Advances in adhesive hydrogels for tissue engineering

Regulating natural galactomannan into composite hydrogels for improved adhesion, anti-swelling capability and efficient dye pollution removal

Constructing bio-based composite hydrogel materials are receiving much interest, while regulating the interactions of the hydrogel components and integrating functions for multi-application meet various challenges. Herein, composite hydrogels were prepared by cross-linking of poly-acrylamide (PAM) and poly-N-[3-(Dimethylamino) propyl] acrylamide (PDMAPAA), assisted by natural galactomannan (GM) regulation. Even distribution and compatibility of GM in the three-dimensional materials were proved by a series of chemical and morphological characterizations, which favored the improvement of mechanical properties (~80 kPa) and flexibility. Besides, the hydrogels were well-connected with double networks of noncovalent intermolecular hydrogen bonding interactions and hydrophobic interactions, in addition to covalent-linked polymers. Due to great amount of inner hydrogen bond linkages, the hydrogels present satisfying anti-swelling capabilities (<15 %), exhibiting high potential for application in water treatment. Meanwhile, abundant surface functional groups provided possibilities to form interactive layer with the various substrates surface, exhibiting highly adhesive properties. Significant dyes adsorption capabilities were revealed on the hydrogels according to the electrostatic attraction with Congo red and hydrogen bond interactions with Brilliant green respectively. Thus, the proposed composite hydrogels integrated multi-functions due to the tuning the surface groups and cross-linking interactions, which provided deeper understanding on bio-based materials on fields of water treatment and environmental protection.

Bioinspired Asymmetric-Adhesion Janus Hydrogel Patch Regulating by Zwitterionic Polymers for Wet Tissues Adhesion and Postoperative Adhesion Prevention

Asymmetrically adhesive hydrogel patch with robust wet tissue adhesion simultaneously anti-postoperative adhesion is essential for clinical applications in internal soft-tissue repair and postoperative anti-adhesion. Herein, inspired by the lubricative role of serosa and the underwater adhesion mechanism of mussels, an asymmetrically adhesive hydrogel Janus patch is developed with adhesion layer (AL) and anti-adhesion layer (anti-AL) through an in situ step-by-step polymerization process in the mold. The AL exhibits excellent adhesion to internal soft-tissues. In contrast, the anti-AL demonstrated ultralow fouling property against protein and fibroblasts, which hinders the early and advanced stages of development of the adhesion. Moreover, the Janus patch simultaneously promotes tissue regeneration via ROS clearance capability of catechol moieties in the AL. Results from in vivo experiments with rabbits and rats demonstrate that the AL strongly adheres to traumatized tissue, while the anti-AL surface demonstrate efficacy in preventing of post-abdominal surgery adhesions in contrast to clinical patches. Considering the advantages in terms of therapeutic efficacy and off the shelf, the Janus patch developed in this work presents a promise for preventing postoperative adhesions and promoting regeneration of internal tissue defects.

Biodegradable Natural Hydrogels for Tissue Engineering, Controlled Release, and Soil Remediation

This article provides insights into hydrogels of the most promising biodegradable natural polymers and their mechanisms of degradation, highlighting the different possibilities of controlling hydrogel degradation rates. Since biodegradable hydrogels can be designed as scaffolding materials to mimic the physical and biochemical properties of natural tissues, these hydrogels have found widespread application in the field of tissue engineering and controlled release. In the same manner, their potential as water reservoirs, macro- and microelement carriers, or matrixes for the selective adsorption of pollutants make them excellent candidates for sustainable soil amendment solutions. Accordingly, this article summarizes the recent advances in natural biodegradable hydrogels in the fields of tissue engineering, controlled release, and soil remediation, emphasizing the new opportunities that degradability and its tunability offer for the design and applicability of hydrogels.

