Fourth-Generation Antibiotic Gatifloxacin Encapsulated by

Subscriber access provided by University of Sussex Library

Interface Components: Nanoparticles, Colloids, Emulsions, Surfactants, Proteins, Polymers

Fourth-Generation Antibiotic Gatifloxacin Encapsulated by Microemulsions: Structural and Probing Dynamics Muhammad Faizan Nazar, Muhammad Yasir Siddique, Muhammad Atif Saleem, Muddassar Zafar, Faisal Nawaz, Muhammad Ashfaq, Asad Muhammad Khan, Hafiz Muhammad Abd Ur Rahman, MUHAMMAD TAHIR, and Azwan Mat Lazim Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b01775 • Publication Date (Web): 15 Aug 2018 Downloaded from http://pubs.acs.org on August 15, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Fourth-Generation Antibiotic Gatifloxacin Encapsulated by Microemulsions: Structural and Probing Dynamics Muhammad Faizan Nazar1*, Muhammad Yasir Siddique1, Muhammad Atif Saleem1, Muddassar Zafar2, Faisal Nawaz3, Muhammad Ashfaq1, Asad Muhammad Khan4*, Hafiz Muhammad Abd Ur Rahman5, Muhammad Bilal Tahir6, Azwan Mat Lazim7

1 2 3

Department of Chemistry, University of Gujrat, Gujrat 50700, Pakistan.

Department of Biochemistry & Biotechnology, University of Gujrat, Gujrat 50700, Pakistan.

Department of Basic Sciences and Humanities, University of Engineering and Technology Lahore (Faisalabad Campus), Pakistan. 4

Department of Chemistry, COMSATS Institute of Information Technology, Abbottabad, 22060, Pakistan. 5

Department of Chemistry, Forman Christian College (A Charted University), Lahore 54590, Pakistan. 6

7

Department of Physics, University of Gujrat, Gujrat 50700, Pakistan.

School of Chemical Sciences and Food Technology, Faculty of Science and Technology, University Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia.

* Corresponding author E-mail address:

[email protected], [email protected] (M.F. Nazar) [email protected] (A.M. Khan)

Cell #:

0092533643331(210), 00923016942411 (M.F. Nazar)

Postal Address:

Office # JBH-09, Department of Chemistry, Hafiz Hayat Campus, University of Gujrat, Gujrat 50700, Pakistan. (M.F. Nazar)

Page 1 of 27 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 27

ABSTRACT To overcome the increased disease rate, utilizing of the versatile broad spectrum antibiotic drugs in controlled drug delivery systems has been a challenging and complex consignment. However, with the development of microemulsion (µE) based formulations, drugs can be effectively encapsulated and transferred to the target source. Herein, two biocompatible oil-in-water (o/w) µE formulations comprising clove oil/ tween 20/ ethylene glycol/ water (Formulation-A) and clove oil/ tween 20/ 1-butanol/ water (Formulation-B) were developed for encapsulating the gatifloxacin (GTF), a fourth-generation antibiotic. The pseudoternary phase diagrams were mapped at a constant surfactant/cosurfactant (1:1) ratio to boundary the existence of a monophasic isotropic region for as-formulated µEs. Multiple complementary characterization techniques, namely conductivity (σ), viscosity (η) and optical microscopy were used to study the gradual changes that occurred in the microstructure of as-formulated µEs, indicating the presence of a percolation transformation to a bicontinuous permeate flow. GTF showed good solubility, 3.2 wt. % at pH 6.2 and 4.0 wt. % at pH 6.8, in optimum µE of Formulation A and Formulation B, respectively. Each loaded µE formulation showed long-term stability over 8 months of storage. Moreover, no observable aggregation of GTF was found as revealed by Scanning Transmission Electron Microscopy (STEM) and peak to peak correlation of IR analysis, indicating the stability of GTF inside the formulation. The average particle size of each µE, measured by Dynamic light scattering, increased upon loading GTF, intending the accretion of drug in the interfacial layers of microdomains. Likewise, fluorescence probing sense an interfacial hydrophobic environment to GTF molecules in any of the examined formulations, which may be of significant interest for understanding the kinetics of drug release.

KEYWORDS:

Biocompatible,

Pseudoternary,

Isotropic,

Microstructure,

Percolation,

Bicontinuous, Interfacial


Page 3 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

INTRODUCTION Over recent decades, microencapsulation of therapeutic molecules utilizing soft materials has been developed as imperative technology for controlled release of effective drugs to targeted sites.1-8 The development of drug encapsulation, therefore its solubility and bioavailability, remains one of the most challenging aspects of drug delivery. The undesired bio-distribution of the drug in the bulk phase may cause undesirable side effects, thereby exposing its toxicity. Thus, in order to enhance drug uptake/absorption after administration in vivo and to protect them from enzymatic degradation, they are dispersed in a suitable delivery system. The choice of solubility improvement method depends on the nature of the drug, the site of absorption and the desired dosage form characteristics.9-11 Microemulsion (µE) based drug carrier systems exhibit high-performance functionality owing to their ease of formulation, biocompatibility and structural diversity.12-17 For completeness, microemulsions (µEs) are optically isotropic, transparent, and thermodynamically stable microfluids of two immiscible liquids (typically oil and water), homogenized by surfactants and often formulated in conjunction with co-surfactants.18-21 As a smart drug carrier system, µEs play an important role in local, oral, nasal, ocular, transdermal and parenteral drug delivery and sustained release formulations of active pharmaceutical ingredients.22-27 Drug release mechanism mainly depends upon the structural type of µE, i.e. either water-in-oil (w/o), oil-in-water (o/w), or bicontinuous domain.21,28,29 Most significantly, drugs that are poorly permeable across the diffusional barriers and have low water solubility are transported with the support of µEs. The path of absorption, particle size, solubility and distribution of drug among µE components are the prime factors which directly affect absorption of drug from µEs.24,30 The purpose of this work was to develop a biocompatible µE formulation with high loading capacity for the amphiphilic antibiotic gatifloxacin (GTF). The GTF (Figure S1 in the Supporting Information section) is an effective fourth-generation antibacterial agent that is resistant to bacterial infections and bacterial conjunctivitis.31,32 In the present study, two biocompatible oilin-water (o/w) µE formulations comprising clove oil/ tween 20/ ethylene glycol/ water (Formulation-A) and clove oil/ tween 20/ 1-butanol/ water (Formulation-B) were developed for the encapsulation and improved loading of GTF. Eugenol (4-allyl-2-methoxyphenol) and isoeugenol (4-propenyl-2-methoxyphenol) are the basic components of clove oil and have strong anti-inflammatory, antibacterial, antiseptic, antiviral, and anti-inflammatory properties and Page 3 of 27 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 27

