Microfabricated silicon microneedles for nonviral cutaneous gene delivery

Unravelling the role of microneedles in drug delivery: Principle, perspectives, and practices

In recent year, the research of transdermal drug delivery systems has got substantial attention towards the development of microneedles (MNs). This shift has occurred due to multifaceted advantages of MNs as they can be utilized to deliver the drug deeper to the skin with minimal invasion, offer successful delivery of drugs and biomolecules that are susceptible to degradation in gastrointestinal tract (GIT), act as biosensors, and help in monitoring the level of biomarkers in the body. These can be fabricated into different types based on their applications as well as material for fabrication. Some of their types include solid MNs, hollow MNs, coated MNs, hydrogel forming MNs, and dissolving MNs. These MNs deliver the therapeutics via microchannels deeper into the skin. The coated and hollow MNs have been found successful. However, they suffer from poor drug loading and blocking of pores. In contrast, dissolving MNs offer high drug loading. These MNs have also been utilized to deliver vaccines and biologicals. They have also been used in cosmetics. The current review covers the different types of MNs, materials used in their fabrication, properties of MNs, and various case studies related to their role in delivering therapeutics, monitoring level of biomarkers/hormones in body such as insulin. Various patents and clinical trials related to MNs are also covered. Covered are the major bottlenecks associated with their clinical translation and potential future perspectives.

Nanoscale-tipped wire array injections transfer DNA directly into brain cells ex vivo and in vivo

Genetic modification to restore cell functions in the brain can be performed through the delivery of biomolecules in a minimally invasive manner into live neuronal cells within brain tissues. However, conventional nanoscale needles are too short (lengths of ~10 µm) to target neuronal cells in ~1‐mm‐thick brain tissues because the neuronal cells are located deep within the tissue. Here, we report the use of nanoscale‐tipped wire (NTW) arrays with diameters < 100 nm and wire lengths of ~200 µm to address biomolecule delivery issues. The NTW arrays were manufactured by growth of silicon microwire arrays and nanotip formation. This technique uses pinpoint, multiple‐cell DNA injections in deep areas of brain tissues, enabling target cells to be marked by fluorescent protein (FP) expression vectors. This technique has potential for use for electrophysiological recordings and biological transfection into neuronal cells. Herein, simply pressing an NTW array delivers and expresses plasmid DNA in multiple‐cultured cells and multiple‐neuronal cells within a brain slice with reduced cell damage. Additionally, DNA transfection is demonstrated using brain cells ex vivo and in vivo. Moreover, knockdown of a critical clock gene after injecting a short hairpin RNA (shRNA) and a genome‐editing vector demonstrates the potential to genetically alter the function of living brain cells, for example, pacemaker cells of the mammalian circadian rhythms. Overall, our NTW array injection technique enables genetic and functional modification of living cells in deep brain tissue areas, both ex vivo and in vivo.

Microneedle systems for delivering nucleic acid drugs

Background

Nucleic acid-based gene therapy is a promising technology that has been used in various applications such as novel vaccination platforms for infectious/cancer diseases and cellular reprogramming because of its fast, specific, and effective properties. Despite its potential, the parenteral nucleic acid drug formulation exhibits instability and low efficacy due to various barriers, such as stability concerns related to its liquid state formulation, skin barriers, and endogenous nuclease degradation. As promising alternatives, many attempts have been made to perform nucleic acid delivery using a microneedle system. With its minimal invasiveness, microneedle can deliver nucleic acid drugs with enhanced efficacy and improved stability.

Area covered

This review describes nucleic acid medicines' current state and features and their delivery systems utilizing non-viral vectors and physical delivery systems. In addition, different types of microneedle delivery systems and their properties are briefly reviewed. Furthermore, recent advances of microneedle-based nucleic acid drugs, including featured vaccination applications, are described.

Expert opinion

Nucleic acid drugs have shown significant potential beyond the limitation of conventional small molecules, and the current COVID-19 pandemic highlights the importance of nucleic acid therapies as a novel vaccination platform. Microneedle-mediated nucleic acid drug delivery is a potential platform for less invasive nucleic acid drug delivery. Microneedle system can show enhanced efficacy, stability, and improved patient convenience through self-administration with less pain.

Transdermal delivery for gene therapy

Gene therapy is a critical constituent of treatment approaches for genetic diseases and has gained tremendous attention. Treating and preventing diseases at the genetic level using genetic materials such as DNA or RNAs could be a new avenue in medicine. However, delivering genes is always a challenge as these molecules are sensitive to various enzymes inside the body, often produce systemic toxicity, and suffer from off-targeting problems. In this regard, transdermal delivery has emerged as an appealing approach to enable a high efficiency and low toxicity of genetic medicines. This review systematically summarizes outstanding transdermal gene delivery methods for applications in skin cancer treatment, vaccination, wound healing, and other therapies.

