Biodegradable inverse opals with controlled discoloration

Abstract

Photonic crystals have been used for structural coloration and photonic applications owing to their photonic bandgap properties. They can exhibit sparking interference colors by prohibiting the light propagation in a visible range, and this colors can be tuned by the structural properties. When the photonic structures are composed of functional materials, their functionalities can also be expressed visually. To accomplish this, inverse opals, the negative replica of the opals, are remarkable due to their potential for abundant selection of matrix materials. Here, we report a pragmatic approach to fabricate inverse opals with biodegradable matrix for controlled discoloration. To avoid uncontrolled infiltration and drying processes, we use thermal embedding of silica particles into the polymer film by using capillary wetting phenomena. With partially-embedded silica particles, optimal substrate for dip-coating was producible regardless of material wetting properties. Moreover, by embedding the opal templates into the underlying polymer film, uniform insertion of matrix materials was achievable. These processes succeed in fabrication of biodegradable inverse opals, and also can serve as a general method to produce a wide range of polymeric inverse opals. In case of biodegradable inverse opals, as structure degrades gradually over time by hydrolysis, they can show discoloration on time. Their degradation rate is also controllable by varying the pore sizes and the pH condition of aqueous medium. Therefore, by tracing the discoloration of inverse opals, period is predictable, and this can be used as periodic indicators for food, drug and cosmetic products.