Effect of Surfactants on the Self-Assembly of a Model Elastin-like Block Corecombinamer: From Micelles to an Aqueous Two-Phase System Guillermo Pinedo-Martín, Emilio Castro, Laura Martín, Matilde Alonso, and J. Carlos Rodríguez-Cabello* Bioforge Group, University of Valladolid, CIBER-BBN, Paseo de Bele ́ n 11, 47011 Valladolid, Spain * S Supporting Information ABSTRACT: Recent advances in genetic engineering now allow the synthesis of protein-based block corecombinamers derived from elastin-like peptide sequences with complete control of chemistry and molecular weight, thereby resulting in unique physical and biological properties. The individual blocks of the elastin-like block corecombinamers (ELbcR’s) display different phase behaviors in aqueous solution, which leads to the thermally triggered self-assembly of nano-objects ranging from micelles to vesicles. Herein, the interaction of cationic surfactant dodecyl trimethylammonium bromide (DTAB), anionic surfactant dodecyl sodium sulfate (SDS), and nonionic surfactant octyl-β-glucopyranoside (OG) with an ELbcR has been investigated by dynamic light scattering (DLS), the ζ potential and cryo-transmission electron microscopy (cryo-TEM). At 65 °C and neutral pH in aqueous solution, the ELbcR (E50A40) is associated into micelles with a diameter of 150 nm comprising a hydrophobic (A) core and a hydrophilic (E) anionic (from the glutamic acid residues) corona. The size of these self-assemblies can be controlled by adjusting the cosurfactant concentrations. Although the effects of surfactants on the self-assembly behavior of ELbcR’s depend on the hydrocarbon chain length and headgroup of the surfactants, a general tendency to increase in size, which in some cases leads to flocculation and a phase-separated state, is observed. These results support the use of surfactants as a highly interesting means of controlling the self-assembly of ELbcR’s in aqueous solution as well as their use in drug delivery and purification processes. ■ INTRODUCTION The interaction of amphiphilic copolymers with low-molecular- weight surfactants has attracted considerable attention in recent years because of the possibility of designing nano-objects with novel functionalities 1,2 as a result of the fact that the addition of surfactants may induce the aggregation of the copolymer or may change the aggregation state of the pure polymeric micelles. 3 Copolymers and surfactants frequently carry opposite charges, meaning that the interaction between them is similar to the formation of polyelectrolyte complexes. 4 Surfactant- copolymer interactions are primarily governed by both electrostatic (between the surfactant head groups and the polyelectrolyte side groups) and hydrophobic interactions (between the hydrophobic backbone of the polyelectrolyte and the alkyl chains of the surfactant). 5-7 The binding of ionic surfactants to oppositely charged polyelectrolytes occurs via two mechanisms: initially by ion exchange and then, at higher surfactant concentrations, by cooperative binding. 8 The polyelectrolyte nature of these complexes and the fact that multicomponent materials can enable better control of the aggregation properties compared to that of single surfactant complexes 9 make them promising candidates for a wide range of possible applications, 10 for example (a) in the controlled release of drugs, taking advantage of the specific binding properties of a copolymer with a very small amount of surfactant in the coating, 11 (b) in mimicking the cytoplasmic organization of cellular microcompartments, and (c) in the puri fication of proteins and the extraction of other biomolecules. 12 Elastin-like block corecombinamers (ELbcR’s) 13,14 have been widely studied as a family of thermosensitive polymers. All functional elastin-like recombinamers (ELRs) present a reversible phase transition in response to changes in temper- ature. 15 In aqueous solution, below a certain transition temperature (T t ), the polymer chains adopt a fully hydrated disordered conformation, whereas once the temperature is increased to above T t the polymers collapse into a phase- separated state. This folding is completely reversible if the temperature of the solution is decreased below T t . 16-19 The aggregation behavior of ELbcR’s has been found to be strongly dependent on the polymer composition, polymer concentration, and presence of additives in terms of both transition temperatures (T t ) and the structure of the micelles. 20 ELbcR’s are particularly attractive as block copolymers that self- assemble into nanoparticles in aqueous systems because of the exquisite control over the polypeptide sequence, which is the primary determinant of self-assembly afforded by recombinant synthesis. 21,22 Received: February 4, 2014 Revised: March 10, 2014 Published: March 11, 2014 Article pubs.acs.org/Langmuir © 2014 American Chemical Society 3432 dx.doi.org/10.1021/la500464v | Langmuir 2014, 30, 3432-3440