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Technical Briefs

Biomechanical Property of a Natural Microneedle: The Caterpillar Spine

[+] Author and Article Information
G. J. Ma, L. T. Shi

State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Faculty of Vehicle Engineering and Mechanics,  Dalian University of Technology, Dalian, 116024, People’s Republic of China

C. W. Wu1

State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Faculty of Vehicle Engineering and Mechanics,  Dalian University of Technology, Dalian, 116024, People’s Republic of Chinacwwu@dlut.edu.cn

1

Corresponding author.

J. Med. Devices 5(3), 034502 (Aug 18, 2011) (6 pages) doi:10.1115/1.4004651 History: Received January 06, 2011; Revised June 08, 2011; Published August 18, 2011; Online August 18, 2011

Recently, microneedles (or microneedle arrays) for transdermal drug delivery have received increasing attention because they can provide painless, minimal invasiveness and time-released drug delivery. However, it is very difficult to design such an eligible microneedle that meets all the requirements for mechanical strength, small insertion force, and good biocompatibility. In this paper, we investigate a biomicroneedle: caterpillar spine. It is found that this type of biomicroneedle can pierce mouse skin using a very small force (about 173 μN) without fracture and buckling failures. Such excellent properties are mainly a result of its optimal geometry evolved by Nature, the high hardness, and the reasonable high elastic modulus near the tip end. This finding may provide an inspiration for the development of improved transdermal drug delivery microneedles.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

SEM images of one Parasa Consocia caterpillar spine. The front part of the spine are magnified by (a) 1000, (b) 10,000 and (c) 10,000, (d) 50,000, respectively. The inset in (a) shows a photo of the Parasa Consocia caterpillar. The specimens are cut from the black cluster of spines marked by a white circle in the inset. (b) and (c) are images of the two sides of the tip. The two black solid lines in (b) are just for guide, to depict a profile of a taper cone. Compared with the taper-conelike shape of the artificial microneedles, the spine has a fat profile except for the ultrasharp tip apex.

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Figure 2

(a) The photo and (b) the schematic of the µ-FTS. 1: light source, 2: force sensor and upper static holder, 3: spine sample, 4: skin layer mounted on a sphere, 5: moving holder, 6: CCD camera, 7: control computer. The force sensor and upper static holder are fixed on a steel column. The moving holder is fixed on the stage which can be adjusted manually by two screws in the horizontal directions and can be moved automatically by a motor in the vertical direction. The CCD camera is fixed horizontally on the stage which can be manually adjusted by three screws in three-dimensional directions. During the experiments, the data of force, displacement and CCD image can be recorded automatically by the computer using the special control software provided by the manufacturer. An acoustic enclose is equipped to minimize the amount of acoustic noise.

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Figure 3

(a) Two-dimensional perspective image of one single caterpillar spine captured using the µ-CTS and SEM images of the cross sections at different positions, (b) near the tip, and (c) a little farther from the tip

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Figure 4

A typical force-displacement curves obtained during the Parasa Consocia caterpillar spine insertion into the mouse skin. The inset is a real-time CCD camera image during the insertion into the skin.

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Figure 5

Typical curve of the compression force versus the displacement of a caterpillar spine, showing a sawtoothlike shape. Two CCD images of spine being pressed against a brass rod surface at different time and one SEM image of the broken cross section are given in the insets.

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Figure 6

A typical force-displacement curve obtained from the bending test of one single Parasa Consocia caterpillar spine. The experiment schematic is given as an inset in this figure. During the experiment, the spine base is horizontally fixed on the lower stage of the µ-FTS, and a blade is vertically fixed on the upper stage. The spine can be regarded as a cantilver with a concentrated load acted on the end. The insets give a CCD image of the spine with bending deformation and an SEM image of the cross section of the spine after fracture.

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Figure 7

(a) The shape of an equal strength beam with hollow circular cross section and constant wall thickness. The inner profile is depicted by the two dotted lines. (b) Comparison of the equal strength beam (yellow) and the Parasa Consocia caterpillar spine.

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Figure 8

Distributions of (a) hardness and (b) elastic modulus on the Parasa Consocia caterpillar spine surface along the length. The inset in (a) is a typical nanoindentation curve and the insets in (b) are the SEM images of a caterpillar spine with the locations of nanoindentation marked.

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Figure 9

(a) AFM height image and (b) AFM phase contrast image of a Parasa Consocia caterpillar spine near the necklike groove as shown in Figs.  11

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