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Meletin sustained-release gliadin nanoparticles prepared via solvent surface modification on blending electrospraying
Applied Surface Science 434 (2018) 1040–1047
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Meletin sustained-release gliadin nanoparticles prepared via solvent surface modification on blending electrospraying Yao-Yao Yang a,1 , Man Zhang a,1 , Zhe-Peng Liu b,∗ , Ke Wang a , Deng-Guang Yu a,∗∗ a b
School of Materials Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology, 516 Jungong Road, Shanghai 200093, China
a r t i c l e
i n f o
Article history: Received 12 August 2017 Received in revised form 10 October 2017 Accepted 4 November 2017 Available online 6 November 2017 Keywords: Modified coaxial electrospraying Working interfaces Microformation Sustained release Nanoparticles Gliadin
a b s t r a c t Almost all electrospraying processes are carried out under an air-solution interface, thereby overlooking the potential influence of an additional solvent surface modification between air and the working solution. A pure solvent was explored to temporarily and dynamically surround the solutions utilized for blending electrospraying, which contained a guest drug meletin and a protein drug carrier gliadin. The new modified processes created protein-based medicated nanoparticles (P2) with higher quality than their counterparts (P1) from blending processes, as demonstrated by the SEM and TEM images. Although the particles from the two processes were similar (nanocomposites), and the particles P1 were larger than P2, the later provided a better meletin sustained-release profile than the former. This finding was verified by the smaller initial burst release, longer sustained-release time period, and shorter late leveling-off stage. These unanticipated results were attributed to the rounder surface, the more uniform size distribution, and the smaller total surface area of particles P2 than P1. The microformation mechanism of the modified coaxial process was suggested. The protocols reported here paved a new way for the development of new kinds of functional nanoparticles by modifying the interfaces of working fluids during electrospraying. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Electrospraying is one of the advanced electrohydrodynamic atomization (EHDA) methods and can generate micro/nanoparticles/solid films or can create nanosurfaces with unique properties aside from its broad applications in mass spectrometry [1–4]. During the process, electrostatic energy is used to treat working fluids, thereby solidifying them. All these processes have been carried out naturally and typically in a gas atmosphere; the result is the effective evaporation of the solvent from the interfaces between the working fluids and their surrounding air environment for complete solidification [5–7]. The most common protocol for implementing the electrospraying process is to pump a working fluid into an electrical field through a metal capillary, which is often a blending solu-
∗ Corresponding author. ∗ ∗ Corresponding author at: School of Materials Science & Engineering, University of Shanghai for Science and Technology, 516 Jungong Road, Shanghai 200093, China. E-mail addresses: [email protected] (Z.-P. Liu), [email protected] (D.-G. Yu). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.apsusc.2017.11.024 0169-4332/© 2017 Elsevier B.V. All rights reserved.
tion comprising a matrix and a functional additive [5]. Coaxial electrospraying is an upgrade version of the traditional blending electrospraying that exploits a coaxial spray head to lead two different working solutions into the electrical fields simultaneously [8,9]. This advanced technology is very popular because of the usefulness of core-shell nanostructures in designing and tailoring the functional performance of structural nanomaterials [10–14]. Regardless of the single-fluid blending, the double-fluid coaxial, or the tri-axial electrospraying, a successful EHDA process for creating the desired solid particles requires suitable manipulation of the solvent evaporation rate from the working solutions to match the electrical actions. Thus, considerable efforts have been made to optimize the working conditions and certain auxiliary facilities to help in spray drying [15]. Meanwhile, although several studies have tried to elaborate the hydrodynamic interfacial phenomena during working processes [16–19], studies on intentional manipulation of the processes through air-solution interfaces are lacking. Such manipulation comprises a new concept for developing novel functional nanomaterials through electrospraying. This situation may be explained by the usage of dilute solutions only in electrospraying. An additional heat flow is sometimes needed to facilitate the creations of solid particles. Thus, introducing an additional solvent into the electrospraying process, as a possible method for manip-
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ulating the air-solution interfaces to create high quality products, seems impossible. Most recently, the traditional concept about coaxial electrospinning (the counterpart of electrospraying) was terminated by a modified coaxial process, where sheath solvent was utilized to generate high quality monolithic nanofibers other than coresheath nanofibers [20,21]. The idea of exploiting a solvent to modify the dynamic working interfaces during electrospinning is quickly developing into tri-axial processes and multiple-fluid complex electrospinning processes [22–24]. Thus, traditional coaxial electrospraying process may be also modified based on a similar strategy. Numerous possibilities are available for materials design and development, in which an outer layer solvent is used to manipulate the traditional blending electrospraying processes. During the past half century, polymer has functioned as the backbone to support the development of pharmaceutics. Most of the oral drug sustained-release dosage forms are based on the properties of polymeric matrices to improve their therapeutic effect, safety, and patient convenience. New methods (particularly those based on advanced nanotechnologies) and new drug carriers are frequently introduced into this field to develop medicated materials with improved drug sustained-release profiles [25,26]. Among different kinds of pharmaceutical excipients (such as synthetic polymers, natural macromolecules, and inorganic graphene oxide and carbon nanotubes), plant-derived natural products (such as polysaccharides cellulose, alginates, pectin, inulin, carageenans, rosin, gums, and mucilages), and proteins (such as zein, gliadin, soy protein, gluten, legumin, and lectin) are frequently combined with new protocols to create new types of drug sustained-release nanomaterials [27–29]. Gliadin is a type of prolamin. It is a class of proteins present in wheat and several other cereals within the grass genus Triticum. As a product derived from natural sources, it has good biocompatibility and biodegradability and can be used without concerns regarding the presence of monomer or initiator residues, which are present in the synthetic materials [30–32]. Thus, gliadin has been studied extensively for its potential applications to a wide variety of fields, including medicated materials. Gliadin-based medicated products in the forms of filaments, nanofibers, microspheres and nanoparticles have been prepared using wet spinning, electrospinning, spraying, and blending electrospraying; it has high potential to be developed into commercial tablets or capsules [33–36]. We investigated a modified coaxial electrospraying process, in which an additional shell solvent was used to modify the working interfaces of the traditional blending electrospraying. Gliadin was utilized as a drug carrier. Meletin, a plant flavonoid found in many plants and foods and has been broadly applied to the treatment of diabetes, conditioning of the heart and blood vessels, prevention of cancer, treatment of chronic prostate infections, increasing endurance, and improving athletic performance [37]. It is exploited as a model active pharmaceutical ingredient. In Chinese traditional medicine, meletin is often used to prevent asthma, eliminate phlegm, and relieve cough, a sustained release profile after oral administration is highly desired for its high therapeutic effects [38]. Meletin-loaded gliadin nanoparticles from the modified coaxial processes are characterized in detail and compared with the medicated particles from the blending electrospraying.
