Permeability enhancement for transdermal delivery of large molecule using low-frequency sonophoresis combined with microneedles

Recent progress on the development of bioinspired surfaces with high aspect ratio microarray structures: From fabrication to applications

Surfaces with high aspect ratio microarray structures can implement sophisticated assignment in typical fields including microfluidics, sensor, biomedicine, et al. via regulating their deformation or the material properties. Inspired by natural materials and systems, for example sea cockroaches, water spiders, cacti, lotus leaves, rice leaves, and cedar leaves, many researchers have focused on microneedle functional surface studies. When the surface with high aspect ratio microarray structures is stimulated by the external fields, such as optical, electric, thermal, magnetic, the high aspect ratio microarray structures can undergo hydrophilic and hydrophobic switching or shape change, which may be gifted the surfaces with the ability to perform complex task, including directional liquid/air transport, targeted drug delivery, microfluidic chip sensing. In this review, the fabrication principles of various surfaces with high aspect ratio microarray structures are classified and summarized. Mechanisms of liquid manipulation on hydrophilic/hydrophobic surfaces with high aspect ratio microarray structures are clarified based on Wenzel model, Cassie model, Laplace pressure theories and so on. Then the intelligent control strategies have been demonstrated. The applications in microfluidic, drug delivery, patch sensors have been discussed. Finally, current challenges and new insights of future prospects for dynamic manipulation of liquid/air based on biomimetic surface with high aspect ratio microarray structures are also addressed.

Microneedle and Polymeric Films: Delivery of Proteins, Peptides and Nucleic Acids

In the last 20 years, protein, peptide and nucleic acid-based therapies have become the fastest growing sector in the pharmaceutical industry and play a vital role in disease therapy. However, the intrinsic sensitivity and large molecular sizes of biotherapeutics limit the available routes of administration. Currently, the main administration routes of biomacromolecules, such as parenteral, oral, pulmonary, nasal, rectal and buccal routes, each have their limitations. Several non-invasive strategies have been proposed to overcome these challenges. Researchers were particularly interested in microneedles (MNs) and polymeric films because of their less invasiveness, convenience and greater potential to preserve the bioactivity of biotherapeutics. By facilitating with MNs and polymeric films, biomacromolecules could provide significant benefits to patients suffering from various diseases such as cancer, diabetes, infectious and ocular diseases. However, before these devices can be used on patients, how to upscale MN manufacture in a cost-effective and timely manner, as well as the long-term safety of MN and polymeric film applications necessitates further investigation.

Tiny titans- unravelling the potential of polysaccharides and proteins based dissolving microneedles in drug delivery and theranostics: A comprehensive review

In recent years, microneedles (MNs) have emerged as a promising alternative to traditional drug delivery systems in transdermal drug delivery. The use of MNs has demonstrated significant potential in improving patient acceptance and convenience while avoiding the invasiveness of traditional injections. Dissolving, solid, hollow, coated, and hydrogel microneedles are among the various types studied for drug delivery. Dissolving microneedles (DMNs), in particular, have gained attention for their safety, painlessness, patient convenience, and high delivery efficiency. This comprehensive review primarily focuses on different types of microneedles, fabrication methods, and materials used in fabrication of DMNs such as hyaluronic acid, chitosan, alginate, gelatin, collagen, silk fibroin, albumin, cellulose and starch, to list a few. The review also provides an exhaustive discussion on the applications of DMNs, including the delivery of vaccines, cosmetic agents, contraceptives, hormone and genes, and other therapeutic applications like for treating cancer, skin diseases, and diabetes, among others, are covered in this review. Additionally, this review highlights some of the DMN systems that are presently undergoing clinical trials. Finally, the review discusses current advances and trends in DMNs, as well as future prospective directions for this ground-breaking technology in drug delivery.

Peptide-containing nanoformulations: Skin barrier penetration and activity contribution

Transdermal drug delivery presents a less invasive pathway, circumventing the need to pass through the gastrointestinal tract and liver, thereby reducing drug breakdown, initial metabolism, and gastrointestinal discomfort. Nevertheless, the unique composition and dense structure of the stratum corneum present a significant barrier to transdermal delivery. This article presents an overview of the current developments in peptides and nanotechnology to address this challenge. Initially, we sum up peptide-containing nanoformulations for transdermal drug delivery, examining them through the lenses of both inorganic and organic materials. Particular emphasis is placed on the diverse roles that peptides play within these nanoformulations, including conferring functionality upon nanocarriers and enhancing the biological efficacy of drugs. Subsequently, we summarize innovative strategies for enhancing skin penetration, categorizing them into passive and active approaches. Lastly, we discuss the therapeutic potential of peptide-containing nanoformulations in addressing a range of diseases, drawing insights from the biological activities and functions of peptides. Furthermore, the challenges hindering clinical translation are also discussed, providing valuable insights for future advancements in transdermal drug delivery.

