Complex Hydrogels Based on Multiply Interpenetrated Polymer Networks: Enhancement of Mechanical Properties via Network Multiplicity and Monomer Concentration

Abstract

We present the preparation and study of the compressive mechanical and swelling properties of multiply interpenetrated, from double to quintuple (5-fold), polymeric hydrogels based on N,N-dimethylacrylamide (DMAAm) crosslinked with N,N′-methylenebis(acrylamide) (MBAAm), using five different monomer concentrations, from 1 to 5 M. Our results showed enhancement of the fracture stress, fracture energy density, and Young's modulus with network multiplicity and DMAAm monomer concentration. Fracture strain was found to substantially improve only when increasing the monomer concentration from 1 to 3 M and network multiplicity from 1 to 2. The best-performing multiple polymer hydrogel was the quintuple network prepared at 5 M DMAAm concentrations, which exhibited a record fracture stress of 51 MPa, a fracture strain of 88%, a fracture energy density of 5.5 MJ m −3 , and a Young's modulus of 2.1 MPa. Normalized values of the fracture stress and fracture energy density calculated by multiplication of the corresponding original values by the aqueous swelling degrees also increased with network multiplicity and monomer concentration, suggesting a net gain in mechanical property enhancement, primarily originating from network multiplicity. Combined analysis of the swelling and Young's modulus measurements on the multiply interpenetrated polymeric hydrogels allowed the calculation of the concentration of the elastically ef fective polymer chains in the bulk, which was independent of monomer concentration but increased linearly with network multiplicity, suggesting a corresponding increase in the concentration of trapped entanglements and/or strain hardening.

On Going to a New Era of Microgel Exhibiting Volume Phase Transition

“…The design and use of cross-linking agents might be the key to the future of functional microgels. In the research of bulk gels, new technologies such as interpenetrating polymer network [ 97 , 98 ], nanocomposite gel [ 99 ], tetra-gel [ 100 ], and slide ring gel [ 101 ] have been applied to get the gels with a characteristic nanostructure.…”

Multiple Network Hydrogels: A Study of Their Nanoindentation Hardness

“…However, these electrical charges in the polymers may be undesired for certain applications involving, for example, biomacromolecules, such as proteins, DNA, RNA, or polysaccharides, which are usually also charged and may interact electrostatically with the DN hydrogel. The charge problem has since been addressed by the replacement of the polyelectrolyte first network by nonionic polymer first networks and their interpenetration more than once, and, in particular, twice, three and four times, leading to triple (TN), quadruple (QN), and quintuple (5 × N) networks, respectively, to make up for the much lower equilibrium swelling of the nonionic first network compared to its polyelectrolytic counterpart used in the classical DN hydrogels. The approaches of TN, QN, and 5 × N hydrogels were successful, by providing totally nonionic multiple network hydrogels with enhanced mechanical properties.…”

Multiply Interpenetrating Polymer Networks: Preparation, Mechanical Properties, and Applications

“…In 2018, our group [29] reported the preparation and study of the compressive mechanical properties of quintuple (5×N) polymer hydrogels (and also their SN, DN, TN and QN precursors) of DMAAm cross-linked with MBAAm, and using five different monomer concentrations, from 1 to 5 M. We found that as network multiplicity and DMAAm monomer concentration increased, fracture stress and Young’s modulus also increased. This resulted in the quintuple network prepared at 5 M DMAAm concentrations being the best-performing multiple polymer hydrogel, displaying a compressive fracture stress and a compressive Young’s modulus of 51 and 2.1 MPa, respectively.…”

“…In a very recent study [30], we used nanoindentation to characterize the hardness of some of the above-mentioned [29] multiple network hydrogels. Nanoindentation is a modern method for the characterization of the mechanical properties of even very fragile materials, with the requirement for only a small amount of sample.…”

“…Moreover, due the universality of this procedure, a great variety of monomers and cross-linkers can be employed, resulting in the preparation of TN hydrogels [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26] with unique physical or chemical properties. Very recently, the DN concept has been further extended by preparing quadruple-network (QN) hydrogels [27,28] and quintuple-network (5×N) hydrogels [29,30], which also possess enhanced mechanical properties.…”