Thermal Annealing of Polyelectrolyte Multilayers: An Effective Approach for the Enhancement of Cell Adhesion

Abstract

are fundamental in determining cell adhesion at different scales. [5,6] For a good cell adhesion, it is necessary that the substrate stiffness be adequate to generate forces to balance the intracellular tension generated by stress fibers. [7] A surface chemistry based on biocompatible elements that do not have a negative impact on proliferation is as well needed. Furthermore, the material should be capable of adsorbing a certain amount of proteins from the cell culture media, as cells adhered to a substrate do not interact directly with the material surface but with the proteins coming from biological fluids that deposit on it. [8,9] A large number of different materials mimicking aspects of the interactions between cells and their environment have been employed to increase cell adhesion: natural and synthetic polyelectrolyte multilayers (PEMs), protein-coated polyacrylamide or poly(dimethylsiloxane) polymeric substrates with tunable stiffness, [10] hydrogels that can be biochemically and mechanically altered by chemical functionalization or by varying cross-linking density, respectively. [11] Furthermore, microgels have been used alone to fabricate thin film substrates or combined with polyelectrolytes (PE) in PEMs. [12] The layer-by-layer (LbL) technique provides a simple method for the noncovalent modification of surfaces and implants with biocompatible polymers and the engineering of scaffolds. [13,14] LbL technique is based on the electrostatic interaction between oppositely charged polyelectrolytes that are sequentially assembled on top of a charged surface. LbL represents a powerful strategy for modifying surfaces and endowing them with specific components. PEMs fabricated by the LbL technique in combination with novel templates, new microfabrication methods, and the incorporation of bioactive molecules and stimuli-sensitive polymers are very appealing for the spatial modulation of bio-and physicochemical properties of materials to influence cell fate. [15] The PEMs can be fabricated on the basis of biopolyelectrolytes [16] forming a biocompatible cushion on which proteins, peptide sequences, and other biomolecules can be covalently bound or assembled, impacting on cell functionalities, not only on cell adhesion but also on cell growth and migration. [17] The properties of the PEMs in regard to cell adhesion can be tuned by changing the conditions for polyelectrolyte assembling, i.e., the ionic strength and pH of its solutions, and the layer composition.Polyelectrolyte multilayers (PEMs) have many potential applications in tissue engineering and regenerative medicine. However, the softness of biocompatible PEMs results in limited cell adhesion. A novel strategy for the enhancement of cell adhesion on PEMs based on thermal annealing is presented here. The impact of thermal annealing at 37 ºC of poly-l-lysine (PLL) and alginate (Alg) polyelectrolyte multilayers on the adhesion of human lung cancer A549 and myoblast C2C12 cell lines is studied. The properties of the PEMs after annealing are characterized by m...

Adsorption and Exchangeability of Fibronectin and Serum Albumin Protein Corona on Annealed Polyelectrolyte Multilayers and Their Consequences on Cell Adhesion

“…The number of FN proteins adsorbed from cell culture medium, and the strength of their interaction with the Chi/HA PEM would be smaller than that required for achieving proper cell adhesion characteristics. [18][19][20] In the present work, we show that protein adsorption on either adhesive or nonadhesive substrates exhibits distinctive behavior upon annealing. [37,38] Results from protein adsorption and exchangeability assays allow us to rationalize the observed adhesion characteristics of the different cell lines tested in previous works.…”

“…[47] The changes in the physicochemical properties of PEMs upon annealing [18][19][20] affect the proteinsubstrate interaction. This increased interaction is reflected in the decrease in the exchangeability of adhesion proteins adsorbed either in contact with the surface substrate, or mediated by nonadhesion, tightly attached BSA layers.…”

“…We have shown in previous works that thermal annealing of PLL/ Alg PEMs results in an increase in cell adhesion, while the annealing of Chi/HA results in a decrease in cell adhesion. [18][19][20] For PLL/Alg PEMs, thermal annealing increases the Young's modulus of the sample, produces a more hydrophobic surface with a contact angle approaching 90°, enhances the negative charge, and decreases the roughness (Figure 1d). [18][19][20] For PLL/Alg PEMs, thermal annealing increases the Young's modulus of the sample, produces a more hydrophobic surface with a contact angle approaching 90°, enhances the negative charge, and decreases the roughness (Figure 1d).…”

“…Values of FN density on PLL/Alg PEMs are in the order of magnitude of those reported for a FN monolayer, that is, 0.28, 0.40, and 0.32 µg cm −2 . [18] It has been shown that FN interacts with cell protein integrins (α 5 β 1 ) more tightly when adsorbed to surfaces displaying negative moieties, such as carboxyl, sulfonic, or hydroxyl groups, favoring cell adhesion. [22] Upon annealing, the surface charge, wettability, topography, and mechanical properties of PLL/Alg PEMs are modified.…”

Multilayer assembly of ionic starches on old corrugated container recycled cellulosic fibers

“…Polyelectrolyte thin film layers obtained by LbL deposition are continuously studied due to their potential applications in various technologies, and interesting fundamental questions arise from their complex nature . Numerous parameters such as temperature, charge density and molecular weight of polyelectrolyte, ionic strength and pH value of polyelectrolyte solutions, adsorption time and rinsing procedure affect the assembly mechanism of the polyelectrolyte or growth model of the films . Moreover, the structure and interfacial properties of PEMs are governed by the choice of polycation/polyanion pairs, the surface properties of substrates and interactions between the two polyelectrolytes constituting the multilayer …”