Flexible Microneedle Array Patch for Chronic Wound Oxygenation and Biofilm Eradication

Chronic nonhealing wounds are a growing socioeconomic problem that affects more than 6 million people annually solely in the United States. These wounds are colonized by bacteria that often develop into biofilms that act as a physical and chemical barrier to therapeutics and tissue oxygenation leading to chronic inflammation and tissue hypoxia. Although wound debridement and vigorous mechanical abrasion techniques are often used by clinical professionals to manage and remove biofilms from wound surfaces, such methods are highly nonselective and painful. In this study, we have developed a flexible polymer composite microneedle array that can overcome the physicochemical barriers (i.e., bacterial biofilm) present in chronic nonhealing wounds and codeliver oxygen and bactericidal agents. The polymeric microneedles are made by using a facile UV polymerization process of polyvinylpyrrolidone and calcium peroxide onto a flexible polyethylene terephthalate substrate for conformable attachment onto different locations of the human body surface. The microneedles effectively elevate the oxygen levels from 8 to 12 ppm once dissolved over the course of 2 h while also providing strong bactericidal effects on both liquid and biofilm bacteria cultures of both Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacterial strains commonly found in dermal wounds. Furthermore, the results from the ex vivo assay on a porcine wound model indicated successful insertion of the microneedles into the tissue while also providing effective bactericidal properties against both Gram-positive and Gram-negative within the complex tissue matrix. Additionally, the microneedles demonstrate high levels of cytocompatibility with less than 10% of apoptosis throughout 6 days of continuous exposure to human dermal fibroblast cells. The demonstrated flexible microneedle array can provide a better approach for increasing the effectiveness of topical tissue oxygenation as well as the treatment of infected wounds with intrinsically antibiotic resistant biofilms.

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

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

Recent advances on microneedle arrays-mediated technology in cancer diagnosis and therapy

Regarding the increasing prevalence of cancer throughout the globe, the development of novel alternatives for conventional therapies is inevitable to circumvent limitations such as low efficacy, complications, and high cost. Recently, microneedle arrays (MNs) have been introduced as a novel, minimally invasive, and low-cost approach. MNs can delivery both small molecule and macromolecular drugs or even nanoparticles (NPs) to the tumor tissue in a safe and controlled manner. Relying on the recent promising outcomes of MNs in transdermal delivery of anticancer agents, this review is aimed to summarize constituent materials, fabrication methods, advantages, and limitations of different types of MNs used in cancer therapy applications. This review paper also presents the potential use of MNs in transdermal delivery of NPs for effective chemotherapy, gene therapy, immunotherapy, photodynamic, and photothermal therapy. Additionally, MNs are currently explored as routine point-of-care health monitoring devices for transdermal detection of cancer biomarkers or physiologically relevant analytes which will be addressed in this paper. Despite the promising potential of MNs for cancer therapy and diagnosis, several limitations have impeded their therapeutic efficacy and real-time applicability that are addressed in this paper.

Mathematical Modelling, Simulation and Optimisation of Microneedles for Transdermal Drug Delivery: Trends and Progress

In the last two decades, microneedles (MNs) have received significant interest due to their potential for painless transdermal drug delivery (TDD) and minimal skin damage. MNs have found applications in a range of research and development areas in drug delivery. They have been prepared using a variety of materials and fabrication techniques resulting in MN arrays with different dimensions, shapes, and geometries for delivery of a variety of drug molecules. These parameters play crucial roles in determining the drug release profiles from the MNs. Developing mathematical modelling, simulation, and optimisation techniques is vital to achieving the desired MN performances. These will then be helpful for pharmaceutical and biotechnological industries as well as professionals working in the field of regulatory affairs focusing on MN based TDD systems. This is because modelling has a great potential to reduce the financial and time cost of both the MNs' studies and manufacturing. For example, a number of robust mathematical models for predicting the performance of the MNs in vivo have emerged recently which incorporate the roles of the structural and mechanical properties of the skin. In addressing these points, this review paper aims to highlight the current status of the MN modelling research, in particular, the modelling, simulation and optimisation of the systems for drug delivery. The theoretical basis for the simulation of MN enhanced diffusion is discussed within this paper. Thus, this review paper provides a better understanding of the modelling of the MN mediated drug delivery process.

