The incorporation of essential oils into the oil phase of oil-in-water microemulsions is an emerging strategy for the development of stable water-based topical formulations. The introduction of a suitable polymer to formulate film-forming microemulsions may improve topical administration; however, the effect of formulation variables on film quality attributes has not been studied. In this study, thermodynamically stable microemulsion concentrates consisting of surfactant (Kolliphor^® RH40), alone or in combination with cosurfactant Transcutol^® at surfactant-to-cosurfactant mass ratio 7:3, cosolvent (propylene glycol), and synthetic oils (medium-chain triglycerides or isopropyl myristate) with tea tree, cinnamon, or thyme essential oil were formulated and diluted with hypromellose solution in a water/isopropanol mixture (1:1 w/w) to produce film-forming microemulsions. The type and concentration of synthetic and essential oils and cosurfactant influenced the dynamics of structural transformations upon dilution as well as the rheological behavior, viscosity, and pH of film-forming microemulsions. Films obtained by casting film-forming microemulsions were opalescent, smooth, flexible, and swellable in artificial sweat and water. The weight and yield of films increase with the synthetic oils present and without cosurfactant added. Optimizing the ratio of essential oil/synthetic oil, the type of synthetic oil, and the inclusion/exclusion of cosurfactant allows for achieving the targeted film attributes for cosmetic and pharmaceutical applications, including wound treatment.

Films and film-forming systems (FFS) are increasingly recognized for their potential as convenient carriers for precise and efficient drug delivery to or via the skin and mucous membranes. Among them, those based on hypromellose as a film-forming polymer demonstrate many favorable characteristics. To better understand the role of hypromellose in topical films and film-forming drug delivery systems, this review presents physicochemical characteristics and film-forming performances of different types of hypromellose. Furthermore, the review encompasses relevant studies demonstrating the broad application of hypromellose as a film-forming agent in films and FFS for dermal, oromucosal, vaginal, ocular, and nasal application, reflecting the growing interest of researchers in this field. It also highlights the observed advantages of hypromellose over other film-forming polymers and implies future development of films and FFS in general.

There is great interest in development of film-forming systems for dermal (topical or transdermal) drug delivery (FFSDDD) due to their unique property to form a thin, continuous film upon administration to the skin surface, offering numerous advantages compared to conventional topical preparations. The primary research challenge in the FFSDDD development is the formulation of a carrier that represents a polymer solution in a volatile and non-volatile solvents mixture. We examined the influence of the film-forming polymer (hypromellose) concentration and the type and concentration of nonvolatile solvent (propylene glycol or macrogol 400) and volatile solvent (ethanol or isopropanol) on the physicochemical (pH and transmittance) and rheological properties of the film-forming solution (FFS) and the properties of the film formed. FFS containing 2.5% of hypromellose and 1.25% and 5% propylene glycol form films with the most desirable pH, appearance, viscosity, and flexibility, so they can be considered promising dermal drug delivery carriers.

Background/Objectives: Topical ketoprofen gels are limited by the need for frequent reapplication, short skin residence time, and the risk of sunlight-induced photoallergic dermatitis. Film-forming solutions (FFSs) allow for extended retention; however, the solvents used may affect the polymer film’s characteristics. The present study aimed to elucidate the effect of macrogol 400 and isopropanol and develop a hypromellose-based ketoprofen FFS using a design of experiments (DoE) approach. Methods: A 3² full factorial design was applied to investigate the effects of macrogol 400 (0–5%, w/w) (X₁) and isopropanol (25–50%, w/w) concentrations (X₂) on film mechanical properties (tensile strength (Y₁), elongation at break (Y₂), and Young’s modulus (Y₃)). The DoE-based placebo and ketoprofen-loaded FFSs were characterized for their physicochemical, rheological, and textural properties, while the corresponding films were evaluated for appearance, weight, stickiness, and mechanical properties. In vitro ketoprofen release from the drug-loaded FFS was also evaluated. Results: Macrogol 400 concentration was identified as a significant factor influencing film mechanical properties. As a film plasticizer, macrogol 400 improved film mechanical properties up to the optimal concentration (2.75%), whereas the water/isopropanol ratio mainly affected the applicative (rheological and textural) properties of the FFSs. Ketoprofen incorporation significantly reduced the film tensile strength and elongation at break. In vitro release testing demonstrated 58.52% ketoprofen release after 6 h, with the Weibull model showing the best fit to the release profile. Conclusions: Macrogol 400 and isopropanol have a complex, mutually conditioned influence on the application characteristics of hypromellose-based FFS and the mechanical characteristics of the films. Incorporation of ketoprofen into the selected placebo formulation significantly reduced film deformability but yielded a thin, transparent film with favorable in vitro drug-release characteristics. The developed FFS represents a promising topical dosage form for non-steroidal anti-inflammatory drugs and warrants further investigation, particularly in terms of skin retention and in vivo performance.