A Novel Method for Preparing Poly(vinyl alcohol) Hydrogels: Preparation, Characterization, and Application
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This work provides a new method to prepare poly(vinyl alcohol) (PVA) hydrogel. Compared with the traditional repeated freeze–thaw method, the physical cross-linking method was adopted to prepare a high-strength hydrogel in one step. The morphology, melting, and crystallization behavior and mechanical properties of the hydrogel were investigated. The hydrogel has a high water content and reswelling rate, as well as a high melting temperature and mechanical strength. It also has a stable cross-linked structure in the temperature range of 25–65 °C. The hydrogel fracture surface shows ductile and brittle fracture morphology. The protrusions in the hydrogel three-dimensional topography are more numerous and homogeneous when the solvent preparation ratio is 4–6. On the basis of the good plasticity of the hydrogels, tubular hydrogels with inner diameters of 1–6 mm are also prepared to widen their applications.Keywords:
Vinyl alcohol
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ABSTRACT Hydrogels are a class of polymeric network materials embedded in a water‐rich environment. They are widely applied in drug delivery, actuator, and sensor. However, conventional hydrogels encountered limits from their poor mechanical property. Recent researches in hydrogels have been focusing on mechanical enhancement, ranging from design of microstructures to adjustment of compositions in hydrogels. Here, the design and fabrication strategies of high‐strength hydrogels, as well as major progress in their typical strength‐support applications are systemically reviewed. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56 , 1325–1335
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The relatively weak mechanical properties of hydrogels remain a major drawback for their application as load-bearing tissue scaffolds. Previously, we developed cell-laden double-network (DN) hydrogels that were composed of photocrosslinkable gellan gum (GG) and gelatin. Further research into the materials as tissue scaffolds determined that the strength of the DN hydrogels decreased when they were prepared at cell-compatible conditions, and the encapsulated cells in the DN hydrogels did not function as well as they did in gelatin hydrogels. In this work, we developed microgel-reinforced (MR) hydrogels from the same two polymers, which have better mechanical strength and biological properties in comparison to the DN hydrogels. The MR hydrogels were prepared by incorporating stiff GG microgels into soft and ductile gelatin hydrogels. The MR hydrogels prepared at cell-compatible conditions exhibited higher strength than the DN hydrogels and the gelatin hydrogels, the highest strength being 2.8 times that of the gelatin hydrogels. MC3T3-E1 preosteoblasts encapsulated in MR hydrogels exhibited as high metabolic activity as in gelatin hydrogels, which is significantly higher than that in the DN hydrogels. The measurement of alkaline phosphatase (ALP) activity and the amount of mineralization showed that osteogenic behavior of MC3T3-E1 cells was as much facilitated in the MR hydrogels as in the gelatin hydrogels, while it was not as much facilitated in the DN hydrogels. These results suggest that the MR hydrogels could be a better alternative to the DN hydrogels and have great potential as load-bearing tissue scaffolds.
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Hydrogels are a class of polymeric network materials embedded in a water‐rich environment. They are widely applied in drug delivery, actuator, and sensor. However, conventional hydrogels encountered limits from their poor mechanical property. Recent researches on hydrogels has been focusing on mechanical enhancement, ranging from design of microstructures to adjustment of compositions in hydrogels. Here, the design and fabrication strategies of high‐strength hydrogels, as well as major progress in their typical strength‐support applications are systemically reviewed. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1325–1335
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Hydrogels are frequently used biomaterials due to their similarity in hydration and structure to biological tissues. However, their utility is limited by poor mechanical properties, namely, a lack of strength and stiffness that mimic that of tissues, particularly load-bearing tissues. Thus, numerous recent strategies have sought to enhance and tune these properties in hydrogels, including interpenetrating networks (IPNs), macromolecular cross-linking, composites, thermal conditioning, polyampholytes, and dual cross-linking. Individually, these approaches have achieved hydrogels with either high strength (σf > 10 MPa), high stiffness (E > 1 MPa), or, less commonly, both high strength and stiffness (σf > 10 MPa and E > 1 MPa). However, only certain unique combinations of these approaches have been able to synergistically achieve retention of a high, tissuelike water content as well as high strength and stiffness. Applying such methods to stimuli-responsive hydrogels has also produced robust, smart biomaterials. Overall, methods to achieve hydrogels that simultaneously mimic the hydration, strength, and stiffness of soft and load-bearing tissues have the potential to be used in a much broader range of biomedical applications.
