Exploring pH-Sensitive Hydrogels Using an Ionic Soft Contact Lens: An Activity Using Common Household Materials

• Published in: Journal of chemical education Vol. 91; no. 10; pp. 1671 - 1674
• Main Authors: Chen, Yueh-Huey, He, Yu-Chi, Yaung, Jing-Fun
• Format: Journal Article
• Language: English
• Published: Easton American Chemical Society and Division of Chemical Education, Inc 14.10.2014; Division of Chemical Education, Inc and ACS Publications Division of the American Chemical Society; American Chemical Society
• Subjects: Acids; Baking; Biomaterials; Biomedical materials; Chemical activity; Chemistry; College Science; Contact lenses; Contraction; Functional groups; Hands on Science; High Schools; Hydrogels; Intermolecular forces; Ions; Laboratory Experiments; Lenses; Methacrylic acid; Molecular interactions; Molecular Structure; Organic chemistry; Osmosis; Plastics; Polyhydroxyethyl methacrylate; Polymers; Science Instruction; Scientific Concepts; Secondary School Science; Sodium bicarbonate; Swelling; Teaching methods; Topics; Undergraduate Study; Vinegar; First-Year Undergraduate/General; Hands-On Learning/Manipulatives; Polymer Chemistry; Hydrogen Bonding; Acids/Bases; High School/Introductory Chemistry; Aqueous Solution Chemistry; General Public
• ISSN: 0021-9584; 1938-1328
• DOI: 10.1021/ed400833b

Hydrogels of the so-called smart polymers or environment-sensitive polymers are important modern biomaterials. Herein, we describe a hands-on activity to explore the pH-responsive characteristics of hydrogels using a commercially available ionic soft contact lens that is a hydrogel of poly(2-hydroxyethyl methacrylate-co-methacrylic acid), poly(HEMA-co-MAA). The observed oscillatory swelling and contracting behaviors of the ionic soft contact lens in response to the changes in solution pH exhibit the reversible pH-responsive property of the hydrogel. Chemical structures of functional groups and the associated intermolecular forces in connection with the physical states of the hydrogel are demonstrated. Solutions of household materials such as vinegar, baking soda, and table salt were used to provide solutions with various conditions. This activity covers the chemistry of polymers and the topics relevant for general chemistry such as molecular interactions, acid–base reaction, solution concentration, and osmosis. The swelling and contracting of the ionic soft contact lens in solutions with various tonicities also make a unique class demonstration for teaching the topic of osmosis due to the quick response of the lens to the environmental solutions.