# Nano-patterned polyelectrolyte multilayers

We have developed a block copolymer-based nano-patterning approach that enables to assemble polyelectrolytes and nanoparticles bearing charges on alternating domains using electrostatic self-assembly.

In our initial papers (2016-2017) we explored the fundamentals of this laterally confined assembly; later papers (2017-present) demonstrate how these nano-patterns could be applied.

Shen, M. - Y. ; Yuran, S. ; Aviv, Y. ; Ayalew, H. ; Luo, C. - H. ; Tsai, Y. - H. ; Reches, M. ; Yu, H. - H. ; Shenhar, R. Electrically Responsive, Nanopatterned Surfaces for Triggered Delivery of Biologically Active Molecules into Cells. ACS Applied Materials & Interfaces 2019, 11, 1201-1208.Abstract

Polyelectrolyte multilayers (PEMs) assembled layer-by-layer have emerged as functional polymer films that are both stable and capable of containing drug molecules for controlled release applications. Most of these applications concentrate on sustained release, where the concentration of the released molecules remains rather constant with time. However, high-efficiency delivery requires obtaining high local concentrations at the vicinity of the cells, which is achieved by triggered release. Here, we show that a nanopatterned PEM platform demonstrates superior properties with respect to drug retention and triggered delivery. A chemically modified block copolymer film was used as a template for the selective deposition of poly(ethylene imine) and a charged derivative of the electroactive poly(3,4-ethylenedioxythiophene) together with a drug molecule. This nanopatterned PEM shows the following advantages: (1) high drug loading; (2) enhanced retention of the bioactive molecule; (3) release triggered by an electrochemical stimulus; (4) high efficacy of drug delivery to cells adsorbed on the surface compared to the delivery efficacy of a similar concentration of drug to cells suspended in a solution.

Asor, L. ; Nir, S. ; Oded, M. ; Reches, M. ; Shenhar, R. Nano-patterned polyelectrolyte multilayers assembled using block copolymer templates: The combined effect of ionic strength and nano-confinement. Polymer 2017, 126, 56-64.Abstract

Polyelectrolyte multilayers gain their importance from their applicability to a wide variety of functional building blocks. The ability to create these multilayers as laterally nano-patterned films, which has only been scarcely investigated so far, augments the functionality of the multilayer and makes it valuable for applications that require nanoscale features or periodic arrangement, such as photonic devices, catalytic surfaces, and biomedical applications. In this study we reveal how the lateral confinement imposed by block copolymer nano-domains in thin film templates affects the assembly of the deposited poly electrolyte layers at different ionic strengths, and how the combined effects of nano-confinement and ionic strength dictate the final structure of the multilayer. These fundamental insights provide the basis for successful construction of nano-patterned, functional coatings. (C) 2017 Elsevier Ltd. All rights reserved.

Wagner, T. ; Oded, M. ; Shenhar, R. ; Böker, A. Two-dimensionally ordered AuNP array formation via microcontact printing on lamellar diblock copolymer films. Polymers for Advanced Technologies 2017, 28, 623-628.Abstract

The construction of nano-sized, two-dimensionally ordered nanoparticle (NP) superstructures is important for various advanced applications such as photonics, sensing, catalysis, or nano-circuitry. Currently, such structures are fabricated using the templated organization approach, in which the templates are mainly created by photo-lithography or laser-lithography and other invasive top-down etching procedures. In this work, we present an alternative bottom-up preparation method for the controlled deposition of NPs into hierarchical structures. Lamellar polystyrene-block-poly(2-vinylpyridinium) thin films featuring alternating stripes of neutral PS and positively charged P2VP domains serve as templates, allowing for the selective adsorption of negatively charged gold NPs. Dense NP assembly is achieved by a simple immersion process, whereas two-dimensionally ordered arrays of NPs are realized by microcontact printing (mu CP), utilizing periodic polydimethylsiloxane wrinkle grooves loaded with gold NPs. This approach enables the facile construction of hierarchical NP arrays with variable geometries. Copyright (C) 2016 John Wiley & Sons, Ltd.