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magenta, trifluoroacetic acid (TFA), and trifluoroethanol (TFE) were provided by the Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All other chemicals were analytical reagents. Water was double distilled before use. 2.2. Electrospinning All processes were implemented using an in-house coaxial electrospraying system, which comprised a power supply (ZGF60 kV/2 mA, Wuhan Huatian Corp., Wuhan, China), two syringe ® pumps (KDS100, Cole-Parmer , Vernon Hills, USA), a home-made coaxial spray head and a collector composed of cardboard wrapped with aluminum foil. The blending solutions contained 6% gliadin (w/v) and 1% meletin (w/v) in a mixture consisting of TFA and TFE in a volume ratio of 50:50. Basic magenta (5 × 10−6 g/mL) was added into the blending solution to optimize the experimental conditions. These fluids were driven by using the core syringe pump. The shell fluid was pure TFE. The pump used to drive the shell TFE was switched off to prepare particles P1 directly from the blending electrospraying process with a core fluid flow rate of 1.0 mL/h. Under a fixed core fluid flow rate of 1.0 mL/h, a series of shell solvent flow rates was used. The particles prepared from a shell fluid flow rate of 0.3 mL/h were denoted as particles P2. The particle collected distance and the applied voltage were fixed at 15 cm and 21 kV, respectively. 2.3. Morphology and structure The prepared particles were evaluated using a scanning electron microscope (SEM, FEI Quanta 450 FEG, USA). Prior to microscopy, the samples were sputter coated with platinum under a nitrogen atmosphere for 90 s. The diameters of the particles were estimated by measuring the sizes of 100 particles from the SEM images using ImageJ software (National Institutes of Health, Bethesda, USA). The inner structure of particles were investigated using a H-800 transmission electron microscope (TEM; Hitachi, Tokyo, Japan). TEM samples were prepared by placing a lacey carbon-coated copper grid on the collector during electrospraying process. 2.4. Physical forms X-ray powder diffraction (XRD) patterns were recorded using a Bruker X-ray powder diffractometer Bruker-AXS with CuK␣ radiation (Karlsruhe, Germany). The raw gliadin/meletin powders and particulate samples were analyzed between 2 angles from 5◦ to 60◦ . The topographies of raw meletin and gliadin were observed using a XP-700 polarized optical microscope (OM, Shanghai Changfang Optical Instrument, Shanghai, China). 2.5. Compatibility The raw meletin/gliadin powders and their particles were subjected to attenuated total reflectance (ATR)–Fourier transform infrared (FTIR) analysis using Spectrum 100 FTIR Spectrometer (PerkinElmer, Billerica, USA) over a range of 600–4000 cm−1 at a resolution of 2 cm−1 .
2. Materials and methods
2.6. In vitro dissolution tests
2.1. Materials
In vitro dissolution tests were performed using a RCZ-8A dissolution apparatus (Tianjin University Radio Factory, Tianjin, China). Samples equivalent to 30 mg of meletin (i.e., 0.21 g medicated particles) were placed into the dissolution cells, in which the dissolution medium (900 mL physiological saline) was maintained at a
Meletin (purity > 98%, No. MUST-15071603) was purchased from the Beijing Aoke Biological Technology Co., Ltd. (Beijing, China). Gliadin (extracted from wheat, Mn = 30,000 g/mol), basic
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constant temperature of (37 ± 1) ◦ C. The paddle frequency was consistent at 50 rpm. A UV–Vis spectrophotometer (UV-2102PC, Unico Instrument Co. Ltd., Shanghai, China) was used to measure the concentration of dissolved TC at a wavelength of = 370 nm according to the Chinese Pharmacopoeia. All experiments were repeated six times. 3. Results and discussion 3.1. Modified coaxial electrospraying Traditionally, blending electrospraying is a single-fluid process with all the ingredients co-dissolved in one solution. In contrast, coaxial electrospraying is a double-fluid process that produces core-shell structures. In the literature, blending and coaxial electrospraying processes have their own systems. In the present study, the developed electrospraying system included both the traditional blending and the modified coaxial processes (Fig. 1a). When the shell fluid flow rate (Fs ) is switched off (i.e., Fs = 0 mL/h), the process became a typical blending spraying; when Fs 䊐 0 mL/h, the process became a double-fluid coaxial spraying. The developed modified coaxial electrospraying exploited a coaxial spray head and an additional pump to manipulate a thin layer of solvent TFE covering the core blending solution during electrospraying. This modification temporarily and dynamically modified the air-solution working interfaces, thereby adjusting the removal of solvent from the core blending solution and its solidification behavior. Thus, the new modified coaxial process generated monolithic nanoparticles compared with the traditional coaxial electrospraying, which resulted in core-shell particles. A diagram of the homemade coaxial spray head and its connection with the power supply and the two working fluids are shown in Fig. 1b. The diameters of the inner and outer capillaries of the spray head were 0.3 and 1.2 mm, respectively. The core blending solution was directly pumped into the spray head from its syringe, whereas the shell solvent TFE was pumped to the spray head through an elastic silicone tube. High voltage could be applied to the working fluids through an alligator clip connected to the inner metal capillary. Under the optimized conditions, a typical blending electrospraying process conducted at a shell fluid flow rate of 0 mL/h but with a core fluid flow rate of 1.0 mL/h to prepare particles P1 is shown in Fig. 2a1. In this figure, a whole red Taylor cone (Fig. 2a2) is followed by a Columbic explosion atomization region beginning from a convergent point. The collected particles spread over an area with an estimated diameter of 23 cm (Fig. 2a3). When the modified coaxial electrospraying processes were performed under a shell-to-core fluid flow rate ratio of 0.3/1.0 mL/h during the preparation of particles P2, a typical electrospraying process is shown in Fig. 2b1. Its Taylor cones had a compound structure, with the red core fluid encapsulated by the colorless shell solvent (Fig. 2b2). Unexpectedly, the collected particles P2 spread over an area with an estimated diameter of 16 cm (Fig. 2b3); such area was significantly smaller than particles P1. 3.2. Morphology and structure of the prepared particles The SEM images of the mophology details of the crude gliadin/meletin powders and their electrosprayed particles are shown in Fig. 3. The crude gliadin particles have a flat globular shape, wrinkle surface, and broad size distribution (Fig. 3a). The raw meletin particles show a typical needle crystalline morphology (Fig. 3b). The SEM images of the electrosprayed particles prepared under a fixed flow rate of core fluid (1.0 mL/h) and a series of shell solvent
flow rate of 0 (i.e. the blending electrospraying for creating particles P1), 0.1, and 0.3 mL/h (particles P2) are exhibited in Fig. 3c, d, and e, respectively. The trends are clear that large shell solvent flow rates resulted in rounder morphology, smoother surface, and narrower size distribution of the particles. However, excessive shell solvent would result in incompletely dried nanoparticles and their binding together when in contact (Fig. 3f). Particles P1 and P2 have an estimated diameters of 890 ± 180 and 570 ± 80 nm, respectively. The TEM images of electrosprayed particles P1 and P2 are shown in Fig. 4, which reveal the details on inner structural characteristics. As expected, particles P2 from the modified coaxial process had a uniform inner structure with a round morphology, as reflected by the circular shape and a similar gray level in Fig. 4a. However, particles P1 from the blending electrospraying had a series of irregular shapes and a broad size distribution. These products showed multiple gray levels within one each particles (Fig. 4b). The differences of gray level in TEM images generated under the bright field can be attributed to three aspects, namely, elements, densities, and thicknesses. Apparently, the different gray levels within particles P1 were mainly a direct result of varied thicknesses because all the particles had the same elements and their densities were not significantly different. This result corroborated the crumpled morphologies of particles P1 in their SEM images.
