Topical drug delivery in humans with a single photomechanical wave

Transdermal Drug Delivery Systems (TDDS): Recent Advances and Failure Modes

Transdermal drug delivery systems (TDDS), commonly refered to as "patches", present a nonintrusive technique to provide medication without the need for invasive procedures. These products adhere to the skin and gradually release a specific dosage of medicine at a defined rate into the bloodstream. Compared with other methods of drug delivery, TDDS offer benefits such as reduced invasiveness, convenience for patients, and avoidance of the metabolic processes that occur when drugs are orally consumed. Throughout time, TDDS have been used to provide medications for various medical conditions (such as nicotine, fentanyl, nitroglycerin, and clonidine), and their potential for delivering biologics is currently being explored. This review investigates the current literature on the drug delivery efficacy of medical TDDS through the transdermal route. Additionally, the review addresses potential risks and failure modes associated with TDDS design and development as well as strategies for mitigating such risks. A thorough understanding of failure modes provides a blueprint to mitigate failure and produce high-quality efficacious therapeutics.

Skin emitted volatiles analysis for noninvasive diagnosis: the current advances in sample preparation techniques for biomedical application

Human skin emits a series of volatile compounds from the skin due to various metabolic processes, microbial activity, and several external factors. Changes in the concentration of skin volatile metabolites indicate many diseases, including diabetes, cancer, and infectious diseases. Researchers focused on skin-emitted compounds to gain insight into the pathophysiology of various diseases. In the case of skin volatolomics research, it is noteworthy that sample preparation, sampling protocol, analytical techniques, and comprehensive validation are important for the successful integration of skin metabolic profiles into regular clinical settings. Solid-phase microextraction techniques and polymer-based active sorbent traps were developed to capture the skin-emitted volatile compounds. The primary advantage of these sample preparation techniques is the ability to efficiently and targetedly capture skin metabolites, thus improving the detection of the biomarkers associated with various diseases. In further research, polydimethyl-based patches were utilized for skin research due to their biocompatibility and thermal stability properties. The microextraction sampling tools coupled with high sensitive Gas Chromatography-Mass Spectrometer provided a potential platform for skin volatolomes, thus emerging as a state-of-the-art analytical technique. Later, technological advancements, including the design of wearable sensors, have enriched skin-based research as it can integrate the information from skin-emitted volatile profiles into a portable platform. However, individual-specific hydration, temperature, and skin conditions can influence variations in skin volatile concentration. Considering the subject-specific skin depth, sampling time standardization, and suitable techniques may improve the skin sampling techniques for the potential discovery of various skin-based marker compounds associated with diseases. Here, we have summarised the current research progress, limitations, and technological advances in skin-based sample preparation techniques for disease diagnosis, monitoring, and personalized healthcare applications.

Transdermal Drug Delivery Systems: A Focused Review of the Physical Methods of Permeation Enhancement

The skin is the body's largest organ and serves as a site of administration for various medications. Transdermal drug delivery systems have several advantages over traditional delivery systems. It has both local and systemic therapeutic properties. Controlled plasma drug levels, reduced dosing frequency, and avoidance of hepatic first-pass metabolism are just a few of these systems' advantages. To achieve maximum efficacy, it is critical to understand the kinetics, physiochemical properties of the drug moiety, and drug transport route. This manuscript focused on the principles of various physical means to facilitate transdermal drug delivery. Some examples are iontophoresis, electrophoresis, photomechanical waves, ultrasound, needleless injections, and microneedles. Mechanical, chemical, magnetic, and electrical energy are all used in physical methods. A major advantage of physical methods is their capability to abbreviate pain, which can be used for effective disease management. Further investigation should be carried out at the clinical level to understand these methods for effective drug delivery.

Digital automation of transdermal drug delivery with high spatiotemporal resolution

Transdermal drug delivery is of vital importance for medical treatments. However, user adherence to long-term repetitive drug delivery poses a grand challenge. Furthermore, the dynamic and unpredictable disease progression demands a pharmaceutical treatment that can be actively controlled in real-time to ensure medical precision and personalization. Here, we report a spatiotemporal on-demand patch (SOP) that integrates drug-loaded microneedles with biocompatible metallic membranes to enable electrically triggered active control of drug release. Precise control of drug release to targeted locations (<1 mm2), rapid drug release response to electrical triggers (<30 s), and multi-modal operation involving both drug release and electrical stimulation highlight the novelty. Solution-based fabrication ensures high customizability and scalability to tailor the SOP for various pharmaceutical needs. The wireless-powered and digital-controlled SOP demonstrates great promise in achieving full automation of drug delivery, improving user adherence while ensuring medical precision. Based on these characteristics, we utilized SOPs in sleep studies. We revealed that programmed release of exogenous melatonin from SOPs improve sleep of mice, indicating potential values for basic research and clinical treatments.

