In vivo assessment of safety of microneedle arrays in human skin

Microneedling in facial recalcitrant melasma: report of a series of 22 cases

Melasma is a chronic skin disorder that results in symmetrical, blotchy, brownish facial pigmentation. It is more common in women than in men, it generally starts between 20 and 40 years, and it can lead to considerable embarrassment and distress. The aims of this article is to evaluate the treatment with the microneedling method in 18 female and 4 male with recalcitrant melasma. All patients demonstrated good results. In conclusion, microneedles appears to be a promising therapeutic method for melasma.

Paediatricians' opinions of microneedle-mediated monitoring: a key stage in the translation of microneedle technology from laboratory into clinical practice

Microneedle (MN) arrays could offer an alternative method to traditional drug delivery and blood sampling methods. However, acceptance among key end-users is critical for new technologies to succeed. MNs have been advocated for use in children and so, paediatricians are key potential end-users. However, the opinions of paediatricians on MN use have been previously unexplored. The aim of this study was to investigate the views of UK paediatricians on the use of MN technology within neonatal and paediatric care. An online survey was developed and distributed among UK paediatricians to gain their opinions of MN technology and its use in the neonatal and paediatric care settings, particularly for MN-mediated monitoring. A total of 145 responses were obtained, with a completion response rate of 13.7 %. Respondents believed an alternative monitoring technique to blood sampling in children was required. Furthermore, 83 % of paediatricians believed there was a particular need in premature neonates. Overall, this potential end-user group approved of the MN technology and a MN-mediated monitoring approach. Minimal pain and the perceived ease of use were important elements in gaining favour. Concerns included the need for confirmation of correct application and the potential for skin irritation. The findings of this study provide an initial indication of MN acceptability among a key potential end-user group. Furthermore, the concerns identified present a challenge to those working within the MN field to provide solutions to further improve this technology. The work strengthens the rationale behind MN technology and facilitates the translation of MN technology from lab bench into the clinical setting.

Multifunctional particle-constituted microneedle arrays as cutaneous or mucosal vaccine adjuvant-delivery systems

To overcome drawbacks of current injection vaccines, such as causing needle phobia, needing health professionals for inoculation, and generating dangerous sharps wastes, researchers have designed novel vaccines that are combined with various microneedle arrays (MAs), in particular, with the multifunctional particle-constructed MAs (MPMAs). MPMAs prove able to enhance vaccine stability through incorporating vaccine ingredients in the carrier, and can be painlessly inoculated by minimally trained workers or by self-administration, leaving behind no metal needle pollution while eliciting robust systemic and mucosal immunity to antigens, thanks to delivering vaccines to cutaneous or mucosal compartments enriched in professional antigen-presenting cells (APCs). Especially, MPMAs can be easily integrated with functional molecules fulfilling targeting vaccine delivery or controlling immune response toward a Th1 or Th2 pathway to generate desired immunity against pathogens. Herein, we introduce the latest research and development of various MPMAs which are a novel but promising vaccine adjuvant delivery system (VADS).

Microneedle characterisation: the need for universal acceptance criteria and GMP specifications when moving towards commercialisation

With interest in microneedles as a novel drug transdermal delivery system increasing rapidly since the late 1990s (Margetts and Sawyer Contin Educ Anaesthesia Crit Care Pain. 7(5):171-76, 2007), a diverse range of microneedle systems have been fabricated with varying designs and dimensions. However, there are still very few commercially available microneedle products. One major issue regarding microneedle manufacture on an industrial scale is the lack of specific quality standards for this novel dosage form in the context of Good Manufacturing Practice (GMP). A range of mechanical characterisation tests and microneedle insertion analysis techniques are used by researchers working on microneedle systems to assess the safety and performance profiles of their various designs. The lack of standardised tests and equipment used to demonstrate microneedle mechanical properties and insertion capability makes it difficult to directly compare the in use performance of candidate systems. This review highlights the mechanical tests and insertion analytical techniques used by various groups to characterise microneedles. This in turn exposes the urgent need for consistency across the range of microneedle systems in order to promote innovation and the successful commercialisation of microneedle products.

Towards pain-free diagnosis of skin diseases through multiplexed microneedles: biomarker extraction and detection using a highly sensitive blotting method

Immunodiagnostic microneedles provide a novel way to extract protein biomarkers from the skin in a minimally invasive manner for analysis in vitro. The technology could overcome challenges in biomarker analysis specifically in solid tissue, which currently often involves invasive biopsies. This study describes the development of a multiplex immunodiagnostic device incorporating mechanisms to detect multiple antigens simultaneously, as well as internal assay controls for result validation. A novel detection method is also proposed. It enables signal detection specifically at microneedle tips and therefore may aid the construction of depth profiles of skin biomarkers. The detection method can be coupled with computerised densitometry for signal quantitation. The antigen specificity, sensitivity and functional stability of the device were assessed against a number of model biomarkers. Detection and analysis of endogenous antigens (interleukins 1α and 6) from the skin using the device was demonstrated. The results were verified using conventional enzyme-linked immunosorbent assays. The detection limit of the microneedle device, at ≤10 pg/mL, was at least comparable to conventional plate-based solid-phase enzyme immunoassays.

