Low-frequency Sonophoresis Research Articles

A compact and low-frequency drive ultrasound transducer for facilitating cavitation-assisted drug permeation via skin.

Low-frequency sonophoresis has emerged as a promising minimally invasive transdermal drug delivery method. However, effectively inducing cavitation on the skin surface with a compact, low-frequency ultrasound transducer poses a significant challenge. This paper presents a modified design of a low-frequency ultrasound transducer capable of generating ultrasound cavitation on the skin surfaces. The transducer comprises a piezoelectric ceramic disk and a bowl-shaped acoustic resonator. A conical slit structure was incorporated into the modified transducer design to amplify vibration displacement and enhance the maximum sound pressure. The FEM-based simulation results confirmed that the maximum sound pressure at the resonance frequency of 78 kHz was increased by 1.9 times that of the previous design. Ultrasound cavitation could be experimentally observed on the gel surface. Moreover, 3 min of ultrasound treatment significantly improved the caffeine permeability across an artificial membrane. These results demonstrated that this transducer holds promise for enhancing drug permeation by generating ultrasound cavitation on the skin surface.

Transdermal drug delivery using low-frequency sonophoresis: COMSOL simulation of piezoelectric array transducers

This study explores the design and simulation of specialized sonophoretic transducers aimed at enhancing the transdermal delivery of large drugs. We examine different elements of the transducer's design, such as the choice of materials, its dimensions, and the matching of acoustic impedance. We selected PZT-4, from the lead zirconate titanate (PZT) group, as the main material due to its excellent piezoelectric features and durability. We also use polymer matrices to make the transducer less rigid. The simulation outcomes, using COMSOL Multiphysics, cover five different transducer array sizes (8x5, 10x6, 12x8, 14x9, and 16x10) within the frequency range of 20-40 kHz. We measure the acoustic pressure at a depth of 0.1 mm under the skin, which is key for successful drug delivery through the skin. Our results show how increasing the size of the array affects the transducer's efficiency. We confirm our simulation results by comparing them with a previously published ANSYS simulation and finding good alignment. This comparison adds reliability to our methods and outcomes. The study also proposes creating a small, wrist-mounted device for drug delivery that could be combined with drug patches, making it user-friendly. Moreover, we stress the need to follow Mechanical Index (MI) guidelines to avoid damaging the skin. Overall, our findings highlight the importance of the array size in the performance of the transducer and confirm the validity of our simulation approach, paving the way for innovative solutions in drug delivery that could have wide applications in healthcare.

Comparative study of permeation effects between vibrating microneedle and low-frequency sonophoresis systems.

Microneedle transdermal administration and low-frequency ultrasound represent two important physical penetration-promoting methods for enhancing drug penetration. This article aims to investigate and compare the effects of drug penetration enhancement through transdermal administration using vibrating microneedles versus low-frequency sonophoresis. In Vitro permeation studies were conducted using Valia-Chien double chamber diffusion cells to evaluate the transdermal delivery of tetramethylpyrazine hydrochloride (TMPH). The TMPH concentration in the receiving compartment was determined using high-performance liquid chromatography (HPLC). Several combinations of microneedles and ultrasound settings were investigated, including different needle heights, vibration frequencies, exposure times, and assorted distances of ultrasound horn and skin. The results revealed the vibrating microneedle system as the most efficacious treatment to increase the TMPH permeability into the rat skin. The combination of a larger needle, higher frequency, and a 3-min exposure led to a 41.92-fold increase in cumulative permeability compared to the control group. The ultrasound treatment exhibited a moderate enhancement effect on TMPH skin penetration. Using a horn-to-skin distance of 3mm and a 3-min exposure resulted in a 4.34-fold increase in TMPH cumulative permeation compared to the control group. It could be concluded that while both the vibrating microneedle and the low-frequency ultrasound systems act as penetration enhancers for promoting the TMPH permeation through the skin, the vibrating microneedle system notably demonstrates a more effective penetration-promoting effect.

Low-Frequency Ultrasound Sensitive Piezo1 Channels Regulate Keloid-Related Characteristics of Fibroblasts.