Observation on the efficacy of 1565-nm non-ablative fractional laser combined with compound betamethasone topical application on the treatment of early scar in Chinese patients

The objective of the study was to evaluate the efficacy of combining 1565-nm non-ablative fractional laser with low-dose compound betamethasone topical application in the treatment of immature early red hypertrophic scar. We enrolled 38 cases of patients who had immature red hypertrophic scar due to surgery or trauma which are all less than 6 months old. About 28 patients were assigned to the treatment group, and 10 patients were assigned to the control group. The patients in the treatment group were all treated with 1565-nm non-ablative fractional laser with the following parameters: spot size 10-16 mm, round or square-shaped according to lesional morphology, fluence 20-35 mJ/cm², and density 150-200 microspot/cm². The treated area was then applied immediately with low-dose compound betamethasone through topical application. Treatment cycles were repeated every month for a total 5 months. Photos were taken before the start of the treatment, and then monthly after. Vancouver Scar Scale score was used to evaluate the scar changes; all the patients were followed up for 3 more months after the last treatment. All side effects were documented. The patients in the control group received no treatment at all. All the parameters were recorded as the same as the treatment group. The total VSS score after the combination therapy is 0.96 ± 1.53, which in comparison with prior treatment VSS score 8.86 ± 1.43, showed a significant reduction following the treatments (P < 0.001). The control group without any treatment shows VSS score 7.10 ± 0.99 at the end of the study vs VSS score 7.70 ± 0.82 at the start of the study (P > 0.05). The patient satisfaction rate reaches 89.2% after treatment, The major side effects reported include 3 patients with post-inflammatory hyperpigmentation (10.7% of patients in the treatment group), and other minor discomfort such as transient warmth, erythema, and swelling of treatment sites. The combination approach using 1565-nm non-ablative laser and low dose of local application of compound betamethasone can effectively improve the immature red hypertrophic scar with no significant side effects; this should provide our practitioners with a new weapon in fighting those hard-to-manage early scar formations.

Recent advances in transdermal drug delivery systems: a review

Various non-invasive administrations have recently emerged as an alternative to conventional needle injections. A transdermal drug delivery system (TDDS) represents the most attractive method among these because of its low rejection rate, excellent ease of administration, and superb convenience and persistence among patients. TDDS could be applicable in not only pharmaceuticals but also in the skin care industry, including cosmetics. Because this method mainly involves local administration, it can prevent local buildup in drug concentration and nonspecific delivery to tissues not targeted by the drug. However, the physicochemical properties of the skin translate to multiple obstacles and restrictions in transdermal delivery, with numerous investigations conducted to overcome these bottlenecks. In this review, we describe the different types of available TDDS methods, along with a critical discussion of the specific advantages and disadvantages, characterization methods, and potential of each method. Progress in research on these alternative methods has established the high efficiency inherent to TDDS, which is expected to find applications in a wide range of fields.

Design and Evaluation of Dissolving Microneedles for Enhanced Dermal Delivery of Propranolol Hydrochloride

Oral propranolol hydrochloride has been the first-line treatment for infantile hemangioma (IH), whereas systemic exposure to propranolol has the potential of causing serious adverse reactions. Dermal delivery of propranolol is preferable due to high local drug concentration and fewer adverse effects. However, propranolol hydrochloride (BCS class I) is highly hydrophilic and has difficulty in penetrating the stratum corneum (SC) barrier. Dissolving microneedles (MNs) are an efficient tool for overcoming the barrier of the SC and enhancing dermal drug delivery. In this study, propranolol hydrochloride-loaded dissolving MNs were fabricated by using hyaluronic acid and polyvinyl pyrrolidone as matrix materials. Controllable drug loading in needle tips was achieved by a two-step casting procedure. The needles were good in mechanical strength for penetrating the SC while presented excellent dissolving capability for releasing propranolol hydrochloride. In comparison with the solution counterpart, irrespective of being applied to intact skin or solid MNs-pretreated skin, dissolving MNs significantly increased the permeability and skin retention of propranolol. In conclusion, dissolving MNs could be a potential approach for enhancing dermal delivery of propranolol to treat IH.