Hydrogel-Forming Microneedle Arrays Allow Detection of Drugs and Glucose In Vivo: Potential for Use in Diagnosis and Therapeutic Drug Monitoring

We describe, for the first time the use of hydrogel-forming microneedle (MN) arrays for minimally-invasive extraction and quantification of drug substances and glucose from skin in vitro and in vivo. MN prepared from aqueous blends of hydrolysed poly(methyl-vinylether-co-maleic anhydride) (11.1% w/w) and poly(ethyleneglycol) 10,000 daltons (5.6% w/w) and crosslinked by esterification swelled upon skin insertion by uptake of fluid. Post-removal, theophylline and caffeine were extracted from MN and determined using HPLC, with glucose quantified using a proprietary kit. In vitro studies using excised neonatal porcine skin bathed on the underside by physiologically-relevant analyte concentrations showed rapid (5 min) analyte uptake. For example, mean concentrations of 0.16 μg/mL and 0.85 μg/mL, respectively, were detected for the lowest (5 μg/mL) and highest (35 μg/mL) Franz cell concentrations of theophylline after 5 min insertion. A mean concentration of 0.10 μg/mL was obtained by extraction of MN inserted for 5 min into skin bathed with 5 μg/mL caffeine, while the mean concentration obtained by extraction of MN inserted into skin bathed with 15 μg/mL caffeine was 0.33 μg/mL. The mean detected glucose concentration after 5 min insertion into skin bathed with 4 mmol/L was 19.46 nmol/L. The highest theophylline concentration detected following extraction from a hydrogel-forming MN inserted for 1 h into the skin of a rat dosed orally with 10 mg/kg was of 0.363 μg/mL, whilst a maximum concentration of 0.063 μg/mL was detected following extraction from a MN inserted for 1 h into the skin of a rat dosed with 5 mg/kg theophylline. In human volunteers, the highest mean concentration of caffeine detected using MN was 91.31 μg/mL over the period from 1 to 2 h post-consumption of 100 mg Proplus^® tablets. The highest mean blood glucose level was 7.89 nmol/L detected 1 h following ingestion of 75 g of glucose, while the highest mean glucose concentration extracted from MN was 4.29 nmol/L, detected after 3 hours skin insertion in human volunteers. Whilst not directly correlated, concentrations extracted from MN were clearly indicative of trends in blood in both rats and human volunteers. This work strongly illustrates the potential of hydrogel-forming MN in minimally-invasive patient monitoring and diagnosis. Further studies are now ongoing to reduce clinical insertion times and develop mathematical algorithms enabling determination of blood levels directly from MN measurements.

Microneedles: bench to bedside

Microneedles are tiny micron-sized structures, made of a variety of materials, used to minimally disrupt the outermost layer of the skin for enhancing the delivery of therapeutic molecules across the skin. They are sufficiently long enough just to breach the stratum corneum barrier but too short to reach the nerve endings that perceive pain. Treating the skin using microneedles results in the creation of aqueous microchannels that promote delivery of molecules practically of any size. Small molecules, proteins, vaccines and diagnostic agents can be delivered using microneedles. This technology that has started with microstructures made of metal and silicon has now undergone significant advances in the last decade and currently there are microneedle products in the market.

Microneedle-based drug and vaccine delivery via nanoporous microneedle arrays

In the literature, several types of microneedles have been extensively described. However, porous microneedle arrays only received minimal attention. Hence, only little is known about drug delivery via these microneedles. However, porous microneedle arrays may have potential for future microneedle-based drug and vaccine delivery and could be a valuable addition to the other microneedle-based drug delivery approaches. To gain more insight into porous microneedle technologies, the scientific and patent literature is reviewed, and we focus on the possibilities and constraints of porous microneedle technologies for dermal drug delivery. Furthermore, we show preliminary data with commercially available porous microneedles and describe future directions in this field of research.

Microneedle applications in improving skin appearance

Microneedles (MNs) are micron-sized, minimally invasive devices that breach the outermost layer of the skin, the stratum corneum (SC), creating transient, aqueous pores in the skin and facilitating the transport of therapeutic molecules into the epidermis. Following many years of extensive research in the area of MN-mediated trans- and intra-dermal drug delivery, MNs are now being exploited in the cosmeceutical industry as a means of disrupting skin cell architecture, inducing elastin and collagen expression and deposition. They are also being used as vehicles to deliver cosmeceutic molecules across the skin, in addition to their use in combinatorial treatments with topical agents or light sources. This review explores the chronology of microneedling methodologies, which has led to the emergence of MN devices, now extensively used in cosmeceutical applications. Recent developments in therapeutic molecule and peptide delivery to the skin via MN platforms are addressed and some commercially available MN devices are described. Important safety and regulatory considerations relating to MN usage are addressed, as are studies relating to public perception of MN, as these will undoubtedly influence the acceptance of MN products as they progress towards commercialisation.

