Microneedle: Various techniques of fabrications and evaluations

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Microneedles find widespread use; researchers must perfect the techniques for optimally inserting them into the skin, and complete the integration of microneedles into a full diagnostic, monitoring or drug delivery system. Microneedles are expected to be less painful than conventional hypodermic needles because they are too small to significantly stimulate nerve endings. A painless "microneedle" that mimics the way a female mosquito sucks blood has been built by engineers in India and Japan. The needle could be used to draw blood, inject drugs, and as a glucose-level monitor for diabetics. The needle is also strong enough to penetrate as far as 3 millimetres into skin and reach capillary blood vessels. Its size compared to earlier models also means that surface tension effects are exploited further, and the same capillary flow that draws water up into trees helps draw blood into the microneedle.

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... Pioneering works (8,(11)(12)(13)(14) presented in the last decade have demonstrated that transdermal delivery using microneedlearrays (MNAs) can overcome the aforementioned challenges while retaining advantages of cutaneous delivery, thus enabling bolus or sustained delivery of a broad range of biologics through the cutaneous route. These devices include an array of microneedles, with dimensions ranging from 100 to 1,000 μm in width and up to 1 mm in length, that are used to breach the SC, and enable delivery of drugs and vaccines to viable epidermis. ...
Design and evaluate a new micro-machining based approach for fabricating dissolvable microneedle arrays (MNAs) with diverse geometries and from different materials for dry delivery to skin microenvironments. The aims are to describe the new fabrication method, to evaluate geometric and material capability as well as reproducibility of the method, and to demonstrate the effectiveness of fabricated MNAs in delivering bioactive molecules. Precise master molds were created using micromilling. Micromolding was used to create elastomer production molds from master molds. The dissolvable MNAs were then fabricated using the spin-casting method. Fabricated MNAs with different geometries were evaluated for reproducibility. MNAs from different materials were fabricated to show material capability. MNAs with embedded bioactive components were tested for functionality on human and mice skin. MNAs with different geometries and from carboxymethyl cellulose, polyvinyl pyrrolidone and maltodextrin were created reproducibly using our method. MNAs successfully pierce the skin, precisely deliver their bioactive cargo to skin and induce specific immunity in mice. We demonstrated that the new fabrication approach enables creating dissolvable MNAs with diverse geometries and from different materials reproducibly. We also demonstrated the application of MNAs for precise and specific delivery of biomolecules to skin microenvironments in vitro and in vivo.
... The purpose of this study is to assess the effect of skin pretreatment with a microneedle roller on the local and transdermal delivery of DCF from a commercially available gel (Voltaren Õ ) and from a commercially available iontophoretic patch filled with a DCF solution. Microneedle rollers were introduced on the market mainly for use in cosmetics 12 . Indeed, the micro-damage to the skin produced by the microneedle rollers can possibly increase collagen production during the physiological repair process and thus improves the overall appearance of the skin. ...
Skin pretreatment with a microneedle roller (microporation (MP)) appears a simple and inexpensive technique to increase transdermal delivery of topically applied drug products. This study investigates the effect of MP on the passive and iontophoretic delivery of diclofenac (DCF) by quantifying dermis and plasma levels of DCF in a rabbit model. New Zealand albino female rabbits received either: (i) a topical application of 4 g of Voltaren® 1% gel with or without pretreatment with a microroller (0.5 mm needle length; density 23 microneedles per cm(2) area) or (ii) a DCF solution (40 mg/2.5 mL) via iontophoresis (IOMED transQ(E) medium size patch), with or without microroller pretreatment. A 300 µA/cm(2) cathodic current was applied for 20 min for a total of 80 mA. DCF concentrations were monitored in dermis with microdialysis sampling every 20 min for 5 h. Plasma samples were collected over the same period. In the passive delivery studies, microroller pretreatment increased Cmax by 1.5- and 2.0-fold in skin and plasma, respectively, and AUC by 1.5- and 2.4-fold in skin and plasma, respectively. In the iontophoresis delivery studies, microporation increased Cmax by 2.0-fold both in skin and in plasma, and AUC by 1.1- and 1.8-fold in skin and plasma, respectively. In conclusion, microneedle pretreatment increased significantly the systemic exposure of DCF from either passive or iontophoretic delivery, whereas the effect in skin was less pronounced.
... In this scenario, microneedles are mounted on a cylindrical surface and can be rolled across the skin, such that each microneedle may pierce the skin multiple times as the roller rotates across the skin. Most uses of microneedle rollers have not involved drug delivery, but are designed to cause microdamage to the skin, which induces collagen production during the skin repair process for cosmetic purposes [18]. More recently, microneedle rollers have been proposed and studied to increase skin permeability for pharmaceutical applications [19][20][21][22]. ...
Microneedle rollers have been used to treat large areas of skin for cosmetic purposes and to increase skin permeability for drug delivery. In this study, we introduce a polymer microneedle roller fabricated by inclined rotational UV lithography, replicated by micromolding hydrophobic polylactic acid and hydrophilic carboxy-methyl-cellulose. These microneedles created micron-scale holes in human and porcine cadaver skin that permitted entry of acetylsalicylic acid, Trypan blue and nanoparticles measuring 50nm and 200nm in diameter. The amount of acetylsalicylic acid delivered increased with the number of holes made in the skin and was 1-2 orders of magnitude greater than in untreated skin. Lateral diffusion in the skin between holes made by microneedles followed expected diffusional kinetics, with effective diffusivity values that were 23-160 times smaller than in water. Compared to inserting microneedles on a flat patch, the sequential insertion of microneedles row by row on a roller required less insertion force in full-thickness porcine skin. Overall, polymer microneedle rollers, prepared from replicated polymer films, offer a simple way to increase skin permeability for drug delivery.
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