Drug dose control via contact and drying cycle.

<p>(A) The amount of rhodamine B rose exponentially as the number of contact and drying cycles and PVP concentration increased (n = 3). Data are shown as mean ± s.e.m. Images indicate that rhodamine B-encapsulated spherical structures created through contact and drying cycles increased when using 20 (upper) and 40% (bottom) PVP solution. (B) After the microneedle formation step, Troy MNs were fabricated as sharp tips without drug (white arrow) over inner spherical structures containing drug (gray arrow). Scale bars, 500 μm.</p

Schematic illustration of the CCDP process.

<p>The total process consisted of two independent steps. (A) In the first step (drug encapsulation), pillars were contacted with a mixed drug-polymer solution and then lifted and dried with air blowing. This contact and drying cycle was repeated to optimize drug encapsulation, producing spherical structures on each pillar. (B) In the second step (microneedle formation), polymer solution without drug was used to prevent loss of drug during DMN fabrication, resulting in sharp tipped-DMNs on the end surface of the pillars.</p

<i>In vivo</i> skin penetration study.

<p>(A) Troy MNs were assembled with an applicator into an array (5 × 5). (B) The applicator was applied to rat dorsal skin vertically by hand. (C) Image of skin with applied Troy MNs. The array of red spots indicates the penetrated site of rhodamine B-encapsulated Troy MNs and the white dotted line represents the vertically sliced line used to obtain sectional tissue. (D) Skin sectional image. Red spots mark delivered rhodamine B in the skin and the white arrow indicates undissolved parts of DMNs. Scale bars, 10 mm (A, B) and 1.0 mm (C, D).</p

The Troy Microneedle: A Rapidly Separating, Dissolving Microneedle Formed by Cyclic Contact and Drying on the Pillar (CCDP)

<div><p>In dissolving microneedle (DMN)-mediated therapy, complete and rapid delivery of DMNs is critical for the desired efficacy. Traditional patch-based DMN delivery, however, may fail due to incomplete delivery from insufficient skin insertion or rapid separation of microneedles due to their strong bond to the backing film. Here, we introduce the Troy microneedle, which was created by cyclic contact and drying on the pillar (CCDP), and which enabled simultaneous complete and rapid delivery of DMN. This CCDP process could be flexibly repeated to achieve a specific desired drug dose in a DMN. We evaluated DMN separation using agarose gel, and the Troy microneedle achieved more complete and rapid separation than other, more deeply dipped DMN, primarily because of the Troy’s minimal junction between the DMN and pillar. When Troy microneedles were applied to pig cadaver skin, it took only 15 s for over 90% of encapsulated rhodamine B to be delivered, compared to 2 h with application of a traditional DMN patch. <i>In vivo</i> skin penetration studies demonstrated rapid DMN-separation of Troy microneedles still in solid form before dissolution. The Troy microneedle overcomes critical issues associated with the low penetration efficiency of flat patch-based DMN and provides an innovative route for DMN-mediated therapy, combining patient convenience with the desire drug efficacy.</p></div

Comparative drug delivery efficiency study.

<p>(A) Drug delivery efficiency by controlled application time. With the Troy MN, more than 90% of the encapsulated rhodamine B separated from the pillar within 15s after application (dotted square). The DMN patch needed 500 times longer for 90% of encapsulated rhodamine B delivery. (B) <i>In vitro</i> skin permeation profile. The total amount of rhodamine B encapsulated in the Troy MNs rapidly diffused into the receptor chamber within 5 h. Diffusion kinetics were slower for the DMN patch, on the other hand, where 20% the encapsulated rhodamine B still had not diffused after 9 h (n = 3). Data are shown as mean ± s.d. (C-E) Schematic illustration of complete drug delivery and rapid diffusion of Troy MNs compared to a flat DMN patch. (C, D) The Troy MN completely penetrated into the skin, allowing the DMNs to be embedded in the skin. The traditional DMN patch, however, did not fully insert into the skin and residual drug remained on the backing film after application. (E) After application, Troy MNs yielded rapid drug permeability comparing to the DMN patch.</p

DMN-separation study with agarose gel and schematic illustration of DMN-separation mechanism.