One Stone Three Birds: Silver Sulfadiazine Modulates the Stability and Dynamics of Hydrogels for Infected Wound Healing

Dynamic covalent bond hydrogels have demonstrated significant application potential in biomedical fields for their dynamic reversibility. However, the contradiction between the stability and dynamics of the hydrogel restricts its application. Here, utilizing silver sulfadiazine (AgSD) as a catalyst, hyaluronic acid-based hydrogels are constructed through imine bond crosslinking and incorporated disulfide bonds within the same crosslinking chain. It is found that AgSD can accelerate the formation of imine crosslinking bonds to improve the stability of hydrogels, thereby shortening the gelation time by ≈36.9 times, enhancing compression strength and adhesion strength by ≈2.4 times and 1.7 times, respectively, while inhibiting swelling and degradation rates to ≈2.1 times and 3.7 times. Besides, AgSD can coordinate with disulfide bonds to enhance the dynamics of hydrogel, enhancing the hydrogel self-healing efficiency by ≈2.3 times while reducing the relaxation time by ≈25.1 times. Significantly, AgSD imparts remarkable antibacterial properties to the hydrogel, thereby effectively facilitating the healing of bacterial infected wounds. Consequently, introducing AgSD enables hydrogels to possess concurrent stability, dynamics, and antibacterial properties. This strategy of regulating hydrogels by introducing AgSD provides a valuable reference for the application of dynamic covalent bonds.

Recent Advances in the Degradability and Applications of Tissue Adhesives Based on Biodegradable Polymers

In clinical practice, tissue adhesives have emerged as an alternative tool for wound treatments due to their advantages in ease of use, rapid application, less pain, and minimal tissue damage. Since most tissue adhesives are designed for internal use or wound treatments, the biodegradation of adhesives is important. To endow tissue adhesives with biodegradability, in the past few decades, various biodegradable polymers, either natural polymers (such as chitosan, hyaluronic acid, gelatin, chondroitin sulfate, starch, sodium alginate, glucans, pectin, functional proteins, and peptides) or synthetic polymers (such as poly(lactic acid), polyurethanes, polycaprolactone, and poly(lactic-co-glycolic acid)), have been utilized to develop novel biodegradable tissue adhesives. Incorporated biodegradable polymers are degraded in vivo with time under specific conditions, leading to the destruction of the structure and the further degradation of tissue adhesives. In this review, we first summarize the strategies of utilizing biodegradable polymers to develop tissue adhesives. Furthermore, we provide a symmetric overview of the biodegradable polymers used for tissue adhesives, with a specific focus on the degradability and applications of these tissue adhesives. Additionally, the challenges and perspectives of biodegradable polymer-based tissue adhesives are discussed. We expect that this review can provide new inspirations for the design of novel biodegradable tissue adhesives for biomedical applications.

A review of cellulose-based catechol-containing functional materials for advanced applications

With the increment in global energy consumption and severe environmental pollution, it is urgently needed to explore green and sustainable materials. Inspired by nature, catechol groups in mussel adhesion proteins have been successively understood and utilized as novel biomimetic materials. In parallel, cellulose presents a wide class of functional materials rating from macro-scale to nano-scale components. The cross-over among both research fields alters the introduction of impressive materials with potential engineering properties, where catechol-containing materials supply a general stage for the functionalization of cellulose or cellulose derivatives. In this review, the role of catechol groups in the modification of cellulose and cellulose derivatives is discussed. A broad variety of advanced applications of cellulose-based catechol-containing materials, including adhesives, hydrogels, aerogels, membranes, textiles, pulp and papermaking, composites, are presented. Furthermore, some critical remaining challenges and opportunities are studied to mount the way toward the rational purpose and applications of cellulose-based catechol-containing materials.