Enhanced skin neocollagenesis through the transdermal delivery of poly-L-lactic acid microparticles by using a needle-free supersonic atomizer

In this study, a spindle-type nozzle was designed to accelerate poly-L-lactic acid (PLLA) microparticles to supersonic velocities for the transdermal delivery of these microparticles to rats. This approach is needle- and pain-free and enhances skin collagen regeneration. The addition of PLLA microparticles at a concentration of 2 mg/mL did not hinder the growth of 3 T3 fibroblasts and Raw264.7 macrophages. The TNF-α assay revealed no obvious inflammation effect of PLLA microparticles at a concentration of 1 mg/mL. A time-lapse recording revealed that after being cocultured with PLLA microparticles for 24 h, Raw264.7 macrophages gradually approached and surrounded the PLLA microparticles. When 3 T3 fibroblasts were cocultured with Raw264.7 macrophages, which were stimulated using PLLA microparticles, collagen synthesis was increased by approximately 60 % compared with that in samples without PLLA microparticles. In vivo animal experiments indicated that after the transdermal delivery of 10 shots of PLLA microparticles through the supersonic atomizer, no obvious changes or damage to the back skin of Sprague-Dawley rats was observed. More importantly, numerous PLLA microparticles penetrated the rat epidermis into the dermal layer. We found macrophages and fibroblasts present close to the PLLA microparticles. Moreover, only mild or no inflammation reaction was observed. Masson staining revealed that after 6-week implantation, 6 % and 12 % of PLLA microparticles significantly stimulated collagen regeneration in 6-week-old and 32-week-old rats. In addition, picrosirius red staining revealed a significant increase in collagen regeneration, especially for type III collagen, following the 6-week implantation of PLLA microparticles. In summary, this study demonstrated an easy, pain-free, nondestructive approach for introducing PLLA microparticles into the dermal layer by using a supersonic atomizer to stimulate collagen regeneration in vivo.

Transdermal drug delivery via microneedles for musculoskeletal systems

As the population is ageing and lifestyle is changing, the prevalence of musculoskeletal (MSK) disorders is gradually increasing with each passing year, posing a serious threat to the health and quality of the public, especially the elderly. However, currently prevalent treatments for MSK disorders, mainly administered orally and by injection, are not targeted to the specific lesion, resulting in low efficacy along with a series of local and systemic adverse effects. Microneedle (MN) patches loaded with micron-sized needle array, combining the advantages of oral administration and local injection, have become a potentially novel strategy for the administration and treatment of MSK diseases. In this review, we briefly introduce the basics of MNs and focus on the main characteristics of the MSK systems and various types of MN-based transdermal drug delivery (TDD) systems. We emphasize the progress and broad applications of MN-based transdermal drug delivery (TDD) for MSK systems, including osteoporosis, nutritional rickets and some other typical types of arthritis and muscular damage, and in closing summarize the future prospects and challenges of MNs application.

3D-Printed Integrated Ultrasonic Microneedle Array for Rapid Transdermal Drug Delivery

Transdermal drug delivery (TDD) is an attractive alternative to oral and hypodermic injection drug administration, and is poised to increase its impact on medicine and pharmaceutical design. Microneedles (MNs) are a new minimally invasive TDD method widely used in medicine and cosmetology. MNs create a microscale channel from the stratum corneum to the dermis and enable drug delivery of hydrophilic and macromolecular into the skin. Although MNs allow different drugs to penetrate the stratum corneum, they cannot provide an extra driving force for drug transport in tissue. To overcome this limitation and achieve fast, controllable drug delivery, an integrated 3D-printed ultrasonic MN array (USMA) device consisting of hollow MNs and an ultrasonic transducer is proposed. The hollow MNs enable drug to penetrate the stratum corneum, and the ultrasound transmitted through the MNs provides the driving force for drug transportation in tissue. Using methylene blue and bovine serum albumin as model drugs, we tested the drug delivery performance of USMA on porcine skin; the results show that USMA significantly enhanced the delivery efficiency of model drugs. Besides, USMA obviously reduced MNs insertion force and tissue damage, which were well-tolerated and gentle. This study suggests that the integrated ultrasonic MN array has great potential for clinical drug delivery with high efficiency and lessening the suffering of patients.

