Exploring the Role of Nanoparticles in Enhancing Mechanical Properties of Hydrogel Nanocomposites

Abstract

Over the past few decades, research studies have established that the mechanical properties of hydrogels can be largely impacted by the addition of nanoparticles. However, the exact mechanisms behind such enhancements are not yet fully understood. To further explore the role of nanoparticles on the enhanced mechanical properties of hydrogel nanocomposites, we used chemically crosslinked polyacrylamide hydrogels incorporating silica nanoparticles as the model system. Rheological measurements indicate that nanoparticle-mediated increases in hydrogel elastic modulus can exceed the maximum modulus that can be obtained through purely chemical crosslinking. Moreover, the data reveal that nanoparticle, monomer, and chemical crosslinker concentrations can all play an important role on the nanoparticle mediated-enhancements in mechanical properties. These results also demonstrate a strong role for pseudo crosslinking facilitated by polymer–particle interactions on the observed enhancements in elastic moduli. Taken together, our work delves into the role of nanoparticles on enhancing hydrogel properties, which is vital to the development of hydrogel nanocomposites with a wide range of specific mechanical properties.

Role of Nanoparticle-Polymer Interactions on the Development of Double-Network Hydrogel Nanocomposites with High Mechanical Strength

“…Not surprisingly, we observed that both pAAM and alginate concentrations played an important role on SiNP-mediated enhancements in the modulus of pAAm-alginate DN hydrogels. The decreasing role of nanoparticles with increasing polymer concentrations observed in this study, for pAAm-alginate DN hydrogels, is consistent with previous studies that demonstrate a decreased impact of nanoparticles on the hydrogel modulus at higher monomer concentrations [15]. Values for relative elastic modulus were calculated by normalizing the values for the hydrogel nanocomposites to those for neat hydrogels not containing SiNPs.…”

“…Our results indicated the existence of a 'global' saturation point for DN hydrogel nanocomposites, beyond which it becomes less plausible to enhance elastic modulus by simply increasing the concentration of the second network hydrogel or nanoparticles. A similar phenomenon previously reported for single-network hydrogels describes that saturations in the combined crosslinking density (i.e., the sum of chemical crosslinker-and nanoparticle-mediated crosslinking densities) may lead to upper limits in the gains in elastic modulus achievable through the addition of nanoparticles [15]. In summary, the mechanistic understandings previously derived using single-network hydrogel systems may be applied to guide the design of DN hydrogel nanocomposites for various applications that directly benefit from the development of hydrogels with high mechanical strengths.…”

“…One approach that has gained significant interest over the past couple of decades is the incorporation of nanoparticles, which can enable the formation of additional crosslinks within the polymer network and contribute to enhancements in the mechanical strength of hydrogels. It has been shown that nanoparticle mediated physical crosslinking can complement chemical crosslinking and that the combination of chemical and physical crosslinking can lead to enhancements in elastic modulus greater than with either alone [14][15][16]. However, previous work suggests that there might be an upper limit to enhancements in mechanical strength achievable through the addition of nanoparticles, possibly due to the existence of a saturation point in the gains achievable through a combination of chemical and physical crosslinking [15,18].…”

“…It has been shown that nanoparticle mediated physical crosslinking can complement chemical crosslinking and that the combination of chemical and physical crosslinking can lead to enhancements in elastic modulus greater than with either alone [14][15][16]. However, previous work suggests that there might be an upper limit to enhancements in mechanical strength achievable through the addition of nanoparticles, possibly due to the existence of a saturation point in the gains achievable through a combination of chemical and physical crosslinking [15,18]. Another method to improve the mechanical strength of hydrogels is to create hybrid hydrogels by combining two different polymers with contrasting properties [19].…”

Role of Nanoparticle–Polymer Interactions on the Development of Double-Network Hydrogel Nanocomposites with High Mechanical Strength

“…One approach that has gained significant interest over the past couple of decades is the incorporation of nanoparticles, which can enable the formation of additional crosslinks within the polymer network and contribute to enhancements in the mechanical strength of hydrogels. It has been shown that nanoparticle-mediated physical crosslinking can complement chemical crosslinking and that the combination of chemical and physical crosslinking can lead to enhancements in an elastic modulus that is greater than with either alone [14][15][16]. However, previous work suggests that there might be an upper limit to enhancements in mechanical strength achievable through the addition of nanoparticles, possibly due to the existence of a saturation point in the gains achievable through a combination of chemical and physical crosslinking [15,17,18].…”