Interactions Affecting the Mechanical Properties of Macromolecular Microsphere Composite Hydrogels

Abstract

Macromolecular microsphere composite (MMC) hydrogel is a kind of tough hydrogel fabricated by using peroxidized macromolecular microspheres as polyfunctional initiating and cross-linking centers (PFICC). The contribution of chemical cross-linking (covalent bonding) and physical cross-linking (chain entanglement and hydrogen bonding) to the mechanical properties are understood by testing the hydrogels, which were swollen in water or aqueous urea solutions to different water contents. The as-prepared MMC gels exhibited moderate moduli (60-270 kPa), high fracture tensile stresses (up to 0.54 MPa), high extensibilities (up to 2500%), and high fracture energies (270-770 J m(-2)). The moduli of the swollen gels decrease dramatically, but there are no significant changes in fracture tensile strength and fracture strain, even slight increases. More interestingly, the swollen gels show much-enhanced fracture energies, higher than 2000 J m(-2). A gradual decrease in the hysteresis ratio and residual strain is also found in the cyclic tensile testing of the hydrogels that were swollen to different water contents. The covalent bonding determines the tensile strength and fracture energy of the MMC gels, whereas the physical entanglement and hydrogen bonding among the polymer chains contributes mainly to the modulus of the MMC gels, and they are also the main reason for the presence of hysteresis in the loading-unloading cycles.

Microgel reinforced composite hydrogels with pH-responsive, self-healing properties

“…This result is different from other microgel reinforced hydrogels having been reported [36,39,[43][44][45], in which the strength increase with the rising microgels concentration. This is likely due to the different concentrations of polymer solutions.…”

“…Recently, a successful approach to fabricate higher strength composite hydrogels via microgels as cross-linkers has been proposed by several groups [31][32][33][34][35][36][37][38][39][40][41][42][43]. In general, the MC gels were fabricated by using ␥-ray [44], UV [38] or tertbutylhydroperoxide [45] to introduce peroxy groups onto the surfaces of the evenly distributed microgels, and then polymer chains covalently attached to the microgels through the grafting polymerization of monomers initiated by the microgels.…”

Bioprinting Using Mechanically Robust Core–Shell Cell‐Laden Hydrogel Strands

“…The strengths of the hybrids were much higher than the sums of the individual components, suggesting a synergistic effect (Figure S3, Supporting Information). This synergistic effect is likely due to the entanglement of alginate and PEGDA chains; chain entanglement in hydrogels is a contributor to their mechanical properties . The 9:2 and 8:3 hybrid gels showed an increase in all three mechanical properties (modulus, UTS, and failure strain) compared to pure alginate gels, with a maximum 65% increase in UTS for the 8:3 hybrid gels (Table S1, Supporting Information).…”

Mechanical properties of tough hydrogels synthesized with a facile simultaneous radiation polymerization and cross-linking method

“…The G of the hydrogels synthesized with 20 wt.% solution were in the range of 20-160 J/m 2 , whereas those synthesized with 10 wt.% solution were in the range of 10-34 J/m 2 . Both are bigger than those of normal PAAm hydrogels (10 0 J/m 2 ), but less than those of DN gels (10 2~1 0 3 J/m 2 )(Furukawa et al 2008;Tanaka et al 2005b) and MMC gels (up to 2×10 3 J/m 2 )(Jiang et al 2013).…”