Keloids are benign fibroproliferative tumors that severely diminish the quality of life due to discomfort, dysfunction, and disfigurement. Recently, ultrasound technology as a noninvasive adjuvant therapy is developed to optimize treatment protocols. However, the biophysical mechanisms have not yet been fully elucidated. Here, it is proposed that piezo-type mechanosensitive ion channel component 1 (Piezo1) plays an important role in low-frequency sonophoresis (LFS) induced mechanical transduction pathways that trigger downstream cellular signaling processes. It is demonstrated that patient-derived primary keloid fibroblasts (PKF), NIH 3T3, and HFF-1 cell migration are inhibited, and PKF apoptosis is significantly increased by LFS stimulation. And the effects of LFS is diminished by the application of GsMTx-4, the selective inhibitor of Piezo1, and the knockdown of Piezo1. More importantly, the effects of LFS can be imitated by Yoda1, an agonist of Piezo1 channels. Establishing a patient-derived xenograft keloid implantation mouse model further verified these results, as LFS significantly decreased the volume and weight of the keloids. Moreover, blocking the Piezo1 channel impaired the effectiveness of LFS treatment. These results suggest that LFS inhibits the malignant characteristics of keloids by activating the Piezo1 channel, thus providing a theoretical basis for improving the clinical treatment of keloids.

Mechanisms underlying the influence of skin properties on a single cavitation bubble in low-frequency sonophoresis

As a safe and effective method for systemic transdermal drug delivery (TDD), sonophoresis has drawn much attention from researchers. Despite numerous studies confirming cavitation as the main reason for sonophoresis, the effect skin has on cavitation bubble dynamics remains elusive due to the difficulty of experimental challenges. For a start, we reveal how single cavitation bubble (SCB) dynamics are affected by skin properties, including elasticity, hydrophilicity and texture. We use polydimethylsiloxane (PDMS) to simulate human skin and record the temporary evolution of SCBs with synchronous ultrafast photography. The influences of skin properties on SCBs are concluded: 1) SCBs collapse later near walls with better elasticities and generate microjets with higher speed; 2) SCBs collapse later near hydrophilic walls with slower microjets; and 3) the existence of a texture structure on walls also delays the time of bubble collapse near them and slows the velocities of microjets (v) during collapses.

Low-Frequency Sonophoresis as an Active Approach to Potentiate the Transdermal Delivery of Agomelatine-Loaded Novasomes: Design, Optimization, and Pharmacokinetic Profiling in Rabbits.

The first melatonergic antidepressant drug, agomelatine (AGM), is commonly used for controlling major depressive disorders. AGM suffers low (< 5%) oral bioavailability owing to the hepatic metabolism. The current work investigated the potential of low-frequency sonophoresis on enhancing transdermal delivery of AGM-loaded novasomes and, hence, bioavailability of AGM. Drug-loaded novasomes were developed using free fatty acid (stearic acid or oleic acid), surfactant (span 60 or span 80), and cholesterol via thin-film hydration technique. The systems (N1-N16) were assessed for zeta potential (ZP), particle size (PS), encapsulation efficiency (EE%), and drug percent released after 0.5h (Q0.5h) and 8h (Q8h), drug-crystallinity, morphology, and ex vivo drug permeation. Skin pre-treatment with low-frequency ultrasound (LFU) waves, via N13-novasomal gel systems, was optimized to enhance ex vivo drug permeation. Influences of LFU mode (continuous or pulsed), duty cycle (50% or 100%), and application period (10 or 15min) were optimized. The pharmacokinetics of the optimized system (N13-LFU-C4) was assessed in rabbits. N13 was the best achieved novasomal system with respect to PS (471.6nm), ZP (- 63.6 mv), EE% (60.5%), Q0.5h (27.8%), Q8h (83.9%), flux (15.5μg/cm2/h), and enhancement ratio (6.9). N13-LFU-C4 was the optimized novasomal gel system (desirability; 0.997) which involves skin pre-treatment with LFU in a continuous mode, at 100% duty cycle, for 15min. Compared to AGM dispersion, the significantly (P < 0.05) higher flux (26.7μg/cm2/h), enhancement ratio (11.9), Cmax (118.23ng/mL), and relative bioavailability (≈ 8.6 folds) could elucidate the potential of N13-LFU-C4 system in improving transdermal drug permeability and bioavailability.

