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Article

Development and Characterization of Citalopram-Loaded Thermosensitive Polymeric Micelles for Nasal Administration

by
Fatima Rajab
,
Bence Sipos
*,
Gábor Katona
and
Ildikó Csóka
Institute of Pharmaceutical Technology and Regulatory Affairs, University of Szeged, Eötvös Street 6, H-6720 Szeged, Hungary
*
Author to whom correspondence should be addressed.
Pharmaceutics 2025, 17(9), 1147; https://doi.org/10.3390/pharmaceutics17091147
Submission received: 18 July 2025 / Revised: 25 August 2025 / Accepted: 31 August 2025 / Published: 1 September 2025
(This article belongs to the Section Nanomedicine and Nanotechnology)
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Abstract

Background/Objectives: The intranasal (IN) route of administration is a promising non-invasive approach for brain targeting, bypassing the blood–brain barrier and enhancing bioavailability. Citalopram hydrobromide (CT), a widely prescribed sparingly water-soluble selective serotonin reuptake inhibitor (SSRI), faces challenges with oral and intravenous administration, including delayed onset, adverse effects, and patient compliance issues. Methods: This study aimed to develop a novel thermoresponsive polymeric micelle (PM) system based on Pluronic® copolymers (Pluronic F127 and Poloxamer 188) improving CT’s solubility, stability, and nasal permeability for enhanced antidepressant efficacy. A preliminary study was conducted to select the optimized formulation. The preparation process involved using the thin-film hydration method, followed by freeze-drying. Comprehensive evaluations of optimized formulation characteristics included Z-average, polydispersity index (PdI), thermal behavior (lower critical solution temperature, LCST), encapsulation efficiency, X-ray powder diffraction (XRPD), thermodynamic solubility, and biological stability. Additionally, in vitro CT release and CT permeability in nasal conditions were studied. Stability under storage was also evaluated. Results: The optimized CT-PM formulation showed nanoscale micelle size (Z-average of 31.41 ± 0.99 nm), narrow size distribution (polydispersity index = 0.241), and a suitable thermal behavior for intranasal delivery (lower critical solution temperature (LCST) ~31 °C). Encapsulation efficiency reached approximately 90%, with an amorphous structure confirmed via XRPD, leading to a 95-fold increase in CT solubility. The formulation demonstrated appropriate biological and physical stability. In vitro studies showed a 25-fold faster CT release from optimized formulation compared to the initial CT, while CT-PM permeability in nasal conditions increased four-fold. Conclusions: This novel nanoscale thermosensitive formulation is a value-added strategy for nasal drug delivery systems, offering enhanced drug solubility, rapid drug release, stability, and improved permeability. This smart nanosystem represents a promising platform to overcome the limitations of conventional CT administration, improving therapeutic outcomes and patient compliance in depression management.

Graphical Abstract

1. Introduction

Depression is one of the most common mental health diseases and a dominant cause of disability around the world. According to the World Health Organization (WHO), it impacts approximately 280 million people worldwide and is associated with 700,000 suicides annually [1]. Many obstacles result from depression that could decrease the patient’s quality of life, such as difficulties in concentration, lack of social activities, and suicidal thoughts [2]. Moreover, it has been recognized as an individual risk factor for cardiovascular disease [3,4]. Although several treatment approaches, including psychotherapies and pharmaceutical treatments, are applied, under 50% of patients fully recover [5,6]. Selective serotonin reuptake inhibitors (SSRIs), the current first line, are widely used antidepressants due to their tolerability, efficacy, and safety [7]. Citalopram hydrobromide (CT) is one of the most prescribed SSRIs, which has the safest drug interaction profile due to its relatively low protein binding compared to other SSRIs [7]. It also has the highest selectivity for inhibiting serotonin reuptake compared to noradrenaline reuptake [7,8]. CT has been used as an efficient treatment in anxiety disorders such as panic disorder and obsessive-compulsive disorder, as well as post-stroke depression, dementia, depression, and addiction disorder [8,9,10,11,12,13]. Currently, the available CT formulations in the market are oral products, i.e., tablets and intravenous (IV) injections. Orally administered CT faces significant challenges such as the delayed onset of action and gastrointestinal disorders, including nausea, vomiting, diarrhea, appetite change, and constipation, while IV injections, despite their faster onset, are undesirable due to their invasive delivery method [14]. These issues negatively impact on the patient’s life quality and compliance, which are crucial for the success of therapy [15].
Intranasal (IN) administration offers a promising non-invasive approach. The unique anatomy of the nasal cavity and its direct connection with the brain through the olfactory and trigeminal pathways allow for bypassing of the blood–brain barrier (BBB) and offer targeted nose-to-brain drug access, which is especially beneficial in acute situations [16]. Additionally, the high vascularity and large surface area of the nasal mucosa enhance systemic drug absorption, allowing for the use of lower drug doses compared to oral administration with enhanced efficiency [17]. These outstanding advantages of IN delivery alongside the avoidance of the hepatic first-pass metabolism play a remarkable role in accelerating the drug onset of action and lowers the risk of systemic side effects [17]. CT was employed as a model active agent in order to enhance its bioavailability, as it is considered suitable for intranasal administration due to its lipophilicity and preferred molecular weight (405.31 g/mol) below 1000 g/mol [18].
The promising potential of intranasal delivery of antidepressant-loaded nanosystems was reported in previous studies [19,20,21]. Venlafaxine was loaded into IN PLGA nanoparticles, which demonstrated effective brain uptake with low cytotoxicity and an enhanced in vivo antidepressant-like effect [19]. Duloxetine has also been incorporated into an IN thermoreversible cubosomal gel containing lipids, PF127, and P188. It showed significant greater brain bioavailability [20]. A nanoemulsion was designed for the IN delivery of paroxetine and exhibited a remarkable increase in in vivo permeability [21].
Polymeric micelles (PMs) are nanosized self-assembled colloidal structures created from amphiphilic biocompatible copolymers. These co-polymers, formed of hydrophilic head groups and hydrophobic tail groups, self-arrange into core–lipid micelles in aqueous media. This unique structure can ameliorate the solubility and bioavailability of many water-insoluble drugs [22,23]. Furthermore, its biological stability protects the drug from enzymatic degradation, while its small size (10–100 nm) allows for enhanced permeability and expedites infiltration through the brain’s narrow capillaries [24,25]. Various co-polymers, including thermosensitive polymers, can form PMs under the title of smart drug delivery systems [26,27]. These polymers, such as Pluronics®, are fully water soluble and exist in an extended form below a specific temperature, the lower critical solution temperature (LCST), which is considered their phase transition temperature. When the medium temperature is raised over the LCST, the micelle undergoes a size reduction due to the dehydration process of the polymer’s hydrophilic groups, which decreases their solubility and leads to a shrinkage in micelle size [28]. It was also shown that Pluronics® modulate the efflux transmembrane transporter P-glycoprotein at the BBB, thus boosting the brain penetration of Pluronic®-loaded antidepressants [16]. Previous research has demonstrated the advantages of intranasal Risperidone-loaded Pluronic micelles (Pluronic® F127 and Pluronic® F108) in providing rapid drug release with higher permeation rate [29]. Pluronic® F127 (PF127) (also known as Poloxamer® 407) is characterized by its thermoresponsive properties at intranasal temperature (32–35 °C), along with its ability to form stable micelles and encapsulate hydrophobic drugs, thereby augmenting their solubility and stability in aqueous environments, with a hydrophilic–lipophilic balance (HLB) value of 22 [30,31,32]. In contrast, Poloxamer® 188 (P188) (also known as Pluronic F68) exhibits weaker thermosensitive behavior but offers higher solubilization ability due to its greater hydrophilicity and higher HLB value (29) [32,33,34]. It was also reported that P188 shows a “stealth” effect by minimizing protein adsorption and avoiding rapid elimination by the reticuloendothelial system (RES) [32]. These two Pluronics® have received Food and Drug Administration (FDA) approval for use in pharmaceutical and biomedical applications in vivo and were recognized as biocompatible and safe for intranasal delivery with the absence of mucosal irritation or toxicity [32,35,36]. The combination of PF127 with P188 in intranasal delivery is expected to achieve balanced thermal behavior, boosted drug solubility and permeability, faster onset of action, enhanced bioavailability, and optimized drug encapsulation, leading collectively to superior brain penetration while also addressing the challenge many patients face with swallowing oral dosage forms and avoiding the inconvenience of IV administration.
Eventually, the present study describes a novel formulation of optimized Pluronic-based thermoresponsive micelles of citalopram for intranasal administration. Based on preliminary studies, a carrier system was developed with adequate colloidal properties, which could overcome the limitations of systemic side effects and retarded onset of action by enhancing citalopram solubility and exploiting the temperature-triggered drug release properties of thermosensitive PMs highlighting the critical role of optimizing thermoresponsive polymer blends to improve the intranasal delivery of antidepressants. This manuscript details the comprehensive physicochemical characterization, in vitro release, and in vitro evaluation of drug permeability in intranasal conditions, laying the groundwork for future advancements in the targeted intranasal delivery of antidepressants with appropriate therapeutic efficacy.

