In vivo assessment of safety of microneedle arrays in human skin

Microneedle arrays are promising devices for the delivery of drugs and vaccines into or the skin. However, little is known about the safety of the microneedles. In this study we obtained insight in the ability of microneedles to disrupt the skin barrier, which was evaluated by transepidermal water loss (TEWL). We also determined the safety in terms of skin irritation (skin redness and blood flow) and pain sensation. We applied microneedle arrays varying in length and shape on the ventral forearms of 18 human volunteers. An effect of needle length was observed, as TEWL and redness values after treatment with solid microneedle arrays of 400mum were significantly increased compared to 200mum. The blood flow showed a similar trend. Needle design also had an effect. Assembled microneedle arrays induced higher TEWL values than the solid microneedle arrays, while resulting in less skin irritation. However, for all microneedles the irritation was minimal and lasted less than 2h. In conclusion, the microneedle arrays used in this study are able to overcome the barrier function of the skin in human volunteers, are painless and cause only minimal irritation. This opens the opportunity for dermal and transdermal delivery of drugs and vaccines.     

Controlled transdermal delivery of model drug compounds by MEMS microneedle array

This article reports an in vitro study of microneedle-array-enhanced transdermal transport of model drug compounds dispersed in chitosan films. Each microneedle array has 400 out-of-plane, needle-shaped microstructures fabricated using micro-electro-mechanical systems (MEMS) technology to ensure adequate mechanical strength and high precision, and consistency. A nanometer coating on the microneedles ensured the biocompatibility that is important in the application of transdermal drug delivery. Model drugs selected to investigate skin permeation in vitro were calcein, a small molecule (molecular weight, 623 d) that has little skin penetration, and bovine serum albumin (BSA) (molecular weight, 66,000 d), a hydrophilic biological macromolecule. A Franz permeation cell was used to characterize the permeation rate of calcein and BSA through the rat skin. The transdermal transport behavior of BSA was investigated from solid films coated on the surface of microneedle arrays with various chitosan concentrations, film thicknesses, and BSA contents. The BSA permeation rate decreased with the increase of the chitosan concentration; the thicker the film, the slower the permeation rate. In addition, the permeation rate increased with the increase of BSA loading dose. A linear relationship existed between the permeation rate and the square root of the BSA loading dose. Results showed that the chitosan hydrophilic polymer film acts as a matrix that can regulate the BSA release rate. The controlled delivery of BSA can be achieved using the BSA-containing chitosan matrix film incorporated with the microneedle arrays. This will provide a possible way for the transdermal delivery of macromolecular therapeutic agents such as proteins and vaccines.     

Influence of the delivery systems using a microneedle array on the permeation of a hydrophilic molecule, calcein.

Despite the advantages of drug delivery through the skin, such as easy accessibility, convenience, prolonged therapy, avoidance of the liver first-pass metabolism and a large surface area, transdermal drug delivery is only used with a small subset of drugs because most compounds cannot cross the skin at therapeutically useful rates. Recently, a new concept was introduced known as microneedles and these could be pierced to effectively deliver drugs using micron-sized needles in a minimally invasive and painless manner. In this study, biocompatible polycarbonate (PC) microneedle arrays with various depths (200 and 500mum) and densities (45, 99 and 154ea/cm(2)) were fabricated using a micro-mechanical process. The skin permeability of a hydrophilic molecule, calcein (622.5D), was examined according to the delivery systems of microneedle, drug loading, depth of the PC microneedle, and density of the PC microneedle. The skin permeability of calcein was the highest when the calcein gel was applied to the skin with the 500mum-depth PC microneedle, simultaneously. In addition, the skin permeability of calcein was the highest when 0.1g of calcein gel was coupled to the 500mum-depth PC microneedle (154ea/cm(2)) as well as longer microneedles and larger density of microneedles. Taken together, this study suggests that a biocompatible PC microneedle might be a suitable tool for transdermal drug delivery system of hydrophilic molecules with the possible applications to macromolecules such as proteins and peptides.     

