Ultrasound-mediated transdermal protein delivery

A Review of Clinical Translation of Inorganic Nanoparticles

Inorganic nanoparticles are widely used for therapeutic and diagnostic purposes as they offer unique features as compared with their organic and polymeric counterparts. As such, inorganic nanoparticles represent an exciting opportunity to develop drug delivery and imaging systems that are poised to tackle unique challenges which are currently unaddressed in clinical settings. Despite these clear advantages, very few inorganic nanoparticle systems have entered the clinic. Here, we review the current clinical landscape of inorganic nanoparticle systems and their opportunities and challenges, with particular emphasis on gold-, iron-oxide- and silica-based nanoparticle systems. Key examples of inorganic nanoparticles that are currently being investigated in the clinic (e.g., trials which are recruiting or currently active but not completed) are highlighted, along with the preclinical work that these examples have leveraged to transition from the lab to the clinic.

Spatiotemporal drug delivery using laser-generated-focused ultrasound system

Laser-generated-focused ultrasound (LGFU) holds promise for the high-precision ultrasound therapy owing to its tight focal spot, broad frequency band, and stable excitation with minimal ultrasound-induced heating. We here report the development of the LGFU as a stimulus for promoted drug release from microgels integrated with drug-loaded polymeric nanoparticles. The pulsed waves of ultrasound, generated by a carbon black/polydimethylsiloxane (PDMS)-photoacoustic lens, were introduced to trigger the drug release from alginate microgels encapsulated with drug-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles. We demonstrated the antibacterial capability of this drug delivery system against Escherichia coli by the disk diffusion method, and antitumor efficacy toward the HeLa cell-derived tumor spheroids in vitro. This novel LGFU-responsive drug delivery system provides a simple and remote approach to precisely control the release of therapeutics in a spatiotemporal manner and potentially suppress detrimental effects to the surrounding tissue, such as thermal ablation.

Ultrasound-enhanced transdermal delivery: recent advances and future challenges

The skin is a formidable diffusion barrier that restricts passive diffusion to small (<500 Da) lipophilic molecules. Methods used to permeabilize this barrier for the purpose of drug delivery are maturing as an alternative to oral drug delivery and hypodermic injections. Ultrasound can reversibly and non-invasively permeabilize the diffusion barrier posed by the skin. This review discusses the mechanisms of ultrasound-permeability enhancement, and presents technological innovations in equipment miniaturization and recent advances in permeabilization capabilities. Additionally, potentially exciting applications, including protein delivery, vaccination, gene therapy and sensing of blood analytes, are discussed. Finally, the future challenges and opportunities associated with the use of ultrasound are discussed. It is stressed that developing ultrasound for suitable applications is key to ensure commercial success.

A Review of Clinical Translation of Inorganic Nanoparticles

Inorganic nanoparticles are widely used for therapeutic and diagnostic purposes as they offer unique features as compared with their organic and polymeric counterparts. As such, inorganic nanoparticles represent an exciting opportunity to develop drug delivery and imaging systems that are poised to tackle unique challenges which are currently unaddressed in clinical settings. Despite these clear advantages, very few inorganic nanoparticle systems have entered the clinic. Here, we review the current clinical landscape of inorganic nanoparticle systems and their opportunities and challenges, with particular emphasis on gold-, iron-oxide- and silica-based nanoparticle systems. Key examples of inorganic nanoparticles that are currently being investigated in the clinic (e.g., trials which are recruiting or currently active but not completed) are highlighted, along with the preclinical work that these examples have leveraged to transition from the lab to the clinic.

Quantitative evaluation of sonophoresis efficiency and its dependence on sonication parameters and particle size

Transdermal drug delivery makes a critical contribution to medical practice and some advantages over conventional oral administration and hypodermic injection. Enhancement of percutaneous absorption or penetration of therapeutic agents (ie, drugs and macromolecules) by ultrasound, termed sonophoresis, has been applied and studied for decades. In this study, the penetration percentage through porcine ear skin specimens was determined quantitatively by measuring the fluorescence from nanoparticles of 60, 220, and 840 nm in size in a receptor chamber at different sonication parameters (ie, duty cycle, 20%-100%; acoustic intensity, 0.3-1.0 W/cm(2); duration, 7-30 minutes; and frequency, 1 MHz). In general, the sonophoresis efficiency increased with the acoustic intensity, duty cycle, and sonication duration but decreased with the particle size (mean ± SD, 62.6% ± 5.4% for 60-nm versus 11.9% ± 1.1% for 840-nm polystyrene nanospheres after 30 minutes of sonication at 0.5 W/cm(2) and a 100% duty cycle; P < .05). On scanning electron microscopy the pore size remained the same (≈100 μm), but more flakes were observed with the progress of sonication. In summary, sonophoresis efficiency is dependent on the ultrasound parameters and particle size. Sufficient sonication would lead to satisfactory penetration of even submicrometer objects through the pores.

