Abstract
Extensive experimental and theoretical research over the past several decades has pursued strategies to develop hydrogels with high mechanical strength. Our study investigated the effect of combining two approaches, addition of nanoparticles and crosslinking two different polymers (to create double-network hydrogels), on the mechanical properties of hydrogels. Our experimental analyses revealed that these orthogonal approaches may be combined to synthesize hydrogel composites with enhanced mechanical properties. However, the enhancement in double network hydrogel elastic modulus due to incorporation of nanoparticles is limited by the ability of the nanoparticles to strongly interact with the polymers in the network. Moreover, double-network hydrogel nanocomposites prepared using lower monomer concentrations showed higher enhancements in elastic moduli compared to those prepared using high monomer concentrations, thus indicating that the concentration of hydrogel monomers used for the preparation of the nanocomposites had a significant effect on the extent of nanoparticle-mediated enhancements. Collectively, these results demonstrate that the hypotheses previously developed to understand the role of nanoparticles on the mechanical properties of hydrogel nanocomposites may be extended to double-network hydrogel systems and guide the development of next-generation hydrogels with extraordinary mechanical properties through a combination of different approaches.
Highlights
Unique properties of hydrogels have enabled their use in a wide range of applications in biotechnology, bioengineering, and medicine [1,2]
Consistent with the hypothesis and measurements of elastic modulus, the values for relative swellability of pAAm-agarose and pAAm nanocomposites were comparable. These results indicated that the lack of enhancements in the elastic modulus of pAAm-agarose nanocomposites relative to pAAm nanocomposites can be explained by limited interactions between agarose and silica nanoparticles (SiNPs), which dilutes the positive impact of nanoparticles on the modulus of DN hydrogels prepared using agarose
SiNPs were chosen as a model nanoparticle, given its ability to positively interact with pAAm and serve as a pseudo crosslinker to enhance the extent of crosslinking in the polymer network [25]
Summary
Unique properties of hydrogels have enabled their use in a wide range of applications in biotechnology, bioengineering, and medicine [1,2]. Researchers have taken advantage of the ability of hydrogels to swell or shrink in response to external stimuli (e.g., pH, temperature) to develop biosensors for the detection of biomolecules [4,5]. Their highly porous and hydrated polymer structure mimics the extracellular cellular matrix and renders them highly suitable for in vitro cell culture, and several studies have demonstrated the successful use of hydrogels to encapsulate mammalian cells in a 3D physiological-like environment and develop in vitro models of cell proliferation, migration, and differentiation [6,7,8,9,10]. Hydrogels cannot mimic stiffer tissues, which hinders their use for orthodontic or orthopedic applications [12,13]
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