2. Materials and Methods

2.1. Materials

Pluronic® F127 (PF127) (PEG95-PPG62-PEG95 (poly(ethylene-glycol)–block–poly(propylene-glycol)–block–poly (ethylene glycol); average molecular weight: 12,500 Da) was acquired from Sigma Aldrich Co., Ltd. (Budapest, Hungary). Poloxamer® 188 (P188) (PEG38-PPG29-PEG38(poly(ethylene-glycol)–block–poly(propylene-glycol)–block–poly (ethylene glycol); average molecular weight: 8600 Da) was acquired from ThermoFisher GmbH (Kandel, Germany). Citalopram hydrobromide (CT; 1-[3-(dimethylamino) propyl]-1-(4-fluorophenyl)-1,3-dihydro-2-benzofuran-5-carbonitrile hydrobromide; water solubility: <0.1 mg/mL; logP: 3.58; molecular weight: 405.31 g/mol; oral bioavailability: 80%) was purchased from Tokyo chemical industry co., LTD (Tokyo, Japan). Ethanol 96% v/v was acquired from Merck, Ltd. (Budapest, Hungary). NaCl 0.9% (w/v) was purchased from B. Braun Melsungen AG (Melsungen, Germany). The simulated nasal electrolyte solution (SNES pH 5.6) was prepared using the following materials: 0.59 g/L of anhydrous calcium chloride (CaCl2), 8.77 g/L of sodium chloride (NaCl), and 2.98 g/L of potassium chloride (KCl) dissolved in 1000 mL of purified water and adjusted to pH 5.6 [37]. The phosphate buffer solution (PBS pH 7.4) contains 0.20 g/L KCl, 8.00 g/L NaCl, 0.12 g/L KH2PO4, and 1.44 g/L Na2HPO4 × 2 H2O dissolved in 1000 mL purified water and adjusted to pH 7.4 [38]. The artificially simulated cerebrospinal fluid (aCSF) was prepared from 0.5 mM Na2SO4, 5.8 mM D-glucose, 0.5 mM KH2PO4, 0.2 M NaCl, 1.2 mM CaCl2, 0.5 mM KH2PO4, 1.8 mM MgCl2, and 2 mM KCl and set to pH 7.4 [39]. All the chemicals of the dissolution media—SNES, PBS, and CSF—were obtained from Sigma-Aldrich Co., Ltd. (Budapest, Hungary). Analytical-grade acetonitrile was obtained from Merck Ltd. (Budapest, Hungary). The purified water in all experiments was obtained from a Milli-Q® Gradient Water Purification System (Merck Ltd., Budapest, Hungary).

2.2. Quantitative Analysis of CT via High-Performance Liquid Chromatography (HPLC)

The quantitative determination of CT was performed via high-pressure liquid chromatography (HPLC) using an Agilent 1260 Infinity (Agilent Technologies, Santa Clara, CA, USA) instrument. The stationary phase was a Kinetex® C18 column (5 µm, 150 mm × 4.6 mm, Phenomenex, Torrance, CA, USA). The mobile phases were the following: (A) 0.1 M sodium acetate buffer (pH 7.0) and (B) methanol. The separation was performed by gradient elution with the following program: The initial (A:B) ratio of 45:55 remained until 1 min, which changed to a ratio of 30:70 by 5 min, which remained until 7 min. The injection volume was 10 µL. The separation was performed for 7 min at 30 °C with a flow rate of 0.8 mL/min. Chromatograms were detected at 239 ± 4 nm using a UV-Vis diode array detector. The retention time was 7.57 min. The limit of detection (LOD) and limit of quantification (LOQ) of CT were 2.49 and 7.55 ppm, respectively. The HPLC method was validated based on robustness and repeatability. The calibration was performed from 2 to 10 µg/mL and from 0.2 to 1.0 mg/mL, where the determination coefficients of linearity (R2) values were 0.9996 and 0.9992, respectively. Chromatograms were evaluated using ChemStation B.04.03 Software (Agilent Technologies, Santa Clara, CA, USA).

2.3. Formulation of CT-Loaded Polymeric Micelles

The thin-film hydration method was applied to formulate CT-PMs. Various amounts of PF127, as presented in Table 1, and 40 mg of P188 were dissolved in a mixture of 4 mL of water and 16 mL of 96% ethanol. Then, 2 mL of 5 mg/mL CT ethanolic solution was added. This mixture was stirred constantly at room temperature for one hour, then transferred to a round-bottom flask for drying via a Büchi R-210 (Büchi, Flawil, Switzerland) rotary vacuum evaporator at 60 °C for approximately one hour. The pressure gradually reduced from 1000 to 100 mbar at a rate of 100 mbar per minute. The generated thin film was rehydrated with 10 mL of purified water and ultrasonicated at room temperature for 3 min. After rehydration, the formulations were fractioned into 1 mL samples in vials and freeze-dried using a ScanVac CoolSafe 100–9 (LaboGene, ApS, Lynge, Denmark) at −40 °C under a 0.013 mbar pressure for 12 h. The secondary drying was for 6 h under a 0.013 mbar pressure at 25 °C. The preparation method is presented in Figure 1.

2.4. Characterization of the Polymeric Micelles

2.4.1. Determination of LCST

The dynamic light scattering (DLS) method was employed to monitor variations in the Z-average, which refers to the micelle size, and polydispersity index (PdI), as the micelle size distribution, of the CT-loaded PM to determine the LCST via Malvern Zetasizer Nano ZS (Malvern Instruments, Worcestershire, UK). The freeze-dried samples, prepared using ScanVac CoolSafe 100–9 (LaboGene, ApS, Lynge, Denmark), by freezing and drying at −40 °C under a 0.013 mbar pressure for 12 h, followed by secondary drying for 6 h under a 0.013 mbar pressure at 25 °C, were dissolved in purified water. Then, the samples were transferred to disposable folded capillary cells and kept inside during the process of measuring at increasing temperatures, ranging from 25.0 to 40 °C at 1 °C increments, with a refractive index of 1.6 [29,40,41]. The temperature at which a sharp increase in Z-average is observed, followed by a radical descent, is considered the LCST [29]. All measurements were carried out in triplicate (n = 3), and the results are expressed as the mean ± SD.

2.4.2. Determination of Micelle Size and Size Distribution

The investigations into the Z-average and PdI of the optimized formulation and blank micelles were carried out by the DLS method (Malvern Instruments, Worcestershire, UK) at an approximate temperature of 35 °C to closely mimic the nasal cavity temperature and assess micelle thermal behavior [31]. All measurements were carried out in triplicate (n = 3), and the results are expressed as the mean ± SD.

2.4.3. Determination of Encapsulation Efficiency (EE%)

The indirect method was used to determine the encapsulation efficiency of CT-PM [42]. The freeze-dried samples were dissolved in 1 mL of purified water and placed in Eppendorf® tubes. The Hermle Z323 K high-performance refrigerated centrifuge (Hermle AG, Gosheim, Germany) was used to separate the CT-loaded micelles from the aqueous media by centrifugation with a speed of 13,500 rpm at 4 °C for 45 min. Quantitative measurements were performed via HPLC. The measurements were conducted in triplicate (n = 3) and the results are expressed as the average ± SD. The following equation was applied to calculate EE:
E E   % =   I n i t i a l   C T   mg − M e a s u r e d   C T   i n   t h e   s u p r e n a t a n t     ( mg ) I n i t i a l   C T   ( mg )   × 100

2.4.4. Determination of the Thermodynamic Solubility

The saturation method was utilized to determine the enhancement of CT’s thermodynamic solubility in water [42]. An excessive amount of freeze-dried cakes was added to 1 mL of dissolution medium at 25 °C until visible sedimentation occurred, and continuously stirred for 72 h. The solutions were filtered through a 0.22 µm polyether sulfone (PES) membrane filter. The CT concentration in the filtrate was determined via HPLC. All measurements were performed in triplicate (n = 3), and the results are expressed as the mean ± SD.

