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Hydrogel prepared by cylindrical mold. (a) Schematic diagram of preparation of hydrogel by cylindrical mold; (b)–(c) Digital photographs of hydrogel, overall view and cross section, respectively; (d)–(f) Morphology of hydrogel at different positions; positions were marked out in (a) with corresponding letters: (d) Center of radial pattern, SEM images of hydrogel after freeze-drying; (e) Orientation in radial pattern, CLSM image, bright field; (f) Concentric layers, CLSM image, bright field.
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Hydrogels with organized structure have attracted remarkable attentions for bio-related applications. Among the preparation of hierarchical hydrogel materials, fabrication of hydrogel with multi-layers is an important branch. Although the generation mechanism of layers had been fully discussed, sub-layer structure was not sufficiently studied. In t...
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... of hydrogel structure. Hydrogel prepared by single opening mold was an illustration of structural characteristics of this system. Hydrogels with more complicated architecture could be fabricated based on this mechanism by cylindrical mold (Fig. 8 a and b). In these hydrogels, the layered-oriented structure could be clearly seen (Fig. 8 c, d, e, and f). Layers were in the form of concentric circles, which were all parallel to the primary hydrogel layer. And orientation presented a radial pattern, which was along the diffusion direction of OH 2 . The morphology of hydrogel prepared by ...
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... of hydrogel structure. Hydrogel prepared by single opening mold was an illustration of structural characteristics of this system. Hydrogels with more complicated architecture could be fabricated based on this mechanism by cylindrical mold (Fig. 8 a and b). In these hydrogels, the layered-oriented structure could be clearly seen (Fig. 8 c, d, e, and f). Layers were in the form of concentric circles, which were all parallel to the primary hydrogel layer. And orientation presented a radial pattern, which was along the diffusion direction of OH 2 . The morphology of hydrogel prepared by cylindrical mold confirmed the structural characteristics discussed above. The direction ...
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Citations
... To characterize the structural properties of the vessels in a wet state, we visualized freshly printed vessels containing FITC-labelled dextran macromolecules with a confocal microscope. The wet hydrogel shows a porous structure ( Figure S9, SI), with smaller surface pores ( Figure S9A, SI) and larger pores in the intrinsic layers ( Figure S9 B-D, SI) [75], demonstrating the pore-forming capacity of our hydrogels [43,44]. Diffusional permeability of the hydrogel vessel may be seen in Fig. 6H in 4-6 s of perfusion. ...
Vascularization is crucial for providing nutrients and oxygen to cells while removing waste. Despite advances in 3D-bioprinting, the fabrication of structures with void spaces and channels remains challenging. This study presents a novel approach to create robust yet flexible and permeable small (600–1300 μm) artificial vessels in a single processing step using 3D coaxial extrusion printing of a biomaterial ink, based on tyramine-modified polyethylene glycol (PEG-Tyr). We combined the gelatin biocompatibility/activity, robustness of PEG-Tyr and alginate with the shear-thinning properties of methylcellulose (MC) in a new biomaterial ink for the fabrication of bioinspired vessels. Chemical characterization using NMR and FTIR spectroscopy confirmed the successful modification of PEG with Tyr and rheological characterization indicated that the addition of PEG-Tyr decreased the viscosity of the ink. Enzyme-mediated crosslinking of PEG-Tyr allowed the formation of covalent crosslinks within the hydrogel chains, ensuring its stability. PEG-Tyr units improved the mechanical properties of the material, resulting in stretchable and elastic constructs without compromising cell viability and adhesion. The printed vessel structures displayed uniform wall thickness, shape retention, improved elasticity, permeability, and colonization by endothelial-derived - EA.hy926 cells. The chorioallantoic membrane (CAM) and in vivo assays demonstrated the hydrogel's ability to support neoangiogenesis. The hydrogel material with PEG-Tyr modification holds promise for vascular tissue engineering applications, providing a flexible, biocompatible, and functional platform for the fabrication of vascular structures.