新型经皮传递胰岛素透明质酸微针制剂的制备及性能考察

目的证明透明质酸微针制剂在药物经皮传递系统方面的应用前景。方法通过皮肤及微针的显微照片考察微针刺入皮肤的性能和在大鼠体内的溶解性能;用皮肤刺激性实验评价透明质酸微针的安全性;以人的离体皮肤为透皮释药模型,通过体外经皮通透实验考察微针对模型药物胰岛素经皮吸收的促进作用。结果微针能够均匀刺穿角质层,在皮肤表面产生与微针一致的阵列形状,在皮肤断面可观察到直至真皮层的通道;在大鼠体内使用1 h后,针体能够完全溶解,皮肤刺激性指数为1.7,属于轻度刺激性;体外经皮实验中,微针中的胰岛素能够以活性形式释放,与同剂量的溶液相比,微针对胰岛素的体外经皮吸收具有显著的促进作用,稳态通透速率达75.33×10-6U.cm-2.h-1。结论以透明质酸为基质制备的微针具有良好的皮肤刺入性、溶解性和轻度的刺激性,对于生物大分子类药物的经皮吸收有明显的促进作用,具有良好的开发前景。     

Microneedles and other physical methods for overcoming the stratum corneum barrier for cutaneous gene therapy

The outermost layer of skin, the epidermis, has developed formidable physical and immunological barrier properties that prevent infiltration of deleterious chemicals and pathogens. Consequently, transdermal delivery of medicaments is currently restricted to a limited number of low molecular weight drugs. As a corollary, there has been significant recent interest in providing strategies that disrupt or circumvent the principal physical barrier, the stratum corneum, for the efficient cutaneous delivery of macromolecular and nucleic acid based therapeutics. These strategies include: electrical methods, intradermal injection, follicular delivery, particle acceleration, laser ablation, radiofrequency ablation, microscission, and microneedles. The application of microfabricated microneedle arrays to skin creates transient pathways to enable transcutaneous delivery of drugs and macromolecules. Microneedle use is simple, pain-free, and causes no bleeding, with further advantages of convenient manufacture, distribution, and disposal. To date, microneedles have been shown to deliver drug, peptide, antigen, and DNA efficiently through skin. Robust and efficient microneedle designs and compositions can be inserted into the skin without fracture. Further progress in microneedle array design, microneedle application apparatus, and integrated formulation will confirm this methodology as a realistic clinical strategy for delivering a range of medicaments, including DNA, to and through skin.     

表面活性剂-醇质体增强多烯紫杉醇经皮给药的渗透性研究(英文)

皮肤的屏障作用使大部分药物无法实现透皮给药。本文以改善难溶性大分子模型药物多烯紫杉醇(docetaxel,DTX)的经皮渗透性为主体思路,研制了DTX的表面活性剂-醇质体(surfactant-ethanlic liposomes,SEL)。SEL由磷脂、乙醇、胆酸钠、DTX和磷酸盐缓冲液组成,采用薄膜分散法制备。对SEL的囊泡形态(冷冻蚀刻电镜法)、粒径大小及分布进行了表征,并测定包封率和载药量。采用体外扩散池实验研究了DTX表面活性剂-醇质体的经皮渗透性。结果表明,当磷脂与表面活性剂的比例为85:15时,DTX的稳态透皮速率和累计透皮量均为最高,且优于表面活性剂脂质体、醇质体和普通脂质体。最优处方的粒径分布、形态和载药量均较为稳定。本研究表明,通过将DTX包载于SEL中可显著改善DTX的经皮渗透性。     