Safety of laser-generated shockwave treatment for bacterial biofilms in a cutaneous rodent model

Bacterial biofilms are often found in chronically infected wounds. Biofilms protect bacteria from antibiotics and impair wound healing. Surgical debridement is often needed to remove the biofilm from an infected wound. Laser-generated shockwave (LGS) treatment is a novel tissue-sparing treatment for biofilm disruption. Previous studies have demonstrated that LGS is effective in disrupting biofilms in vitro. In this study, we aim to determine the safety threshold of the LGS technology in an in vivo rodent model. To understand the in vivo effects of LGS on healthy cutaneous tissue, the de-haired dorsal skin of Sprague-Dawley rats were treated with LGS at three different peak pressures (118, 296, 227 MPa). These pressures were generated using a 1064 nm Nd/YAG laser (pulse duration 5 ns and laser fluence of 777.9 mJ) with laser spot size diameters of 2.2, 3.0, and 4.2 mm, respectively. Following treatment, the animals were observed for 72 h, and a small subset was euthanized at 1-h, 24-h, and 72-h post-treatment and assessed for tissue injury or inflammation under histology. Each treatment group consisted of 9 rats (n = 3/time point for 1-h, 24-h, 72-h post-treatment). An additional 4 control (untreated) rats were included in the analysis, for a total of 31 animals. Gross injuries occurred in 21 (77%) animals and consisted of minor erythema, with prevalence positively correlated with peak pressure (p < 0.05). Of injuries under gross observation, 94% resolved within 24 h. Under histological analysis, the injuries and tissue inflammation were found to be localized to the epidermis and superficial dermis. LGS appears to be well tolerated by cutaneous tissue for the laser energy settings shown to be effective against bacterial biofilm in vitro. All injuries incurred, at even the highest peak pressures, were clinically mild and resolved within 1 day. This lends further support to the overall safety of LGS and serves to translate LGS towards in vivo efficacy studies.

Intestinal iontophoresis from mucoadhesive patches: a strategy for oral delivery

Biologics have limited permeability across the intestine and are prone to degradation in the acidic-proteolytic milieu of the gastrointestinal tract, leading to poor oral bioavailability. Iontophoresis is a promising technology that can substantially improve transport of drugs across biological barriers and has been particularly explored for skin. In this study, we investigated whether iontophoresis across the intestine can be utilized to improve oral insulin transport. Application of electric current to intestinal cells resulted in opening of the tight junctions in vitro and a consequent about 3-fold improvement in paracellular transport of insulin. When evaluated in vivo using insulin-loaded mucoadhesive patches, iontophoresis produced profound hypoglycemia (63% blood glucose drop in 3 h) without damaging the intestinal tissue and the efficacy depended on insulin dose and current density. This study presents a proof of principle for intestinal iontophoresis as a novel method for oral protein delivery.

Opportunities for Photoacoustic-Guided Drug Delivery

Photoacoustic imaging (PAI) is rapidly becoming established as a viable imaging modality for small animal research, with promise of near-future human clinical translation. In this review, we discuss emerging prospects for photoacoustic-guided drug delivery. PAI presents opportunities for applications related to drug delivery, mainly with respect to either monitoring drug effects or monitoring drugs themselves. PAI is well-suited for imaging disease pathology and treatment response. Alternatively, PAI can be used to directly monitor the accumulation of various light-absorbing contrast agents or carriers with theranostic properties.

Lasers as an approach for promoting drug delivery via skin

INTRODUCTION

Using lasers can be an effective drug permeation-enhancement approach for facilitating drug delivery into or across the skin. The controlled disruption and ablation of the stratum corneum (SC), the predominant barrier for drug delivery, is achieved by the use of lasers. The possible mechanisms of laser-assisted drug permeation are the direct ablation of the skin barrier, optical breakdown by a photomechanical wave and a photothermal effect. It has been demonstrated that ablative approaches for enhancing drug transport provide some advantages, including increased bioavailability, fast treatment time, quick recovery of SC integrity and the fact that skin surface contact is not needed. In recent years, the concept of using laser techniques to treat the skin has attracted increasing attention.

AREAS COVERED

This review describes recent developments in using nonablative and ablative lasers for drug absorption enhancement. This review systematically introduces the concepts and enhancement mechanisms of lasers, highlighting the potential of this technique for greatly increasing drug absorption via the skin. Lasers with different wavelengths and types are employed to increase drug permeation. These include the ruby laser, the erbium:yttrium-gallium-garnet laser, the neodymium-doped yttrium-aluminum-garnet laser and the CO2 laser. Fractional modality is a novel concept for promoting topical/transdermal drug delivery. The laser is useful in enhancing the permeation of a wide variety of permeants, such as small-molecule drugs, macromolecules and nanoparticles.

EXPERT OPINION

This potential use of the laser affords a new treatment for topical/transdermal application with significant efficacy. Further studies using a large group of humans or patients are needed to confirm and clarify the findings in animal studies. Although the laser fluence or output energy used for enhancing drug absorption is much lower than for treatment of skin disorders and rejuvenation, the safety of using lasers is still an issue. Caution should be used in optimizing the feasible conditions of the lasers in balancing the effectiveness of permeation enhancement and skin damage.

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.

Laser microporation of the skin: prospects for painless application of protective and therapeutic vaccines

Introduction:

In contrast to muscle and subcutaneous tissue, the skin is easily accessible and provides unique immunological properties. Increasing knowledge about the complex interplay of skin-associated cell types in the development of cutaneous immune responses has fueled efforts to target the skin for vaccination as well as for immunotherapy.