Cavitation-enhanced delivery of insulin in agar and porcine models of human skin

Ultrasound-assisted transdermal insulin delivery offers a less painful and less invasive alternative to subcutaneous insulin injections. However, ultrasound-based drug delivery, otherwise known as sonophoresis, is a highly variable phenomenon, in part dependent on cavitation. The aim of the current work is to investigate the role of cavitation in transdermal insulin delivery. Fluorescently stained, soluble Actrapid insulin was placed on the surface of human skin-mimicking materials subjected to 265 kHz, 10% duty cycle focused ultrasound. A confocally and coaxially aligned 5 MHz broadband ultrasound transducer was used to detect cavitation. Two different skin models were used. The first model, 3% agar hydrogel, was insonated with a range of pressures (0.25-1.40 MPa peak rarefactional focal pressure-PRFP), with and without cavitation nuclei embedded within the agar at a concentration of 0.05% w/v. The second, porcine skin was insonated at 1.00 and 1.40 MPa PRFP. In both models, fluorescence measurements were used to determine penetration depth and concentration of delivered insulin. Results show that in agar gel, both insulin penetration depth and concentration only increased significantly in the presence of inertial cavitation, with up to a 40% enhancement. In porcine skin the amount of fluorescent insulin was higher in the epidermis of those samples that were exposed to ultrasound compared to the control samples, but there was no significant increase in penetration distance. The results underline the importance of instigating and monitoring inertial cavitation during transdermal insulin delivery.

Evaluation of ultrasound and glucose synergy effect on the optical clearing and light penetration for human colon tissue using SD-OCT

Topical application optical clearing agents (OCAs) can effectively enhance the tissue optical clearing on the human colon tissue, which has been demonstrated in our previous studies. Nevertheless, the strong light scattering still limits the diffusion rate of OCAs and penetration depth of light into the tissue. In this study, in order to further increase the diffusion of the OCA of glucose into tissue, we employ a method to improve the glucose permeability and light penetration with ultrasound (sonophoretic delivery, SP) and glucose (G) synergy on human normal and cancerous colon tissues in vitro, which was measured and quantified with spectral-domain optical coherence tomography (SD-OCT) technology. To evaluate the effect of ultrasound mediation, the percentages of OCT signal enhancement (PSE) and 1/e light-penetration depth were calculated for G alone and ultrasound-G treatments. The PSE was calculated at approximately 313 μm from the sample tissue surface. For normal and cancerous colon tissues the PSE were about 91.1 ± 10.6% and 65.3% ± 12.3% with 30% G/SP, but for the 30% G alone treatment it was about 78.6 ± 11.2% and 54.5% ± 9.3%, respectively. The max value of 1/e light-penetration depth for normal colon tissue was 0.47 ± 0.02 mm with 30% G alone and 0.60 ± 0.05 mm (p < 0.05)with 30% G/SP synergy. However, for the cancerous colon tissue the max value was 0.45 ± 0.01 mm and 0.57 ± 0.03 mm (p < 0.05), respectively. The obtained permeability coefficients showed a significant enhancement with ultrasound mediation. The mean permeability coefficients of 30% G/SP in normal and cancerous colon tissues were (6.3 ± 0.16) × 10(-6) cm/s and (12.1 ± 0.34) × 10(-6) cm/s (p < 0.05), respectively. These preliminary experiments showed that ultrasound can effectively enhance the tissue optical clearing and glucose diffusion rate as well as increase the light-penetration depth into biotissues.

Cutaneous drug delivery: an update

Cutaneous delivery of therapeutics represents a proven and attractive option for treating a variety of dermatologic conditions with minimal systemic side effects. Although there have been many innovations in drug delivery systems, the number of effective cutaneous drugs remains small, primarily because of the stratum corneum permeability barrier. Overcoming this barrier safely and reversibly to deliver large hydrophilic drugs cutaneously is one of the major challenges in the field of dermatologic therapy.

