  Citation: Stavarache, C.; Vinatoru, M.; Mason, T. Transport of Magnetic Polyelectrolyte Capsules in Various Environments. Coatings 2022, 12, 259. https://doi.org/10.3390/ coatings12020259 Academic Editor: Cédric C. Buron Received: 20 December 2021 Accepted: 13 February 2022 Published: 15 February 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). coatings Article Transport of Magnetic Polyelectrolyte Capsules in Various Environments Carmen Stavarache 1,2, *, Mircea Vinatoru 3 and Timothy Mason 2 1 “Costin D. Nenitescu” Institute of Organic Chemistry, 202B Splaiul Independentei, 060023 Bucharest, Romania 2 Faculty of Health and Life Sciences, Coventry University, Priory Street, Coventry CV1 5FB, UK; apx077@coventry.ac.uk 3 Sonochem Centre Ltd., Bank Gallery, High Street, Kenilworth CV8 1LY, UK; mircea@sonochemcentre.com * Correspondence: stavarachec@yahoo.com; Tel.: +40-213167900; Fax: +40-213121601 Abstract: Microcapsules consisting of eleven layers of polyelectrolyte and one layer of iron oxide nanoparticles were fabricated. Two types of nanoparticles were inserted as one of the layers within the microcapsule’s walls: Fe 2 O 3 , ferric oxide, having a mean diameter (Ø) of 50 nm and superpara- magnetic Fe 3 O 4 having Ø 15 nm. The microcapsules were suspended in liquid environments at a concentration of 10 8 caps/mL. The suspensions were pumped through a tube over a permanent magnet, and the accumulation within a minute was more than 90% of the initial concentration. The design of the capsules, the amount of iron embedded in the microcapsule, and the viscosity of the transportation fluid had a rather small influence on the accumulation capacity. Magnetic microcapsules have broad applications from cancer treatment to molecular communication. Keywords: polyelectrolyte magnetic capsules; transport; drug delivery; molecular communication 1. Introduction Drug delivery systems are formulations or medical devices designed to transport the therapeutic agent to the specific site where it is needed (organ, tissue), followed by con- trolled release, in a reduced dose, thus minimizing undesirable side effects [1–3]. Numerous types of delivery systems, including liposomes, carbon nanotubes, micelles, dendrimers, and nanofibers, are under investigation as cytotoxic drug carriers [4,5]. Biopolymers such as animal-originated proteins and plant-originated carbohydrates are biocompatible, biodegradable, and antibacterial and thus also suited as drug carriers [6,7]. Polyelectrolyte capsules (PEs) are versatile drug carriers due to their constitution and properties [8,9]. Their fabrication involves a layer-by-layer technique: the construction of shells by alternating adsorption of oppositely charged polymers, either of natural origin (nu- cleic acids [10,11], pectin [12,13], alginate [14,15]), chemically adapted (chitosan [12,16,17], chitin [18]), or artificial (polyvinyl [19], polyacrylic acid [20,21], methacrylic acid [22], polystyrene [23], polyacrylamides [24], alkyl-trialkyl ammonium salts [22]). This tech- nique allows the incorporation of other materials between polymer layers (biomolecules, nanoparticles). Polyelectrolyte assembly is conducted on a sacrificial template core that easily decom- poses in basic or acid media without affecting the polyelectrolyte capsule. The core can be fabricated from carbonates (CaCO 3 , CdCO 3 , MnCO 3 ) or oxides (SiO 2 , TiO 2 )[25–27]. The core can incorporate various materials (drugs, peptides, genes, or proteins) by preloading methods or can be dissolved once the capsules are fabricated, making room for drugs, peptides, genes, or proteins in so-called post-loading methods [28–31]. According to Robert Langer and Nikolaos Peppas, there are four types of drug delivery systems, depending on the mechanism of drug release: diffusion-controlled, chemically controlled, solvent-activated, and stimuli-controlled [32]. Coatings 2022, 12, 259. https://doi.org/10.3390/coatings12020259 https://www.mdpi.com/journal/coatings