Areas covered:

This review provides an overview on skin layers and their resident immunocompetent cell types. Advantages and shortcomings of standard methods and innovative technologies to circumvent the outermost skin barrier are addressed. Studies employing fractional skin ablation by infrared lasers for cutaneous delivery of drugs, as well as high molecular weight molecules such as protein antigens or antibodies, are reviewed, and laserporation is introduced as a versatile transcutaneous vaccination platform. Specific targeting of the epidermis or the dermis by different laser settings, the resulting kinetics of uptake and transport and the immune response types elicited are discussed, and the potential of this transcutaneous delivery platform for allergen-specific immunotherapy is demonstrated.

Expert opinion:

Needle-free and painless vaccination approaches have the potential to replace standard methods due to their improved safety and optimal patient compliance. The use of fractional laser devices for stepwise ablation of skin layers might be advantageous for both vaccination against microbial pathogens, as well as immunotherapeutic approaches, such as allergen-specific immunotherapy. Thorough investigation of the underlying immunological mechanisms will help to provide the knowledge for a rational design of transcutaneous protective/therapeutic vaccines.

Drug delivery through the skin: molecular simulations of barrier lipids to design more effective noninvasive dermal and transdermal delivery systems for small molecules, biologics, and cosmetics

The delivery of drugs through the skin provides a convenient route of administration that is often preferable to injection because it is noninvasive and can typically be self-administered. These two factors alone result in a significant reduction of medical complications and improvement in patient compliance. Unfortunately, a significant obstacle to dermal and transdermal drug delivery alike is the resilient barrier that the epidermal layers of the skin, primarily the stratum corneum, presents for the diffusion of exogenous chemical agents. Further advancement of transdermal drug delivery requires the development of novel delivery systems that are suitable for modern, macromolecular protein and nucleotide therapeutic agents. Significant effort has already been devoted to obtain a functional understanding of the physical barrier properties imparted by the epidermis, specifically the membrane structures of the stratum corneum. However, structural observations of membrane systems are often hindered by low resolutions, making it difficult to resolve the molecular mechanisms related to interactions between lipids found within the stratum corneum. Several models describing the molecular diffusion of drug molecules through the stratum corneum have now been postulated, where chemical permeation enhancers are thought to disrupt the underlying lipid structure, resulting in enhanced permeability. Recent investigations using biphasic vesicles also suggested a possibility for novel mechanisms involving the formation of complex polymorphic lipid phases. In this review, we discuss the advantages and limitations of permeation-enhancing strategies and how computational simulations, at the atomic scale, coupled with physical observations can provide insight into the mechanisms of diffusion through the stratum corneum.

Hydration effects on skin microstructure as probed by high-resolution cryo-scanning electron microscopy and mechanistic implications to enhanced transcutaneous delivery of biomacromolecules

Although hydration is long known to improve the permeability of skin, penetration of macromolecules such as proteins is limited and the understanding of enhanced transport is based on empirical observations. This study uses high-resolution cryo-scanning electron microscopy to visualize microstructural changes in the stratum corneum (SC) and enable a mechanistic interpretation of biomacromolecule penetration through highly hydrated porcine skin. Swollen corneocytes, separation of lipid bilayers in the SC intercellular space to form cisternae, and networks of spherical particulates are observed in porcine skin tissue hydrated for a period of 4-10 h. This is explained through compaction of skin lipids when hydrated, a reversal in the conformational transition from unilamellar liposomes in lamellar granules to lamellae between keratinocytes when the SC skin barrier is initially established. Confocal microscopy studies show distinct enhancement in penetration of fluorescein isothiocyanate-bovine serum albumin (FITC-BSA) through skin hydrated for 4-10 h, and limited penetration of FITC-BSA once skin is restored to its natively hydrated structure when exposed to the environment for 2-3 h. These results demonstrate the effectiveness of a 4-10 h hydration period to enhance transcutaneous penetration of large biomacromolecules without permanently damaging the skin.

Enhancement of transdermal drug delivery via synergistic action of chemicals

Transdermal drug delivery is an attractive alternative to conventional techniques for administration of systemic therapeutics. One challenge in designing transdermal drug delivery systems is to overcome the natural transport barrier of the skin. Chemicals offer tremendous potential in overcoming the skin barrier to enhance transport of drug molecules. Individual chemicals are however limited in their efficacy in disrupting the skin barrier at low concentrations and usually cause skin irritation at high concentrations. Multicomponent mixtures of chemicals, however, have been shown to provide high skin permeabilization potency as compared to individual chemicals without necessarily causing irritation. Here we review systems employing synergistic mixtures of chemicals that offer superior skin permeation enhancement. These synergistic systems include solvent mixtures, microemulsions, eutectic mixtures, complex self-assembled vesicles and inclusion complexes. Methods for design and discovery of such synergistic systems are also discussed.