Overcoming the challenges in administering biopharmaceuticals: formulation and delivery strategies

The formulation and delivery of biopharmaceutical drugs, such as monoclonal antibodies and recombinant proteins, poses substantial challenges owing to their large size and susceptibility to degradation. In this Review we highlight recent advances in formulation and delivery strategies--such as the use of microsphere-based controlled-release technologies, protein modification methods that make use of polyethylene glycol and other polymers, and genetic manipulation of biopharmaceutical drugs--and discuss their advantages and limitations. We also highlight current and emerging delivery routes that provide an alternative to injection, including transdermal, oral and pulmonary delivery routes. In addition, the potential of targeted and intracellular protein delivery is discussed.

Penetration depth, concentration and efficiency of transdermal α-arbutin delivery after ultrasound treatment with albumin-shelled microbubbles in mice

Recently, the feasibility and effects of using microbubbles (MBs) as an ultrasound (US) contrast agent for enhancing the penetration in transdermal delivery in vivo have been demonstrated, but the mechanism and efficiency are unclear. This study demonstrates the penetration depth, concentration and efficiency of transdermal α-arbutin delivery during 4 weeks after US treatment with MBs in mice. Experimental animals were randomly divided into the following four groups (n = 5 animals per group): (1) penetrating α-arbutin alone (C), (2) US combined with penetrating α-arbutin, (3) US combined with MBs and penetrating α-arbutin, and (4) US combined with diluted MBs and penetrating α-arbutin (UBD). The penetration depths in agarose phantoms and pigskin were 47 and 84% greater for group UBD, respectively, than for group C. The in vitro skin penetration by 2% α-arbutin after 3 h was 83% greater in group UBD than in group C. The degree of in vivo skin whitening (quantified as the luminosity index) in group UBD significantly increased by 25% after 1 week, 34% after 2 weeks, and then stabilized after 3 weeks at 37% in C57BL/6J mice over a 4-week experimental period. Our results indicate that combined treatment with optimal US and MBs can increase skin permeability so as to enhance α-arbutin delivery to inhibit melanogenesis without damaging the skin in mice.

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.

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-triggered disruption and self-healing of reversibly cross-linked hydrogels for drug delivery and enhanced chemotherapy

Biological systems are exquisitely sensitive to the location and timing of physiologic cues and drugs. This spatiotemporal sensitivity presents opportunities for developing new therapeutic approaches. Polymer-based delivery systems are used extensively for attaining localized, sustained release of bioactive molecules. However, these devices typically are designed to achieve a constant rate of release. We hypothesized that it would be possible to create digital drug release, which could be accelerated and then switched back off, on demand, by applying ultrasound to disrupt ionically cross-linked hydrogels. We demonstrated that ultrasound does not permanently damage these materials but enables nearly digital release of small molecules, proteins, and condensed oligonucleotides. Parallel in vitro studies demonstrated that the concept of applying temporally short, high-dose "bursts" of drug exposure could be applied to enhance the toxicity of mitoxantrone toward breast cancer cells. We thus used the hydrogel system in vivo to treat xenograft tumors with mitoxantrone, and found that daily ultrasound-stimulated drug release substantially reduced tumor growth compared with sustained drug release alone. This approach of digital drug release likely will be applicable to a broad variety of polymers and bioactive molecules, and is a potentially useful tool for studying how the timing of factor delivery controls cell fate in vivo.

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.

Ultrasound-triggered regulation of blood glucose levels using injectable nano-network

The integration of an injectable insulin-encapsulated nano-network with a focused ultrasound system (FUS) can remotely regulate insulin release both in vitro and in vivo. A single subcutaneous injection of the nano-network with intermittent FUS administration facilitates reduction of the blood glucose levels in type 1 diabetic mice for up to 10 d.

Physical energy for drug delivery; poration, concentration and activation

Techniques for controlling the rate and duration of drug delivery, while targeting specific locations of the body for treatment, to deliver the cargo (drugs or DNA) to particular parts of the body by what are becoming called "smart drug carriers" have gained increased attention during recent years. Using such smart carriers, researchers have also been investigating a number of physical energy forces including: magnetic fields, ultrasound, electric fields, temperature gradients, photoactivation or photorelease mechanisms, and mechanical forces to enhance drug delivery within the targeted cells or tissues and also to activate the drugs using a similar or a different type of external trigger. This review aims to cover a number of such physical energy modalities. Various advanced techniques such as magnetoporation, electroporation, iontophoresis, sonoporation/mechnoporation, phonophoresis, optoporation and thermoporation will be covered in the review. Special emphasis will be placed on photodynamic therapy owing to the experience of the authors' laboratory in this area, but other types of drug cargo and DNA vectors will also be covered. Photothermal therapy and theranostics will also be discussed.