3.3. Microformation mechanisms A blending electrospraying process comprises four successive steps, as follows: charging working fluids, forming Taylor cone, atomizing droplets, and collecting final particles. The formation of Taylor cone is a key element for initiating an electrospraying process, which is a balance of a series of parameters, particularly the electrical fields and the properties of working fluids. The atomization region is the most important step for the physical state of the final particles, where the solidification process occurs as a result of a series of simultaneously occurring phenomena. Two main phenomena had a close relationship with the dynamic airsolution interfaces of all the atomized droplets, one is the solvent outward evaporation from the surfaces of droplets, and the other is the polymer and other additives inward migration, diffusion, and chain entanglement from their surfaces. When an additional solvent is applied to the surface of working fluid previously treated using blending electrospraying, the formation of Taylor cone and the atomization are profoundly modified. A diagram is shown in Fig. 5. Initiating the electrospraying was easier because of the low surface tension and low viscosity of the surrounding solvent compared with the blending working fluid. However, favorable results from the shell solvents mainly occurred at the atomization region. In all the electrospraying processes, the nascent nearmonodisperse droplets after the Columbic explosion rapidly split and shrunk because of the accumulation of surface charges and the fast evaporation of solvents resulting from the large surface areas. The first positive result from the surrounding solvent is that the Columbic splitting may further occur more times in the modified coaxial process than in the blending process because of the presence of the solvent layer on the droplets. More times splitting in the atomization region should promote the formation of solid particles with smaller size. The second positive result from the surrounding solvent is related to the outward evaporation of solvent of blending solutions. The surrounding solvent can effectively prevent the possible premature formation of semi-solid shell on the droplets, which frequently occur during blending electrospraying. The presence of a layer of solvent on the droplets in the modified coaxial processes acted as a bridge, thereby promoting the evaporation of core sol-
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Fig. 1. (a) A diagram of the implementation of blending and modified coaxial electrospraying using one system. (b) Connection of the coaxial spray head with the two syringe pumps and the power supply.
Fig. 2. Observations of the blending electrospraying for preparing particles P1 (a1, a2 and a3) and the modified coaxial electrospraying for fabricating particles P2 (b1, b2 and b3).
vents through a large range of splitting times, enhancing diffusions with small resistance, and allowing possible extractions. The third positive result from the surrounding solvent is related to the inward behavior of solute molecules within the droplets, particularly the migration, entanglement, and condensation of inner polymeric molecules. In the blending electrospraying, the fast evaporation of solvents quickly increased the viscosity of working fluids, which in turn retarded the migration, diffusion, transmission, and entanglement of polymer molecules within the droplets. When an additional layer of solvent is provided around the droplets, the polymer diffused easily inside the droplets. Instead of concentrating on the surface, the polymer was distributed homogeneously throughout the droplet, thereby facilitating the maintenance of droplet integrity during contraction because of drying without collapsing. Besides more splitting, the favorable outward evaporation of solvent, and favorable inward migration of solutes from the airsolvent-solution interfaces, the surrounding layer solvent kept a stable and robust atomization process, thereby resisting interference from the environment. These factors acted together during the electrospraying processes to ensure the formation of a uniform product with a small size, smooth surface, a narrow size distribution, few satellites, and compact inner structures. In Fig. 2, the collection circle of particles P1 (Fig. 2a3) had an estimated diameter of 23 cm, which was larger than the circle of particles P2 (16 cm in Fig. 2b3). This phenomenon can be explained by the force analysis during the electrospraying processes. As shown in Fig. 5, a droplet in the atomization region
received a series of forces from the electrical field (FE ), the gravity force (G), and the repelling forces (Fr ) from all the surrounding droplets. Compared with droplets in the blending electrospraying, the droplets in the modified coaxial process had a larger gravity force and smaller repelling forces. The former resulted from the exhaustion of inner solvent and a compact inner structure of the formed solid particles. The latter had close relationship with more spitting times, in which more charges were removed with the evaporation of solvent. Thus, the large G and small Fr resulted in the quicker deposition of the particles P2; particles P2 were more concentrated in their collector than particles P1, i.e., 16 cm < 23 cm.
3.4. Physical state of components and their compatibility The XRD patterns of the crude materials (meletin and gliadin) and their particles P1/P2 are shown in Fig. 6. As anticipated, the drug meletin powders showed sharp peaks in their XRD patterns, thereby suggesting the presence of crystal materials. In contrast, gliadin patterns had no sharp peaks, indicating that it was an amorphous matrix. These results were verified by the polarized optical microscopic images in Fig. 6, in which meletin showed bright colors, including blue, red, and yellow, whereas gliadin particles exhibited only gray colour. The electrosprayed particles P1/P2 were similar amorphous composites, regardless of the electrospraying processes. After being electrosprayed with the protein, the crystalline meletin particles lost their original physical status. The fast
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Fig. 3. SEM images of the particles: (a) crude gliadin; (b) crude meletin; (c), (d), (e), and (f) electrosprayed particles prepared under a shell solvent flow rates of 0 (particles P1), 0.1, 0.3 (particles P2), and 0.5 mL/h, respectively.
Fig. 4. TEM images of the electrosprayed particles: (a) P2; (b) P1.
drying electrospraying processes distributed the drug molecules homogeneously all over the gliadin matrices. The ATR-FTIR spectra of meletin, gliadin, and their electrosprayed particles from the blending and coaxial processes are
shown in Fig. 7. The FTIR spectra of gliadin had two typical absorbance bands of 1653 and 1545 cm−1 , which were attributed to the vibrations of the C O and C N groups, respectively. Three welldefined peaks were visible for pure crystalline meletin, at 1669,
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3.5. Sustained-release performances
Fig. 5. Influence of an additional temporarily air-solvent-polymer solution interfaces on the formation of electrosprayed particles.