Photosensitiser delivery for photodynamic therapy. Part 1: Topical carrier platforms

BACKGROUND

Photodynamic therapy (PDT) is a medical treatment in which a combination of a photosensitising drug and visible light causes destruction of selected cells. Due to the lack of true selectivity of preformed photosensitisers for neoplastic tissue and their high molecular weights, PDT of superficial skin lesions has traditionally been mediated by topical application of the porphyrin precursor 5-aminolevulinic acid (ALA).

OBJECTIVE

This article aims to review the traditional formulation-based approaches taken to topical delivery of ALA and discusses the more innovative strategies investigated for enhancement of PDT mediated by topical application of ALA and preformed photosensitisers.

METHODS

All of the available published print and online literature in this area was reviewed. As drug delivery of agents used in PDT is still something of an emerging field, it was not necessary to go beyond literature from the last 30 years.

RESULTS/CONCLUSION

PDT of neoplastic skin lesions is currently based almost exclusively on topical application of simple semisolid dosage forms containing ALA or its methyl ester. Until expiry of patents on the current market-leading products, there is unlikely to be a great incentive to engage in design and evaluation of innovative formulations for topical PDT, especially those containing the more difficult-to-deliver preformed photosensitisers.

Skin pretreatment with an Er:YAG laser promotes the transdermal delivery of three narcotic analgesics

Because of their low oral bioavailabilities and short half-lives, it may be more feasible to administer narcotic analgesics via the skin. However, this delivery method is limited by the low permeability of the stratum corneum (SC). The aim of this study was to enhance the transdermal delivery of three narcotic drugs, including morphine, nalbuphine, and buprenorphine, with an erbium:yttrium-aluminum-garnet (Er:YAG) laser pretreatment. In an in vitro pig skin permeation experiment, Er:YAG laser pretreatment of the skin produced a 10~35-fold enhancement in drug permeation that was dependent on the laser fluence and the narcotic analgesic used. The permeation of morphine and nalbuphine showed higher enhancement with Er:YAG laser treatment as compared to that of buprenorphine. This may have been due to the higher lipophilicity and molecular mass of buprenorphine than the other two narcotic drugs. A photomechanical wave was generated by filtering laser radiation through a polystyrene target. The experimental results showed that a single photomechanical wave was sufficient to enhance morphine permeation by sevenfold. This enhancement was significantly lower than that produced by direct laser irradiation, indicating the predominant mechanism of SC ablation by the Er:YAG laser for transdermal drug delivery.

The nature of ultrasound–SLS synergism during enhanced transdermal transport

Ultrasound and sodium lauryl sulfate (SLS) exhibit a synergistic effect on transdermal transport, when applied simultaneously on the skin. The synergistic mechanism is not fully understood. Previous studies have shown that application of ultrasound simultaneously with SLS, results in enhanced mass transfer and improved penetration and dispersion of the surfactant. In this study we demonstrate that simultaneous application of ultrasound and SLS leads to modification of the pH profile of the stratum corneum. This pH modification within the stratum corneum's microenvironment, can affect both the structure of the lipid layers and the activity of SLS as a chemical enhancer due to its improved lipophilic solubility. The altered pH profile that results in improved SLS lipophilic solubility, together with improved SLS penetration and dispersion, can explain the synergistic enhancing effect of ultrasound and SLS on transdermal transport.

Emerging strategies for the transdermal delivery of peptide and protein drugs

Transdermal delivery has been at the forefront of research addressing the development of non-invasive methods for the systemic administration of peptide and protein therapeutics generated by the biotechnology revolution. Numerous approaches have been suggested for overcoming the skin's formidable barrier function; whereas certain strategies simply act on the drug formulation or transiently increase the skin permeability, others are designed to bypass or even remove the outermost skin layer. This article reviews the technologies currently under investigation, ranging from those in their early-stage of development, such as laser-assisted delivery to others, where feasibility has already been demonstrated, such as microneedle systems, and finally more mature techniques that have already led to commercialisation (e.g., velocity-based technologies). The principles, mechanisms involved, potential applications, limitations and safety considerations are discussed for each approach, and the most advanced devices in each field are described.

