Relationships between skin's electrical impedance and permeability in the presence of chemical enhancers

Toward the eco-friendly cosmetic cleansing assisted by the micro-bubbly jet

While numerous types of chemical cosmetic cleansers have been presented, those with sensitive skin may still experience some irritation while using them. Moreover, the environmental issue of chemical agents has been documented repeatedly. To address these, we suggest the potential application of a micro-sized bubble-laden water jet to cleanse the cosmetics without (or less) using chemical detergents. We devised a venturi-type nozzle with a mesh and air holes capable of generating massive fine bubbles. By testing with the foundation and lip tint (known to be highly adhesive) coated on the synthetic leather and artificial skin surfaces, we measured that the cleansing performance of the bubbly jet is much better (even without the chemical agent) than the single-phase liquid jet. As a mechanism for enhanced removal, it is understood that the greater kinetic energy of the jet due to the acceleration of the effective liquid-air mixture flow and the direct bubble-cosmetic collisions play essential roles. We believe that the present results will spur the development of environment-friendly cleaning methods.

Nanoformulations for dermal delivery of imiquimod: The race of "soft" against "hard"

Imiquimod (IMQ) is an immunostimulating agent used in the treatment of basal cell carcinoma and actinic keratosis. Due to its low solubility and poor skin bioavailability, the dermal formulation of IMQ remains challenging. In analogy to tyre compounds used in Formula 1 racing, we compare four types of nanosystems belonging to three groups: (i) "hard" nanoparticles in the form of IMQ nanocrystals, (ii) "intermediate" nanoparticles in the form of liposomes and lipid nanocapsules, and (iii) "soft" nanoparticles in the form of a nanoemulsion based on oleic acid. The nanoemulsion and nanocrystals were able to incorporate the highest amount of IMQ (at least 2 wt%) compared to liposomes (0.03 wt%) and lipid nanocapsules (0.08 wt%). Regarding size, liposomes, and lipid nanocapsules were rather small (around 40 nm) whereas nanocrystals and nanoemulsion were larger (around 200 nm). All developed nanoformulations showed high efficiency to deliver IMQ into the skin tissue without undesirable subsequent permeation through the skin to acceptor. Especially, the 2 wt% IMQ nanoemulsion accumulated 129 μg/g IMQ in the skin, compared to 34 μg/g of a 5 wt% commercial cream. The effects of the respective nanoparticulate systems were discussed with respect to their possible diffusion kinetics (Brownian motion vs. settling) in the aqueous phase.

Liquid crystalline nanogel targets skin cancer via low-frequency ultrasound treatment

The potential of low-frequency ultrasound (LFU) combined with nanotechnology-based formulations in improving skin tumors topical treatment was investigated. The impact of solid lipid nanoparticles (SLN) and hydrophilic nanogels as coupling media on LFU-induced skin localized transport regions (LTR) and the penetration of doxorubicin (DOX) in LFU-pretreated skin was evaluated. SLN were prepared by the microemulsion technique and liquid crystalline nanogels using Poloxamer. In vitro, the skin was pretreated with LFU until skin resistivity of ∼1 KΩ.cm2 using the various coupling media followed by evaluation of DOX penetration from DOX-nanogel and SLN-DOX in skin layers. Squamous cell carcinoma (SCC) induced in mice was LFU-treated using the nanogel with the LFU tip placed 5 mm or 10 mm from the tumor surface, followed by DOX-nanogel application. LFU with nanogel coupling achieved larger LTR areas than LFU with SLN coupling. In LFU-pretreated skin, DOX-nanogel significantly improved drug penetration to the viable epidermis, while SLN-DOX hindered drug transport through LTR. In vivo, LFU-nanogel pretreatment with the 10 mm tip distance induced significant tumor inhibition and reduced tumor cell numbers and necrosis. These findings suggest the importance of optimizing nanoparticle-based formulations and LFU parameters for the clinical application of LFU technology in skin tumor treatment.

Electrical Bioimpedance Analysis for Evaluating the Effect of Pelotherapy on the Human Skin: Methodology and Experiments

BACKGROUND

Pelotherapy is the traditional procedure of applying curative muds on the skin's surface-shown to have a positive effect on the human body and cure illnesses. The effect of pelotherapy is complex, functioning through several mechanisms, and depends on the skin's functional condition. The current research objective was to develop a methodology and electrodes to assess the passage of the chemical and biologically active compounds of curative mud through human skin by performing electrical bioimpedance (EBI) analysis.

METHODS

The methodology included local area mud pack and simultaneous tap water compress application on the forearms with the comparison to the measurements of the dry skin. A custom-designed small-area gold-plated electrode on a rigid printed circuit board, in a tetrapolar configuration, was designed. A pilot study experiment with ten volunteers was performed.

RESULTS

Our results indicated the presence of an effect of pelotherapy, manifested by the varying electrical properties of the skin. Distinguishable difference in the measured real part of impedance (R) emerged, showing a very strong correlation between the dry and tap-water-treated skin (r = 0.941), while a poor correlation between the dry and mud-pack-treated skin (r = 0.166) appeared. The findings emerged exclusively in the frequency interval of 10 kHz …1 MHz and only for R.

CONCLUSIONS

EBI provides a promising tool for monitoring the variations in the electrical properties of the skin, including the skin barrier. We foresee developing smart devices for promoting the exploitation of spa therapies.

Investigation of β-caryophyllene as terpene penetration enhancer: Role of stratum corneum retention

Terpenes are usually used as penetration enhancers (PE) for transdermal drug delivery (TDD) of various molecules. However, TDD of hydrophilic macromolecules is becoming an urgent challenge due to their potent activities. The aim of this study was to investigate the potential application of β-caryophyllene (β-CP), a sequiterpene, as PE for TDD of hydrophilic macromolecules for the first time. Commonly used PEs, namely azone and 1,8-cineole (1,8-CN), were applied as controls. Transepidermal water loss (TEWL) analysis revealed that the reduction of skin barrier function caused by β-CP was reversible. Transdermal experiments showed that when skin was treated with β-CP or azone, there was a significant permeation-enhancing effect on fluorescein isothiocyanate (FITC) and FITC-dextran with different molecular weight (MW) of 4k or 10k. CLSM analysis confirmed that β-CP and azone can facilitate the penetration of FD-4k through epidermis and dermis. However, the cytotoxicity of azone against epidermal keratinocytes was significantly higher than β-CP and 1,8-CN. Additionally, application of β-CP and 1,8-CN didn't increase erythema index (EI) but the EI values of azone group increased significantly and irreversibly, indicating the high biocompatibility of the natural terpenes. β-CP had better permeation-enhancing effect and higher stratum corneum (SC) retention than 1,8-CN due to its increased carbon chain length and lipophilicity, as further demonstrated by molecular dynamics (MD) simulation studies. Skin electrical resistance (SER) and attenuated total reflection fourier transform infrared spectroscopy (ATR-FTIR) studies revealed a significant interfering effect of β-CP on SC lipids. Taken together, β-CP exhibited significant penetration enhancement of hydrophilic macromolecules due to its SC retention and SC lipid fluidization ability.

