Transdermal delivery of heparin and low-molecular weight heparin using low-frequency ultrasound

Semi-invasive wearable clinic: Solution-processed smart microneedle electronics for next-generation integrated diagnosis and treatment

The integrated smart electronics for real-time monitoring and personalized therapy of disease-related analytes have been gradually gaining tremendous attention. However, human tissue barriers, including the skin barrier and brain-blood barrier, pose significant challenges for effective biomarker detection and drug delivery. Microneedle (MN) electronics present a promising solution to overcome these tissue barriers due to their semi-invasive structures, enabling effective drug delivery and target-analyte detection without compromising the tissue configuration. Furthermore, MNs can be fabricated through solution processing, facilitating large-scale manufacturing. This review provides a comprehensive summary of the recent three-year advancements in smart MNs development, categorized as follows. First, the solution-processed technology for MNs is introduced, with a focus on various printing technologies. Subsequently, smart MNs designed for sensing, drug delivery, and integrated systems combining diagnosis and treatment are separately summarized. Finally, the prospective and promising applications of next-generation MNs within mediated diagnosis and treatment systems are discussed.

A Conformable Ultrasound Patch for Cavitation-Enhanced Transdermal Cosmeceutical Delivery

Increased consumer interest in healthy-looking skin demands a safe and effective method to increase transdermal absorption of innovative therapeutic cosmeceuticals. However, permeation of small-molecule drugs is limited by the innate barrier function of the stratum corneum. Here, a conformable ultrasound patch (cUSP) that enhances transdermal transport of niacinamide by inducing intermediate-frequency sonophoresis in the fluid coupling medium between the patch and the skin is reported. The cUSP consists of piezoelectric transducers embedded in a soft elastomer to create localized cavitation pockets (0.8 cm² , 1 mm deep) over larger areas of conformal contact (20 cm² ). Multiphysics simulation models, acoustic spectrum analysis, and high-speed videography are used to characterize transducer deflection, acoustic pressure fields, and resulting cavitation bubble dynamics in the coupling medium. The final system demonstrates a 26.2-fold enhancement in niacinamide transport in a porcine model in vitro with a 10 min ultrasound application, demonstrating the suitability of the device for short-exposure, large-area application of sonophoresis for patients and consumers suffering from skin conditions and premature skin aging.

Tailored mechanosensitive nanogels release drugs upon exposure to different levels of stenosis

Owing to the unhealthy lifestyle and genetic susceptibility of today's population, atherosclerosis is one of the global leading causes of life-threatening cardiovascular diseases. Although a rapid intervention is required for severe blood vessel constrictions, a systemic administration of anticoagulant drugs is not the preferred method of choice as the associated risk of bleeding complications is high. In this study, we present mechanosensitive nanogels that exhibit tunable degrees of disintegration upon exposure to different levels of stenosis. Those nanogels can be further functionalized to encapsulate charged drug molecules such as heparin, and they efficiently release their cargo when passing stenotic constrictions; however, passive drug leakage in the absence of mechanical shear stress is very low. Furthermore, heparin molecules liberated from those mechanosensitive nanogels show a similar blood clot lysis efficiency as the free drug molecules, which demonstrates that drug encapsulation into those nanogels does not interfere with the functionality of the cargo. Thus, the hemocompatible and mechanoresponsive nanogels developed here represent a smart and efficient drug delivery platform that can offer safer solutions for vascular therapy.

Microneedle patch-assisted transdermal administration of recombinant hirudin for the treatment of thrombotic diseases

The painless microneedle patch (MNP), widely explored for transdermal drug delivery of macromolecules, can overcome the limitations of traditional administrations of protein and polypeptide anticoagulant drugs. We constructed a recombinant hirudin-loaded microneedle patch, suitable for patients with thrombotic diseases requiring long-term preventive medication. The recombinant hirudin-loaded dissoluble microneedle patch (RHDMNP) was created using a mold casting technique and polyvinylpyrrolidone and polyvinyl alcohol were used as the matrix material with a 1:1.2 ratio. We prepared bilayer RHDMNPs with pyramidal appearance and 0.37 N/needle strength. The intradermal dissolution height of the microneedle reached approximately 78.67% of the total height, and 68.12% of the drug was delivered into the skin. The 12-hour cumulative permeation of the MNP was 21.69 ± 3.90 μg/cm². The MNP showed a T_max of 1.5 h, C_max of 144 ± 71 ng/mL, and area under curve (AUC) of 495 ± 66 ng/mL·min compared to T_max of 0.5 h, C_max of 249 ± 89 ng/mL, and AUC of 944 ± 65 ng/mL·min for the subcutaneous injection group. Both in vivo and in vitro experiments showed that the RHDMNP exerted effective anticoagulant effects, prevented the incidence of acute pulmonary embolism, and revealed the potential for venous thrombosis prevention.

