**1. Introduction**

Skin, the largest organ of the human body, is an important protective organ that can safeguard the body against various dangers such as pathogens, toxins, ultraviolet radiation, and mechanical damage [1]. Skin has three main layers, namely, the epidermis, dermis, and hypodermis, each of which has a unique composition and function that contributes to the overall protection against external environmental factors [2]. Critical burns and wounds are amongst the most prevalent life-threatening dangers. The healing process of open skin includes the restoration of the skin's normal protective layer following trauma caused by accident or an intentional surgical procedure. This healing process has several integrated

**Citation:** Rizg, W.Y.; Hosny, K.M.; Eshmawi, B.A.; Alamoudi, A.J.; Safhi, A.Y.; Murshid, S.S.A.; Sabei, F.Y.; Al Fatease, A. Tailoring of Geranium Oil-Based Nanoemulsion Loaded with Pravastatin as a Nanoplatform for Wound Healing. *Polymers* **2022**, *14*, 1912. https:// 10.3390/polym14091912

Academic Editors: Ariana Hudita and José Antonio Gabaldón Hernández

Received: 26 March 2022 Accepted: 29 April 2022 Published: 7 May 2022

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**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/).

and coordinated successive phases, namely, hemostasis, inflammation, proliferation, revascularization, and remodeling [3,4]. A person's age, sex, level of stress, and pre-existing medical conditions all affect the time needed for complete wound healing [5]. Wounds associated with diabetes are a significant type that result from the stress diabetes causes in the body. The wound healing process is impaired in diabetic patients due to neuropathy, hypoxia, decreased immunity, fibroblastic dysfunction, and impaired angiogenesis [6,7]. Treatment strategies to accelerate the wound healing process were assessed, and many of them showed positive results [8–10].

Statin drugs are among the important cholesterol-lowering agents used currently [11]. Besides their powerful cholesterol-lowering activity, they have desirable effects on wound healing in many animal models [12,13]. Treatment of different wound animal models with statins led to an increase in vascular endothelial growth factor (VEGF), an important inducer of angiogenesis and promoter of wound healing [14,15]. Statins also improved epithelialization and enhanced the mechanical strength of the skin, both of which improved the healing of wounds [16]. Pravastatin (PV) is one of the statins; it was patented in 1980 and approved for clinical use in 1989. Like other statins, PV exerts its hypolipidemic action by inhibiting the enzyme HMG-CoA reductase, which is expressed in the liver and plays a pivotal role in cholesterol output [17]. In a recent clinical trial involving patients who received radiation for head and neck cancer, PV was administered in a dosage of 40 mg/day for 12 months. The results showed that PV was an efficient antifibrotic agent, and this finding supports the theory that PV could reverse radio-induced fibrosis and enhance the wound-healing process [18].

Geranium (Gr) oil is an essential oil extracted from the plant *Pelargonium graveolens* that was cultivated originally in South Africa and then distributed in Asia and the Middle East [19]. Gr oil is known traditionally for its calming effects on emotional distresses such as frustration, anger, and anxiety and its ability to lower high blood pressure [20]. Gr oil possesses immune-boosting properties and immune-modulating properties against natural killer cells [21]. Recent studies showed anticancer activity of this essential oil that resulted from two of its major components, citronellol and trans-geraniol [22,23]. The aerial parts of *P. graveolens* have been used for wound healing because they possess antimicrobial activity against *Staphylococcus aureus, Candida glabrata, Bacillus subtilis, Enterococcus faecalis, Candida krusei, Mycobacterium tuberculosis,* and *Mycobacterium intracellulare* [24]. Rose geranium oil has its own market in the cosmetic, perfume, and aromatherapy industries. Its antiinflammatory and palliative effects on the skin make this essential oil a good candidate for many topical formulations [25,26].

Self-nanoemulsifying drug delivery systems (SNEDDS) are anhydrous mixtures of a low-solubility drug, an oil, a surfactant, and a cosurfactant with a droplet size of less than 100 nm [27]. These nanoemulsions have been used extensively in recent times in dermal applications owing to their nanosized droplets, which enhance the solubility and transdermal permeation of the incorporated drug [28–30]. Different low-solubility drugs from different drug classes, such as antiviral drugs, immunomodulators, nonsteroidal antiinflammatory drugs, and lipid-lowering agents, have been incorporated in nanoemulsion formulations [31–33]. Besides the ease of making nanoemulsion formulations, they readily gain acceptance from authorities because they are considered to be drugs that are generally recognized as safe during manufacturing [34].

A design of experiment (DOE) approach was used in the formulation of the varying dosage forms in this study to choose the optimal formulation and test its biological activity. The DOE has been used extensively in nanotechnology formulations to help researchers study the interactions of drug excipients, solve problems during formulation, study the process parameters and how they affect each other, and reduce the number of experiments to reach the optimal formulation [35].

To our knowledge, no studies have been done to investigate the combined effect of statins and Gr oil in treating burn wounds. Therefore, the objective of this study was to introduce a transdermal drug delivery system containing a Gr oil–based nanoemulsion

loaded with PV (Gr-PV-NE). The intended choice of a transdermal drug delivery system was made based on its localized action and the droplet size of the nanoemulsion, which could promote skin membrane permeation and avoid presystemic metabolism and efflux mechanisms [36,37].

#### **2. Materials and Methods**

#### *2.1. Materials*

PV was acquired as a generous gift from the Saudi Arabian Japanese (SAJA) Pharmaceutical Company Limited (Jeddah, Saudi Arabia). Gr oil was purchased from the Beutysway Commercial Foundation (Jeddah, Saudi Arabia). Tween 80 and Span 80 were purchased from Sigma-Aldrich Co. (St. Louis, MO, USA). Transcutol was a gift from Gattefosse (Saint-Priest, France). High-performance liquid chromatography–grade methanol and acetonitrile were obtained from Merck (Darmstadt, Germany). All other reagents and chemicals were of analytical grade.