Fig. 6. XRD patterns of the crude materials (meletin and gliadin) and their electrosprayed nanoparticles P1 and P2, and the polarized optical microscopic images of gliadin and meletin.
The sustained drug-release profiles of meletin from the particles P1 and P2 are shown in Fig. 8a. Both of them showed a typical sustained release over a certain time period. However, particles P2 provided a better performance than P1 in the following aspects. First, particles P2 had a smaller initial burst release effect (28.8% for the first hour) than P1 (44.7% for the first hour). Second, particles P1 released 91.1% of the loaded cargoes at a time period of 8 h, whereas particles P2 released 93.7% at a time period of 16 h, thereby suggesting a longer sustained release profile. Third, at the late stage of drug release, the delayed leveling off release is a common phenomenon to drug sustained-release materials and solid dosage forms. The release of the last 10% of loaded cargoes took about 13 and 9 h for particles P1 and P2, respectively. This indicated that the former had a longer time period of the negative phenomenon, which often does not give an effective delivery to ensure a minimum effective serum concentration after oral administration [24]. Gliadin is not soluble in water. Thus, the drug release was controlled by a diffusion mechanism. The diffusion processes (including the inward diffusion of water molecules into the particles and the outward diffusion of meletin molecules into the bulk dissolution media) always occurs along the shortest distance. Thus, although particles P1 had an apparently larger size than particles P2, their irregular shape meant that there were many diffusion routes with different lengths for the water and meletin molecules. Among these routes, the shortest routes play a role in the manipulation of the release rates of the loaded drug molecules, as shown in the inset diagram of Fig. 8a. These routes in particles P1 were often extremely smaller than the diffusion radii of particles P2. Meanwhile, the irregular shapes and a broader size distributions of P1 indicated an extreme increase of the total surface area and the related drug surface distribution, which in turn resulted in a larger initial burst release than particles P2. This case exemplified the conclusions of Lahann et al. in their review, in which the material shapes often profoundly influenced their functional performance [39]. To further investigate the controlled drug release mechanisms of these particles, the release data were analyzed as per the Korsmeyer Peppas Equation (1) or (2), as follows [40]: Q =
Mt = kt n M∞
ln Q = n ln t + ln k Fig. 7. ATR-FTIR spectra of the crude materials (meletin and gliadin) and their electrosprayed nanoparticles P1 and P2, and their chemical formulas.
1615, and 1513 cm-1 , corresponding to its benzene ring and C O group. However, all peaks for meletin were absent in the spectra of the electrosprayed particles P1/P2; only two bands of 1649 and 1544 cm--1 can be identified obviously. The disappearance of meletin C O group bands, the shift to lower wavenumbers of peaks assigned to the C O and C N stretching vibrations in gliadin, and the disappearance of peaks in the fingerprint region of the meletin spectra jointly suggested that hydrogen bonding occurred between the gliadin and meletin molecules within the composite particles. This result can also be speculated from their chemical formulas in Fig. 7, which indicated that both meletin and gliadin molecules acted proton acceptors and proton donors. Thus, the XRD and ATR-FTIR results verified that meletin-loaded gliadin particles P1 and P2 were all amorphous homogeneous nanocomposites, in which the components had fine compatibility because of hydrogen bonding; other secondary interactions, such as hydrophobic and electrostatic forces, may have occurred as well.
(1) (2)
where Q is the drug release in percentage, Mt is the amount of drug released at time t, M∞ is the total amount of drug released, k is the kinetic parameter, and n is the release exponent indicative of the drug release mechanism. The regressed results are exhibited in Fig. 8b. P1 and P2 particles had the following power equations: Q1 = 47.42 t0.36 (R = 0.9782) and Q2 = 29.92 t0.41 (R = 0.9978), respectively. All their diffusion indexes n were lower than the critical value of 0.45, thereby indicating that the contained cargoes were similarly freed from particles P1 and P2 through a typical Fickian diffusion mechanism. Since the first publication on coaxial electrospraying, all the reported coaxial processes have exploited a solution containing a polymer or other solutes as a sheath fluid to generate core-shell micro-/nano-structures [41]. In sharp contrast, our experiments demonstrated that high quality monolithic composites could be generated using the coaxial electrospraying under the condition that pure solvents were explored as the shell fluids. The concept of exploiting solvent to modify the dynamic working interfaces during electrospraying can be further expanded to a series of other complicated electrospraying processes, such as the tri-axial electrospraying with an outer layer of solvent and side-by-side
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Fig. 8. In vitro drug release profiles of P1 and P2 (a) and the regressed treatment of drug release data according to the Peppas equation (b).
electrospraying with a co-layer of outer solvent. Certainly, the “outer layer solvent” can be expanded to many other dilute solutions that cannot be used on solid products using traditional electrospraying processes. Thus, many functional nanomaterials may be similarly designed and developed through nanocoating using the dilute solutions. Meanwhile, some influences of partial air–solvent–solution electrohydrodynamic interfaces on the working processes and the final products still require further investigations when different kinds of solvents are exploited. Some solvents may only stabilize the entire electrospraying process, whereas other solvents may even extract the inner solvents; the rest may coagulate the inner polymers or other solutes. As for the application of the modified coaxial process in the field of nanomedicine, it can be utilized facilely to control structures at the nanometer level, thereby leading to significantly changed properties of the medicated nanoparticles. Thus, the process results in products that are different from products prepared using traditional protocols. 4. Conclusions To the best of our knowledge, a dynamic surface modification of pure solvent on the traditional blending electrospraying was successfully conducted for the first time. The new modified electrospraying process maintained a continuous, stable, and smooth preparation of meletin-loaded gliadin medicated nanoparticles. Compared with the particles from the blending electrospraying, the particles from the modified processes had better quality in terms of size, size distributions, external morphology, and inner structure, as demonstrated by SEM and TEM images. XRD results demonstrated that all the particles were monolithic protein-based nanocomposites and that meletin molecules were homogeneously distributed all over the gliadin matrices. The in vitro dissolution tests demonstrated that the particles from the new processes could provide better functional performance for meletin sustained release, as reflected by the smaller initial burst releases, longer drug sustained-release periods, and smaller late leveling-off releases. The rounder shape, the increased homogeneity of particle size, and the smaller surface of the particles from the modified coaxial processes jointly resulted in better functional performances. Both the microformation mechanism and drug controlled-release mechanism were suggested. To summarize the concept of traditional coaxial electrospraying, the application of a solvent temporarily and dynamically on the surface of a working fluid is a new way of developing new types of electrosprayed functional nanomaterials. Acknowledgments This research is financially supported by the National Natural Science Foundation of China (No. 51373101).
