Light-induced transformation of vesicles to micelles and vesicle-gels to sols† Hyuntaek Oh, a Vishal Javvaji, a Nicholas A. Yaraghi, a Ludmila Abezgauz, b Dganit Danino b and Srinivasa R. Raghavan * a Vesicles are self-assembled nanocontainers that are used for the controlled release of cosmetics, drugs, and proteins. Researchers have been seeking to create photoresponsive vesicles that could enable the triggered release of encapsulated molecules with accurate spatial resolution. While several photoresponsive vesicle formulations have been reported, these systems are rather complex as they rely on special light-sensitive amphiphiles that require synthesis. In this study, we report a new class of photoresponsive vesicles based on two inexpensive and commercially available amphiphiles. Specifically, we employ p-octyloxydiphenyliodonium hexafluoroantimonate (ODPI), a cationic amphiphile that finds use as a photoinitiator, and a common anionic surfactant, sodium dodecylbenzenesulfonate (SDBS). Mixtures of ODPI and SDBS form “catanionic” vesicles at certain molar ratios due to ionic interactions between the cationic and anionic headgroups. When irradiated with ultraviolet (UV) light, ODPI loses its charge and, in turn, the vesicles are converted into micelles due to the loss of ionic interactions. In addition, a mixture of these photoresponsive vesicles and a hydrophobically modified biopolymer gives a photoresponsive vesicle-gel. The vesicle-gel is formed because hydrophobes on the polymer insert into vesicle bilayers and thus induce a three-dimensional network of vesicles connected by polymer chains. Upon UV irradiation, the network is disrupted because of the conversion of vesicles to micelles, with the polymer hydrophobes getting sequestered within the micelles. As a result, the gel is converted to a sol, which manifests as a 40 000-fold light-induced drop in sample viscosity. Introduction Vesicles are nanoscale containers formed by a variety of amphiphilic molecules, including lipids, surfactants, and block copolymers. 1–3 They consist of an aqueous core enclosed by a bilayer of the amphiphiles. Vesicles have attracted much interest owing to their potential for the encapsulation and controlled release of substances such as drugs in pharmaceu- tical applications, avors and nutrients in foods, fragrances and dyes in cosmetics and textiles, etc. 3–9 Payloads encapsulated in the core of vesicles tend to get released slowly through passive diffusion through the bilayer membrane. 10,11 However, passive release usually does not deliver a high payload concentra- tion. 10–12 An alternative is to engineer the vesicles for active release; i.e., so that they deliver their entire payload upon acti- vation by an external trigger, such as pH, temperature, ions, enzymes, ultrasound, and light. 10–15 Light is an attractive stimulus for triggering release from vesicles due to its high spatial resolution, i.e., it can induce release of encapsulated molecules at a precise location with micron-scale resolution. 10–12 Accordingly, many researchers have designed light-responsive vesicles, typically using custom- synthesized lipids. 10–12 For example, vesicles have been created using lipids that contain photocrosslinkable, 16,17 photo- isomerizable, 18–21 or photocleavable groups. 22,23 These vesicles exhibit either light-induced disruption of their bilayers or light- activated opening of pores in their bilayers—in both cases, active release of encapsulated payload from the vesicles is triggered by light. However, synthesis of photoresponsive lipids is usually a complex process that requires skills in organic and biochemistry. Thus, the complexity of these previous systems makes them difficult to replicate and scale-up for commercial application. There is a lack of simple and low-cost routes to making photoresponsive vesicles, which is the motivation for the present study. In our efforts to develop a simple class of photoresponsive vesicles, we focus on vesicles formed by single-tailed amphi- philes (surfactants) due to their simplicity and ease of prepa- ration. 24–27 It is well-known that a mixture of cationic and anionic surfactants can spontaneously self-assemble into nanoscale unilamellar vesicles in water. 24 These “catanionic” a Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD 20742-2111, USA b Department of Biotechnology and Food Engineering, Technion – Israel Institute of Technology, Haifa, 32000, Israel. E-mail: sraghava@umd.edu † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3sm52184b Cite this: Soft Matter, 2013, 9, 11576 Received 13th August 2013 Accepted 25th October 2013 DOI: 10.1039/c3sm52184b www.rsc.org/softmatter 11576 | Soft Matter , 2013, 9, 11576–11584 This journal is ª The Royal Society of Chemistry 2013 Soft Matter PAPER Published on 08 November 2013. Downloaded by University of Maryland - College Park on 27/02/2014 15:36:04. View Article Online View Journal | View Issue