... By using conductive hydrogels, it is possible to produce self-supported substrates endowed with interesting mechanical properties, including resistance under tensile deformation, good flexibility, and self-healing properties [2]. The elaboration of flexible strain sensors using conductive hydrogels is achievable through diverse methods, such as utilizing molds of varying shapes or employing cutting-edge 3D printing technology [34][35][36]. The often-overlooked porosity, a result of the freeze-drying process [37,38], significantly influences the material's overall characteristics. ...
Conductive hydrogels are of interest for highly flexible sensor elements. We compare conductive hydrogels and hydrogel foams in view of strain-sensing applications. Polyvinyl alcool (PVA) and poly(3,4-ethylenedioxythiophene (PEDOT:PSS) are used for the formulation of conductive hydrogels. For hydrogel foaming, we have investigated the influence of dodecylbenzenesulfonate (DBSA) as foaming agent, as well as the influence of air incorporation at various mixing speeds. We showed that DBSA acting as a surfactant, already at a concentration of 1.12% wt, efficiently stabilizes air bubbles, allowing for the formulation of conductive PVA and PVA/PEDOT:PSS hydrogel foams with low density (<400 kg/m3) and high water uptake capacity (swelling ratio > 1500%). The resulting Young moduli depend on the air-bubble incorporation from mixing, and are affected by freeze-drying/rehydration. Using dielectric broadband spectroscopy under mechanical load, we demonstrate that PVA/PEDOT:PSS hydrogel foams exhibit a significant decrease in conductivity under mechanical compression, compared to dense hydrogels. The frequency-dependent conductivity of the hydrogels exhibits two plateaus, one in the low frequency range, and one in the high frequency range. We find that the conductivity of the PVA/PEDOT:PSS hydrogels decreases linearly as a function of pressure in each of the frequency regions, which makes the hydrogel foams highly interesting in view of compressive strain-sensing applications.
... Layered spatially oriented chitosan-containing materials, which have been intensely studied recently, are promising for use in tissue engineering (bone tissue replacement), regenerative medicine (a temporary construct for restoring epithelial and connective tissue), and also for the development of controlled drug delivery systems [1][2][3][4][5]. Such materials are of particular importance to manufacture scaffolds [6][7][8][9]. The layered structure provides high porosity, which is important for biomedical applications [2,10]. ...
... To obtain layered materials, intermittent precipitation reactions are used, among others, leading to the formation of Liesegang structures. A feature of the process of their preparation is the layer-by-layer periodic nature of the interaction of the salt chitosan form ([~-NH3] + ) with alkali during the reaction of the polymer-analogous salt → base transformation, accompanied by deprotonation (neutralization) of the polycation to form a water-insoluble chitosan basic form ([~-NH2]↓) [6,11]. As a result, the formation of nu-merous intra-and intermolecular hydrogen bonds in macrochains, the occurrence of hydrophobic interactions, and the formation of chitosan base crystallites proceed in the system cyclically rather than simultaneously, in a local layer space each time. ...
... The described method can be used in various ways, e.g., layer-oriented hydrogel materials were obtained by ion-induced precipitation of chitosan acetate in highly concentrated alkali media (5-10% NaOH) [6,12,13]. A solution of the salt chitosan form was either placed into a mold of one configuration or another with a hole at the top, specifying the desired architecture of the resulting product, and kept in an alkaline medium [6], or subjected to repeated alternation of neutralization of protonated amino groups and soaking in water [12]. ...
For the first time, anisotropic hydrogel material with a highly oriented structure was obtained by the chemical reaction of polymer-analogous transformation of chitosan glycolate—chitosan base using triethanolamine (TEA) as a neutralizing reagent. Tangential bands or concentric rings, depending on the reaction conditions, represent the structural anisotropy of the hydrogel. The formation kinetics and the ratio of the positions of these periodic structures are described by the Liesegang regularities. Detailed information about the bands is given (formation time, coordinate, width, height, and formation rate). The supramolecular ordering anisotropy of the resulting material was evaluated both by the number of Liesegang bands (up to 16) and by the average values of the TEA diffusion coefficient ((15–153) × 10−10 and (4–33) × 10−10 m2/s), corresponding to the initial and final phase of the experiment, respectively. The minimum chitosan concentration required to form a spatial gel network and, accordingly, a layered anisotropic structure was estimated as 1.5 g/dL. Morphological features of the structural anisotropic ordering of chitosan Liesegang structures are visualized by scanning electron microscopy. The hemocompatibility of the material obtained was tested, and its high sorption–desorption properties were evaluated using the example of loading–release of cholecalciferol (loading degree ~35–45%, 100% desorption within 25–28 h), which was observed for a hydrophobic substance inside a chitosan-based material for the first time.
