Kwang Lee

Dissolving microneedles for transdermal drug administration prepared by stepwise controlled drawing of maltose.

Dissolving microneedles, three-dimensional polymer structures with microscale cross-sectional dimensions, have been introduced as a means of safe transdermal drug delivery. Most dissolving microneedles have been fabricated using a traditional micro-casting method that cures biopolymers within three-dimensional mold, nevertheless, repeated molding process may cause damage to encapsulated drugs, a critical hurdle for clinical application. Here, we describe the stepwise controlled drawing technique that can directly fabricate dissolving microneedle from maltose by precise controlling the drawing time and the viscosity of the maltose. Controlled drawing shaped the particular sharp-conical microneedles of 1200 μm length with tip diameter of 60 μm, and dissolved within 20 min in-vivo after inserting to the skin. This technique surpasses the limitations of micro-casting for dissolving microneedle. Furthermore, transdermal delivery of impermeable hydrophilic molecules such as ascorbic acid-2-glucoside and niacinamide was confirmed as inhibition of cutaneous hypermelanosis. We anticipate that controlled drawing technique will be suitable to design dissolving microneedles for use in minimally invasive transcutaneous drug delivery to patients.

Drawing Lithography: Three‐Dimensional Fabrication of an Ultrahigh‐Aspect‐Ratio Microneedle

Adv. Mater. 2010, 22, 483–486 2010 WILEY-VCH Verlag Gm T IO N Microneedles, that is, 3D micromechanical structures with microscale cross-sectional dimensions, have been introduced as an alternative to hypodermic needles for minimally invasive drug delivery and blood extraction. In particular, microneedles can be used for the delivery of transdermal biomolecules (e.g., proteins, vaccines, DNA, antibodies, or genes). Microneedles can be fabricated as a solid with a drug-coated surface, as a biodegradable polymer encapsulating a drug, or as a hollow needle, through which drug solution can be transported. Although some drugs have been successfully delivered by solid and biodegradable microneedles, the application of drugs in solution, as well as the use of this method to achieve sufficient doses for therapeutic effects, remains difficult. Nevertheless, solid and biodegradable microneedles can be used for topical drug delivery but not for blood sampling. Hollow-type microneedles, which replace traditional hypodermic needles, can be used for injection as well as blood sampling, allowing for their integration into a full diagnostic, monitoring system. Various types of hollow microneedles have been fabricated using subtractive micromanufacturing methods such as photolithography, deep reactive ion etching, and deep X-ray lithography of LIGA (Lithographie, Galvanoformung, and Abformung), which is based on the inherently planar geometries of 2D substrates. However, the maximum height of these microneedles is only several hundred micrometers due to limitations of subtractive projection lithography. This height limitation makes penetration of the skin barrier and precise intradermal drug delivery difficult; hence, an ultrahighaspect-ratio (UHAR) microneedle is required to overcome these limitations. In this study, we propose ‘‘drawing lithography’’ without the need for a mask and light irradiation, an additive method, in which the thermosetting polymer is drawn directly from a 2D solid surface to produce a UHAR and a 3D microneedle with a height of two millimeters. Here, we administrated insulin to diabetic rats with a minimally invasive intradermal drug delivery using a UHAR microneedle and confirmed the drug delivery effect of the microneedle by the down regulated blood glucose level. In drawing lithography, the thermosetting polymer (viscoelastic) is shaped into a particular microstructure by controlled drawing of the liquid form. The final UHARmicroneedle mold is then solidified by thermal curing. Both steps are critical for successful drawing lithography. Although most thermosetting polymers are suitable for drawing lithography, we used SU-8 2050 (see Experimental section) because its photoresistant properties are easily controlled with temperature, enabling the precise control of drawing and microstructure formation. SU-8 was spin-coated onto a glass substrate (Fig. 1a). Curing, which provides external excitation to themonomers present in the resin, increases the fracture strength. The fracture strength of uncured SU-8 was 0.48N and the vertical stress induced by drawing exceeded the tensile strength of uncured SU-8, even at the low drawing rate of 1mm s , resulting in drawing failure. A 20min cooling period increased the fracture strength to 1.80N, which prevented breakage at a continuous drawing rate of 10mm s . After contacting a 3 3 patterned pillar (Fig. 1b), the photoresist was subjected to axial strain by drawing. This caused the photoresist to ‘‘pop’’ into a wasp-waist shape between the substrate and the pillar. This structure was maintained during speedand position-controlled drawing (Fig. 1c). Further drawing extended this structure by producing a conical-shaped bridge in the opposite direction. The axial strain was less than the tensile strength of the extending photoresist during construction of the predetermined UHAR microstructure. After obtaining the desired UHAR microneedle mold, we completely cured the polymeric bridge by thermal curing (Fig. 1d). This prevented relaxation of the liquid-based UHAR microstructure, which would have otherwise collapsed. The final UHAR-microneedle mold was obtained by secondary drawing to separate the lower part of the conical microstructure from the frame (Fig. 1e). Secondary drawing was performed at a rate that would induce a strength greater than the tensile strength of the cured hard polymer. Because the separation of the 3D microstructure consistently occurred at the bridge, which had a very narrow throat, the resultant microneedle-mold height was constant for the same drawing conditions (Supporting Information, Table S1). In drawing lithography, the patterns of the fabricated microneedle molds are determined by the pattern of pillars (Fig. 1, inset) that contact and draw the thermosetting polymer. In contrast to traditional photolithography, this technique requires no mask or UV irradiation to create the pattern and UHAR microstructure.