Keratin Formed Bioadhesive Ophthalmic Gel for the Bacterial Conjunctivitis Treatment

Keratin has the potential to function as the gel matrix in an ophthalmic formulation for the encapsulation of the macrolide antibiotic azithromycin. The quality of this formulation was thoroughly evaluated through various analyses, such as in vitro release assessment, rheological examination, intraocular retention studies in rabbits, assessment of bacteriostatic efficacy, and safety evaluations. It is worth mentioning that the gel demonstrated shear thinning properties and exhibited characteristics of an elastic solid, thereby confirming its structural stability. The gel demonstrated a notable affinity for mucosal surfaces in comparison to traditional azithromycin aqueous solutions. In vitro release testing revealed that drug release transpired via diffusion mechanisms, following a first-order kinetic release pattern. Additionally, the formulated gel exhibited remarkable antibacterial efficacy against Staphylococcus aureus and Pseudomonas aeruginosa in bacteriostatic evaluations. Lastly, safety assessments confirmed that the gel eye drops induced minimal irritation and displayed no apparent cytotoxicity, indicating their good safety and biocompatibility for ocular application. Thus, these findings indicated that the prepared azithromycin gel eye drops complied with the requisite standards for ophthalmic preparations.

Multifunctional chitosan-based lanthanide luminescent hydrogel with stretchability, adhesion, self-healing, color tunability and antibacterial ability

Lanthanide luminescent hydrogels have broad application prospects in various fields. However, most of lanthanide hydrogels possess relatively simple functions, which is not conducive to practical applications. Therefore, it is becoming increasingly urgent to develop multifunctional hydrogels. Herein, a multifunctional chitosan-based lanthanide luminescent hydrogel with ultra-stretchability, multi-adhesion, excellent self-healing, emission color tunability, and good antibacterial ability was prepared by a simple one-step free radical polymerization. In this work, our designed lanthanide complexes [Ln(4-VDPA)3] contain three reaction sites, which can be copolymerized with N-[tris(hydroxymethyl) methyl] acrylamide (THMA), acrylamide (AM), and diacryloyl poly(ethylene glycol) (DPEG) to form the first chemical crosslinking network, while hydroxypropyltrimethyl ammonium chloride chitosan (HACC) interacts with the hydroxyl and amino groups derived from the chemical crosslinking network through hydrogen bonds to form the second physical crosslinking network. The structure of the double network as well as the dynamic hydrogen bond and lanthanide coordination endow the hydrogel with excellent stretchability, adhesion and self-healing properties. Moreover, the introduction of lanthanide complexes and chitosan makes the hydrogel exhibit outstanding luminescence and antibacterial performances. This research not only realizes the simple synthesis of multifunctional luminescent hydrogels, but also provides a new idea for the fabrication of biomass-based hydrogels as intelligent and sustainable materials.

Facile Bond Exchanging Strategy for Engineering Wet Adhesion and Antioxidant/Antibacterial Thin Layer over a Dynamic Hydrogel via the Carbon Dots Derived from Tannic Acid/ε-Polylysine

Adhesive hydrogels, playing an essential role in stretchable electronics, soft robotics, tissue engineering, and so forth, upon functioning often need to adhere to various substrates in wet conditions and simultaneously exhibit antibacterial/antioxidant properties while possessing the intrinsic stretchability and elasticity of the hydrogel network intact. Therefore, simple approaches to conveniently access adhesive hydrogels with multifunctional surfaces are being pursued. Herein, a facile strategy has been proposed to construct multifunctional adhesive hydrogels via surface engineering of a multifunctional carbon dot (CD)-decorated polymeric thin layer by dynamic bond exchange. By this strategy, a double cross-linked network hydrogel of polyacrylamide (PAM) and oxidized dextran (ODA) was engineered with a unique dense layer over the Schiff base hydrogel matrix by aqueous solution immersion of PA-120, versatile CDs derived from tannic acid (TA) and ε-polylysine (PL). Without any additional agents, the PA-120 CDs with residual polyphenolic/catechol and amine moieties were incorporated into the surface structure of the hydrogel network by the combined action of the Schiff base and hydrogen bonds to form a dense surface layer that can exhibit high wet adhesive performance via the amine-polyphenol/catechol pair. The armor-like dense architecture also endowed hydrogels with considerably enhanced tensile/compression properties and excellent antioxidant/antibacterial abilities. Besides, the single-sided modified Janus hydrogel and completely surface-modified hydrogel can be flexibly developed through this approach. This strategy will provide new insights into the preparation and application of surface-modified hydrogels featuring multiple functions and tunable interfacial properties.

