Research Advances in Mechanical Properties and Applications of Dual Network Hydrogels (original) (raw)
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Nonionic Double and Triple Network Hydrogels of High Mechanical Strength
Macromolecules, 2014
Among the hydrogels prepared in recent years, double network (DN) hydrogels exhibit the highest compression strength, toughness, and fracture energies. However, synthesis of DN hydrogels with extraordinary mechanical properties is limited to polyelectrolyte networks, which hinders their widespread applications. Herein, we prepared nonionic DN and triple network (TN) hydrogels based on polyacrylamide (PAAm) and poly(N,N-dimethylacrylamide) (PDMA) with a high mechanical strength by sequential polymerization reactions. The TN approach is based on the decrease of the translational entropy of the second monomer upon its polymerization in the first network, so that additional solvent (third monomer) can enter into DN hydrogel to assume its new thermodynamic equilibrium. The first network of TN hydrogels comprises chemically cross-linked PAAm or PDMA while the second and third networks are linear polymers. To increase the degree of inhomogeneity of the first network hydrogel, an oligomeric ethylene glycol dimethacrylate was used as a cross-linker in the gel preparation. Depending on the concentration of the first network cross-linker and on the molar ratio of the second and third to the first network units, TN hydrogels contain 89−92% water and exhibit high compressive fracture stresses (up to 19 MPa) and compressive moduli (up to 1.9 MPa).
Double-network hydrogel with high mechanical strength prepared from two biocompatible polymers
Journal of Applied Polymer Science, 2009
Novel double-network (DN) hydrogels with high mechanical strength have been fabricated with two biocompatible polymers, poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG), through a simple freezing and thawing method. Some properties of the obtained hydrogels, such as the mechanical strength, rheological and thermodynamic behavior, drug release, and morphology, have been characterized. The results reveal that in sharp contrast to most common hydrogels made with simple natural or synthetic polymers, PVA/PEG hydrogels can sustain a compressive pressure as high as several megapascals, highlighting their potential application as biomedical materials. In addition, a model for describing the structural formation of PVA/PEG DN hydrogels is proposed: the condensed PVA-rich phase forms microcrystals first, which bridge with one another to form a rigid and inhomogeneous net backbone to support the shape of the hydrogel, and then the dilute PEG-rich phase partially crystallizes among the cavities or voids of the backbone; meanwhile, there are entanglements of molecular chains between the two polymers. Moreover, a mechanism is also proposed to explain the high mechanical strength of PVA/PEG DN hydrogels. It is suggested that the free motion of PEG clusters in the cavities of PVA networks can prevent the crack from growing to a macroscopic level because the linear PEG chains in the cavities effectively absorb the crack energy and relax the local stress either by viscous dissipation or by large deformation of the PEG chains. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Biomechanical properties of high-toughness double network hydrogels
Biomaterials, 2005
This study evaluated the wear property of four novel double-network (DN) hydrogels, which was composed of two kinds of hydrophilic polymers, using pin-on-flat wear testing. The gels involve PAMPS-PAAm gel which consists of poly(2-acrylamide-2metyl-propane sulfonic acid) and polyacrylamide, PAMPS-PDAAAm gel which consists of poly(2-acrylamide-2-metyl-propane sulfonic acid) and poly(N,N 0 -dimetyl acrylamide), Cellulose/PDMAAm gel which consists of bacterial Cellulose and poly dimetylacrylamide, and Cellulose-Gelatin gel which consists of bacterial Cellulose and Gelatin. Ultra-high molecular weight polyethylene (UHMWPE) was used as a control of a clinically available material. Using a reciprocating apparatus, 10 6 