Microneedles for transdermal drug delivery

The success of transdermal drug delivery has been severely limited by the inability of most drugs to enter the skin at therapeutically useful rates. Recently, the use of micron-scale needles in increasing skin permeability has been proposed and shown to dramatically increase transdermal delivery, especially for macromolecules. Using the tools of the microelectronics industry, microneedles have been fabricated with a range of sizes, shapes and materials. Most drug delivery studies have emphasized solid microneedles, which have been shown to increase skin permeability to a broad range of molecules and nanoparticles in vitro. In vivo studies have demonstrated delivery of oligonucleotides, reduction of blood glucose level by insulin, and induction of immune responses from protein and DNA vaccines. For these studies, needle arrays have been used to pierce holes into skin to increase transport by diffusion or iontophoresis or as drug carriers that release drug into the skin from a microneedle surface coating. Hollow microneedles have also been developed and shown to microinject insulin to diabetic rats. To address practical applications of microneedles, the ratio of microneedle fracture force to skin insertion force (i.e. margin of safety) was found to be optimal for needles with small tip radius and large wall thickness. Microneedles inserted into the skin of human subjects were reported as painless. Together, these results suggest that microneedles represent a promising technology to deliver therapeutic compounds into the skin for a range of possible applications.     

Trypsin as a novel potential absorption enhancer for improving the transdermal delivery of macromolecules

Objectives The aim was to assess the effect of trypsin on the transdermal delivery of macromolecules by applying its specific biochemical properties to the stratum corneum of the skin. Methods Fluorescein isothiocyanate (FITC)‐labelled dextrans (FDs), with molecular weights of 4 to 250 kDa, and FITC‐insulin were used as model macromolecules and a model polypeptide, and the in‐vitro transdermal permeation experiments, with or without trypsin (0.1–2.5%), were carried out using rat skin and cultured human epidermis. The mechanism for the enhancement of trypsin was also studied using fluorescence and conventional light microscopy. Key findings Trypsin significantly increased the transdermal permeability of all FDs through the rat skin (2.0‐ to 10.0‐fold). It also markedly enhanced the permeation of FD4 through three‐dimensional cultured human epidermis (3.1‐fold), which was used to evaluate the transport pathways other than the transfollicular route. Furthermore, the permeation flux of FITC‐insulin was increased by 10.0‐fold with trypsin pretreatment (from 0.02 ± 0.00 to 0.20 ± 0.07 μg/cm² per h). Mechanistic studies indicated that trypsin affects both the intercellular pathway and the hair follicular route, and may alter stratum corneum protein structures, thereby affecting skin barrier properties. Conclusions This study suggests that trypsin could be effective as a biochemical enhancer for the transdermal delivery of macromolecules including peptide and protein drugs.     

Enhanced delivery of hydrophilic peptides in vitro by transdermal microneedle pretreatment

The aims of this study were to investigate the utility of solid microneedle arrays (150 µm in length) in enhancing transdermal delivery of peptides and to examine the relationship between peptide permeation rates and D₂O flux. Four model peptides were used (Gly–Gln–Pro–Arg [tetrapeptide-3, 456.6 Da], Val–Gly–Val–Ala–Pro–Gly [hexapeptide, 498.6 Da], AC–Glu–Glu–Met–Gln–Arg–Arg–NH₂ [acetyl hexapeptide-3, 889 Da] and Cys–Tyr–Ile–Gln–Asn–Cys–Pro–Leu–Gly–NH₂ [oxytocin, 1007.2 Da]). The influence of microneedle pretreatment on skin permeation was evaluated using porcine ear skin with Franze diffusion cell. Peptide permeation across the skin was significantly enhanced by microneedle pretreatment, and permeation rates were dependent on peptide molecular weights. A positive correlation between D₂O flux and acetyl hexapeptide-3 clearances suggests that convective solvent flow contributes to the enhanced transdermal peptide delivery. It is concluded that solid microneedle arrays are effective devices to enhance skin delivery of peptides.KEY WORDS: Microneedle, Peptide, Transdermal, Convective solvent flow     

Permeation of sumatriptan succinate across human skin using multiple types of self-dissolving microneedle arrays fabricated from sodium hyaluronate