... SEM images of the acrylamide/sodium methacrylate hydrogel including 10 wt% sodium methacrylate and acrylamide/sodium methacrylate/kaolin semi-IPN composite hydrogel including 10 wt% sodium methacrylate are shown in Figure 7. The acrylamide/sodium methacrylate hydrogel had regular layered structure which provides water uptake easily (Nie et al. 2015). However, the semi-IPN composite hydrogel consisted of porous structure as well as layers. ...
With the advantages of their self-healing, stimuli-response ability, water sorption capacity and shape memory, hydrogels have been commonly utilized. However, new strategies have been developed to enhance mechanical and thermal properties of hydrogels in addition to increase their water sorption. In this study, stimuli-responsive acrylamide/sodium methacrylate based hydrogels were synthesized with the optimization of sodium methacrylate amount by free radical polymerization. With the incorporation of optimum amount of polyethylene glycol 400 (PEG-400) into the hydrogel network, semi-interpenetrating polymer network (semi-IPN) hydrogels were prepared. With the addition of kaolin, swelling properties of the semi-IPN composite hydrogels were investigated in water under the effect of different pH and temperature. Maximum swelling percent of the semi-IPN composite hydrogels was determined as 24214% at pH 7 and 25 °C. Fourier transform infrared spectroscopy (FTIR) analyses revealed that hydrogel samples were successfully synthesized. Morphological structure of hydrogel samples was examined by scanning electron microscopy (SEM) analyses. Both of the water motion through the hydrogel layered structure and water diffusion into the pores made the semi-IPN composite hydrogel more swollen material compared to the acrylamide/sodium methacrylate based hydrogel.
... Fuentes-Caparrós et al. showed that in their example case printing process heavily influenced to the hydrogel properties. [135] Previously, for example, Nie et al. [136] and Nguyen et al. [137] have also studied mechanical properties of multilayered hydrogel constructs, but only focused on individual layers. ...
3D-bioprinting has become a valid technique for tissue and organ regeneration, as the printing of living cells is allowed while the hydrogel-based ink material provides them mechanical and structural support. Self-healing shear-thinning hydrogel inks can be considered most promising ink materials for extrusion-based bioprinting (EBB), because the ink can be extruded due to the decrease in viscosity under shear, and self-healed after removing the shear, which ensures safe printing of cells and shape fidelity after bioprinting. To achieve the best final bioprinting result, some printing technique, ink material and biological aspects of bioprinting need to be considered. In addition, the versatile characterization of pre- and post-printing properties of the inks helps to improve the final bioprinted constructs. However, despite the great advances in 3D-bioprinting, ink related challenges such as opposing characteristics, and lack of controllable micro-environment, or technological challenges such as the need to increase printing speed and print resolution must be resolved. In terms of ink characterization, more standardization is also needed. In addition, the computational modeling would help to improve the performance of the bioprinted construct. Thus, the future of 3D-bioprinting is going towards larger multifunctional tissue/organ constructs with multi-scale vascularization and innervation. Multiple printing techniques are probably combined, but also completely new techniques are needed. Further, multimaterial printing would enable heterogeneity and gradients to the construct. On the other hand, using 4D-bioprinting, the dynamic nature of complex organs could be added to the construct. By combining bioprinting with microphysiological platforms (tissue- or organ-on-a-chip systems) the development of functional tissues and organs intended for implantation would go forward. The translation of EBB into clinical practice is still in the early stages, but EBB has a great potential in regenerative medicine after the challenges, such as biomimicry, reproducibility or up-scaling related issues have been overcome. In this review, the design aspects related to extrusion-based bioprinting technique, the property requirements for ideal bioink, the biological aspects of 3D-bioprinting, and the characterization of the pre- and post-printing properties of bioinks are presented. Also, the challenges and future prospects of 3D-bioprinting are discussed.