Evaluation of the effect of polymeric microneedle arrays of varying geometries in combination with a high-velocity applicator on skin permeability and irritation

Polymeric microneedles offer the advantages of being both mass-producible and inexpensive. However, their weakness lies in the fact that they are not adequate for sharp fabrication of a needle tip, which is an important factor for effective penetration. We hypothesized that effective penetration can be achieved using a high-velocity application system. Therefore, in the present study, we investigated the influence of various polymeric microneedle array geometries on skin permeability and irritation using such a system. Volar forearms of 16 healthy volunteers were treated using the microneedle system with four different parameters: applicator velocity (4.3, 6, and 8.5 m/s), tip radius (10, 15, and 20 μm), length (100, 200, and 300 μm), and number of needles (189 and 305 on a 50-mm(2) area). A higher velocity of piercing clearly enhanced skin permeability and damage. A larger tip radius resulted in lower skin permeability and irritation at an applicator velocity of 4.3 m/s but did not have an effect at 6 m/s. Skin permeability was positively variable, ranging from 100 to 200 μm of needle length, and needle number showed no influence in the range investigated. In conclusion, a faster application speed could significantly enhance skin permeability and damage and compensate for insufficient penetration of the larger tip radius and shorter needles, which are also important factors for effective insertion.

The role of microneedles for drug and vaccine delivery

INTRODUCTION

Transdermal drug delivery offers a number of advantages for the patient, not only due to its non-invasive and convenient nature, but also due to factors such as avoidance of first-pass metabolism and prevention of gastrointestinal degradation. It has been demonstrated that microneedles (MNs) can increase the number of compounds amenable to transdermal delivery by penetrating the skin's protective barrier, the stratum corneum, and creating a pathway for drug permeation to the dermal tissue below.

AREAS COVERED

MNs have been extensively investigated for drug and vaccine delivery. The different types of MN arrays and their delivery capabilities are discussed in terms of drugs, including biopharmaceutics and vaccines. Patient usage and effects on the skin are also considered.

EXPERT OPINION

MN research and development is now at the stage where commercialisation is a viable possibility. There are a number of long-term safety questions relating to patient usage which will need to be addressed moving forward. Regulatory guidance is awaited to direct the scale-up of the manufacturing process alongside provision of clearer patient instruction for safe and effective use of MN devices.

A proposed model membrane and test method for microneedle insertion studies

A commercial polymeric film (Parafilm M^®, a blend of a hydrocarbon wax and a polyolefin) was evaluated as a model membrane for microneedle (MN) insertion studies. Polymeric MN arrays were inserted into Parafilm M^® (PF) and also into excised neonatal porcine skin. Parafilm M^® was folded before the insertions to closely approximate thickness of the excised skin. Insertion depths were evaluated using optical coherence tomography (OCT) using either a force applied by a Texture Analyser or by a group of human volunteers. The obtained insertion depths were, in general, slightly lower, especially for higher forces, for PF than for skin. However, this difference was not a large, being less than the 10% of the needle length. Therefore, all these data indicate that this model membrane could be a good alternative to biological tissue for MN insertion studies. As an alternative method to OCT, light microscopy was used to evaluate the insertion depths of MN in the model membrane. This provided a rapid, simple method to compare different MN formulations. The use of Parafilm M^®, in conjunction with a standardised force/time profile applied by a Texture Analyser, could provide the basis for a rapid MN quality control test suitable for in-process use. It could also be used as a comparative test of insertion efficiency between candidate MN formulations.

Hydrogel-forming microneedle arrays can be effectively inserted in skin by self-application: a pilot study centred on pharmacist intervention and a patient information leaflet

PURPOSE

To investigate, for the first time, the influence of pharmacist intervention and the use of a patient information leaflet on self-application of hydrogel-forming microneedle arrays by human volunteers without the aid of an applicator device.

METHODS

A patient information leaflet was drafted and pharmacist counselling strategy devised. Twenty human volunteers applied 11 × 11 arrays of 400 μm hydrogel-forming microneedle arrays to their own skin following the instructions provided. Skin barrier function disruption was assessed using transepidermal water loss measurements and optical coherence tomography and results compared to those obtained when more experienced researchers applied the microneedles to the volunteers or themselves.