Non-transdermal microneedles for advanced drug delivery

Microneedles (MNs) have been used to deliver drugs for over two decades. These platforms have been proven to increase transdermal drug delivery efficiency dramatically by penetrating restrictive tissue barriers in a minimally invasive manner. While much of the early development of MNs focused on transdermal drug delivery, this technology can be applied to a variety of other non-transdermal biomedical applications. Several variations, such as multi-layer or hollow MNs, have been developed to cater to the needs of specific applications. The heterogeneity in the design of MNs has demanded similar variety in their fabrication methods; the most common methods include micromolding and drawing lithography. Numerous materials have been explored for MN fabrication which range from biocompatible ceramics and metals to natural and synthetic biodegradable polymers. Recent advances in MN engineering have diversified MNs to include unique shapes, materials, and mechanical properties that can be tailored for organ-specific applications. In this review, we discuss the design and creation of modern MNs that aim to surpass the biological barriers of non-transdermal drug delivery in ocular, vascular, oral, and mucosal tissue.

Three-Step Thermal Drawing for Rapid Prototyping of Highly Customizable Microneedles for Vascular Tissue Insertion

Microneedles (MNs) have been extensively developed over the last two decades, and highly efficient drug delivery was demonstrated with their minimal invasiveness via a transdermal route. Recently, MNs have not only been applied to the skin but also to other tissues such as blood vessels, scleral tissue, and corneal tissue. In addition, the objective of the MN application has been diversified, ranging from drug delivery to wound closure and biosensing. However, since most MN fabrication methods are expensive and time-consuming, they are inappropriate to prototype MNs for various tissues that have different and complex anatomies. Although several drawing-based techniques have been introduced for rapid MN production, they fabricated MNs with limited shapes, such as thin MNs with wide bases. In this study, we propose a three-step thermal drawing for rapid, prototyping MNs that can have a variety of shapes and can be fabricated on curved surfaces. Based on the temperature control of polymer bridge formation during thermal drawing, the body profile and aspect ratios of MNs were conveniently controlled, and the effect of temperature control on the body profile of MNs was explained. Thermally drawn MNs with different shapes were fabricated both on flat and curved surfaces, and they were characterized in terms of their mechanical properties and insertion into vascular tissue to find an optimal shape for vascular tissue insertion.

Evaluation of a Particulate Breast Cancer Vaccine Delivered via Skin

Breast cancer impacts female population globally and is the second most common cancer for females. With various limitations and adverse effects of current therapies, several immunotherapies are being explored. Development of an effective breast cancer vaccine can be a groundbreaking immunotherapeutic approach. Such approaches are being evaluated by several clinical trials currently. On similar lines, our research study aims to evaluate a particulate breast cancer vaccine delivered via skin. This particulate breast cancer vaccine was prepared by spray drying technique and utilized murine breast cancer whole cell lysate as a source of tumor-associated antigens. The average size of the particulate vaccine was 1.5 μm, which resembled the pathogenic species, thereby assisting in phagocytosis and antigen presentation leading to further activation of the immune response. The particulate vaccine was delivered via skin using commercially available metal microneedles. Methylene blue staining and confocal microscopy were used to visualize the microchannels. The results showed that microneedles created aqueous conduits of 50 ± 10 μm to deliver the microparticulate vaccine to the skin layers. Further, an in vivo comparison of immune response depicted significantly higher concentration of serum IgG, IgG2a, and B and T cell (CD4+ and CD8+) populations in the vaccinated animals than the control animals (p < 0.001). Upon challenge with live murine breast cancer cells, the vaccinated animals showed five times more tumor suppression than the control animals confirming the immune response activation and protection (p < 0.001). This research paves a way for individualized immunotherapy following surgical tumor removal to prolong relapse episodes.

Toward Understanding Drug Incorporation and Delivery from Biocompatible Metal-Organic Frameworks in View of Cutaneous Administration

Although metal-organic frameworks (MOFs) have widely demonstrated their convenient performances as drug-delivery systems, there is still work to do to fully understand the drug incorporation/delivery processes from these materials. In this work, a combined experimental and computational investigation of the main structural and physicochemical parameters driving drug adsorption/desorption kinetics was carried out. Two model drugs (aspirin and ibuprofen) and three water-stable, biocompatible MOFs (MIL-100(Fe), UiO-66(Zr), and MIL-127(Fe)) have been selected to obtain a variety of drug-matrix couples with different structural and physicochemical characteristics. This study evidenced that the drug-loading and drug-delivery processes are mainly governed by structural parameters (accessibility of the framework and drug volume) as well as the MOF/drug hydrophobic/hydrophilic balance. As a result, the delivery of the drug under simulated cutaneous conditions (aqueous media at 37 °C) demonstrated that these systems fulfill the requirements to be used as topical drug-delivery systems, such as released payload between 1 and 7 days. These results highlight the importance of the rational selection of MOFs, evidencing the effect of geometrical and chemical parameters of both the MOF and the drug on the drug adsorption and release.