2.4.5. Biological Stability Test

The effect of the presence of our optimized formulation in biological media SNES (pH 5.6), PBS (pH 7.4) and CSF (pH 7.4) on micelle size and zeta potential was evaluated using DLS. The freeze-dried samples were dissolved in the biological media. The solutions were incubated at 35 °C for SNES and 36.5 °C for PBS and CSF [43,44]. Then, aliquots were taken at pre-established time intervals (0, 0.5, 1, and 2 h). The measurements were performed in triplicate (n = 3), and the results are presented as means ± SD.

2.5. Physical Stability

Physical stability was tested to describe the colloidal stability of the polymeric micelles upon storage. Samples were investigated in the liquid and solid states via DLS. Samples were investigated under two conditions, based on the ICH Q1A (R2) guideline [45]: 5 ± 3 °C in a refrigerator and at 25 ± 2 °C under ambient conditions. Solid samples were dissolved in purified water at each pre-determined time point. The measurements were performed in triplicate (n = 3), and the results are presented as means ± SD.

2.6. X-Ray Powder Diffraction Study

The crystalline structure of the freeze-dried products was characterized with X-ray powder diffraction (XRPD) using a Bruker D8 Advance X-ray diffractometer (Bruker AXS GmbH, Karlsruhe, Germany) with Cu K λI radiation (λ = 1.5406 Å) and a VANTEC-1 detector. In total, 40 kV of voltage and 40 mA of amperage were used during the measurements. The angular range was 3° to 4° 2θ with a step time of 0.1 s and a step size of 0.007°. The manipulations and evaluations were carried out using EVA Software v6.

2.7. In Vitro Nasal Applicability Studies

2.7.1. In Vitro Drug Release Study

The dialysis bag method was applied to perform the drug release study under sink conditions in case of polymeric micelle formulation. Initially, 1 mL of the in-water dissolved freeze-dried formulation (concentration: 1 mg/mL) and initial CT aqueous suspension (the reference, concentration: 1 mg/mL) was placed in presoaked dialysis tubes (Spectra/Por®, MWCO 12–14 kDa, Spectrum Laboratories Inc., Rancho Dominguez, CA, USA) and fully submerged in 25 mL of SNES (pH 5.6) at 35 ± 0.5 °C to be stirred at 100 rpm for 1 h using a Hanson SR8 Plus apparatus (Teledyne Hanson Research, Chatsworth, CA, USA). Sample volumes (100 µL) were withdrawn at 1, 3, 5, 10, 15, 30, and 60 min. HPLC was employed to measure the quantity of dissolved CT in the dissolution medium. The measurements were carried out in triplicate (n = 3) and the results are presented as means ± SD.

2.7.2. Mathematical Analysis of the Drug Release

The obtained cumulative CT release data of the optimized formulation and CT aqueous suspension were subjected to different mathematical approaches (zero-order, first-order, Hixson–Crowell, Higuchi, and Korsmeyer–Peppas models). The DDsolver® add-in software was applied to interpret the release kinetics and determine the rate constant (K) and regression coefficient (R2) values of each model. The optimal model was chosen based on the highest value of R2 [46,47].

2.7.3. In Vitro Drug Permeation Study

In order to investigate the formulation tendencies to passive diffusion as the main absorption mechanism at the nasal mucosa, a modified Side-by-side® horizontal diffusion test was performed. An isopropyl myristate-impregnated cellulose membrane with a surface of 0.785 cm2 was utilized as the diffusion barrier between the donor and acceptor cells. The study was conducted at 36.5 °C. The volume of both cells was 9 mL. The donor medium was composed of SNES (pH 5.6) while the acceptor phase was PBS (pH 7.4). Then, 50 µL samples were withdrawn from the acceptor phase in predetermined time intervals, and the quantification of CT was performed via HPLC. The Flux (J) (µg/cm2) was quantified by dividing the amount of CT permeated through the membrane by the surface of the inserted membrane and the experiment’s duration (µg/cm2/h). The permeability coefficient (Kp) was calculated from J and the drug concentration in the donor phase (Cd (µg/cm3)) according to the following equation:
K p cm h = J C d

2.8. Statistical Analysis

Statistical analyses were performed using GraphPad Prism version 10.1.2 (GraphPad Software, San Diego, CA, USA). One-way analysis of variance (ANOVA) was applied, with p-values less than 0.05 considered statistically significant. Data are presented as the mean ± standard deviation (SD) based on three independent experiments (n = 3).

3. Results

3.1. Characterization of the Micelles in a Liquid State

3.1.1. Preliminary Studies

The optimal formulation was selected based on the critical parameters of thermosensitive polymeric micelles. Z-average is an essential attribute as it affects pharmacokinetics, stability, and the capability of brain penetration [48]. The optimal range of Z-average is 10–100 nm [24,49]. PdI is also a required parameter due to its indication to the uniformity degree of the micelle size. For polymeric micelles, PdI desirable value is ≤0.3 as it ensures higher stability and less aggregation tend [49,50]. Evaluation Thermal response, which is presented as LCST, is considered a key-factor in thermoresponsive polymeric micelles. LCST value should be high enough to prevent triggered drug release at ambient temperature, ensuring stability and facilitating the administration, and low enough to induce drug release at intranasal temperature (32–35 °C) [32]. Z-average, PdI, and LCST were measured by DLS method. According to the results presented in Table 2, CT-PM3 exhibited the most favorable characteristics. In contrast, formulations CT-PM1 and CT-PM2 showed higher PdI values, suggesting less uniform micelle distribution, while CT-PM4 exhibited a significantly larger particle size (90.13 ± 0.23 nm) and a higher LCST (36 °C), which may reduce its suitability for intranasal administration.
Based on these findings, CT-PM3 was selected as the optimal formulation for further development and evaluation.

3.1.2. Determination of the LCST

In order to assess the thermal behavior of CT-loaded polymeric micelles, the Z-average and PdI of the optimized formulation (CT-PM3) were measured at a temperature range of 25 to 40 °C. As shown in Figure 2, the Z-average showed higher values at temperatures under 32 °C with PdI > 0.3, which indicates a polydisperse size distribution. A sharp increase at approximately 31 °C was followed by a monodisperse fall (PdI ≤ 0.3) in Z-average. This remarkable situation suggests an ideal LCST value of 31 °C for our optimized formulation, as it exceeds room temperature yet remains below the nasal temperature (35 °C). This polydispersity increase in size at lower temperatures might be connected to the formation of large, loose clusters of correlated micelles and the existence of some monomers. At higher temperatures, these aggregations separate as a result of the dehydration and degradation of PEG chains. Meanwhile, hydrophobic groups in the micelle’s core intensify, the hydrogen bonds (H-bonds) of the hydrophilic groups in the micelle’s corona with the aqueous solution weaken, and the monomers vanish and eventually lead to a monodisperse reduction in micelle size [51,52,53,54].

3.1.3. Micelle Size and Size Distribution

The DLS method was used to measure the Z-average and PdI of our optimized formulation and blank micelles at 35 °C. Nose-to-brain delivery could ideally be achieved with a particle size below 200 nm. Furthermore, the optimal size range of polymeric micelles is from 10 to 100 nm, which optimizes circulation time and evades the uptake by monophagocytic system (MPS) and renal filtration [24,49]. As shown in Table 3, the Z-average and PdI of CT-PM3 were within the acceptable range. Additionally, the size of the CT-loaded PM showed significantly increased Z-average compared to the blank PM (p < 0.0001). Probably, the added drug particles interacted with the polymer’s molecules, which led to a reduction in the number of surfactant molecules per micelle compared to the pure Pluronic® solution. Additionally, the concentration of Pluronic® F127 (1.1% w/v) and Poloxamer® 188 (0.4% w/v) in our optimized formulation is above their critical micelle concentration (CMC), approximately 0.1 and 0.03%, respectively. As a result, the extra molecules are likely involved in the formation of additional micelles, which leads to a reduction in Z-average [55,56]. Moreover, the intermolecular interactions could be formed between the CT molecules and the hydrophobic core of micelles via Van der Waals bonds, resulting in a more compact micelle core compared to unloaded micelles [57].
The narrow size distribution is also considered crucial for PM to ensure high stability, a predictable drug release profile, and consistent cellular uptake [58]. PdI is a criterion to evaluate the width of the size distribution of particles in a range of 0 to 1. The PdI value ≤ 0.3 signifies a monodisperse size distribution, which is highly desirable [49,50]. The results of PdI of both blank and CT-loaded micelles were less than 0.3, which indicates a homogenous particle size distribution.
The zeta potential of our formulation is almost negligible, yet the charge of both used co-polymers is near-neutral. It has been reported in previous studies that micelles with neutral or mildly negative surface charge can efficiently cross the nasal mucosa and exhibit prolonged blood circulation [29,59].