aphrodisiac and stimulatory effects as well.33 Tween 20 (Figure S2) is a biocompatible nonionic emulsifier widely used as an inert carrier in many pharmaceutical preparations.34,35 The cosurfactants (1-butanol and ethylene glycol) were used to overcome any additional input of energy in the key packaging parameters of Tween 20. Before applying µE as a drug delivery vehicle, it is important to examine the microstructure of the µE domain.21,28,29,36 In the current work, prior to the loading of the GTF with the µE formulation, various complementary characterization techniques, i.e. conductivity (σ ), viscosity (η), optical microscopy, and pseudo-ternary phase diagram were used to study the gradual changes in µE microstructures. In addition, the loading capacity, storage stability, optical structure and microstructure of the best GTF-loaded µE was evaluated. The stability of GTF in µE was examined by peak-to-peak correlation of Fourier Transform Infrared (FTIR) spectroscopy and Scanning Transmission Electron Microscopy (STEM). The average particle size of the drug-loaded and drug-free optimal µE was measured by Dynamic Light Scattering (DLS), while the confinement of GTF in the optimal µE microdomain was studied by fluorescence measurement. The high loading capacity of GTF (3.2 wt. % in Formulation A at pH = 6.2 and 4.0 wt. % in Formulation B at pH = 6.8) highlights the interesting features of the µE based formulation for understanding drug release kinetics in pharmaceutical sciences.

EXPERIMENTAL SECTION Materials and Chemicals. Ethylene Glycol (99.8%), 1-butanol (99.5%), Tween® 20 (polyoxyethylene sorbitan monolaurate) and clove oil were purchased from Sigma-Aldrich. Gatifloxacin (98%, M.W 375.39 g. mol-1) was obtained from Lahore Chemical and Pharmaceutical Works Pvt. Ltd., Lahore, Pakistan. Deionized water was used for dilution and for other experimental purposes.

Microemulsion Preparation and Drug Incorporation. The pseudoternary phase diagrams were delineated (Figure 1) using the oil (clove oil), surfactant (Tween 20; HLB = 16.7), and water as aqueous phase. Ethylene glycol and 1-butanol were used as cosurfactant in µE Formulation-A (µE-A) and Formulation-B (µE-B), respectively. In order to obtain a stable and transparent µE formulation, the oil was first mixed with a surfactant/cosurfactant (1:1) mixture and then water was added to obtain the desired µE composition (Figure 1). To study the progression of Page 4 of 27 ACS Paragon Plus Environment

Page 5 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

morphological transformation from an oil-rich (w/o) system to a water-rich (o/w) system, a water dilution line AB was selected at a constant oil-to-surfactant ratio. Under the continuous stirring, GTF of 3.2 wt. % at pH 6.2 and 4.0 wt. % at pH 6.8 was dissolved in an optimal µE formulation (optimized after electrical conductivity and viscosity analyses) comprising 35.0% of ethylene glycol, 35.0% of Tween 20, 11.0% of clove oil and 19.0% of water (µE-A) and 40.0% of 1-butanol, 40.0% of Tween 20, 12.0% of clove oil and 8.0% of water (µE-B), respectively. Each of the samples (unloaded and drug-loaded µEs) were stable, remaining clear and transparent over 8 months of storage.

Microemulsion Characterization Centrifugation Assay and Microscopic Measurements. To reveal the stability of pure and drugloaded µE, developed formulations were centrifuged at 5500 rpm for 15 min using Hermle Z200 centrifuge machine. Whereas, to reveal the structural transitions in all the µE systems, biological microscope (LABOMED FLR Lx 400; Jenoptic, Germany) was used with 4x/10x/40x/100x magnification.

Electrical Conductivity and Viscosity Measurements. The type of phase inversion and continuous phase of µE systems were tested with the help of conductivity measurement. The electric conductivity (σ) was measured through Conductivity Meter (ADWA AD-3000, Hungry) whereas, viscosities were measured at 25±1ºC with calibrated Brookfield viscometer (LVDV– 2T) at 100 rpm by washing and rinsing the viscometer at each measurement The measurements were accomplished by attenuating surfactant, oil, cosurfactant mixture with distilled water (along the dilution line AB, in Figure 1).

Spectroscopic Measurements. The infrared (IR) spectra of pure and drug-loaded µEs were recorded on Bruker FTIR (Alpha series) from 600 to 4000 cm-1. Steady-state fluorescence (SSF) measurements were conducted on a Spectrofluorophotometer (Shimadzu, RF-6000) using a lownoise photomultiplier detector. The used light source was LED and operating voltage was 5.0 V dc. Slit width (ex. 5.0 nm, em. 5.0 nm) was adjusted in order to obtain good resolution of the bands. The fluorescence spectra of GTF in aqueous phase, individual oil phase, surfactant/cosurfactant (1:1) mixture, and in any of the optimum µE system were recorded in the Page 5 of 27 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 27

range of 300–800 nm with excitation at 295 nm. To determine the optimal excitation wavelength and to check the stability of probe molecules residing inside the microdomain environment, 3Dfluorescence spectra were obtained by successively varying the excitation wavelength.

Particle Size Analysis. The average droplet size and polydispersity index (PDI) of all the formulations was measured with Zetasizer (Malvern, Nano ZSP). Size distributions of µE droplets (GTF-free and GTF-loaded) were measured at room temperature without sample filtration. The instrument was equipped with a 635 nm laser, and the light scattering was detected at 173° by a back scattering technology (NIBS, Non-Invasive Back-Scatter). All the measurements were performed in triplicate.

