In this article, the multicomponent copolymers were prepared by the copolymerization of two hydrophobic silicon-containing monomers bis(trimethylsilyloxy) methylsilylpropyl glycerol methacrylate (SiMA) and tris(trimethylsiloxy)-3-methacryloxypropylsilane (TRIS) with three hydrophilic monomers 2-hydroxyethyl methacrylate, N-vinylpyrrolidone, and N,N-dimethyl acrylamide. The copolymers were hydrated to form transparent silicone hydrogels. The oxygen permeability coefficients (Dk) of hydrogels were measured, and their relationships with the equilibrium water contents (EWC) and the types and contents of silicon containing monomers as well as the phase separation structures of silicone hydrogels were analyzed in detail. The results showed that the EWC decreased as the increase of SiMA content. The relationship between Dk and SiMA content, as well as that between Dk and EWC, showed inverted bell curve distributions, which meant two main factors, i.e., silicon-oxygen bond in silicone and water in hydrogel, contributed to oxygen permeation and followed a mutual inhibition competition mechanism. The internal morphologies of the hydrogels were observed by transmission electron microscope, and the results showed that the hydrogels presented two different phase separation structures depending on the types of the silicon-containing monomers. The silicone phase in SiMA containing hydrogel presented to be a granular texture, while the silicone phase in TRIS containing hydrogel formed a fibrous texture which resulted in a higher Dk value. These results could help to design a silicone hydrogel with better properties and wider application.

Three series of multicomponent silicone hydrogels were prepared by the copolymerization of two hydrophobic silicon monomers bis(trimethylsilyloxy) methylsilylpropyl glycerol methacrylate (SiMA) and tris(trimethylsiloxy) 3-methacryloxypropylsilane (TRIS) with three hydrophilic monomers. The surface hydrophilicity of the silicone hydrogels was characterized by contact angle measurements, and an interesting phenomenon was found that the silicone hydrogels made from less hydrophobic monomer SiMA possess more hydrophobic surfaces than those made from TRIS. The surface properties such as morphology and elemental composition of the silicone hydrogels were explored by scanning electron microscopy (SEM) imaging and energy dispersive spectrometry (EDS) analysis, and their relationships with the surface hydrophilicity were investigated in details. The results show neither the surface morphology nor the elemental composition has obvious impact on the surface hydrophilicity. Atomic force microscopy (AFM) imaging revealed that SiMA hydrogel had a more significant phase separation structure, which also made its surface uneven: a lot of tiny holes were observed on the surface. This surface phase separation structure made SiMA hydrogel more difficult to be wetted by water or PBS buffer, i.e., more hydrophobic than TRIS hydrogel. On the basis of these results, we propose that the phase separation structure as well as the nature of silicon monomers might be the fundamental reasons of surface hydrophilicity. These results could help to design a silicone hydrogel with better surface properties and wider application.

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