Transdermal delivery of macromolecules by erbium:YAG laser

The aim of this study was to assess the effect of molecular weight (MW) on the transdermal delivery of macromolecules by erbium:yttrium-aluminum-garnet (Er:YAG) laser treatment. Fluorescein isothiocyanate (FITC)-labeled dextran (FD) of increasing MWs (4.4, 19.4, 38, and 77 kDa) was used as the model macromolecules to investigate the skin permeation in vitro. Fluorescence microscopy and scanning electron microscopic (SEM) images were utilized to examine the transport mechanisms of the macromolecules via the skin after laser treatment. The results indicate a significant increase in the permeation of FITC and FD across skin treated by the laser. The MWs of macromolecules and laser fluences were found to play important roles in controlling macromolecular absorption. Transdermal delivery of FD with a MW of at least 77 kDa could be achieved with laser treatment. Follicular routes were significant for FITC permeation, whereas intercellular pathways played important roles on the delivery of FD. Ablation of the stratum corneum (SC) layer, photomechanical stress on intercellular regions, and alterations of the morphology and arrangement of corneocytes are possible mechanisms of how the Er:YAG laser promotes macromolecular delivery. No alteration of viable skin morphology was observed after laser treatment and the partly ablation of the SC may be reversible. Hexameric insulin showed higher skin permeation than did FD with similar MWs (38 kDa) with laser enhancement. From the study presented herein, it is concluded that the Er:YAG laser can be effective for transdermal delivery of macromolecules and hydrophilic permeants such as peptides and protein-based drugs.

Enhancement of topical 5-aminolaevulinic acid delivery by erbium:YAG laser and microdermabrasion: a comparison with iontophoresis and electroporation

BACKGROUND

5-aminolaevulinic acid (ALA) is used as a protoporphyrin IX-precursor for the photodynamic therapy of superficial skin cancer and cutaneous metastases of internal malignancies. However, the permeability of hydrophilic ALA across the skin is very low.

OBJECTIVES AND METHODS

The objective of this study was to optimize and enhance the in vitro skin permeation of ALA by two resurfacing techniques: erbium:yttrium-aluminium-garnet (Erb:YAG) laser and microdermabrasion. Light microscopic changes in pig skin caused by these techniques were also compared. The electrically assisted methods, iontophoresis and electroporation, were also used to facilitate ALA permeation across laser- or microdermabrasion-treated skin.

RESULTS

Among the modalities tested in this study the Erb:YAG laser showed the greatest enhancement of ALA permeation. The laser fluence was found to play an important role in controlling the drug flux, producing enhancement ratios from 4-fold to 246-fold relative to the control. The skin permeation of ALA across microdermabrasion-treated skin was approximately 5-15-fold higher than that across intact skin. Both the ablated effect of the stratum corneum (SC) and ALA flux were proportional to the treatment duration of microdermabrasion. The application of iontophoresis or electroporation alone also increased the ALA permeation by approximately 15-fold and 2-fold, respectively. The incorporation of iontophoresis or electroporation with the resurfacing techniques caused a profound synergistic effect on ALA permeation.

CONCLUSIONS

This basic study has encouraged the further investigation of ALA permeation by laser or microdermabrasion.

Ultrasound and transdermal drug delivery

Transdermal drug delivery offers an attractive alternative to the conventional drug delivery methods of oral administration and injection. However, the stratum corneum acts as a barrier that limits the penetration of substances through the skin. Application of ultrasound 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, namely transdermal drug delivery and transdermal monitoring. Particular attention is paid to proposed enhancement mechanisms and future trends in the field of cutaneous vaccination and gene delivery.

Transdermal drug delivery with a pressure wave

Pressure waves, which are generated by intense laser radiation, can permeabilize the stratum corneum (SC) as well as the cell membrane. These pressure waves are compression waves and thus exclude biological effects induced by cavitation. Their amplitude is in the hundreds of atmospheres (bar) while the duration is in the range of nanoseconds to a few microseconds. The pressure waves interact with cells and tissue in ways that are probably different from those of ultrasound. Furthermore, the interactions of the pressure waves with tissue are specific and depend on their characteristics, such as peak pressure, rise time and duration. A single pressure wave is sufficient to permeabilize the SC and allow the transport of macromolecules into the epidermis and dermis. In addition, drugs delivered into the epidermis can enter the vasculature and produce a systemic effect. For example, insulin delivered by pressure waves resulted in reducing the blood glucose level over many hours. The application of pressure waves does not cause any pain or discomfort and the barrier function of the SC always recovers.

Photodestruction of human dental plaque bacteria: enhancement of the photodynamic effect by photomechanical waves in an oral biofilm model

BACKGROUND AND OBJECTIVES

Periodontal disease results from the accumulation of subgingival bacterial biofilms on tooth surfaces. There is reduced susceptibility of these biofilms to antimicrobials for reasons that are not known. The goals of this study were to investigate the photodynamic effects of a conjugate between the photosensitizer (PS) chlorin(e6) (c(e6)) and a poly-L-lysine (pL) with five lysine residues on human dental plaque bacteria as well as on biofilms of the oral species Actinomyces naeslundii after their exposure to photomechanical waves (PW) generated by a laser in the presence of the conjugate.