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Abstract High-strength chitosan hydrogels (H-CS) were prepared without external crosslinker based on a LiOH/urea solvent system. The resultant H-CS hydrogels showed much better mechanical properties than conventional chitosan hydrogels (L-CS). Mechanical properties of H-CS can be tuned by adjusting the concentration of chitosan solution. SEM images of freeze-dried H-CS hydrogels displayed well-defined, interconnected, three-dimensional porous network structures that could greatly improve their mechanical properties. H-CS hydrogels fabricated in this study show great potential as a structural and functional material in the biomedical field.
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The relatively weak mechanical properties of hydrogels remain a major drawback for their application as load-bearing tissue scaffolds. Previously, we developed cell-laden double-network (DN) hydrogels that were composed of photocrosslinkable gellan gum (GG) and gelatin. Further research into the materials as tissue scaffolds determined that the strength of the DN hydrogels decreased when they were prepared at cell-compatible conditions, and the encapsulated cells in the DN hydrogels did not function as well as they did in gelatin hydrogels. In this work, we developed microgel-reinforced (MR) hydrogels from the same two polymers, which have better mechanical strength and biological properties in comparison to the DN hydrogels. The MR hydrogels were prepared by incorporating stiff GG microgels into soft and ductile gelatin hydrogels. The MR hydrogels prepared at cell-compatible conditions exhibited higher strength than the DN hydrogels and the gelatin hydrogels, the highest strength being 2.8 times that of the gelatin hydrogels. MC3T3-E1 preosteoblasts encapsulated in MR hydrogels exhibited as high metabolic activity as in gelatin hydrogels, which is significantly higher than that in the DN hydrogels. The measurement of alkaline phosphatase (ALP) activity and the amount of mineralization showed that osteogenic behavior of MC3T3-E1 cells was as much facilitated in the MR hydrogels as in the gelatin hydrogels, while it was not as much facilitated in the DN hydrogels. These results suggest that the MR hydrogels could be a better alternative to the DN hydrogels and have great potential as load-bearing tissue scaffolds.
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Tough hydrogels have emerged as a promising class of materials to target load-bearing applications, where the material has to resist multiple cycles of extreme mechanical impact. A variety of chemical interactions and network architectures have been used to enhance the mechanical properties and fracture mechanics of hydrogels. In recent years, the mechanical properties of high-performance hydrogels are benchmarked, however this is often incomplete as important variables like water content are largely ignored. In this review, we aim to clarify the reported mechanical properties of state-of-the-art tough hydrogels by providing a comprehensive library of fracture and mechanical property data. First, we briefly discuss modes of energy dissipation at work in tough hydrogels, which we use to categorize the individual data sets. Next, we introduce common methods for mechanical characterization of high-performance hydrogels, followed by a detailed analysis of the current materials and their (fracture) mechanical properties. Finally, we consider several current applications, compare high-performance hydrogels with natural materials, and discuss promising future opportunities of tough hydrogels.
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Hydrogels are there-dimensional polymer network in which the voids are filled with water.Hydrogels have been widely used in various fields including biomedical engineering.However,they have very limited applicability due to their poor mechanical strength.Therefore,many efforts have been focused on the enhancement of mechanical properties of hydrogels.This review mainly introduces some novel high strength hydrogels,such as slide-ring hydrogels,double network hydrogels,composite hydrogels and others and analyzes the factors affecting mechanical properties of hydrogels.Biocompatible,degradable,injectable,loading growth factor and high strength hydrogels as major research directions.
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