... The gelation process of chitosan (CS) hydrogels by alkaline neutralization of solubilized CS in acidic aqueous medium was visualized by fluorescence microscopic imaging 43,44 . This synthesis route contributed to the formation of a hierarchically oriented structure along the diffusion direction of OH − . ...
Functionalized hydrogels play an important part in chemistry, biology, and material science due to their unique microstructures. Characterization of these microstructures is the fundamental issue to improve the optical, mechanical, and biochemical performance of functionalized hydrogels. With the rapid development of fluorescence microscopy, a growing number of researchers have attempted to utilize this easily operated, noninvasive, and high-contrast technique to visualize the fine microstructure of hydrogels. Integration of a confocal system into fluorescence microscopy allows the sectioning and reconstruction of 3D hydrogel networks. The live recording function offers in situ and real-time images of dynamic behaviors within hydrogels. The development of super-resolution fluorescence microscopy has significantly promoted imaging quality from the submicron scale to the nanoscale. Based on these spectacular achievements, we reviewed the recent advances in fluorescence microscopic visualization of internal morphologies, mechanical properties, and dynamic structural changes. The scope of this review is to provide inspiration for researchers in chemistry, material science, and biology to study and fabricate functionalized hydrogels with the assistance of fluorescence microscopic visualization. This review highlights the recent advances in fluorescence microscopic visualization of synthetic hydrogels, bio-macromolecular hydrogels, organohydrogels, and supramolecular hydrogels. Topics related to the structural changes of hydrogels, hydrogel mechanics, and super-resolution imaging of hydrogels based on fluorescence microscopy are introduced. The design concepts, imaging mechanisms, and potential applications of the novel fluorescence visualization strategies are discussed in detail. Finally, our opinions on the major challenges of current research, possible solutions, and future directions are shared.
... These hierarchical hydrogel constructs, may be tailored for biochemically, morphologically, and mechanically diverse microenvironments to have a wide range of uses in drug encapsulation and release. Recent studies explore new dimensions for preparation methods and formation mechanisms using the same materials (Table 1) [79,80]. But multilayered hydrogels made of different materials are still rare in the field of drug delivery. ...
... Jingyi Nie et al. [80] have studied the mechanism of the orientation of sublayer structure during the chitosan (CS) hydrogel formation and the influence of the structure on mechanical performance. The desired orientation and structure are extensively required for specialized fields application. ...
In recent practices, multi-stimuli responsive polymers that respond to diverse physiological or externally applied stimuli are proven to have great utility as regenerative biomaterials. These biocompatible intelligent materials are designed to “detect” the surrounding physiological environments and release encapsulated therapeutic cargos into particular sites on-demand delivery basis. Multi-layered “smart” hydrogels with the arrangement of various functional layers have been the materials of choice for drug delivery. The first part of the review highlights the formation mechanism of multi-layered structures using different methods. In addition, their morphology, orientation, and formulation aspects were also presented. Moreover, recent studies and potential applications are also highlighted. We have also discussed the 3D bioprinting-electrospinning approach for designing smart hydrogels as a new perspective for expanding their applications in controlled drug delivery and tissue engineering.
... The synthesis of CS hydrogels was based on previously reported methods with some modifications [39][40][41]. The procedure was carried as follows: CS (% w/v) was dissolved in 35 mL of AAc solution (1% v/v). ...