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Full Length Article
Meletin sustained-release gliadin nanoparticles prepared via solvent surface modification on blending electrospraying Yao-Yao Yang a,1 , Man Zhang a,1 , Zhe-Peng Liu b,∗ , Ke Wang a , Deng-Guang Yu a,∗∗ a b
School of Materials Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology, 516 Jungong Road, Shanghai 200093, China
a r t i c l e
i n f o
Article history: Received 12 August 2017 Received in revised form 10 October 2017 Accepted 4 November 2017 Available online 6 November 2017 Keywords: Modified coaxial electrospraying Working interfaces Microformation Sustained release Nanoparticles Gliadin
a b s t r a c t Almost all electrospraying processes are carried out under an air-solution interface, thereby overlooking the potential influence of an additional solvent surface modification between air and the working solution. A pure solvent was explored to temporarily and dynamically surround the solutions utilized for blending electrospraying, which contained a guest drug meletin and a protein drug carrier gliadin. The new modified processes created protein-based medicated nanoparticles (P2) with higher quality than their counterparts (P1) from blending processes, as demonstrated by the SEM and TEM images. Although the particles from the two processes were similar (nanocomposites), and the particles P1 were larger than P2, the later provided a better meletin sustained-release profile than the former. This finding was verified by the smaller initial burst release, longer sustained-release time period, and shorter late leveling-off stage. These unanticipated results were attributed to the rounder surface, the more uniform size distribution, and the smaller total surface area of particles P2 than P1. The microformation mechanism of the modified coaxial process was suggested. The protocols reported here paved a new way for the development of new kinds of functional nanoparticles by modifying the interfaces of working fluids during electrospraying. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Electrospraying is one of the advanced electrohydrodynamic atomization (EHDA) methods and can generate micro/nanoparticles/solid films or can create nanosurfaces with unique properties aside from its broad applications in mass spectrometry [1–4]. During the process, electrostatic energy is used to treat working fluids, thereby solidifying them. All these processes have been carried out naturally and typically in a gas atmosphere; the result is the effective evaporation of the solvent from the interfaces between the working fluids and their surrounding air environment for complete solidification [5–7]. The most common protocol for implementing the electrospraying process is to pump a working fluid into an electrical field through a metal capillary, which is often a blending solu-
∗ Corresponding author. ∗ ∗ Corresponding author at: School of Materials Science & Engineering, University of Shanghai for Science and Technology, 516 Jungong Road, Shanghai 200093, China. E-mail addresses: [email protected] (Z.-P. Liu), [email protected] (D.-G. Yu). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.apsusc.2017.11.024 0169-4332/© 2017 Elsevier B.V. All rights reserved.
tion comprising a matrix and a functional additive [5]. Coaxial electrospraying is an upgrade version of the traditional blending electrospraying that exploits a coaxial spray head to lead two different working solutions into the electrical fields simultaneously [8,9]. This advanced technology is very popular because of the usefulness of core-shell nanostructures in designing and tailoring the functional performance of structural nanomaterials [10–14]. Regardless of the single-fluid blending, the double-fluid coaxial, or the tri-axial electrospraying, a successful EHDA process for creating the desired solid particles requires suitable manipulation of the solvent evaporation rate from the working solutions to match the electrical actions. Thus, considerable efforts have been made to optimize the working conditions and certain auxiliary facilities to help in spray drying [15]. Meanwhile, although several studies have tried to elaborate the hydrodynamic interfacial phenomena during working processes [16–19], studies on intentional manipulation of the processes through air-solution interfaces are lacking. Such manipulation comprises a new concept for developing novel functional nanomaterials through electrospraying. This situation may be explained by the usage of dilute solutions only in electrospraying. An additional heat flow is sometimes needed to facilitate the creations of solid particles. Thus, introducing an additional solvent into the electrospraying process, as a possible method for manip-
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ulating the air-solution interfaces to create high quality products, seems impossible. Most recently, the traditional concept about coaxial electrospinning (the counterpart of electrospraying) was terminated by a modified coaxial process, where sheath solvent was utilized to generate high quality monolithic nanofibers other than coresheath nanofibers [20,21]. The idea of exploiting a solvent to modify the dynamic working interfaces during electrospinning is quickly developing into tri-axial processes and multiple-fluid complex electrospinning processes [22–24]. Thus, traditional coaxial electrospraying process may be also modified based on a similar strategy. Numerous possibilities are available for materials design and development, in which an outer layer solvent is used to manipulate the traditional blending electrospraying processes. During the past half century, polymer has functioned as the backbone to support the development of pharmaceutics. Most of the oral drug sustained-release dosage forms are based on the properties of polymeric matrices to improve their therapeutic effect, safety, and patient convenience. New methods (particularly those based on advanced nanotechnologies) and new drug carriers are frequently introduced into this field to develop medicated materials with improved drug sustained-release profiles [25,26]. Among different kinds of pharmaceutical excipients (such as synthetic polymers, natural macromolecules, and inorganic graphene oxide and carbon nanotubes), plant-derived natural products (such as polysaccharides cellulose, alginates, pectin, inulin, carageenans, rosin, gums, and mucilages), and proteins (such as zein, gliadin, soy protein, gluten, legumin, and lectin) are frequently combined with new protocols to create new types of drug sustained-release nanomaterials [27–29]. Gliadin is a type of prolamin. It is a class of proteins present in wheat and several other cereals within the grass genus Triticum. As a product derived from natural sources, it has good biocompatibility and biodegradability and can be used without concerns regarding the presence of monomer or initiator residues, which are present in the synthetic materials [30–32]. Thus, gliadin has been studied extensively for its potential applications to a wide variety of fields, including medicated materials. Gliadin-based medicated products in the forms of filaments, nanofibers, microspheres and nanoparticles have been prepared using wet spinning, electrospinning, spraying, and blending electrospraying; it has high potential to be developed into commercial tablets or capsules [33–36]. We investigated a modified coaxial electrospraying process, in which an additional shell solvent was used to modify the working interfaces of the traditional blending electrospraying. Gliadin was utilized as a drug carrier. Meletin, a plant flavonoid found in many plants and foods and has been broadly applied to the treatment of diabetes, conditioning of the heart and blood vessels, prevention of cancer, treatment of chronic prostate infections, increasing endurance, and improving athletic performance [37]. It is exploited as a model active pharmaceutical ingredient. In Chinese traditional medicine, meletin is often used to prevent asthma, eliminate phlegm, and relieve cough, a sustained release profile after oral administration is highly desired for its high therapeutic effects [38]. Meletin-loaded gliadin nanoparticles from the modified coaxial processes are characterized in detail and compared with the medicated particles from the blending electrospraying.