Design of hydrogel-based wearable EEG electrodes for medical applications

The electroencephalogram (EEG) is considered to be a promising method for studying brain disorders. Because of its non-invasive nature, subjects take a lower risk compared to some other invasive methods, while the systems record the brain signal. With the technological advancement of neural and material engineering, we are in the process of achieving continuous monitoring of neural activity through wearable EEG. In this article, we first give a brief introduction to EEG bands, circuits, wired/wireless EEG systems, and analysis algorithms. Then, we review the most recent advances in the interfaces used for EEG recordings, focusing on hydrogel-based EEG electrodes. Specifically, the advances for important figures of merit for EEG electrodes are reviewed. Finally, we summarize the potential medical application of wearable EEG systems.

Ionic Liquid-Mediated Transdermal Delivery of Thrombosis-Detecting Nanosensors

Blood clotting disorders such as pulmonary embolism are associated with high morbidity and mortality. A large portion of thrombotic events occur postoperative and after hospital discharge. Therefore, easily applicable, noninvasive, and long-term monitoring of thrombosis occurrence is critical for urgent clinical intervention. Here, the use is proposed of ionic liquids as a skin transport facilitator to deliver thrombin-sensitive nanosensors that enable prolonged monitoring of pulmonary embolism. Co-formulation of nanosensors with choline and geranic acid (CAGE) ionic liquids demonstrates significant transdermal diffusion into the dermis of the skin and provides sustained release into the blood throughout 72 h. Upon reaching the systemic circulation, the nanosensors release reporter molecules into the urine by responding to activation of the clotting cascade and retain a diagnostic power for 24 h in an acute pulmonary embolism mouse model. These results demonstrate a proof-of-concept disease monitoring system that can be topically applied by patients and potentially reduce mortality and high cost of hospitalization.

Hydrogels and Cubic Liquid Crystals for Non-Invasive Sampling of Low-Molecular-Weight Biomarkers—An Explorative In Vivo Study

The molecular composition of human skin is altered due to diseases, which can be utilized for non-invasive sampling of biomarkers and disease diagnostics. For this to succeed, it is crucial to identify a sampling formulation with high extraction efficiency and reproducibility. Highly hydrated skin is expected to be optimal for increased diffusion of low-molecular-weight biomarkers, enabling efficient extraction as well as enhanced reproducibility as full hydration represents a well-defined endpoint. Here, the aim was to explore water-based formulations with high water activities, ensuring satisfactory skin hydration, for non-invasive sampling of four analytes that may serve as potential biomarkers, namely tryptophan, tyrosine, phenylalanine, and kynurenine. The included formulations consisted of two hydrogels (chitosan and agarose) and two different liquid crystalline cubic phases based on the polar lipid glycerol monooleate, which were all topically applied for 2 h on 35 healthy subjects in vivo. The skin status of all sampling sites was assessed by electrical impedance spectroscopy and transepidermal water loss, enabling explorative correlations between biophysical properties and analyte abundancies. Taken together, all formulations resulted in the successful and reproducible collection of the investigated biomarkers. Still, the cubic phases had an extraction capacity that was approximately two times higher compared to the hydrogels.

N-Alkylmorpholines: Potent Dermal and Transdermal Skin Permeation Enhancers

Transdermal drug delivery is an attractive non-invasive method offering numerous advantages over the conventional routes of administration. The main obstacle to drug transport is, however, the powerful skin barrier that needs to be modulated, for example, by transdermal permeation enhancers. Unfortunately, there are still only a few enhancers showing optimum properties including low toxicity and reversibility of enhancing effects. For this reason, we investigated a series of new N-alkylmorpholines with various side chains as potential enhancers in an in vitro permeation study, using three model permeants (theophylline, indomethacin, diclofenac). Moreover, electrical impedance, transepidermal water loss, cellular toxicity and infrared spectroscopy measurements were applied to assess the effect of enhancers on skin integrity, reversibility, toxicity and enhancers' mode of action, respectively. Our results showed a bell-shaped relationship between the enhancing activity and the hydrocarbon chain length of the N-alkylmorpholines, with the most efficient derivatives having 10-14 carbons for both transdermal and dermal delivery. These structures were even more potent than the unsaturated oleyl derivative. The best results were obtained for indomethacin, where particularly the C10-14 derivatives showed significantly stronger effects than the traditional enhancer Azone. Further experiments revealed reversibility in the enhancing effect, acceptable toxicity and a mode of action based predominantly on interactions with stratum corneum lipids.

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.

3D Printing-A "Touch-Button" Approach to Manufacture Microneedles for Transdermal Drug Delivery

Microneedles (MNs) represent the concept of attractive, minimally invasive puncture devices of micron-sized dimensions that penetrate the skin painlessly and thus facilitate the transdermal administration of a wide range of active substances. MNs have been manufactured by a variety of production technologies, from a range of materials, but most of these manufacturing methods are time-consuming and expensive for screening new designs and making any modifications. Additive manufacturing (AM) has become one of the most revolutionary tools in the pharmaceutical field, with its unique ability to manufacture personalized dosage forms and patient-specific medical devices such as MNs. This review aims to summarize various 3D printing technologies that can produce MNs from digital models in a single step, including a survey on their benefits and drawbacks. In addition, this paper highlights current research in the field of 3D printed MN-assisted transdermal drug delivery systems and analyzes parameters affecting the mechanical properties of 3D printed MNs. The current regulatory framework associated with 3D printed MNs as well as different methods for the analysis and evaluation of 3D printed MN properties are outlined.

Initial Method for Characterization of Tympanic Membrane Drug Permeability in Human Temporal Bones In Situ

Background and Introduction: Acute otitis media is the most common reason for a visit to the pediatrician, often requiring systemic administration of oral antibiotics. Local drug therapy applied to the middle ear could avoid side effects associated with systemic antibiotic administration, however in the majority of patients this would require drugs to diffuse across an intact tympanic membrane. Experimental methods for testing trans-tympanic drug flux in human tissues in situ would be highly valuable to guide drug therapy development for local drug delivery to the middle ear.

