# Development of a Mouthwash Using Freeze-Drying Technique: An Optimization Study  
[PERSON]  
1 Department of Pharmaceutical Technology and Biopharmacy, Faculty of Pharmacy, \"[PERSON]\" University of Medicine and Pharmacy, 41 V. Babes Street, 400012 Cluj-Napoca, Romania; [EMAIL_ADDRESS] (S.M.I. ); [EMAIL_ADDRESS] (M.A.) [PERSON]  
2 Department of Dermopharmacy and Cosmetics, Faculty of Pharmacy, \"[PERSON]\" University of Medicine and Pharmacy, 12 I. Crenaga Street, 400010 Cluj-Napoca, Romania; [EMAIL_ADDRESS] (D.-R.A.); [EMAIL_ADDRESS] (M.L.M. ); [EMAIL_ADDRESS] (C.B.) [PERSON]  
1 Department of Pharmaceutical Technology and Biopharmacy, Faculty of Pharmacy, \"[PERSON]\" University of Medicine and Pharmacy, 41 V. Babes Street, 400012 Cluj-Napoca, Romania; [EMAIL_ADDRESS] (S.M.I. ); [EMAIL_ADDRESS] (M.A.) [PERSON]  
3 Department of Dermopharmacy and Cosmetics, Faculty of Pharmacy, \"[PERSON]\" University of Medicine and Pharmacy, 12 I. Crenaga Street, 400010 Cluj-Napoca, Romania; [EMAIL_ADDRESS] (D.-R.A.); [EMAIL_ADDRESS] (M.L.M. ); [EMAIL_ADDRESS] (C.B.) [PERSON]  
4 Department of Molecular Biology and Biotechnology, Faculty of Biology and Geology, \"Babes-Bolyai\" University, 1 M. Kogalniceanu Street, 400084 Cluj-Napoca, Romania; [EMAIL_ADDRESS]  
[PERSON]  
4 Department of Molecular Biology and Biotechnology, Faculty of Biology and Geology, \"Babes-Bolyai\" University, 1 M. Kogalniceanu Street, 400084 Cluj-Napoca, Romania; rahela. Out of the preparation methods, freeze-drying is employed to preserve the properties of pharmaceutical and cosmetic products [3]. Freeze-drying, also called \"lyophilization\" or \"cryodesiccation\" represents a drying technique that involves the removal of the solvent (usually water) by freezing and further evaporation by sublimation upon heating. During the lyophilization process, more than 90% of the containing water is lost. When reaching room temperature, the freeze-dried product remains dry and must be rehydrated before being used. Thus, the water removal prevents bacterial growth and stability issues, but also the need of adding preservatives [4]. The freeze-drying technique allows the development of lyophilized cosmetic compositions that are more stable than traditional products [5] and ensures the long-term stability of the bioactive compounds [3]. The medicinal use of the dried thallus of _Cetraria islandica_ (L.). Acharius s.l. from the _Parmeliaceae_ family, also known as Island moss or _Lichen islandicus_ has been documented thoroughly. The principal phytoconstituents are polysaccharides, 25-50% (lichenan, isolichenan), lichen acids (depsidones fumaroprotocetraric acid, protolichesterinic acid and usnic acid), and minerals [6]. Several in vitro studies indicate the antimicrobial, immunomodulating, anti-inflammatory, antiviral, and antioxidative activity of the _Cetraria islandica_ aqueous and ethanolic extracts [6]. The data obtained during in vitro studies are supported by in vivo studies investigating the activation of the reticuloendothelial system, anti-inflammatory, anti-proliferative, and antioxidative effects. Moreover, available clinical data support the efficacy of _Cetraria islandica_ extract for the treatment of inflammations of oral mucosa and dryness of the oral cavity [6]. Developed initially by the pharmaceutical industry, the Quality by Design (QbD) concept was adopted lately by the cosmetic industry as a systematic approach for obtaining high-quality products with the desired product performance. The main goals of the QbD paradigm include the design of robust formulations and manufacturing processes to reliably provide the required product quality [7]. Application of QbD principles relies on the use of Design of Experiments (DoE), a basic concept in formulation and optimization which significantly reduces the number of tests, time, and costs [8].