Insulin delivery systems combined with microneedle technology

Diabetes, a metabolic disorder of glucose, is a serious chronic disease and an important public health problem. Insulin is one of the hormones for modulating blood glucose level and the products of which is indispensable for most diabetes patients. Introducing microneedles (MNs) to insulin delivery is promising to pave the way for modulating glucose level noninvasively of diabetes patients, as which born to be painless, easy to handle and no need of any power supply. In this work, we review the process of insulin delivery systems (IDSs) based on MN technology in terms of two categories: drug free MNs and drug loaded MNs. Drug free MNs include solid MNs ("poke and patch"), hollow MNs ("poke and flow") and reservoir-based swelling MNs ("poke and swell R-type"), and drug loaded MNs include coated MNs ("coat and poke"), dissolving MNs ("poke and release") and insulin incorporated swelling MNs ("poke and swell I-type"). Majority researches of MN-based IDSs have been conducted by using hollow MNs or dissolving MNs, and almost all clinical trials for MN-based IDSs have employed hollow MNs. "Poke and patch" approach dramatically increase skin permeability compared to traditional transdermal patch, but MNs fabricated from silicon or metal may leave sharp waste in the skin and cause a safety issue. "Poke and flow" approach, similar to transitional subcutaneous (SC) injection, is capable of producing faster insulin absorption and action than SC injection but may associate with blockage, leakage and low flow rate. Coated MNs are able of retaining the activity of drug, which loaded in a solid phase, for a long time, however have been relatively less studied for insulin application as the low drug dosing. "Poke and release" approach leaves no biohazardous sharp medical waste and is capable of rapid drug release. "Poke and swell R-type" can be seen as a combination of "poke and flow" and "poke and patch" approach, while "poke and swell I-type" is an approach between "coat and poke" and "poke and release" approach. Insulin MNs are promising for painless diabetes therapeutics, and additional efforts for addressing fundamental issues including the drug loading, the PK/PD profile, the storage and the safety of insulin MNs will accelerate the clinical transformation.

Combined use of nanocarriers and physical methods for percutaneous penetration enhancement

Dermal and transdermal drug delivery (due to its non-invasiveness, avoidance of the first-pass metabolism, controlling the rate of drug input over a prolonged time, etc.) have gained significant acceptance. Several methods are employed to overcome the permeability barrier of the skin, improving drug penetration into/through skin. Among chemical penetration enhancement methods, nanocarriers have been extensively studied. When applied alone, nanocarriers mostly deliver drugs to skin and can be used to treat skin diseases. To achieve effective transdermal drug delivery, nanocarriers should be applied with physical methods, as they act synergistically in enhancing drug penetration. This review describes combined use of frequently used nanocarriers (liposomes, novel elastic vesicles, lipid-based and polymer-based nanoparticles and dendrimers) with the most efficient physical methods (microneedles, iontophoresis, ultrasound and electroporation) and demonstrates superiority of the combined use of nanocarriers and physical methods in drug penetration enhancement compared to their single use.

Efficacy of functional microarray of microneedles combined with topical tranexamic acid for melasma: A randomized, self-controlled, split-face study

To evaluate the efficacy of a functional microarray of microneedles (MNs) plus topical tranexamic acid (TA) for melasma in middle-aged women in China.Thirty female subjects with melasma were enrolled in this study. The left or right side of the face was chosen randomly to be pretreated with a functional microarray of MNs, followed by topical 0.5% TA solution once per week for 12 weeks. The other half-face was the control, treated with a sham device plus topical 0.5% TA solution. At baseline and at weeks 4, 8, and 12 of treatment, clinical (photographic) evaluations and parameters determined by Visia were recorded. At baseline and week 12, patient satisfaction scores and the biophysical parameters measured by Mexameter were also recorded. Side effects were evaluated at baseline and at the end of the 12 weeks.In total, 28 women (93.3%) completed the study. The brown spots' scores measured by Visia were significantly lower on the combined therapy side than on the control side at 12 weeks after starting treatment; there was no significant difference between sides at 4 or 8 weeks. After 12 weeks, melanin index (MI) decreased significantly in both 2 groups, and the MI was significantly less on the combined side at week 12. Transepidermal water loss, roughness, skin hydration, skin elasticity, and erythema index showed no significant differences between 2 sides at baseline, 4, 8, and 12 weeks after treatment. Physicians' evaluations of photographs showed better results at week 12 with combined therapy: >25% improvement was observed in the MNs plus TA side in 25 patients, and in the TA side in only 10 patients. Subjective satisfaction scores on both sides increased significantly. The participants were more satisfied with the results of the combined therapy side than the control side. No obvious adverse reactions were observed throughout the study.Combined therapy with a functional microarray of MNs and topical TA solution is a promising treatment for melasma.