RESULTS

Volunteer self-application of the 400 μm microneedle design resulted in an approximately 30% increase in skin transepidermal water loss, which was not significantly different from that seen with self-application by the more experienced researchers or application to the volunteers. Use of optical coherence tomography showed that self-application of microneedles of the same density (400 μm, 600 μm and 900 μm) led to percentage penetration depths of approximately 75%, 70% and 60%, respectively, though the diameter of the micropores created remained quite constant at approximately 200 μm. Transepidermal water loss progressively increased with increasing height of the applied microneedles and this data, like that for penetration depth, was consistent, regardless of applicant.

CONCLUSION

We have shown that hydrogel-forming microneedle arrays can be successfully and reproducibly applied by human volunteers given appropriate instruction. If these outcomes were able to be extrapolated to the general patient population, then use of bespoke MN applicator devices may not be necessary, thus possibly enhancing patient compliance.

Self-setting bioceramic microscopic protrusions for transdermal drug delivery

Self-setting bioceramic microneedles are fabricated using a simple manufacturing procedure under mild conditions and could be substitutes for current microneedles.

Microneedle-iontophoresis combinations for enhanced transdermal drug delivery

It has recently been proposed that the combination of skin barrier impairment using microneedles (MNs) coupled with iontophoresis (ITP) may broaden the range of drugs suitable for transdermal delivery as well as enabling the rate of delivery to be achieved with precise electronic control. However, few reports exist on the combination of ITP with in situ drug-loaded polymeric MN delivery systems. Our in vitro permeation studies revealed that MN enhances transdermal drug delivery. The combination of dissolving MN and ITP did not further enhance the extent of delivery of the low molecular weight drug ibuprofen sodium after short application periods. However, the extent of peptide/protein delivery was significantly enhanced when ITP was used in combination with hydrogel-forming MN arrays. As such, hydrogel-forming MN arrays show promise for the electrically controlled transdermal delivery of biomacromolecules in a simple, one-step approach, though further technical developments will be necessary before patient benefit is realized.

Microneedles for intradermal and transdermal drug delivery

The formidable barrier properties of the uppermost layer of the skin, the stratum corneum, impose significant limitations for successful systemic delivery of broad range of therapeutic molecules particularly macromolecules and genetic material. Microneedle (MN) has been proposed as a strategy to breach the stratum corneum barrier function in order to facilitate effective transport of molecules across the skin. This strategy involves use of micron sized needles fabricated of different materials and geometries to create transient aqueous conduits across the skin. MN, alone or with other enhancing strategies, has been demonstrated to dramatically enhance the skin permeability of numerous therapeutic molecules including biopharmaceuticals either in vitro, ex vivo or in vivo experiments. This suggested the promising use of MN technology for various possible clinical applications such as insulin delivery, transcutaneous immunisations and cutaneous gene delivery. MN has been proved as minimally invasive and painless in human subjects. This review article focuses on recent and future developments for MN technology including the latest type of MN design, challenges and strategies in MNs development as well as potential safety aspects based on comprehensive literature review pertaining to MN studies to date.

Potential of microneedle-assisted micro-particle delivery by gene guns: a review

CONTEXT

Gene guns have been used to deliver deoxyribonucleic acid (DNA) loaded micro-particle and breach the muscle tissue to target cells of interest to achieve gene transfection.

OBJECTIVE

This article aims to discuss the potential of microneedle (MN) assisted micro-particle delivery from gene guns, with a view to reducing tissue damage.

METHODS

Using a range of sources, the main gene guns for micro-particle delivery are reviewed along with the primary features of their technology, e.g. their design configurations, the material selection of the micro-particle, the driving gas type and pressure. Depending on the gene gun system, the achieved penetration depths in the skin are discussed as a function of the gas pressure, the type of the gene gun system and particle size, velocity and density. The concept of MN-assisted micro-particles delivery which consists of three stages (namely, acceleration, separation and decoration stage) is discussed. In this method, solid MNs are inserted into the skin to penetrate the epidermis/dermis layer and create holes for particle injection. Several designs of MN array are discussed and the insertion mechanism is explored, as it determines the feasibility of the MN-based system for particle transfer.

RESULTS

This review suggests that one of the problems of gene guns is that they need high operating pressures, which may result in direct or indirect tissue/cells damage. MNs seem to be a promising method which if combined with the gene guns may reduce the operating pressures for these devices and reduce tissue/cell damages.

CONCLUSIONS

There is sufficient potential for MN-assisted particle delivery systems.

Children&s views on microneedle use as an alternative to blood sampling for patient monitoring

Objectives

To explore children's views on microneedle use for this population, particularly as an alternative approach to blood sampling, in monitoring applications, and so, examine the acceptability of this approach to children.

Methods

Focus groups were conducted with children (aged 10–14 years) in a range of schools across Northern Ireland. Convenience sampling was employed, i.e. children involved in a university-directed community-outreach project (Pharmacists in Schools) were recruited.