Transdermal delivery of heparin using low-frequency sonophoresis in combination with sponge spicules for venous thrombosis treatment.

This study reports that the use of low-frequency sonophoresis (LFS) in combination with sponge Haliclona sp. spicules (SHS), referred to as cSoSp (combined Sonophoresis and Spicules), can enhance the transdermal drug delivery in a synergistic manner. The topical application of cSoSp in vitro significantly enhanced the skin absorption of Fluorescent-Dextrans (4000 Da, FD-4K), a model drug of low-molecular-weight heparin (LMWH). The utilization of cSoSp dramatically increased the transdermal flux of FD-4K (188.6 ± 93.7 ng cm-2 h-1) compared to LFS (5.8 ± 3.1 ng cm-2 h-1) and SHS (3.2 ± 1.2 ng cm-2 h-1) among others. The mechanism of action of cSoSp could be attributed to the synergism between plenty of long-lasting nano-channels created by SHS and the disorders of SC lipids made by shock waves of LFS, which improves the homogeneity of the cavitation effects. Furthermore, LMWH (3000 Da) was transdermally delivered by using cSoSp to treat both superficial venous thrombosis (SVT) and deep venous thrombosis (DVT) in the marginal ear vein of rabbits with a good therapeutic effect. Furthermore, skin irritation and toxicity studies using guinea pigs indicated that cSoSp was nonirritating without any morphological changes in the keratinocytes. cSoSp offers a promising strategy to enhance the transdermal delivery of hydrophilic macromolecules such as heparin.

Comparison the Efficacy of EMLA Cream versus EMLA with High Frequency Sonophoresis in Decreasing Onset Time to Topical Anaesthesia in Adult Volunteers: A Pilot Study

Background: Sonophoresis or phonophoresis is a well-known transdermal drug delivery mechanism. Usage of high frequency ultrasound for sonophoresis was initiated in late 1950s while the usage of low-frequency sonophoresis was investigated significantly during the past two decades. The objective was to analyze the efficacy of high frequency ultrasound probe in the penetration of EMLA cream in decreasing onset time for topical anaesthesia in adult healthy volunteers. Methods: A prospective, open labelled, comparative study was conducted on patients reporting at the Pain Clinic our institute. Subjects received the intervention USG probe with EMLA either on the left or the right hand based on a random number chart, with the other hand of the same subject acting as a control. In group USG, the probe was applied directly on the cream without any added pressure. Sensory testing was done every 10 minutes by pin prick on both the hands of the patients NRS scores of both the hands were recorded at 10.20,30 and 40 minutes. Results: Total 20 patients were selected for the study. Although a significant decrease in the pain scores in both the groups was observed after 40minutes, (p&lt;0.05) both the groups are comparable at each point of time. We could not find any significant decrease in pain scores when groups are compared in intervals during the study period. Conclusion: There is no significant difference in decreasing the intensity of pain scores upon application of ultrasound over EMLA in an adult population. Further studies have to be done to prove the efficacy in a larger population and pediatric ones.

Integrated effects of fractional laser microablation and sonophoresis on skin immersion optical clearing in vivo.

This study is aimed to find an approach for effective skin optical clearing in vivo using polyethylene glycol 300 (PEG-300) as an optical clearing agent in combination with physical enhancers: fractional laser microablation (FLMA) and/or low-frequency sonophoresis. In this study albino outbred rats were used. Light attenuation coefficient and optical clearing potential (OCP) of these approaches were evaluated in upper (from ~70 to ~200 μm) and middle (from ~200 to ~400 μm) dermis separately using optical coherence tomography. In 30 minutes, OCP of sonophoresis in combination with FLMA and PEG-300 in the upper dermis was the maximal (2.3 ± 0.4) in comparison with other treatments in this time point. The most effective approach for optical clearing of middle dermis was PEG-300 and sonophoresis; but the maximal value of OCP (1.6 ± 0.1) was achieved only in 90 minutes.