Innovations in hydrogel-based manufacturing: A comprehensive review of direct ink writing technique for biomedical applications

Direct ink writing (DIW) stands as a pioneering additive manufacturing technique that holds transformative potential in the field of hydrogel fabrication. This innovative approach allows for the precise deposition of hydrogel inks layer by layer, creating complex three-dimensional structures with tailored shapes, sizes, and functionalities. By harnessing the versatility of hydrogels, DIW opens up possibilities for applications spanning from tissue engineering to soft robotics and wearable devices. This comprehensive review investigates DIW as applied to hydrogels and its multifaceted applications. The paper introduces a diverse range of printing techniques while providing a thorough exploration of DIW for hydrogel-based printing. The investigation aims to explain the progress made, challenges faced, and potential trajectories that lie ahead for DIW in hydrogel-based manufacturing. The fundamental principles underlying DIW are carefully examined, specifically focusing on rheological attributes and printing parameters, prompting a comprehensive survey of the wide variety of hydrogel materials. These encompass both natural and synthetic variations, all of which can be effectively harnessed for this purpose. Furthermore, the review explores the latest applications of DIW for hydrogels in biomedical areas, with a primary focus on tissue engineering, wound dressing, and drug delivery systems. The document not only consolidates the existing state of DIW within the context of hydrogel-based manufacturing but also charts potential avenues for further research and innovative breakthroughs.

Body temperature-induced adhesive hyaluronate/gelatin-based hybrid hydrogel dressing for promoting skin regeneration

Skin wound management faces significant clinical challenges, including continuous bacterial infection and inflammation. Therefore, developing removable hydrogel dressings with intrinsic multifunctional properties is highly desirable. In this study, a body temperature-induced adhesive and removable hydrogel was designed to treat skin defect wounds. The HA/Gel-R-Ag hybrid gel was prepared by incorporating a silver ion-crosslinked sulfhydryl hyaluronate/gelatin-based polymeric gel network into a supramolecular rhein gel network, thereby significantly enhancing its mechanical properties. Temperature-responsive gelatin chains give the hybrid gel reversible tissue adhesiveness and detachment, thus avoiding secondary injury to wounds when changing the hydrogels. The hybrid gel exhibited excellent bactericidal ability owing to the antibacterial capacity of the silver ions and rhein. Moreover, both HA and rhein endowed the hybrid gel with immunoregulatory effects by promoting macrophage polarization from pro-inflammatory M1 phenotype to anti-inflammatory M2 phenotype. In a full-thickness skin defect mouse mode, this porous, degradable, and biocompatible HA/Gel-R-Ag hybrid gel boosted skin regeneration by inhibiting inflammation and promoting collagen deposition and angiogenesis. It is thus a simple method for widening the application range of mechanically weak rhein gels and providing a promising wound dressing material with multiple intrinsic functions for treating skin wounds.

Poly (ε-caprolactone)-Based Scaffolds with Multizonal Architecture: Synthesis, Characterization, and In Vitro Tests