Key findings

A total of 86 children participated in 13 focus groups across seven schools in Northern Ireland. A widespread disapproval for blood sampling was evident, with pain, blood and traditional needle visualisation particularly unpopular aspects. In general, microneedles had greater visual acceptability and caused less fear. A patch-based design enabled minimal patient awareness of the monitoring procedure, with personalised designs, e.g. cartoon themes, favoured. Children's concerns included possible allergy and potential inaccuracies with this novel approach; however, many had confidence in the judgement of healthcare professionals if deeming this technique appropriate. They considered paediatric patient education critical for acceptance of this new approach and called for an alternative name, without any reference to ‘needles’.

Conclusions

The findings presented here support the development of blood-free, minimally invasive techniques and provide an initial indication of microneedle acceptability in children, particularly for monitoring purposes. A proactive response to these unique insights should enable microneedle array design to better meet the needs of this end-user group. Further work in this area is recommended to ascertain the perspectives of a purposive sample of children with chronic conditions who require regular monitoring.

Dissolving polymer microneedle patches for rapid and efficient transdermal delivery of insulin to diabetic rats

This study presents a dissolving microneedle patch, composed of starch and gelatin, for the rapid and efficient transdermal delivery of insulin. The microneedles completely dissolve after insertion into the skin for 5 min, quickly releasing their encapsulated payload into the skin. A histological examination shows that the microneedles have sufficient mechanical strength to be inserted in vitro into porcine skin to a depth of approximately 200 μm and in vivo into rat skin to 200-250 μm depth. This penetration depth does not induce notable skin irritation or pain sensation. To evaluate the feasibility of using these dissolving microneedles for diabetes treatment insulin-loaded microneedles were administered to diabetic rats using a homemade applicator. Pharmacodynamic and pharmacokinetic results show a similar hypoglycemic effect in rats receiving insulin-loaded microneedles and a subcutaneous injection of insulin. The relative pharmacological availability and relative bioavailability of insulin were both approximately 92%, demonstrating that insulin retains its pharmacological activity after encapsulation and release from the microneedles. Storage stability analysis confirms that more than 90% of the insulin remained in the microneedles even after storage at 25 or 37°C for 1 month. These results confirm that the proposed starch/gelatin microneedles enable stable encapsulation of bioactive molecules and have great potential for transdermal delivery of protein drugs in a relatively painless, rapid, and convenient manner.

Microneedle-assisted percutaneous delivery of naltrexone hydrochloride in yucatan minipig: in vitro-in vivo correlation

Although microneedle-assisted transdermal drug delivery has been the subject of multiple scientific investigations, very few attempts have been made to quantitatively relate in vitro and in vivo permeation. The case of naltrexone hydrochloride is not an exception. In the present study, a pharmacokinetic profile obtained following a "poke and patch" microneedle application method in the Yucatan minipig is reported. The profile demonstrates a rapid achievement of maximum naltrexone hydrochloride plasma concentration followed by a relatively abrupt concentration decline. No steady state was achieved in vivo. In an attempt to correlate the present in vivo findings with formerly published in vitro steady-state permeation data, a diffusion-compartmental mathematical model was developed. The model incorporates two parallel permeation pathways, barrier-thickness-dependent diffusional resistance, microchannel closure kinetics, and a pharmacokinetic module. The regression analysis of the pharmacokinetic data demonstrated good agreement with an independently calculated microchannel closure rate and in vitro permeation data. Interestingly, full-thickness rather than split-thickness skin employed in in vitro diffusion experiments provided the best correlation with the in vivo data. Data analysis carried out with the model presented herein provides new mechanistic insight and permits predictions with respect to pharmacokinetics coupled with altered microchannel closure rates.

Next generation intra- and transdermal therapeutic systems: using non- and minimally-invasive technologies to increase drug delivery into and across the skin

The number of drug molecules approved by the regulatory authorities for transdermal administration is relatively modest - less than two dozen. Many other therapies might benefit from the advantages offered by the transdermal route. That they have not already done so is due to the exceptional efficacy of the stratum corneum as a diffusional barrier and its remarkable ability to restrict molecular transport. As a result only extremely potent therapeutics possessing the necessary physicochemical properties can be delivered by passive diffusion across intact skin at pharmacologically relevent rates. This has led to the development of several delivery technologies that might be used to expand the range of medicinal agents that can be administered transdermally with the requisite delivery kinetics. There are essentially two approaches: (i) provide an improved driving force to increase the rate of transport (i.e., act on the molecule) or (ii) modify the properties of the microenvironment through which diffusion must occur (i.e., act on the stratum corneum). The challenge for the latter approach is to compromise the barrier in a reversible and relatively painless manner that minimises irritation, is practical for chronic conditions and has minimal risk of infection. Here, we review some of the physical methods that have been used to either transiently perturb the skin barrier or to provide additional driving forces to facilitate molecular transport with a particular focus on technologies that have either led to marketed products or have at least reached the clinical development stage.