Transdermal delivery of proteins using a combination of iontophoresis and microporation

Aim: This study aimed to investigate transdermal delivery of proteins using combination of microporation and iontophoresis (ITP). Materials & methods & results: Delivery of model protein, Alexa Fluor 555 bovine serum albumin conjugate (AF-BSA) using ITP alone, microneedle (MN) alone, and ITP plus MN combination was assessed using confocal microscopy. Compared to MN alone, combination of MN plus ITP significantly increased skin's penetration depth of AF-BSA (300 vs 110 μm) and achieved lateral distribution of the model protein. Average fluorescence intensity quantified around each microchannel was 23.7-fold (8.2-fold, in vivo) higher for combination treatment compared with MN alone, in vitro. After 1 h in vitro permeation study, the unlabeled BSA amount delivered across skin was found to be 0, 1.4, 0.63 and 14 μg by passive, MN alone, ITP alone and ITP plus MN combination delivery, respectively.

Therapeutic ultrasound as a treatment modality for chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is a chronic infective, inflammatory upper respiratory disease. While the current medical treatment of CRS focuses on the systemic and topical use of steroids and/or antibiotics, many bacteria residing on mucosal surfaces of patients with CRS exist in a biofilm state, making them resistant to most systemic antibiotics. Alternative therapeutic strategies that include blocking bacterial molecular communication, inhibiting biofilm matrix production and breaking down bacterial biofilms are all being explored. Physical therapies such as therapeutic ultrasound (US) have been advocated and utilized as a treatment modality for CRS for many years. US may have antiinflammatory actions and can also be used for the local delivery of drugs through the skin. Therapeutic US, which has been shown in clinical studies to be an effective treatment for both acute rhinosinusitis and CRS, offers significant potential in CRS management.

Skin permeabilization for transdermal drug delivery: recent advances and future prospects

INTRODUCTION

Transdermal delivery has potential advantages over other routes of administration. It could reduce first-pass metabolism associated with oral delivery and is less painful than injections. However, the outermost layer of the skin, the stratum corneum (SC), limits passive diffusion to small lipophilic molecules. Therefore, methods are needed to safely permeabilize the SC so that ionic and larger molecules may be delivered transdermally.

AREAS COVERED

This review focuses on low-frequency sonophoresis, microneedles, electroporation and iontophoresis, and combinations of these methods to permeabilize the SC. The mechanisms of enhancements and developments in the last 5 years are discussed. Potentially high-impact applications, including protein delivery, vaccination and sensing are presented. Finally, commercial interest and clinical trials are discussed.

EXPERT OPINION

Not all permeabilization methods are appropriate for all applications. Focused studies into applications utilizing the advantages of each method are needed. The total dose and kinetics of delivery must be considered. Vaccination is one application where permeabilization methods could make an impact. Protein delivery and analyte sensing are also areas of potential impact, although the amount of material that can be delivered (or extracted) is of critical importance. Additional work on the miniaturization of these technologies will help to increase commercial interest.

Stabilizing in vitro ultrasound-mediated gene transfection by regulating cavitation

It is well known that acoustic cavitation can facilitate the inward transport of genetic materials across cell membranes (sonoporation). However, partially due to the unstationary behavior of the initiation and leveling of cavitation, the sonoporation effect is usually unstable, especially in low intensity conditions. A system which is able to regulate the cavitation level during sonication by modulating the applied acoustic intensity with a feedback loop is implemented and its effect on in vitro gene transfection is tested. The regulated system provided better time stability and reproducibility of the cavitation levels than the unregulated conditions. Cultured hepatoma cells (BNL) mixed with 10 μg luciferase plasmids are exposed to 1-MHz pulsed ultrasound with or without cavitation regulation, and the gene transfection efficiency and cell viability are subsequently assessed. Experimental results show that for all exposure intensities (low, medium, and high), stable and intensity dependent, although not higher, gene expression could be achieved in the regulated cavitation system than the unregulated conditions. The cavitation regulation system provides a better control of cavitation and its bioeffect which are crucial important for clinical applications of ultrasound-mediated gene transfection.

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.