Materials and Methods: A total of 30 cadaveric human temporal bones were characterized by trans-tympanic impedance testing to determine how steps in tissue processing and storage might impact intactness of the tympanic membrane and thus suitability for use in studies of trans-tympanic drug flux. Ciprofloxacin drug solutions of varying concentrations were then applied to the lateral surface of the tympanic membrane in eight samples, and middle ear aspirate was collected over the following 48 h to evaluate trans-tympanic flux to the middle ear.

Results: Tissue processing steps that involved extensive tissue manipulation were consistently associated with evidence of microperforations in the tympanic membrane tissue. Maintaining the tympanic membrane in situ within the temporal bone, while using an otologic drill to obtain transmastoid access to the middle ear, was demonstrated as a reliable, non-damaging technique for accessing both lateral and medial surfaces for trans-tympanic flux testing. Results in these bones demonstrated trans-tympanic flux of ciprofloxacin when administered at sufficiently high concentration.

Discussion and Conclusion: The study describes key techniques and best practices, as well as pitfalls to avoid, in the development of a model for studying trans-tympanic drug flux in human temporal bones in situ. This model can be a valuable research tool in advancing progress toward eventual clinical studies for trans-tympanic drug delivery to the middle ear.

A thermal activated and differential self-calibrated flexible epidermal biomicrofluidic device for wearable accurate blood glucose monitoring

This paper reports a flexible electronics-based epidermal biomicrofluidics technique for clinical continuous blood glucose monitoring, overcoming the drawback of the present wearables, unreliable measurements. A thermal activation method is proposed to improve the efficiency of transdermal interstitial fluid (ISF) extraction, enabling extraction with a low current density to notably reduce skin irritation. An Na⁺ sensor and a correction model are proposed to eliminate the effect of individual differences, which leads to fluctuations in the amount of ISF extraction. An electrochemical sensor with a 3D nanostructured working electrode surface is designed to enable precise in situ glucose measurement. A differential structure is proposed to eliminate the effect of passive perspiration, which leads to inaccurate blood glucose prediction. Fabrications of the epidermal biomicrofluidic device including formation of flexible electrodes, nanomaterial modification, and enzyme immobilization are fully realized by inkjet printing to enable facile manufacturing with low cost, which benefits practical production.

Development of curcumin-loaded composite phospholipid ethosomes for enhanced skin permeability and vesicle stability

Ethosomes are widely applied as the carriers for the transdermal delivery of hydrophobic and hydrophilic drugs. Herein, curcumin-loaded ethosomes (CE) with different phospholipid composition were formulated and thoroughly compared. A significant interaction between the unsaturated phosphatidylcholine (PC) and saturated hydrogenated phosphatidylcholine (HPC) was found by molecular simulation and differential scanning calorimetry (DSC), which led to the reduction of PC peroxidation with the presence of HPC. Subsequently, the composite phospholipid ethosomes containing curcumin were prepared for the first time to evaluate their properties in comparison with the conventional ethosomes composed of PC (CE-P) or HPC (CE-H). CE with PC/HPC ratio of 1:1 (CE-P1H1) with the best vesicle stability and flexibility significantly decreased the uptake by HaCaT cells compared to CE-H and free curcumin, indicating reduced skin cell toxicity. Compared with free curcumin, CE-P1H1 had the highest transdermal efficiency (p < 0.001), followed by CE-P (p < 0.05), partly due to the fact that CE-P1H1 could disturb lipid domain of stratum corneum (SC). Moreover, CE-P1H1 was found to promote curcumin for deep penetration of the skin via the hair follicles route. Our study has shown that using composite phospholipid ethosomes as lipid vesicular carriers could enhance transdermal penetration of drugs and increase in the vesicle stability.

Correlations Between Skin Barrier Integrity and Delivery of Hydrophilic Molecules in the Presence of Penetration Enhancers

PURPOSE

We investigated the potential correlations between skin barrier integrity and hydrophilic drugs distribution in skin in the presence of different types of penetration enhancers (PEs) and their combinations.

METHODS

We measured skin conductivity to evaluate skin barrier integrity before and after the topical application of different chemical PEs, physical PE, peptide PE and their combinations in vitro. We also investigated their effect on the skin distribution profiles of two hydrophilic model drugs, Fluorescein sodium (376 Da) and Fluorescein isothiocyanate-dextrans 10 (10 KDa).

RESULTS

The physical PE significantly increased the skin conductivity compared to all other PEs, while the peptide PE had no effect on it. The drug deposition in different skin layers was not only dependent on PE applied but also its own molecular weight. We further found two excellent correlations: one (R² = 0.9388) between skin barrier integrity and total skin absorption of FNa and another one(R² = 0.9212) between skin barrier integrity and the deposition of FNa in dermis and receptor in presence of chemical or physical PEs and their combinations.

CONCLUSIONS

The total skin absorption or the deposition in dermis and receptor of small hydrophilic drug in the presence of chemical and physical PEs and their combinations show a good correlation with skin barrier integrity. However, such correlations hold true neither for large hydrophilic drug nor for peptide PE. All good relationships found in this work will allow screening suitable PEs or combinations by measuring the skin conductivity induced by corresponding PEs. Graphical Abstract The total skin absorption of small hydrophilic drug shows a good correlation with skin barrier integrity in the presence of chemical and physical penetration enhancers and their combinations. However, such a correlation hold true neither for large hydrophilic drug nor for peptide penetration enhancer.

Topical Application of Exosomes Derived from Human Umbilical Cord Mesenchymal Stem Cells in Combination with Sponge Spicules for Treatment of Photoaging

Purpose

The topical application of exosomes secreted by mesenchymal stem cells (MSC-Exos) on the skin is a very new and interesting topic in the medical field. In this study, we aimed to investigate whether marine sponge Haliclona sp. spicules (SHSs) could effectively enhance the skin delivery of human umbilical cord-derived MSC-Exos (hucMSC-Exos), and further evaluate the topical application of hucMSC-Exos combined with SHSs in rejuvenating photoaged mouse skin.

Materials and Methods

SHSs were isolated from the explants of sponge Haliclona sp. with our proprietary method, and hucMSC-Exos were prepared from the conditioned medium of hucMSCs using ultracentrifugation. The effects of SHSs on the skin penetration of fluorescently labeled hucMSC-Exos were determined using confocal microscopy in vitro (porcine skin) and in vivo (mouse skin). The therapeutic effects of hucMSC-Exos coupled with SHSs against UV-induced photoaging in mice were assessed by using microwrinkles analysis, pathohistological examination and real-time RT-PCR. We also tested the skin irritation caused by the combination of hucMSC-Exos and SHSs in guinea pigs.