Combined effect of sonophoresis and a microemulsion on the dermal delivery of celecoxib

The aim of this study was to evaluate the intensity of sonophoresis at which the skin penetration of celecoxib was enhanced and to study the combined effects of sonophoresis and microemulsion application on the dermal delivery of celecoxib. The sonophoresis intensity that provided the highest skin penetration enhancement of celecoxib was 30 Watts/cm². However, the combination of sonophoresis and the microemulsion resulted in a decrease in celecoxib skin penetration. The results of a confocal laser scanning microscopy study using the colocalization analysis of multifluorescently labeled particles revealed that the reduction in skin penetration of celecoxib from the combination of sonophoresis and a microemulsion resulted from a decrease in transfollicular penetration, which is the major skin absorption pathway of the microemulsion.

Physical triggering strategies for drug delivery

Physically triggered systems hold promise for improving drug delivery by enhancing the controllability of drug accumulation and release, lowering non-specific toxicity, and facilitating clinical translation. Several external physical stimuli including ultrasound, light, electric fields and magnetic fields have been used to control drug delivery and they share some common features such as spatial targeting, spatiotemporal control, and minimal invasiveness. At the same time, they possess several distinctive features in terms of interactions with biological entities and/or the extent of stimulus response. Here, we review the key advances of such systems with a focus on discussing their physical mechanisms, the design rationales, and translational challenges.

Production of LMWH-conjugated core/shell hydrogels encapsulating paclitaxel for transdermal delivery: In vitro and in vivo assessment

Topical applications that reduce systemic toxic effects while increasing therapeutic efficacy are a promising alternative strategy. The aim of this study was to provide an enhanced transdermal delivery of low molecular weight heparin (LMWH) through the stratum corneum by using cationic carrier as a novel permeation enhancer. Recent studies have shown that heparin-conjugated biomaterials can be effective in inhibiting tumor growth during cancer treatment due to their high ability to bind growth factors. Paclitaxel (PCL) was co-encapsulated into the same cationic carrier for the purpose of improving of therapeutic efficacy for a combined cancer treatment with LMWH. In vitro and in vivo studies showed that the LMWH and PCL release was significantly affected by polymer molecular weight and block composition. Skin penetration tests have indicated that larger amounts of LMWH were absorbed from LMWH-gel conjugate through SC, than aqueous formula. However, it was found that the plasma transition of LMWH released from gel conjugate was lower compared to the plasma concentration of LMWH released from aqueous solution. It is recommended that PCL-loaded LMWH-conjugated core/shell hydrogels can be used as promising drug release systems for transdermal applications that can improve therapeutic efficacy and reduce side effects in a combined cancer treatment.

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.

Study on the refractive index matching effect of ultrasound on optical clearing of bio-tissues based on the derivative total reflection method

In recent years, the tissue optical clearing (OC) technique in the biomedicine field has drawn lots of attention. Various physical and chemical methods have been introduced to improve the efficacy of OC. In this study, the effect of the combination of glycerol and ultrasound treatment on OC of in vitro porcine muscle tissues has been investigated. The refractive index (RI) matching mechanism of OC was directly observed based on the derivative total reflection method. A theoretical model was used to simulate the proportion of tissue fluid in the illuminated area. Moreover, the total transmittance spectra have been obtained by a spectrometer over the range from 450 nm to 700 nm. The administration of glycerol and ultrasound has led to an increase of the RI of background medium and a more RI matching environment was achieved. The experimental results support the validity of the ultrasound treatment for OC. The RI matching mechanism has been firstly quantitatively analyzed based on the derivative total reflection method.

Fetal membrane transport enhancement using ultrasound for drug delivery and noninvasive detection

PURPOSE

The purpose of this research was to evaluate the effect of ultrasound on mass transport across fetal membrane for direct fetal drug delivery and sensing of the amniotic fluid in a noninvasive manner.

