On the mechanical strength of biocompatible semi-IPNs of polyvinyl alcohol and polyacrylamide

Mishra, Shefali; Bajpai, R.; Katare, R.; Bajpai, Anjali

doi:10.1007/s00542-007-0427-9

Cited by 13 publications

(10 citation statements)

References 28 publications

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“…S2); evidently PAAm and PVA are not mutually soluble. 25 X-ray diffraction measurements confirmed the formation of crystallites ( Supplementary Fig. S3).…”

Section: Resultsmentioning

confidence: 60%

Stiff, strong, and tough hydrogels with good chemical stability

2014

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Most hydrogels have poor mechanical properties, severely limiting their scope of applications.Here we report on a hybrid hydrogel that combines extremely high stiffness, strength, and toughness, while maintaining physical integrity in electrolyte solutions. The hydrogel consists of a hydrophilic polymer network that is covalently cross-linked and a second polymer network that can crystallize. We show that the crystallites serve as physical cross-links for the second network.The crystallites contribute to the high stiffness and strength of the hydrogel; they unzip and dissipate energy under deformation, and reform due to the incompatibility of the two polymers in the hydrogel. The crystallite-toughened hydrogel can achieve an elastic modulus of 5 MPa, a strength of 2.5 MPa, and a fracture energy of 14,000 Jm -2 . Unlike alginate-based hybrid hydrogels, this hydrogel preserves its mechanical properties in electrolyte solutions and could be considered for further development in a variety of engineering applications. 20 Unfortunately, hydrogels synthesized using this method are compliant and brittle. 22 It is possible to achieve higher stiffness and toughness using a dry-anneal method, but only at the expense of a much lower water content ( Supplementary Fig. S1). 23 Muratoglu and coworkers polymerized acrylamide monomers in the pores of a PVA hydrogel to form uncross-linked chains, and showed that the equilibrium water content of the resulting gels increased with acrylamide content, while the coefficient of friction, tear strength and creep resistance decreased. 21Here we propose that a hybrid network of a crystalline polymer and a covalently crosslinked hydrophilic polymer may form a hydrogel with robust mechanical properties and good chemical stability: the crystalline polymer can generate a large number of crystallites to serve as physical cross-links that are both stable and reversible; the covalently cross-linked hydrophilic polymer maintain the elasticity of the network during deformation and controls the swelling of the hydrogel. We describe one such hybrid hydrogel that combines extremely high stiffness, strength, and toughness. The hydrogel consists of a hydrophilic polyacrylamide (PAAm) polymer network that is covalently cross-linked and a PVA network that forms crystallites. We show that the PVA crystallites result in a high cross-link density, thus producing a gel of remarkable stiffness and strength. The crystallites unzip under deformation, dissipating energy in the process and yielding a hydrogel with exceptional toughness. After deformation, unzipped crystallites recover at room temperature due to the incompatibility of the two polymers in the gel. The 4 crystallite-toughened hydrogel can achieve an elastic modulus of 5 MPa, a strength of 2.5 MPa, and a fracture energy of 14,000 Jm -2 . Moreover, these properties are stable, even in concentrated electrolyte solutions. ResultsWe prepared the hybrid hydrogels in a simple three-step protocol. First, we form a cross- Supplementary Fig. S2); e...

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“…S2); evidently PAAm and PVA are not mutually soluble. 25 X-ray diffraction measurements confirmed the formation of crystallites ( Supplementary Fig. S3).…”

Section: Resultsmentioning

confidence: 60%

Stiff, strong, and tough hydrogels with good chemical stability

2014

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“…These results suggest that these gels containing physical bonds may also contain mesoscale structure. In fact, phase separation was observed in PAAm-PVA gels (11,36). We also see that the β of PA gels and Ca-alginate/PAAm gels with ionic bonds is orders of magnitude smaller than the PAAm-PVA hydrogels without ionic bonds, which suggests that strong physical bonds play a role to suppress the crack growth in the slow mode regime.…”

