Mucoadhesive In Situ Gelling Liquid Crystalline Precursor System to Improve the Vaginal Administration of Drugs

In-situ gel: A smart carrier for drug delivery

In-situ gel technology is a promising drug delivery strategy that undergoes a 'sol to gel' transition upon administration, providing controlled and prolonged drug release. These gels are composed of cross-linked 3D networks of polymers, with hydrogels being a specific type of absorbing water while retaining their shape. Gelation can be triggered by various stimuli, such as temperature, pH, ions, and light. They offer several advantages like improved patient compliance, extended drug residence time, localized drug delivery, etc, but also have some disadvantages like drug degradation and limited mechanical strength. In-situ gel falls into three categories: temperature-sensitive, ion-sensitive, and pH-sensitive, but multi-responsive gels that respond to multiple stimuli have better drug release characteristics. The mechanism of in-situ gel formation involves physical and chemical mechanisms. There are various applications of in-situ gel, like ocular drug delivery, nose-to-brain delivery, etc. In this review, we have discussed the types, and mechanisms of in-situ gel & use of in-situ gel in the treatment of different diseases through various routes like buccal, vaginal, ocular, nasal, etc., along with its use in targeted drug delivery.

Mucoadhesive liquid crystal precursor system for photodynamic therapy of oral cancer mediated by methylene blue

Oral cancer is one of the most prevalent types of cancer head and neck cancers worldwide. Photodynamic therapy (PDT) has demonstrated great potential against cancers, reducing long-term morbidity. In this study, we investigated the incorporation of methylene blue (MB) in a mucoadhesive liquid crystal precursor system (LCPS) for oral cancer treatment. The photostability and the in vitro release, permeation, and retention profile of MB-loaded LCPS (MB-LCPS) were investigated, as well as its in vitro PDT activity against normal (HaCaT) and tumoral (HSC-3) cell lines. LCPS increased the photostability of MB and exhibited a prolonged release profile of MB. In addition, LCPS increased the retention of MB in the porcine esophageal mucosa by around 3 times higher than the MB solution. The retention of MB in LCPS was around 2 times greater than its permeability, which is suitable for guaranteeing the maintenance of the therapy in the oral cavity. In vitro cytotoxicity assay indicated that MB-LCPS increased the antitumoral activity of MB after 20 min of irradiation at 660 nm and 12.5 J/cm2. The results obtained suggest that the developed formulation is an interesting strategy for the potential application in the treatment of oral cancer by PDT.

Enhancing Antifungal Treatment of Candida albicans with Hypericin-Loaded Nanostructured Lipid Carriers in Hydrogels: Characterization, In Vitro, and In Vivo Photodynamic Evaluation

BACKGROUND

Vulvovaginal candidiasis (VVC) is a worldwide public health problem caused predominantly by the opportunistic polymorphic fungus Candida albicans, whose pathogenicity is associated with its morphological adaptability. To potentiate the treatment of C. albicans-induced VVC by an alternative method as photodynamic therapy (PDT), hypericin (Hy), a potent photosensitizer compound was incorporated into a nanostructured lipid carrier (NLC) and dispersed in hydrogel (HG).

METHODS

After preparation of the sonication process, an NLC loaded with Hy was dispersed in HG based on Poloxamer 407 and chitosan obtaining Hy.NLC-HG. This hydrogel system was physically and chemically characterized and its in vitro and in vivo photodynamic and antifungal effects were evaluated.

RESULTS

Through scanning electron microscopy, it was possible to observe a hydrogel system with a porous polymeric matrix and irregular microcavities. The Hy.NLC-HG system showed mucoadhesive properties (0.45 ± 0.08 N) and a satisfactory injectability (15.74 ± 4.75 N.mm), which indicates that it can be easily applied in the vaginal canal, in addition to a controlled and sustained Hy release profile from the NLC-HG of 28.55 ± 0.15% after 720 min. The in vitro antibiofilm assay significantly reduced the viability of C. albicans (p < 0.001) by 1.2 log10 for Hy.NLC-HG/PDT and 1.9 log10 for PS/PDT, Hy.NLC/PDT, and free RB/PDT, compared to the PBS/PDT negative control. The in vivo antifungal evaluation showed that animals treated with the vaginal cream (non-PDT) and the PDT-mediated Hy.NLC-HG system showed a significant difference of p < 0.001 in the number of C. albicans colonies (log) in the vaginal canal, compared to the inoculation control group.