Results

In vitro results showed that hucMSC-Exos could not readily penetrate through porcine skin by themselves. However, SHSs increased the skin absorption of exosomes by a factor of 5.87 through creating microchannels. Similar penetration enhancement of hucMSC-Exos was observed after SHSs treatment in mice. The combined use of hucMSC-Exos and SHSs showed significant anti-photoaging effects in mice, including reducing microwrinkles, alleviating histopathological changes, and promoting the expression of extracellular matrix constituents, whereas hucMSC-Exos alone produced considerably weaker effects. Skin irritation test showed that the combination of hucMSC-Exos and SHSs caused slight irritation, and the skin recovered shortly.

Conclusion

SHSs provide a safe and effective way to enhance the skin delivery of MSC-Exos. Moreover, the combination of MSC-Exos and SHSs may be of much use in the treatment of photoaging.

Esters of terpene alcohols as highly potent, reversible, and low toxic skin penetration enhancers

Skin penetration/permeation enhancers are compounds that improve (trans)dermal drug delivery. We designed hybrid terpene-amino acid enhancers by conjugating natural terpenes (citronellol, geraniol, nerol, farnesol, linalool, perillyl alcohol, menthol, borneol, carveol) or cinnamyl alcohol with 6-(dimethylamino)hexanoic acid through a biodegradable ester linker. The compounds were screened for their ability to increase the delivery of theophylline and hydrocortisone through and into human skin ex vivo. The citronellyl, bornyl and cinnamyl esters showed exceptional permeation-enhancing properties (enhancement ratios up to 82) while having low cellular toxicities. The barrier function of enhancer-treated skin (assessed by transepidermal water loss and electrical impedance) recovered within 24 h. Infrared spectroscopy suggested that these esters fluidized the stratum corneum lipids. Furthermore, the citronellyl ester increased the epidermal concentration of topically applied cidofovir, which is a potent antiviral and anticancer drug, by 15-fold. In conclusion, citronellyl 6-(dimethylamino)hexanoate is an outstanding enhancer with an advantageous combination of properties, which may improve the delivery of drugs that have a limited ability to cross biological barriers.

Skin delivery of hyaluronic acid by the combined use of sponge spicules and flexible liposomes

We demonstrated that the topical combined use of sponge Haliclona sp. spicules (SHS) and flexible liposomes (FL), referred to as SFLS (SHS-Flexible Liposomes combined System), can result in synergy to improve the skin absorption and deposition of hyaluronic acid (HA), especially in deep skin layers, both in vitro and in vivo. SHS treatment can result in skin micro-channels which are continuous, deep enough (48.6 ± 13.5 μm) and available in large quantities (850 ± 125 micro-channels per mm2). These micro-channels gradually closed up in 120 h and also allowed the intact vesicles of flexible liposomes and vesicle-bound or vesicle-encapsulated HA to penetrate into the skin-deep layers under the driving force of transdermal osmotic gradients. Specifically, SFLS topical application enhanced the penetration of FITC-HA (MW: 250 kDa) into porcine skin in vitro up to 23.2 ± 3.7%, which is 19.4 ± 3.1-fold (p < 0.001) that of a Phosphate Buffered Saline (PBS) group, 3.4 ± 0.5-fold (p < 0.01) that of an SHS group and 3.6 ± 0.6-fold (p < 0.01) that from the combined use of a Dermaroller and flexible liposomes. Moreover, SFLS can lead to significantly enhanced skin deposition of HA in all skin layers, especially in deep skin layers: up to 86.8 ± 4.1% of HA absorbed by skin was accumulated in deep skin layers. The effectiveness of SFLS topical application was also confirmed in vivo by using BALB/c mice. In addition, a skin irritation and toxicity study showed that the SFLS treatment may cause very minimal redness and the skin can recover in a short time. In sum, the combined use of SHS and FL (SFLS) offers a promising strategy to safely and effectively improve the skin delivery of hydrophilic biomacromolecules such as HA.

Design Principles of Ionic Liquids for Transdermal Drug Delivery

Ionic liquids (ILs) and deep eutectic solvents have shown great promise in drug delivery applications. Choline-based ILs, in particular choline and geranic acid (CAGE), have been used to enhance the transdermal delivery of several small and large molecules. However, detailed studies outlining the design principles of ILs for transdermal drug delivery are still lacking. Using two model drugs of differing hydrophilicities, acarbose and ruxolitinib and 16 ILs, the dependence of skin penetration on the chemical properties of ILs is examined. First, the impact of ion stoichiometry on skin penetration of drugs is assessed using CAGE, which evidences that a molar ratio of 1:2 of choline to geranic acid yields the highest delivery. Subsequently, variants of CAGE are prepared using anions with structural similarity to geranic acid and cations with structural similarity to choline at a ratio of 1:2. Mechanistic studies reveal that the potency of ILs in enhancing transdermal drug delivery correlates inversely with the inter-ionic interactions as determined by 2D NMR spectroscopy. Using this understanding, a new IL is designed, and it provides the highest delivery of ruxolitinib of all ILs tested here. Overall, these studies provide a generalized framework for optimizing ILs for enhancing skin permeability.

Effect of Chemical Permeation Enhancers on Skin Permeability: In silico screening using Molecular Dynamics simulations

Breaching of the skin barrier is essential for delivering active pharmaceutical ingredients (APIs) for pharmaceutical, dermatological and aesthetic applications. Chemical permeation enhancers (CPEs) are molecules that interact with the constituents of skin’s outermost and rate limiting layer stratum corneum (SC), and increase its permeability. Designing and testing of new CPEs is a resource intensive task, thus limiting the rate of discovery of new CPEs. In-silico screening of CPEs in a rigorous skin model could speed up the design of CPEs. In this study, we performed coarse grained (CG) molecule dynamics (MD) simulations of a multilayer skin lipid matrix in the presence of CPEs. The CPEs are chosen from different chemical functionalities including fatty acids, esters, and alcohols. A multi-layer in-silico skin model was developed. The CG parameters of permeation enhancers were also developed. Interactions of CPEs with SC lipids was studied in silico at three different CPE concentrations namely, 1% w/v, 3% w/v and 5% w/v. The partitioning and diffusion coefficients of CPEs in the SC lipids were found to be highly size- and structure-dependent and these dependencies are explained in terms of structural properties such as radial distribution function, area per lipid and order parameter. Finally, experimentally reported effects of CPEs on skin from the literature are compared with the simulation results. The trends obtained using simulations are in good agreement with the experimental measurements. The studies presented here validate the utility of in-silico models for designing, screening and testing of novel and effective CPEs.