How physical techniques improve the transdermal permeation of therapeutics: A review

BACKGROUND

Transdermal delivery is very important in pharmaceutics. However, the barrier function of the stratum corneum hinders drugs absorption. How to improve transdermal delivery efficiency is a hot topic. The key advantages of physical technologies are their wide application for the delivery of previously nonappropriate transdermal drugs, such as proteins, peptides, and hydrophilic drugs. Based on the improved permeation of drugs delivered via multiple physical techniques, many more diseases may be treated, and transdermal vaccinations become possible. However, their wider application depends on the related convenient and portable devices. Combined products comprising medicine and devices represent future commercial directions of artificial intelligence and 3D printing.

METHODS

A comprehensive search about transdermal delivery assisted by physical techniques has been carried out on Web of Science, EMBASE database, PubMed, Wanfang Database, China National Knowledge Infrastructure, and Cochrane Library. The search identified and retrieved the study describing multiple physical technologies to promote transdermal penetration.

RESULTS

Physical technologies, including microneedles, lasers, iontophoresis, sonophoresis, electroporation, magnetophoresis, and microwaves, are summarized and compared. The characteristics, mechanism, advantages and disadvantages of physical techniques are clarified. The individual or combined applicable examples of physical techniques to improve transdermal delivery are summarized.

CONCLUSION

This review will provide more useful guidance for efficient transdermal delivery. More therapeutic agents by transdermal routes become possible with the assistance of various physical techniques.

Microneedle system: a modulated approach for penetration enhancement

The microneedles show advantages over transdermal drug delivery systems on account of better skin permeation bypassing the stratum corneum. To increase the flux of permeation, penetration enhancement techniques like physical and chemical methods are combined with a trans-epidermal delivery system across the skin causing minimal pain. These techniques include iontophoresis, sonophoresis, and electroporation for physical enhancement of drug delivery via topical route by either disrupting the structure of the stratum corneum or by creating pores/micro-channels within the skin. The use of chemical penetrants such as ethanol, lipids, surfactants, and terpenes improves the release kinetics by mechanisms like fluidization of lipids, denaturation of proteins, etc. A combination of microneedles and these techniques show a significant increase in the permeability of drugs across the skin by 5-10 times compared to microneedles alone. This review article focuses on various advanced strategies like the use of drug-polymer complexes, application of ultrasound frequency or tolerable electric current, formation of nano-formulations, etc. with microneedle delivery for transportation of high payload of actives, macromolecules, antibodies, gene, proteins, and peptides. In the near future, microneedle systems will offer potential targeted drug delivery, self-sealable administration across the skin, and minimally invasive vaccine transportation in cancer, diabetes, Alzheimer's, and cardiovascular diseases.HighlightsPhysical penetration enhancement techniques: iontophoresis, electroporation, and sonophoresis.Chemical penetration enhancers: polymers, lipids, surfactants.Strategies to use microneedle system with penetration enhancement techniques.The significant difference in the penetration ability of high payload actives.

An overview of microneedle applications, materials, and fabrication methods

Microneedle-based microdevices promise to expand the scope for delivery of vaccines and therapeutic agents through the skin and withdrawing biofluids for point-of-care diagnostics - so-called theranostics. Unskilled and painless applications of microneedle patches for blood collection or drug delivery are two of the advantages of microneedle arrays over hypodermic needles. Developing the necessary microneedle fabrication processes has the potential to dramatically impact the health care delivery system by changing the landscape of fluid sampling and subcutaneous drug delivery. Microneedle designs which range from sub-micron to millimetre feature sizes are fabricated using the tools of the microelectronics industry from metals, silicon, and polymers. Various types of subtractive and additive manufacturing processes have been used to manufacture microneedles, but the development of microneedle-based systems using conventional subtractive methods has been constrained by the limitations and high cost of microfabrication technology. Additive manufacturing processes such as 3D printing and two-photon polymerization fabrication are promising transformative technologies developed in recent years. The present article provides an overview of microneedle systems applications, designs, material selection, and manufacturing methods.

Topical delivery of gambogic acid assisted by the combination of low-frequency ultrasound and chemical enhancers for chemotherapy of cutaneous melanoma

Anti-cutaneous melanoma activity of the skin-delivered gambogic acid (GA) has been reported in our previous study. However, it is difficult for GA to diffuse passively through intact skin without any enhancement means. In this study, a combination of chemical enhancers (EN: azone and propylene glycol) and physical ultrasound (US) was used to improve the percutaneous permeation of GA and enhance the anti-melanoma activity. The enhancement effect of the combination of EN and US (EN-US) on GA in vitro and in vivo was studied, and the enhancement mechanism and skin irritation were also evaluated. We showed that the parameters of US application at a constant frequency (30 kHz) with a duty cycle of 100% and intensity of 1.75 W/cm² for 20 min were optimal. In vitro, EN-US showed a considerable enhancement of the permeation of GA, and the enhancement effect was stronger than that with the use of EN or US alone. In vivo antitumor study showed that the tumor growth was significantly inhibited after percutaneous administration of GA by EN-US, more than in the intravenous injection group. The penetration enhancement mechanism revealed that EN-US not only altered the structure of lipid bilayers and keratins to reduce the barrier effect of the stratum corneum but also produced diffusion channels in the skin under the cavitation effect of US, thereby promoting the skin penetration of GA. In addition, there was no observable skin irritation in mice after treatment with EN-US. Our study demonstrated that the combination of EN and US improved the skin permeation and retention of GA to enhance the anti-melanoma activity. This method also provides technical guidance for the future development of topical and transdermal therapeutic system of GA.