METHODS

Post-delivery human fetal membranes (chorioamnion) were used for in vitro experiments, in which the effect of ultrasound on transport across fetal membrane of fluorescent model molecule (250 kDa) was evaluated. Ex vivo experiments were carried out on a whole rat amniotic sac. The model molecule or alpha-fetoprotein was injected into the amniotic sac through the placenta. Transport of these molecules across pre- and post-insonation of the amniotic sac was evaluated. The ultrasound enhancement's mechanism was also assessed.

RESULTS

The greatest enhancement in mass transport (43-fold) in vitro was achieved for 5 min of insonation (20 kHz, 4.6 W/cm(2), 5 mm distance). Ex vivo results showed a rapid increase (23-fold) in mass transport of the model molecule and also for alphafetoprotein following 30 s of insonation (20 kHz, 4.6 W/cm(2), 5 mm distance).

CONCLUSIONS

Mass transport across fetal membranes was enhanced post-insonation both in vitro and ex vivo in a reversible and transient manner. We suggest that exterior (to the amniotic sac) ultrasound-induced cavitation is the main mechanism of action.

Ultrasound mediated transdermal drug delivery

Transdermal drug delivery offers an attractive alternative to the conventional drug delivery methods of oral administration and injections. However, the stratum corneum serves as a barrier that limits the penetration of substances to the skin. Application of ultrasound (US) irradiation to the skin increases its permeability (sonophoresis) and enables the delivery of various substances into and through the skin. This review presents the main findings in the field of sonophoresis in transdermal drug delivery as well as transdermal monitoring and the mathematical models associated with this field. Particular attention is paid to the proposed enhancement mechanisms and future trends in the fields of cutaneous vaccination and gene therapy.

Exploitation of acoustic cavitation-induced microstreaming to enhance molecular transport

Ultrasound (US) exposure of soft tissues, such as the skin, has been shown to increase permeability, enhancing the passage of drug molecules via passive processes such as diffusion. However, US regimes have not been exploited to enhance active convective transport of drug molecules from a donor layer, such as a gel, into another medium. A layered tissue-mimicking material (TMM) was used as a model for a drug donor layer and underlying soft tissue to test penetration of agents in response to a range of US parameters. Influence of agent molecular mass (3-2000 kDa), US frequency (0.256/1.1 MHz) and US pressure (0-10 MPa) on transport was characterised. Agents of four different molecular sizes were embedded within the TMM with or without cavitation nuclei (CN) and US applied to achieve inertial cavitation. Post-insonation, samples were analysed to determine the concentration and penetration distance of agent transported. US exposure substantially enhanced transport. At both US frequencies, enhancement of transport was significantly higher (p < 0.05) above the cavitation threshold, and CN reduced the pressure at which cavitation, and therefore transport, was achieved. Acoustic cavitation activity and related phenomena was the predominant transport mechanism, and addition of CN significantly enhanced transport within a range of clinically applicable acoustic pressures. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci.

Sonophoresis in transdermal drug deliverys

Transdermal drug delivery (TDD) has several significant advantages compared to oral drug delivery, including elimination of pain and sustained drug release. However, the use of TDD is limited by low skin permeability due to the stratum corneum (SC), the outermost layer of the skin. Sonophoresis is a technique that temporarily increases skin permeability such that various medications can be delivered noninvasively. For the past several decades, various studies of sonophoresis in TDD have been performed focusing on parameter optimization, delivery mechanism, transport pathway, or delivery of several drug categories including hydrophilic and high molecular weight compounds. Based on these various studies, several possible mechanisms of sonophoresis have been suggested. For example, cavitation is believed to be the predominant mechanism responsible for drug delivery in sonophoresis. This review presents details of various studies on sonophoresis including the latest trends, delivery of various therapeutic drugs, sonophoresis pathways and mechanisms, and outlook of future studies.