Strategies for the Nonclinical Safety Assessment of Vaccines

Over the past century, vaccines have made a large impact on public health. Prophylactic vaccines prevent disability and disease, saving millions of dollars in potential health-care spending. Since prophylactic vaccines are administered to healthy individuals, including infants and children, it is important to demonstrate the safety of vaccines preclinically prior to testing the vaccine in clinical studies. A benefit-to-risk profile is considered for each individual vaccine and depends on many factors including preclinical and clinical toxicities that are observed, frequency of administration and intended target population. For prophylactic vaccines, in particular, the concerns about potential risks often outweigh the perception of benefit [1]. Therefore, over the past decade, there has been an increased focus on nonclinical safety assessment of vaccines, including toxicity testing.

Use of microneedle array devices for continuous glucose monitoring: a review

Microneedle array devices provide the opportunity to overcome the barrier characteristics of the outermost skin layer, the stratum corneum. This novel technology can be used as a therapeutic tool for transdermal drug delivery, including insulin, or as a diagnostic tool providing access to dermal biofluids, with subsequent analysis of its contents. Over the last decade, the use of microneedle array technology has been the focus of extensive research in the field of transdermal drug delivery. More recently, the diagnostic applications of microneedle technology have been developed. This review summarizes the existing evidence for the use of microneedle array technology as biosensors for continuous monitoring of the glucose content of interstitial fluid, focusing also on mechanics of insertion, microchannel characteristics, and safety profile.

Hydrogel-Forming Microneedle Arrays for Enhanced Transdermal Drug Delivery

Unique microneedle arrays prepared from crosslinked polymers, which contain no drug themselves, are described. They rapidly take up skin interstitial fluid upon skin insertion to form continuous, unblockable, hydrogel conduits from attached patch-type drug reservoirs to the dermal microcirculation. Importantly, such microneedles, which can be fabricated in a wide range of patch sizes and microneedle geometries, can be easily sterilized, resist hole closure while in place, and are removed completely intact from the skin. Delivery of macromolecules is no longer limited to what can be loaded into the microneedles themselves and transdermal drug delivery is now controlled by the crosslink density of the hydrogel system rather than the stratum corneum, while electrically modulated delivery is also a unique feature. This technology has the potential to overcome the limitations of conventional microneedle designs and greatly increase the range of the type of drug that is deliverable transdermally, with ensuing benefits for industry, healthcare providers and, ultimately, patients.

Microneedles for drug and vaccine delivery

Microneedles were first conceptualized for drug delivery many decades ago, but only became the subject of significant research starting in the mid-1990's when microfabrication technology enabled their manufacture as (i) solid microneedles for skin pretreatment to increase skin permeability, (ii) microneedles coated with drug that dissolves off in the skin, (iii) polymer microneedles that encapsulate drug and fully dissolve in the skin and (iv) hollow microneedles for drug infusion into the skin. As shown in more than 350 papers now published in the field, microneedles have been used to deliver a broad range of different low molecular weight drugs, biotherapeutics and vaccines, including published human studies with a number of small-molecule and protein drugs and vaccines. Influenza vaccination using a hollow microneedle is in widespread clinical use and a number of solid microneedle products are sold for cosmetic purposes. In addition to applications in the skin, microneedles have also been adapted for delivery of bioactives into the eye and into cells. Successful application of microneedles depends on device function that facilitates microneedle insertion and possible infusion into skin, skin recovery after microneedle removal, and drug stability during manufacturing, storage and delivery, and on patient outcomes, including lack of pain, skin irritation and skin infection, in addition to drug efficacy and safety. Building off a strong technology base and multiple demonstrations of successful drug delivery, microneedles are poised to advance further into clinical practice to enable better pharmaceutical therapies, vaccination and other applications.

Microneedle pretreatment enhances the percutaneous permeation of hydrophilic compounds with high melting points

Background

Two commercially available microneedle rollers with a needle length of 200 μm and 300 μm were selected to examine the influence of microneedle pretreatment on the percutaneous permeation of four non-steroidal anti-inflammatory drugs (diclofenac, ibuprofen, ketoprofen, paracetamol) with different physicochemical drug characteristics in Franz-type diffusion cells. Samples of the receptor fluids were taken at predefined times over 6 hours and were analysed by UV–VIS high-performance liquid-chromatography. Histological examinations after methylene blue application were additionally performed to gather information about barrier disruption.

Results

Despite no visible pores in the stratum corneum, the microneedle pretreatment resulted in a twofold (200 μm) and threefold higher (300 μm) flux through the pretreated skin samples compared to untreated skin samples for ibuprofen and ketoprofen (LogK_ow > 3, melting point < 100°C). The flux of the hydrophilic compounds diclofenac and paracetamol (logK_ow < 1, melting point > 100°C) increased their amount by four (200 μm) to eight (300 μm), respectively.