Enhanced Drug Permeation into Human Keloid Tissues by Sonophoresis-Assisted Microneedling

Keloids are disfiguring pathological scars that could cause pain and pruritus. The conventional treatments, such as bolus injection of drugs or surgery, are invasive and require a personal visit to clinic. Microneedle (MN) technology has great potential to offer a self-administered and minimally invasive treatment of keloids. However, drugs delivered using MNs suffer from limited penetration in keloid tissue. This study demonstrates enhanced drug penetration in human keloid scar tissue by combining MN and sonophoresis.

Cosmetic, Biomedical and Pharmaceutical Applications of Fish Gelatin/Hydrolysates

There are several reviews that separately cover different aspects of fish gelatin including its preparation, characteristics, modifications, and applications. Its packaging application in food industry is extensively covered but other applications are not covered or covered alongside with those of collagen. This review is comprehensive, specific to fish gelatin/hydrolysate and cites recent research. It covers cosmetic applications, intrinsic activities, and biomedical applications in wound dressing and wound healing, gene therapy, tissue engineering, implants, and bone substitutes. It also covers its pharmaceutical applications including manufacturing of capsules, coating of microparticles/oils, coating of tablets, stabilization of emulsions and drug delivery (microspheres, nanospheres, scaffolds, microneedles, and hydrogels). The main outcomes are that fish gelatin is immunologically safe, protects from the possibility of transmission of bovine spongiform encephalopathy and foot and mouth diseases, has an economic and environmental benefits, and may be suitable for those that practice religious-based food restrictions, i.e., people of Muslim, Jewish and Hindu faiths. It has unique rheological properties, making it more suitable for certain applications than mammalian gelatins. It can be easily modified to enhance its mechanical properties. However, extensive research is still needed to characterize gelatin hydrolysates, elucidate the Structure Activity Relationship (SAR), and formulate them into dosage forms. Additionally, expansion into cosmetic applications and drug delivery is needed.

Recent advances in combination of microneedles and nanomedicines for lymphatic targeted drug delivery

Numerous diseases have been reported to affect the lymphatic system. As such, several strategies have been developed to deliver chemotherapeutics to this specific network of tissues and associated organs. Nanotechnology has been exploited as one of the main approaches to improve the lymphatic uptake of drugs. Different nanoparticle approaches utilized for both active and passive targeting of the lymphatic system are discussed here. Specifically, due to the rich abundance of lymphatic capillaries in the dermis, particular attention is given to this route of administration, as intradermal administration could potentially result in higher lymphatic uptake compared to other routes of administration. Recently, progress in microneedle research has attracted particular attention as an alternative for the use of conventional hypodermic injections. The benefits of microneedles, when compared to intradermal injection, are subsequently highlighted. Importantly, microneedles exhibit particular benefit in relation to therapeutic targeting of the lymphatic system, especially when combined with nanoparticles, which are further discussed. However, despite the apparent benefits provided by this combination approach, further comprehensive preclinical and clinical studies are now necessary to realize the potential extent of this dual-delivery platform, further taking into consideration eventual usability and acceptability in the intended patient end-users. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Biodegradable microneedles fabricated with carbohydrates and proteins: Revolutionary approach for transdermal drug delivery

There has been a surge in the use of transdermal drug delivery systems (TDDS) for the past few years. The market of TDDS is expected to reach USD 7.1 billion by 2023, from USD 5.7 billion in 2018, at a CAGR of 4.5%. Microneedles (MNs) are a novel class of TDDS with advantages of reduced pain, low infection risk, ease of application, controlled release of therapeutic agents, and enhanced bioavailability. Biodegradable MNs fabricated from natural polymers have become the center of attention among formulation scientists because of their recognized biodegradability, biocompatibility, ease of fabrication, and sustainable character. In this review, we summarize the various polysaccharides and polypeptide based biomaterials that are used to fabricate biodegradable MNs. Particular emphasis is given to cellulose and its derivatives, starch, and complex carbohydrate polymers such as alginates, chitosan, chondroitin sulfate, xanthan gum, pullulan, and hyaluronic acid. Additionally, novel protein-based polymers such as zein, collagen, gelatin, fish scale and silk fibroin (polyamino acid) biopolymers application in transdermal drug delivery have also been discussed. The current review will provide a unique perspective to the readers on the developments of biodegradable MNs composed of carbohydrates and protein polymers with their clinical applications and patent status.