Micro-Needling Depth Penetration, Presence of Pigment Particles, and Fluorescein-Stained Platelets: Clinical Usage for Aesthetic Concerns

BACKGROUND

Aesthetic micro-needling (MN) has demonstrated skin permeability to cosmeceutical ingredients and platelet-rich plasma by creating reversible micro-channels in the skin.

OBJECTIVES

The purposes of this study were to determine: (1) actual needle depth-penetrations by adjusting needle lengths in a disposable tip of an electric MN device; (2) time-dependent passage of pigment and platelets; and (3) safety and efficacy profiles in patients.

METHODS

Excised micro-needled pre-auricular skin was used to determine actual depths of tissue penetration with six needle lengths, and the presence of massaged pigment particles (histological examination) and fluorescein-labeled platelets (confocal laser microscopy) in 1 mm depth micro-channels over an hour. Patients were treated for wrinkles and skin laxity, scars, and alopecia with cosmeceuticals and plasma-rich platelets.

RESULTS

Actual needle penetrations closely matched settings up to 1.0 mm, but were less consistent at settings from 1.5 to 2.5 mm. The optimal time for massaging pigment particles and labeled platelet-rich plasma (PRP) down 1.0 mm micro-channels was between 5 to 30 minutes after MN. Patients treated in the Skin Care Center (cosmeceuticals, 0.25-1 mm depth) and Surgical Center (PRP, 0.25-2.5 mm) demonstrated statistically significant improvements (P ≤ .05) in wrinkle effacement, skin laxity, scar softening, and hair growth by Patient and Observer Satisfaction Scores at 12 months. The average hair count in a 10 mm spot size at baseline (88.3 ± 22.5) increased at the 12 month evaluation period (133.6 ± 13.8). All patients experienced minimal side-effects.

CONCLUSIONS

MN alone or in combination therapy resulted in safe and effective treatments from implemented guidelines.

LEVEL OF EVIDENCE

3 Therapeutic.

Dissolving microneedles for DNA vaccination: Improving functionality via polymer characterization and RALA complexation

DNA vaccination holds the potential to treat or prevent nearly any immunogenic disease, including cancer. To date, these vaccines have demonstrated limited immunogenicity in vivo due to the absence of a suitable delivery system which can protect DNA from degradation and improve transfection efficiencies in vivo. Recently, microneedles have been described as a novel physical delivery technology to enhance DNA vaccine immunogenicity. Of these devices, dissolvable microneedles promise a safe, pain-free delivery system which may simultaneously improve DNA stability within a solid matrix and increase DNA delivery compared to solid arrays. However, to date little work has directly compared the suitability of different dissolvable matrices for formulation of DNA-loaded microneedles. Therefore, the current study examined the ability of 4 polymers to formulate mechanically robust, functional DNA loaded dissolvable microneedles. Additionally, complexation of DNA to a cationic delivery peptide, RALA, prior to incorporation into the dissolvable matrix was explored as a means to improve transfection efficacies following release from the polymer matrix. Our data demonstrates that DNA is degraded following incorporation into PVP, but not PVA matrices. The complexation of DNA to RALA prior to incorporation into polymers resulted in higher recovery from dissolvable matrices, and increased transfection efficiencies in vitro. Additionally, RALA/DNA nanoparticles released from dissolvable PVA matrices demonstrated up to 10-fold higher transfection efficiencies than the corresponding complexes released from PVP matrices, indicating that PVA is a superior polymer for this microneedle application.

Microneedling: Advances and widening horizons

Microneedling is a very simple, safe, effective, and minimally invasive therapeutic technique. It was initially introduced for skin rejuvenation, however, now it is being used for a very wide range of indications including acne scar, acne, post-traumatic/burn scar, alopecia, skin rejuvenation, drug delivery, hyperhidrosis, stretch marks, and many more. Moreover, during the last 10 years, many new innovations have been made to the initial instrument, which was used for microneedling. This technique can be combined with other surgical techniques to provide better results. In particular, it is a very safe technique for dark skin types, where risk of postinflammatory pigmentation is very high with other techniques that damage the epidermis. In this review article, we are updating on the different instruments now available for this procedure, and its efficacy when performed alone or in combination with other techniques for various indications.