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magenta, trifluoroacetic acid (TFA), and trifluoroethanol (TFE) were provided by the Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All other chemicals were analytical reagents. Water was double distilled before use. 2.2. Electrospinning All processes were implemented using an in-house coaxial electrospraying system, which comprised a power supply (ZGF60 kV/2 mA, Wuhan Huatian Corp., Wuhan, China), two syringe ® pumps (KDS100, Cole-Parmer , Vernon Hills, USA), a home-made coaxial spray head and a collector composed of cardboard wrapped with aluminum foil. The blending solutions contained 6% gliadin (w/v) and 1% meletin (w/v) in a mixture consisting of TFA and TFE in a volume ratio of 50:50. Basic magenta (5 × 10−6 g/mL) was added into the blending solution to optimize the experimental conditions. These fluids were driven by using the core syringe pump. The shell fluid was pure TFE. The pump used to drive the shell TFE was switched off to prepare particles P1 directly from the blending electrospraying process with a core fluid flow rate of 1.0 mL/h. Under a fixed core fluid flow rate of 1.0 mL/h, a series of shell solvent flow rates was used. The particles prepared from a shell fluid flow rate of 0.3 mL/h were denoted as particles P2. The particle collected distance and the applied voltage were fixed at 15 cm and 21 kV, respectively. 2.3. Morphology and structure The prepared particles were evaluated using a scanning electron microscope (SEM, FEI Quanta 450 FEG, USA). Prior to microscopy, the samples were sputter coated with platinum under a nitrogen atmosphere for 90 s. The diameters of the particles were estimated by measuring the sizes of 100 particles from the SEM images using ImageJ software (National Institutes of Health, Bethesda, USA). The inner structure of particles were investigated using a H-800 transmission electron microscope (TEM; Hitachi, Tokyo, Japan). TEM samples were prepared by placing a lacey carbon-coated copper grid on the collector during electrospraying process. 2.4. Physical forms X-ray powder diffraction (XRD) patterns were recorded using a Bruker X-ray powder diffractometer Bruker-AXS with CuK␣ radiation (Karlsruhe, Germany). The raw gliadin/meletin powders and particulate samples were analyzed between 2 angles from 5◦ to 60◦ . The topographies of raw meletin and gliadin were observed using a XP-700 polarized optical microscope (OM, Shanghai Changfang Optical Instrument, Shanghai, China). 2.5. Compatibility The raw meletin/gliadin powders and their particles were subjected to attenuated total reflectance (ATR)–Fourier transform infrared (FTIR) analysis using Spectrum 100 FTIR Spectrometer (PerkinElmer, Billerica, USA) over a range of 600–4000 cm−1 at a resolution of 2 cm−1 .
2. Materials and methods
2.6. In vitro dissolution tests
2.1. Materials
In vitro dissolution tests were performed using a RCZ-8A dissolution apparatus (Tianjin University Radio Factory, Tianjin, China). Samples equivalent to 30 mg of meletin (i.e., 0.21 g medicated particles) were placed into the dissolution cells, in which the dissolution medium (900 mL physiological saline) was maintained at a
Meletin (purity > 98%, No. MUST-15071603) was purchased from the Beijing Aoke Biological Technology Co., Ltd. (Beijing, China). Gliadin (extracted from wheat, Mn = 30,000 g/mol), basic
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constant temperature of (37 ± 1) ◦ C. The paddle frequency was consistent at 50 rpm. A UV–Vis spectrophotometer (UV-2102PC, Unico Instrument Co. Ltd., Shanghai, China) was used to measure the concentration of dissolved TC at a wavelength of = 370 nm according to the Chinese Pharmacopoeia. All experiments were repeated six times. 3. Results and discussion 3.1. Modified coaxial electrospraying Traditionally, blending electrospraying is a single-fluid process with all the ingredients co-dissolved in one solution. In contrast, coaxial electrospraying is a double-fluid process that produces core-shell structures. In the literature, blending and coaxial electrospraying processes have their own systems. In the present study, the developed electrospraying system included both the traditional blending and the modified coaxial processes (Fig. 1a). When the shell fluid flow rate (Fs ) is switched off (i.e., Fs = 0 mL/h), the process became a typical blending spraying; when Fs 䊐 0 mL/h, the process became a double-fluid coaxial spraying. The developed modified coaxial electrospraying exploited a coaxial spray head and an additional pump to manipulate a thin layer of solvent TFE covering the core blending solution during electrospraying. This modification temporarily and dynamically modified the air-solution working interfaces, thereby adjusting the removal of solvent from the core blending solution and its solidification behavior. Thus, the new modified coaxial process generated monolithic nanoparticles compared with the traditional coaxial electrospraying, which resulted in core-shell particles. A diagram of the homemade coaxial spray head and its connection with the power supply and the two working fluids are shown in Fig. 1b. The diameters of the inner and outer capillaries of the spray head were 0.3 and 1.2 mm, respectively. The core blending solution was directly pumped into the spray head from its syringe, whereas the shell solvent TFE was pumped to the spray head through an elastic silicone tube. High voltage could be applied to the working fluids through an alligator clip connected to the inner metal capillary. Under the optimized conditions, a typical blending electrospraying process conducted at a shell fluid flow rate of 0 mL/h but with a core fluid flow rate of 1.0 mL/h to prepare particles P1 is shown in Fig. 2a1. In this figure, a whole red Taylor cone (Fig. 2a2) is followed by a Columbic explosion atomization region beginning from a convergent point. The collected particles spread over an area with an estimated diameter of 23 cm (Fig. 2a3). When the modified coaxial electrospraying processes were performed under a shell-to-core fluid flow rate ratio of 0.3/1.0 mL/h during the preparation of particles P2, a typical electrospraying process is shown in Fig. 2b1. Its Taylor cones had a compound structure, with the red core fluid encapsulated by the colorless shell solvent (Fig. 2b2). Unexpectedly, the collected particles P2 spread over an area with an estimated diameter of 16 cm (Fig. 2b3); such area was significantly smaller than particles P1. 3.2. Morphology and structure of the prepared particles The SEM images of the mophology details of the crude gliadin/meletin powders and their electrosprayed particles are shown in Fig. 3. The crude gliadin particles have a flat globular shape, wrinkle surface, and broad size distribution (Fig. 3a). The raw meletin particles show a typical needle crystalline morphology (Fig. 3b). The SEM images of the electrosprayed particles prepared under a fixed flow rate of core fluid (1.0 mL/h) and a series of shell solvent
flow rate of 0 (i.e. the blending electrospraying for creating particles P1), 0.1, and 0.3 mL/h (particles P2) are exhibited in Fig. 3c, d, and e, respectively. The trends are clear that large shell solvent flow rates resulted in rounder morphology, smoother surface, and narrower size distribution of the particles. However, excessive shell solvent would result in incompletely dried nanoparticles and their binding together when in contact (Fig. 3f). Particles P1 and P2 have an estimated diameters of 890 ± 180 and 570 ± 80 nm, respectively. The TEM images of electrosprayed particles P1 and P2 are shown in Fig. 4, which reveal the details on inner structural characteristics. As expected, particles P2 from the modified coaxial process had a uniform inner structure with a round morphology, as reflected by the circular shape and a similar gray level in Fig. 4a. However, particles P1 from the blending electrospraying had a series of irregular shapes and a broad size distribution. These products showed multiple gray levels within one each particles (Fig. 4b). The differences of gray level in TEM images generated under the bright field can be attributed to three aspects, namely, elements, densities, and thicknesses. Apparently, the different gray levels within particles P1 were mainly a direct result of varied thicknesses because all the particles had the same elements and their densities were not significantly different. This result corroborated the crumpled morphologies of particles P1 in their SEM images.