Skin Electrical Resistance Measurement of Oxygen-Containing Terpenes as Penetration Enhancers: Role of Stratum Corneum Lipids

The measurement of skin electrical resistance (SER) has drawn a great deal of attention for the rapid screening of transdermal penetration enhancers (PEs). However, the mechanisms underlying the SER measurement are still unclear. This study was to investigate the effects and mechanisms of seven oxygen-containing terpenes on the SER kinetics. Stratum corneum (SC) lipids were proved to play a key role in SER measurement. Then, the factors affecting the SER measurement were optimized. By the determination of SER kinetics, cyclic terpenes (1,8-cineole, terpinen-4-ol, menthol and α-terpineol) were demonstrated to possess higher enhancement ratio (ER) values compared with linear terpenes (linalool, geraniol and citral). For the first time, the linear correlation was found between ER of terpenes and the interaction energy of terpene⁻ceramide complexes revealed by molecular simulation. The attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) analysis revealed that the effect of cyclic terpenes on SC lipid arrangement was obviously stronger than that of linear terpenes. In addition, by evaluating HaCaT skin cell viability, little difference was found between the toxicities of cyclic and linear terpenes. In conclusion, measurement of SER could be a feasible approach for the efficient evaluation of the PEs that mainly act on SC lipids.

Characterization of cavitation-radiated acoustic power using diffraction correction

A method is developed for compensating absolute pressure measurements made by a calibrated passive cavitation detector (PCD) to estimate the average acoustic power radiated from a region of interest (ROI) defined to encompass all cavitating bubbles. A diffraction correction factor for conversion of PCD-measured pressures to cavitation-radiated acoustic power per unit area or volume is derived as a simple analytic expression, accounting for position- and frequency-dependent PCD sensitivity. This approach can be applied to measurements made by any PCD without precise knowledge of the number, spatial, or temporal distribution of cavitating bubbles. The diffraction correction factor is validated in simulation for a wide range of ROI dimensions and frequencies. The correction factor is also applied to emission measurements obtained during in vitro ultrasound-enhanced sonophoresis experiments, allowing comparison of stable cavitation levels between therapeutic configurations with different source center frequencies. Results incorporating sonication at both 0.41 and 2.0 MHz indicate that increases in skin permeability correlate strongly with the acoustic power of subharmonic emissions radiated per unit skin area.

Transdermal insulin delivery using choline-based ionic liquids (CAGE)

Transdermal delivery of pharmaceuticals using ionic liquids and deep eutectic solvents (DES) has attracted significant interest due to the inherent tunability of the molecules and their capacity to transport large molecules across the skin. Several key properties of DESs including viscosity, miscibility and possible transport enhancement can be controlled through the choice of ions and their ratio in DES. Herein we investigate the effect of cation/anion ratio using Choline and Geranic acid (CAGE) based DES. We synthesized variants of CAGE by controlling the ratio of Choline to Geranic acid over a range of 1:4 to 2:1. Physicochemical properties including viscosity, conductivity and diffusivity were measured. Effect of CAGE on skin permeability was assessed using insulin in ex vivo porcine skin. Each variant was found to have distinct properties, including interionic interactions, viscosity, and conductivity. In addition, the effect of CAGE on stratum corneum lipids, as assessed by FTIR, was dependent on its composition. Transport enhancement was also composition-dependent, as the variants containing excess geranic acid (1:2 and 1:4, but not geranic acid alone) exhibited higher insulin delivery into the dermis compared to other compositions, demonstrating the importance of investigating the effect of ion ratios on drug delivery.

Effects of Ceramide and Dihydroceramide Stereochemistry at C-3 on the Phase Behavior and Permeability of Skin Lipid Membranes

Ceramides (Cer) are key components of the skin permeability barrier. Sphingosine-based CerNS and dihydrosphingosine-based CerNdS (dihydroCer) have two chiral centers; however, the importance of the correct stereochemistry in the skin barrier Cer is unknown. We investigated the role of the configuration at C-3 of CerNS and CerNdS in the organization and permeability of model skin lipid membranes. Unnatural l-threo-CerNS and l-threo-CerNdS with 24-C acyl chains were synthesized and, along with their natural d-erythro-isomers, incorporated into membranes composed of major stratum corneum lipids (Cer, free fatty acids, cholesterol, and cholesteryl sulfate). The membrane microstructure was investigated by X-ray powder diffraction and infrared spectroscopy, including deuterated free fatty acids. Inversion of the C-3 configuration in CerNS and CerNdS increased phase transition temperatures, had no significant effects on lamellar phases, but also decreased the proportion of orthorhombic packing and decreased lipid mixing in the model membranes. These changes in membrane organization resulted in membrane permeabilities that ranged from unchanged to 5-fold higher (depending on the permeability markers, namely, water loss, electrical impedance, flux of theophylline, and flux of indomethacin) compared to membranes with natural CerNS/NdS isomers. Thus, the physiological d-erythro stereochemistry of skin Cer and dihydroCer appears to be essential for their correct barrier function.

Ionic liquids for addressing unmet needs in healthcare

Advances in the field of ionic liquids have opened new applications beyond their traditional use as solvents into other fields especially healthcare. The broad chemical space, rich with structurally diverse ions, and coupled with the flexibility to form complementary ion pairs enables task-specific optimization at the molecular level to design ionic liquids for envisioned functions. Consequently, ionic liquids now are tailored as innovative solutions to address many problems in medicine. To date, ionic liquids have been designed to promote dissolution of poorly soluble drugs and disrupt physiological barriers to transport drugs to targeted sites. Also, their antimicrobial activity has been demonstrated and could be exploited to prevent and treat infectious diseases. Metal-containing ionic liquids have also been designed and offer unique features due to incorporation of metals. Here, we review application-driven investigations of ionic liquids in medicine with respect to current status and future potential.

Assessment of skin permeability to topically applied drugs by skin impedance and admittance

OBJECTIVE

Pharmacokinetic and pharmacodynamic studies of topically applied drugs are commonly performed by sampling of interstitial fluid with dermal open flow microperfusion and subsequent analysis of the samples. However, the reliability of results from the measured concentration-time profile of the penetrating drug suffers from highly variable skin permeability to topically applied drugs that is mainly caused by inter- and intra-subject variations of the stratum corneum. Thus, statistically significant results can only be achieved by performing high numbers of experiments. To reduce the expenditures needed for such high experiment numbers we aimed to assess the correlation between skin permeability and skin impedance/skin admittance.

APPROACH

We performed an ex vivo drug penetration study with human skin, based on the hypothesis that inter-subject variations of the respective concentration-time profiles can be correlated with variations of the passive electrical properties of the skin. Therefore, skin impedance and skin admittance were related to the skin permeability to the model drug Clobetasol-17-proprionate.

MAIN RESULTS

The measured low frequency skin impedance and the skin admittance correlated linearly with the drug concentration-time profiles from dermal sampling.