Engineering approaches to transdermal drug delivery: a tribute to contributions of prof. Robert Langer

Transdermal drug delivery continues to provide an advantageous route of drug administration over injections. While the number of drugs delivered by passive transdermal patches has increased over the years, no macromolecule is currently delivered by the transdermal route. Substantial research efforts have been dedicated by a large number of researchers representing varied disciplines including biology, chemistry, pharmaceutics and engineering to understand, model and overcome the skin's barrier properties. This article focuses on engineering contributions to the field of transdermal drug delivery. The article pays tribute to Prof. Robert Langer, who pioneered the engineering approach towards transdermal drug delivery. Over a period spanning nearly 25 years since his first publication in the field of transdermal drug delivery, Bob Langer has deeply impacted the field by quantitative analysis and innovative engineering. At the same time, he has inspired several generations of engineers by collaborations and mentorship. His scientific insights, innovative technologies, translational efforts and dedicated mentorship have transformed the field.

The effect of sonophoresis on topical anesthesia: a pilot project

The dental anesthesia sonophoresis device (DASD) is a novel device that is intended to reduce the discomfort associated with intraoral mucosa needle puncture. The DASD produces ultrasonic energy that provides a sonophoretic effect on the oral mucosa, generating microchannels through the lipids between the keratinized cells that make up the stratum corneum. Once the topical anesthetic has permeated the stratum corneum, it quickly diffuses through the soft tissue, desensitizing the nerve endings and reducing the perception of pain caused by needle penetration. The aim of this study is to evaluate whether topical anesthesia applied using the DASD will reduce the discomfort of the needle puncture when compared to the control device. A split-mouth model, using 50 healthy subjects with puncture site at the maxillary canine vestibule, was used for this study. Subjects received a needle puncture on both sides of the mouth. Prior to the needle puncture, there was randomized application of 5% lidocaine with the DASD and a control device. Subjects rated their discomfort after needle punctures utilizing the visual analog scale pain scoring system. There was no statistically significant difference in the pain perception using the DASD versus the control device.

Optoacoustic tweezers: a programmable, localized cell concentrator based on opto-thermally generated, acoustically activated, surface bubbles

We present a programmable, biocompatible technique for dynamically concentrating and patterning particles and cells in a microfluidic device. Since our technique utilizes opto-thermally generated, acoustically activated, surface bubbles, we name it "optoacoustic tweezers". The optoacoustic tweezers are capable of concentrating particles/cells at any prescribed locations in a microfluidic chamber without the use of permanent structures, rendering it particularly useful for the formation of flexible, complex cell patterns. Additionally, this technique has demonstrated excellent biocompatibility and can be conveniently integrated with other microfluidic units. In our experiments, micro-bubbles were generated by focusing a 405 nm diode laser onto a gold-coated glass chamber. By properly tuning the laser, we demonstrate precise control over the position and size of the generated bubbles. Acoustic waves were then applied to activate the surface bubbles, causing them to oscillate at an optimized frequency. The resulting acoustic radiation force allowed us to locally trap particles/cells, including 15 μm polystyrene beads and HeLa cells, around each bubble. Cell-adhesion tests were also conducted after cell concentrating to confirm the biocompatibility of this technique.

The experimental evaluation and molecular dynamics simulation of a heat-enhanced transdermal delivery system

Transdermal delivery systems are useful in cases where preferred routes such as the oral route are not available. However, low overall extent of delivery is seen due to the permeation barrier posed by the skin. Chemical penetration enhancers and invasive methods that disturb the structural barrier function of the skin can be used to improve transdermal drug delivery. However, for suitable drugs, a fast-releasing transdermal delivery system can be produced by incorporating a heating source into a transdermal patch. In this study, a molecular dynamics simulation showed that heat increased the diffusivity of the drug molecules, resulting in faster release from gels containing ketoprofen, diclofenac sodium, and lidocaine HCl. Simulations were confirmed by in vitro drug release studies through lipophilic membranes. These correlations could expand the application of heated transdermal delivery systems for use as fast-release-dosage forms.

Safety evaluation of stamp type digital microneedle devices in hairless mice

Background

Microneedles provide a minimally invasive means to transport molecules into the skin. A number of specific strategies have been employed to use microneedles for transdermal delivery.

Objective

The purpose of this study was to investigate the safety of two new digital microneedle devices (Digital Hand® and Digital Pro®; Bomtech Electronics Co., Ltd., Seoul, Korea) for the perforation of skin in skin-hairless-1 mice. This device replaces conventional needles and is designed specifically for intradermal delivery.

Methods

We used two newly developed digital microneedle devices to perforate the skin of skin-hairless-1 mice. We conducted a comparative study of the two digital microneedle devices and DTS® (Disk type-microneedle Therapy System; DTS lab., Seoul, Korea). To evaluate skin stability, we performed visual and dermatoscopic inspections, measurements of transepidermal water loss, and biopsies.