STUDY DESIGN/MATERIALS AND METHODS

Subgingival plaque samples from 12 patients with chronic destructive periodontitis were divided in 3 groups that were incubated for 5 minutes with 5 microM c(e6) equivalent from the pL-c(e6) conjugate in the presence of fresh medium (group I), PBS (group II), and 80% PBS/20% ethylenediaminetetra-acetic acid (EDTA) (group III) and were exposed to red light. Also, biofilms of A. naeslundii (formed on bovine enamel surfaces) were exposed to PW in the presence of 5 microM c(e6) equivalent from the pL-c(e6) conjugate and were then irradiated with red light. The penetration depth of the conjugate was measured by confocal scanning laser microscopy (CSLM). In both cases, after illumination serial dilutions were prepared and aliquots were spread over the surfaces of blood agar plates. Survival fractions were calculated by counting bacterial colonies.

RESULTS

The PS/light combination achieved almost 90% killing of human dental plaque species. In biofilms of A. naeslundii, CSLM revealed that PW were sufficient to induce a 50% increase in the penetration depth of the pL-c(e6) conjugate into the biofilm. This enabled its destruction (99% killing) after photodynamic therapy (PDT).

CONCLUSIONS

PW-assisted photodestruction of dental plaque may be a potentially powerful tool for treatment of chronic destructive periodontal disease.

Ultrastructural evidence of stratum corneum permeabilization induced by photomechanical waves

Photomechanical waves (high amplitude pressure transients generated by lasers) have been shown to permeabilize the stratum corneum in vivo and facilitate the transport of macromolecules into the viable epidermis. The permeabilization of the stratum corneum is transient and its barrier function recovers. Sites on the volar forearm of humans were exposed to photomechanical waves and biopsies were obtained immediately after the exposure and processed for electron microscopy. Electron microscopy showed an expansion of the lacunar spaces within the stratum corneum lipid bilayers but no changes in the organization of the secreted lamellar bodies at the stratum corneum-stratum granulosum boundary. The combination of photomechanical waves and sodium lauryl sulfate enhances the efficiency of transdermal delivery and delays the recovery of the barrier function of the stratum corneum. Electron microscopy from sites exposed to photomechanical waves and sodium lauryl sulfate showed that the lacunar spaces expanded significantly more and the secreted lamellar bodies also appeared to be altered. In either case, there were no changes in the papillary dermis. These observations support the hypothesis that the photomechanical waves induce the expansion of the lacunar spaces within the stratum corneum leading to the formation of transient channels.

Photomechanical delivery of 100-nm microspheres through the stratum corneum: implications for transdermal drug delivery

BACKGROUND AND OBJECTIVES

Photomechanical waves (PWs) render the stratum corneum permeable and allow molecules to diffuse into the epidermis. The aim of this study was to investigate the probe size that could be delivered through the stratum corneum and into the epidermis.

STUDY DESIGN/MATERIALS AND METHODS

A single PW was applied onto the rat skin in vivo. Aqueous suspensions of fluorescent microspheres, 100 nm in diameter, were used as probes for transdermal delivery. The presence of the microspheres in the epidermis was measured by a fiber-based spectrofluorimeter after the stratum corneum was removed by tape-stripping (TS).

RESULTS

Exposure of the rat skin to a PW permeabilized the stratum corneum and allowed the fluorescent microspheres to diffuse into the epidermis.

CONCLUSIONS

The experiments show that PWs can facilitate the delivery of very large molecules and probes into the epidermis.

Laser-induced shock waves enhance sterilization of infected vascular prosthetic grafts

BACKGROUND AND OBJECTIVE

Bacteria that cause infection of vascular prosthetic grafts produce an exopolysaccharide matrix known as biofilm. Growth in biofilms protects the bacteria from leukocytes, antibodies and antimicrobial drugs. Laser-generated shock waves (SW) can disrupt biofilms and increase drug penetration. This study investigates the possibility of increasing antibiotic delivery and sterilization of vascular prosthetic graft.

STUDY DESIGN/MATERIALS AND METHODS

Strains of Staphylococcus epidermidis and S. aureus were isolated from infected prosthetic grafts obtained directly from patients. Dacron grafts were inoculated with the isolated bacteria, which were allowed to form adherent bacterial colonies. The colonized grafts underwent the following treatments: (a) antibiotic (vancomycin) alone; (b) antibiotic and SW (c) saline only; and (d) saline and SW. Six hours after treatment, the grafts were sonicated, the effluent was cultured and the colony forming units (CFU) were counted.

RESULTS

CFU recovered from control grafts colonized by S. epidermidis were comparable: saline, 3.05 x 10(8) and saline+SW 3.31 x 10(8). The number of S. epidermidis CFU diminished to 7.61 x 10(6) after antibiotic treatment but the combined antibiotic+SW treatment synergistically decreased CFU number to 1.27 x 10(4) (P<0.001). S. aureus showed a higher susceptibility to the antibiotic: 2.26 x 10(6) CFU; antibiotic +SW treatment also had an incremental effect: 8.27 x 10(4) CFU (P<0.001).

