Semi-IPN- and IPN-Based Hydrogels

Antibacterial and Anti-Inflammatory Polysaccharide from Fructus Ligustri Lucidi Incorporated in PVA/Pectin Hydrogels Accelerate Wound Healing

In cutaneous wound healing, an overproduction of inflammatory chemokines and bacterial infections impedes the process. Hydrogels can maintain a physiologically moist microenvironment, absorb chemokines, prevent bacterial infection, inhibit bacterial reproduction, and facilitate wound healing at a wound site. The development of hydrogels provides a novel treatment strategy for the entire wound repair process. Here, a series of Fructus Ligustri Lucidi polysaccharide extracts loaded with polyvinyl alcohol (PVA) and pectin hydrogels were successfully fabricated through the freeze-thaw method. A hydrogel containing a 1% mixing weight ratio of FLL-E (named PVA-P-FLL-E1) demonstrated excellent physicochemical properties such as swellability, water retention, degradability, porosity, 00drug release, transparency, and adhesive strength. Notably, this hydrogel exhibited minimal cytotoxicity. Moreover, the crosslinked hydrogel, PVA-P-FLL-E1, displayed multifunctional attributes, including significant antibacterial properties, earlier re-epithelialization, production of few inflammatory cells, the formation of collagen fibers, deposition of collagen I, and faster remodeling of the ECM. Consequently, the PVA-P-FLL-E1 hydrogel stands out as a promising wound dressing due to its superior formulation and enhanced healing effects in wound care.

Hydrogel-Based Flexible Electronics

Flexible electronics is an emerging field of research involving multiple disciplines, which include but not limited to physics, chemistry, materials science, electronic engineering, and biology. However, the broad applications of flexible electronics are still restricted due to several limitations, including high Young's modulus, poor biocompatibility, and poor responsiveness. Innovative materials aiming for overcoming these drawbacks and boost its practical application is highly desirable. Hydrogel is a class of 3D crosslinked hydrated polymer networks, and its exceptional material properties render it as a promising candidate for the next generation of flexible electronics. Here, the latest methods of synthesizing advanced functional hydrogels and the state-of-art applications of hydrogel-based flexible electronics in various fields are reviewed. More importantly, the correlation between properties of the hydrogel and device performance is discussed here, to have better understanding of the development of flexible electronics by using environmentally responsive hydrogels. Last, perspectives on the current challenges and future directions in the development of hydrogel-based multifunctional flexible electronics are provided.

Semi-IPN hydrogels of collagen and gum arabic with antibacterial capacity and controlled release of drugs for potential application in wound healing

The preparation of hydrogels based on biopolymers like collagen and gum arabic gives a chance to provide novel options that can be used in biomedical field. Through a polymeric semi-interpenetration technique, collagen-based polymeric matrices can be associated with gum arabic while controlling its physicochemical and biological properties. To create novel hydrogels with their potential use in the treatment of wounds, the semi-interpenetration process, altering the concentration (0-40% by wt) of gum arabic in a collagen matrix is explored. The ability of gum arabic to create intermolecular hydrogen bonds in the collagen matrix enables the development of semi-interpenetrating polymeric networks (semi-IPN)-based hydrogels with a faster gelation time and higher crosslinking. Amorphous granular surfaces with linked porosity are present in matrices with 30% (by wt) of gum arabic, enhancing the storage modulus and thermal degradation resistance. The hydrogels swell to very high extent in hydrolytic and proteolytic environments, good hemocompatibility, and suppression of growth of pathogens like E. coli, and all it is enhanced by gum arabic included them, in addition to enabling the controlled release of ketorolac. The chemical composition of theses semi-IPN matrices have no deleterious effects on monocytes or fibroblasts, promoting their proliferation, and lowering alpha tumor necrosis factor (α-TNF) secretion in human monocytes.

Porous biomaterials for tissue engineering: a review

The field of biomaterials has grown rapidly over the past decades. Within this field, porous biomaterials have played a remarkable role in: (i) enabling the manufacture of complex three-dimensional structures; (ii) recreating mechanical properties close to those of the host tissues; (iii) facilitating interconnected structures for the transport of macromolecules and cells; and (iv) behaving as biocompatible inserts, tailored to either interact or not with the host body. This review outlines a brief history of the development of biomaterials, before discussing current materials proposed for use as porous biomaterials and exploring the state-of-the-art in their manufacture. The wide clinical applications of these materials are extensively discussed, drawing on specific examples of how the porous features of such biomaterials impact their behaviours, as well as the advantages and challenges faced, for each class of the materials.