Microneedle Technology: An Insight into Recent Advancements and Future Trends in Drug and Vaccine Delivery

Over the last decade, microneedle (MN) induced microporation multifunctional approaches to enhance the delivery of drugs through the skin. MN technology included micron-sized needles to create microchannels into the Stratum corneum of skin, the most significant protective layer. Delivery of drugs and vaccines through the transdermal route is an alternative route for hypodermic and oral. It overcomes the problems associated with gastrointestinal along with drug deterioration. It is affordable, noninvasive, painless, simple, and self-administered techniques that provide prolonged release of drugs to enhance patient compliance. The MN delivery focused on biopharmaceuticals like proteins or peptides. The novel concepts have drawn interest in using these techniques in tandem with other enhancement approaches. This review article discussed the latest advancements in MN technology. It emphasized types of MNs, methodology, mechanisms, strategies for delivery of several drugs and vaccines, and significant challenges in the marketing of biopharmaceuticals. Furthermore, relevant U.S. patents and clinical trials based on MNs are also accentuated. Therefore, MN techniques will play a pivotal role in promoting clinical applications and innovative research for scientists and researchers working in the pharmaceutical field.

Skin Permeation of Nanoparticles: Mechanisms Involved and Critical Factors Governing Topical Drug Delivery

Transdermal route has been an ever sought-after means of drug administration, regarded as being the most convenient and patient compliant. However, skin poses a great barrier to the entry of the external particles including bacteria, viruses, allergens, and drugs as well (mostly hydrophilic or high molecular weight drugs), consequent to its complex structure and composition. Among the various means of enhancing drug permeation through the skin, e.g. chemical permeation enhancers, electroporation, thermophoresis, etc. drug delivery through nanoparticles has been of great interest. Current literature reports a vast number of nanoparticles that have been implicated for drug delivery through the skin. However, a precise account of critical factors involved in drug delivery and mechanisms concerning the permeation of nanoparticles through the skin is necessary. The purpose of this review is to enumerate the factors crucial in governing the prospect of drug delivery through skin and classify the skin permeation mechanisms of nanoparticles. Among the various mechanisms discussed are the ones governed by principles of kinetics, osmotic gradient, adhesion, hydration, diffusion, occlusion, electrostatic interaction, thermodynamics, etc. Among the most common factors affecting skin permeation of nanoparticles that are discussed include size, shape, surface charge density, composition of nanoparticles, mechanical stress, pH, etc.

Microneedle Mediated Transdermal Delivery of Protein, Peptide and Antibody Based Therapeutics: Current Status and Future Considerations

The success of protein, peptide and antibody based therapies is evident - the biopharmaceuticals market is predicted to reach $388 billion by 2024 [1], and more than half of the current top 20 blockbuster drugs are biopharmaceuticals. However, the intrinsic properties of biopharmaceuticals has restricted the routes available for successful drug delivery. While providing 100% bioavailability, the intravenous route is often associated with pain and needle phobia from a patient perspective, which may translate as a reluctance to receive necessary treatment. Several non-invasive strategies have since emerged to overcome these limitations. One such strategy involves the use of microneedles (MNs), which are able to painlessly penetrate the stratum corneum barrier to dramatically increase transdermal drug delivery of numerous drugs. This review reports the wealth of studies that aim to enhance transdermal delivery of biopharmaceutics using MNs. The true potential of MNs as a drug delivery device for biopharmaceuticals will not only rely on acceptance from prescribers, patients and the regulatory authorities, but the ability to upscale MN manufacture in a cost-effective manner and the long term safety of MN application. Thus, the current barriers to clinical translation of MNs, and how these barriers may be overcome are also discussed.

Advances in Ultrasound Mediated Transdermal Drug Delivery

Low frequency ultrasound-assisted drug delivery has been widely investigated as a non-invasive method to enhance the transdermal penetration of drugs. Using this technique, a brief application of ultrasound is used to permeabilize skin for a prolonged time. In this review, an overview on ultrasound is detailed to help explain the parameters that could be modulated to obtain the desired ultrasound parameters for enhanced transdermal drug delivery. The mechanisms of enhancement and the latest developments in the area of ultrasound-assisted transdermal drug delivery are discussed. Special emphasis is placed on the effects of ultrasound when used in combination with microneedles, electroporation and iontophoresis, and penetration enhancers. Further, this review summarizes the effect of ultrasound on skin integrity and the regulatory requirements for commercialization of the ultrasound based transdermal delivery instruments.