SIGNIFICANCE

Skin permeability can be assessed by measuring the passive electrical properties of the skin, which enables correction of skin permeability variations. This allows reduction of experiment numbers in future pharmacokinetic and pharmacodynamic studies with human skin ex vivo and in vivo and leads to diminished study costs.

Transdermal Permeation of Drugs in Various Animal Species

Excised human skin is utilized for in vitro permeation experiments to evaluate the safety and effect of topically-applied drugs by measuring its skin permeation and concentration. However, ethical considerations are the major problem for using human skin to evaluate percutaneous absorption. Moreover, large variations have been found among human skin specimens as a result of differences in age, race, and anatomical donor site. Animal skins are used to predict the in vivo human penetration/permeation of topically-applied chemicals. In the present review, skin characteristics, such as thickness of skin, lipid content, hair follicle density, and enzyme activity in each model are compared to human skin. In addition, intra- and inter-individual variation in animal models, permeation parameter correlation between animal models and human skin, and utilization of cultured human skin models are also descried. Pig, guinea pig, and hairless rat are generally selected for this purpose. Each animal model has advantages and weaknesses for utilization in in vitro skin permeation experiments. Understanding of skin permeation characteristics such as permeability coefficient (P), diffusivity (D), and partition coefficient (K) for each skin model would be necessary to obtain better correlations for animal models to human skin permeation.

Skin Delivery of Hydrophilic Biomacromolecules Using Marine Sponge Spicules

We report the development of sponge Haliclona sp. spicules, referred to as SHS, and its topical application in skin delivery of hydrophilic biomacromolecules, a series of fluorescein isothiocyanate-dextrans (FDs). SHS are silicious oxeas which are sharp-edged and rod-shaped (∼120 μm in length and ∼7 μm in diameter). SHS can physically disrupt skin in a dose-dependent manner and retain within the skin over at least 72 h, which allows sustained skin penetration of hydrophilic biomacromolecules. The magnitude of enhancement of FD delivery into skin induced by SHS treatment was dependent on its molecular weight. Specifically, SHS topical application enhanced FD-10 (MW: 10 kDa) penetration into porcine skin in vitro by 33.09 ± 7.16-fold compared to control group (p < 0.01). SHS dramatically increased the accumulation of FD-10 into and across the dermis by 62.32 ± 13.48-fold compared to the control group (p < 0.01). In vivo experiments performed using BALB/c mice also confirmed the effectiveness of SHS topical application; the skin absorption of FD-10 with SHS topical application was 72.14 ± 48.75-fold (p < 0.05) and 15.39 ± 9.91-fold (p < 0.05) higher than those from the PBS and Dermaroller microneedling, respectively. Further, skin irritation study and transepidermal water loss (TEWL) measurement using guinea pig skin in vivo indicated that skin disruption induced by SHS treatment is self-limited and can be recovered with time and efficiently. SHS can offer a safe, effective, and sustained skin delivery of hydrophilic biomacromolecules and presents a promising platform technology for a wide range of cosmetic and medical applications.

Potential of Stratum Corneum Lipid Liposomes for Screening of Chemical Skin Penetration Enhancers

The evaluation of effective skin chemical penetration enhancers (CPEs) is a crucial process in the development of transdermal and dermal formulations with the capacity to overcome the stratum corneum barrier. In the present study, we aimed to investigate the potential of stratum corneum lipid liposomes (SCLLs) as an alternative tool for the screening of various types and concentrations of CPEs. SCLLs were prepared using a thin-film hydration technique, and two types of fluorescent probes (sodium fluorescein [FL] or 1,6-diphenyl-1,3,5-hexatriene [DPH] were entrapped separately into SCLLs (FL-SCLL and DPH-SCLL, respectively). FL leakage from SCLLs as well as the fluidity of DPH-SCLLs were determined after incubating with various types of CPEs as a function of their concentrations. The obtained results showed a concentration-dependent relationship for most CPEs both for FL leakage and the fluidity of SCLLs. When observing these data in detail, however, the concentration profiles could be classified into five main categories depending on the mode of action of the CPEs. These results strongly suggest the usefulness of SCLLs for high-throughput screening of effective CPEs as well as the understanding of their possible mode of action, especially in the early stage of skin formulation development.

Galactosyl Pentadecene Reversibly Enhances Transdermal and Topical Drug Delivery

PURPOSE

To study new skin penetration/permeation enhancers based on amphiphilic galactose derivatives.

METHODS

Two series of alkyl and alkenyl galactosides were synthesized and evaluated for their enhancing effect on transdermal/topical delivery of theophylline (TH), hydrocortisone (HC) and cidofovir (CDV), reversibility of their effects on transepidermal water loss (TEWL) and skin impedance, interaction with the stratum corneum using infrared spectroscopy, and cytotoxicity on keratinocytes and fibroblasts.

RESULTS

Initial evaluation identified 1-(α-D-galactopyranosyl)-(2E)-pentadec-2-ene A15 as a highly potent enhancer - it increased TH and HC flux through human skin 8.5 and 5 times, respectively. Compound A15 increased the epidermal concentration of a potent antiviral CDV 7 times over that reached by control and Span 20 (an established sugar-based enhancer). Infrared spectroscopy of human stratum corneum indicated interaction of A15 with skin barrier lipids but not proteins. These effects of A15 on the skin barrier were reversible (both TEWL and skin impedance returned to baseline values within 24 h after A15 had been removed from skin). In vitro toxicity of A15 on HaCaT keratinocytes and 3T3 fibroblasts was acceptable, with IC₅₀ values over 60 μM.

CONCLUSIONS

Galactosyl pentadecene A15 is a potent enhancer with low toxicity and reversible action.

Transdermal Iontophoretic Delivery of Lysine-Proline-Valine (KPV) Peptide Across Microporated Human Skin

Lysine-proline-valine (KPV) is a C-terminal peptide fragment of α-melanocyte stimulating hormone with potent anti-inflammatory properties. Present study investigates various transdermal enhancement strategies such as iontophoresis (ITP), microneedles (MN), and their combination (ITP + MN) on KPV delivery across dermatomed human skin. KPV attains a positive charge at pH less than 7.0, thus anodal ITP was used. The influence of current strength, KPV concentration, and duration of current application on the KPV delivery was investigated. At defined ITP parameters, the influence of MN on KPV delivery (ITP + MN) across skin was also determined. KPV permeation was less than detectable levels (limit of detection, 0.01 μg/mL) by simple passive diffusion. However, KPV permeation was increased to 4.4 μg/cm²/h by MN treatment. Furthermore, ITP and ITP + MN increased the permeation rate by 8 and 35 fold, respectively, as compared to MN alone. The skin retention levels of KPV by MN, ITP, and ITP + MN were increased by 5, 10, and 10 fold, respectively, as compared to passive diffusion. Confocal studies indicate that fluorescein isothiocyanate-labeled KPV migrated through the stratum corneum, along the microchannels and into the lower epidermal tissue because the fluorescence was observed beyond the depth of 100 μm.