CONCLUSIONS

This study demonstrates that laser-generated shock waves have no effects alone, but can enhance the effectiveness of antibiotics against bacteria associated with prosthetic vascular graft biofilms, suggesting that this treatment may be of value as adjunctive therapy for prosthetic graft infections.

The effect of laser treatment on skin to enhance and control transdermal delivery of 5-fluorouracil

The effect of three lasers (i.e., the ruby, erbium:YAG, and CO2) on the ability to enhance and control skin permeation of 5-fluorouracil (5-FU) was studied in vitro. Light microscopic and ultrastructural (scanning electron microscopic) changes in the nude mouse skin were also compared for these lasers. The histological observations and permeation profiles of each laser differed because the three lasers produce different physical and physiologic effects when striking the skin. The skin permeation of 5-FU could be moderately promoted by a single photomechanical wave generated by the ruby laser (at 4.0 and 7.0 J/cm(2)) without adversely affecting the viability or structure of the skin. The stratum corneum (SC) layer in the skin was partly ablated by an erbium:YAG laser, resulting in a greater enhancement effect on skin permeation of 5-FU. The flux of 5-FU across erbium:YAG laser-treated skin was 53-133-fold higher than that across intact skin. Both SC ablation and a thermal effect may contribute to the effect of the CO2 laser on skin structure. Lower energies of the CO2 laser did not modulate 5-FU permeation. A 36-41-fold increase in 5-FU flux was observed after exposure to higher fluences (4.0 and 7.0 J/cm(2)) of the CO2 laser. Histological changes induced by both the erbium:YAG and CO2 lasers had completely recovered within 4 days.

Permeabilization and recovery of the stratum corneum in vivo: the synergy of photomechanical waves and sodium lauryl sulfate

BACKGROUND AND OBJECTIVE

Photomechanical waves render the stratum corneum permeable and allow macromolecules to diffuse into the epidermis and dermis. The aim of this study was to investigate the combined action of photomechanical waves and sodium lauryl sulfate, an anionic surfactant, for transdermal delivery.

STUDY DESIGN/MATERIALS AND METHODS

A single photomechanical wave was applied to the skin of rats in the presence of sodium lauryl sulfate. The sodium lauryl sulfate solution was removed and aqueous solutions of rhodamine-B dextran (40 kDa molecular weight) were applied to the skin at time points 2, 30, and 60 minutes post-exposure. The presence of rhodamine-B dextran in the skin was measured by fluorescence emission spectroscopy in vivo and fluorescence microscopy of frozen biopsies.

RESULTS

The use of sodium lauryl sulfate delayed the recovery of the stratum corneum barrier and extended the time available for the diffusion of dextran through it.

CONCLUSION

The combination of photomechanical waves and surfactants can enhance transdermal drug delivery.

Novel mechanisms and devices to enable successful transdermal drug delivery

Optimisation of drug delivery through human skin is important in modern therapy. This review considers drug-vehicle interactions (drug or prodrug selection, chemical potential control, ion pairs, coacervates and eutectic systems) and the role of vesicles and particles (liposomes, transfersomes, ethosomes, niosomes). We can modify the stratum corneum by hydration and chemical enhancers, or bypass or remove this tissue via microneedles, ablation and follicular delivery. Electrically assisted methods (ultrasound, iontophoresis, electroporation, magnetophoresis, photomechanical waves) show considerable promise. Of particular interest is the synergy between chemical enhancers, ultrasound, iontophoresis and electroporation.

Photomechanical transdermal delivery: the effect of laser confinement

BACKGROUND AND OBJECTIVE

Photomechanical waves can transiently permeabilize the stratum corneum and facilitate the delivery of drugs into the epidermis and dermis. The present study was undertaken to assess the effect of pulse characteristics to the penetration depth of macromolecules delivered into the skin.

STUDY DESIGN/MATERIALS AND METHODS

Photomechanical waves were generated by confined ablation with a Q-switched ruby laser. Fluorescence microscopy of frozen biopsies was used to assay the delivery of macromolecules through the stratum corneum and determine the depth of penetration.

RESULTS

Photomechanical waves generated by confined ablation of the target have a longer rise time and duration than those generated by direct ablation. Confined ablation required a lower radiant exposure (from approximately 7 J/cm(2) to approximately 5 J/cm(2)) for an increase in the depth of delivery (from approximately 50 microm to approximately 400 microm).

CONCLUSIONS

Control of the characteristics of the photomechanical waves is important for transdermal delivery as they can affect the depth of drug penetration into the dermis.