Available formulations of sumatriptan succinate (SS) have low bioavailability or are associated with site reactions. We developed various types of self-dissolving microneedle arrays (MNs) fabricated from sodium hyaluronate as a new delivery system for SS and evaluated their skin permeation and irritation in terms of clinical application. In vitro permeation studies with human skin, physicochemical properties (needle length, thickness and density), and penetration enhancers (glycerin, sodium dodecyl sulfate and lauric acid diethanolamide) were investigated. SS-loaded high-density MNs of 800?µm in length were the optimal formulation and met clinical therapeutic requirements. Penetration enhancers did not significantly affect permeation of SS from MNs. Optical coherence tomography images demonstrated that SS-loaded high-density MNs (800?µm) uniformly created drug permeation pathways for the delivery of SS into the skin. SS-loaded high-density MNs induced moderate primary skin irritations in rats, but the skin recovered within 72?h of removal of the MNs. These findings suggest that high-density MNs of 800?µm in length are an effective and promising formulation for transdermal delivery of SS. To our knowledge, this is the first report of SS permeation across human skin using self-dissolving MNs.     

Enhanced transdermal delivery of low molecular weight heparin by barrier perturbation

The purpose of this work was to investigate the in vitro transdermal delivery of low molecular weight heparin (LMWH). Hairless rat skin was mounted on Franz diffusion cells and treated with various enhancement strategies. Passive flux was essentially zero and remained low even after iontophoresis (0.065 U cm(-2) h(-1)) or application of ultrasound (0.058 U cm(-2) h(-1)). A significant increase in flux across tape stripped skin (4.0 U cm(-2) h(-1)) suggests the interaction of stratum corneum (SC) with LMWH which was confirmed using Differential Scanning Calorimetry and Fourier Transform-Infrared spectrophotometry. Maltose microneedles were then employed as a means to locally disrupt and bypass the SC. Transepidermal water loss (TEWL) and transcutaneous electrical resistance (TER) were measured to confirm the barrier disruption. Microneedles breached the SC resulting in increased TEWL, decreased TER and enhanced LMWH permeability (0.175 U cm(-2) h(-1)). Microneedles when used in conjunction with iontophoresis had a synergistic effect on LMWH delivery resulting in enhancement of flux by 14.7-fold as compared to iontophoresis used alone. Confocal laser scanning microscopy substantiated the evidence about LMWH interaction with SC. In conclusion, LMWH was shown to interact with SC and therefore tape stripping or microneedles dramatically increased its delivery due to disruption of the SC skin barrier.     

尼莫地平水凝胶贴剂的制备及其体外透皮性能研究

目的:制备尼莫地平水凝胶贴剂,并考察不同因素对尼莫地平体外透皮性的影响。方法:以羧甲基纤维素钠为骨架材料制备尼莫地平水凝胶贴剂,采用透皮扩散试验仪,以离体小鼠皮肤为屏障进行体外透皮实验,高效液相色谱法测定药物浓度,并计算药物累积透皮量Q和透皮速率常数Js。以Q值和Js值为指标,筛选投药量、透皮促进剂的种类(薄荷醇、氮酮、油酸)和用量。结果:最佳投药量为4 mg·cm-2,不同透皮促进剂对尼莫地平均有透皮促进作用,其中以5%油酸作用最显著。以5%油酸为透皮促进剂制备的样品的透皮吸收行为符合零级动力学过程,Js值为28.10μg·cm-2·h-1,12 h单位面积Q值为342.58μg·cm-2。结论:尼莫地平水凝胶贴剂可以开发为经皮给药制剂。     