Droplet-born air blowing: Novel dissolving microneedle fabrication

The microneedle-mediated drug delivery system has been developed to provide painless self-administration of drugs in a patient-friendly manner. Current dissolving microneedle fabrication methods, however, require harsh conditions for biological drugs and also have problems standardizing the drug dose. Here, we suggested the droplet-born air blowing (DAB) method, which provides gentle (4-25 °C) and fast (≤10min) microneedle fabrication conditions without drug loss. The amount of drug in the microneedle can be controlled by the pressure and time of droplet dispenser and the air blowing shapes this droplet to the microneedle, providing a force sufficient to penetrate skin. Also, the introduction of a base structure of two layered DAB-microneedle could provide complete drug delivery without wasting of drug. The DAB-based insulin loaded microneedle shows similar bioavailability (96.6±2.4%) and down regulation of glucose level compared with subcutaneous injection. We anticipate that DAB described herein will be suitable to design dissolving microneedles for use in biological drug delivery to patients.

Drawing lithography for microneedles: a review of fundamentals and biomedical applications.

A microneedle is a three-dimensional (3D) micromechanical structure and has been in the spotlight recently as a drug delivery system (DDS). Because a microneedle delivers the target drug after penetrating the skin barrier, the therapeutic effects of microneedles proceed from its 3D structural geometry. Various types of microneedles have been fabricated using subtractive micromanufacturing methods which are based on the inherently planar two-dimensional (2D) geometries. However, traditional subtractive processes are limited for flexible structural microneedles and makes functional biomedical applications for efficient drug delivery difficult. The authors of the present study propose drawing lithography as a unique additive process for the fabrication of a microneedle directly from 2D planar substrates, thus overcoming a subtractive process shortcoming. The present article provides the first overview of the principal drawing lithography technology: fundamentals and biomedical applications. The continuous drawing technique for an ultrahigh-aspect ratio (UHAR) hollow microneedle, stepwise controlled drawing technique for a dissolving microneedle, and drawing technique with antidromic isolation for a hybrid electro-microneedle (HEM) are reviewed, and efficient biomedical applications by drawing lithography-mediated microneedles as an innovative drug and gene delivery system are described. Drawing lithography herein can provide a great breakthrough in the development of materials science and biotechnology.

A high-capacity, hybrid electro-microneedle for in-situ cutaneous gene transfer

Cutaneous gene transfer is limited by biological barriers such as skin and cellular membranes; complex approaches are required to overcome these biological barriers, simultaneously. Non-integrated systems that separate cutaneous permeation from intracellular transfection have been used to overcome skin and cellular barriers, respectively, however, do not provide sufficient doses of the gene to local tissue, resulting in inefficient gene transfer in-situ. Although integrated systems for cutaneous gene transfer are available, their safety has been questioned and it is difficult to transfer sufficient amounts of genes due to cumbersome sterilization procedures and the small size of the reservoir. Here, we demonstrate stepwise-aligned cutaneous permeation, cutaneous release, and intracellular transfection using a hybrid electro-microneedle (HEM), which designed as a monolithic hybrid assembly of a dissolving microneedle and an electrode, anomalously. Furthermore, as proof-of-principle, we use the HEM for in-situ cutaneous transfer of p2CMVmIL-12 to successfully treat B16F10 subcutaneous tumors in a mouse model. The HEM described herein holds great promise for cutaneous gene therapy of cancers and for vaccines.

A Minimally Invasive Blood-Extraction System: Elastic Self-Recovery Actuator Integrated with an Ultrahigh- Aspect-Ratio Microneedle

A minimally invasive blood-extraction system is fabricated by the integration of an elastic self-recovery actuator and an ultrahigh-aspect-ratio microneedle. The simple elastic self-recovery actuator converts finger force to elastic energy to provide power for blood extraction and transport without requiring an external source of power. This device has potential utility in the biomedical field within the framework of complete micro-electromechanical systems.