Results

The two novel digital microneedle devices did not induce significant abnormalities of the skin on visual or dermatoscopic inspection, regardless of needle size (0.25~2.0 mm). No significant histopathological changes, such as inflammatory cell infiltration, desquamation of the stratum corneum, or disruption of the basal layer, were observed. The digital microneedle devices and microneedle therapy system produced similar results on measures of skin stability.

Conclusion

These two novel digital microneedle devices are safe transdermal drug delivery systems.

Magnetic nanoparticle-based approaches to locally target therapy and enhance tissue regeneration in vivo

Magnetic-based systems utilizing superparamagnetic nanoparticles and a magnetic field gradient to exert a force on these particles have been used in a wide range of biomedical applications. This review is focused on drug targeting applications that require penetration of a cellular barrier as well as strategies to improve the efficacy of targeting in these biomedical applications. Another focus of this review is regenerative applications utilizing tissue engineered scaffolds prepared with the aid of magnetic particles, the use of remote actuation for release of bioactive molecules and magneto-mechanical cell stimulation, cell seeding and cell patterning.

Antidermatitic perspective of hydrocortisone as chitosan nanocarriers: an ex vivo and in vivo assessment using an NC/Nga mouse model

The aim of this study to administer hydrocortisone (HC) percutaneously in the form of polymeric nanoparticles (NPs) to alleviate its transcutaneous absorption, and to derive additional wound-healing benefits of chitosan. HC-loaded NPs had varied particle sizes, zeta potentials, and entrapment efficiencies, when drug-to-polymer mass ratios increased from 1:1 to 1:8. Ex vivo permeation analysis showed that the nanoparticulate formulation of HC significantly reduced corresponding flux [∼24 µg/(cm(2) h)] and permeation coefficient (∼4.8 × 10(-3) cm/h) of HC across the full thickness NC/Nga mouse skin. The nanoparticulate formulation also exhibited a higher epidermal (1610 ± 42 µg/g of skin) and dermal (910 ± 46 µg/g of skin) accumulation of HC than those associated with control groups. An in vivo assessment using an NC/Nga mouse model further revealed that mice treated with the nanoparticulate system efficiently controlled transepidermal water loss [15 ± 2 g/(m(2) h)], erythema intensity (232 ± 12), dermatitis index (mild), and thickness of skin (456 ± 27 µm). Taken together, histopathological examination predicted that the nanoparticulate system showed a proficient anti-inflammatory and antifibrotic activity against atopic dermatitic (AD) lesions. Our results strongly suggest that HC-loaded NPs have promising potential for topical/transdermal delivery of glucocorticoids in the treatment of AD.

Devices for overcoming biological barriers: the use of physical forces to disrupt the barriers

Overcoming biological barriers including skin, mucosal membranes, blood brain barrier as well as cell and nuclear membrane constitutes a key hurdle in the field of drug delivery. While these barriers serve the natural protective function in the body, they limit delivery of drugs into the body. A variety of methods have been developed to overcome these barriers including formulations, targeting peptides and device-based technologies. This review focuses on the use of physical methods including acoustic devices, electric devices, high-pressure devices, microneedles and optical devices for disrupting various barriers in the body including skin and other membranes. A summary of the working principles of these devices and their ability to enhance drug delivery is presented.

Novel non-invasive methods of insulin delivery

INTRODUCTION

Insulin has usually been administered subcutaneously in the treatment of diabetes mellitus. Alternative delivery routes of insulin are expected to overcome some limitations, mainly concerned with the possibility of hypoglycemia episodes, weight gain and inadequate post-meal glucose control, in order to lead a better patient compliance.

AREAS COVERED

This review article covers all the most relevant non-invasive insulin delivery methods under development, respective technology and clinical data available according to their status of development. Special focus is given to the systems with late clinical trial evidences, their achievements and pitfalls. Pulmonary and oral appear to be the most advantageous routes, with regard to the long list of potentially marketed products.

EXPERT OPINION

Alternative insulin delivery to the subcutaneous administration is more and more close to the success, being fundamental that any optimized technology could overcome the overall low mucosal bioavailability of insulin, mostly due to its early degradation before absorption, inactivation and digestion by proteolytic enzymes and poor permeability across mucosal epithelium because of its high molecular weight and lack of lipophilicity.