Tissue engineering is vital in treating injuries and restoring damaged tissues, aiming to accelerate regeneration and optimize the complex healing process. In this study, multizonal scaffolds, designed to mimic tissues with bilayer architecture, were prepared using the rotary jet spinning technique (RJS scaffolds). Polycaprolactone and different concentrations of alginate hydrogel (2, 4, and 6% m/v) were used. The materials were swollen in pracaxi vegetable oil (PO) (Pentaclethra macroloba) and evaluated in terms of surface morphology, wettability, functional groups, thermal behavior, crystallinity, and cytotoxicity. X-ray diffraction (XRD) showed the disappearance of the diffraction peak 2θ = 31.5° for samples from the polycaprolactone/pracaxi/alginate (PCLOA) group, suggesting a reduction of crystallinity according to the presence of PO and semi-crystalline structure. Wettability gradients (0 to 80.91°) were observed according to the deposition layer and hydrogel content. Pore diameters varied between 9.27 μm and 37.57 μm. Molecular interactions with the constituents of the formulation were observed via infrared spectra with Fourier transform (FTIR), and their influence was detected in the reduction of the maximum degradation temperature within the groups of scaffolds (polycaprolactone/alginate (PCLA) and PCLOA) about the control. In vitro tests indicated reduced cell viability in the presence of alginate hydrogel and PO, respectively.

Facile Synthesis of Highly Stretchable, Tough, and Photodegradable Hydrogels

Recently, highly stretchable and tough hydrogels that are photodegradable on-demand have been reported. Unfortunately, the preparation procedure is complex due to the hydrophobic nature of the photocrosslinkers. Herein, a simple method is reported to prepare photodegradable double-network (DN) hydrogels that exhibit high stretchability, toughness, and biocompatibility. Hydrophilic ortho-nitrobenzyl (ONB) crosslinkers incorporating different poly(ethylene glycol) (PEG) backbones (600, 1000, and 2000 g mol-1 ) are synthesized. These photodegradable DN hydrogels are prepared by the irreversible crosslinking of chains by using such ONB crosslinkers, and the reversible ionic crosslinking between sodium alginate and divalent cations (Ca2+ ). Remarkable mechanical properties are obtained by combining ionic and covalent crosslinking and their synergistic effect, and by reducing the length of the PEG backbone. The rapid on-demand degradation of these hydrogels is also demonstrated by using cytocompatible light wavelength (λ = 365 nm) that degrades the photosensitive ONB units. The authors have successfully used these hydrogels as skin-worn sensors for monitoring human respiration and physical activities. A combination of excellent mechanical properties, facile fabrication, and on-demand degradation holds promise for their application as the next generation of substrates or active sensors eco-friendly for bioelectronics, biosensors, wearable computing, and stretchable electronics.

Additive manufacturing of sustainable biomaterials for biomedical applications

Biopolymers are promising environmentally benign materials applicable in multifarious applications. They are especially favorable in implantable biomedical devices thanks to their excellent unique properties, including bioactivity, renewability, bioresorbability, biocompatibility, biodegradability and hydrophilicity. Additive manufacturing (AM) is a flexible and intricate manufacturing technology, which is widely used to fabricate biopolymer-based customized products and structures for advanced healthcare systems. Three-dimensional (3D) printing of these sustainable materials is applied in functional clinical settings including wound dressing, drug delivery systems, medical implants and tissue engineering. The present review highlights recent advancements in different types of biopolymers, such as proteins and polysaccharides, which are employed to develop different biomedical products by using extrusion, vat polymerization, laser and inkjet 3D printing techniques in addition to normal bioprinting and four-dimensional (4D) bioprinting techniques. This review also incorporates the influence of nanoparticles on the biological and mechanical performances of 3D-printed tissue scaffolds. This work also addresses current challenges as well as future developments of environmentally friendly polymeric materials manufactured through the AM techniques. Ideally, there is a need for more focused research on the adequate blending of these biodegradable biopolymers for achieving useful results in targeted biomedical areas. We envision that biopolymer-based 3D-printed composites have the potential to revolutionize the biomedical sector in the near future.