3.1.4. Characterization of Solubilization

The thermodynamic solubility and the encapsulation efficiency of the optimized formulation were determined. Using the saturation method, the thermodynamic solubility of CT revealed a 95-fold increase (p < 0.0001), from 15.460 ± 0.032 µg/mL to 1479.342 ± 0.145 µg/mL, upon incorporation into polymeric micelles (CT-PM). The highly achieved encapsulation efficiency of CT, reaching 88.85 ± 1.23%, could explain this CT solubility enhancement. The lipophilic drug incorporation into the micelle core occurs by forming hydrophobic interactions, such as Van der Waals bonds, with PPO groups in the micelle core, while the hydrophilic shell facilitates solubilization by forming H-bonds with the aqueous environment [23,60]. Moreover, the nanoscale dimensions of mixed micelles play an important role in augmenting solubility [23,61].

3.1.5. Biological Stability Test

The stability of optimized formulation in biological solutions, SNES, PBS, and CSF was evaluated by measuring the Z-average by the DLS method at predetermined time intervals. This test indicates the micelle’s behavior after intranasal administration. The obtained results in Figure 3 revealed a notable increase in Z-average after 0.5 h of incubation. Since biological media have a high ionic strength due to their elevated electrolyte content, it has been suggested in previous studies that they affect micelles in several aspects. Electrolytes with elevated concentrations might increase the physically entrapped water within the PEO chain network in the micelle corona, while disrupting the H-bonds between the water molecules and ether groups as a result of the dehydration and degradation of PEO chains. This collapse of PEO chains leads to a roughened micellar surface and greater asymmetry. Consequently, these effects contribute to an increase in the Z-average [62,63].

3.2. Physical Stability

The results of the physical stability test can be found in Figure 4. There was only a slight increase in micelle size in the liquid state at 25 °C storage conditions, but it is statistically insignificant. Overall, the formulations show adequate stability and do not decrease polymeric micelle performance over the investigated period.

3.3. X-Ray Powder Diffraction Study (XRPD)

The X-ray powder diffraction study compared the crystallinity of the individual components and the final freeze-dried formulation (CT-PM3). The diffractograms can be seen in Figure 5. CT in its pure form indicates high crystallinity with sharp, intense peaks throughout the measured temperatures, especially between 5° and 30°. In comparison, the polymeric micelle-forming copolymers showed an amorphous nature. Poloxamer 188® shows a broad halo pattern with no distinct sharp peak, and similarly, Pluronic F127® shows a slightly more defined broad hump around 20°, which is typical of amorphous materials. The final formulation, CT-PM3, also shows an amorphous nature. It indicates complete amorphization due to the encapsulation of CT into the polymeric matrix, which in solid form acts as an amorphous molecular dispersion within the other amorphous polymers.

3.4. In Vitro Nasal Applicability Studies

3.4.1. In Vitro Drug Release Study

Evaluating drug release is essential for assessing the efficiency of the drug delivery system compared to the initial drug, as it serves as a critical biopharmaceutical parameter. Based on the data in Figure 6, at each measured time point, CT-PM3 showed a significantly higher release rate (p < 0.0001) compared to the initial CT. The first 15–20 min is the crucial timeframe, as it is the duration of formulation residence in the nasal mucosa before being cleared by the mucociliary clearance mechanisms. [37]. At the 15 min mark, ca. 50% released from CT-PM3, which is 25 times higher than the ca. 2% release from pure CT. This accelerated drug release could be strongly associated with the reduction in micelle size and increased porosity as a result of the degradation of PEO chains in the micelle corona under the effect of temperature and electrolytes. [49,62,63]. Moreover, the obtained results emphasize the major increase in CT thermodynamic solubility.
Calculated parameters for drug release kinetics profiles are shown in Table 4. The highest value of R2 and the closest to 1.0 was considered as the criterion for choosing the fitted model [46]. The results revealed that the most appropriate kinetics model for initial CT release in SNES was the Korsmeyer–Peppas model (R2 = 0.9953). Although the Korsmeyer–Peppas model is commonly used to explain drug release from polymeric matrices, it has the flexibility to describe complex release situations with more than one mechanism in non-polymer-based systems [64,65], whereas the first-order model demonstrates the best fitted model of drug release from CT-PM3 (R2 = 0.9809), indicating the dependence of the release mechanism on the concentration of the drug within the micelles [66].

3.4.2. In Vitro Drug Permeation Study

A modified Side-by-side® horizontal diffusion test was performed to evaluate the in vitro nasal diffusion of CT-PM3 compared to the initial CT. The data, shown in Figure 7, revealed a significantly higher cumulative drug permeation for CT-PM3 at all measured intervals (p < 0.0001), with the optimized formulation achieving an approximately 4-fold increase over pure CT. In addition, the biopharmaceutical parameters (Figure 8) demonstrate the superior flux (J) of CT-PM3 compared to the initial CT.
This improvement is a result of the enhanced CT dissolution, micelle nanoscale size, micelle thermosensitive behavior, and the surfactant nature of the polymers, which collectively facilitate absorption through the membrane. The promoted permeability indicates the capability of this delivery system to provide a faster onset of action and enhance bioavailability via intranasal administration.

4. Discussion

In this study, a citalopram-loaded thermosensitive polymeric micelle formulation was developed and evaluated to assess its suitability as a brain-targeted intranasal delivery system for citalopram. This formulation was prepared by the thin-film hydration method, a widely used laboratory and pilot-scale technique for forming polymeric micelles and mixed micellar systems because it ensures good control over drug/polymer ratios, drug loading, and micelle size while remaining amenable to scale-up when process parameters are optimized [67]. Following formation, the product was stabilized and converted to a solid state; XRPD demonstrated an absence of crystalline reflections consistent with the drug residing in an amorphous state within the micellar structure [68]. Preservation of this amorphous character through solidification was achieved using freeze-drying. Several recent reports and reviews document that freeze-drying is an effective route to retain amorphous solid dispersion and to stabilize polymeric nanocarriers [69,70,71].
Physicochemical characterization at nasal temperature (35 °C) showed that the micelle size is approximately 31.4 nm with a PdI of 0.240, indicating a narrow size distribution and limited aggregation, as well as a size and homogeneity that favor diffusion across the nasal mucosa and reduced mucociliary clearance to larger particulates. Additionally, the near-neutral zeta potential enhanced mucosal compatibility and colloidal stability. Neutral or slightly negative surfaces often strike a balance between mucoadhesion and permeation for nose-to-brain targeting [72,73]. In stability testing, both liquid and freeze-dried forms maintained acceptable micelle size and colloidal performance after 4 weeks at ambient and refrigerated conditions, proving that freeze-drying was an effective strategy to ensure physical stability for this nanocarrier.
A notable functional attribute of the polymeric micelles was that it possesses a thermosensitive behavior, with an LCST value of approx. 31 °C. This value is kinetically convenient, as it supports stability at room temperature while facilitating a targeted triggered drug release at the nasal cavity temperature of 35 °C [32]. Blending Pluronics is also a highly reported tactic to tune gelation or thermosensitive nature, just like in this case for nasal applications.
The encapsulation efficiency of 88.85 ± 1.23% was achieved, signifying the quite efficient loading of CT into the micelle core. Furthermore, A 95-fold increase in CT thermodynamic solubility was achieved compared to the initial CT. The substantial 95-fold increase can be due the following synergistic mechanisms: (i) nanoscale solubilization with low micelle size; (ii) high encapsulation efficiency reducing the fraction of free crystalline drug; and (iii) the amorphous state of CT after freeze-drying, also contributing to rapid dissolution [74,75,76]. Incubation in biological media (SNES, PBS, and CSF) revealed a Z-average increase after 0.5 h due to ionic interactions and PEO chain deterioration. Nevertheless, the system demonstrated proper resistance to ionic strength fluctuations, confirming its suitability for intranasal delivery.
The in vitro drug release and permeation data further validated the formulation’s functional advantages, as a 25-fold increase in drug release and a 4-fold increase in nasal drug flux was experienced compared to unformulated CT. Such improvements are consistent with the effects of the highly efficient solubilization, the reduced diffusion path lengths for drug molecules desorbing from nanoscale carriers, and the thermokinetic behavior triggered by the nasal conditions [77,78].

5. Conclusions

In summary, it can be claimed that the thermosensitive polymeric micelle system is a promising approach to tackle the challenges of intranasal administration of brain-targeted drugs. However, further in vivo pharmacokinetics, long-term stability, and cytotoxicity investigations should be conducted to confirm safety, real efficacy, and reproducibility. Moreover, this formulation could serve as a base for additional developments in the field of intranasal delivery systems.