In vivo real-time monitoring system of electroporation mediated control of transdermal and topical drug delivery

Electroporation (EP) is a physical method for the delivery of molecules into cells and tissues, including the skin. In this study, in order to control the degree of transdermal and topical drug delivery, EP at different amplitudes of electric pulses was evaluated. A new in vivo real-time monitoring system based on fluorescently labeled molecules was developed, for the quantification of transdermal and topical drug delivery. EP of the mouse skin was performed with new non-invasive multi-array electrodes, delivering different amplitudes of electric pulses ranging from 70 to 570 V, between the electrode pin pairs. Patches, soaked with 4 kDa fluorescein-isothiocyanate labeled dextran (FD), doxorubicin (DOX) or fentanyl (FEN), were applied to the skin before and after EP. The new monitoring system was developed based on the delivery of FD to and through the skin. FD relative quantity was determined with fluorescence microscopy imaging, in the treated region of the skin for topical delivery and in a segment of the mouse tail for transdermal delivery. The application of electric pulses for FD delivery resulted in enhanced transdermal delivery. Depending on the amplitude of electric pulses, it increased up to the amplitude of 360 V, and decreased at higher amplitudes (460 and 570 V). Topical delivery steadily enhanced with increasing the amplitude of the delivered electric pulses, being even higher than after tape stripping used as a positive control. The non-invasive monitoring of the delivery of DOX, a fluorescent chemotherapeutic drug, qualitatively and quantitatively confirmed the effects of EP at 360 and 570 V pulse amplitudes on topical and transdermal drug delivery. Delivery of FEN at 360 and 570 V pulse amplitudes verified the observed effects as obtained with FD and DOX, by the measured physiological responses of the mice as well as FEN plasma concentration. This study demonstrates that with the newly developed non-invasive multi-array electrodes and with the varying electric pulse amplitude, the amount of topical and transdermal drug delivery to the skin can be controlled. Furthermore, the newly developed monitoring system provides a tool for rapid real-time determination of both, transdermal and topical delivery, when the delivered molecule is fluorescent.

Laser-engineered dissolving microneedles for active transdermal delivery of nadroparin calcium

There is an urgent need to replace the injection currently used for low molecular weight heparin (LMWH) multidose therapy with a non- or minimally invasive delivery approach. In this study, laser-engineered dissolving microneedle (DMN) arrays fabricated from aqueous blends of 15% w/w poly(methylvinylether-co-maleic anhydride) were used for the first time in active transdermal delivery of the LMWH nadroparin calcium (NC). Importantly, an array loading of 630IU of NC was achieved without compromising the array mechanical strength or drug bioactivity. Application of NC-DMNs to dermatomed human skin (DHS) using the single-step 'poke and release' approach allowed permeation of approximately 10.6% of the total NC load over a 48-h study period. The cumulative amount of NC that permeated DHS at 24h and 48h attained 12.28±4.23IU/cm(2) and 164.84±8.47IU/cm(2), respectively. Skin permeation of NC could be modulated by controlling the DMN array variables, such as MN length and array density as well as application force to meet various clinical requirements including adjustment for body mass and renal function. NC-loaded DMN offers great potential as a relatively low-cost functional delivery system for enhanced transdermal delivery of LMWH and other macromolecules.

Ultrasound-mediated transdermal drug delivery: mechanisms, scope, and emerging trends

The use of ultrasound for the delivery of drugs to, or through, the skin is commonly known as sonophoresis or phonophoresis. The use of therapeutic and high frequencies of ultrasound (≥0.7MHz) for sonophoresis (HFS) dates back to as early as the 1950s, while low-frequency sonophoresis (LFS, 20-100kHz) has only been investigated significantly during the past two decades. Although HFS and LFS are similar because they both utilize ultrasound to increase the skin penetration of permeants, the mechanisms associated with each physical enhancer are different. Specifically, the location of cavitation and the extent to which each process can increase skin permeability are quite dissimilar. Although the applications of both technologies are different, they each have strengths that could allow them to improve current methods of local, regional, and systemic drug delivery. In this review, we will discuss the mechanisms associated with both HFS and LFS, specifically concentrating on the key mechanistic differences between these two skin treatment methods. Background on the relevant physics associated with ultrasound transmitted through aqueous media will also be discussed, along with implications of these phenomena on sonophoresis. Finally, a thorough review of the literature is included, dating back to the first published reports of sonophoresis, including a discussion of emerging trends in the field.

Tolerance of low-frequency ultrasound sonophoresis: a double-blind randomized study on humans

BACKGROUND

Sonophoresis [low-frequency ultrasound (US)] has been used in animals and in vitro to investigate enhanced percutaneous absorption of drugs. No study focused on its clinical human tolerance has been published as yet.