cycles of friction between a flat specimen and ceramic pin were repeated in water under a contact pressure of 0.1 MPa. To determine the depth and the roughness of the concave lesion created by wear, a confocal laser microscope was used. As a result, the maximum wear depth of the PAMPS-PDMAAm gel (3.20 mm) was minimal in the five materials, while there was no significant difference compared to UHMWPE. There were significant differences between UHMWPE and one of the other three gels. The PAMPS-PAAm gel (9.50 mm), the Cellulose-PDMAAm gel (7.80 mm), and the Cellulose-Gelatin gel (1302.40 mm). This study demonstrated that the PAMPS-PDMAAm DN gel has an amazing wear property as a hydrogel that is comparable to the UHMWPE. In addition, the PAMPS-PAAm and Cellulose-PDMAAm DN gels are also resistant to wear to greater degrees than conventionally reported hydrogels. On the other hand, this study showed that the Cellulose-Gelatin DN gel was not resistant to wear. r
Engineering the Microstructure of Hydrogels to Achieve Enhanced Mechanical Properties
Hydrogels are three-dimensional, cross-linked, polymeric networks that are typically soft materials that contain more than 90% water. Many technologies require hydrogels with improved mechanical properties (modulus, failure properties and toughness). Drawing inspiration from biological systems that are complex and highly ordered, yet constructed efficiently, this dissertation advances understanding of multi-component hydrogels. This work also develops correlating relationships of composition, water content, microstructure network properties and mechanical properties. This dissertation investigates three multi-component hydrogel systems which fall into the category of interpenetrating network (IPN): two or more networks which are interlaced, independent of each other and each network is covalently cross-linked. (1) Semi-IPN hydrogels: A subcategory of IPNs in which two or more networks are interlaced and independent of each other, but one is chemically cross-linked and one is an entangled polymer. A systematic study of the formulations of single-network (SN) and semi-IPNs of agarose and poly(ethylene glycol) diacrylate (PEGDA) showed that these gels typically exhibited an effect somewhat greater than the sum of the two component SNs, in moduli, fracture stress and toughness. The semi-IPNs of agarose/PEGDA also behaved as ideal elastomers. Imaging hydrated semi-IPNs of agarose/PEGDA using scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that the semi-IPNs had pores sizes that are between the two SNs, 1-4 μm pores. The pore size decreased as the PEGDA concentration was increased. (2) Double-network (DN) hydrogels: A subcategory of IPNs in which two independent, I want first want to acknowledge my committee members Drs. Stevin Gehrke, Cory Berkland, Michael Detamore, Paulette Spencer and Laird Forrest for their intellect, support and suggestions as well as challenging me though out my PhD journey. I also would like to acknowledge many of the professors inside and outside of the chemical engineering department who helped my academic career, particularly, Drs.
Toughening of Hydrogels with Double Network Structure
e-Journal of Surface Science and Nanotechnology, 2005
Hydrogels are made of swollen polymer networks containing more than 90% water. If modified with free chains on their surface, gels exhibit low surface friction and thus have been attractive candidates as artificial cartilage and low frictional materials. However, most hydrogels are mechanically too weak to be used as any load bearing devices. We have overcome this problem by synthesizing hydrogels with a double network (DN) structure. Despite of 90% water, these tough gels exhibit a fracture stress of 170 kg/cm 2 , similar to that of cartilage. Extremely high mechanical property is due to peculiarly inhomogeneous structure of DN gels. The inhomogeneous structure is thought that large 'voids' of the first network may exist, and the second polymers exist in 'voids' of first network act as 'molecular crack-stopper' in DN gels, keeping the crack from growing to a macroscopic level.