Morphology of GTF-free and GTF-loaded µEs. The morphology of GTF-free and GTF-loaded µEs was evaluated with scanning electron microscope (FEI, Nova Nano-SEM 450) operating at 15 kV at working distance of 5 mm equipped with STEM detector under A-B mode. For this, the samples were prepared by putting a drop from their aqueous suspension onto carbon coated copper grids and air dried. Afterwards, they were coated with 1% ammonium molybdate solution, which was blotted after 10 sec. and further dried before STEM analysis.

RESULTS AND DISCUSSION Phase Studies. Phase diagram aids in determining correlation between the phase behaviour of a particular mixture and its constituents.22 Figure 1 reveals pseudoternary phase diagrams formed and dilution line chosen as working region, by bringing in contact suitable ratios of ethylene glycol, tween 20, clove oil, water (µE-A) and 1-butanol, tween 20, clove oil, water (µE-B). Area of existence of larger isotropic region µE in the phase diagram formed spontaneously at room temperature incorporating surfactant/cosurfactant (Smix) in 1:1 ratio for both of the formulations.


Page 7 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 1. Pseudoternary phase diagram showing µE region (green shaded) of formulations (A & B). The dilution line (AB with red color) of each formulation, selected for further investigations. The highlighted mark (blue color) on dilution line represents the optimal µE composition of each formulation.

Figure 1 clearly indicates that µE region is larger and more fitting for µE-B than for µE-A. Variation in µE region owes to the difference of co-surfactants employed in two formulation as chain length compatibility of oil with co-surfactant and surfactant is one of the major factors which determines µE structure formation.37 Interestingly, there was no significant difference between the µE area (Figure 1) and the physicochemical properties (Table 1) of the ethylene glycol system (µE-A) and 1-butanol system (µE-B). Compared to 1-butanol, ethylene glycol with a shorter hydrocarbon chain has a higher water solubility; therefore, it has a higher tendency to diffuse from the oil phase into the aqueous phase during the dilution process. However, the preparation of µE with ethylene glycol is a time consuming process as it was difficult to emulsify the water-induced gel structure.38 The water dilution line AB was selected at a constant oil-to-Smix ratio to study the evolution of morphological transformation from an oil-rich (w/o) system to a water-rich (o/w) system without visual phase separation. This water dilution has the advantages of rapidness, accuracy and economy. However, the different types of microstructural changes in the structure cannot be determined from the phase diagram depicted by aqueous titration.21,29,39-42 Therefore, to explore the gradual changes occurring in the single-phase region of µE, the conductivity (σ), viscosity (η), and optical microscopic analysis were used as a weight fraction of the aqueous component, Φw (wt %), along the dilution line AB (shown in Figure 1). Page 7 of 27 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 27

Electrical Conductivity Measurements. In the µE microdomain, the assessment of the structural transition and prediction of a conductive network channel (bi-continuous µE), conductometry is a convenient method.21,29,43 Phase transition from w/o to o/w µE through bicontinuous channel was accessed through electrical conductivity (σ) measurements as a function of weight fraction of aqueous component (Φw) along the dilution line AB for the oil/Smix. The plot of σ and its first derivative (dσ/dΦ) versus Φw for each of the formulation are shown in Figure 2.

Figure 2. Variation of electrical conductivity (σ) and viscosity (η) as a function of Φw (wt %) along the dilution line AB of each formulation (shown in Figure 1). Φw (0-32 wt %) for Formulation A and Φw (0-15 wt %) for Formulation B.

As clearly seen in Figure 2, the bi-continuous region for µE-A starts at ~14% Φw, called as percolation threshold (Φp), below which slight increase is observed in Φw value (w/o µE, at Φw < 14% ). An abrupt change occurs at (Φw > 25%) values indicating a decrease in σ due to increase in water content. More water content leads to the development of oil in water (o/w) µE, thereby causing phase transition at Φb. First derivative (dσ/dΦ) with Φw increasing values further aided to determine the phase transition in µE domains. At Φw value of ~20%, maximum first derivative value is observed indicating the existence of stable bi-continuous microstructure in this particular Page 8 of 27 ACS Paragon Plus Environment

Page 9 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

region. For µE-B, the corresponding values of Φw for all are suggested transition in microstructure are, the percolation threshold (Φp ~ 5%), the phase inversion (Φb ~ 9%) and the bi-continuous channel (dσ/dΦ ~ 7%).21,29,43-47

Viscosity Measurements. As viscosity mainly depends on droplet size, therefore it has been extensively useful technique to observe the transformation in microstructure of µE.21,29,48-50 Viscosity (η) and its first derivative (dη/dΦ) were plotted as a function of Φw along the dilution line for both systems of µE-A and µE-B, as shown in Figure 2. Likewise for electrical conductivity data, same trend in structural transformation was observed within µE microdomain. The consistent increase of η with Φw is observed for each formulation, that might be helpful for the slow diffusion of drug at infinite dilution.51,52

Optical Microscopic Studies. Biological microscope was employed to visualize the bicontinuous channels in µE and to determine the progression in microstructure phase transition from w/o to o/w through bi-continuous phase.21,53 Dispersed spherical droplets of oil and water in their respective continuous phases constructing w/o and o/w µE are shown in Figure 3(a) and 3(c) for µE-A and Figure 3(d) and 3(f) for µE-B, respectively. Whereas, Figure 3(b) and 3(e) represents bi-continuous channel for µE-A and µE-B, respectively which are formed by network of spherical droplets. The proposed microstructure changes in µE are also sketched in Figure 3 that represents phase transition in microstructure of µE with dilution by water, which is in good agreement with the previously published work.21,53


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 27

Figure 3. Microscopic images of formulations (A & B) with proposed microstructure variations in µE with dilution.

On account of electrical conductivity, viscosity and optical microscopy measurements, optimal µE formulation comprising clove oil (11.0%), water (19.0%), Tween 20 (35.0%), ethylene glycol (35.0%) for (µE-A) and clove oil (12.0%), water (8.0%), Tween 20 (40.0%), 1-butanol (40.0%) for (µE-B) were selected for further analyses. The values of the measured parameters are tabulated in Table 1.