Effect of Ultrasound Intensity and Mode on Piroxicam Transport Across Three-Dimensional Skin Equivalent Epiderm™.

Transdermal drug delivery has many advantages compared to other routes. However, the barrier function of the stratum corneum limits the use of the skin as an administrative route for medications. Different methods were investigated to alter the barrier function of the stratum corneum and it was found that applying different ultrasound waves could enhance the skin's permeability. The aim of this work is to study the effect of ultrasonic waves on the alteration of skin natural barrier function, to improve the permeability of the skin to Piroxicam using three-dimension skin (EpiDermTM) as a skin model for the investigation. The effect of ultrasound at 1 MHz and 20 kHz on the permeation of Piroxicam across the three-dimensional skin equivalent using a Franz diffusion cell, was evaluated and the concentration of Piroxicam in the receiving compartment was determined using liquid chromatography method. The permeation of Piroxicam enhanced by 199% when therapeutic ultrasound at 1 MHz frequency was used. Significant permeation enhancement was also found upon utilizing low frequency sonophoresis at 20 kHz (427%) with no apparent damage to the membrane. Sonophoresis has a positive effect on enhancing skin permeability. The enhancement level was largely dependent on the sonication factors; frequency, intensity and length of treatment. Multiple mechanisms of action might be involved in permeation improvement of the piroxicam molecule. Those mechanisms are largely dependent on the ultrasonic conditions.

Low-Frequency Sonophoresis of Chinese Medicine Formula Improves Efficacy of Malignant Pleural Effusion Treatment.

To evaluate whether low-frequency ultrasound-facilitated transdermal delivery of a Chinese medicine (CM) formula could improve the efficacy of intrapleural administration of interleukin-2 (IL-2) in treatment of malignant pleural effusion (MPE). A total of 110 eligible participants were randomized into the low-frequency sonophoresis (LFS) of CM (LSF/CM) group (55 cases) and the control group (55 cases) by simple randomization using a random number table. The control group was treated with an intrapleural administration of IL-2; and the LFS/CM group was treated with LFS of a CM gel formulation, combined with the same IL-2 injection as in the control group. The CM formula consisted of Semen Lepidii, Semen Sinapis, Ramulus Cinnamomi, Poriacocos, Herba Lycopi, and Radix Paeoniae Rubra. After 2-week treatment, the therapeutic outcome was determined by the change of the amount of MPE, which was evaluated by B-scan ultrasound and/or chest X-ray, and the change of quality of life (QOL) scores, which were evaluated by the Eastern Cooperative Oncology Group (ECOG) performance status. A significantly higher objective remission rate (ORR) was obtained with intrapleural IL-2 plus LFS/CM than IL-2 treatment alone (P=0.049). In addition, more patients in the LFS/CM group than in the control group had an improved QOL score (P=0.048), and no patients in the LFS/CM group had a reduced QOL. LFS of CM formulation could effectively alleviate MPE and improve the QOL of cancer patients.

Electrically and Ultrasonically Enhanced Transdermal Delivery of Methotrexate.

In this study, we used sonophoresis and iontophoresis to enhance the in vitro delivery of methotrexate through human cadaver skin. Iontophoresis was applied for 60 min at a 0.4 mA/sq·cm current density, while low-frequency sonophoresis was applied at a 20 kHz frequency (2 min application, and 6.9 W/sq·cm intensity). The treated skin was characterized by dye binding, transepidermal water loss, skin electrical resistance, and skin temperature measurement. Both sonophoresis and iontophoresis resulted in a significant reduction in skin electrical resistance as well as a marked increase in transepidermal water loss value (p < 0.05). Furthermore, the ultrasonic waves resulted in a significant increase in skin temperature (p < 0.05). In permeation studies, the use of iontophoresis led to a significantly higher drug permeability than the untreated group (n = 4, p < 0.05). The skin became markedly more permeable to methotrexate after the treatment by sonophoresis than by iontophoresis (p < 0.01). A synergistic effect for the combined application of sonophoresis and iontophoresis was also observed. Drug distribution in the skin layers revealed a significantly higher level of methotrexate in the sonicated skin than that in iontophoresis and untreated groups. Iontophoresis and low-frequency sonophoresis were found to enhance the transdermal and intradermal delivery of methotrexate in vitro.