High-Throughput Screening of Potential Skin Penetration-Enhancers Using Stratum Corneum Lipid Liposomes: Preliminary Evaluation for Different Concentrations of Ethanol

In this study, we developed a technique for high-throughput screening (HTS) of skin penetration-enhancers using stratum corneum lipid liposomes (SCLLs). A fluorescent marker, sodium fluorescein (FL), entrapped in SCLLs was prepared to provide a preliminary evaluation of the effect of different concentrations of ethanol on the disruption effect of SCLLs, which is an alternative for skin penetration-enhancing effects. In addition, SCLLs containing a fluorescent probe (DPH, TMA-DPH, or ANS) were also prepared and utilized to investigate SCLL fluidity. The results using SCLL-based techniques were compared with conventional skin permeation and skin impedance test using hairless rat skin. The obtained correlations were validated between FL leakage, SCLL fluidity with various probes, or skin impedance and increases in the skin permeation enhancement ratio (ER) of caffeine as a model penetrant. As a result, FL leakage and SCLL fluidity using ANS were considered to be good indices for the skin penetration-enhancing effect, suggesting that the action of ethanol on the SC lipid and penetration-enhancing is mainly on the polar head group of intercellular lipids. In addition, this screening method using SCLL could be utilized as an alternative HTS technique for conventional animal tests. Simultaneously, the method was found to be time-saving and sensitive compared with a direct assay using human and animal skins.

Microneedle characterisation: the need for universal acceptance criteria and GMP specifications when moving towards commercialisation

With interest in microneedles as a novel drug transdermal delivery system increasing rapidly since the late 1990s (Margetts and Sawyer Contin Educ Anaesthesia Crit Care Pain. 7(5):171-76, 2007), a diverse range of microneedle systems have been fabricated with varying designs and dimensions. However, there are still very few commercially available microneedle products. One major issue regarding microneedle manufacture on an industrial scale is the lack of specific quality standards for this novel dosage form in the context of Good Manufacturing Practice (GMP). A range of mechanical characterisation tests and microneedle insertion analysis techniques are used by researchers working on microneedle systems to assess the safety and performance profiles of their various designs. The lack of standardised tests and equipment used to demonstrate microneedle mechanical properties and insertion capability makes it difficult to directly compare the in use performance of candidate systems. This review highlights the mechanical tests and insertion analytical techniques used by various groups to characterise microneedles. This in turn exposes the urgent need for consistency across the range of microneedle systems in order to promote innovation and the successful commercialisation of microneedle products.

Development of edge-activated liposomes for siRNA delivery to human basal epidermis for melanoma therapy

Delivery of macromolecules such as siRNA into cells that reside in the basal epidermis of the skin is a major challenge due to the transport barriers that need to be overcome. siRNAs have potential therapeutic applications in various dermatological diseases such as psoriasis, atopic dermatitis, and cancer. Unfortunately, a low permeability of siRNA through the stratum corneum and epidermis has significantly limited its use for topical application. The objective of this study was to develop a topical siRNA delivery system that can permeate through the stratum corneum and viable epidermis and efficiently deposit therapeutic levels of siRNA to the basal epidermis/upper dermis where melanoma cells reside. To achieve this objective, a series of liposome compositions that contained various concentrations of edge activator in their structures were prepared and then complexed with siRNA at different ratios to generate a small library of liposome-siRNA complexes (lipoplexes) with different physicochemical properties. In this study we used melanoma as a disease model. Through use of quantitative imaging analysis, we identified the necessary design parameters for effective permeation of lipoplexes through the skin layers and deposition at the upper dermis. The ability of the formulated lipoplexes to internalize into melanoma cells, knockdown the expression of the BRAF protein and induce cell death in melanoma cells was studied by fluorescent microscopy, in-cell immunofluorescence assay and WST-1 cell proliferation assay. By providing direct quantitative and qualitative microscopy evidence, the results of this study demonstrate for the first time that the passive delivery of an edge-activated liposomal formulation can effectively carry siRNA through the stratum corneum and deposit it at the lower epidermis/upper dermis.

A microneedle-based method for the characterization of diffusion in skin tissue using doxorubicin as a model drug

Hollow microneedles can overcome the stratum corneum (SC) barrier and deposit a compound directly into the viable epidermis or the dermis, unlike adhesive patches that rely on drug diffusion across the SC. The traditional one-dimensional methods used to study the diffusivity of drugs across the skin layers are not very accurate for hollow microneedles, since the ejection of compounds out of microneedle lumens resembles a point-source spreading in all directions and is highly dependent on injection depth. This paper presents a technique that is useful for studying drug injection using hollow microneedles at various depths below the SC. This technique uses confocal microscopy to image the distribution of a fluorescent compound in the skin after injection. The fluorescence distribution in the skin is observed over time and applied to a spherical Gaussian diffusion model for limited source diffusion to determine the diffusion coefficient of the compound in the skin. Applied to freshly excised pig skin, the diffusion coefficient for the anti-cancer drug doxorubicin was measured as 4.61 × 10(-9) cm(2)/s, while the diffusion coefficient in previously refrigerated or frozen pig skin was 1.31 × 10(-8) cm(2)/s and 4.21 × 10(-8) cm(2)/s, respectively. Our data suggests that skin storage conditions can substantially alter the diffusion of drugs. The use of refrigerated and, even more so, previously frozen skin should be avoided for quantitative transdermal drug delivery studies.

Engineering Stent Based Delivery System for Esophageal Cancer Using Docetaxel

Esophageal cancer patients are often diagnosed as "advanced" cases. These patients are subjected to palliative stenting using self-expanding metallic stents (SEMS) to maintain oral alimentation. Unfortunately, SEMS get reoccluded due to tumor growth, in and over the stent struts. To investigate potential solutions to this problem, docetaxel (DTX) delivery films were prepared using PurSil AL 20 (PUS), which can be used as a covering material for the SEMS. Drug-polymer miscibility and interactions were studied. Bilayer films were prepared by adhering the blank film to the DTX loaded film in order to maintain the unidirectional delivery to the esophagus. In vitro release and the local DTX delivery were studied using in vitro permeation experiments. It was found that DTX and PUS were physically and chemically compatible. The bilayer films exhibited sustained release (>30 days) and minimal DTX permeation through esophageal tissues in vitro. The rate-determining step for the DTX delivery was calculated. It was found that >0.9 fraction of rate control lies with the esophageal tissues, suggesting that DTX delivery can be sustained for longer periods compared to the in vitro release observed. Thus, the bilayer films can be developed as a localized sustained delivery system in combination with the stent.