Microneedles: an innovative platform for gene delivery

The advent of microneedle (MN) technology has provided a revolutionary platform for the delivery of therapeutic agents, particularly in the field of gene therapy. For over 20 years, the area of gene therapy has undergone intense innovation and progression which has seen advancement of the technology from an experimental concept to a widely acknowledged strategy for the treatment and prevention of numerous disease states. However, the true potential of gene therapy has yet to be achieved due to limitations in formulation and delivery technologies beyond parenteral injection of the DNA. Microneedle-mediated delivery provides a unique platform for the delivery of DNA therapeutics clinically. It provides a means to overcome the skin barriers to gene delivery and deposit the DNA directly into the dermal layers, a key site for delivery of therapeutics to treat a wide range of skin and cutaneous diseases. Additionally, the skin is a tissue rich in immune sentinels, an ideal target for the delivery of a DNA vaccine directly to the desired target cell populations. This review details the advancement of MN-mediated DNA delivery from proof-of-concept to the delivery of DNA encoding clinically relevant proteins and antigens and examines the key considerations for the improvement of the technology and progress into a clinically applicable delivery system.

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.

Optically monitored drug delivery patch based on porous silicon and polymer microneedles

Fabrication and characterization of an optically monitored hybrid patch for local administration of drugs, based on polymeric micro-needles and a porous silicon free-standing membrane, are reported. The micro-needles are realized by an innovative photolithographic approach that allows fine tuning of geometrical parameters, using polyethylene glycol and a commercial photo-catalyzer. The porous silicon multilayer not only increases the storage of a relevant amount of the drug, but also offers a continuous, naked-eye monitoring of the drug delivery process. As a proof-of-concept experiment, we report our results on the release of a dye molecule (fluorescein, 332 Da) in a phosphate saline buffer.

Nucleic acid delivery into skin for the treatment of skin disease: Proofs-of-concept, potential impact, and remaining challenges

Nucleic acids (NAs) hold significant potential for the treatment of several diseases. Topical delivery of NAs for the treatment of skin diseases is especially advantageous since it bypasses the challenges associated with systemic administration which suffers from enzymatic degradation, systemic toxicity and lack of targeting to skin. However, the skin's protective barrier function limits the delivery of NAs into skin after topical application. Here, we highlight strategies for enhancing delivery of NAs into skin, and provide evidence that translation of topical NA therapies could have a transformative impact on the treatment of skin diseases.

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.

Development of cup shaped microneedle array for transdermal drug delivery

Microneedle technology is one of the attractive methods in transdermal drug delivery. However, the clinical applications of this method are limited owing to: complexity in the preparation of multiple coating solutions, drug leakage while inserting the microneedles into the skin and the outer walls of the solid microneedle can hold limited quantity of drug. Here, the authors present the fabrication of an array of rectangular cup shaped silicon microneedles, which provide for reduced drug leakage resulting in improvement of efficiency of drug delivery and possibility of introducing multiple drugs. The fabricated solid microneedles with rectangular cup shaped tip have a total height of 200 μm. These cup shaped tips have dimensions: 60 × 60 μm (length × breadth) with a depth of 60 μm. The cups are filled with drug using a novel in-house built drop coating system. Successful drug dissolution was observed when the coated microneedle was used on mice. Also, using the above method, it is possible to fill the cups selectively with different drugs, which enables simultaneous multiple drug delivery.

Inkjet printing of transdermal microneedles for the delivery of anticancer agents

A novel inkjet printing technology is introduced as a process to coat metal microneedle arrays with three anticancer agents 5-fluororacil, curcumin and cisplatin for transdermal delivery. The hydrophilic graft copolymer Soluplus(®) was used as a drug carrier and the coating formulations consisted of drug-polymer solutions at various ratios. A piezoelectric dispenser jetted microdroplets on the microneedle surface to develop uniform, accurate and reproducible coating layers without any material losses. Inkjet printing was found to depend on the nozzle size, the applied voltage (mV) and the duration of the pulse (μs). The drug release rates were determined in vitro using Franz type diffusion cells with dermatomed porcine skin. The drug release rates depended on the drug-polymer ratio, the drug lipophilicity and the skin thickness. All drugs presented increased release profiles (750 μm skin thickness), which were retarded for 900 μm skin thickness. Soluplus assisted the drug release especially for the water insoluble curcumin and cisplatin due to its solubilizing capacity. Inkjet printing has been shown to be an effective technology for coating of metal microneedles which can then be used for further transdermal drug delivery applications.