Page 11 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Table 1. Physical parameters of optimal GTF-free and GTF-loaded µEs.

Formulation A (µE-A)

Formulation B (µE-B)

clove oil (11.0%), water

clove oil (12.0%), water (8.0%),

(19.0%), Tween 20 (35.0%),

Tween 20 (40.0%), 1-butanol

ethylene glycol (35.0%)

(40.0%)

GTF-free

GTF-loaded

GTF-free

GTF-loaded

conductivity (µS/cm)

24.4 ± 1.2

28.7 ± 1.8

9.1 ± 0.7

12.2 ± 0.9

viscosity (cP)

21.2 ± 0.7

24.5 ± 0.8

16.0 ± 0.5

18.4 ± 0.5

62.7 ± 1.8

116.6 ± 2.7

68.9 ± 1.5

126.5 ± 2.6

physical property

particle size (nm) 2

-13

diffusion constant (cm /s)

3.28 × 10

zeta potential (mV)

-27.6 ± 2.1

drug solubility stability fluorescence FTIR

1.53 × 10

-13

3.96 × 10

-37.5 ± 2.9

-13

-34.2 ± 3.2

3.2 wt. % at pH of 6.2

1.87 × 10-13 -40.9 ± 3.7

4.0 wt. % at pH of 6.8

over 8 months storage GTF possibly reside in the interfacial film of µE no observable intermolecular interaction among GTF and µE components

The results showed good solubility of GTF, i.e. 3.2 wt. % at pH 6.2 and 4.0 wt. % at pH 6.8, in optimum µE µE-A and µE-B, respectively. Each loaded µE formulation showed long-term stability over 8 months of storage. Moreover, no aggregation of GTF was found indicating the stability of GTF inside the formulation revealed by Scanning Transmission Electron Microscopy and peak to peak correlation of IR analysis. The average particle size of each µE, measured by Dynamic light scattering, increases upon loading of GTF, suggesting the accumulation of drug in the interfacial layers of microdomains. Likewise, fluorescence measurements indicated that the GTF most likely sense an interfacial environment in any of the examined systems. The detail of all measured parameters are described in succeeding sections.

Infrared Study. Fourier Transforms Infrared (FTIR) spectroscopy was utilized to examine the possible interactions between GTF and µE excipients and to check the chemical stability of GTF in microstructure of µE. FTIR spectrum of pure GTF powder has been shown in Figure S3 (in


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 27

the Supporting Information section), whereas FTIR spectral data of µE-A and µE-B and their corresponding GTF-loaded formulations are drawn in Figure 4.

Figure 4. Infrared spectra of drug-free and drug-loaded µEs. FTIR spectrum of pure GTF powder has been shown in Figure S3 (in the Supporting Information section).

In the IR spectrum of GTF (Figure S3), the carboxylate-stretching band (C=O)c was observed at 1727 cm-1, while the pyridine carbonyl (C=O)p was observed at 1638 cm-1. The peak of hydroxyl group (O-H) was found at 3412 cm-1, whereas the peaks at 1542 cm-1 and 820 cm-1 were assigned to aromatic stretching and C-H bending, respectively. The peaks at 1066 cm-1 and 1280 cm-1 were attributed to stretching of C-F and C-N, respectively. All the characteristic peaks of drugloaded µE-A and µE-B have been conserved as in their correspondent plain drug-free formulations, as shown in Figure 4. The IR spectrum of the drug-loaded µE in parallel with the drug-free µE indicated high compatibility of the drug with µE excipients. The peak-to-peak correlation show complete dissolution of the aggregate-free drug in the formulation matrix as also reported in previous studies.54-57

Dynamic Light Scattering Study. To determine the average particle sizes, polydispersity, and zeta potentials of drug-free and drug-loaded µE formulations, Dynamic Light Scattering (DLS) Page 12 of 27 ACS Paragon Plus Environment

Page 13 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

technique was employed. As seen in Figure 5, the size distribution of drug-free and drug-loaded µE droplets ranged from 62–117 nm for µE-A, whereas for µE-B, this ranged from 69–127 nm, indicating the presence of drug in the droplet of µE. All the formulations showed a single peak, indicating a mono-modal size distribution of droplets. The results are summarized in Table 1.

Figure 5. The particle size distribution of drug-loaded and drug-free optimal µEs analyzed by DLS.

Smaller droplet size with a narrow size distribution are produced by a system containing ethylene glycol then using 1-butanol as a cosurfactant (Figure S4). The average particle size increased after the addition of the drug to each µE formulation, which may be due to the accumulation of GTF in the droplet interface layer supported by earlier studies.21,50,58 The low polydispersity index (PDI) also indicates higher uniformity of droplet size in each formulation (Figure 5). Moreover, the negative zeta potential values of each formulation is indicative of colloidal stability (Figure S5). As, a highly stable µE has zeta-potential either > 30mV or < -30mV due to electrostatic repulsion among nanoparticles.59,60 In our study, the zeta-potential of drug-free µEs was -27.6 mV (µE-A) and -34.2 mV (µE-B), demonstrating a high stability of these µEs. Comparatively, the high negative zeta potentials of the GTF-loaded µEs (Table 1) indicating the high stability of these GTF-loaded formulations which on storage also have un-effected zeta potentials (see Figure S4). Similar kind of results were found and reported by other researchers.60-63 The translational droplet diffusion coefficient (D) was measured from the Stokes-Einstein relation (equation 1). Page 13 of 27 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

D=

k BT 6πηr

Page 14 of 27

(1)

Where, kB and T are the Boltzmann constant and the absolute temperature. η is the viscosity of the µE and r is the hydrodynamic radius of droplets obtained from DLS measurements. The calculated values of the diffusion coefficient of drug-free and drug-loaded µEs are tabulated in Table 1. The results showed that the diffusion coefficients are higher for 1-butanol comprising µE (µE-B) compared to ethylene glycol based µE (µE-A), indicating the better penetration enhancing properties and improved mucoadhesion performance with more CH and was in agreement with the results obtained from viscosity measurements.64,65

Scanning Transmission Electron Microscopy. Figure 6 exhibits the Scanning Transmission Electron Microscopy (STEM) images of as-formulated GTF-free and GTF-loaded µE which has been used to perceive the surface and bulk microstructure of the drug-free and drug-loaded µE. As shown in Figure 6, there are no significant transformations in the morphologies of the GTFfree and GTF-loaded µE. The visual size of the particles is small before the loading of drug (Figure 6A and 6B) but after drug loading the particle size is increased (Figure 6A' and 6B'), that support the DLS results.


