A-B-A triblock copolymer comparisons. This study provides insight into the structure-property relationships of A-AB-A supramolecular triblock copolymers that result from tunable association strengths.

Tissue adhesive hydrogel bioelectronics

Flexible bioelectronics have promising applications in electronic skin, wearable devices, biomedical electronics, etc. Hydrogels have unique advantages for bioelectronics due to their tissue-like mechanical properties and excellent biocompatibility. Particularly, conductive and tissue adhesive hydrogels can self-adhere to bio-tissues and have great potential in implantable wearable bioelectronics. This review focuses on the recent progress in tissue adhesive hydrogel bioelectronics, including the mechanism and preparation of tissue adhesive hydrogels, the fabrication strategies of conductive hydrogels, and tissue adhesive hydrogel bioelectronics and applications. Some perspectives on tissue adhesive hydrogel bioelectronics are provided at the end of the review.