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Research Papers

Fiber Optic Microneedles for Transdermal Light Delivery: Ex Vivo Porcine Skin Penetration Experiments

[+] Author and Article Information
Mehmet A. Kosoglu1

Department of Mechanical Engineering, Virginia Tech, 100L1 Randolph Hall, Blacksburg, VA 24061kosoglu@vt.edu

Robert L. Hood

School of Biomedical Engineering and Sciences, Virginia Tech, Room 325, ICTAS Building, Stanger Street, Blacksburg, VA 24061robert86@vt.edu

Ye Chen

Department of Mechanical Engineering, Virginia Tech, 100L1 Randolph Hall, Blacksburg, VA 24061chenye@vt.edu

Yong Xu

Department of Electrical and Computer Engineering, Virginia Tech, 467 Whittemore, Blacksburg, VA 24061yong@vt.edu

Marissa Nichole Rylander

Virginia Tech–Wake Forest University School of Biomedical Engineering and Sciences, and Department of Mechanical Engineering, Virginia Tech, Room 325, ICTAS Building, Stanger Street, Blacksburg, VA 24061mnr@vt.edu

Christopher G. Rylander

Virginia Tech–Wake Forest University School of Biomedical Engineering and Sciences, and Department of Mechanical Engineering, Virginia Tech, Room 325, ICTAS Building, Stanger Street, Blacksburg, VA 24061cgr@vt.edu

1

Corresponding author.

J Biomech Eng 132(9), 091014 (Sep 03, 2010) (7 pages) doi:10.1115/1.4002192 History: Received January 29, 2010; Revised June 15, 2010; Posted July 19, 2010; Published September 03, 2010; Online September 03, 2010

Shallow light penetration in tissue has been a technical barrier to the development of light-based methods for in vivo diagnosis and treatment of epithelial carcinomas. This problem can potentially be solved by utilizing minimally invasive probes to deliver light directly to target areas. To develop this solution, fiber optic microneedles capable of delivering light for either imaging or therapy were manufactured by tapering step-index silica-based optical fibers employing a melt-drawing process. Some of the microneedles were manufactured to have sharper tips by changing the heat source during the melt-drawing process. All of the microneedles were individually inserted into ex vivo pig skin samples to demonstrate the feasibility of their application in human tissues. The force on each microneedle was measured during insertion in order to determine the effects of sharper tips on the peak force and the steadiness of the increase in force. Skin penetration experiments showed that sharp fiber optic microneedles that are 3 mm long penetrate through 2 mm of ex vivo pig skin specimens. These sharp microneedles had a minimum average diameter of 73μm and a maximum tip diameter of 8μm. Flat microneedles, which had larger tip diameters, required a minimum average diameter of 125μm in order to penetrate through pig skin samples. Force versus displacement plots showed that a sharp tip on a fiber optic microneedle decreased the skin’s resistance during insertion. Also, the force acting on a sharp microneedle increased more steadily compared with a microneedle with a flat tip. However, many of the sharp microneedles sustained damage during skin penetration. Two designs that did not accrue damage were identified and will provide a basis of more robust microneedles. Developing resilient microneedles with smaller diameters will lead to transformative, novel modes of transdermal imaging and treatment that are less invasive and less painful for the patient.

FIGURES IN THIS ARTICLE
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Copyright © 2010 by American Society of Mechanical Engineers
Topics: Force , Fibers , Skin , Microneedles
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References

Figures

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Figure 1

(a) Schematic illustration of melanoma being photothermally treated by laterally diffused laser energy from fiber optic microneedles. The dashed ellipses denote the light diffusion profile and corresponding treatment zone. (b) Color microscope image of a fiber optic microneedle delivering red laser light (λ=633 nm, 0.5 mm leakage length in air).

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Figure 2

Process for manufacturing fiber optic microneedles and geometrical parameters

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Figure 3

(a) Bright field image of a sharp fiber optic microneedle (S8) used in this study. (b) Bright field image of a flat fiber optic microneedle (F3) used in this study. (c) Color microscope image of a sharp fiber optic microneedle delivering red laser light near the tip (λ=633 nm, 0.1 mm leakage length in air).

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Figure 4

(a) Experimental setup. (b) Image of a successful penetration experiment (S11).

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Figure 5

Force versus displacement for flat microneedle F5

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Figure 6

Force versus displacement for flat microneedle F8

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Figure 7

Force versus displacement for sharp microneedles S5, S8, and S10

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Figure 8

Force versus displacement for sharp microneedles S11 and S12

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Figure 9

Force versus time plot for flat microneedles F5 and F8

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Figure 10

Force versus time plot for sharp microneedles S8 and S11

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Figure 11

Microneedles before and after insertion

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Figure 12

Theoretical versus experimental values for Fcr

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