Micro-stratified architectures based on successive stacking of alginate gel layers and poly(l-lysine)–hyaluronic acid multilayer films aimed at tissue engineering

Abstract

A micro-stratified 3D scaffold was designed by successive stacking of alginate gel layers (AGLs) and poly(L-lysine)–hyaluronic acid (PLL–HA) multilayer films. AGLs are obtained by complexation of alginate by Ca²⁺ ions. Alginate solutions are first sprayed onto a solid substrate inclined such that the excess of solution be removed by natural drainage. A CaCl₂ solution is then either sprayed onto the substrate or the alginate covered substrate is dipped into a CaCl₂ solution. The spraying of the CaCl₂ solution leads to micro-porous AGLs, whereas the dipping in a CaCl₂ aqueous solution leads to a more homogeneous gel layer without porosity. The second process also allows the formation of AGLs with a controlled thickness. With the goal of stacking different AGLs and PLL–HA films, the influence of a PLL–HA precursor film on the formation of AGLs is firstly investigated. It is found that when an alginate solution is sprayed on a PLL–HA multilayer built in the presence of CaCl₂, the multilayer plays the role of reservoir of Ca²⁺ ions and of PLL chains, which both diffuse out of the multilayer film and complex alginate chains. This leads to the formation of a “pre-alginate gel”. When this film is further dipped in the CaCl₂ solution, an additional AGL forms, which is, however, free of PLL chains. Finally after the build-up of a PLL–HA film on the top of AGL, we succeeded in designing micro-stratified 3D scaffolds constituted by alternating strata of AGLs and PLL–HA films. This micro-stratified gel provides a new scaffold design with a perfectly controlled build-up: AGL aims to be a 3D scaffold for cell culture, and the PLL–HA multilayers should act as reservoirs for biologically active molecules.