Conclusion

Commercially available microneedle rollers with 200–300 μm long needles enhance the drug delivery of topically applied non-steroidal anti-inflammatory drugs and represent a valuable tool for percutaneous permeation enhancement particularly for substances with poor permeability due to a hydrophilic nature and high melting points.

Dissolving polymeric microneedle arrays for electrically assisted transdermal drug delivery

It has recently been proposed that the combination of skin barrier impairment using microneedles (MNs) coupled with iontophoresis (ITP) may broaden the range of drugs suitable for transdermal delivery, as well as enabling the rate of delivery to be achieved with precise electronic control. However, no reports exist on the combination of ITP with in situ drug loaded polymeric MN delivery systems. Furthermore, although a number of studies have highlighted the importance of MN design for transdermal drug delivery enhancement, to date, there has been no systematic investigation of the influence of MN geometry on the performance of polymeric MN arrays which are designed to remain in contact with the skin during the period of drug delivery. As such, for the first time, this study reports on the effect of MN heigth and MN density upon the transdermal delivery of small hydrophilic compounds (theophylline, methylene blue, and fluorescein sodium) across neonatal porcine skin in vitro, with the optimised MN array design evaluated for its potential in the electrically faciliatated delivery of peptide (bovine insulin) and protein (fluorescein isothiocyanate-labelled bovine serum albumin (FTIC-BSA)) macromolecules. The results of the in vitro drug release investigations revealed that the extent of transdermal delivery was dependent upon the design of the MN array employed, whereby an increase in MN height and an increase in MN density led to an increase in the extent of transdermal drug delivery achieved 6h after MN application. Overall, the in vitro permeation studies revealed that the MN design containing 361 MNs/cm(2) of 600 μm height resulted in the greatest extent of transdermal drug delivery. As such, this design was evaluated for its potential in the MN mediated iontophoretic transdermal delivery. Whilst the combination of MN and ITP did not further enhance the extent of small molecular weight solute delivery, the extent of peptide/protein release was significantly enhanced when ITP was used in combination of the soluble PMVE/MA MN arrays. For example, the cumulative amount of insulin permeated across neonatal porcine skin at 6h was found to be approximately 150 μg (3.25%), 227 μg (4.85%) and 462 μg (9.87%) for ITP, MN, and MN/ITP delivery strategies, respectively. Similarly, the cumulative amount of FTIC-BSA delivered across neonatal porcine skin after a 6h period was found to be approximately 110 μg (4.53%) for MN alone and 326 μg (13.40%) for MN in combination with anodal ITP (p<0.001). As such, drug loaded soluble PMVE/MA MN arrays show promise for the electrically controlled transdermal delivery of biomacromolecules in a simple, one-step approach.

Microneedle delivery: clinical studies and emerging medical applications

The concept of microneedle drug delivery was described three decades ago; however, effective clinical demonstration has only occurred within the past 10–15 years. Substantial progress in microneedle design and fabrication including extensive in vitro, ex vivo, and in vivo preclinical evaluation with various drugs, vaccines and other agents has transpired over the last decade. In contrast with this large volume of preclinical data, there are relatively few published microneedle clinical studies. To date, the clinical investigative focus has included testing to reduce dermal barrier properties and enhance transdermal delivery; evaluation of enhanced vaccine antigenicity, including development of the first commercial microneedle product for intradermal influenza vaccination; evaluation of altered microneedle protein pharmacokinetics and pharmacodynamics, especially for insulin; and evaluation of the pain and other perceptions associated with microneedle usage. This review summarizes the various aspects of microneedle clinical evaluation to date and identifies areas requiring further clinical evaluation.

Towards tailored vaccine delivery: needs, challenges and perspectives

The ideal vaccine is a simple and stable formulation which can be conveniently administered and provides life-long immunity against a given pathogen. The development of such a vaccine, which should trigger broad and strong B-cell and T-cell responses against antigens of the pathogen in question, is highly dependent on tailored vaccine delivery approaches. This review addresses vaccine delivery in its broadest scope. We discuss the needs and challenges in the area of vaccine delivery, including restrictions posed by specific target populations, potentials of dedicated stable formulations and devices, and the use of adjuvants. Moreover, we address the current status and perspectives of vaccine delivery via several routes of administration, including non- or minimally invasive routes. Finally we suggest possible directions for future vaccine delivery research and development.

Microneedles: an emerging transdermal drug delivery system

OBJECTIVES

One of the thrust areas in drug delivery research is transdermal drug delivery systems (TDDS) due to their characteristic advantages over oral and parenteral drug delivery systems. Researchers have focused their attention on the use of microneedles to overcome the barrier of the stratum corneum. Microneedles deliver the drug into the epidermis without disruption of nerve endings. Recent advances in the development of microneedles are discussed in this review for the benefit of young scientists and to promote research in the area.