Page 15 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 6. STEM images of (A) GTF-free µE-A, (B) GTF-free µE-B, (A´) GTF-loaded µE-A, (B´) GTF-loaded µEB.

The imaging also showed the weakly polydisperse collection of spherical particles for each of the formulation. However, the size distribution histograms of all micrographs reveal narrow size distribution of droplets, as shown in Figure S5 (in Supporting Information). The STEM images of drug-free µEs indicate average particle size of 50−75 nm, which on GTF loading ranged to 100−125 nm, similar to that obtained by DLS.

Fluorescence Measurements. In order to locate the dissolved drug in the microdomains of the µE system, SSF measurements have been performed extensively because the fluorescence of the amphipathic moiety largely depends on the polarity of the medium.21,29,36,64-69 Figure 7 shows the fluorescence spectra of GTF in aqueous phase, oil phase, optimal µE formulation and Smix for each formulation.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 27

Figure 7. Fluorescence spectra of GTF in aqueous phase, individual oil phase, optimum µE formulation, S/CoS (Smix) of each formulation.

As indicated in Figure 7, the emission maximum (λem) of GTF is 450 nm in aqueous phase (characteristic of GTF), whereas it appears at 467 nm in oil phase. However, λem of GTF in Smix of both formulations, µE-A and µE-B, are situated at 489 nm and 468 nm respectively. Moreover, the λem of GTF in µE-A and µE-B are at 482 nm and 475 nm respectively, as shown in Figure 7. A comparison of the λem of GTF in various media exhibit the close confinement of GTF molecules in µE, rather than pure bulk phases. The results show that as the hydrophobicity of the inner core increases, the GTF molecules drag deeper into the interfacial membrane and stop its movement to the bulk volume of the water. These findings support the high solubility of GTF, 3.2 wt. % and 4.0 wt. %, in µE-A and µE-B respectively. Although, the original pattern of GTF fluorescence signal observed in pure water and oil are also preserved in the optimum µEs and S/CoS; however, the fluorescent spectrum of GTF in µEs was Page 16 of 27 ACS Paragon Plus Environment

Page 17 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

more similar to that in nonpolar solvent other than in water, suggesting that GTF is protected from water. Therefore, it can be concluded that the GTF is located at the core of the µEs, including the hydrophobic palisade layer and the oil phase. The location of GTF is primarily caused by its high lipophilicity due to the hydrophobic forces between GTF and the hydrophobic chain. Moreover, the fluorescence intensity of GTF in µE was lower than that in water. The redshift of fluorescence spectra and the decrease of fluorescence intensity were mainly caused by the effect of solvent polarity. This indicated that more GTF was distributed in the non-polar microenvironment, which included the oil phase and the hydrophobic group of surfactant.69,70 Three-dimensional (3D) fluorescence spectroscopy or excitation-emission matrix spectroscopy was used to check the stability of probe (GTF) molecules residing inside the microdomain environment over 8 months storage period. The 3D-fluorescence spectral behavior of GTF was quickly obtained while varying the excitation wavelength, as presented in Figure 8.

Figure 8. 3D-fluorescence spectral diagrams of GTF in optimum µE formulations with varying the excitation wavelength over 8 months storage period.

All the above phenomenon and analysis revealed the proliferation of solubilized GTF inside the core of the µEs, including the hydrophobic palisade layer and the oil phase, which is actually the reason behind controlled release of it thereby preventing irritation despite of its toxic nature.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 27

CONCLUSIONS Two new microemulsion (µE) were formulated comprising four-components, Tween 20/ clove oil/ethylene glycol/water (µE-A) and Tween 20/clove oil/1-butanol/water (µE-B) for improving the loading capability of a potent antibiotic, Gatifloxacin (GTF). The phase transformation in the µE microdomain were explored via electrical conductivity, viscosity and optical microscopic measurements. DLS was utilized to measure the change in average particle size of µE upon the addition of GTF. Moreover, FTIR and steady-state fluorescence measurements were used to determine the stability and confinement of GTF encapsulated in µE matrix. Results demonstrate that the as-formulated µEs, holding aggregation-free drug molecules remained stable and clear over a period of 8 months storage. The results indicate that the ethylene glycol-based formulation (µE-A) acts as a potential sustained release delivery system rather than a formulation containing 1-butanol (µE-B) because of the high viscosity and smaller droplet size. Although glycol-based formulations are time consuming due to the high viscosity of ethylene glycol, this prevents droplet coalescence and uniform distribution of droplets. The measurements also indicate that GTF molecules most likely sense an interfacial hydrophobic environment of as-formulated µEs, which may lead to a controlled release of drug. However, before the implementation of asformulated µEs extensive research is still required to acquire their conventional formulations as adaptable drug-delivery vehicles.


Page 19 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

ASSOCIATED CONTENT Supporting Information Supplementary data associated with this article shows basic molecular structures of Gatifloxacin (drug) and Tween 20 (surfactant) as well as IR spectrum of pure powder Gatifloxacin. The data also contain zeta potential distribution and size distribution histograms of drug-loaded and drugfree µEs analyzed by DLS.

ACKNOWLEDGEMENTS Authors express gratitude to the Department of Chemistry, University of Gujrat, Pakistan for the provision of lab facility. The authors also extend their sincere appreciations to Higher Education Commission of Pakistan for providing financial support through NRPU Project No. 4557.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 27

REFERENCES (1)

Abbaspourrad, A.; Datta, S. S.; Weitz, D. A. Controlling Release from pH-Responsive Microcapsules. Langmuir 2013, 29, 12697–12702.