CONCLUSIONS

Thus, we demonstrate the pharmaceutical, antifungal, and photodynamic potential of hydrogel systems for Hy vaginal administration.

Lyotropic liquid crystal mesophases as transdermal delivery systems for lipophilic drugs: A comparative study

The present work aimed to evaluate different Liquid Crystal Mesophases (LCM) as transdermal drug delivery systems (TDDS) for nifedipine (NFD), a lipophilic drug model. The formulations composed of water, Citrus sinensis essential oil (CSEO), PPG-5-CETETH-20, and Olive oil ester PEG-7 were obtained and characterized by polarized light microscopy (PLM), rheology, small-angle x-ray scattering (SAXS), Fourier transform infrared coupled with an attenuated total reflection accessory (FTIR-ATR) and in vitro assays: bioadhesion, drug release, skin permeation, and retention tests. As a result, changes in component proportions led to several transparent viscous systems with an anisotropic profile. PLM and SAXS proved the presence of lamellar (S1), hexagonal (S3), and lamellar + hexagonal (S2) LCM, and rheology showed a high viscoelasticity profile. LCMs were able to adhere to the skin, and S2 achieved higher adhesion strength. NFD (5 mg/mL) has not modified the organization of LCMs. Results also showed that S3 promoted higher permeation and retention and higher disorganization of stratum corneum lipids, which is the main permeation-enhancing mechanism. Thus, the formulations obtained can carry and improve drug delivery through the skin and are promising TDDS for lipophilic drug administration, such as NFD.

Hypericin: A natural anthraquinone as promising therapeutic agent

BACKGROUND

Hypericin is a prominent secondary metabolite mainly existing in genus Hypericum. It has become a research focus for a quiet long time owing to its extensively pharmacological activities especially the anti-cancer, anti-bacterial, anti-viral and neuroprotective effects. This review concentrated on summarizing and analyzing the existing studies of hypericin in a comprehensive perspective.

METHODS

The literature with desired information about hypericin published after 2010 was gained from electronic databases including PubMed, SciFinder, Science Direct, Web of Science, China National Knowledge Infrastructure databases and Wan Fang DATA.

RESULTS

According to extensive preclinical and clinical studies conducted on the hypericin, an organized and comprehensive summary of the natural and artificial sources, strategies for improving the bioactivities, pharmacological activities, drug combination of hypericin was presented to explore the future therapeutic potential of this active compound.

CONCLUSIONS

Overall, this review offered a theoretical guidance for the follow-up research of hypericin. However, the pharmacological mechanisms, pharmacokinetics and structure activity relationship of hypericin should be further studied in future research.

Intravaginal Drug Delivery Systems to Treat the Genitourinary Syndrome of Menopause: Towards the Design of Safe and Efficacious Estrogen-loaded Prototypes

Estrogens locally delivered to the vagina by tablets, capsules, rings, pessaries, and creams are the most common and highly recommended platforms to treat the genitourinary syndrome of menopause (GSM). Estradiol, an essential estrogen, is routinely administered alone, or in combination with progestins, to effectively alleviate the symptoms associated with moderate to severe menopause when non-pharmacological interventions are not indicated. Since the risk and side effects of estradiol use depends on the administered amount and duration of use, the lowest effective dose of estradiol is recommended when long-term treatment is required. Although there is a wealth of data and literature comparing vaginally administered estrogen-containing products, there is a lack of information revealing the effect of the delivery system used and formulation constituent's attributes on the efficacy, safety, and patient acceptability of these dosage forms. This review therefore aims to classify and compare various designs of commercially available and non-commercial vaginal 17β-estradiol formulations and analyze their performance in terms of systemic absorption, efficacy, safety, and patient satisfaction and acceptance. The vaginal estrogenic platforms included in this review are the currently marketed and investigational 17β-estradiol tablets, softgel capsules, creams, and rings for the treatment of GSM, based on their different design specifications, estradiol loads, and materials used in their preparation. Additionally, the mechanisms of the effects of estradiol on GSM have been discussed, as well as their potential impact on treatment efficacy and patient compliance.