This work studied the influence of hydrogel’s physical properties (geometry and hierarchical roughness) on the in vitro sorption/release profiles of molecules. To achieve this goal, chitosan (CS) solutions were cast in 3D-printed (3DP) molds presenting intricate shapes (cubic and half-spherical with/without macro surface roughness) and further immersed in alkaline solutions of NaOH and NaCl. The resulting physically crosslinked hydrogels were mechanically stable in aqueous environments and successfully presented the shapes and geometries imparted by the 3DP molds. Sorption and release profiles were evaluated using methyl orange (MO) and paracetamol (PMOL) as model molecules, respectively. Results revealed that distinct MO sorption/PMOL release profiles were obtained according to the sample’s shape and presence/absence of hierarchical roughness. MO sorption capacity of CS samples presented both dependencies of hierarchical surface and geometry parameters. Hence, cubic samples without a hierarchical surface presented the highest (up to 1.2 × greater) dye removal capacity. Moreover, PMOL release measurements were more dependent on the surface area of hydrogels, where semi-spherical samples with hierarchical roughness presented the fastest (~1.13 × faster) drug delivery profiles. This work demonstrates that indirect 3DP (via fused filament fabrication (FFF) technology) could be a simple strategy to obtain hydrogels with distinct sorption/release profiles.
... 2 Again, native wet hydrogels can be changed to aerogels, xerogel or other functional dry materials after the removal of water. 3 However, hydrogels have got enhanced attention for their structural tenability and excellent rheological property. Most of the bioapplications are associated with hydrogels as they can absorb water, the most preferred biological solvent and major constituent of body cells. ...
The basic structure of hydrogels can be defined as a polymeric, hydrophilic and three-dimensional network. A wide range of physical or chemical interactions lead to the crosslinking to build the structural features. Recent advancement of research emphasized on the physiological stimuli responsive nature of those hydrogel framework due to enhancement of bio-applications. In this context, natural biopolymers exhibiting the sensitivity towards the local environment like pH, temperature, redox etc. generate a strong foundation and around them most of the natural physiological procedures are circulated. Recently, the scientists focused on the polysaccharide as an extensively used natural biopolymer for hydrogel preparation among several other biomacromolecules, due to highest natural abundance being an essential components of easily available daily foods like fruits and grains. However, certain additional properties can trigger the stimuli sensitivity along with various biomedical applications stimulated from the mother nature. They can be incorporated through functionalization. For example, an intermediate platform between saline injections and solid scaffolds can be delivered through introducing in situ cross-linking nature of gel matrix through reversible or irreversible sol-gel transition. Moreover, infection risks and recovery time can be reduced through including ease of injectability, hence cause patient's relaxation. Again, self-healing gel can exhibit an excellent tissue damage recovery within body-system. This review delivers synthetic outline of natural polysaccharide-based hydrogel framework. A detailed impression on different types of physiological stimuli sensitivity along with in situ, injectable and self-healing properties of these hydrogels and their importance from biomedical applicative perspective are projected in this article further. Lastly, some major biomedical applications are emphasized.
... Furthermore, researchers use LSCM to analyze the oriented structure within multilayered hydrogels [209] and use magnetic resonance imaging and X-ray tomography to measure the pore size of hydrogels in the wet state [219,220]. Although a series of techniques are available for analysis purposes, contrast and resolution play significant roles in imaging, affecting analysis results [221]. ...
Hydrogels are three-dimensional crosslinked hydrophilic polymer networks with great potential in drug delivery, tissue engineering, wound dressing, agrochemicals application, food packaging, and cosmetics. However, conventional synthetic polymer hydrogels may be hazardous and have poor biocompatibility and biodegradability. Algal polysaccharides are abundant natural products with biocompatible and biodegradable properties. Polysaccharides and their derivatives also possess unique features such as physicochemical properties, hydrophilicity, mechanical strength, and tunable functionality. As such, algal polysaccharides have been widely exploited as building blocks in the fabrication of polysaccharide-based hydrogels through physical and/or chemical crosslinking. In this review, we discuss the extraction and characterization of polysaccharides derived from algae. This review focuses on recent advances in synthesis and applications of algal polysaccharides-based hydrogels. Additionally, we discuss the techno-economic analyses of chitosan and acrylic acid-based hydrogels, drawing attention to the importance of such analyses for hydrogels. Finally, the future prospects of algal polysaccharides-based hydrogels are outlined.