(2)

Negrini, R.; Mezzenga, R. pH-Responsive Lyotropic Liquid Crystals for Controlled Drug Delivery. Langmuir 2011, 27, 5296–5303.

(3)

Zahr, A. S.; de Villiers, M.; Pishko, M. V. Encapsulation of Drug Nanoparticles in SelfAssembled Macromolecular Nanoshells. Langmuir 2005, 21, 403–410.

(4)

Teixeira, R. F. A.; van den Berg, O.; Nguyen, L-T. T.; Fehér, K.; Du Prez, F. E. Microencapsulation of Active Ingredients Using PDMS as Shell Material. Macromolecules 2014, 47, 8231–8237.

(5)

Stuart, M. A.; Huck, W. T.; Genzer, J.; Müeller, M.; Ober, C.; Stamm, M.; Sukhorukov, G. B.; Szleifer, I.; Tsukruk, V. V.; Urban, M.; et al. Emerging Applications of StimuliResponsive Polymer Materials. Nat. Mater. 2010, 9, 101−113.

(6)

Tourné-Péteilh, C.; Coasne, B.; In, M.; Brevet, D.; Devoisselle, J.-M.; Vioux, A.; Viau, L. Surfactant Behavior of Ionic Liquids Involving a Drug: From Molecular Interactions to Self-Assembly. Langmuir 2014, 30, 1229−1238.

(7)

Chen, Y.; Liu, L. Modern Methods for Delivery of Drugs across the Blood-Brain Barrier. Adv. Drug Delivery Rev. 2012, 64, 640−665.

(8)

Wang, J.; Wang, Y.; Liang, W. Delivery of Drugs to Cell Membranes by Encapsulation in PEG-PE Micelles. J. Controlled Release 2012, 160, 637−651.

(9)

Gupta, S. Biocompatible Microemulsion Systems for Drug Encapsulation and Delivery. Curr. Sci. 2011, 101, 174−188.

(10) Edward, K. H.; Li, D. Drug like Properties: Concept, Structure, Design and Methods, from ADME to Toxicity Optimization. Elsevier; 2008. Solubility; p. p. 56. (11) Savjani, K. T.; Gajjar, A. K.; Savjani, J. K. Drug Solubility: Importance and Enhancement Techniques. ISRN Pharm. 2012, 2012, 195727. (12) Hegde, R. R.; Verma, A.; Ghosh, A. Microemulsion: New Insights into the Ocular Drug Delivery. ISRN Pharm. 2013, 2013, 1−11. (13) Singh, M. D.; Mital, N.; Kaur, G. Topical Drug Delivery Systems: A Patent Review. Expert Opin. Ther. Pat. 2016, 26, 213−228.


Page 21 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(14) Peters, B. J.; Groninger, A. S.; Fontes, F. L. Crick, D. C.; Crans. D. C. Differences in Interactions of Benzoic Acid and Benzoate with Interfaces. Langmuir 2016, 32, 9451– 9459. (15) Acharya, D. P.; Hartley, P. G. Progress in Microemulsion Characterization. Curr. Opin. Colloid Interface Sci. 2012, 17, 274−280. (16) Sapra, B.; Thatai, P.; Bhandari, S.; Sood, J.; Jindal, M.; Tiwary, A. A Critical Appraisal of Microemulsions for Drug Delivery: Part I. Ther. Delivery 2013, 4, 1547−1564. (17) Sapra, B.; Thatai, P.; Bhandari, S.; Sood, J.; Jindal, M.; Tiwary, A. A Critical Appraisal of Microemulsions for Drug Delivery: Part II. Ther. Delivery 2014, 5, 83−94. (18) Deng, L.; Taxipalati, M.; Sun, P.; Que, F.; Zhang, H. Phase Behavior, Microstructural Transition, Antimicrobial and Antioxidant Activities of a Water-Dilutable Thymol Microemulsion. Colloids Surf. B 2015, 136, 859−866. (19) Perlstein, M.; Aserin, A.; Wachtel, E. J.; Garti, N. Propofol Solubilization and Structural Transformations in Dilutable Microemulsion. Colloids Surf. B 2015, 136, 282−290. (20) Butani, D.; Yewale, C.; Misra, A. AmphotericinB: Topical Microemulsion: Formulation, Characterization and Evaluation. Colloids Surf. B 2014, 116, 351−358. (21) Nazar, M. F.; Saleem, M. A.; Bajwa, S. N.; Yameen, B.; Ashfaq, M.; Zafar, M. N.; Zubair, M. Encapsulation of Antibiotic Levofloxacin in Biocompatible Microemulsion Formulation: Insights from Microstructure Analysis. J. Phys. Chem. B. 2017, 121, 437−443. (22) Lawrence, M. J.; Rees, G. D. Microemulsion-Based Media as Novel Drug Delivery Systems. Adv. Drug Delivery Rev. 2000, 45, 89−121. (23) Aggarwal, N.; Goindi, S.; Khurana, R. Formulation, Characterization and Evaluation of an Optimized Microemulsion Formulation of Griseofulvin for Topical Application. Colloids Surf. B 2013, 105, 158−166. (24) Spernath, A.; Aserin, A. Microemulsions as Carriers for Drugs and Nutraceuticals. Adv. Colloid Interface Sci. 2006, 128−130, 47−64. (25) Hu, J.; Akula, N.; Wang, N. Development of a Microemulsion Formulation for Antimicrobial SecA Inhibitors. PLoS One 2016, 11, No. e0150433.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 27

(26) Leng, P.; Zhang, Z.; Li, Q.; Zhao, M.; Pan, G. Microemulsion Formulation of Carbendazim and its In Vitro Antifungal Activities Evaluation. Plos One 2014, 9, No. e109580. (27) Aloisio, C.; de Oliveira, A. G.; Longhi, M. Cyclodextrin and Meglumine-Based Microemulsions as a Poorly Water-Soluble Drug Delivery System. J. Pharm. Sci. 2016, 105, 2703−2711. (28) Yaghmur, A.; Rappolt, M.; Østergaard, J.; Larsen, C.; Larsen, S. W. Characterization of Bupivacaine-Loaded