Topical delivery of siRNA into skin using SPACE-peptide carriers

Short-interfering RNAs (siRNAs) offer a potential tool for the treatment of skin disorders. However, applications of siRNA for dermatological conditions are limited by their poor permeation across the stratum corneum of the skin and low penetration into the skin's viable cells. In this study, we report the use of SPACE-peptide in combination with a DOTAP-based ethosomal carrier system to enhance skin delivery of siRNA. A DOTAP-based SPACE Ethosomal System significantly enhanced siRNA penetration into porcine skin in vitro by 6.3±1.7-fold (p<0.01) with an approximately 10-fold (p<0.01) increase in epidermis accumulation of siRNA compared to that from an aqueous solution. Penetration of siRNA was also enhanced at the cellular level. Internalization of SPACE-peptide occurred in a concentration dependent manner marked by a shift in intracellular distribution from punctate spots to diffused cytoplasmic staining at a peptide concentration of 10mg/mL. In vitro delivery of GAPDH siRNA by SPACE peptide led to 83.3±3.0% knockdown relative to the control. In vivo experiments performed using female BALB/C mice also confirmed the efficacy of DOTAP-SES in delivering GAPDH-siRNA into skin. Topical application of DOTAP-SES on mice skin resulted in 63.2%±7.7% of GAPDH knockdown, which was significantly higher than that from GAPDH-siRNA PBS (p<0.05). DOTAP-SES formulation reported here may open new opportunities for cutaneous siRNA delivery.

Calcium phosphate nanoparticles: second-generation nonviral vectors in gene therapy

Adverse effects of viral vectors, instability of naked DNA, cytotoxicity and low transfection of cationic lipids, cationic polymers and other synthetic vectors are currently severe limitations in gene therapy. In addition to targeting a specific cell type, an ideal nonviral vector must manifest an efficient endosomal escape, render sufficient protection of DNA in the cytosol and help provide an easy passage of cytosolic DNA to the nucleus. Virus-like size calcium phosphate nanoparticles have been found to overcome many of these limitations in delivering genes to the nucleus of specific cells. This review has focused on some applications of DNA-loaded calcium phosphate nanoparticles as nonviral vectors in gene delivery, and their potential use in gene therapy, as well as highlighting the mechanistic studies to probe the reason for high transfection efficiency of the vector. It has been demonstrated that calcium ions play an important role in endosomal escape, cytosolic stability and enhanced nuclear uptake of DNA through nuclear pore complexes. The special role of exogenous calcium ions to overcome obstacles in practical realization of this field suggests that calcium phosphate nanoparticles are not 'me too' synthetic vectors and can be designated as second-generation nonviral vectors for gene therapy.

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.

Novel engineered systems for oral, mucosal and transdermal drug delivery

Technological advances in drug discovery have resulted in increasing number of molecules including proteins and peptides as drug candidates. However, how to deliver drugs with satisfactory therapeutic effect, minimal side effects and increased patient compliance is a question posted before researchers, especially for those drugs with poor solubility, large molecular weight or instability. Microfabrication technology, polymer science and bioconjugate chemistry combine to address these problems and generate a number of novel engineered drug delivery systems. Injection routes usually have poor patient compliance due to their invasive nature and potential safety concerns over needle reuse. The alternative non-invasive routes, such as oral, mucosal (pulmonary, nasal, ocular, buccal, rectal, vaginal), and transdermal drug delivery have thus attracted many attentions. Here, we review the applications of the novel engineered systems for oral, mucosal and transdermal drug delivery.

Gene silencing following siRNA delivery to skin via coated steel microneedles: In vitro and in vivo proof-of-concept

The development of siRNA-based gene silencing therapies has significant potential for effectively treating debilitating genetic, hyper-proliferative or malignant skin conditions caused by aberrant gene expression. To be efficacious and widely accepted by physicians and patients, therapeutic siRNAs must access the viable skin layers in a stable and functional form, preferably without painful administration. In this study we explore the use of minimally-invasive steel microneedle devices to effectively deliver siRNA into skin. A simple, yet precise microneedle coating method permitted reproducible loading of siRNA onto individual microneedles. Following recovery from the microneedle surface, lamin A/C siRNA retained full activity, as demonstrated by significant reduction in lamin A/C mRNA levels and reduced lamin A/C protein in HaCaT keratinocyte cells. However, lamin A/C siRNA pre-complexed with a commercial lipid-based transfection reagent (siRNA lipoplex) was less functional following microneedle coating. As Accell-modified "self-delivery" siRNA targeted against CD44 also retained functionality after microneedle coating, this form of siRNA was used in subsequent in vivo studies, where gene silencing was determined in a transgenic reporter mouse skin model. Self-delivery siRNA targeting the reporter (luciferase/GFP) gene was coated onto microneedles and delivered to mouse footpad. Quantification of reporter mRNA and intravital imaging of reporter expression in the outer skin layers confirmed functional in vivo gene silencing following microneedle delivery of siRNA. The use of coated metal microneedles represents a new, simple, minimally-invasive, patient-friendly and potentially self-administrable method for the delivery of therapeutic nucleic acids to the skin.