Early steps of cryopreservation of day one honeybee (Apis mellifera) embryos treated with low-frequency sonophoresis

Honeybees, major providers of pollination, are endangered in many areas. Embryo cryopreservation may be a very useful tool to maintain their genetic diversity. However, it is complex in insects, because embryos are chill sensitive and are surrounded by two protectant membranes, the chorion and vitelline. These membranes prevent penetration of cryoprotectant in the embryos. This study aimed to test different conditions of embryo preparation before cryopreservation, including low-frequency sonophoresis, a physical method of permeabilization, and passages through cryoprotectant solutions. Apis mellifera ligustica embryos were collected in artificial cell plugs 7.5 h after queens had been caged, in two different seasons (winter, spring) and were then incubated in vitro overnight (16.5 h). Embryos were individually sonicated and then incubated in three cryoprotectant baths (B1 = 10%, B2 = 20% and B3 = 40% of cryoprotectant) and quenched in liquid nitrogen. Artificial cell plugs and in vitro incubation device were efficient in producing future embryos hatching. Embryos stained ruby red with rhodamine B after sonophoresis treatment indicated that low-frequency ultrasound had permeabilized embryos. According to the treatment, different significant hatching rates were obtained after sonophoresis (up to 25%). After three cryoprotectant incubations, best hatching rates were obtained after 10 min in B1 and B2, and 40 s in B3. These results show that sonophoresis is an efficient tool to permeabilize the chorion and vitelline membrane of the day one honeybee embryo allowing a hatching rate of more than 20%. They also show that the season is an important variability factor.

A New Low-frequency Sonophoresis System Combined with Ultrasonic Motor and Transducer

Low frequency sonophoresis (LFS) is currently being attempted as a transdermal drug delivery method in clinical areas. However, it lacks both an effective control method and the equipment to satisfy the varying drug dosage requirements of individual patients. Herein, a novel method aimed at controlling permeability is proposed and developed, using a pressure control strategy which is based on an accurate, adjustable and non-invasive ultrasound transdermal drug delivery system in in vitro LFS. The system mainly consists of a lead screw linear ultrasonic motor and an ultrasonic transducer, in which the former offers pressure and the latter provides ultrasound wave in the liquid. The ultrasound can enhance non-invasive permeation and the pressure from the motor can control the permeability. The calculated and experimental results demonstrate that the maximum pressure on artificial skin is under the area with the maximum vibration amplitude of the ultrasonic transducer, and the total pressure consists of acoustic pressure from the transducer and approximate static pressure from the motor. Changing the static pressure from the ultrasonic motor can effectively control the non-invasive permeability, by adjusting the duty ratio or the amplitude of the motor’s driving voltage. In addition, the permeability control of calcein by thrust control is realized in 15 min, indicating the suitability of this method for application in accurate medical technology. The obtained results reveal that the issue of difficult permeability control can be addressed, using this control method in in vitro LFS to open up a route to the design of accurate drug delivery technology for individual patients.

Enhancement of Galantamine HBr Skin Permeation Using Sonophoresis and Limonene-Containing PEGylated Liposomes.