METHODS

We aimed to assess the bioeffects of low-frequency US in vivo on human skin in a double-blind randomized-controlled study. We applied pulse-mode US at 36 kHz for 5 min in a step procedure of increasing dosage, from 1.57 to 3.50 W/cm(2), and placebo. The primary outcome was toxic effects of the procedure, defined as a pain score >40 on a 0-100 mm visual analogue scale or necrosis. Erythema (scored from 0 to 3 in severity) was also evaluated. The secondary outcomes were measurements of skin thickness by high-resolution skin imaging, of skin capacitance and temperature.

RESULTS

We included 34 healthy volunteers. We found no pain score >38 and no skin necrosis with either US or placebo. Erythema was systematically observed immediately after US application, but after 1 day, we observed three cases in the knee group. The most frequent adverse effect was tinnitus. We observed no marked increase in temperature or cutaneous thickness after US or placebo. Cutaneous capacitance increased immediately after both applications.

CONCLUSION

Such data demonstrating good tolerance of sonophoresis can be useful before the initiation of a clinical trial of the therapeutic use of low-frequency sonophoresis in humans.

Low-frequency sonophoresis: application to the transdermal delivery of macromolecules and hydrophilic drugs

IMPORTANCE OF THE FIELD

Transdermal delivery of macromolecules provides an attractive alternative route of drug administration when compared to oral delivery and hypodermic injection because of its ability to bypass the harsh gastrointestinal tract and deliver therapeutics non-invasively. However, the barrier properties of the skin only allow small, hydrophobic permeants to traverse the skin passively, greatly limiting the number of molecules that can be delivered via this route. The use of low-frequency ultrasound for the transdermal delivery of drugs, referred to as low-frequency sonophoresis (LFS), has been shown to increase skin permeability to a wide range of therapeutic compounds, including both hydrophilic molecules and macromolecules. Recent research has demonstrated the feasibility of delivering proteins, hormones, vaccines, liposomes and other nanoparticles through LFS-treated skin. In vivo studies have also established that LFS can act as a physical immunization adjuvant. LFS technology is already clinically available for use with topical anesthetics, with other technologies currently under investigation.

AREAS COVERED IN THIS REVIEW

This review provides an overview of mechanisms associated with LFS-mediated transdermal delivery, followed by an in-depth discussion of the current applications of LFS technology for the delivery of hydrophilic drugs and macromolecules, including its use in clinical applications.

WHAT THE READER WILL GAIN

The reader will gain an insight into the field of LFS-mediated transdermal drug delivery, including how the use of this technology can improve on more traditional drug delivery methods.

TAKE HOME MESSAGE

Ultrasound technology has the potential to impact many more transdermal delivery platforms in the future due to its unique ability to enhance skin permeability in a controlled manner.

Transdermal delivery of proteins

Transdermal delivery of peptides and proteins avoids the disadvantages associated with the invasive parenteral route of administration and other alternative routes such as the pulmonary and nasal routes. Since proteins have a large size and are hydrophilic in nature, they cannot permeate passively across the skin due to the stratum corneum which allows the transport of only small lipophilic drug molecules. Enhancement techniques such as chemical enhancers, iontophoresis, microneedles, electroporation, sonophoresis, thermal ablation, laser ablation, radiofrequency ablation and noninvasive jet injectors aid in the delivery of proteins by overcoming the skin barrier in different ways. In this review, these enhancement techniques that can enable the transdermal delivery of proteins are discussed, including a discussion of mechanisms, sterility requirements, and commercial development of products. Combination of enhancement techniques may result in a synergistic effect allowing increased protein delivery and these are also discussed.

Novel sulfated polysaccharides disrupt cathelicidins, inhibit RAGE and reduce cutaneous inflammation in a mouse model of rosacea

BACKGROUND

Rosacea is a common disfiguring skin disease of primarily Caucasians characterized by central erythema of the face, with telangiectatic blood vessels, papules and pustules, and can produce skin thickening, especially on the nose of men, creating rhinophyma. Rosacea can also produce dry, itchy eyes with irritation of the lids, keratitis and corneal scarring. The cause of rosacea has been proposed as over-production of the cationic cathelicidin peptide LL-37.