The Contributions of the Celtic Masters and Their Associates

This article summarizes the work of 4 researchers in the field of percutaneous absorption - Keith Brain, Mark Cronin, Dermot McCafferty and John Pugh. It summarizes their main achievements in this field and reviews their major contributions to the broader subject area.

Polymeric microdevices for transdermal and subcutaneous drug delivery

Low cost manufacturing of polymeric microdevices for transdermal and subcutaneous drug delivery is slated to have a major impact on next generation devices for administration of biopharmaceuticals and other emerging new formulations. These devices range in complexity from simple microneedle arrays to more complicated systems incorporating micropumps, micro-reservoirs, on-board sensors, and electronic intelligence. In this paper, we review devices currently in the market and those in the earlier stages of research and development. We also present two examples of the research in our laboratory towards using phase change liquids in polymeric structures to create disposable micropumps and the development of an elastomeric reservoir for MEMS-based transdermal drug delivery systems.

A scalable fabrication process of polymer microneedles

While polymer microneedles may easily be fabricated by casting a solution in a mold, either centrifugation or vacuumizing is needed to pull the viscous polymer solution into the microholes of the mold. We report a novel process to fabricate polymer microneedles with a one-sided vacuum using a ceramic mold that is breathable but water impermeable. A polymer solution containing polyvinyl alcohol and polysaccharide was cast in a ceramic mold and then pulled into the microholes by a vacuum applied to the opposite side of the mold. After cross-linking and solidification through freeze-thawing, the microneedle patch was detached from the mold and transferred with a specially designed instrument for the drying process, during which the patch shrank evenly to form an array of regular and uniform needles without deformation. Moreover, the shrinkage of the patches helped to reduce the needles’ size to ease microfabrication of the male mold. The dried microneedle patches were finally punched to the desired sizes to achieve various properties, including sufficient strength to penetrate skin, microneedles-absorbed water-swelling ratios, and drug-release kinetics. The results showed that the microneedles were strong enough to penetrate pigskin and that their performance was satisfactory in terms of swelling and drug release.

Indirect rapid prototyping of antibacterial acid anhydride copolymer microneedles

Microneedles are needle-like projections with microscale features that may be used for transdermal delivery of a variety of pharmacologic agents, including antibacterial agents. In the study described in this paper, an indirect rapid prototyping approach involving a combination of visible light dynamic mask micro-stereolithography and micromolding was used to prepare microneedle arrays out of a biodegradable acid anhydride copolymer, Gantrez(®) AN 169 BF. Fourier transform infrared spectroscopy, energy dispersive x-ray spectrometry and nanoindentation studies were performed to evaluate the chemical and mechanical properties of the Gantrez(®) AN 169 BF material. Agar plating studies were used to evaluate the in vitro antimicrobial performance of these arrays against Bacillus subtilis, Candida albicans, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Large zones of growth inhibition were noted for Escherichia coli, S. aureus, Enterococcus faecalis and B. subtilis. The performance of Gantrez(®) AN 169 BF against several bacteria suggests that biodegradable acid anhydride copolymer microneedle arrays prepared using visible light dynamic mask micro-stereolithography micromolding may be useful for treating a variety of skin infections.

Modification of microneedles using inkjet printing

In this study, biodegradable acid anhydride copolymer microneedles containing quantum dots were fabricated by means of visible light dynamic mask micro-stereolithography-micromolding and inkjet printing. Nanoindentation was performed to obtain the hardness and the Young's modulus of the biodegradable acid anhydride copolymer. Imaging of quantum dots within porcine skin was accomplished by means of multiphoton microscopy. Our results suggest that the combination of visible light dynamic mask micro-stereolithography-micromolding and inkjet printing enables fabrication of solid biodegradable microneedles with a wide range of geometries as well as a wide range of pharmacologic agent compositions.

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.

Transdermal delivery of proteins

Transdermal delivery of peptides and proteins avoids the disadvantages associated with the invasive parenteral route of administration and other alternative routes such as the pulmonary and nasal routes. Since proteins have a large size and are hydrophilic in nature, they cannot permeate passively across the skin due to the stratum corneum which allows the transport of only small lipophilic drug molecules. Enhancement techniques such as chemical enhancers, iontophoresis, microneedles, electroporation, sonophoresis, thermal ablation, laser ablation, radiofrequency ablation and noninvasive jet injectors aid in the delivery of proteins by overcoming the skin barrier in different ways. In this review, these enhancement techniques that can enable the transdermal delivery of proteins are discussed, including a discussion of mechanisms, sterility requirements, and commercial development of products. Combination of enhancement techniques may result in a synergistic effect allowing increased protein delivery and these are also discussed.

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.