Abstract
Localized vaginal drug delivery can offer safer and more effective treatment options for various conditions, also for pregnant women. However, inadequate retention of formulation in the vaginal cavity hinders efficient treatment. Mucoadhesive drug delivery systems using mucoadhesive polymers may be a promising solution. In this work, the biopolymer chitosan was chosen for its well documented mucoadhesive properties, favorable biopharmaceutical profile, and low toxicity. However, its mucoadhesive abilities may depend on how chitosan is formulated. This study therefore focused on two distinct chitosan formulations, chitosan-coated liposomes and liposomes-in-chitosan hydrogel, to compare mucoadhesiveness across formulations. Additionally, two chitosan molecular weights (LMW and MMW) and four concentrations (0.1 %, 0.3 %, 0.6 % and 1.0 %) were examined, whilst considering site-specific factors like pH, biological fluids, and temperature. The formulations were characterized, and their mucoadhesive behavior evaluated by monitoring changes in viscosity and zeta potential upon mixing with mucin. Liposomes averaged 135 nm in size with a zeta potential of −2.78 mV, where the charge increased with chitosan coating or incorporation into chitosan hydrogel. Both chitosan-coated liposomes and liposomes-in-hydrogel exhibited rheological properties suitable for vaginal application. Mucoadhesion indeed varied based on the formulation, chitosan concentration, molecular weight, pH, and temperature. Notably, liposomes-in-hydrogel formulations demonstrated superior mucoadhesive potential. These findings emphasize the importance of formulation design and environmental factors in optimizing mucoadhesion.
Highlights
- Mucoadhesiveness of chitosan-coated liposomes and chitosan hydrogel was compared.
- Hydrogel formulation was found superior.
- Concentration-dependent correlation was confirmed.
- Environmental factors such as pH and temperature affect the mucoadhesive potential.
Introduction
The vaginal route of drug administration offers a promising alternative to the conventional oral route, whilst additionally enabling localized drug delivery. This approach allows for higher drug concentrations at the target site using lower doses, thereby reducing systemic side effects compared to oral administration. Additionally, topical formulations provide direct treatment at the target site, ensuring safer and more effective options, which may also be suitable for pregnant patients [1,2]. Furthermore, localized therapy can effectively bypass limitations associated with the therapeutic use of certain active substances, such as antifungal or anticancer drugs, which may be linked to systemic toxicity risks [3,4]. Overall, topical vaginal drug delivery strategies offer safer, more effective alternatives for a wide variety of conditions.
However, while localized drug delivery offers numerous advantages, it also comes with its own set of challenges. Inadequate retention in the vaginal cavity poses the most significant challenge for vaginally administered formulations. The mucus turnover at vaginal mucosa as well as the peristaltic movements of the vaginal wall can both result in leakage, particularly for formulations with lower viscosity. This leads to rapid removal from the site of action, hindering effective localized therapy and necessitating frequent applications to maintain therapeutic efficacy [5,6].
To address these challenges, mucoadhesive drug delivery systems have been proposed as a viable solution. These systems adhere to the vaginal mucosa through chemical and/or physical interactions with various mucus components, thereby increasing residence time. A wide range of natural and synthetic polymers has been explored for the development of such systems, with the primary goal of prolonging the retention of the formulation at the application site [[7], [8], [9]]. To obtain the optimal mucoadhesive formulation, several aspects are contributive, such as choice of polymer, type of formulation and the polymer concentration. Selecting the appropriate polymer to impart mucoadhesive properties to nanomaterials is a crucial consideration for their design. There already exist several detailed reviews that discuss the selection of materials, including specific polymers such as chitosan [6].
Chitosan has emerged as a particularly promising candidate due to its favorable biopharmaceutical properties. It is well-tolerated, biocompatible, biodegradable, low-toxic, and exhibits strong bioadhesive properties [[10], [11], [12], [13]]. Its cationic nature allows effective interaction with negatively charged components of mucus, ensuring adhesion to vaginal mucosa [[14], [15], [16]]. Additionally, chitosan’s antimicrobial and anti-inflammatory properties further enhance its suitability for vaginal drug delivery systems [17]. In recent years, numerous chitosan-based drug delivery systems have been developed for vaginal applications, ranging from bioadhesive tablets to more advanced formulations such as hydrogels and nanotechnology-based systems including surface modified liposomes amongst many others [17,18].
In previous work we have focused on two such formulations, namely liposomes-in-hydrogel and chitosan-coated liposomes, where chitosan was primarily used as a way of increasing mucoadhesion [[19], [20], [21]]. We also see these liposomal modifications or additions in other research [22,23]. However, when considering the many different types of chitosan-based formulations, it is important to recognize that the formulation type can influence the properties of chitosan, such as its mucoadhesive and antimicrobial effect [24]. In example, the formulation’s texture and viscosity may affect its interactions with mucus and its spreadability within the vaginal cavity. Over the past decades, various methods have been developed to evaluate adhesive interactions with mucin for numerous substances and formulations. For formulations with low viscosity, such as plain hydrogels and liposomal formulations, rheological methods have been labeled as a suitable choice for assessment [25,26].
Therefore, this study aimed to develop two differently formulated chitosan-liposome drug delivery systems, chitosan-coated liposomes and liposomes-in-chitosan hydrogel, to compare their mucoadhesive properties and assess the impact of formulation. We also investigated the impact of the formulations considering two different chitosan molecular weights and four chitosan concentrations, namely 0.1, 0.3, 0.6 and 1.0 %, and their effect on mucoadhesiveness. Additionally, site specific factors like the pH, biological fluids, and temperature were also considered. To eliminate the influence of potentially confounding variables, the study was conducted without incorporating active molecules in the formulations and was not tied to any specific therapy, focusing instead on its intended application site. Prior to evaluation, the liposomal formulations were characterized, and their mucoadhesive abilities compared based on the method of chitosan incorporation. This comparison was performed by monitoring the changes in viscosity and zeta potential upon interaction with mucin.
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Materials
Chitopharm™ S – low molecular weight (LMW) chitosan (average of 50–450 kDa) and Chitopharm™ M − medium molecular weight (MMW) chitosan (average 350–600 kDa), both sourced from shrimp shell (degree of deacetylation between 75 and 95 %), were kindly provided by Chitinor (Tromsø, Norway). Additionally, Lipoid S100 (phosphatidylcholine content >94 %) was generously donated by Lipoid GmbH (Ludwigshafen, Germany). Glacial acetic acid, glycerol (86 %), and methanol were all procured from VWR International (Fontenay-sous-Bois, France). Cibacron brilliant red 3B-A was obtained from Santa Cruz Biotechnology (Dallas, TX, USA). A range of chemicals including ammonium acetate, D-(+)glucose, sodium chloride, monobasic potassium phosphate, dibasic potassium phosphate, bovine serum albumin, and mucin from porcine stomach (Type III, bound sialic acid 0.5–1.5 %, partially purified powder), along with calcium hydroxide, glycine hydrochloride, and hydrochloric acid were sourced from Sigma-Aldrich (St. Louis, MO, USA). Potassium hydroxide, lactic acid, and urea were purchased from NMD (Oslo, Norway).
Silje Mork, Charlotte Eilertsen, Nataša Škalko-Basnet, May Wenche Jøraholmen, Formulation matters: Assessment of the correlation between mucoadhesiveness and type of chitosan formulation for vaginal application, Journal of Drug Delivery Science and Technology, Volume 114, Part B, 2025, 107564, ISSN 1773-2247, https://doi.org/10.1016/j.jddst.2025.107564.