Touch-actuated microneedle array patch for closed-loop transdermal drug delivery

To date, only approximately 20 drugs synthesized with small molecules have been approved by the FDA for use in traditional transdermal patches (TTP) owing to the extremely low permeation rate of the skin barrier for macromolecular drugs. A novel touch-actuated microneedle array patch (TMAP) was developed for transdermal delivery of liquid macromolecular drugs. TMAP is a combination of a typical TTP and a solid microneedle array (MA). High doses of liquid drug formulations, especially heat-sensitive compounds can be easily filled and stored in the drug reservoir of TMAPs. TMAP can easily penetrate the skin and automatically retract from it to create microchannels through the stratum corneum (SC) layer using touch-actuated ‘press and release’ actions for passive permeation of liquid drugs. Comparison of subcutaneous injection, TTP, solid MA, and dissolvable MA, indicated that insulin-loaded TMAP exhibited the best hypoglycemic effect on type 1 diabetic rats. A ‘closed-loop’ permeation control was also provided for on-demand insulin delivery based on feedback of blood glucose levels (BGLs). Twenty IU-insulin-loaded TMAP maintained the type 1 diabetic rats in a normoglycemic state for approximately 11.63?h, the longest therapeutic duration among all previously reported results on microneedle-based transdermal patches. TMAP possesses excellent transdermal drug delivery capabilities.     

Transdermal Delivery of Naltrexol and Skin Permeability Lifetime after Microneedle Treatment in Hairless Guinea Pigs

Controlled-release delivery of 6-β-naltrexol (NTXOL), the major active metabolite of naltrexone, via a transdermal patch is desirable for treatment of alcoholism. Unfortunately, NTXOL does not diffuse across skin at a therapeutic rate. Therefore, the focus of this study was to evaluate microneedle (MN) skin permeation enhancement of NTXOL’s hydrochloride salt in hairless guinea pigs. Specifically, these studies were designed to determine the lifetime of MN-created aqueous pore pathways. MN pore lifetime was estimated by pharmacokinetic evaluation, transepidermal water loss (TEWL) and visualization of MN-treated skin pore diameters using light microscopy. A 3.6-fold enhancement in steady-state plasma concentration was observed in vivo with MN treated skin with NTXOL HCl, as compared to NTXOL base. TEWL measurements and microscopic evaluation of stained MN-treated guinea pig skin indicated the presence of pores, suggesting a feasible nonlipid bilayer pathway for enhanced transdermal delivery. Overall, MN-assisted transdermal delivery appears viable for at least 48 h after MN-application. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3072-3080, 2010     

物理方法促进胰岛素经皮吸收的实验研究进展

目的胰岛素经皮吸收制剂是一种理想的胰岛素给药方式,但由于皮肤角质层的阻力、胰岛素分子在皮肤中的累积等因素限制了胰岛素的经皮给药。方法本文介绍了微针、电致孔、超声导入、离子导入等物理方法促进胰岛素经皮吸收实验研究进展。结果研究安全、有效、经济、方便的胰岛素透皮吸收物理促渗技术。结论随着对上述新技术、新方法实验研究的深入,物理促渗技术必将为胰岛素透皮吸收制剂的发展开辟更广阔的前景     

Production of dissolvable microneedles using an atomised spray process: Effect of microneedle composition on skin penetration

Dissolvable microneedles offer an attractive delivery system for transdermal drug and vaccine delivery. They are most commonly formed by filling a microneedle mold with liquid formulation using vacuum or centrifugation to overcome the constraints of surface tension and solution viscosity. Here, we demonstrate a novel microneedle fabrication method employing an atomised spray technique that minimises the effects of the liquid surface tension and viscosity when filling molds. This spray method was successfully used to fabricate dissolvable microneedles (DMN) from a wide range of sugars (trehalose, fructose and raffinose) and polymeric materials (polyvinyl alcohol, polyvinylpyrrolidone, carboxymethylcellulose, hydroxypropylmethylcellulose and sodium alginate). Fabrication by spraying produced microneedles with amorphous content using single sugar compositions. These microneedles displayed sharp tips and had complete fidelity to the master silicon template. Using a method to quantify the consistency of DMN penetration into different skin layers, we demonstrate that the material of construction significantly influenced the extent of skin penetration. We demonstrate that this spraying method can be adapted to produce novel laminate-layered as well as horizontally-layered DMN arrays. To our knowledge, this is the first report documenting the use of an atomising spray, at ambient, mild processing conditions, to create dissolvable microneedle arrays that can possess novel, laminate layering.     