J. Mater. Chem. B, 2015
A novel physically linked double-network (DN) hydrogel based on natural polymer konjac glucomannan (KGM) and synthetic polymer polyacrylamide (PAAm) has been successfully developed. Polyvinyl alcohol (PVA) was used as a macro-crosslinker to prepare the PVA-KGM first network hydrogel by a cycle freezing and thawing method for the first time. Subsequent introduction of a secondary PAAm network resulted in super-tough DN hydrogels. The resulting PVA-KGM/PAAm DN hydrogels exhibited unique ability to be freely shaped, cell adhesion properties and excellent mechanical properties, which do not fracture upon loading up to 65 MPa and a strain above 0.98. The mechanical strength and microstructure of the DN hydrogels were investigated as functions of acrylamide (AAm) content and freezing and thawing times. A unique embedded micro-network structure was observed in the PVA-KGM/PAAm DN gels and accounted for the significant improvement in toughness. The fracture mechanism is discussed based on the yielding behaviour of these physically linked hydrogels. † Electronic supplementary information (ESI) available: The frequency (a) and amplitude (b) dependence of storage modulus G 0 of the PVA-KGM hydrogels; the frequency (a) and amplitude (b) dependence of storage modulus G 0 of the PVA-KGM/PAAm DN hydrogels; the effect of MBAA concentration on the compressive strength of the PVA-KGM/PAAm DN hydrogel. See
Journal of Applied Polymer Science, 2013
Hydrogels are polymer networks swollen in water. Because of their soft and wet nature, and their ability to show large volume changes, hydrogels can be useful in many biomedical and actuator applications. In these applications, it is crucial to tune the mechanical and physical properties of a hydrogel in a controllable manner. Here, interpenetrating polymer networks (IPNs) made of a covalently crosslinked network and an ionically crosslinked network were produced to investigate the effective parameters that control the physical and mechanical properties of an IPN hydrogel. Covalently crosslinked polyacrylamide (PAAm) or poly(acrylic acid) (PAA) networks were produced in the presence of alginate (Alg) that was then ionically crosslinked to produce the IPN hydrogels. The effect of ionic crosslinking, degree of covalent crosslinking, AAm : Alg and AA : Alg ratio on the swelling ratio, tensile properties, indentation modulus, and fracture energy of IPN hydrogels was studied. A hollow cylindrical hydrogel with gradient mechanical properties along its length was developed based on the obtained results. The middle section of this hydrogel was designed as a pH triggered artificial muscle, while each end was formulated to be harder, tougher, and insensitive to pH so as to function as a tendonlike material securing the gel muscle to its mechanical supports.
A simple route to interpenetrating network hydrogel with high mechanical strength
Journal of Colloid and Interface Science, 2009
A simple two-step method was introduced to improve the hydrogel mechanical strength by forming an interpenetrating network (IPN). For this purpose, we synthesized polyacrylate/polyacrylate (PAC/PAC), polyacrylate/polyacrylamide (PAC/PAM), polyacrylamide/polyacrylamide (PAM/PAM) and polyacrylamide/poly(vinyl alcohol) (PAM/PVA) IPN hydrogels. The PAC/PAC IPN and PAC/PAM IPN hydrogels showed compressive strength of 70 and 160 kPa, respectively. For the PAM/PAM IPN and PAM/PVA IPN hydrogels, they exhibited excellent tensile strength of 1.2 and 2.8 MPa, and elongations at break of 1750% and 3300%, respectively. A strain relaxation was also observed in the case of PAM series IPN hydrogels. From FTIR, TGA and SEM measurements, we confirmed that physical entanglement, hydrogen bonds and chemical crosslinking played major roles in improving hydrogel strength and toughening. The twostep technique contributes to the understanding of ideal networks, provides a universal strategy for designing high mechanical strength hydrogels, and opening up the biomedical application of hydrogels.
Smart Hydrogels Developed with Inter-Crosslinking Network (ICN) Structure
Journal of Solid Mechanics and Materials Engineering, 2013
Hydrogels have low frictional properties, permeability and biocompatibility thanks to their high water content. However the problem of common gels is their brittleness as industrial materials. In the last decade, several high-strength gels have been developed, promising for applications of gels as new smart industrial materials. Here we study the smartness of novel ultrahigh ductile gels having Inter-Crosslinking Network (ICN), focusing on mechanical properties and structure. Three types of mesh densities of the ICN gels were experimentally determined from the size of internal structure, water content and Young's modulus of tensile test. By comparing the three mesh densities, the relation between the network structure and mechanical properties of the gels is possibly discussed. The new way to evaluate the ductility of the ICN gels was also introduced on the analogy of the small-world network model. The effect of the degree of polymerization on the ductility was discussed.