Ultrasound-assisted convection-enhanced delivery to the brain in vivo with a novel transducer cannula assembly: laboratory investigation

OBJECT

In convection-enhanced delivery (CED), drugs are infused locally into tissue through a cannula inserted into the brain parenchyma to enhance drug penetration over diffusion strategies. The purpose of this study was to demonstrate the feasibility of ultrasound-assisted CED (UCED) in the rodent brain in vivo using a novel, low-profile transducer cannula assembly (TCA) and portable, pocket-sized ultrasound system.

METHODS

Forty Sprague-Dawley rats (350-450 g) were divided into 2 equal groups (Groups 1 and 2). Each group was divided again into 4 subgroups (n = 5 in each). The caudate of each rodent brain was infused with 0.25 wt% Evans blue dye (EBD) in phosphate-buffered saline at 2 different infusion rates of 0.25 μl/minute (Group 1), and 0.5 μl/minute (Group 2). The infusion rates were increased slowly over 10 minutes from 0.05 to 0.25 μl/minute (Group 1) and from 0.1 to 0.5 μl/minute (Group 2). The final flow rate was maintained for 20 minutes. Rodents in the 4 control subgroups were infused using the TCA without ultrasound and without and with microbubbles added to the infusate (CED and CED + MB, respectively). Rodents in the 4 UCED subgroups were infused without and with microbubbles added to the infusate (UCED and UCED + MB) using the TCA with continuous-wave 1.34-MHz low-intensity ultrasound at a total acoustic power of 0.11 ± 0.005 W and peak spatial intensity at the cannula tip of 49.7 mW/cm(2). An additional 4 Sprague-Dawley rats (350-450 g) received UCED at 4 different and higher ultrasound intensities at the cannula tip ranging from 62.0 to 155.0 mW/cm(2) for 30 minutes. The 3D infusion distribution was reconstructed using MATLAB analysis. Tissue damage and morphological changes to the brain were assessed using H & E.

RESULTS

The application of ultrasound during infusion (UCED and UCED + MB) improved the volumetric distribution of EBD in the brain by a factor of 2.24 to 3.25 when there were no microbubbles in the infusate and by a factor of 1.16 to 1.70 when microbubbles were added to the infusate (p < 0.001). On gross and histological examination, no damage to the brain tissue was found for any acoustic exposure applied to the brain.

CONCLUSIONS

The TCA and ultrasound device show promise to improve the distribution of infused compounds during CED. The results suggest further studies are required to optimize infusion and acoustic parameters for small compounds and for larger molecular weight compounds that are representative of promising antitumor agents. In addition, safe levels of ultrasound exposure in chronic experiments must be determined for practical clinical evaluation of UCED. Extension of these experiments to larger animal models is warranted to demonstrate efficacy of this technique.

Physically facilitating drug-delivery systems

Facilitated/modulated drug-delivery systems have emerged as a possible solution for delivery of drugs of interest to pre-allocated sites at predetermined doses for predefined periods of time. Over the past decade, the use of different physical methods and mechanisms to mediate drug release and delivery has grown significantly. This emerging area of research has important implications for development of new therapeutic drugs for efficient treatments. This review aims to introduce and describe different modalities of physically facilitating drug-delivery systems that are currently in use for cancer and other diseases therapy. In particular, delivery methods based on ultrasound, electrical, magnetic and photo modulations are highlighted. Current uses and areas of improvement for these different physically facilitating drug-delivery systems are discussed. Furthermore, the main advantages and drawbacks of these technologies reviewed are compared. The review ends with a speculative viewpoint of how research is expected to evolve in the upcoming years.

Synergistic effect of hyperosmotic agents and sonophoresis on breast tissue optical properties and permeability studied with spectral domain optical coherence tomography

Hyperosmotic agents have shown great potential in tissue optical clearing. However, the low efficiency of the permeation in biological tissues seriously restricts its application in reality. The synergy of sonophoresis as a penetration enhancer and hyperosmotic agents, 20% glucose (G) and 20% mannitol (M), in optical clearing has been investigated by analyzing the variation of the attenuation coefficients and the permeability coefficients. In the sonophoresis experiments, ultrasound (US) was applied for 10 min before applying hyperosmotic agents. Along with the administration of hyperosmotic agents, the samples were monitored with optical coherence tomography (OCT) functional imaging for the next 2 h. The attenuation coefficients of each group were obtained from the 2-D OCT images based on Beer's Law. The original attenuation coefficient is 12.38 ± 0.73 cm-1 in normal breast tissue. After 45 min treatment, it changes to be 5.91 ± 0.82 cm-1 and 4.14 ± 0.67 cm-1 for 20% G and 20% G/US, respectively. The attenuation coefficient of breast cancer tissue is 18.17 ± 1.45 cm-1 at the beginning, and it becomes 8.70 ± 0.87 cm-1 for 20% G and 6.80 ± 0.92 cm-1 for 20% G/US after 30 min. Meanwhile, the permeability coefficients of hyperosmotic agents were much enlarged by the treatment of ultrasound in both breast normal tissue and breast cancer tissue. A significant difference in permeability coefficients between health tissue and tumor tissue was also observed in the experiment (p<0.01).

