Citation: Sandomierski, M.; Chojnacka, M.; Dlugosz, M.; Pokora, M.; Zwoli ´ nska, J.; Majchrzycki, L.; Voelkel, A. Mesoporous Silica Modified with Polydopamine and Zinc Ions as a Potential Carrier in the Controlled Release of Mercaptopurine. Materials 2023, 16, 4358. https:// doi.org/10.3390/ma16124358 Academic Editor: Antonio Gil Bravo Received: 12 May 2023 Revised: 3 June 2023 Accepted: 11 June 2023 Published: 13 June 2023 Copyright: © 2023 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/). materials Article Mesoporous Silica Modified with Polydopamine and Zinc Ions as a Potential Carrier in the Controlled Release of Mercaptopurine Mariusz Sandomierski 1, * , Martyna Chojnacka 1 , Maria Dlugosz 1 , Monika Pokora 2 , Joanna Zwoli ´ nska 2 , Lukasz Majchrzycki 2 and Adam Voelkel 1 1 Institute of Chemical Technology and Engineering, Poznan University of Technology, ul. Berdychowo 4, 60-965 Pozna ´ n, Poland; martyna.j.chojnacka@student.put.poznan.pl (M.C.); maria.dlugosz.pl@gmail.com (M.D.); adam.voelkel@put.poznan.pl (A.V.) 2 Center for Advanced Technologies, Adam Mickiewicz University, Pozna´ n, ul. Uniwersytetu Pozna ´ nskiego 10, 61-614 Pozna ´ n, Poland; monika.pokora@amu.edu.pl (M.P.); joakol1@amu.edu.pl (J.Z.); lukmaj@amu.edu.pl (L.M.) * Correspondence: mariusz.sandomierski@put.poznan.pl Abstract: Mercaptopurine is one of the drugs used in the treatment of acute lymphoblastic leukemia. A problem with mercaptopurine therapy is its low bioavailability. This problem can be solved by preparing the carrier that releases the drug in lower doses but over a longer period of time. In this work, polydopamine-modified mesoporous silica with adsorbed zinc ions was used as a drug carrier. SEM images confirm the synthesis of spherical carrier particles. The particle size is close to 200 nm, allowing for its use in intravenous delivery. The zeta potential values for the drug carrier indicate that it is not prone to agglomeration. The effectiveness of drug sorption is indicated by a decrease in the zeta potential and new bands in the FT-IR spectra. The drug was released from the carrier for 15 h, so all of the drug can be released during circulation in the bloodstream. The release of the drug from the carrier was sustained, and no ‘burst release’ was observed. The material also released small amounts of zinc, which are important in the treatment of the disease because these ions can prevent some of the adverse effects of chemotherapy. The results obtained are promising and have great application potential. Keywords: acute lymphoblastic leukemia; 6-mercaptopurine; polydopamine; drug delivery; zinc 1. Introduction The most common pediatric malignancy is acute lymphoblastic leukemia (ALL) [1]. This disease is responsible for approximately 25% of all childhood cancers and 75–80% of childhood leukemias [2,3]. Survival and cure rates have improved over the past few decades due to the optimal use of antileukemic drugs [4,5]. One of the drugs used in this disease is 6-mercaptopurine (MERC) [6]. MERC is a drug with anti-inflammatory, immunosuppressive, and cytotoxic properties, and its action is dose-dependent. In high doses, it has immunosuppressive and cytotoxic properties, while in small doses, it acts as an anti-inflammatory drug [7,8]. This drug is also used in other diseases: ulcerative colitis and Crohn’s disease [9,10]. A problem with MERC therapy is its low bioavailability, ranging from 10% to 50%, with an average value of 16% [11]. The low bioavailability is due to the short plasma half-life of MERC, which is approximately 1 to 3 h [12]. This problem can be solved by preparing the drug delivery system that releases the drug in lower doses but over a longer period of time. Many modern drug delivery systems have been described in the literature in the last few years. An interesting example are polysialic acid-based drug delivery systems [13]. These systems have been used, for example, in the delivery of drugs in the treatment of cancer and rheumatic and neurological diseases. Particularly important drug delivery systems are those that release the drug in response to stimuli [14]. The stimuli that affect drug release can be divided into: internal stimuli (reactive oxygen species, Materials 2023, 16, 4358. https://doi.org/10.3390/ma16124358 https://www.mdpi.com/journal/materials