Author Contributions

Conceptualization, B.S. and G.K.; methodology, B.S.; software, F.R. and B.S.; validation, B.S., G.K. and I.C.; formal analysis, B.S.; investigation, F.R., B.S. and G.K.; resources, I.C.; data curation, B.S.; writing—original draft preparation, F.R. and B.S.; writing—review and editing, G.K. and I.C.; visualization, F.R. and B.S.; supervision, B.S. and I.C.; project administration, B.S.; funding acquisition, B.S. and I.C. All authors have read and agreed to the published version of the manuscript.

Funding

The APC was funded by the University of Szeged Open Access Fund (Grant Nr. 7870).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are available upon request from the corresponding author.

Acknowledgments

This work was funded by Project no. TKP2021-EGA-32 implemented with support provided by the Ministry of Innovation and Technology of Hungary from the National Research, Development, and Innovation Fund, financed under the TKP2021-EGA funding scheme.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
aCSFartificially simulated cerebrospinal fluid
BBBblood–brain barrier
CMCcritical micelle concentration
CTcitalopram
CT-PMcitalopram-loaded polymeric micelles
DLSdynamic light scattering
EEencapsulation efficiency
PF127Pluronic F-127
FDAfood and drug administration
H-bondshydrogen bonds
HLBhydrophilic–lipophilic balance
HPLChigh-performance liquid chromatography
INintranasal
IVintravenous
LCSTlow critical solution temperature
MPSmonophagocytic system
NCLsnanostructured lipid carriers
P188Poloxamer 188
PBSphosphate buffer solution
PdIpolydispersity index
PEOpoly(ethylene oxide)
PESpolyether sulfone
PMspolymeric micelles
PPOpoly(propylene oxide)
R2regression coefficient
RESreticuloendothelial system
SNESsimulated nasal electrolyte solution
SSRIsselective serotonin reuptake inhibitors
XRPDX-ray powder diffraction
WHOWorld Health Organization