Porcupine-inspired microneedles coupled with an adhesive back patching as dressing for accelerating diabetic wound healing

Diabetes chronic wound is a severe and frequently occurring medical issue in patients with diabetes that often leads to more serious complications. Microneedles (MNs) can be used for wound healing as they can effectively pierce the epidermis and inject drugs into the wound tissue. However, common MN patches cannot provide sufficient skin adhesion to prevent detachment from the wound area. Inspired by the barb hangnail microstructure of porcupine quills, a porcupine quill-like multilayer MN patch with an adhesive back patching for tissue adhesion and diabetic wound healing was designed. Sodium hyaluronate-modified CaO2 nanoparticles and metformin (hypoglycemic agent) were loaded into the polycaprolactone tips of MNs, endowing them with exceptional antibacterial ability and hypoglycemic effect. A flexible and adhesive back patching was formed by polyacrylamide-polydopamine/Cu2+ composite hydrogel, which ensures that the MN patches do not peel off from the application sites and reduce bacterial infection. The bioinspired multilayer structure of MN patches exhibits satisfactory mechanical and antibacterial properties, which is a potential multifunctional dressing platform for promoting wound healing. STATEMENT OF SIGNIFICANCE: The porcupine quill-like microneedles (MNs) with PAM-PDA/Cu2+ (PPC) composite hydrogel back patching have been fabricated, which can enhance the adhesion property of MNs to the skin through a physical interlock of multilayer MNs and chemical bonding of hydrogel patching. CaO2-HA NPs and metformin were loaded into the polycaprolactone tips of MNs, endowing them with the exceptional antibacterial ability and hypoglycemic effect, which could accelerate diabetic wound healing. As a safe and effective strategy in transdermal delivery of drugs, the as-fabricated flexible multilayer MN patch with good antibacterial, hypoglycemic, and biocompatibility has been used to promote the healing of diabetic wound by releasing oxygen and inhibiting inflammation at the wound site.

Self-adhesive, ionic-conductive, mechanically robust cellulose-based organogels with anti-freezing and rapid recovery properties for flexible sensors

Cellulose-based functional gels have received considerable attention because of their good mechanical properties, biocompatibility, and low cost. However, the preparation of cellulose gels with self-adhesion, mechanical robustness, ionic conductivity, anti-freezing ability, and environmental stability remains a challenge. Here, gallic acid esterified microcrystalline cellulose (MCC-GA) was obtained by grafting gallic acid (GA) onto the macromolecular chains of microcrystalline cellulose (MCC) through a one-step esterification method. Then the prepared MCC-GA was dissolved in Lithium chloride/dimethyl sulfoxide (LiCl/DMSO) system and polymerized with acrylic acid (AA) to prepare a multi-functional cellulose-based organogel. The prepared MCC-GA/polyacrylic acid (PAA) organogels exhibited enhanced interfacial adhesion through hydrogen bonding, π-π interactions, and electrostatic interactions. Additionally, the MCC-GA/PAA organogels could withstand 95 % of the compressive deformation and rapidly self-recover owing to chemical cross-linking and dynamic non-covalent interactions. The organogels also exhibited excellent anti-freezing properties (up to -80 °C), solvent retention, and ionic conductivity. Considering its excellent overall performance, the MCC-GA/PAA organogel was used as an effective flexible sensor for human motion detection and is expected to play an important role in the future development of flexible bioelectronics.

Recent Advances in Cellulose-Based Hydrogels: Food Applications

In the past couple of years, cellulose has attracted a significant amount of attention and research interest due to the fact that it is the most abundant and renewable source of hydrogels. With increasing environmental issues and an emerging demand, researchers around the world are focusing on naturally produced hydrogels in particular due to their biocompatibility, biodegradability, and abundance. Hydrogels are three-dimensional (3D) networks created by chemically or physically crosslinking linear (or branching) hydrophilic polymer molecules. Hydrogels have a high capacity to absorb water and biological fluids. Although hydrogels have been widely used in food applications, the majority of them are not biodegradable. Because of their functional characteristics, cellulose-based hydrogels (CBHs) are currently utilized as an important factor for different aspects in the food industry. Cellulose-based hydrogels have been extensively studied in the fields of food packaging, functional food, food safety, and drug delivery due to their structural interchangeability and stimuli-responsive properties. This article addresses the sources of CBHs, types of cellulose, and preparation methods of the hydrogel as well as the most recent developments and uses of cellulose-based hydrogels in the food processing sector. In addition, information regarding the improvement of edible and functional CBHs was discussed, along with potential research opportunities and possibilities. Finally, CBHs could be effectively used in the industry of food processing for the aforementioned reasons.