Circulation Cooling in Continuous Skin Sonoporation at Constant Coupling Fluid Temperatures

Exposure of the skin to low-frequency ultrasound in the Franz diffusion cell has been found to increase the permeability of the skin to molecular transport. In many cases, significant heating of the coupling fluid requires the use of duty cycles that extend the total experimental time. This is a methodological study in which the coupling fluid is circulated between a modified Franz diffusion cell and a heat exchanger to allow for the continuous application of low-frequency ultrasound while the coupling fluid temperature is held constant. Dermatomed porcine skin was exposed to continuous ultrasound at 20 kHz for 10 min at an intensity of 55 W/cm² while the coupling fluid was maintained at one of three target temperatures (13°C, 33°C or 46°C). Foil pitting and passive cavitation detection revealed that inertial cavitation activity decreased with increasing coupling fluid target temperature. Transport measurements revealed an increase in mean donor calcein concentration with increasing coupling fluid temperature, though these were not statistically significant. Taken together these findings suggest that the weakened stratum corneum lipid structure at higher temperatures is more susceptible to the introduction of defects from the jetting of cavitation.

A Thermoelectric Device for Coupling Fluid Temperature Regulation During Continuous Skin Sonoporation or Sonophoresis

During skin sonoporation and sonophoresis, time-consuming duty cycles or fluid replacement is often required to mitigate coupling fluid temperature increases. This study demonstrates an alternative method for temperature regulation: a circulating, thermoelectric system. Porcine skin samples were sonoporated continuously for 10 min at one of three intensities (23.8, 34.2, 39.4 W/m²). A caffeine solution was then applied to the skin and left to diffuse for 20 h. During sonoporation, the system was able to maintain the temperature between 10 and 16°C regardless of the intensity. No increase in transdermal transport was achieved with an intensity of 23.8 W/m². Intensities of 34.2 and 39.4 W/m² resulted in 3.5-fold (p < 0.05) and 3.7-fold (p < 0.05) increases in mean transport, relative to a control case with no ultrasound. From these results, it is concluded that a significant transport increase can be achieved with a system that circulates and cools the coupling fluid during ultrasound application. Relative to the previous methods of temperature control (duty cycles and fluid replacement), use of this circulation system will lead to significant time savings in future experimental studies.

In Vivo Experimental Study of Noninvasive Insulin Microinjection through Hollow Si Microneedle Array

An experimental study of in vivo insulin delivery through microinjection by using hollow silicon microneedle array is presented. A case study was carried out on a healthy human subject in vivo to determine the influence of delivery parameters on drug transfer efficiency. As a microinjection device, a hollow microneedle array (13 × 13 mm²) having 100 microneedles (220 µm high, 130 µm-outer diameter and 50 µm-inner diameter) was designed and fabricated using classical microfabrication techniques. The efficiency of the delivery process was first characterized using methylene blue and a saline solution. Based on these results, the transfer efficiency was found to be predominantly limited by the inability of viable epidermis to absorb and allow higher drug transport toward the capillary-rich region. Two types of fast-acting insulin were used to provide evidence of efficient delivery by hollow MNA to a human subject. By performing blood analyses, infusion of more-concentrated insulin (200 IU/mL, international units (IU)) exhibited similar blood glucose level drop (5–7%) compared to insulin of standard concentration (100 IU/mL), however, significant increase of serum insulin (40–50%) with respect to the preinfusion values was determined. This was additionally confirmed by a distinctive increase of insulin to C-peptide ratio as compared to preinfusion ratio. Moreover, we noticed that this route of administration mimics a multiple dose regimen, able to get a “steady state” for insulin plasma concentration.

A novel ultradeformable liposomes of Naringin for anti-inflammatory therapy

Ultradeformable liposomes were formulated using naringin (NA), a flavanone glycoside, at different concentrations (3, 6 and 9mg/mL). Nanovesicles were small size (∼100nm), regardless of the NA concentration used, and monodisperse (PI<0.30). All formulations showed a high entrapment efficiency (∼88%) and a highly negative zeta potential (around -30mV). The selected formulations were highly biocompatible as confirmed by in vitro studies using 3T3 fibroblasts. In vitro assay showed that the amounts (%) of NA accumulated in the epidermis (∼10%) could explain the anti-inflammatory properties of ultradeformable liposomes. In vivo studies confirmed the higher effectiveness of ultradeformable liposomes respect to betamethasone cream and NA dispersion in reducing skin inflammation in mice. Overall, it can conclude that NA ultradeformable liposomes can be considered as a promising formulation for the treatment of skin inflammatory diseases.