KEY FINDINGS

Microneedles are fabricated using a microelectromechanical system employing silicon, metals, polymers or polysaccharides. Solid coated microneedles can be used to pierce the superficial skin layer followed by delivery of the drug. Advances in microneedle research led to development of dissolvable/degradable and hollow microneedles to deliver drugs at a higher dose and to engineer drug release. Iontophoresis, sonophoresis and electrophoresis can be used to modify drug delivery when used in concern with hollow microneedles. Microneedles can be used to deliver macromolecules such as insulin, growth hormones, immunobiologicals, proteins and peptides. Microneedles containing 'cosmeceuticals' are currently available to treat acne, pigmentation, scars and wrinkles, as well as for skin tone improvement.

SUMMARY

Literature survey and patents filled revealed that microneedle-based drug delivery system can be explored as a potential tool for the delivery of a variety of macromolecules that are not effectively delivered by conventional transdermal techniques.

Permeation of antigen protein-conjugated nanoparticles and live bacteria through microneedle-treated mouse skin

Background:

The present study was designed to evaluate the extent to which pretreatment with microneedles can enhance skin permeation of nanoparticles in vitro and in vivo. Permeation of live bacteria, which are physically nanoparticles or microparticles, through mouse skin pretreated with microneedles was also studied to evaluate the potential risk of microbial infection.

Methods and results:

It was found that pretreatment of mouse skin with microneedles allowed permeation of solid lipid nanoparticles, size 230 nm, with ovalbumin conjugated on their surface. Transcutaneous immunization in a mouse skin area pretreated with microneedles with ovalbumin nanoparticles induced a stronger antiovalbumin antibody response than using ovalbumin alone. The dose of ovalbumin antigen determined whether microneedle-mediated transcutaneous immunization with ovalbumin nanoparticles induced a stronger immune response than subcutaneous injection of the same ovalbumin nanoparticles. Microneedle treatment permitted skin permeation of live Escherichia coli, but the extent of the permeation was not greater than that enabled by hypodermic injection.

Conclusion:

Transcutaneous immunization on a microneedle-treated skin area with antigens carried by nanoparticles can potentially induce a strong immune response, and the risk of bacterial infection associated with microneedle treatment is no greater than that with a hypodermic injection.

Kinetics of skin resealing after insertion of microneedles in human subjects

Over the past decade, microneedles have been shown to dramatically increase skin permeability to a broad range of compounds by creating reversible microchannels in the skin. However, in order to achieve sustained transdermal drug delivery, the extent and duration of skin's increased permeability needs to be determined. In this study, we used electrical impedance spectroscopy to perform the first experiments in human subjects to analyze the resealing of skin's barrier properties after insertion of microneedles. Microneedles having a range of geometries were studied in conjunction with the effect of occlusion to test the hypothesis that increasing microneedle length, number, and cross-sectional area together with occlusion leads to an increase in skin resealing time that can exceed one day. Results indicated that in the absence of occlusion, all microneedle treated sites recovered barrier properties within 2 h, while occluded sites resealed more slowly, with resealing windows ranging from 3 to 40 h depending on microneedle geometry. Upon subsequent removal of occlusion, the skin barrier resealed rapidly. Longer microneedles, increased number of needles, and larger cross-sectional area demonstrated slower resealing kinetics indicating that microneedle geometry played a significant role in the barrier resealing process. Overall, this study showed that pre-treatment of skin with microneedles before applying an occlusive transdermal patch can increase skin permeability for more than one day, but nonetheless allow skin to reseal rapidly after patch removal.

Local transdermal delivery of phenylephrine to the anal sphincter muscle using microneedles

We propose pretreatment using microneedles to increase perianal skin permeability for locally targeted delivery of phenylephrine (PE), a drug that increases resting anal sphincter pressure to treat fecal incontinence. Microneedle patches were fabricated by micromolding poly-lactic-acid. Pre-treatment of human cadaver skin with microneedles increased PE delivery across the skin by up to 10-fold in vitro. In vivo delivery was assessed in rats receiving treatment with or without use of microneedles and with or without PE. Resting anal sphincter pressure was then measured over time using water-perfused anorectal manometry. For rats pretreated with microneedles, topical application of 30% PE gel rapidly increased the mean resting anal sphincter pressure from 7±2 cm H(2)O to a peak value of 43±17 cm H(2)O after 1 h, which was significantly greater than rats receiving PE gel without microneedle pretreatment. Additional safety studies showed that topically applied green fluorescent protein-expressing E. coli penetrated skin pierced with 23- and 26-gauge hypodermic needles, but E. coli was not detected in skin pretreated with microneedles, which suggests that microneedle-treated skin may not be especially susceptible to infection. In conclusion, this study demonstrates local transdermal delivery of PE to the anal sphincter muscle using microneedles, which may provide a novel treatment for fecal incontinence.