Chandaluri, C. G. ; Pelossof, G. ; Tel-Vered, R. ; Shenhar, R. ; Willner, I. Block Copolymer Patterns as Templates for the Electrocatalyzed Deposition of Nanostructures on Electrodes and for the Generation of Surfaces of Controlled Wettability. ACS Applied Materials & Interfaces 2016, 8 1440-1446.Abstract

ITO electrodes modified with a nanopatterned film of polystyrene-block-poly(2-vinylpyridine), PS-b-P2VP, where the P2VP domains are quaternized with iodomethane, are used for selective deposition of redox-active materials. Electrochemical studies (cyclic voltammetry, Faradaic impedance measurements) indicate that the PS domains insulate the conductive surface toward redox labels in solution. In turn, the quaternized P2VP domains electrostatically attract negatively charged redox labels solubilized in the electrolyte solution, resulting in an effective electron transfer between the electrode and the redox label. This phenomenon is implemented for the selective deposition of the electroactive Prussian blue on the nanopatterned surface and for the electrochemical deposition of Au nanoparticles, modified with a monolayer of p-aminothiophenol/2-mercaptoethanesulfonic acid, on the quaternized P2VP domains. The patterned Prussian blue-modified surface enables controlling the wettability properties by the content of the electrochemically deposited Prussian blue. Controlled wettability is unattainable with the homopolymer-modified surface, attesting to the role of the nanopattern.

Oded, M. ; Kelly, S. T. ; Gilles, M. K. ; Müller, A. H. E. ; Shenhar, R. From dots to doughnuts: Two-dimensionally confined deposition of polyelectrolytes on block copolymer templates. Polymer 2016, 107, 406-414.Abstract

The combination of block copolymer templating with electrostatic self-assembly provides a simple and robust method for creating nano-patterned polyelectrolyte multilayers over large areas. The deposition of the first polyelectrolyte layer provides important insights on the initial stages of multilayer buildup. Here, we focus on two-dimensionally confined dots'' patterns afforded by block copolymer films featuring hexagonally-packed cylinders that are oriented normal to the substrate. Rendering the cylinder caps positively charged enables the selective deposition of negatively charged polyelectrolytes on them under salt-free conditions. The initially formed polyelectrolyte nanostructures adopt a toroidal (''doughnut'') shape, which results from retraction of dangling polyelectrolyte segments into the dots'' upon drying. With increasing exposure time to the polyelectrolyte solution, the final shape of the deposited polyelectrolyte transitions from a doughnut to a hemisphere. These insights would enable the creation of patterned polyelectrolyte multilayers with increased control over adsorption selectivity of the additional incoming polyelectrolytes. (C) 2016 Elsevier Ltd. All rights reserved.

Oded, M. ; Müller, A. H. E. ; Shenhar, R. A block copolymer-templated construction approach for the creation of nano-patterned polyelectrolyte multilayers and nanoscale objects. Soft Matter 2016, 12, 8098-8103.Abstract

A block copolymer-based assembly approach for the creation of nano-patterned polyelectrolyte multilayers over cm2-scale areas is presented. Up to 5 bi-layers were selectively assembled on top of specific nanodomains featuring different morphologies. The successful isolation of nanoscale objects corresponding in shape to the template features is also demonstrated. This methodology is applicable to different types of polyelectrolytes, and opens up a new dimension for layer-by-layer construction.

Oded, M. ; Kelly, S. T. ; Gilles, M. K. ; Muller, A. H. E. ; Shenhar, R. Periodic nanoscale patterning of polyelectrolytes over square centimeter areas using block copolymer templates. Soft Matter 2016, 12, 4595-4602.Abstract

Nano-patterned materials are beneficial for applications such as solar cells, opto- electronics, and sensing owing to their periodic structure and high interfacial area. Here, we present a non-lithographic approach for assembling polyelectrolytes into periodic nanoscale patterns over cm(2)-scale areas. Chemically modified block copolymer thin films featuring alternating charged and neutral domains are used as patterned substrates for electrostatic self-assembly. In-depth characterization of the deposition process using spectroscopy and microscopy techniques, including the state-of-the-art scanning transmission X-ray microscopy (STXM), reveals both the selective deposition of the polyelectrolyte on the charged copolymer domains as well as gradual changes in the film topography that arise from further penetration of the solvent molecules and possibly also the polyelectrolyte into these domains. Our results demonstrate the feasibility of creating nano-patterned polyelectrolyte layers, which opens up new opportunities for structured functional coating fabrication.