Biomimetic-Engineered Silicone Hydrogel Contact Lens Materials

Abstract

Contact lenses are one of the most successful applications of biomaterials. The chemical structure of the polymers used in contact lenses plays an important role in determining the function of contact lenses. Different types of contact lenses have been developed based on the chemical structure of polymers. When designing contact lenses, materials scientists consider factors such as mechanical properties, processing properties, optical properties, histocompatibility, and antifouling properties, to ensure long-term wear with minimal discomfort. Advances in contact lens materials have addressed traditional issues such as oxygen permeability and biocompatibility, improving overall comfort, and duration of use. For example, silicone hydrogel contact lenses with high oxygen permeability were developed to extend the duration of use. In addition, controlling the surface properties of contact lenses in direct contact with the cornea tissue through surface polymer modification mimics the surface morphology of corneal tissue while maintaining the essential properties of the contact lens, a significant improvement for long-term use and reuse of contact lenses. This review presents the material science elements required for advanced contact lenses of the future and summarizes the chemical methods for achieving these goals.

Keywords: Silicone hydrogel; antifouling; contact lens materials; lubricity; phosphorylcholine; surface modification.

Figure 1

Chemical structure of representative monomers for the preparation of contact lenses. Monomers mainly used in PHEMA-based hydrogel contact lenses are shown with a blue background, and typical monomers used in silicone hydrogel-based contact lenses are shown with a yellow background. Hydrophilic monomers used in both contact lenses are shown in yellow blocks.

Figure 2

Relationship between equilibrium water content and oxygen permeation of contact lenses.

Figure 3

Schematic representation of phase separation in silicone hydrogel materials.

Figure 4

Molecular design of 2-methacryloyloxyethyl phosphorylcholine inspired by cell membrane structure.

Figure 5

Structure of corneal epithelial surface. (a) Schematic diagram of glycocalyx on the surface of human corneal epithelial cells and (b) interface of corneal tissue.

Figure 6

Biomimetic surface preparation on the silicone hydrogel contact lens. (a) Immobilization of hyaluronic acid. [Reproduced with permission from ref (). Copyright 2018, American Chemical Society, Washington, DC.] (b) Immobilization of proteoglycan and surface functions. [Reproduced with permission from ref (120). Copyright 2021, American Chemical Society, Washington, DC.]

Figure 7

Method for compositing silicone-derived polymers with the MPC polymers.

Figure 8

Modification of silicone substrate by the MPC polymers. (a) Interpenetration network formation between PDMS and MPC polymers. The depth profile of the MPC polymer penetration is observed by infrared microscopy, and the relationship between MPC polymer content and oxygen permeability is indicated. [Reproduced with permission from ref (). Copyright 2010, Elsevier.] (b) The chemical reaction of photoinduced graft polymerization of MPC on PDMS substrate and friction coefficient at the surface under an aqueous medium. [Reproduced with permission from ref (134). Copyright 2008, Elsevier.]

Figure 9

Surface modification of silicone substrate by surface-initiated atom transfer polymerization. (a) Immobilization of an initiator and grafting procedure on silicone hydrogel substrate. Protein adsorption resistance after grafting the poly(MPC) is indicated. [Reproduced with permission from ref (140). Copyright 2020, American Institute of Physics.] (b) Surface-initiated atom transfer polymerization of MPC on model PDMS substrate and bacteria adhesion inhibition performance is indicated. [Reproduced with permission from ref (132). Copyright 2019, American Chemical Society, Washington, DC.]

Figure 10

Surface analysis of MPC polymer-grafted silicone hydrogel contact lens, lehfilcon A. Surface is observed by (a) ESEM under 100% humidity and (b) AFM under water. (c) Surface atom analysis is carried out by XPS and (d) the distribution of phosphate atoms at the surface is determined. [Reproduced with permission from ref (141). Copyright 2021, Elsevier.]

Figure 11

(a) Transmission electron microscopy (TEM) images of a cross-section of the interface of silicone hydrogel substrate and that grafted with the MPC polymer, and natural corneal tissue. (b) AFM images at the surface are also indicated. (c) Surface electric modulus of various substrates and natural corneal tissue is indicated. [Reproduced with permission from ref (142). Copyright 2021, American Chemical Society, Washington, DC.]

Figure 12

Lipid adsorption and absorption after the various silicone hydrogel contact lens immersed in the artificial tear lipid solution for 30 days or 14 days (*). Fluorescent staining of cholesterol ester lipids and triglyceride lipids was carried out and then observed by fluorescence microscopy. [Reproduced with permission from ref (158). Copyright 2022, The Association for Research in Vision and Ophthalmology.]