<p>(A) DMN-separation efficiency according to side junction depth. Rhodamine B-encapsulated DMNs (1 × 3) were inserted into agarose gel and examined right after removing pillars at each designated application time. Side junction depths were set to 30 (contact, not immersion), 200 and 400 μm, and the number of contact (dipping) and drying cycles was set to 5 and 8 times for each depth. As the side junction depth and number of cycles increased, DMN-separation efficiency decreased. Troy system DMNs separated within 5 s due to their minimum binding shape, and DMN volume did not influence separation time (n = 4). Data are shown as mean ± s.e.m. (B) DMN-separation efficiency according to top junction area. Three pillar types with different diameters (170, 350 and 500 μm) were used for Troy MN fabrication, with a uniform side junction depth of 30 μm and 8 contact and drying cycles. Pillar diameter influenced DMN-separation time due to the larger top junction area as pillar diameter increased, necessitating more time for complete DMN-separation (n = 4). Data are shown as mean ± s.e.m. (C) Two different DMNs with different binding shapes between the polymer matrix and pillars were penetrated into the skin. The Troy MN (left) was made only on the end surface of the pillars, while the deep-dipped DMN (right) had a greater side junction area. (D) Interstitial fluid easily permeated to the top junction of the Troy MNs (left square), but the additional polymer matrix on the pillar side walls of the deep-dipped DMNs inhibited interstitial fluid permeation to the top junction (right square). (E) After a few seconds, Troy MNs rapidly separated from the pillar, while more separation time was required for deep-dipped DMNs.</p

Evaluation of skin insertion failure.

<p>(A) DMNs created by 1 to 5 drying cycles completely penetrated the skin, but DMNs generated by 7 or more cycles did not due to the fact that the maximum axial diameter of the MNs was roughly 2.5 folds larger than the pillar after 7 contact and drying cycles (n = 4). Data are shown as mean ± s.d. (B) Skin insertion failure. Broken DMN on the pillar after application. Scale bars, 500 μm.</p

Different curvatures of SU-8 mold of Arched Micro-injector (ARCMI) produced by increasing airflow rate.

<p>(A) The ARCMI curvature was defined as the inverse of the radius of a circle fitting the inner ARCMI curve (Inset). The radius of this circle was measured by photo analysis with real-time microscope. ARCMIs were fabricated with different curvatures and lengths (A). Image of ARCMI molds with various curvatures for lengths of (B) 10 mm length and (C) and 5 mm. ARCMI curvatures depended on both the mold length and rate of airflow. Scale bar: 1 millimeter.</p

Histological analysis of porcine eyes after subretinal injection.

<p>Cryosection and tissue staining (Hematoxyline and Eosin) of the retina-choroid tissue of porcine was performed after subretinal injection with various tip form of Arched Micro-injector such as (A) no curved tip with large outer diameter (200 µm), (B) small outer diameter (100 µm) tip, (C) a 0.15 mm⁻¹ curvature with 100 µm outer diameter and no beveled tip, and (D) a 45° bevel angle tip with 0.15 mm⁻¹ curvature and 100 µm outer diameter. The straight tip caused damage to the retina as well as choroid surface. Lack of a beveled tip tore the retina surface resulting in a larger hole on the retina.</p

Subretinal injection of indocyanine green using the ARCMI in an artificial eye.

<p>(A) The artificial eye was hemispherical composed of two layers consisting of an artificial retina (agarose gel) layer and artificial choroid (polydimethylsilane; PDMS) layer. (B) A straight needle ARCMI (curvature = 0) was difficult to insert into the subretinal space without incurring tissue damage. (C) An ARCMI with a curvature of around 0.15 mm⁻¹ could be inserted into the artificial subretinal space through the agarose gel layer without damaging the PDMS layer. (D) Insertion of a needle with a curvature over 0.3 mm⁻¹ was difficult because of the large surface of contact area with the artificial retina (D). Scale bar: 1 millimeter.</p