Characterization of a new scaffold formed of polyelectrolyte complexes using atomic force and ultrasonic force microscopy.

Poly(acryloxyethyl-trimethylammonium chloride-co-2-hydroxyethyl methacrylate) [poly(Q-co-H)]/ sodium alginate gel (Ca2+) [AlgNa]/poly-l-lysine [PLL] films have been prepared on a mica surface. The structural arrangement and elasticity of the polyelectrolyte complexes have been studied with nanoscale resolution using Atomic Force Microscopy (AFM) and Ultrasonic Force Microscopy (UFM). The elastic contrast on the AlgNa surface is indicative of the formation of a biopolymer network. On the AlgNa film, the surface morphology is mostly characterized by areas with rounded beads (approximately =150 nm in diameter) and polymer strands. Flatter, more homogenous surface regions are also present, presumably related to outdiffused PLL. Incorporation of the poly(Q-co-H) layer results in an increased compactness of the film, and an enhancement of the previous AlgNa topographic features. The unique subsurface sensitivity provided by UFM allows us to resolve the elastic bonding distribution in the buried biopolymer network by imaging from the poly(Q-co-H) overlayer. Provided the biocompatibility of the resulting polyelectrolyte complex film, we propose this system as a novel scaffold for bioengineering applications. The results we present demonstrate the potential of UFM to get insight in the elastic behavior of encapsulated bionetworks.