References

  1. WHO. Depression Fact Sheet. 2017. Available online: https://www.who.int/news-room/fact-sheets/detail/depression (accessed on 8 July 2025).
  2. Gelenberg, A.J.; Freeman, M.P.; Markowitz, J.C.; Rosenbaum, J.F.; Thase, M.E.; Trivedi, M.H.; Van Rhoads, R.S. American Psychiatric Association Practice Guidelines for the Treatment of Patients with Major Depressive Disorder. Am. J. Psychiatry 2010, 167, 9–118. [Google Scholar]
  3. Benton, T.; Staab, J.; Evans, D.L. Medical Co-Morbidity in Depressive Disorders. Ann. Clin. Psychiatry 2007, 19, 289–303. [Google Scholar] [CrossRef]
  4. Harshfield, E.L.; Pennells, L.; Schwartz, J.E.; Willeit, P.; Kaptoge, S.; Bell, S.; Shaffer, J.A.; Bolton, T.; Spackman, S.; Wassertheil-Smoller, S. Association between Depressive Symptoms and Incident Cardiovascular Diseases. JAMA 2020, 324, 2396–2405. [Google Scholar] [CrossRef]
  5. Akil, H.; Gordon, J.; Hen, R.; Javitch, J.; Mayberg, H.; McEwen, B.; Meaney, M.J.; Nestler, E.J. Treatment resistant depression: A multi-scale, systems biology approach. Neurosci. Biobehav. Rev. 2018, 84, 272–288. [Google Scholar] [CrossRef]
  6. Silva, S.; Bicker, J.; Fonseca, C.; Ferreira, N.R.; Vitorino, C.; Alves, G.; Falcão, A.; Fortuna, A. Encapsulated Escitalopram and Paroxetine Intranasal Co-Administration: In Vitro/In Vivo Evaluation. Front. Pharmacol. 2021, 12, 751321. [Google Scholar] [CrossRef]
  7. Vaswani, M.; Linda, F.K.; Ramesh, S. Role of Selective Serotonin Reuptake Inhibitors in Psychiatric Disorders: A Comprehensive Review. Prog. Neuro-Psychopharmacol. Biol. Psychiatry 2003, 27, 85–102. [Google Scholar] [CrossRef]
  8. Baumann, P. Pharmacology and Pharmacokinetics of Citalopram and Other SSRIs. Int. Clin. Psychopharmacol. 1996, 11, 5–12. [Google Scholar] [CrossRef] [PubMed]
  9. Wade, A.G.; Lepola, U.; Koponen, H.J.; Pedersen, V.; Pedersen, T. The Effect of Citalopram in Panic Disorder. Br. J. Psychiatry 1997, 170, 549–553. [Google Scholar] [CrossRef]
  10. Koponen, H.; Lepola, U.; Leinonen, E.; Jokinen, R.; Penttinen, J.; Turtonen, J. Citalopram in the treatment of obsessive-compulsive disorder: An open pilot study. Acta Psychiatr. Scand. 1997, 96, 343–346. [Google Scholar] [CrossRef]
  11. Andersen, G.; Vestergaard, K.; Lauritzen, L. Effective Treatment of Poststroke Depression with the Selective Serotonin Reuptake Inhibitor Citalopram. Stroke 1994, 25, 1099–1104. [Google Scholar] [CrossRef] [PubMed]
  12. Nyth, A.L.; Gottfries, C.G. The Clinical Efficacy of Citalopram in Treatment of Emotional Disturbances in Dementia Disorders a Nordic Multicentre Study. Br. J. Psychiatry 1990, 157, 894–901. [Google Scholar] [CrossRef]
  13. Naranjo, C.A.; Poulos, C.X.; Bremner, K.E.; Lanctôt, K.L. Citalopram Decreases Desirability, Liking, and Consumption of Alcohol in Alcohol-Dependent Drinkers. Clin. Pharmacol. Ther. 1992, 51, 729–739. [Google Scholar] [CrossRef]
  14. Oliva, V.; Lippi, M.; Paci, R.; Del Fabro, L.; Delvecchio, G.; Brambilla, P.; De Ronchi, D.; Fanelli, G.; Serretti, A. Gastrointestinal Side Effects Associated with Antidepressant Treatments in Patients with Major Depressive Disorder: A Systematic Review and Meta-Analysis. Prog. Neuro-Psychopharmacol. Biol. Psychiatry 2021, 109, 110266. [Google Scholar] [CrossRef] [PubMed]
  15. Wang, S.-M.; Han, C.; Bahk, W.-M.; Lee, S.-J.; Patkar, A.A.; Masand, P.S.; Pae, C.-U. Addressing the Side Effects of Contemporary Antidepressant Drugs: A Comprehensive Review. Chonnam Med. J. 2018, 54, 101. [Google Scholar] [CrossRef]
  16. Erdő, F.; Bors, L.A.; Farkas, D.; Bajza, Á.; Gizurarson, S. Evaluation of Intranasal Delivery Route of Drug Administration for Brain Targeting. Brain Res. Bull. 2018, 143, 155–170. [Google Scholar] [CrossRef]
  17. Chung, E.; White, S. (005) Can Novel SDS-089 Nasal Vardenafil Spray Solution Achieve Satisfactory Drug Plasma Level Similar to Oral Vardenafil Formulation? A Bioanalysis Study Comparing Vardenafil Nasal vs. Oral Formulations Using Liquid Chromatography Tandem Mass Spectrometry. J. Sex. Med. 2024, 21, qdae002.005. [Google Scholar] [CrossRef]
  18. Donovan, M.D.; Huang, Y. Large Molecule and Particulate Uptake in the Nasal Cavity: The Effect of Size on Nasal Absorption. Adv. Drug Deliv. Rev. 1998, 29, 147–155. [Google Scholar] [CrossRef]
  19. Cayero-Otero, M.D.; Perez-Caballero, L.; Suarez-Pereira, I.; Hidalgo-Figueroa, M.; Delgado-Sequera, A.; Montesinos, J.M.; Berrocoso, E.; Martín-Banderas, L. Venlafaxine-PLGA Nanoparticles Provide a Fast Onset of Action in an Animal Model of Depression via Nose-to-Brain. Int. J. Pharm. 2025, 678, 125692. [Google Scholar] [CrossRef]
  20. Elsenosy, F.M.; Abdelbary, G.A.; Hassen Elshafeey, A.; Elsayed, I.; Fares, A.R. Brain Targeting of Duloxetine HCL via Intranasal Delivery of Loaded Cubosomal Gel: In Vitro Characterization, Ex Vivo Permeation, and in Vivo Biodistribution Studies. Nanomedicine 2020, 15, 9517–9537. [Google Scholar] [CrossRef] [PubMed]
  21. Pandey, Y.R.; Kumar, S.; Gupta, B.K.; Ali, J.; Baboota, S. Intranasal Delivery of Paroxetine Nanoemulsion via the Olfactory Region for the Management of Depression: Formulation, Behavioural and Biochemical Estimation. Nanotechnology 2015, 27, 25102. [Google Scholar] [CrossRef]
  22. Negut, I.; Bita, B. Polymeric micellar systems—A special emphasis on “smart” drug delivery. Pharmaceutics 2023, 15, 976. [Google Scholar] [CrossRef]
  23. Naharros-Molinero, A.; Caballo-González, M.Á.; de la Mata, F.J.; García-Gallego, S. Direct and reverse Pluronic micelles: Design and characterization of promising drug delivery nanosystems. Pharmaceutics 2022, 14, 2628. [Google Scholar] [CrossRef]
  24. Gandhi, S.; Shastri, D.H.; Shah, J.; Nair, A.B.; Jacob, S. Nasal delivery to the brain: Harnessing nanoparticles for effective drug transport. Pharmaceutics 2024, 16, 481. [Google Scholar] [CrossRef] [PubMed]
  25. Sipos, B.; Rajab, F.; Katona, G.; Csóka, I. Current insights into polymeric micelles for nasal drug delivery. Expert Opin. Drug Deliv. 2025, 22, 1137–1154. [Google Scholar] [CrossRef] [PubMed]
  26. Ghosh, B.; Biswas, S. Polymeric micelles in cancer therapy: State of the art. J. Control. Release 2021, 333, 123–145. [Google Scholar] [CrossRef] [PubMed]
  27. De Villiers, M.; Aramwit, P.; Kwon, G. Nanotechnology in drug delivery. Int. J. Nanomed. 2008, 3, 311–321. [Google Scholar] [CrossRef]
  28. Clark, E.A.; Lipson, J.E.G. LCST and UCST behavior in polymer solutions and blends. Polymer 2012, 53, 536–545. [Google Scholar] [CrossRef]
  29. Sipos, B.; Katona, G. Risperidone-loaded nasal thermosensitive polymeric micelles: Quality by design-based formulation study. Pharmaceutics 2024, 16, 703. [Google Scholar] [CrossRef]
  30. Pourbakhsh, M.; Jabraili, M.; Akbari, M.; Jaymand, M.; Jahanban Esfahlan, R. Poloxamer-based drug delivery systems: Frontiers for treatment of solid tumors. Mater. Today Bio 2025, 32, 101727. [Google Scholar] [CrossRef]
  31. Keck, T.; Leiacker, R.; Riechelmann, H.; Rettinger, G. Temperature profile in the nasal cavity. Laryngoscope 2000, 110, 651–654. [Google Scholar] [CrossRef]
  32. Khaliq, N.U.; Lee, J.; Kim, S.; Sung, D.; Kim, H. Pluronic F-68 and F-127 based nanomedicines for advancing combination cancer therapy. Pharmaceutics 2023, 15, 2102. [Google Scholar] [CrossRef]
  33. Di Spirito, N.A.; Grizzuti, N.; Lutz-Bueno, V.; Urciuoli, G.; Auriemma, F.; Pasquino, R. Pluronic F68 micelles as carriers for an anti-inflammatory drug: A rheological and scattering investigation. Langmuir 2024, 40, 1544–1554. [Google Scholar] [CrossRef]
  34. Dalgakiran, E.A.; Ergin, A.D.; Kacar, G. Properties of Pluronic F68 and F127 micelles interacting with furosemide from coarse-grained molecular simulations as validated by experiments. Colloids Surf. A Physicochem. Eng. Asp. 2023, 666, 131352. [Google Scholar] [CrossRef]
  35. Chen, Y.; Cheng, G.; Hu, R.; Chen, S.; Lu, W.; Gao, S.; Xia, H.; Wang, B.; Sun, C.; Nie, X.; et al. A nasal temperature and pH dual-responsive in situ gel delivery system based on microemulsion of huperzine A: Formulation, evaluation, and in vivo pharmacokinetic study. AAPS PharmSciTech 2019, 20, 301. [Google Scholar] [CrossRef] [PubMed]
  36. Mahajan, H.S.; Jadhao, V.D.; Chandankar, S.M. Pullulan and Pluronic F-127 based in situ gel system for intranasal delivery: Development, in vitro and in vivo evaluation. J. Bioact. Compat. Polym. 2022, 37, 406–418. [Google Scholar] [CrossRef]
  37. Sipos, B.; Katona, G.; Szarvas, F.M.; Budai-Szűcs, M.; Ambrus, R.; Csóka, I. Development of vinpocetine-loaded nasal polymeric micelles via nano-spray-drying. Pharmaceuticals 2023, 16, 1447. [Google Scholar] [CrossRef]
