Ion-induced cell sheet detachment from standard cell culture surfaces coated with polyelectrolytes.

Polyelectrolyte multilayers (PEMs), formed by alternating layer-by-layer deposition of polyanions and polycations, are an ideal substrate for controlling cellular adhesion and behavior. In the present study we propose a simple mechanism for the controlled detachment of C(2)C(12) myoblasts cell sheets from PEMs consisting of poly(l-lysine) and hyaluronic acid with a topmost layer of fibronectin. The multilayers were deposited on two standard cell culture surfaces: glass and polystyrene. Adding a low concentration of nontoxic ferrocyanide to the cell culture medium resulted in erosion of the polyelectrolyte multilayer and rapid detachment of viable cell sheets. Additional Quartz Crystal Microbalance and Atomic Force Microscopy measurements indicated that the detached cells retained their extracellular matrix and that no polyelectrolyte molecules remained bound to the cell sheets. The dissolution of polyelectrolyte multilayers by multivalent ions is a promising approach to cell sheet engineering that could potentially be used for regenerative medicine.

Spontaneous formation of a vesicle multilayer on top of an exponentially growing polyelectrolyte multilayer mediated by diffusing poly-L-lysine.

We observed the spontaneous formation of vesicle-multilayers on top of a polyelectrolyte multilayer (PEM). By varying the thickness of underlying PEM (uPEM) it was possible to tailor the amount of adsorbing liposomes. Thereby, the loading capacity could be increased up to 17 times with respect to a monolayer of vesicles for an uPEM of 50.5 bilayers. We, furthermore, proved that the formation of the vesicle multilayer is due to the ability of poly-L-lysine to diffuse within the uPEM. This method could be interesting for applications in sensors and drug delivery systems where the increase in loading capacity is highly desired.

Chemically tunable electrochemical dissolution of noncontinuous polyelectrolyte assemblies: an in situ study using ecAFM.

The electrochemically triggered dissolution of noncontinuous polyelectrolyte assemblies presenting distinct nanomorphologies and its tuning by chemical cross-linking were monitored locally, in situ, by electrochemical atomic force microscopy. Poly-l-lysine and hyaluronic acid deposited layer-by-layer on indium tin oxide electrodes at specific experimental conditions formed well-defined nanostructures whose morphologies could be easily and precisely followed along the dissolution process. In addition to shrinkage of polyelectrolyte nanodroplets, ecAFM images revealed the faster dissolution of coalesced structures compared to droplet-like complexes, and the readsorption of dissolved polyelectrolytes onto slower dissolving neighboring structures. Covalently cross-linked PLL/HA assemblies dissolved only partially, and exhibited slower dissolution rates compared to native multilayers, with a clear dependence on the cross-link density. Tuning the electrochemical dissolution of polyelectrolyte multilayers through chemical cross-linking opens new prospects for future biomedical applications, such as the development of advanced drug or gene delivery platforms allowing for tightly controlled releases of different compounds at specific rates.