3.3. Microformation mechanisms A blending electrospraying process comprises four successive steps, as follows: charging working fluids, forming Taylor cone, atomizing droplets, and collecting final particles. The formation of Taylor cone is a key element for initiating an electrospraying process, which is a balance of a series of parameters, particularly the electrical fields and the properties of working fluids. The atomization region is the most important step for the physical state of the final particles, where the solidification process occurs as a result of a series of simultaneously occurring phenomena. Two main phenomena had a close relationship with the dynamic airsolution interfaces of all the atomized droplets, one is the solvent outward evaporation from the surfaces of droplets, and the other is the polymer and other additives inward migration, diffusion, and chain entanglement from their surfaces. When an additional solvent is applied to the surface of working fluid previously treated using blending electrospraying, the formation of Taylor cone and the atomization are profoundly modified. A diagram is shown in Fig. 5. Initiating the electrospraying was easier because of the low surface tension and low viscosity of the surrounding solvent compared with the blending working fluid. However, favorable results from the shell solvents mainly occurred at the atomization region. In all the electrospraying processes, the nascent nearmonodisperse droplets after the Columbic explosion rapidly split and shrunk because of the accumulation of surface charges and the fast evaporation of solvents resulting from the large surface areas. The first positive result from the surrounding solvent is that the Columbic splitting may further occur more times in the modified coaxial process than in the blending process because of the presence of the solvent layer on the droplets. More times splitting in the atomization region should promote the formation of solid particles with smaller size. The second positive result from the surrounding solvent is related to the outward evaporation of solvent of blending solutions. The surrounding solvent can effectively prevent the possible premature formation of semi-solid shell on the droplets, which frequently occur during blending electrospraying. The presence of a layer of solvent on the droplets in the modified coaxial processes acted as a bridge, thereby promoting the evaporation of core sol-
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Fig. 1. (a) A diagram of the implementation of blending and modified coaxial electrospraying using one system. (b) Connection of the coaxial spray head with the two syringe pumps and the power supply.
Fig. 2. Observations of the blending electrospraying for preparing particles P1 (a1, a2 and a3) and the modified coaxial electrospraying for fabricating particles P2 (b1, b2 and b3).
vents through a large range of splitting times, enhancing diffusions with small resistance, and allowing possible extractions. The third positive result from the surrounding solvent is related to the inward behavior of solute molecules within the droplets, particularly the migration, entanglement, and condensation of inner polymeric molecules. In the blending electrospraying, the fast evaporation of solvents quickly increased the viscosity of working fluids, which in turn retarded the migration, diffusion, transmission, and entanglement of polymer molecules within the droplets. When an additional layer of solvent is provided around the droplets, the polymer diffused easily inside the droplets. Instead of concentrating on the surface, the polymer was distributed homogeneously throughout the droplet, thereby facilitating the maintenance of droplet integrity during contraction because of drying without collapsing. Besides more splitting, the favorable outward evaporation of solvent, and favorable inward migration of solutes from the airsolvent-solution interfaces, the surrounding layer solvent kept a stable and robust atomization process, thereby resisting interference from the environment. These factors acted together during the electrospraying processes to ensure the formation of a uniform product with a small size, smooth surface, a narrow size distribution, few satellites, and compact inner structures. In Fig. 2, the collection circle of particles P1 (Fig. 2a3) had an estimated diameter of 23 cm, which was larger than the circle of particles P2 (16 cm in Fig. 2b3). This phenomenon can be explained by the force analysis during the electrospraying processes. As shown in Fig. 5, a droplet in the atomization region
received a series of forces from the electrical field (FE ), the gravity force (G), and the repelling forces (Fr ) from all the surrounding droplets. Compared with droplets in the blending electrospraying, the droplets in the modified coaxial process had a larger gravity force and smaller repelling forces. The former resulted from the exhaustion of inner solvent and a compact inner structure of the formed solid particles. The latter had close relationship with more spitting times, in which more charges were removed with the evaporation of solvent. Thus, the large G and small Fr resulted in the quicker deposition of the particles P2; particles P2 were more concentrated in their collector than particles P1, i.e., 16 cm < 23 cm.
3.4. Physical state of components and their compatibility The XRD patterns of the crude materials (meletin and gliadin) and their particles P1/P2 are shown in Fig. 6. As anticipated, the drug meletin powders showed sharp peaks in their XRD patterns, thereby suggesting the presence of crystal materials. In contrast, gliadin patterns had no sharp peaks, indicating that it was an amorphous matrix. These results were verified by the polarized optical microscopic images in Fig. 6, in which meletin showed bright colors, including blue, red, and yellow, whereas gliadin particles exhibited only gray colour. The electrosprayed particles P1/P2 were similar amorphous composites, regardless of the electrospraying processes. After being electrosprayed with the protein, the crystalline meletin particles lost their original physical status. The fast
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Fig. 3. SEM images of the particles: (a) crude gliadin; (b) crude meletin; (c), (d), (e), and (f) electrosprayed particles prepared under a shell solvent flow rates of 0 (particles P1), 0.1, 0.3 (particles P2), and 0.5 mL/h, respectively.
Fig. 4. TEM images of the electrosprayed particles: (a) P2; (b) P1.
drying electrospraying processes distributed the drug molecules homogeneously all over the gliadin matrices. The ATR-FTIR spectra of meletin, gliadin, and their electrosprayed particles from the blending and coaxial processes are
shown in Fig. 7. The FTIR spectra of gliadin had two typical absorbance bands of 1653 and 1545 cm−1 , which were attributed to the vibrations of the C O and C N groups, respectively. Three welldefined peaks were visible for pure crystalline meletin, at 1669,
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3.5. Sustained-release performances
Fig. 5. Influence of an additional temporarily air-solvent-polymer solution interfaces on the formation of electrosprayed particles.