Influence of peptide dendrimers and sonophoresis on the transdermal delivery of ketoprofen

The aim of this study was to determine the individual and combined effects of peptide dendrimers and low frequency ultrasound on the transdermal permeation of ketoprofen. Arginine terminated peptide dendrimers of varying charges (4⁺, 8⁺ and 16⁺, named as A4. A8 and A16 respectively) were synthesized and characterized. Ketoprofen was subjected to passive, peptide dendrimer-assisted and sonophoretic permeation studies (with and without dendrimer application) across Swiss albino mouse skin, both in vitro and in vivo. The studies revealed that the synthesized peptide dendrimers considerably increased the transdermal permeation of ketoprofen and displayed enhancement ratios of up to 3.25 (with A16 dendrimer), compared to passive diffusion of drug alone in vitro. Moreover, the combination of peptide dendrimer treatment and ultrasound application worked in synergy and gave enhancement ratios of up to 1369.15 (with ketoprofen-A16 dendrimer complex). In vivo studies demonstrated that dendrimer and ultrasound-assisted permeation of drug achieved much higher plasma concentration of drug, compared to passive diffusion. Comparison of transdermal and oral absorption studies revealed that transdermal administration of ketoprofen with A8 dendrimer showed comparable absorption and plasma drug levels with oral route. The excised mouse skin after in vivo permeation study with dendrimers and ultrasound did not show major toxic reactions. This study demonstrates that arginine terminated peptide dendrimers combined with sonophoresis can effectively improve the transdermal permeation of ketoprofen.

The Influence of Solid Microneedles on the Transdermal Delivery of Selected Antiepileptic Drugs

The aim of this project was to examine the effect of microneedle rollers on the percutaneous penetration of tiagabine hydrochloride and carbamazepine across porcine skin in vitro. Liquid chromatography-mass spectrometric analysis was carried out using an Agilent 1200 Series HPLC system coupled to an Agilent G1969A TOF-MS system. Transdermal flux values of the drugs were determined from the steady-state portion of the cumulative amount versus time curves. Following twelve hours of microneedle roller application, there was a 6.74-fold increase in the percutaneous penetration of tiagabine hydrochloride (86.42 ± 25.66 µg/cm²/h) compared to passive delivery (12.83 ± 6.30 µg/cm²/h). For carbamazepine in 20% ethanol, passive transdermal flux of 7.85 ± 0.60 µg/cm²/h was observed compared to 10.85 ± 0.11 µg/cm²/h after microneedle treatment. Carbamazepine reconstituted in 30% ethanol resulted in only a 1.19-fold increase in drug permeation across porcine skin (36.73 ± 1.83 µg/cm²/h versus 30.74 ± 1.32 µg/cm²/h). Differences in flux values of untreated and microneedle-treated porcine skin using solid microneedles for the transdermal delivery of tiagabine were statistically significant. Although there were 1.38- and 1.19-fold increases in transdermal flux values of carbamazepine when applied as 20% and 30% ethanol solutions across microneedle-treated porcine skin, respectively, the increases were not statistically significant.

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

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

Transungual permeation: current insights

Nail disorders are beyond cosmetic concern; besides discomfort in the performance of daily chores, they disturb patients psychologically and affect their quality of life. Fungal nail infection (onychomycosis) is the most prevalent nail-related disorder affecting a major population worldwide. Overcoming the impenetrable nail barrier is the toughest challenge for the development of efficacious topical ungual formulation. Sophisticated techniques such as iontophoresis and photodynamic therapy have been proven to improve transungual permeation. This article provides an updated and concise discussion regarding the conventional approach and upcoming novel approaches focused to alter the nail barrier. A comprehensive description regarding preformulation screening techniques for the identification of potential ungual enhancers is also described in this review while highlighting the current pitfalls for the development of ungual delivery.

Effects of Microbubble Size on Ultrasound-Induced Transdermal Delivery of High-Molecular-Weight Drugs

The transdermal delivery of a wide range of high-molecular-weight drugs is limited by the stratum corneum layer of the epidermis representing a significant barrier to penetration across the skin. This study first determined the different effects of different-size ultrasound (US) contrast agents and microbubbles (MBs) for enhancing the transdermal delivery of high-molecular-weight drugs. The effects of US-mediated different-size (1.4, 2.1, and 3.5 μm) MBs (as a contrast agent) and ascorbyl tetraisopalmitate (VC-IP) on enhancing skin transdermal delivery were demonstrated both in vitro and in vivo. The results indicated that at a power density of 3 W/cm² the penetration depth in group US combined with 3.5-μm MBs and penetrating VC-IP (U+3.5) was 34% and 14% higher than those in groups US combined with 1.4-μm MBs and penetrating VC-IP (U+1.4) and US combined with 2.1-μm MBs and penetrating VC-IP (U+2.1), respectively, for the agarose phantoms, while the corresponding increases for pigskin were 37% and 19%.In terms of the skin permeation of VC-IP, the VC-IP concentration in group U+3.5 was 23% and 10% higher in than those in groups U+1.4 and U+2.1, respectively. The whitening effect (luminosity index) of mice skin in group U+3.5 had increased (significantly) by 28% after 1 week, by 34% after 2 weeks, and tended to stabilize after 3 weeks (45%) in C57BL/6J mice over a 4-week experimental period. The results obtained in this study indicate that combining US with MBs of different sizes can produce different degrees of skin permeability so as to enhance the delivery of VC-IP to inhibit melanogenesis, without damaging the skin in mice.