Design and Characterization of Lipid-Surfactant-Based Systems for Enhancing Topical Anti-Inflammatory Activity of Ursolic Acid

Skin inflammation is a symptom of many skin diseases, such as eczema, psoriasis, and dermatitis, which cause rashes, redness, heat, or blistering. The use of natural products with anti-inflammatory properties has gained importance in treating these symptoms. Ursolic acid (UA), a promising natural compound that is used to treat skin diseases, exhibits low aqueous solubility, resulting in poor absorption and low bioavailability. Designing topical formulations focuses on providing adequate delivery via application to the skin surface. The aim of this study was to formulate and characterize lipid-surfactant-based systems for the delivery of UA. Microemulsions and liquid crystalline systems (LCs) were characterized by polarized light microscopy (PLM), rheology techniques, and textural and bioadhesive assays. PLM supported the self-assembly of these systems and elucidated their formation. Rheologic examination revealed pseudoplastic and thixotropic behavior appropriate, and assays confirmed the ability of these formulations to adhere to the skin. In vivo studies were performed, and inflammation induced by croton oil was assessed for response to microemulsions and LCs. UA anti-inflammatory activities of ~60% and 50% were demonstrated by two microemulsions and 40% and 35% by two LCs, respectively. These data support the continued development of colloidal systems to deliver UA to ameliorate skin inflammation.

In vitro and ex vivo models for evaluating vaginal drug delivery systems

Vaginal drug delivery systems are often preferred for treating a variety of diseases and conditions of the female reproductive tract (FRT), as delivery can be more targeted with less systemic side effects. However, there are many anatomical and biological barriers to effective treatment via the vaginal route. Further, biocompatibility with the local tissue and microbial microenvironment is desired. A variety of in vitro and ex vivo models are described herein for evaluating the physicochemical properties and toxicity profile of vaginal drug delivery systems. Deciding whether to utilize organoids in vitro or fresh human cervicovaginal mucus ex vivo requires careful consideration of the intended use and the formulation characteristics. Optimally, in vitro and ex vivo experimentation will inform or predict in vivo performance, and examples are given that describe utilization of a range of methods from in vitro to in vivo. Lastly, we highlight more advanced model systems for other mucosa as inspiration for the future in model development for the FRT.

Curcumin-Loaded Micelles Dispersed in Ureasil-Polyether Materials for a Novel Sustained-Release Formulation

Vulvovaginal candidiasis (VVC) is a vulvar/vaginal infection that affects approximately 75% of women worldwide. The current treatment consists of antimicrobials with hepatotoxic properties and high drug interaction probabilities. Therefore, this study aimed to develop a new treatment to VVC based on micelles containing curcumin (CUR) dispersed in a ureasil-polyether (U-PEO) hybrid. The physical-chemical characterization was carried out in order to observe size, shape, crystallinity degree and particle dispersion in the formulation and was performed by dynamic light scattering (DLS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and through in vitro release study. The results of DLS and SEM exhibited micelles with 35 nm, and encapsulation efficiency (EE) results demonstrated 100% of EE to CUR dispersed in the U-PEO, which was confirmed by the DRX. The release results showed that CUR loaded in U-PEO is 70% released after 10 days, which demonstrates the potential application of this material in different pharmaceutical forms (ovules and rings), and the possibility of multidose based on a single application, suggesting a higher rate of adherence.

p-Coumaric acid loaded into liquid crystalline systems as a novel strategy to the treatment of vulvovaginal candidiasis