Fig. 6. XRD patterns of the crude materials (meletin and gliadin) and their electrosprayed nanoparticles P1 and P2, and the polarized optical microscopic images of gliadin and meletin.
The sustained drug-release profiles of meletin from the particles P1 and P2 are shown in Fig. 8a. Both of them showed a typical sustained release over a certain time period. However, particles P2 provided a better performance than P1 in the following aspects. First, particles P2 had a smaller initial burst release effect (28.8% for the first hour) than P1 (44.7% for the first hour). Second, particles P1 released 91.1% of the loaded cargoes at a time period of 8 h, whereas particles P2 released 93.7% at a time period of 16 h, thereby suggesting a longer sustained release profile. Third, at the late stage of drug release, the delayed leveling off release is a common phenomenon to drug sustained-release materials and solid dosage forms. The release of the last 10% of loaded cargoes took about 13 and 9 h for particles P1 and P2, respectively. This indicated that the former had a longer time period of the negative phenomenon, which often does not give an effective delivery to ensure a minimum effective serum concentration after oral administration [24]. Gliadin is not soluble in water. Thus, the drug release was controlled by a diffusion mechanism. The diffusion processes (including the inward diffusion of water molecules into the particles and the outward diffusion of meletin molecules into the bulk dissolution media) always occurs along the shortest distance. Thus, although particles P1 had an apparently larger size than particles P2, their irregular shape meant that there were many diffusion routes with different lengths for the water and meletin molecules. Among these routes, the shortest routes play a role in the manipulation of the release rates of the loaded drug molecules, as shown in the inset diagram of Fig. 8a. These routes in particles P1 were often extremely smaller than the diffusion radii of particles P2. Meanwhile, the irregular shapes and a broader size distributions of P1 indicated an extreme increase of the total surface area and the related drug surface distribution, which in turn resulted in a larger initial burst release than particles P2. This case exemplified the conclusions of Lahann et al. in their review, in which the material shapes often profoundly influenced their functional performance [39]. To further investigate the controlled drug release mechanisms of these particles, the release data were analyzed as per the Korsmeyer Peppas Equation (1) or (2), as follows [40]: Q =
Mt = kt n M∞
ln Q = n ln t + ln k Fig. 7. ATR-FTIR spectra of the crude materials (meletin and gliadin) and their electrosprayed nanoparticles P1 and P2, and their chemical formulas.
1615, and 1513 cm-1 , corresponding to its benzene ring and C O group. However, all peaks for meletin were absent in the spectra of the electrosprayed particles P1/P2; only two bands of 1649 and 1544 cm--1 can be identified obviously. The disappearance of meletin C O group bands, the shift to lower wavenumbers of peaks assigned to the C O and C N stretching vibrations in gliadin, and the disappearance of peaks in the fingerprint region of the meletin spectra jointly suggested that hydrogen bonding occurred between the gliadin and meletin molecules within the composite particles. This result can also be speculated from their chemical formulas in Fig. 7, which indicated that both meletin and gliadin molecules acted proton acceptors and proton donors. Thus, the XRD and ATR-FTIR results verified that meletin-loaded gliadin particles P1 and P2 were all amorphous homogeneous nanocomposites, in which the components had fine compatibility because of hydrogen bonding; other secondary interactions, such as hydrophobic and electrostatic forces, may have occurred as well.
(1) (2)
where Q is the drug release in percentage, Mt is the amount of drug released at time t, M∞ is the total amount of drug released, k is the kinetic parameter, and n is the release exponent indicative of the drug release mechanism. The regressed results are exhibited in Fig. 8b. P1 and P2 particles had the following power equations: Q1 = 47.42 t0.36 (R = 0.9782) and Q2 = 29.92 t0.41 (R = 0.9978), respectively. All their diffusion indexes n were lower than the critical value of 0.45, thereby indicating that the contained cargoes were similarly freed from particles P1 and P2 through a typical Fickian diffusion mechanism. Since the first publication on coaxial electrospraying, all the reported coaxial processes have exploited a solution containing a polymer or other solutes as a sheath fluid to generate core-shell micro-/nano-structures [41]. In sharp contrast, our experiments demonstrated that high quality monolithic composites could be generated using the coaxial electrospraying under the condition that pure solvents were explored as the shell fluids. The concept of exploiting solvent to modify the dynamic working interfaces during electrospraying can be further expanded to a series of other complicated electrospraying processes, such as the tri-axial electrospraying with an outer layer of solvent and side-by-side
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Fig. 8. In vitro drug release profiles of P1 and P2 (a) and the regressed treatment of drug release data according to the Peppas equation (b).
electrospraying with a co-layer of outer solvent. Certainly, the “outer layer solvent” can be expanded to many other dilute solutions that cannot be used on solid products using traditional electrospraying processes. Thus, many functional nanomaterials may be similarly designed and developed through nanocoating using the dilute solutions. Meanwhile, some influences of partial air–solvent–solution electrohydrodynamic interfaces on the working processes and the final products still require further investigations when different kinds of solvents are exploited. Some solvents may only stabilize the entire electrospraying process, whereas other solvents may even extract the inner solvents; the rest may coagulate the inner polymers or other solutes. As for the application of the modified coaxial process in the field of nanomedicine, it can be utilized facilely to control structures at the nanometer level, thereby leading to significantly changed properties of the medicated nanoparticles. Thus, the process results in products that are different from products prepared using traditional protocols. 4. Conclusions To the best of our knowledge, a dynamic surface modification of pure solvent on the traditional blending electrospraying was successfully conducted for the first time. The new modified electrospraying process maintained a continuous, stable, and smooth preparation of meletin-loaded gliadin medicated nanoparticles. Compared with the particles from the blending electrospraying, the particles from the modified processes had better quality in terms of size, size distributions, external morphology, and inner structure, as demonstrated by SEM and TEM images. XRD results demonstrated that all the particles were monolithic protein-based nanocomposites and that meletin molecules were homogeneously distributed all over the gliadin matrices. The in vitro dissolution tests demonstrated that the particles from the new processes could provide better functional performance for meletin sustained release, as reflected by the smaller initial burst releases, longer drug sustained-release periods, and smaller late leveling-off releases. The rounder shape, the increased homogeneity of particle size, and the smaller surface of the particles from the modified coaxial processes jointly resulted in better functional performances. Both the microformation mechanism and drug controlled-release mechanism were suggested. To summarize the concept of traditional coaxial electrospraying, the application of a solvent temporarily and dynamically on the surface of a working fluid is a new way of developing new types of electrosprayed functional nanomaterials. Acknowledgments This research is financially supported by the National Natural Science Foundation of China (No. 51373101).
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