Multilayer DNA/Poly(allylamine hydrochloride) Microcapsules:  Assembly and Mechanical Properties

Abstract

We report the preparation, characterization, and mechanical properties of DNA/poly(allylamine hydrochloride) (PAH) multilayer microcapsules. The DNA/PAH multilayers were first constructed on a planar support to examine their layer-by-layer buildup. Surface plasmon resonance spectroscopy (SPR) showed a nonlinear growth of the assembly upon each bilayer deposited independently on a concentration of salt. A weak increase in the film thickness with the DNA concentration was, however, detected. A post-treatment of the multilayers in the salt solutions has shown a thinning of the film. The optimal conditions of the planar film growth were used to deposit the same multilayers on the surface of colloidal templates and to study their roughness and morphology with the atomic force microscope (AFM) imaging. When an outer layer is formed by DNA, we observe large domains of oriented parallel DNA loops, while an outer layer formed by PAH shows highly porous morphology. The dissolution of colloidal templates led to a formation of highly porous DNA/PAH microcapsules. We probe their mechanical properties by measuring force-deformation curves with the AFM-related setup. The experiment suggests that the DNA/PAH capsules are softer than capsules made from the flexible polyelectrolytes studied before. The softening is due to both higher permeability and smaller Young's modulus of the shell material. The Young's modulus of the DNA/PAH shells increases after post-treatment in salt solutions of relatively low concentration.

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…The best characterized pair of polyelectrolytes for layer by layer deposition is poly(allyl amine hydrochloride)/poly(sodium styrenesulfonate) (PAH/PSS) (for a review, see [891]). This pair has also been used for all AFM force experiments on PMCs except for [892], where also polyethyleneimine (PEI) and poly(diallyl-dimethyl-ammonium chloride) (PDADMAC) were used as polycations and [893], where DNA was used as polyanion. As template materials, melamine formaldehyde (MF), polylactic acid (PLA), weakly cross-linked polystyrene (PS), and MnCO 3 have been used.…”

“…Future studies could include improvements of the mechanical models including finite permeability of the shells or widen the range of polyelectrolytes. An example for the latter case is the recent paper by Vinogradova et al [893] on PAH/DNA microcapsules. The inclusion of biomolecules as polyelectrolytes or polyamphylytes could also lead to biological applications that mimic biocompartments.…”

Freestanding Nanostructures via Layer‐by‐Layer Assembly

“…[67] Vinogradova et al have also prepared different types of stimuli-sensitive LbL microcapsules with DNA/PAH. [115] Caruso's work on hollow DNA microcapsules comprising negatively charged homopolymeric nucleotides (polyA 20 G 20 / polyT 20 C 20 ) provided interesting results. [116] These microcapsules are likely to have diverse applications in delivery and sensing devices due to their switchable morphology and responsive behavior.…”

“…[74] Vinogradova et al have measured the Young's modulus of DNA/PAH microcapsules by deformation experiments, and found the Young's modulus values to be in the 100 MPa range. [115] Kharlampieva and Sukhishvili have shown an interesting interplay between hydrogen-bonding and electrostatic interactions in hybrid polymer multilayers. [123] A recent study has shown that the microcapsule shell can be ultrasoft, with the apparent elastic modulus being less than 1 MPa.…”

Lyophilization of Protein-Loaded Polyelectrolyte Microcapsules

“…This technique is based on the sequential adsorption of oppositely charged polyelectrolytes onto the surface of charged colloidal particles which are used as templates (2,3). Not only have synthetic polymers (2,4,5) and biopolymers (6)(7)(8) served as layer constituents, but enzymes (9), nucleic acids (6,10), lipids (11) and nanoparticles (12,13) have also been incorporated in LbL shells (14). Furthermore, different types of templates have been considered, including biological cells (15), drug crystals (16,17), organic (18)(19)(20) and inorganic (21,22) colloidal particles.…”