Biologic activities of molecular chaperones and pharmacologic chaperone imidazole-containing dipeptide-based compounds: natural skin care help and the ultimate challenge: implication for adaptive responses in the skin

Accumulation of molecular damage and increased molecular heterogeneity are hallmarks of photoaged skin and pathogenesis of human cutaneous disease. Growing evidence demonstrates the ability of molecular chaperone proteins and of pharmacologic chaperones to decrease the environmental stress and ameliorate the oxidation stress-related and glycation disease phenotypes, suggesting that the field of chaperone therapy might hold novel treatments for skin diseases and aging. In this review, we examine the evidence suggesting a role for molecular chaperone proteins in the skin and their inducer and protecting agents: pharmacologic chaperone imidazole dipeptide-based agents (carcinine and related compounds) in cosmetics and dermatology. Furthermore, we discuss the use of chaperone therapy for the treatment of skin photoaging diseases and other skin pathologies that have a component of increased glycation and/or free radical-induced oxidation in their genesis. We examine biologic activities of molecular and pharmacologic chaperones, including strategies for identifying potential chaperone compounds and for experimentally demonstrating chaperone activity in in vitro and in vivo models of human skin disease. This allows the protein to function and traffic to the appropriate location in the skin, thereby increasing protein activity and cellular function and reducing stress on skin cells. The benefits of imidazole dipeptide antioxidants with transglycating activity (such as carcinine) in skin care are that they help protect and repair cell membrane damage and help retain youthful, younger-looking skin. All skin types will benefit from daily, topical application of pharmacologic chaperone antioxidants, anti-irritants, in combination with water-binding protein agents that work to mimic the structure and function of healthy skin. General strategies are presented addressing ground techniques to improve absorption of usually active chaperone proteins and dipeptide compounds, include encapsulation into hydrophobic carriers, a combination with penetration enhancers, active electrical transport, or chemical modification to increase hydrophobicity.

Influence of the timing of ultrasound application on the penetration of corticosteroids

BACKGROUND

The application of ultrasound to enhance the transdermal transport of drugs is often referred to as 'sonophoresis'. In physiotherapy sonophoresis is applied to the skin through two different procedures: (1) the pre-treatment procedure where the skin is treated with ultrasound irradiation prior to the drug application and (2) a simultaneous treatment mode, where the skin is treated with ultrasound during the application of the pharmacologic substance. The aim of this study was to compare the bioavailability of halcinonide in the stratum corneum comparing the ultrasound pre-treatment vs. the simultaneous treatment method.

METHODS

The effect of pre and simultaneous ultrasound treatment (1 MHz, 1 W/cm(2)) was evaluated on the halcinonide blanching response using tristimulus colorimetry 2 h after the initial application.

RESULTS

Within the evaluation period, only the ultrasound pre-treatment method resulted in a significant blanching response.

CONCLUSION

Timing of the ultrasound application seems to influence the availability and percutaneous penetration process and should be taken into account when estimating the ultrasound enhancing effect.

Materials for diabetes therapeutics

This review is focused on the materials and methods used to fabricate closed-loop systems for type 1 diabetes therapy. Herein, we give a brief overview of current methods used for patient care and discuss two types of possible treatments and the materials used for these therapies-(i) artificial pancreases, comprised of insulin producing cells embedded in a polymeric biomaterial, and (ii) totally synthetic pancreases formulated by integrating continuous glucose monitors with controlled insulin release through degradable polymers and glucose-responsive polymer systems. Both the artificial and the completely synthetic pancreas have two major design requirements: the device must be both biocompatible and be permeable to small molecules and proteins, such as insulin. Several polymers and fabrication methods of artificial pancreases are discussed: microencapsulation, conformal coatings, and planar sheets. We also review the two components of a completely synthetic pancreas. Several types of glucose sensing systems (including materials used for electrochemical, optical, and chemical sensing platforms) are discussed, in addition to various polymer-based release systems (including ethylene-vinyl acetate, polyanhydrides, and phenylboronic acid containing hydrogels).