Vulvovaginal candidiasis (VVC) is an extremely common type of vaginal infection, which is mainly caused by Candida albicans. However, non-albicans Candida species are frequently more resistant to conventional antifungal agents and can represent up to 30% of cases. Due to side effects and increasing antifungal resistance presented by standard therapies, phenolic compounds, such as p-coumaric acid (p-CA), have been studied as molecules from natural sources with potential antifungal activity. p-CA is a poorly water-soluble compound, thus loading it into liquid crystals (LCs) may increase its solubility and effectiveness on the vaginal mucosa. Thereby, here we propose the development of mucoadhesive liquid crystalline systems with controlled release of p-CA, for the local treatment of VVC. Developed LCs consisted of fixed oily and aqueous phases (oleic acid and cholesterol (5:1) and poloxamer dispersion 16%, respectively), changing only the surfactant phase components (triethanolamine oleate (TEA-Oleate) or triethanolamine (TEA), the latter producing TEA-Oleate molecules when mixed with oleic acid). Systems were also diluted in artificial vaginal mucus (1:1 ratio) to mimic the vaginal environment and verify possible structural changes on formulations upon exposure to the mucosa. From the characterization assays, p-CA loaded TEA-Oleate systems presented mucoadhesive profile, liquid crystalline mesophases, well-organized structures and pseudoplastic behaviour, which are desirable parameters for topical formulations. Moreover, they were able to control the release of p-CA throughout the 12 h assay, as well as decrease its permeation into the vaginal mucosa. p-CA showed antifungal activity in vitro against reference strains of C. albicans (SC5314), C. glabrata (ATCC 2001) and C. krusei (ATCC 6258), and exhibited higher eradication of mature biofilms than amphotericin B and fluconazole. In vivo experiments demonstrated that the formulations reduced the presence of filamentous forms in the vaginal lavages and provided an improvement in swelling and redness present in the mice vaginal regions. Altogether, here we demonstrated the potential and feasibility of using p-CA loaded liquid crystalline systems as a mucoadhesive drug delivery system for topical treatment of VVC.

Highlights in poloxamer-based drug delivery systems as strategy at local application for vaginal infections

Infectious diseases related to the vagina include diseases caused by the imbalance of the vaginal flora and by sexually transmitted infections. Some of these present themselves as a public health problem due to the lack of efficient treatment that leads to their complete cure, and others due to the growing resistance to drugs used in therapy. In this sense, new treatment strategies are desirable, with vaginal administration rout being a great choice since can bypass first-pass metabolism and decrease drug interactions and adverse effects. However, it is worth highlighting limitations related to patient's discomfort at application time. Thereby, the use of poloxamer-based drug delivery systems is desirable due its stimuli-sensitive characteristic. Therefore, the present review reports a brief overview of poloxamer properties, biological behavior and advances in poloxamer applications in controlled drug release systems for infectious diseases related to the vagina treatment and prevention.

In vivo study of hypericin-loaded poloxamer-based mucoadhesive in situ gelling liquid crystalline precursor system in a mice model of vulvovaginal candidiasis

The present study reports the performance of the pigment hypericin (HYP)-loaded poloxamer-based mucoadhesive in situ gelling liquid crystalline precursor system (LCPS) for the treatment of vulvovaginal candidiasis (VVC) in mice. LCPS composed of 40% of ethoxylated and propoxylated cetyl alcohol, 30% of oleic acid and cholesterol (7:1), 30% of a dispersion of 16% poloxamer 407 and 0.05% of HYP (HYP-LCPS) was prepared and characterized by polarized light microscopy (PLM), small-angle X-ray scattering (SAXS) and ex vivo permeation and retention studies across vaginal porcine mucosa were performed. In addition, the antifungal properties of the HYP-LCPS were evaluated in a murine in vivo model; for this, infected C57BL female mice groups were treated with both HYP in solution and HYP-LCPS, and after 6 days colony forming unit (CFU)/ml count was performed. PLM and SAXS confirmed that HYP-LCPS is a microemulsion situated in boundary transition region confirming its action as an LCPS. When in contact with simulated vaginal fluid, HYP-LCPS became rigid and exhibited maltase crosses and bragg peaks characteristics of lamellar phase. Ex vivo permeation and retention studies showed that HYP-LCPS provides a localized treatment on the superficial layers of porcine vaginal mucosa. HYP-LCPS induced a significant reduction in the number of CFU/ml in the mice; thus this formulation indicated it is as effective as a commercial dosage form. It was concluded that LCPS maintains the biological activity of HYP and provides an adequate drug delivery system for this lipophilic molecule at the vaginal mucosa, being a promising option in cases of VVC.