Advanced injectable hydrogels for cartilage tissue engineering

The rapid development of tissue engineering makes it an effective strategy for repairing cartilage defects. The significant advantages of injectable hydrogels for cartilage injury include the properties of natural extracellular matrix (ECM), good biocompatibility, and strong plasticity to adapt to irregular cartilage defect surfaces. These inherent properties make injectable hydrogels a promising tool for cartilage tissue engineering. This paper reviews the research progress on advanced injectable hydrogels. The cross-linking method and structure of injectable hydrogels are thoroughly discussed. Furthermore, polymers, cells, and stimulators commonly used in the preparation of injectable hydrogels are thoroughly reviewed. Finally, we summarize the research progress of the latest advanced hydrogels for cartilage repair and the future challenges for injectable hydrogels.

Hydrogels: Properties and Applications in Biomedicine

Hydrogels are crosslinked polymer chains with three-dimensional (3D) network structures, which can absorb relatively large amounts of fluid. Because of the high water content, soft structure, and porosity of hydrogels, they closely resemble living tissues. Research in recent years shows that hydrogels have been applied in various fields, such as agriculture, biomaterials, the food industry, drug delivery, tissue engineering, and regenerative medicine. Along with the underlying technology improvements of hydrogel development, hydrogels can be expected to be applied in more fields. Although not all hydrogels have good biodegradability and biocompatibility, such as synthetic hydrogels (polyvinyl alcohol, polyacrylamide, polyethylene glycol hydrogels, etc.), their biodegradability and biocompatibility can be adjusted by modification of their functional group or incorporation of natural polymers. Hence, scientists are still interested in the biomedical applications of hydrogels due to their creative adjustability for different uses. In this review, we first introduce the basic information of hydrogels, such as structure, classification, and synthesis. Then, we further describe the recent applications of hydrogels in 3D cell cultures, drug delivery, wound dressing, and tissue engineering.

Study of Several Alginate-Based Hydrogels for In Vitro 3D Cell Cultures

Hydrogel, a special system of polymer solutions, can be obtained through the physical/chemical/enzymic crosslinking of polymer chains in a water-based dispersion medium. Different compositions and crosslinking methods endow hydrogel with diverse physicochemical properties. Those hydrogels with suitable physicochemical properties hold manifold functions in biomedical fields, such as cell transplantation, tissue engineering, organ manufacturing, drug releasing and pathological model analysis. In this study, several alginate-based composite hydrogels, including gelatin/alginate (G-A), gelatin/alginate/agarose (G-A-A), fibrinogen/alginate (F-A), fibrinogen/alginate/agarose (F-A-A) and control alginate (A) and alginate/agarose (A-A), were constructed. We researched the advantages and disadvantages of these hydrogels in terms of their microscopic structure (cell living space), water holding capacity, swelling rate, swelling–erosion ratio, mechanical properties and biocompatibility. Briefly, alginate-based hydrogels can be used for three-dimensional (3D) cell culture alone. However, when mixed with other natural polymers in different proportions, a relatively stable network with a good cytocompatibility, mechanical strength and water holding capacity can be formed. The physical and chemical properties of the hydrogels can be adjusted by changing the composition, proportion and cross-linking methods of the polymers. Conclusively, the G-A-A and F-A-A hydrogels are the best hydrogels for the in vitro 3D cell cultures and pathological model construction.