  38. Sipos, B.; Szabó-Révész, P.; Csóka, I.; Pallagi, E.; Dobó, D.G.; Bélteky, P.; Kónya, Z.; Deák, Á.; Janovák, L.; Katona, G. Quality by design based formulation study of meloxicam-loaded polymeric micelles for intranasal administration. Pharmaceutics 2020, 12, 697. [Google Scholar] [CrossRef]
  39. Mohanraj, K.; Sethuraman, S.; Krishnan, U.M. Development of poly(butylene succinate) microspheres for delivery of levodopa in the treatment of Parkinson’s disease. J. Biomed. Mater. Res. B Appl. Biomater. 2013, 101, 840–847. [Google Scholar] [CrossRef]
  40. Beitl, K.; Reimhult, E. Effect of solvent properties on the critical solution temperature of thermoresponsive polymers. Int. J. Mol. Sci. 2024, 25, 7734. [Google Scholar] [CrossRef] [PubMed]
  41. Najafi, M.; Habibi, M.; Fokkink, R.; Hennink, W.E.; Vermonden, T. LCST polymers with UCST behavior. Soft Matter 2021, 17, 2132–2141. [Google Scholar] [CrossRef] [PubMed]
  42. Sipos, B.; Csóka, I.; Budai-Szűcs, M.; Kozma, G.; Berkesi, D.; Kónya, Z.; Balogh, G.T.; Katona, G. Development of dexamethasone-loaded mixed polymeric micelles for nasal delivery. Eur. J. Pharm. Sci. 2021, 166, 105960. [Google Scholar] [CrossRef] [PubMed]
  43. Salamah, M.; Budai-Szűcs, M.; Sipos, B.; Volk, B.; Katona, G.; Balogh, G.T.; Csóka, I. Development and characterization of in situ gelling nasal cilostazol spanlastics. Gels 2025, 11, 82. [Google Scholar] [CrossRef]
  44. Rinaldi, F.; Oliva, A.; Sabatino, M.; Imbriano, A.; Hanieh, P.N.; Garzoli, S.; Mastroianni, C.M.; De Angelis, M.; Miele, M.C.; Arnaut, M.; et al. Antimicrobial essential oil formulation: Chitosan coated nanoemulsions for nose to brain delivery. Pharmaceutics 2020, 12, 678. [Google Scholar] [CrossRef] [PubMed]
  45. International Conference on Harmonisation. ICH Harmonised Tripartite Guideline Stability Testing of New Drug Substances and Products Q1A(R2). 2003. Available online: https://database.ich.org/sites/default/files/Q1A%28R2%29%20Guideline.pdf (accessed on 9 July 2025).
  46. Abdul Rasool, B.K.; Mohammed, A.A.; Salem, Y.Y. The optimization of a dimenhydrinate transdermal patch formulation based on the quantitative analysis of in vitro release data by DDSolver through skin penetration studies. Sci. Pharm. 2021, 89, 33. [Google Scholar] [CrossRef]
  47. Zhang, Y.; Huo, M.; Zhou, J.; Zou, A.; Li, W.; Yao, C.; Xie, S. DDSolver: An add-in program for modeling and comparison of drug dissolution profiles. AAPS J. 2010, 12, 263–271. [Google Scholar] [CrossRef]
  48. Salamah, M.; Volk, B.; Lekli, I.; Bak, I.; Gyöngyösi, A.; Kozma, G.; Kónya, Z.; Szalenkó-Tőkés, Á.; Kiricsi, Á.; Rovó, L.; et al. Preparation, and ex vivo and in vivo characterization of favipiravir-loaded aspasomes and niosomes for nose-to-brain administration. Int. J. Nanomed. 2025, 20, 6489–6514. [Google Scholar] [CrossRef]
  49. Abdul Hussein, H.A.; Maraie, N.K. Tenoxicam-loaded polymeric micelles material: Formulation, optimization, and evaluation. Mater. Today Proc. 2022, 61, 672–680. [Google Scholar] [CrossRef]
  50. Danaei, M.; Dehghankhold, M.; Ataei, S.; Davarani, F.H.; Javanmard, R.; Dokhani, A.; Khorasani, S.; Mozafari, M.R. Impact of particle size and polydispersity index on the clinical applications of lipidic nanocarrier systems. Pharmaceutics 2018, 10, 57. [Google Scholar] [CrossRef]
  51. Wang, M.; Zhan, J.; Xu, L.; Wang, Y.; Lu, D.; Li, Z.; Li, J.; Luo, F.; Tan, H. Synthesis and characterization of PLGA-PEG-PLGA based thermosensitive polyurethane micelles for potential drug delivery. J. Biomater. Sci. Polym. Ed. 2021, 32, 613–634. [Google Scholar] [CrossRef]
  52. Khameh Khorshid, N.; Zhu, K.; Knudsen, K.D.; Bekhradnia, S.; Sande, A.; Nyström, B. Novel structural changes during temperature-induced self-assembling and gelation of PLGA-PEG-PLGA triblock copolymer in aqueous solutions. Macromol. Biosci. 2016, 16, 1838–1852. [Google Scholar] [CrossRef]
  53. Singla, P.; Singh, O.; Sharma, S.; Betlem, K.; Aswal, V.K.; Peeters, M.; Mahajan, R.K. Temperature-dependent solubilization of the hydrophobic antiepileptic drug lamotrigine in different Pluronic micelles—A spectroscopic, heat transfer method, and small-angle neutron scattering study. ACS Omega 2019, 4, 11251–11262. [Google Scholar] [CrossRef]
  54. Basak, R.; Bandyopadhyay, R. Encapsulation of hydrophobic drugs in Pluronic F127 micelles: Effects of drug hydrophobicity, solution temperature, and pH. Langmuir 2013, 29, 4350–4356. [Google Scholar] [CrossRef]
  55. Sharma, P.; Bhatia, S.R. Effect of anti-inflammatories on Pluronic® F127: Micellar assembly, gelation and partitioning. Int. J. Pharm. 2004, 269, 131–143. [Google Scholar] [CrossRef]
  56. Ahmad, Z.; Shah, A.; Siddiq, M.; Kraatz, H.B. Polymeric micelles as drug delivery vehicles. RSC Adv. 2014, 4, 17028–17038. [Google Scholar] [CrossRef]
  57. Chen, S.-F.; Lu, W.-F.; Wen, Z.-Y.; Li, Q.; Chen, J.-H.; Chen, H. Preparation, characterization and anticancer activity of norcantharidin-loaded poly(ethylene glycol)-poly(caprolactone) amphiphilic block copolymer micelles. Die Pharm. 2012, 67, 781–788. [Google Scholar] [CrossRef]
  58. Di, J.; Gao, X.; Du, Y.; Zhang, H.; Gao, J.; Zheng, A. Size, shape, charge and “stealthy” surface: Carrier properties affect the drug circulation time in vivo. Asian J. Pharm. Sci. 2021, 16, 444–458. [Google Scholar] [CrossRef] [PubMed]
  59. Azadkhah Shalmani, A.; Wang, A.; Ahmed, Z.; Sheybanifard, M.; Mihyar, R.; Buhl, E.M.; Pohl, M.; Hennink, W.E.; Kiessling, F.; Metselaar, J.M.; et al. Tunable polymeric micelles for taxane and corticosteroid co-delivery. Drug Deliv. Transl. Res. 2024, 14, 2642–2654. [Google Scholar] [CrossRef] [PubMed]
  60. Sezgin, Z.; Yüksel, N.; Baykara, T. Preparation and characterization of polymeric micelles for solubilization of poorly soluble anticancer drugs. Eur. J. Pharm. Biopharm. 2006, 64, 261–268. [Google Scholar] [CrossRef] [PubMed]
  61. Sipos, B.; Csóka, I.; Ambrus, R.; Schelz, Z.; Zupkó, I.; Balogh, G.T.; Katona, G. Spray-dried indomethacin-loaded polymeric micelles for the improvement of intestinal drug release and permeability. Eur. J. Pharm. Sci. 2022, 174, 106200. [Google Scholar] [CrossRef]
  62. Annunziata, O. The salt-induced diffusiophoresis of nonionic micelles—Does the salt-induced growth of micelles influence diffusiophoresis? Molecules 2024, 29, 3618. [Google Scholar] [CrossRef]
  63. Molina-Bolívar, J.A.; Aguiar, J.; Ruiz, C.C. Growth and hydration of Triton X-100 micelles in monovalent alkali salts: A light scattering study. J. Phys. Chem. B 2002, 106, 870–877. [Google Scholar] [CrossRef]
  64. Heredia, N.S.; Vizuete, K.; Flores-Calero, M.; Pazmiño, V.K.; Pilaquinga, F.; Kumar, B.; Debut, A. Comparative statistical analysis of the release kinetics models for nanoprecipitated drug delivery systems based on poly(lactic-co-glycolic acid). PLoS ONE 2022, 17, e0264825. [Google Scholar] [CrossRef]
  65. Pourtalebi Jahromi, L.; Ghazali, M.; Ashrafi, H.; Azadi, A. A comparison of models for the analysis of the kinetics of drug release from PLGA-based nanoparticles. Heliyon 2020, 6, e03451. [Google Scholar] [CrossRef]
  66. Kapare, H.S.; Metkar, S.R. Micellar drug delivery system: A review. Pharm. Reson. 2020, 2, 21–26. [Google Scholar]
  67. International Conference on Harmonisation. ICH Guideline Q3C (R5) on Impurities: Guideline for Residual Solvents Part II and Part III (PDE for Tetrahydrofuran and N-Methylpyrrolidone). 2011. Available online: https://www.tga.gov.au/sites/default/files/ichq3cr5.pdf (accessed on 9 July 2025).
  68. Hancock, B.C.; Zografi, G. Characteristics and significance of the amorphous state in pharmaceutical systems. J. Pharm. Sci. 1997, 86, 1–12. [Google Scholar] [CrossRef] [PubMed]
  69. Xi, L.; Han, Y.; Liu, C.; Liu, Y.; Wang, Z.; Wang, R.; Zheng, Y. Sonodynamic therapy by phase-transition nanodroplets for reducing epidermal hyperplasia in psoriasis. J. Control. Release 2022, 350, 435–447. [Google Scholar] [CrossRef] [PubMed]
  70. Ojha, T.; Hu, Q.; Colombo, C.; Wit, J.; van Geijn, M.; van Steenbergen, M.J.; Bagheri, M.; Königs-Werner, H.; Buhl, E.M.; Bansal, R.; et al. Lyophilization stabilizes clinical-stage core-crosslinked polymeric micelles to overcome cold chain supply challenges. Biotechnol. J. 2021, 16, 2000212. [Google Scholar] [CrossRef]
  71. Razif, M.R.F.M.; Chan, S.Y.; Widodo, R.T.; Chew, Y.-L.; Hassan, M.; Hisham, S.A.; Rahman, S.A.; Ming, L.C.; Tan, C.S.; Lee, S.-K.; et al. Optimization of a Luteolin-Loaded TPGS/Poloxamer 407 Nanomicelle: The Effects of Copolymers, Hydration Temperature and Duration, and Freezing Temperature on Encapsulation Efficiency, Particle Size, and Solubility. Cancers 2023, 15, 3741. [Google Scholar] [CrossRef] [PubMed]