Promising Drug Delivery Approaches to Treat Microbial Infections in the Vagina: A Recent Update

An optimal host-microbiota interaction in the human vagina governs the reproductive health status of a woman. The marked depletion in the beneficial Lactobacillus sp. increases the risk of infection with sexually transmitted pathogens, resulting in gynaecological issues. Vaginal infections that are becoming increasingly prevalent, especially among women of reproductive age, require an effective concentration of antimicrobial drugs at the infectious sites for complete disease eradication. Thus, topical treatment is recommended as it allows direct therapeutic action, reduced drug doses and side effects, and self-insertion. However, the alterations in the physiological conditions of the vagina affect the effectiveness of vaginal drug delivery considerably. Conventional vaginal dosage forms are often linked to low retention time in the vagina and discomfort which significantly reduces patient compliance. The lack of optimal prevention and treatment approaches have contributed to the unacceptably high rate of recurrence for vaginal diseases. To combat these limitations, several novel approaches including nano-systems, mucoadhesive polymeric systems, and stimuli-responsive systems have been developed in recent years. This review discusses and summarises the recent research progress of these novel approaches for vaginal drug delivery against various vaginal diseases. An overview of the concept and challenges of vaginal infections, anatomy and physiology of the vagina, and barriers to vaginal drug delivery are also addressed.

The role of polysaccharides from natural resources to design oral insulin micro- and nanoparticles intended for the treatment of Diabetes mellitus: A review

Oral administration of insulin (INS) would represent a revolution in the treatment of diabetes, considering that this route mimics the physiological dynamics of endogenous INS. Nano- and microencapsulation exploiting the advantageous polysaccharides properties has been considered an important technological strategy to protect INS against harsh conditions of gastrointestinal tract, in the same time that improve the permeability via transcellular and/or paracellular pathways, safety and in some cases even selectivity for targeting delivery of INS. In fact, some polysaccharides also give to the systems functional properties such as pH-responsiveness, mucoadhesiveness under specific physiological conditions and increased intestinal permeability. In general, all polysaccharides can be functionalized with specific molecules becoming more selective to the cells to which INS is delivered. The present review highlights the advances in the past 10 years on micro- and nanoencapsulation of INS exploiting the unique natural properties of polysaccharides, including chitosan, starch, alginate, pectin, and dextran, among others.

Recent advances in hydrogels as strategy for drug delivery intended to vaginal infections

Vaginal infections represent a clear women health problem due to the several issues as high recurrence rate, drug resistence and emergence of persistent strains. However, achieving improvements in therapeutic efficacy by using conventional formulations intended to vaginal drug delivery remains as a challenge due to anatomy and physiology of the vagina, since the secretion and renewal of vaginal fluids contribute to the removal of the dosage form. Hydrogels have been widely exploited aiming to achieve drug delivery directly into vaginal mucosa for local therapy due to their attractive features as increased residence time of the drug at the action site and control of drug release rates. Some polymers can aggregate specific properties to hydrogels as mucoadhesive, stimuli-responsive and antimicrobial, improving their interaction with the biological interface and therapeutic response. In this review, we highlight the advances, advantages and challenges of the hydrogels as drug and/or nanocarrier vehicles intended to the treatment of vaginal infections, emphasizing also the polymers and their properties more explored on the design these systems to improve the therapeutic effect on the vaginal tissue. In addition, this review can contribute for better exploitation these systems in search of new local treatments for bacterial vaginosis, candidiasis and trichomoniasis.

Recent Advances in the Development of In Situ Gelling Drug Delivery Systems for Non-Parenteral Administration Routes

In situ gelling drug delivery systems have gained enormous attention over the last decade. They are in a sol-state before administration, and they are capable of forming gels in response to different endogenous stimuli, such as temperature increase, pH change and the presence of ions. Such systems can be administered through different routes, to achieve local or systemic drug delivery and can also be successfully used as vehicles for drug-loaded nano- and microparticles. Natural, synthetic and/or semi-synthetic polymers with in situ gelling behavior can be used alone, or in combination, for the preparation of such systems; the association with mucoadhesive polymers is highly desirable in order to further prolong the residence time at the site of action/absorption. In situ gelling systems include also solid polymeric formulations, generally obtained by freeze-drying, which, after contact with biological fluids, undergo a fast hydration with the formation of a gel able to release the drug loaded in a controlled manner. This review provides an overview of the in situ gelling drug delivery systems developed in the last 10 years for non-parenteral administration routes, such as ocular, nasal, buccal, gastrointestinal, vaginal and intravesical ones, with a special focus on formulation composition, polymer gelation mechanism and in vitro release studies.