Formulations Based on

Liquid Crystalline Phases and

Microemulsions: The Effect of Lipid Composition. Langmuir 2012, 28, 2881−2889. (29) Nazar, M. F.; Khan, A. M.; Shah, S. S. Microemulsion System with Improved Loading of Piroxicam: A Study of Microstructure. AAPS PharmSciTech 2009, 10, 1286−1294. (30) Mehta, S. K.; Kaur, G.; Bhasin, K. K. Analysis of Tween Based Microemulsion in the Presence of TB Drug Rifampicin. Colloids Surf. B 2007, 60, 95−104. (31) Perry, C. M.; Ormrod, D.; Hurst, M.; Onrust, S. V. Gatifloxacin: A Review of Its Use in the Management of Bacterial Infections. Drugs 2002, 62, 169−207. (32) Mather, R.; Karenchak, L. M.; Romanowski, E. G.; Kowalski, R. P. Fourth Generation Fluoroquinolones: New Weapons in the Arsenal of Ophthalmic Antibiotics. Am. J. Ophthalmol. 2002, 133, 463−466. (33) Shaaban, H. A. E.; El-Ghorab, A. H.; Shibamoto, T. Bioactivity of Essential Oils and Their Volatile Aroma Components: Review. J. Essent. Oil Res. 2012, 24, 203−212. (34) Li, M.; Si, L.; Pan, H.; Rabba, A. K.; Yan, F.; Qiu, J.; Li, G. Excipients Enhance Intestinal Absorption of Ganciclovir by P-gp Inhibition: Assessed In Vitro by Everted Gut Sac and In Situ by Improved Intestinal Perfusion. Int. J. Pharm. 2011, 403, 37−45. (35) Yamagata, T.; Kusuhara, H.; Morishita, M.; Takayama, K.; Benameur, H.; Sugiyama, Y. Effect of Excipients on Breast Cancer Resistance Protein Substrate Uptake Activity. J. Controlled Release 2007, 124, 1−5. (36) Mehta, S. K.; Kaur, G.; Bhasin, K. K. Incorporation of Antitubercular Drug Isoniazid in Pharmaceutically Accepted Microemulsion: Effect on Microstructure and Physical Parameters. Pharm. Res. 2008, 25, 227−236. (37) Kalam, M. A.; Alshamsan, A.; Aljuffali, I. A.; Mishra, A. K.; Sultana, Y. Delivery of Gatifloxacin Using Microemulsion as Vehicle: Formulation, Evaluation, Transcorneal Page 22 of 27 ACS Paragon Plus Environment

Page 23 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Permeation and Aqueous Humor Drug Determination. Curr. Drug Deliv. 2016, 23, 886−897. (38) Zeng, L.; Xin, X.; Zhang, Y. Development and Characterization of Promising Cremophor EL-Stabilized O/W Nanoemulsions Containing Short-Chain Alcohols as a Cosurfactant. RSC Adv. 2017, 7, 19815–19827. (39) Szumała, P. Structure of Microemulsion Formulated with Monoacylglycerols in the Presence of Polyols and Ethanol. J. Surfactants Deterg. 2015, 18, 97−106. (40) Klossek, M. L.; Marcus, J.; Touraud, D.; Kunz, W. The Extension of Microemulsion Regions by Combining Ethanol with Other Cosurfactants. Colloids Surf. A 2013, 427, 95−100. (41) Klossek, M. L.; Marcus, J.; Touraud, D.; Kunz, W. Highly Water Dilutable Green Microemulsions. Colloids Surf. A 2014, 442, 105−110. (42) Kalaitzaki, A.; Xenakis, A.; Papadimitriou, V. Highly Water Dilutable Microemulsions: A Structural Study. Colloid Polym. Sci. 2015, 293, 1111−1119. (43) Baptista, M. S.; Tran, C. D. Electrical Conductivity, Near-Infrared Absorption, and Thermal Lens Spectroscopic Studies of Percolation of Microemulsions. J. Phys. Chem. B 1997, 101, 4209−4217. (44) Saha, R.; Rakshit, S.; Mitra, R. K.; Pal, S. K. Microstructure, Morphology, and Ultrafast Dynamics of a Novel Edible Microemulsion. Langmuir 2012, 28, 8309−8317. (45) Rahman, A.; Rahman, M. M.; Mollah, M. Y. A.; Susan, Md. A. B. H. Dynamic Percolation and Swollen Behavior of Nanodroplets in 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate/Triton X-100/Cyclohexane Microemulsions. J. Phys. Chem. B 2016, 120, 6995−7002. (46) Dasilva-Carbalhal, J.; Garcia-Rio, L.; Gomez-Diaz, D.; Mejuto, J. C.; RodriguezDafonte,

P.

Influence

of

Crown

Ethers

on

the

Electric

Percolation

of

AOT/Isooctane/Water (W/O) Microemulsions. Langmuir 2003, 19, 5975−5983. (47) Dasilva-Carbalhal, J.; Garcia-Rio, L.; Gomez-Diaz, D.; Mejuto, J. C.; Perez-Lorenzo, M. J. Colloid Interface Sci. 2005, 292, 591−594. (48) Shibaev, A. V.; Molchanov, V. S.; Philippova, O. E. Rheological Behavior of OilSwollen Wormlike Surfactant Micelles. J. Phys. Chem. B 2015, 119, 15938−15946.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 27