This study aimed to investigate the effect of low-frequency sonophoresis (SN) and limonene-containing PEGylated liposomes (PL) on the transdermal delivery of galantamine HBr (GLT). To evaluate the skin penetration mechanism, confocal laser scanning microscopy (CLSM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) were employed. The application of SN led to more GLT penetration into and through the skin than GLT solution alone. The liposomes also improved GLT permeation, and 2% limonene-containing PL (PL-LI2%) exhibited the highest GLT permeation, followed by PL-LI1%, PL-LI0.1%, and PL. The CLSM images of PL-LI2% resulted in the highest fluorescence intensity of fluorescent hydrophilic molecules in the deep skin layer, and the rhodamine PE-labeled liposome membrane was distributed in the intercellular region of the stratum corneum (SC). PL-LI2% induced significant changes in intercellular lipids in the SC, whereas SN had no effect on intercellular lipids of the SC. DSC thermograms showed that the greatest decrease in the lipid transition temperature occurred in PL-LI2%-treated SC. SN might improve drug permeation through an intracellular pathway, while limonene-containing liposomes play an important role in delivering GLT through an intercellular pathway by increasing the fluidity of intercellular lipids in the SC. Moreover, a small vesicle size and high membrane fluidity might enhance the transportation of intact vesicles through the skin.

Acoustic streaming simulation and analyses in in vitro low frequency sonophoresis

Low frequency sonophoresis (LFS) is a type of transdermal drug delivery method, which is useful for enhancing the permeation of hydrophobic and hydrophilic compounds across the skin. At present, the main ultrasonic effects of LFS include cavitation, microstreaming from bubbles, thermal effects, and recently bilayer sonophore effect, in which cavitation effect has been studied to interpret LFS principle since 2003. However, our experimental results show that the acoustic streaming is another factor in high-intensity acoustic input. Therefore, a calculation model is built up based on acoustic equation and turbulence k-ε model in terms of the finite element software COMSOL Multiphysics. In vitro LFS experiment consists of a Langevin-type ultrasonic transducer working at 21kHz and a Franz diffusion system, and Calcein permeations were measured at different acoustic intensities and distance between the transducer horn and skin. Calculated and experimental results demonstrate that the velocity of acoustic streaming in the donor is another important physical effect for the improvement of LFS. When the increase of acoustic intensity can enlarge the acoustic pressure and velocities of acoustic streaming, and enhance Calcein permeation at the same time; However, when the transducer horn was away from the skin surface, the acoustic pressure decreased but the velocity of acoustic streaming increased first and then decreased, and the latter varying tendency is in accordance with Calcein permeation change. Furthermore, calculated results of the line integral along the radial velocity show that spatial synthesis effect of acoustic streaming velocity may be the key factor for the enhancement of Calcein permeation other than the maximum velocity value. Therefore, it can be recognized that the acoustic streaming resulting from the transducer horn may be another important influence factor in in vitro LFS, especially in high acoustic intensity input (>1W/cm2).

Acoustic calculation in low frequency sonopheresis based on bubble dynamics

As a type of transdermal permeability enhancement, low frequency sonophoresis (LFS) has been studied for more than twenty years. The acoustic pressure in LFS is a crucial ultrasonic parameter to improve the permeability, but it is difficult to measure in the drug donor because of its small size and narrow shape. In this paper, an acoustic-piezoelectric coupling model is established based on bubble dynamics, which can be utilized to calculate the acoustic pressure distributions in LFS using a commercial finite element software called COMSOL multiphysics. The calculated results of acoustic pressure are in accordance with the measured values, so this model has great potential for theoretical analyses in acoustic fields of LFS. Calculated and experimental results show that the maximum acoustic pressure is under the transducer’s head, and the value dropped as away from the head due to the acoustic attenuation caused by cavitation; the transducer head should be closer to the skin to obtain larger acoustic pressure on the skin. Therefore, this model can be used to simulate and analyze the characteristics of acoustic fields, as a theoretical tool for the structural design of the ultrasonic transducer applied in LFS.