Comparative Pharmacokinetics of Nimodipine in Rat Plasma and Tissues Following Intraocular, Intragastric, and Intravenous Administration

We investigated the pharmacokinetics of nimodipine (NMD) in rats plasma and tissues following intraocular (io), intragastric (ig), and intravenous (iv) administration at doses of 5.0 mg/kg io and iv and 10.0 mg/kg ig. After a single dose of NMD, plasma, heart, liver, spleen, lung, kidney, and brain samples were collected at the scheduled time points. The concentration of NMD in rat plasma and tissues was determined by high-performance liquid chromatography, and the main pharmacokinetic parameters were calculated and compared. NMD was rapidly absorbed and reached the maximum plasma concentration in approximately 5 min after io administration. The absolute bioavailability after io administration was higher than that after ig administration (40.05% vs. 5.67%). There were significant differences in the tissue distribution of NMD with different administration routes. After io administration, NMD was distributed more in the lung, spleen, and brain tissues, and less in the kidney. The maximum drug concentration after io administration in the heart, liver, spleen, lung, kidney, and brain was 1.00, 0.47, 2.02, 1.47, 0.22, and 5.79 times higher than that after via ig administration, and the area under the curve value was 0.59, 0.78, 1.71, 1.84, 0.25, and 4.59 times greater, respectively. Nimodipine appears to achieve systemic effects via io administration. Compared with ig, io administration could significantly increase NMD distribution in the brain tissue, indicating that NMD could be delivered to the brain via io administration.

Biosurfactant from vaginal Lactobacillus crispatus BC1 as a promising agent to interfere with Candida adhesion

BACKGROUND

Lactobacillus spp. dominating the vaginal microbiota of healthy women contribute to the prevention of urogenital and sexually transmitted infections. Their protective role in the vagina can be mediated by Lactobacillus cells themselves, metabolites or bacterial components, able to interfere with pathogen adhesion and infectivity. Vulvovaginal candidiasis (VVC) is a common genital infection, caused by the overgrowth of opportunistic Candida spp. including C. albicans, C. glabrata, C. krusei and C. tropicalis. Azole antifungal drugs are not always efficient in resolving VVC and preventing recurrent infections, thus alternative anti-Candida agents based on vaginal probiotics have gained more importance. The present work aims to chemically characterize the biosurfactant (BS) isolated from a vaginal Lactobacillus crispatus strain, L. crispatus BC1, and to investigate its safety and antiadhesive/antimicrobial activity against Candida spp., employing in vitro and in vivo assays.

RESULTS

BS isolated from vaginal L. crispatus BC1 was characterised as non-homogeneous lipopeptide molecules with a critical micellar concentration value of 2 mg/mL, and good emulsification and mucoadhesive properties. At 1.25 mg/mL, the BS was not cytotoxic and reduced Candida strains' ability to adhere to human cervical epithelial cells, mainly by exclusion mechanism. Moreover, intravaginal (i.va.) inoculation of BS in a murine experimental model was safe and did not perturb vaginal cytology, histology and cultivable vaginal microbiota. In the case of i.va. challenge of mice with C. albicans, BS was able to reduce leukocyte influx.

CONCLUSIONS

These results indicate that BS from vaginal L. crispatus BC1 is able to interfere with Candida adhesion in vitro and in vivo, and suggest its potential as a preventive agent to reduce mucosal damage occasioned by Candida during VVC.

Ozonated Oils as Antimicrobial Systems in Topical Applications. Their Characterization, Current Applications, and Advances in Improved Delivery Techniques

The search for a wide spectrum of antimicrobial agents that can avoid resistance while maintaining reasonable side effects has led to ozonated oils experiencing an increase in scientific interest and clinical applications. The treatment of vegetable oils with ozone leads to the creation of a reservoir of ozone that slowly releases into the skin thanks to the fact that ozone can be held as ozonides of unsaturated fatty acids. Interest in the use of ozonated oils has meant that several ozonated-vegetable-oil-containing products have been commercialized as cosmetic and pharmaceutical agents, and in innovative textile products with antibacterial activity. New approaches to the delivery of ozonated oils have very recently appeared in an attempt to improve their characteristics and reduce drawbacks, such as an unpleasant odor, high viscosity and undesired effects on skin, including irritation and rashes. The present review focuses on the current status of delivery agents that use ozonated oils as antimicrobial agents in topical (dermal, skin, and soft tissues) treatments. Challenges and future opportunities for these delivery systems will also be discussed.