Enhanced epidermal localization of topically applied steroids using SPACE™ peptide

The balance of efficacy and safety of topical corticosteroids (TCs) depends on their ability to penetrate into and be retained within the skin. Here, we evaluated the ability of SPACE™ peptide to enhance epidermal delivery and localization of three model TCs. In vitro and in vivo skin penetration studies were performed to evaluate penetration of TCs into and across the skin in the presence of various formulations of SPACE™ peptide. Topical formulations of corticosterone containing free SPACE™ peptide produced significantly enhanced epidermal penetration and localization. Ratio of drug deposition in the skin and receiver (efficacy/safety, indicative of ratio of local to systemic uptake) exhibited higher values for SPACE™ peptide-based formulation as compared to aqueous and hydroethanolic solutions and Cortizone™ cream. Mass spectrometry analysis showed that SPACE™ peptide associates with corticosterone, which may explain its enhanced retention effect. SPACE™ peptide also enhanced dermal retention of two more TCs (hydrocortisone and triamcinolone acetonide) compared to the vehicle control. An in vivo study in mice further established the ability of SPACE™ peptide to enhance skin retention of hydrocortisone without producing elevated blood concentrations. These results show that SPACE™ peptide is an effective additive to the formulation for enhanced skin localization of topical steroids.

Topical delivery of Cyclosporine A into the skin using SPACE-peptide

Cyclosporine A (CsA) is used for the treatment of psoriasis; however systemic administration of CsA is potentially life threatening and there are long-term side effects. Topical application of CsA has the potential to overcome this hurdle; however, its use is limited by poor water solubility and low permeability. Here, we report the use of a physical mixture of SPACE-peptide and CsA in an aqueous ethanol solution to enhance the dermal absorption of the drug. The aqueous ethanol solution (hydroethanolic solution) containing 5mg/mL CsA and 50mg/mL of free SPACE-peptide (SP50) delivered about 30% of topically applied CsA into the porcine skin in vitro and led to an approximately 9-fold (p<0.01) increase in accumulation in viable epidermis compared to the hydroethanolic solution without SPACE-peptide (control group). In vivo biodistribution and pharmacokinetic studies performed using SKH1 hairless mice also confirmed the efficacy of SP50 in dermal delivery of CsA and also demonstrated its advantages over other routes in terms of minimizing its systemic absorption. Topical application of SP50 significantly increased the localization of CsA in the target skin (113.1±13.6(μg/g)/mg) compared to all other groups (p<0.01). In addition, SP50 led to significantly higher skin/blood ratio (443.4±181.5) and skin/liver ratio (1059.5±110.8) of CsA compared to all other groups (p<0.01). The SP50 formulation reported here offers a promising approach for the dermal delivery of CsA.

Relations between acoustic cavitation and skin resistance during intermediate- and high-frequency sonophoresis

Enhanced skin permeability is known to be achieved during sonophoresis due to ultrasound-induced cavitation. However, the mechanistic role of cavitation during sonophoresis has been extensively investigated only for low-frequency (LFS, <100 kHz) applications. Here, mechanisms of permeability-enhancing stable and inertial cavitation were investigated by passively monitoring subharmonic and broadband emissions arising from cavitation isolated within or external to porcine skin in vitro during intermediate- (IFS, 100-700 kHz) and high-frequency sonophoresis (HFS, >1 MHz). The electrical resistance of skin, a surrogate measure of the permeability of skin to a variety of compounds, was measured to quantify the reduction and subsequent recovery of the skin barrier during and after exposure to pulsed (1 second pulse, 20% duty cycle) 0.41 and 2.0 MHz ultrasound over a range of acoustic powers (0-21.7 W) for 30 min. During IFS, significant skin resistance reductions and acoustic emissions from cavitation were measured exclusively when cavitation was isolated outside of the skin. Time-dependent skin resistance reductions measured during IFS correlated significantly with subharmonic and broadband emission levels. During HFS, significant skin resistance reductions were accompanied by significant acoustic emissions from cavitation measured during trials that isolated cavitation activity either outside of skin or within skin. Time-dependent skin resistance reductions measured during HFS correlated significantly greater with subharmonic than with broadband emission levels. The reduction of the skin barrier due to sonophoresis was reversible in all trials; however, effects incurred during IFS recovered more slowly and persisted over a longer period of time than HFS. These results quantitatively demonstrate the significance of cavitation during sonophoresis and suggest that the mechanisms and post-treatment longevity of permeability enhancement due to IFS and HFS treatments are different.

Transdermal delivery of insulin by amidated pectin hydrogel matrix patch in streptozotocin-induced diabetic rats: effects on some selected metabolic parameters

PURPOSE

Studies in our laboratory are concerned with developing optional insulin delivery routes based on amidated pectin hydrogel matrix gel. We therefore investigated whether the application of pectin insulin (PI)-containing dermal patches of different insulin concentrations sustain controlled release of insulin into the bloodstream of streptozotocin (STZ)-induced diabetic rats with concomitant alleviation of diabetic symptoms in target tissues, most importantly, muscle and liver.

METHODS

Oral glucose test (OGT) responses to PI dermal matrix patches (2.47, 3.99, 9.57, 16.80 µg/kg) prepared by dissolving pectin/insulin in deionised water and solidified with CaCl2 were monitored in diabetic rats given a glucose load after an 18-h fast. Short-term (5 weeks) metabolic effects were assessed in animals treated thrice daily with PI patches 8 hours apart. Animals treated with drug-free pectin and insulin (175 µg/kg, s.c.) acted as untreated and treated positive controls, respectively. Blood, muscle and liver samples were collected for measurements of selected biochemical parameters.

RESULTS

After 5 weeks, untreated diabetic rats exhibited hyperglycaemia and depleted hepatic and muscle glycogen concentrations. Compared to untreated STZ-induced diabetic animals, OGT responses of diabetic rats transdermally applied PI patches exhibited lower blood glucose levels whilst short-term treatments restored hepatic and muscle glycogen concentrations. Plasma insulin concentrations of untreated diabetic rats were low compared with control non-diabetic rats. All PI treatments elevated plasma insulin concentrations of diabetic rats although the levels induced by high doses (9.57 and 16.80 µg/kg) were greater than those caused by low doses (2.47 and 3.99 µg/kg) but comparable to those in sc insulin treated animals.

CONCLUSIONS

The data suggest that the PI hydrogel matrix patch can deliver physiologically relevant amounts of pharmacologically active insulin.

NOVELTY OF THE WORK

A new method to administer insulin into the bloodstream via a skin patch which could have potential future applications in diabetes management is reported.