METHODOLOGY/PRINCIPAL FINDINGS

We tested a new class of non-anticoagulant sulfated anionic polysaccharides, semi-synthetic glycosaminoglycan ethers (SAGEs) on key elements of the pathogenic pathway leading to rosacea. SAGEs were anti-inflammatory at ng/ml, including inhibition of polymorphonuclear leukocyte (PMN) proteases, P-selectin, and interaction of the receptor for advanced glycation end-products (RAGE) with four representative ligands. SAGEs bound LL-37 and inhibited interleukin-8 production induced by LL-37 in cultured human keratinocytes. When mixed with LL-37 before injection, SAGEs prevented the erythema and PMN infiltration produced by direct intradermal injection of LL-37 into mouse skin. Topical application of a 1% (w/w) SAGE emollient to overlying injected skin also reduced erythema and PMN infiltration from intradermal LL-37.

CONCLUSIONS

Anionic polysaccharides, exemplified by SAGEs, offer potential as novel mechanism-based therapies for rosacea and by extension other LL-37-mediated and RAGE-ligand driven skin diseases.

The importance of microjet vs shock wave formation in sonophoresis

Low-frequency ultrasound application has been shown to greatly enhance transdermal drug delivery. Skin exposed to ultrasound is affected in a heterogeneous manner, thus mass transport through the stratum corneum occurs mainly through highly permeable localized transport regions (LTRs). Shock waves and microjets generated during inertial cavitations are responsible for the transdermal permeability enhancement. In this study, we evaluated the effect of these two phenomena using direct and indirect methods, and demonstrated that the contribution of microjets to skin permeability enhancement is significantly higher than shock waves.

Effects of ultrasound and sodium lauryl sulfate on the transdermal delivery of hydrophilic permeants: Comparative in vitro studies with full-thickness and split-thickness pig and human skin

The simultaneous application of ultrasound and the surfactant sodium lauryl sulfate (referred to as US/SLS) to skin enhances transdermal drug delivery (TDD) in a synergistic mechanical and chemical manner. Since full-thickness skin (FTS) and split-thickness skin (STS) differ in mechanical strength, US/SLS treatment may have different effects on their transdermal transport pathways. Therefore, we evaluated STS as an alternative to the well-established US/SLS-treated FTS model for TDD studies of hydrophilic permeants. We utilized the aqueous porous pathway model to compare the effects of US/SLS treatment on the skin permeability and the pore radius of pig and human FTS and STS over a range of skin electrical resistivity values. Our findings indicate that the US/SLS-treated pig skin models exhibit similar permeabilities and pore radii, but the human skin models do not. Furthermore, the US/SLS-enhanced delivery of gold nanoparticles and quantum dots (two model hydrophilic macromolecules) is greater through pig STS than through pig FTS, due to the presence of less dermis that acts as an artificial barrier to macromolecules. In spite of greater variability in correlations between STS permeability and resistivity, our findings strongly suggest the use of 700microm-thick pig STS to investigate the in vitro US/SLS-enhanced delivery of hydrophilic macromolecules.

Sonophoresis: recent advancements and future trends

OBJECTIVES

Use of ultrasound in therapeutics and drug delivery has gained importance in recent years, evident by the increase in patents filed and new commercial devices launched. The present review discusses new advancements in sonophoretic drug delivery in the last two decades, and highlights important challenges still to be met to make this technology of more use in the alleviation of diseases.

KEY FINDINGS

Phonophoretic research often suffers from poor calibration in terms of the amount of ultrasound energy emitted, and therefore current research must focus on safety of exposure to ultrasound and miniaturization of devices in order to make this technology a commercial reality. More research is needed to identify the role of various parameters influencing sonophoresis so that the process can be optimized. Establishment of long-term safety issues, broadening the range of drugs that can be delivered through this system, and reduction in the cost of delivery are issues still to be addressed.

SUMMARY

Sonophoresis (phonophoresis) has been shown to increase skin permeability to various low and high molecular weight drugs, including insulin and heparin. However, its therapeutic value is still being evaluated. Some obstacles in transdermal sonophoresis can be overcome by combination with other physical and chemical enhancement techniques. This review describes recent advancements in equipment and devices for phonophoresis, new formulations tried in sonophoresis, synergistic effects with techniques such as chemical enhancers, iontophoresis and electroporation, as well as the growing use of ultrasound in areas such as cancer therapy, cardiovascular disorders, temporary modification of the blood-brain barrier for delivery of imaging and therapeutic agents, hormone replacement therapy, sports medicine, gene therapy and nanotechnology. This review also lists patents pertaining to the formulations and techniques used in sonophoretic drug delivery.

