Nanoscaled Morphology and Mechanical Properties of a Biomimetic Polymer Surface on a Silicone Hydrogel Contact Lens

Abstract

Materials taking advantage of the characteristics of biological tissues are strongly sought after in medical science and bioscience. On the natural corneal tissue surface, the highly soft and lubricated surface is maintained by composite structures composed of hydrophilic biomolecules and substrates. To mimic this structure, the surface of a silicone hydrogel contact lens was modified with a biomimetic phospholipid polymer, poly­(2-methacryloyloxyethyl phosphorylcholine) (PMPC), and the nanoscaled morphology and mechanical properties of the surface were confirmed with advanced surface characterization and imaging techniques under an aqueous medium. Concavities and convexities on the nanometer order were recognized on the surface. The surface was completely covered with a PMPC layer and remained intact even after 30 days of clinical use in a human ocular environment. The mechanical properties of the natural corneal tissue and the PMPC-modified surface were similar in the living environment, that is, low modulus and frictional properties comparable to natural tissues. These results show the validity of material preparation by biomimetic methods. The methodologies developed in this study may contribute to future development of human-friendly medical devices.

Surface characterization of an ultra-soft contact lens material using an atomic force microscopy nanoindentation method

“…Scanning transmission electron microscopy (STEM) of sample cross-sections and atomic force microscopy (AFM) of surfaces were employed to conduct a comprehensive imaging of the ultra-soft biomimetic materials examined in this study. This detailed surface characterization was carried out as an extension of our previously published work, where we established that the dynamic branched, polymer-brush structure at the surface of the PMPC-modified lehfilcon A CL exhibits mechanical properties similar to natural corneal tissue 14 . For this reason, we refer to the contact-lens surface as a biomimetic material 14 .…”

“…This detailed surface characterization was carried out as an extension of our previously published work, where we established that the dynamic branched, polymer-brush structure at the surface of the PMPC-modified lehfilcon A CL exhibits mechanical properties similar to natural corneal tissue 14 . For this reason, we refer to the contact-lens surface as a biomimetic material 14 . Figure 3 a,b show cross-sections of the branched PMPC polymer-brush structure on the lehfilcon A CL and the surface of the untreated SiHy base substrate, respectively.…”

“…In our previous work, we presented the lehfilcon A contact lens (CL)—a soft, heterogeneous material that derives all of its ultra-soft surface properties from the underlying biomimetic design, inspired by the ocular corneal surface 14 . This biomaterial was engineered by grafting a branched, crosslinked poly (2-methacryloyloxyethyl phosphorylcholine (MPC)) (PMPC) polymeric layer to a medical-device-grade silicone hydrogel (SiHy) base substrate 15 .…”

Recent progress and perspectives in applications of 2-methacryloyloxyethyl phosphorylcholine polymers in biodevices at small scales

“…4C shows the surface modification procedure and highlights the two advantages of the DMA-MPC-modified surface: (1) bacterial inhibition, which reduces infection, and (2) lubricant formation, which improves the wear performance. In ophthalmology, the synthesis of MPC polymers via free radical polymerization, ATRP, or RAFT have been attempted before merging into interpenetration networks (IPN) such as poly(MPC-co-bis(trimethylsilyloxy)methylsilylpropyl glycerol methacrylate), 99 2-hydroxyethyl methacrylate hydrogel, 104 collagen networks, 100,105,109,110 and silicone hydrogel, 103,106,111,112 to create small optical devices. In addition, MPC polymers can be grafted on small optical devices by spin coating, 113 plasma technology, 107 and salinization 114 etc.…”

Soft Contact Mechanics with Gradient-Stiffness Surfaces

“…However, the confounding problem of interpreting the force–depth data is that the integrated force response at a particular depth necessarily includes the mechanics of the surface to that depth and below. In response, researchers have taken a variety of approaches, starting with the most simple of fitting data to classical and established contact models: Hertz, JKR, and others. − Others have moved beyond homogeneous models to acknowledge a single softer layer atop a stiffer one, ,, with associated elastic foundation models. Whether a half-space or a single laminate surface, both of these models assume homogeneity and linear elasticity.…”