The deposition and subsequent electrochemical dissolution of (PLL/DNA) 6 films on ITO electrodes was studied by means of ecOWLS and in situ AFM. ecOWLS experiments showed that (PLL/DNA) 6 films fabricated at 0 V are stable in physiological buffer (pH 7.4) and that applying a potential above 1.8 V induces only a partial and slow dissolution. On the contrary, the dissolution is much more effective and quicker if a potential is applied already during the deposition of the film. AFM experiments showed that (PLL/DNA) 6 films are constituted of 30 nm high, 100 nm diameter nanodroplets. The film morphology was not affected by the application of a potential during the fabrication. A custom made flow-cell allowed in situ following of the electrochemical dissolution revealing the continuous shrinking of the nanodroplets. The results were interpreted in the light of a model describing the variation of pH induced by the water electrolysis in the proximity of the ITO electrode.
Triggered release of an entrapped dye from vesicles embedded in a polyelectrolyte multilayer (PEM), as a consequence of the electrochemically induced local pH change in the vicinity of the electrode, is reported. The PEM was deposited on an indium tin oxide (ITO) electrode wherein lipid vesicles filled with a fluorescent dye were embedded. The use of vesicles with a strong negative charge and the polyelectrolyte species of the PEM matrix with a polycation as topmost layer enabled the generation of a stable layer of liposomes in the PEM.
The electrochemically tailored degradation of polyelectrolyte assemblies holds great promises for the design of inexpensive, easily prepared and precise controlled release systems. However, the conception of such electrochemically responsive platforms for drug or gene delivery requires a detailed understanding of the degradation process of the polyelectrolyte multilayer in which the active species to release are incorporated. To this end, we assess here the influence of an applied electric potential on different polyelectrolyte systems, combining global and local investigation techniques. In situ atomic force microscopy allows us to evidence morphological changes at the nano-and micro-scale, while the investigation at a larger scale by optical waveguide lightmode spectroscopy brings complementary information relating not only to material release into the bulk solution, but also to ion migration and swelling. Weak and highly hydrated poly(L-lysine)/hyaluronic acid assemblies with thicknesses up to several hundreds of nanometre continuously dissolve upon electrochemical trigger. However, stronger and more compact films made of poly(allylamine hydrochloride) and poly(styrene sulfonate) dissolve only if their thickness is of a few tens of nanometres, while thicker films delaminate from the electrode. Additional results obtained with composite films combining both polyelectrolyte systems allow us to present mechanisms based on the continuous formation of protons at the electrode surface due to water electrolysis which fully describe the dissolution and the delamination processes. In addition, the study also reveals a novel approach for the release of free-standing polyelectrolyte membranes, which is of great interest for the development of mechanical sensors, separation membranes, or micromechanical devices.
Calcein was delivered from a functional coating into viable cells on top of it, upon the application of an electrochemical stimulus. The dye was loaded in liposomes stably embedded in a sandwich of polyelectrolyte multilayers. The covering multilayer was optimized with respect to its chemical composition to be resistant to galvanostatic conditions and to allow for cell growth. Additionally, spatial control over the release was achieved by two different patterning methods: (1) coating the indium tin oxide electrode by a micro-patterned insulator and (2) directly patterning the electrode. The release kinetics could be tuned by regulating the current density.
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