Thermal effect of sonophoresis for accelerating the analgesic effect of local anesthetics on rat tail nerve

Sonophoresis is an ultrasound transdermal drugs delivery system. The eutectic mixture of local anesthetics (EMLA) has been used clinically for anesthesia but requires at least one hour to take effect and lacks of analgesia's objective assessment. We proposed that sonophoresis could reduce the duration of EMLA analgesia effect onset and be assessed by sensory conduction studies. Thirty Wistar adult rats were randomized into normal, control, ultrasound-, and heat-treatment groups. Normal group was received no EMLA cream or ultrasound and heat treatment. The control group received the EMLA cream on the rat tail at 3.5 cm distal to the rat tail base for local anesthesia of tail nerve. Ultrasound- and heat-treatment groups were received ultrasound with different parameters and heat treatment, respectively, before EMLA cream applied. Sensory conduction studies of tail nerve were made before and after treatment every 5 min at least for 60 min in all rats. There was no significant difference between the EMLA control group and heat treatment group. All rats in ultrasound-treatment group exhibit significant difference with EMLA control group and heat-treatment group in time for decreased 20% SNCV except for the 2 W/cm(2), 25 min, 20% in ultrasound-treatment group having no significant difference with heat-treatment group. There was no significant difference between ultrasound-treatment subgroups. In the decrease of amplitude, only the 2 W/cm(2), 5 min, 100% and the 2 W/cm(2), 10 min, 50% in ultrasound-treatment group had significant difference between EMLA control and heat-treatment groups. We have objectively examined the sonophoresis effect of ultrasound by investigating the effects of EMLA. Applying ultrasound for 5 min reduces the onset time of EMLA analgesia from 60 min to less than 20 min. Ultrasound sonophoresis of analgesic drugs is potentially useful in the treatment of carpal tunnel syndrome, tooth extraction, and other applications of analgesia.

Heterogeneity in skin treated with low-frequency ultrasound

Recent experimental evidence using colored, fluorescent permeants suggests that skin treated with low-frequency sonophoresis (LFS) is perturbed in a heterogeneous manner. Macroscopic and microscopic visualization studies, topical penetration studies, transdermal permeability studies, and skin electrical resistivity measurements have shown that discrete domains, referred to as localized transport regions (LTRs), which are formed during LFS treatment of the skin, possess greatly reduced barrier properties, and therefore exhibit increased permeant skin penetration, compared to the surrounding regions of LFS-treated skin. The transformation of LTR formation from a heterogeneous to a homogeneous phenomenon has the potential benefit of increasing the maximum level of transdermal permeability or of reducing the area of skin required to deliver a desired dose of drug transdermally. Future studies, aimed at elucidating both the mechanisms of LTR formation and the limits of nondamaging formation of LTRs in the skin, are required to incorporate these proposed improvements to enhance the efficacy and practical utility of low-frequency sonophoresis.

Low-frequency sonophoresis: current status and future prospects

Application of ultrasound enhances skin permeability to drugs, a phenomenon referred to as sonophoresis. Significant strides have been made in sonophoresis research in recent years, especially under low-frequency conditions (20 kHz<f<100 kHz). This article reviews the mechanistic principles and current status of sonophoresis under low-frequency conditions. Several therapeutic macromolecules including insulin, low-molecular weight heparin, and vaccines have been delivered using low-frequency sonophoresis in vivo. Clinical trials have been performed with several drugs including lidocaine and cyclosporin. Novel theoretical and experimental approaches have provided insights into the mechanisms of low-frequency sonophoresis. Current understanding of these mechanisms is presented.