Section: Respectively With the Global Elongation Ratio λmentioning

confidence: 74%

Mesoscale bicontinuous networks in self-healing hydrogels delay fatigue fracture

Cui

Sun

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

116

101

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Load-bearing biological tissues, such as muscles, are highly fatigue-resistant, but how the exquisite hierarchical structures of biological tissues contribute to their excellent fatigue resistance is not well understood. In this work, we study antifatigue properties of soft materials with hierarchical structures using polyampholyte hydrogels (PA gels) as a simple model system. PA gels are tough and self-healing, consisting of reversible ionic bonds at the 1-nm scale, a cross-linked polymer network at the 10-nm scale, and bicontinuous hard/soft phase networks at the 100-nm scale. We find that the polymer network at the 10-nm scale determines the threshold of energy release rateG0above which the crack grows, while the bicontinuous phase networks at the 100-nm scale significantly decelerate the crack advance until a transitionGtranfar aboveG0. In situ small-angle X-ray scattering analysis reveals that the hard phase network suppresses the crack advance to show decelerated fatigue fracture, andGtrancorresponds to the rupture of the hard phase network.

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“…29,31 The higher crystallinity also likely resulted in the higher tensile properties exhibited by PVA hydrogels (Table 1). 24,32…”

Section: Discussionmentioning

confidence: 99%

“…29,31 The higher crystallinity also likely resulted in the higher tensile properties exhibited by PVA hydrogels (Table 1). 24,32 Both PVA-only and PVA-PEG are pure PVA hydrogels synthesized by FT and theta gelation, respectively, but they exhibit different mechanical properties due to their distinct structures. PVA-PEG hydrogels have large vacant pores due to the bulky PEG phase separation, where phase is subsequently exchanged with water during rehydration.…”

Section: Discussionmentioning

confidence: 99%

Quantifying the lubricity of mechanically tough polyvinyl alcohol hydrogels for cartilage repair

Ling

Bodugoz-Senturk

Nanda

et al. 2015

Proc Inst Mech Eng H

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Polyvinyl alcohol hydrogels are biocompatible and can be used as synthetic articular cartilage. Their mechanical characteristics can be tailored by various techniques such as annealing or blending with other hydrophilic polymers. In this study, we quantified the coefficient of friction of various candidate polyvinyl alcohol hydrogels against cobalt-chrome alloy or swine cartilage using a new rheometer-based method. We investigated the coefficient of friction of polyvinyl alcohol-only hydrogels and blends with polyethylene glycol, polyacrylic acid, and polyacrylamide against swine cartilage and polished cobalt-chrome surfaces. The addition of the functional groups to polyvinyl alcohol, such as acrylamide (semi-interpenetrating network) and acrylic acid (blend), significantly reduced the coefficient of friction. The coefficient of friction of the polyvinyl alcohol-only hydrogel was measured as 0.4 ± 0.03 against cobalt-chrome alloy, and 0.09 ± 0.004 against cartilage, while those measurements for the polyvinyl alcohol-polyacrylic acid blends and polyvinyl alcohol-polyacrylamide semi-interpenetrating network were 0.07 ± 0.01 and 0.1 ± 0.003 against cobalt-chrome alloy, and 0.03 ± 0.001 and 0.02 ± 0.001 against cartilage, respectively. There was no significant or minimal difference in the coefficient of friction between samples from different regions of the knee, or animals, or when the cartilage samples were frozen for 1 day or 2 days before testing. However, changing lubricant from deionized water to ionic media, for example, saline or simulated body fluid, increased the coefficient of friction significantly.

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On the mechanical strength of biocompatible semi-IPNs of polyvinyl alcohol and polyacrylamide

Cited by 13 publications

References 28 publications

Stiff, strong, and tough hydrogels with good chemical stability

Stiff, strong, and tough hydrogels with good chemical stability

Mesoscale bicontinuous networks in self-healing hydrogels delay fatigue fracture

Quantifying the lubricity of mechanically tough polyvinyl alcohol hydrogels for cartilage repair

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