  72. Rabiee, N.; Ahmadi, S.; Afshari, R.; Khalaji, S.; Rabiee, M.; Bagherzadeh, M.; Fatahi, Y.; Dinarvand, R.; Tahriri, M.; Tayebi, L.; et al. Polymeric Nanoparticles for Nasal Drug Delivery to the Brain: Relevance to Alzheimer’s Disease. Adv. Ther. 2020, 4, 2000076. [Google Scholar] [CrossRef]
  73. Maher, R.; Moreno-Borrallo, A.; Jindal, D.; Mai, B.T.; Ruiz-Hernandez, E.; Harkin, A. Intranasal Polymeric and Lipid-Based Nanocarriers for CNS Drug Delivery. Pharmaceutics 2023, 15, 746. [Google Scholar] [CrossRef]
  74. Senthilkumar, M.; Dash, S.; Vigneshwari, R.; Paulraj, E. Aceclofenac-loaded Pluronic F108/L81 mixed polymeric micelles: Effect of HLB on solubilization. Des Monomers Polym 2022, 25, 1–11. [Google Scholar] [CrossRef] [PubMed]
  75. Vambhurkar, G.; Jain, N.; Srinivasarao, D.A.; Famta, P.; Singh, S.B.; Srivastava, S. Drug Solubilization and Drug Release from Polymeric Micelles. In Polymeric Micelles: Principles, Perspectives and Practices; Singh, S.K., Gulati, M., Mutalik, S., Dhanasekaran, M., Dua, K., Eds.; Springer: Singapore, 2023; pp. 87–109. [Google Scholar] [CrossRef]
  76. Gutiérrez-Saucedo, R.A.; Gómez-López, J.C.; Villanueva-Briseño, A.A.; Topete, A.; Soltero-Martínez, J.F.A.; Mendizábal, E.; Jasso-Gastinel, C.F.; Taboada, P.; Figueroa-Ochoa, E.B. Pluronic F127 and P104 Polymeric Micelles as Efficient Nanocarriers for Loading and Release of Single and Dual Antineoplastic Drugs. Polymers 2023, 15, 2249. [Google Scholar] [CrossRef] [PubMed]
  77. Gu, J.; Cai, X.; Raza, F.; Zafar, H.; Chu, B.; Yuan, H.; Wang, T.; Wang, J.; Feng, X. Preparation of a minocycline polymer micelle thermosensitive gel and its application in spinal cord injury. Nanoscale Adv. 2024, 6, 5874–5888. [Google Scholar] [CrossRef]
  78. Long, H.; Tian, W.; Jiang, S.; Zhao, J.; Zhou, J.; He, Q.; Tang, Z.; Shen, W.; Wang, J. A dual drug delivery platform based on thermo-responsive polymeric micelle capped mesoporous silica nanoparticles for cancer therapy. Microporous Mesoporous Mater. 2022, 338, 111943. [Google Scholar] [CrossRef]
Pharmaceutics 17 01147 g001
Figure 1. Schematic presentation of the formulation of citalopram-loaded thermosensitive polymeric micelles.
Figure 1. Schematic presentation of the formulation of citalopram-loaded thermosensitive polymeric micelles.
Pharmaceutics 17 01147 g001
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Figure 2. Variations in micelle size (expressed as Z-average) (A) and variations in micelle size distribution (expressed as polydispersity index) (B) within the temperature range of 25–40 °C. Results are presented as means ± SD (n = 3).
Figure 2. Variations in micelle size (expressed as Z-average) (A) and variations in micelle size distribution (expressed as polydispersity index) (B) within the temperature range of 25–40 °C. Results are presented as means ± SD (n = 3).
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Figure 3. Micelle size changes (expressed as Z-average) in the presence of SNES (pH 5.6), PBS (pH 7.4), and CSF (pH 7.4). Results are presented as means ± SD (n = 3). Statistical analysis: *, p < 0.01; **, p < 0.001; ****, p < 0.00001. Statistical analysis is compared to the initial measured point.
Figure 3. Micelle size changes (expressed as Z-average) in the presence of SNES (pH 5.6), PBS (pH 7.4), and CSF (pH 7.4). Results are presented as means ± SD (n = 3). Statistical analysis: *, p < 0.01; **, p < 0.001; ****, p < 0.00001. Statistical analysis is compared to the initial measured point.
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Figure 4. Results of physical stability investigation of CT-PM3: (A,B) solid state: Z-average (A) and PdI (B); (C,D) liquid state: Z-average (C) and PdI (D) at ambient temperature and fridge conditions. Results are presented as means ± SD (n = 3). All data are considered to be statistically non-significant (n.s., p > 0.01).
Figure 4. Results of physical stability investigation of CT-PM3: (A,B) solid state: Z-average (A) and PdI (B); (C,D) liquid state: Z-average (C) and PdI (D) at ambient temperature and fridge conditions. Results are presented as means ± SD (n = 3). All data are considered to be statistically non-significant (n.s., p > 0.01).
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Figure 5. Diffractograms of CT-PM3, the initial polymeric micelle-forming components, and the active substance, citalopram (CT).
Figure 5. Diffractograms of CT-PM3, the initial polymeric micelle-forming components, and the active substance, citalopram (CT).
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Figure 6. In vitro drug release profile of the optimized formulation in SNES (pH 5.6) compared to the initial CT. Results are presented as means ± SD (n = 3). Statistical analysis: ****, p < 0.00001.
Figure 6. In vitro drug release profile of the optimized formulation in SNES (pH 5.6) compared to the initial CT. Results are presented as means ± SD (n = 3). Statistical analysis: ****, p < 0.00001.
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Figure 7. In vitro drug permeation study of the optimized formulation compared to the initial CT. Results are presented as means ± SD (n = 3). Statistical analysis: ****, p < 0.00001; ns, not significant.
Figure 7. In vitro drug permeation study of the optimized formulation compared to the initial CT. Results are presented as means ± SD (n = 3). Statistical analysis: ****, p < 0.00001; ns, not significant.
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Figure 8. Calculated biopharmaceutical parameters of CT-PM3 cumulative permeability profile compared to initial CT (CT-SUSP). Flux (J) (A) and permeability coefficient (Kp) (B). Results are presented as means ± SD (n = 3). Statistical analysis: ****, p < 0.00001.
Figure 8. Calculated biopharmaceutical parameters of CT-PM3 cumulative permeability profile compared to initial CT (CT-SUSP). Flux (J) (A) and permeability coefficient (Kp) (B). Results are presented as means ± SD (n = 3). Statistical analysis: ****, p < 0.00001.
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Table 1. Composition of CT-loaded polymeric micelles formulations (CT-PM).
Table 1. Composition of CT-loaded polymeric micelles formulations (CT-PM).
FormulationCT (mg/mL)P188 (mg)PF127 (mg)
CT-PM154090
CT-PM2540100
CT-PM3540110
CT-PM4540120
Table 2. Results of Z-average, PdI, and LCST measurements of CT-PM formulations. Data are presented as mean ± SD (n = 3).
Table 2. Results of Z-average, PdI, and LCST measurements of CT-PM formulations. Data are presented as mean ± SD (n = 3).
FormulationZ-Average at 35 °C (nm)PdI at 35 °CLCST (°C)
CT-PM136.44 ± 1.330.519 ± 0.4429
CT-PM234.51 ± 2.470.447 ± 0.82330
CT-PM331.41 ± 0.990.241 ± 0.02931
CT-PM490.13 ± 0.230.365 ± 0.94136
Table 3. Results of Z-average and PdI measurements of blank PM and CT-PM3. Data are presented as mean ± SD (n = 3).
Table 3. Results of Z-average and PdI measurements of blank PM and CT-PM3. Data are presented as mean ± SD (n = 3).
FormulationZ-Average at 35 °C
(nm)		PdI
Blank PM38.75 ± 3.240.248 ± 0.028
CT-PM331.41 ± 0.990.241 ± 0.029
Table 4. Obtained kinetic parameters of initial CT and CT-PM3.
Table 4. Obtained kinetic parameters of initial CT and CT-PM3.
Model C-SUSPCT-PM3
Zero-orderk0 (µg min−1)0.0711.767
R2−0.5850.742
First-order K1 (min−1) × 10−3 0.0010.042
R2−0.5640.981
Korsmeyer–PeppasKK-P (min−n) × 10−31.25810.132
n0.2250.539
R20.9950.964
HiguchikH (µg min−1/2)0.50811.595
R20.6170.961
Hixon–CrowellkH-C (µg1/3 min−1) × 10−30.0000.012
R2−0.5710.964
Best fit Korsmeyer–PeppasFirst order
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Rajab, F.; Sipos, B.; Katona, G.; Csóka, I. Development and Characterization of Citalopram-Loaded Thermosensitive Polymeric Micelles for Nasal Administration. Pharmaceutics 2025, 17, 1147. https://doi.org/10.3390/pharmaceutics17091147

AMA Style

Rajab F, Sipos B, Katona G, Csóka I. Development and Characterization of Citalopram-Loaded Thermosensitive Polymeric Micelles for Nasal Administration. Pharmaceutics. 2025; 17(9):1147. https://doi.org/10.3390/pharmaceutics17091147

Chicago/Turabian Style

Rajab, Fatima, Bence Sipos, Gábor Katona, and Ildikó Csóka. 2025. "Development and Characterization of Citalopram-Loaded Thermosensitive Polymeric Micelles for Nasal Administration" Pharmaceutics 17, no. 9: 1147. https://doi.org/10.3390/pharmaceutics17091147

APA Style

Rajab, F., Sipos, B., Katona, G., & Csóka, I. (2025). Development and Characterization of Citalopram-Loaded Thermosensitive Polymeric Micelles for Nasal Administration. Pharmaceutics, 17(9), 1147. https://doi.org/10.3390/pharmaceutics17091147

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