Pharmacokinetic and pharmacodynamic studies following percutaneous absorption of erythropoietin micropiles to rats

To ascertain the pharmacological activity of erythropoietin (EPO) administered by self-dissolving micropiles (SDMP), four kinds of EPO SDMPs were prepared and were administered to rats in 4 consecutive days at 200, 500, 1000 and 2300 IU/kg. After the start of the experiment, blood samples were obtained once a day for 10 days and percent circulating reticulocytes were counted using Miller technique. At the lower doses, 200 and 500 IU/kg, pharmacological activity of EPO was not obtained. By increasing EPO dose to 1000 IU/kg, circulating reticulocytes significantly increased at days 4, 5, 6 and 7 after the start of the experiment and the average value for the change in reticulocyte levels during day 1 and day 5 was 170.9%. With the highest dose, 2300 IU/kg, higher circulating reticulocytes levels started to increase at the 4th day after the start of the experiment and maintained from day 5 to day 10. The average of the changes in reticulocyte from day 5 to day 10 was 251%. Dose-dependent circulating reticulocytes increase was observed at the higher dose range, 1000 and 2300 IU/kg. To study the linearity on the serum EPO level vs. time curves, pharmacokinetic experiment was performed with rats. After the administration of EPO SDMPs to rats, 200, 500, 1000 and 2300 IU/kg, serum EPO levels gradually increased and reached to the maximum level, C(max), at 18 h after administration. The C(max)s were 100.4+/-11.7 mIU/ml (200 IU/kg), 346.6+/-11.8 mIU/ml (500 IU/kg), 391.6+/-17.6 mIU/ml (1000 IU/kg), and 1094.9+/-114.8 mIU/ml (2300 IU/kg), respectively. AUCs were 1407+/-231, 3843+/-402, 5363+/-482 and 15,566+/-1894 mIU h/ml. Linear relation was obtained between serum EPO level and EPO dose administered as SDMP. With histological study, any adverse effect was not found out on the skin where SDMPs were administered for consecutive 4 days. These results suggest the usefulness of SDMP as a new percutaneous delivery system of EPO.

Transdermal delivery of heparin using pulsed current iontophoresis

PURPOSE

In clinical practice heparin has to be administered by injection with obvious disadvantages; thus, transdermal delivery by electrically assisted methods have been studied. In this study we evaluated the efficacy of a Food and Drug Administration-approved pulsed current iontophoresis system in delivering heparin through living rat skin.

METHODS

Fluorescent and radioactive heparin as well as a commercial heparin preparation were delivered through rat skin via a pulsed current iontophoresis system.

RESULTS

Pulsed current iontophoresis allowed fluorescent heparin to cross the stratum corneum localizing in epidermis and dermis. Unfractionated, high-, and low molecular weight fraction pools, obtained by fractionating [35S]-unfractionated heparin on a molecular weight sieve, were then separately tested. Pulsed current iontophoresis elicited the transdermal delivery of low molecular weight heparin, but not that of high molecular weight heparin. Finally, pulsed current iontophoresis of an unfractionated pharmaceutical heparin preparation significantly decreased plasmatic factor Xa activity.

CONCLUSIONS

We hypothesize that this technique could be used to administer low molecular weight heparin in a cost-efficient and safe manner without the need for syringes and needles.

Investigation into the potential of low-frequency ultrasound facilitated topical delivery of Cyclosporin A

The potential for low-frequency ultrasound facilitated topical transport of Cyclosporin A was investigated using rat skin. Studies of intensity and exposure time acting on the deposition of Cyclosporin A into deeper skin of in vitro sonophoresis were performed. Low-frequency ultrasound increased the amount of Cyclosporin A retained in the skin only seven times than the passive diffusion. Furthermore, we also tested the synergistic effect of ultrasound and other approaches such as chemical enhancers and electroporation on topical drug delivery of Cyclosporin A. We found that the efficacy of low-frequency ultrasound in enhancing topical delivery could be further increased by pretreatment of skin with chemical enhancers, such as laurocapram (Azone) and sodium lauryl sulfate (SLS). Meanwhile only a small amount was seen to across the full skin into the receiver compartment. Trimodality treatment comprising of pretreatment with Azone+ultrasound in combination followed by electroporation was not effective in enhancing the topical delivery of Cyclosporin A. However, this combination strategy increased the penetration of Cyclosporin A through rat skin by order of 15. The histopathological findings revealed that there was almost no change observed in the structure of skin after ultrasound or combination with ultrasound and enhancers as compared with the control group. In general, the enhanced skin accumulation of Cyclosporin A by the combination of low-frequency ultrasound and chemical enhancers could help significantly to optimize the targeting of the drug without of a concomitant increase of the systemic side effects.