(49) Formariz, T. P.; Chiavacci, L. A.; Scarpa, M. V.; Silva-Júnior, A. A.; Egito, E. S.; Terrugi, C. H.; Franzini, C. M.; Sarmento, V. H.; Oliveira, A. G. Structure and Viscoelastic Behavior of Pharmaceutical Biocompatible Anionic Microemulsions Containing the Antitumoral Drug Compound Doxorubicin. Colloids Surf. B 2010, 77, 47−53. (50) Kaur, G.; Chiappisi, L.; Prévost, S.; Schweins, R.; Gradzielski, M.; Mehta, S. K. Probing the Microstructure of Nonionic Microemulsions with Ethyl Oleate by Viscosity, ROESY, DLS, SANS, and Cyclic Voltammetry. Langmuir 2012, 28, 10640−10652. (51) Mitra, R. K.; Paul, B. K. Physicochemical Investigations of Microemulsification of Eucalyptus Oil and Water Using Mixed Surfactants (AOT+Brij-35) and Butanol. J. Colloid Interface Sci. 2005, 283, 565−577. (52) Ibrahim, H. K.; El-Leithy, I. S.; Makky, A. A. Mucoadhesive Nanoparticles as Carrier Systems for Prolonged Ocular Delivery of Gatifloxacin/Prednisolone Bitherapy, Mol. Pharm. 2010, 7, 576-585. (53) Mehta, S. K.; Kaur, G.; Bhasin, K. K. Tween-Embedded MicroemulsionsPhysicochemical and Spectroscopic Analysis for Antitubercular Drugs. AAPS PharmSciTech 2010, 11, 143−153. (54) Pople, P. V.; Singh, K. K. Targeting Tacrolimus to Deeper Layers of Skin with Improved Safety for Treatment of Atopic Dermatitis. Int. J. Pharm. 2010, 398, 165−178. (55) Barot, B. S.; Parejiya, P. B.; Patel, H. K.; Mehta, D. M.; Shelat, P. K. MicroemulsionBased Antifungal Gel Delivery to Nail for the Treatment of Onychomycosis: Formulation, Optimization, and Efficacy Studies. Drug Delivery Transl. Res. 2012, 2, 463−476. (56) Patel, M. R.; Patel, R. B.; Parikh, J. R.; Patel, B. G. Formulation Consideration and Skin Retention Study of Microemulsion Containing Tazarotene for Targeted Therapy of Acne. J. Pharm. Invest. 2016, 46, 55−66. (57) Patel, R. B.; Patel, M. R.; Bhatt, K. K.; Patel, B. G. Risperidone Loaded Mucoadhesive Microemulsion for Intranasal Delivery: Formulation, Development, Physicochemical


Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Characterization and Ex Vivo Evaluation. J. Drug Delivery Sci. Technol. 2013, 23, 561−567. (58) Erdal, M. S.; Özhan, G.; Mat, M. C.; Özsoy, Y.; Güngör, S. Colloidal Nanocarriers for the Enhanced Cutaneous Delivery of Naftifine: Characterization Studies and In Vitro and In Vivo Evaluations. Int. J. Nanomed. 2016, 11, 1027−1037. (59) Aliberti, A. L. M.; de Queiroz, A. C.; Praça, F. S. G.; Eloy, J. O.; Bentley, M. V. L. B.; Medina, W. S. G. Ketoprofen Microemulsion for Improved Skin Delivery and In Vivo Anti-inflammatory Effect. AAPS PharmSciTech 2017, 18, 2783−2791. (60) Chen, Y. C.; Chen, B. H. Preparation of Curcuminoid Microemulsions from Curcuma Longa L. to Enhance Inhibition Effects on Growth of Colon Cancer Cells HT-29. RSC Adv. 2018, 8, 2323−2337. (61) Lakshmi, P.; Kumar, G. A. Nanosuspension Technology: A Review. Int. J. Pharm. Pharm. Sci. 2010, 2, 35–40. (62) Sari, T. P.; Mann, B.; Kumar, R.; Singh, R. R. B.; Sharma, R.; Bhardwaj, M.; Athira, S. Preparation and Characterization of Nanoemulsion Encapsulating Curcumin. Food Hydrocolloids 2014, 43, 540–546. (63) Lin, C. C.; Lin, H. Y.; Chi, M. H.; Shen, C. M.; Chen, H. W.; Yang, W. J.; Lee, M. H. Preparation of Curcumin Microemulsions with Food-Grade Soybean Oil/Lecithin and their Cytotoxicity on the HepG2 Cell Line. Food Chem. 2014, 154, 282–290. (64) Khan, M. F.; Singh, M. K.; Sen, S. Measuring Size, Size Distribution, and Polydispersity of Water-in-Oil Microemulsion Droplets using Fluorescence Correlation Spectroscopy: Comparison to Dynamic Light Scattering. J. Phys. Chem. B 2016, 120, 1008−1020. (65) Pal, N.; Verma, S. D.; Singh, M. K.; Sen, S. Fluorescence Correlation Spectroscopy: An Efficient Tool for Measuring Size, Size-Distribution and Polydispersity of Microemulsion Droplets in Solution. Anal. Chem. 2011, 83, 7736−7744. (66) Ding, L.; Dominska, M.; Fang, Y.; Blanchard, G. J. Fluorescence and Electrochemistry Studies of Pyrene-Functionalized Surface Adlayers to Probe the Microenvironment Formed by Cholesterol. Electrochim. Acta 2008, 53, 6704−6713.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 27

(67) Zielińska, K.; Wilk, K. A.; Jezierski, A.; Jesionowski, T. Microstructure and Structural Transition in Microemulsions Stabilized by Aldonamide-Type Surfactants. J. Colloid Interface Sci. 2008, 321, 408−417. (68) Bermejo, R.; Tobaruela, D. J.; Talavera, E. M.; Orte, A.; Alvarez-Pez, J. M. Fluorescent

Behavior

of

B-phycoerythrin

in

Microemulsions

of

Aerosol

OT/water/isooctane. J. Colloid Interface Sci. 2003, 263, 616−624. (69) Zhang, J.; Lv, Y.; Zhao, S.; Wang, B.; Tan, M.; Xie, H.; Lv, G.; Ma, X. Effect of Lipolysis on Drug Release from Self-microemulsifying Drug Delivery Systems (SMEDDS) with Different Core/Shell Drug Location. AAPS PharmSciTech 2014, 15, 731−740. (70) Kaur, G.; Mehta. K. Probing Location of Anti-TB Drugs Loaded in Brij 96 Microemulsions Using Thermoanalytical and Photophysical Approach. J. Pharm. Sci.

2014, 103, 937–944.


Page 27 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Abstract Graphics


Fourth-Generation Antibiotic Gatifloxacin Encapsulated by

Recommend Documents