Delivery of large molecular protein using flat and short microneedles prepared using focused ion beam (FIB) as a skin ablation tool

Many studies have been reported in the literature on the effects of various geometries and lengths of microneedles (MNs) on transdermal drug delivery using a variety of drug molecules. In particular, sharp-tipped MNs have been used to disrupt the top layer of the skin, namely, stratum corneum (SC). It has also been shown that short- and flat-tipped MNs can pierce the SC and they have the potential to increase drug permeability. However, there is little work that explores MNs as a skin ablative tool with a view to increasing skin permeability. To address this point, well-defined small patterns (size of individual pattern 10–20 μm) on the tip of flat MN (tip radius of individual MN ∼250 μm) were created and their effects evaluated on the permeability of bovine serum albumin (BSA), which is chosen as a model drug of high molecular weight. The patterns on the tip of flat MN act as rough surfaces (e.g. like sand paper) which when applied on the surface of the skin ablate the SC layer. Focused ion beam (FIB) has been used as the fabrication technique for the MNs. The permeability data are then compared with the other data for flat- and sharp-tipped MN. The permeability data from passive diffusion experiments are used as the reference case. The exact number of MNs or patterns in the flat and patterned MN patches is not considered as important as they have not been designed to pierce the skin. However, this is an important consideration in the case of sharp MNs as they pierce and create cavities in the skin. It is found that the delivery of BSA with the fabricated flat and patterned MNs gave similar but somewhat lower drug permeation profile in comparison to the sharp MNs. Passive diffusion showed no permeation, as would be expected due to the large size of the chosen molecule.

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.

Advances in the bioanalytical study of drug delivery across the skin

The study of a drug's dermal penetration profile provides important pharmaceutical data for the rational development of topical and transdermal delivery systems because the skin is a broadly used delivery route for local and systemic drugs and a potential route for gene therapy and vaccines. Monitoring drug penetration across the skin and quantifying its levels in different skin layers have been constant challenges due to the detection limitations of the available techniques, as well as the inherent interference in this tissue. This review explores and discusses several bionalytical methods that are indispensable tools to study drugs across the skin. In addressing the main topic, we structure the review highlighting the skin as an important route of drug administration and its structure, skin membrane models most used and its properties, in vitro and in vivo assays most used in the study of drug delivery to the skin, the techniques for processing the skin for subsequent analysis by bioanalytical methods that have a theoretical and practical approach showing its applicability, limitations and also including examples of its use. This review has a comprehensive approach in order to help researchers design their experiments and update the applicability and advances in this area of expertise.

Potential of combined ultrasound and microneedles for enhanced transdermal drug permeation: a review

Transdermal drug delivery (TDD) is limited by the outer layer of the skin, i.e., the stratum corneum. Research on TDD has become very active in the recent years and various technologies have been developed to overcome the resistance of the stratum corneum to molecular diffusion. In particular, researchers have started to consider the possibility of combining the TDD technologies in order to have further increase in drug permeability. Both microneedles (MNs) and ultrasound are promising technologies. They achieve enhancement in drug permeation via different mechanisms and therefore give a good potential for combining with each other. This review will focus on discussing the potential of this combinational technique along with other important issues, e.g., the mechanisms of ultrasound and MNs as it is and these mechanisms which are coupled via the two systems (i.e. MNs and ultrasound). We discuss the possible ways to achieve this combination as well as how this combination would increase the permeability. Some of the undeveloped (weaker) research areas of MNs and sonophoresis are also discussed in order to understand the true potential of combining the two technologies when they are developed further in the future. We propose several hypothetical combinations based on the possible mechanisms involved in MNs and ultrasound. Furthermore, we carry out a cluster analysis by which we determine the significance of this combinational method in comparison with some other selected combinational methods for TDD (e.g., MNs and iontophoresis). Using a time series analysis tool (ARIMA model), the current trend and the future development of combined MNs and ultrasound are also analysed. Overall, the review in this paper indicates that combining MNs and ultrasound is a promising TDD method for the future.

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.