Porous Scaffolds Based on Polydopamine/Chondroitin Sulfate/Polyvinyl Alcohol Composite Hydrogels

In this paper, porous scaffolds based on composite hydrogels were fabricated using polydopamine (PDA), chondroitin sulfate (CS), and polyvinyl alcohol (PVA) via the freezing/thawing method. Different characteristics of the prepared composite hydrogels, including the pore sizes, compression strength, lap shear strength, mass loss, and cytocompatibility were investigated. Scanning electron microscope images (SEM) displayed the hydrogel pore sizes, ranging from 20 to 100 μm. The composite hydrogel exhibited excellent porosity of 95.1%, compression strength of 5.2 MPa, lap shear strength of 21 kPa on porcine skin, and mass loss of 16.0%. In addition, the composite hydrogel possessed good relative cell activity of 97%. The PDA/CS/PVA hydrogel is cytocompatible as a starting point, and it can be further investigated in tissue engineering.

A tough and mechanically stable adhesive hydrogel for non-invasive wound repair

Wound healing has been a great challenge throughout human history. Improper treatment for wounds is so easy to lead to infection and a series of serious symptoms, even death. Because of the ability of absorbing fluid and keeping a moist environment, the hydrogel with 3D networks is ideal candidate for wound dressing. More important, it has good biocompatibility. However, most of the hydrogel dressings reported have weak mechanical properties and adhesion properties, which greatly limit their clinical application. Herein, a tough adhesive hydrogel with good mechanical stability for non-invasive wound repair is reported. The hydrogel is composed of polyethylene glycol dimethacrylate (PEGDA), chitosan (CS) and chitin nano-whisker (CW). PEGDA and CS form interpenetrating network hydrogel through free radical polymerization reaction under the UV light. The introduction of CW further enhances the toughness of the hydrogel. The pH-sensitive CS can form adhesion to various materials through topological adhesion. As a wound closure repair material, PEGDA/CS/CW hydrogel not only has the characteristic of effectively closing the wound, defending against invading bacteria, and keeping the wound clean, but also has good tensile and mechanical stability, which is expected to realize the closure and repair of joints and other moving parts of the wound. This adhesive hydrogel is proven a promising material for wound closure repair.

Synthesis, characterization, and biological activities of new conjugates of Guanosine grafted on polyvinyl alcohol, carbohydrate chitosan, and cellulose

Guanosine (GU) is a purine nucleoside that has different biological applications. This study aimed to synthesize, characterize, and enhance the biological activities of GU through its covalently grafting on polyvinyl alcohol (PVA), chitosan (CS), and cellulose (CL). In this regard, the conjugation was constructed by different linkers such as chloroacetyl chloride, 2-bromopropionyl bromide, and epichlorohydrin (EPCH). The resulted novel conjugates were characterized by FT-IR, 1H-NMR, GPC, and TGA techniques. FT-IR spectra revealed the main characteristic groups, O–H, N–H, C=O and C=N of GU moieties. Furthermore, 1H-NMR spectra showed the aromatic C–H, O–H, and N–H protons of the grafted GU moieties. Two decomposition stages of grated polymers with high thermal stability are illustrated by TGA. GU showed no antifungal activity against Aspergillus fumigatus and Candida albicans. However, its conjugates: P-1A, P-1B, P-2A, P-2B, P-3A, and P-3B displayed significant antifungal effect with inhibitory zones in the range 8–11 mm. As compared to GU group, most of GU-polymer conjugates showed significant in vivo antitumor activity against EAC-bearing mice via the reduction in total tumor volume. In summary, these conjugates are biologically active macromolecules and may act as candidate carrier systems for other applications such as drug delivery.