Polysaccharide hydrogels: Functionalization, construction and served as scaffold for tissue engineering

Polysaccharide hydrogels have been widely utilized in tissue engineering. They interact with the organismal environments, modulating the cargos release and realizing of long-term survival and activations of living cells. In this review, the potential strategies for modification of polysaccharides were introduced firstly. It is not only used to functionalize the polysaccharides for the consequent formation of hydrogels, but also used to introduce versatile side groups for the regulation of cell behavior. Then, techniques and underlying mechanisms in inducing the formation of hydrogels by polysaccharides or their derivatives are briefly summarized. Finally, the applications of polysaccharide hydrogels in vivo, mainly focus on the performance for alleviation of foreign-body response (FBR) and as cell scaffolds for tissue regeneration, are exemplified. In addition, the perspectives and challenges for further research are addressed. It aims to provide a comprehensive framework about the potentials and challenges that the polysaccharide hydrogels confronting in tissue engineering.

Micropatterned gellan gum-based hydrogels tailored with laminin-derived peptides for skeletal muscle tissue engineering

The efficacy of current therapies for skeletal muscle disorders/injuries are limited urging the need for new treatments. Skeletal muscle tissue engineered platforms represent a promising tool to shed light on the pathophysiology of skeletal muscle disorders/injuries and to investigate the efficacy of new therapies. Herein, we developed a skeletal muscle platform composed of aligned and differentiated myoblasts on micropatterned gellan gum (GG)-based hydrogels tailored with a laminin-derived peptide. To this aim, the binding of murine skeletal muscle cells (C2C12) to different laminin-derived peptides (CIKVAVS (V), KNRLTIELEVRTC (T), and RKRLQVQLSIRTC (Q)) and the binding of laminin-derived peptides to chemically functionalized GG was studied. C2C12-binding to peptide V, T and Q was 10%, 48% and 25%, whereas the peptide tethering to GG was 60%, 40% and 31%, respectively. Peptide-biofunctionalized hydrogels prepared with different polymer content showed different mechanics and peptide exposure at hydrogel surface. Cellular adhesion was detected in all hydrogel formulations, but spreading and differentiation was only promoted in peptide Q-biofunctionalized hydrogels and preferably in stiffer hydrogels. Myoblast alignment was promoted in micropatterned hydrogel surfaces. Overall, the engineered skeletal muscle herein proposed can be further explored as a platform to better understand skeletal muscle disorders/injuries and to screen new therapies.

Salecan-Clay Based Polymer Nanocomposites for Chemotherapeutic Drug Delivery Systems; Characterization and In Vitro Biocompatibility Studies

Salecan is a microbial polysaccharide suitable to obtain hydrogel for biomedical applications due to the excellent hydrophilicity and biocompatibility properties. In this work, Salecan of different concentrations was introduced into polymethacrylic acid (PMAA) in the presence of clay to form novel semi synthetic hydrogel nanocomposites systems and loaded afterwards with doxorubicin (DOX). The physical-chemical characteristics of the nanocomposites systems and their effect on the viability, and morphology of MDBK (Madin-Darby bovine kidney), HT-29 human colorectal adenocarcinoma and Colo 205 human colon adenocarcinoma cell lines were investigated. DOX release from the nanocomposite systems, cell up-take and subsequent effect on cell proliferation was also analyzed. It was found that Salecan concentration determined the swelling behavior, structural parameters and morphological features of the nanocomposite systems. The hydrogen bonds strongly influenced the formation of PMAA-Salecan-clay systems, each component bringing its own contribution, thus demonstrating the achievement of an advanced crosslinked network and a more compacted hydrogel nanocomposite morphology. All the synthesized nanocomposites had negligible toxicity to normal MDBK cells and chemoresistent HT-29 cell line, whereas in the case of Colo 205 cells a decrease by 40% of the cell viability was obtained for the sample containing the highest amount of Salecan. This effect was correlated with the lowest pore size distribution leading to highest available specific surface area and entrapped amount of DOX which was further released from the nanocomposite sample. Corroborating all the data it can be suggested that the synthesized nanocomposites with Salecan and clay could be good candidates as vehicles for chemotherapeutic agents.

