Evaluation of 3D Printability and Biocompatibility of Microfluidic Resin for Fabrication of Solid Microneedles

Abstract

In this study, we have employed Digital Light Processing (DLP) printing technology for the fabrication of solid microneedle (MN) arrays. Several arrays with various geometries, such as cones, three-sided pyramids and four-sided pyramids, with different height to aspect ratios of 1:1, 2:1 and 3:1, were printed. Post-processing curing optimizations showed that optimal mechanical properties of the photocurable resin were obtained at 40 °C and 60 min. Ex vivo skin studies showed that piercing forces, penetration depth and penetration width were affected by the MN geometry and height to aspect ratio. Cone-shaped MNs required lower applied forces to penetrate skin and showed higher penetration depth with increasing height to aspect ratio, followed by three-sided and four-sided printed arrays. Cytotoxicity studies presented 84% cell viability of human fibroblasts after 2.5 h, suggesting the very good biocompatibility of the photocurable resin. Overall, DLP demonstrated excellent printing capacity and high resolution for a variety of MN designs.

Keywords: 3D printing; Digital Light Processing; biocompatibility; mechanical properties; microneedles; piercing.

Figure 1

CAD design of the MNs on SolidWorks. (a) Pyramid, (b) 3-sided pyramided and (c) 4-sided pyramids. Height to aspect ratio from left to right (1:1, 2:1 and 3:1).

Figure 2

SEM images of 3D-printed MNs. (a) Cone, (b) 3-sided pyramid and (c) 4-sided pyramid MNs.

Figure 3

Obtained values on (a) compressive modulus and (b) yield strength by exposing all the printed cylinders to different curing settings.

Figure 4

Piercing tests in porcine skin: (a–c) force/needle vs. displacement data for all designs; (d) insertion force/needle for all designs.

Figure 5

Digital photographs showing (a) untreated skin: A1–A9; (b) MN piercing: B1–B9; (c) piercing remarks: C1–C9 for all MN designs.

Figure 6

False color 2D still images of 3D-printed MNs (cone design; C1, C2 and C3) showing the real-time penetration into the mouse skin using OCT. (a) Skin sample as control before experiment; (b) insertion of C1 design; (c) insertion of C2 design; (d) insertion of C3 design, respectively (scale bar 300 µm).

Figure 7

False color 2D still images of 3D-printed MNs (3-sided pyramid design; 3P1, 3P2 and 3P3) showing the real-time penetration into the mouse skin using OCT. (a) Skin sample as control before experiment; (b) insertion of 3P1 design; (c) insertion of 3P2 design; (d) insertion of 3P3 design, respectively (scale bar 300 µm).

Figure 8

False color 2D still images of 3D-printed MNs (4-sided pyramid design; 4P1, 4P2 and 4P3) showing the real-time penetration into the mouse skin using OCT. (a) Skin sample as control before experiment; (b) insertion of 4P1 design; (c) insertion of 4P2 design; (d) insertion of 4P3 design, respectively (scale bar 100 µm).

Figure 9

Obtained values on MN axial force measurements considering (a) 1:1 ratio; (b) different ratios and geometries.

Figure 10

Cell imaging with blue and green staining. Human dermal fibroblasts in the concentration of 1 × 10⁵ cells per well were seeded on 96-well plates without disks (control), UV-sterilized and media-soaked disks for 2 h and 48 h, respectively, and 2 h UV-sterilized disks only. Staining was carried out according to the manufacturer’s guidelines for 30 min and plates were centrifuged before imaging via ZOE Fluorescent Cell Imager (Bio-Rad Laboratories) at 4× magnification. DAPI (blue dye) represents the nuclei of all the cells and GFP (green dye) represents the nuclei of damaged cells. The colocalization was analyzed from a minimum of 3 representative images from three independent experiments after 2.5 h incubation. Data are represented individually and as average ± SEM. Scale bar 100 µm.

Figure 11

Cell viability evaluation for control, UV disks soaked in media and UV disks.