Thermal analyses of in vitro low frequency sonophoresis

As a type of transdermal drug delivery method, low frequency sonophoresis (LFS) has been investigated during the last twenty years and is currently being attempted in a clinical setting. However, the safety of low frequency ultrasound on humans has not been completely guaranteed with high-intensity ultrasound. Thermal damage, one of the challenges in the LFS process, e.g., burns, epidermal detachment and necrosis of tissues, hinders its widespread applications. To predict and impede the overheating problems in LFS, an acoustic-flow-thermal finite element method (FEM) based on COMSOL Multiphysics software is proposed in this paper to achieve thermal analyses. The temperature distribution and its rising curves in in vitro LFS are obtained by the FEM method and experimental measurements. Both simulated and experimental maximum temperatures are larger than the safety value (e.g., 42°C on human tissues) when the driving voltage is higher than 40V (5.5W input electric power), which proves that the overheating problem really exists in high-intensity ultrasound. Furthermore, the results show that the calculated temperature rising curves in in vitro LFS correspond to the experimental results, proving the effectiveness of this FEM method. In addition, several potential thermal influence factors have been studied, including a duty ratio and amplitude of the driving voltage, and liquid height in the donor, which may be helpful in restraining the temperature increase to limit thermal damage. According to the calculated and experimental results, the former two factors are sensitive to the rise in temperature, but a small scale of liquid volume increase can enhance the permeation of Calcein without obvious temperature change. Hence, the above factors can be synthetically utilized to restrain the rise in temperature with little sacrifice of permeation ability. So this acoustic-flow-thermal FEM method could be applied to an optimized LFS system design and simulating the thermal analyses of LFS in healthy human body in terms of safe thermal limits.

Effect of Combination of Low-Frequency Sonophoresis or Electroporation with Iontophoresis on the Mannitol Flux or Electroosmosis through Excised Skin.

In vitro permeation studies of mannitol were conducted across excised hairless mouse skin to determine and compare the enhancing effect of electroporation (EP) or sonophoresis (SP) combined with iontophoresis (IP) on the electroosmotic flow, and to analyze the enhancement mechanism of these combined methods. Mannitol flux was utilized as an index for the electroosmotic flow due to its low molecular weight and no electrorepulsion effect. The combination of SP and IP (SP/IP) resulted in an apparent increase of electroosmotic flow (no effect was sometimes observed by SP/IP), while that of EP and IP (EP/IP) had no synergistic enhancing effect on the electroosmosis. Next, the combined effect of tape-stripping (TS) and IP (TS/IP) was examined in a similar manner to clarify the difference between the SP/IP and EP/IP effects on electroosmosis. When the TS number increased from 0 to 3, the electroosmotic flow increased with the TS number. However, no further increase was observed when the TS number became more than 3, and the flow started to decrease when the TS number became 5. The electric charge of the skin surface was then measured after SP or TS application. When SP was applied, the skin surface charge became much more negative and the electroosmotic flow by SP/IP was markedly increased. Thus, an increase in the electroosmotic flow across the skin during IP application can be obtained not by EP and TS, but by SP. The combined use of SP and IP is a promising means for the enhanced skin delivery of non-electrolyte drugs.

Mechanistic study of decreased skin penetration using a combination of sonophoresis with sodium fluorescein-loaded PEGylated liposomes with d-limonene.

The effect of low frequency sonophoresis (SN, 20 kHz) on the skin transport of sodium fluorescein (NaFI)-loaded liposomes was investigated. An in vitro skin penetration study in open and blocked hair follicles was performed, and confocal laser scanning microscopy and scanning electron microscopy were used to visualize the penetration pathways. The results showed that SN significantly increased the flux of NaFI solution, whereas it significantly decreased the flux of NaFI-loaded polyethylene glycol-coated (PEGylated) liposomes with D-limonene (PL-LI). SN did not significantly affect the flux of NaFI-loaded conventional liposomes and PEGylated liposomes. In the blocked follicles, the flux of NaFI-loaded PL-LI both with and without SN decreased, indicating that NaFI-loaded PL-LI penetrated the skin via the transfollicular pathway. A confocal laser scanning microscopy image showed that in the skin without SN, the fluorescence intensity of NaFI-loaded PL-LI was observed in the skin and along the length of hair inside the skin, whereas in the skin with applied SN, the fluorescence intensity was detected only on the top of hair outside the skin. From scanning electron microscopy images, SN dislocated the corneocytes and reduced the deposition of PL-LI around hair follicles. These results revealed that SN may partially plug hair follicle orifices and reduce percutaneous absorption through the follicular pathway.