Effect of microneedle on the pharmacokinetics of ketoprofen from its transdermal formulations

Non-invasive transdermal delivery using microneedle arrays was recently introduced to deliver a variety of large and hydrophilic compounds into the skin, including proteins and DNA. In this study, a microneedle array was applied to the delivery of a hydrophobic drug, ketoprofen, to determine if transdermal delivery in rats can be improved without the need for permeation enhancers. The ability of a microneedle to increase the skin permeability of ketoprofen was tested using the following procedure. A microneedle array was inserted into the lower back skin of a rat using a clip for 10 min. Subsequently, 24 mg/kg of a ketoprofen gel was loaded on the same site where the microneedle had been applied. Simultaneously, the microneedle was coated with 24 mg/kg of a ketoprofen gel, and inserted into the skin using a clip for 10 min. As a negative control experiment, only 24 mg/kg of the ketoprofen gel was applied to the shaved lower back of a rat. Blood samples were taken at the indicated times. The plasma concentration (C_p) was obtained as a function of time (t), and the pharmacokinetic parameters were calculated using the BE program. The group loaded with the microneedle coated with ketoprofen gel showed a 1.86-fold and 2.86-fold increase in the AUC and C_max compared with the ketoprofen gel alone group. These results suggest that a microneedle can be an ideal tool for transdermal delivery products.     

Microneedles: a valuable physical enhancer to increase 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. Recently, the use of micron-scale needles in increasing skin permeability has been proposed and shown to dramatically increase transdermal delivery. Microneedles have been fabricated with a range of sizes, shapes, and materials. Most in vitro drug delivery studies have shown these needles to increase skin permeability to a broad range of drugs that differ in molecular size and weight. In vivo studies have demonstrated satisfactory release of oligonucleotides and insulin and the induction of immune responses from protein and DNA vaccines. Microneedles inserted into the skin of human subjects were reported to be painless. For all these reasons, microneedles are a promising technology to deliver drugs into the skin. This review presents the main findings concerning the use of microneedles in transdermal drug delivery. It also covers types of microneedles, their advantages and disadvantages, enhancement mechanisms, and trends in transdermal drug delivery.     

微针与新型经皮给药载体结合的研究进展

经皮给药系统具有给药方便、血药浓度稳定、无首过效应等优点,但皮肤的屏障作用使得药物难以透过皮肤。近年来,出现了很多新型经皮给药的药物载体,如脂质体、醇质体、囊泡等,这些能通过化学方法促进药物的经皮渗透。而微针能穿透皮肤角质层形成微孔通道,通过物理方法促进药物的渗透,将微针与新型经皮给药载体结合能显著提高药物的经皮吸收的速率。本文对微针与新型经皮给药载体结合的最新研究进行了综述,并展望了微针辅助新型药物载体经皮给药的发展前景。     

Development of a novel self-dissolving microneedle array of alendronate, a nitrogen-containing bisphosphonate: evaluation of transdermal absorption, safety, and pharmacological effects after application in rats

Alendronate is a nitrogen-containing bisphosphonate that is widely used for the treatment of osteoporosis. In this study, we developed a novel self-dissolving micron-size needle array (microneedle array) containing alendronate, which was fabricated by micromodeling technologies using hyaluronic acid as a basic material. Micron-scale pores in the skin were seen after the application of the alendronate-loaded microneedle array, verifying establishment of transdermal pathways for alendronate. The absorption of alendronate after the application of alendronate-loaded microneedle array was almost equivalent to that after subcutaneous administration, and the bioavailability of alendronate was approximately 90% in rats. Furthermore, delivery of alendronate via this strategy effectively suppressed the decrease in the width of the growth plate in a rat model of osteoporosis. Although mild cutaneous irritation was observed after the application of the alendronate-loaded microneedle array, it resolved by day 15. These findings indicate that this alendronate-loaded microneedle array is a promising transdermal formulation for the treatment of osteoporosis.