Large-Scale Spinning Approach to Engineering Knittable Hydrogel Fiber for Soft Robots

Efforts to impart responsiveness to environmental stimuli in artificial hydrogel fibers are crucial to intelligent, shape-memory electronics and weavable soft robots. However, owing to the vulnerable mechanical property, poor processability, and the dearth of scalable assembly protocols, such functional hydrogel fibers are still far from practical usage. Herein, we demonstrate an approach toward the continuous fabrication of an electro-responsive hydrogel fiber by using the self-lubricated spinning (SLS) strategy. The polyelectrolyte inside the hydrogel fiber endows it with a fast electro-response property. After solvent exchange with triethylene glycol (TEG), the maximum tensile strength of the hydrogel fiber increases from 114 kPa to 5.6 MPa, far superior to those hydrogel fiber-based actuators reported previously. Consequently, the flexible and mechanical stable hydrogel fiber is knitted into various complex geometries on demand such as a crochet flower, triple knot, thread tube, pentagram, and hollow cage. Additionally, the electrochemical-responsive ionic hydrogel fiber is capable of acting as soft robots underwater to mimic biological motions, such as Mobula-like flapping, jellyfish-mimicking grabbing, sea worm-mimicking multi-degree of freedom movements, and human finger-like smart gesturing. This work not only demonstrates an example for the large-scale production of previous infeasible hydrogel fibers, but also provides a solution for the rational design and fabrication of hydrogel woven intelligent devices.

Smart nanotheranostic hydrogels for on-demand cancer management

Theranostics is a revolution in cancer therapy. Hydrogels have many implications as a drug delivery vehicle and theranostics hydrogels could be a model nanotherapeutic for simultaneous cancer diagnosis and treatment.

Semi-Interpenetrating Polymer Network of Hyaluronan and Chitosan Self-Healing Hydrogels for Central Nervous System Repair

The repair of the central nervous system (CNS) is a major challenge because of the difficulty for neurons or axons to regenerate after damages. Injectable hydrogels have been developed to deliver drugs or cells for neural repair, but these hydrogels usually require conditional stimuli or additional catalysts to control the gelling process. Self-healing hydrogels, which can be injected locally to fill tissue defects after stable gelation, are attractive candidates for CNS treatment. In the current study, the self-healing hydrogel with a semi-interpenetrating polymer network (SIPN) was prepared by incorporation of hyaluronan (HA) into the chitosan-based self-healing hydrogel. The addition of HA allowed the hydrogel to pass through a narrow needle much more easily. As the HA content increased, the hydrogel showed a more packed nanostructure and a more porous microstructure verified by coherent small-angle X-ray scattering and scanning electron microscopy. The unique structure of SIPN hydrogel enhanced the spreading, migration, proliferation, and differentiation of encapsulated neural stem cells in vitro. Compared to the pristine chitosan-based self-healing hydrogel, the SIPN hydrogel showed better biocompatibility, CNS injury repair, and functional recovery evaluated by the traumatic brain injury zebrafish model and intracerebral hemorrhage rat model. We proposed that the SIPN of HA and chitosan self-healing hydrogel allowed an adaptable environment for cell spreading and migration and had the potential as an injectable defect support for CNS repair.

Tough hydrogel module towards an implantable remote and controlled release device

On-demand controllable drug delivery systems enable the administration of precise dosages and thus have the potential to improve overall healthcare.

pH-responsive chitosan based hydrogels affect the release of dapsone: Design, set-up, and physicochemical characterization

Dapsone (DAP) is a bactericidal agent used in the treatment of leprosy, caused by Mycobacterium leprae. Despite its therapeutic potential, DAP has low solubility, which results in allow therapeutic index and a high microbial resistance. Recently, new approaches were used to increase the DAP solubility. In particular, the use of interpenetrating polymer network (IPN)-hydrogels based chitosan (CS) for the controlled release of DAP provides some advantages because they can modify their swelling properties and network structures as a response to environmental stimuli. The aim of this study was to synthesize and physicochemically characterize pH-responsive chitosan/polymer hydrogels to control the release of DAP. For this reason, different combination of polymers, such as polyvinyl pyrrolidone, polyethylene glycol and hydroxypropyl methylcellulose, and concentrations of the cross-linking agents (glutaraldehyde) were used and then blended to the CS. The resulting hydrogels were evaluated in terms of physicochemical and swelling properties, rheological analysis and in vitro release of DAP at different pHs (1.2-6.8). Hydrogels were further characterized by Fourier transformed infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) analysis. pH-responsive DAP-loaded hydrogels may represent the set-up for developing potential oral formulations for the treatment of leprosy caused by Mycobacterium leprae.