Citation: Nasr, A.M.; Mortagi, Y.I.; Elwahab, N.H.A.; Alfaifi, M.Y.; Shati, A.A.; Elbehairi, S.E.I.; Elshaarawy, R.F.M.; Kamal, I. Upgrading the Transdermal Biomedical Capabilities of Thyme Essential Oil Nanoemulsions Using Amphiphilic Oligochitosan Vehicles. Pharmaceutics 2022, 14, 1350. https://doi.org/10.3390/ pharmaceutics14071350 Academic Editors: Peng Quan, Chao Liu, Maria Cristina Bonferoni and Pao-Chu Wu Received: 12 May 2022 Accepted: 23 June 2022 Published: 25 June 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/). pharmaceutics Article Upgrading the Transdermal Biomedical Capabilities of Thyme Essential Oil Nanoemulsions Using Amphiphilic Oligochitosan Vehicles Ali M. Nasr 1 , Yasmin I. Mortagi 2 , Nashwa H. Abd Elwahab 3 , Mohammad Y. Alfaifi 4 , Ali A. Shati 4 , Serag Eldin I. Elbehairi 4,5 , Reda F. M. Elshaarawy 6,7, * and Islam Kamal 1 1 Department of Pharmaceutics, Faculty of Pharmacy, Port Said University, Port Said 42526, Egypt; a.nasr@pharm.psu.edu.eg (A.M.N.); islamkamal@pharm.psu.edu.eg (I.K.) 2 Department of Pharmaceutics, Faculty of Pharmacy, Sinai University, Alarish 45511, Egypt; yasmin.mohamed@su.edu.eg 3 Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, Sinai University-Kantara Branch, Ismailia 41636, Egypt; nashwa.abdelwahab@su.edu.eg 4 Biology Department, Faculty of Science, King Khalid University, Abha 9004, Saudi Arabia; alfaifi@kku.edu.sa (M.Y.A.); aaalshati@kku.edu.sa (A.A.S.); serag@kku.edu.sa (S.E.I.E.) 5 Cell Culture Lab, Egyptian Organization for Biological Products and Vaccines (VACSERA Holding Company), 51 Wezaret El-Zeraa St., Agouza, Giza 12654, Egypt 6 Department of Chemistry, Faculty of Science, Suez University, Suez 43533, Egypt 7 Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine Universität Düsseldorf, 40225 Düsseldorf, Germany * Correspondence: reda.elshaarawy@suezuniv.edu.eg or reel@hhu.de Abstract: (1) Background: Thymus vulgaris L. (thyme) essential oil (TEO) has gained much attention because of its long history of medicinal usage. However, the lack of precise chemical profiling of the TEO and methods to optimize the bioactivity and delivery of its constituents has hampered its research on quality control and biological function; (2) Methods: The current study aimed to analyze the TEO’s chemical composition using the GC-MS method and identify its key components. Another objective of this work is to study the impact of the protective layer of amphiphilic oligochitosan (AOC) on the physicochemical stability and transdermal potentials of TEO multilayer nanoemulsions formulated by the incorporation of TEO, Tween80, lecithin (Lec), and AOC; (3) Results: The AOC protective layer significantly improved the stability of TEO-based NEs as revealed by the constancy of their physicochemical properties (particle size and zeta potential) during storage for a week. Excessive fine-tuning of thyme extract NEs and the AOC protective layer’s persistent positive charge have been contributed to the thyme extract’s improved anti-inflammatory, transdermal, and anti-melanoma potentials; (4) Conclusions: the AOC-coated NEs could offer novel multifunctional nanoplatforms for effective transdermal delivery of lipophilic bioactive materials. Keywords: thyme oil multilayer nanoemulsions; release kinetics; transdermal delivery; anti-inflammatory; anti-melanoma 1. Introduction In recent years, the use of nanoemulsion-based systems to deliver lipophilic bioactive ingredients such as vaccines, proteins, vitamins, essential oils [1], preservatives, antimi- crobial [2], anticancer [3], antiviral, anti-inflammatory, ophthalmic [4], and Alzheimer’s drugs [5] has attracted great interest. Embedding bioactive ingredients into the nanoemul- sions (NEs) enhances their physicochemical stability, imparts functional potentials, and increases bioavailability as well as transdermal permeability, all of which affect the na- noemulsion’s end-use properties in medicinal and cosmetic applications [6]. Although Pharmaceutics 2022, 14, 1350. https://doi.org/10.3390/pharmaceutics14071350 https://www.mdpi.com/journal/pharmaceutics