Author's personal copy Bionic soft crystalline lens materials for MEMs applications based on self-assembling amphiphilic block copolymer/nanoparticle hybrids Chun-Jie Chang a , Yi-Lung Yang a , Yu-Ping Lee b , Chi-Ju Chiang b , Chi-An Dai a,b,⇑ , Jyh-Chien Chen d , Yao-Yi Cheng e , Chien-Chun Chen b , Ming-Wei Liu f , Wen-Pin Shih c , Jia-Yush Yen c a Institute of Polymer Science and Engineering, National Taiwan University, Taipei 106, Taiwan b Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan c Department of Mechanical Engineering, National Taiwan University, Taipei 106, Taiwan d Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan e Institute of Organic and Polymeric Materials, National Taipei University of Technology, Taipei 106, Taiwan f Taiwan Adventist Hospital, Taipei 106, Taiwan article info Article history: Available online 21 December 2010 Keywords: Artificial lens Nanoparticles Soft materials UV crosslinking abstract In this study, a biomimetic crystalline lens with properties that combine the softness of a hydrogel com- parable to that of a human lens for adjustable focus and the property for image aberration correction with gradient refractive index (GRIN) was developed by the self-organization of an amphiphilic block copoly- mer blended with high refractive index titanium nanoparticles (TiO 2 ). The hydrogel lens was prepared by using a thermally responsive poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PPO– PEO–PPO) triblock copolymer (Poloxamer 407) with the lower-critical solution temperature (LCST) property that can be injectable into the eye capsule as a liquid below its LCST and solidifies as a soft gel above the LCST at the human body temperature. By chemical modification of the triblock copolymer with double bonds on its chain-ends (Poloxamer 407A), the soft lens network can be made by using UV crosslinking of the hydrogel. To further increase the refractive index (RI) of the hydrogel lens network and to match its RI to that of the human lens (=1.41), highly visible-light transparent titanium dioxide (TiO 2 ) nanoparticles were introduced into the hydrogel lens network. To create a biomimetic GRIN lens as in the human’s eyes, an electric field method was also used to induce an axial diffusion of TiO 2 nanoparticles from the center of the lens where TiO 2 nanoparticles were first injected to the edge. The above method demonstrates the potential to use the hydrogel/nanoparticle hybrid as an injectable replacement for a soft optical lens system with an adjustable focus for future MEMs application. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction The human crystalline lens is a plate like transparent lens, con- taining about 65% of water and 35% of organic materials [1]. By flexing the ciliary muscle, the shape and curvature of the crystal- line lens can be changed, and thus, objects in the different dis- tances can be focused. However, the human crystalline lens loses its transparency when aging or being exposed to external factors such as UV-light. This chronic disease is called the cataract disease. Cataract can cause a serious illness of blindness if the patients are not treated properly. One common surgical treatment to correct cataract disease is to replace the defected human lens with an arti- ficial crystalline lens. Currently, artificial crystalline lens is often made from poly(methyl methacrylate) (PMMA) [2]. PMMA has a good light transmittance, but at the room temperature, PMMA is rather rigid such that it cannot be easily inserted into the eye cap- sule without a big wound cut (about 7–8 mm). Therefore, a long recovery from the surgery is often expected. Currently, a new treatment method was proposed that requires only millimeter-sized surgical wound for the lens replacement. If the crystalline lens capsule can be preserved, an injectable soft lens material can be refilled back into the capsule by needles [3]. Since the surgery requires only a minimum damage of the lens capsule, the shape of the capsule remains the same as before. In 1964, Kessler [4] was the first to use liquid-like silicone for injection into crystalline lens capsule of rabbits. In recent years, a number of studies involving ersatz materials to simulate the human crystal- line lens have also been reported. For example, several groups from Parel et al. [5] and Agarwall et al. [6] used silicon rubbers as the soft lens material. In this study, we use a UV irradiation method for crosslinking hydrogel network, thus preventing the leakage of injected material from the lens capsule. To mimic the human crys- talline lens, the degree of light penetration of ersatz materials 0167-9317/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2010.12.024 ⇑ Corresponding author at: Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan. Tel.: +886 2 3366 3051; fax: +886 2 2362 3040. E-mail address: polymer@ntu.edu.tw (C.-A. Dai). Microelectronic Engineering 88 (2011) 1737–1741 Contents lists available at ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee