Surface-dependent effect of functional silica fillers on photocuring kinetics of hydrogel materials

Modification of Thiol-Ene Ionogels with Octakis(methacryloxypropyl) Silsesquioxane

The effect of polyhedral oligomeric silsesquioxane (POSS) on the synthesis and properties of hybrid organic–inorganic ionogels was investigated using octakis(methacryloxypropyl) silsesquioxane (methacryl-POSS). Ionogels were prepared in situ by thiol-ene photopolymerization of triallyl isocyanurate with pentaerythritol tetrakis(3-mercaptopropionate) in a mixture of imidazolium ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImNTf₂) and propylene carbonate (PC). Investigations included the kinetics of hybrid materials formation and selected physical and mechanical properties. The disadvantage of ionogels without the methacryl-POSS modifier is leakage and insufficient mechanical properties. Modifying the thiol-ene matrix by the addition of methacryl-POSS made it possible to obtain non-leaking ionogels with improved mechanical and conductive properties. The steric hindrance of POSS cages and high-density network formation played important roles in ionogel synthesis: decrease of polymerization rate (with almost no effect on conversion), as well as dimensions of the formed polymer spheres during dispersion polymerization (highly cross-linked polymer has poorer solubility in polymerizing medium at a similar conversion, and nucleation begins at lower conversion), an increase of glass transition temperature and puncture strength. Hybrid ionogels with high ionic conductivity in the range of 4.0–5.1 mS∙cm⁻¹ with the maximum parameter for 1.5 wt.% addition of the methacryl-POSS were obtained, which can be associated with ion-pair dissociations in ionic liquid clusters caused by methacryl-POSS.

High-Performance Photopolymerized Poly(vinyl alcohol)/Silica Nanocomposite Hydrogels with Enhanced Cell Adhesion

Poly(vinyl alcohol) (PVA) hydrogels have been considered as promising implants for various soft tissue engineering applications because of their tissue-like viscoelasticity and biocompatibility. However, two critical barriers including lack of sufficient mechanical properties and non-tissue-adhesive characterization limit their application as tissue substitutes. Herein, PVA is methacrylated with ultralow degrees of substitution of methacryloyl groups to produce PVA-glycidyl methacrylate (GMA). Subsequently, the PVA-GMA/methacrylate-functionalized silica nanoparticle (MSi)-based nanocomposite hydrogels are developed via the photopolymerization approach. Interestingly, both PVA-GMA-based hydrogels and PVA-GMA/MSi-based nanocomposite hydrogels exhibit outstanding compressive properties, which cannot be damaged through compressive stress-strain tests in the allowable scope of a tensile tester. Moreover, PVA-GMA/MSi-based nanocomposite hydrogels demonstrate excellent tensile properties compared with neat PVA-GMA-based hydrogels, and 15-, 14-, and 24-fold increase in fracture stress, elastic modulus, and toughness, respectively, is achieved for the PVA-GMA/MSi-based hydrogels with 10 wt % of MSi. These remarkable enhancements can be ascribed to the amount of long and flexible polymer chains of PVA-GMA and the strong interactions between the MSi and PVA-GMA chains. More interestingly, exciting improvements in the cell adhesion can also be successfully achieved by the incorporation of MSi nanoparticles.