Title page for ETD etd-11012011-054509


Type of Document Dissertation
Author Kosoglu, Mehmet Alpaslan
Author's Email Address kosoglu@vt.edu
URN etd-11012011-054509
Title Fiberoptic Microneedles for Transdermal Light Delivery
Degree PhD
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Rylander, Christopher G. Committee Chair
Paul, Mark R. Committee Member
Robertson, John L. Committee Member
Rylander, Marissa Nicole Committee Member
Xu, Yong Committee Member
Keywords
  • buckling
  • subdermal
  • MEMS
  • optical
  • hyperthermia
  • laser
Date of Defense 2011-10-19
Availability unrestricted
Abstract
Shallow light penetration in tissue has been a technical barrier to the development

of photothermal therapies for cancers in the epithelial tissues and skin. This problem can

potentially be solved by utilizing minimally invasive probes to deliver light directly to

target areas potentially >2 mm deep within tissue. To develop this solution, fiber optic

microneedles capable of delivering light for therapy were manufactured.

We have manufactured fiberoptic microneedles by tapering silica-based optical

fibers employing a melt-drawing process. These fiberoptic microneedles were 35 to 139

microns in diameter and 3 mm long. Some of the microneedles were manufactured to have

sharper tips (tip diameter < 8 microns) by changing the heat source during the melt-drawing

process. All of the microneedles were individually inserted into ex vivo porcine skin

samples to demonstrate the feasibility of their application in human tissues. Skin

penetration experiments showed that sharp fiber optic microneedles with a minimum

average diameter of 73 microns and a maximum tip diameter of 8 microns were able to penetrate

skin without buckling. Flat microneedles, which had larger tip diameters, required a

minimum average diameter of 125 microns in order to penetrate through porcine 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.

Melt-drawn fiberoptic microneedles provided a means to mechanically penetrate

dermal tissue and deliver light directly into a localized target area. We also described an

alternate fiberoptic microneedle design with the capability of delivering more diffuse, but

therapeutically useful photothermal energy using hydrofluoric acid etching of optical

fibers. Microneedles etched for 10, 30, and 50 minutes, and an optical fiber control was

compared for their ability to deliver diffuse light using three techniques. First, red light

delivery from the microneedles was evaluated by imaging the reflectance of the light

from a white paper. Second, spatial temperature distribution of the paper in response to

near-IR light (1,064 nm, 1 W, CW) was recorded using infrared thermography. Third, ex

vivo adipose tissue response during 1,064 nm, (5 W, CW) irradiation was recorded with

bright field microscopy. Increasing etching time decreased microneedle diameter (from

125 to 33 microns), resulting in increased uniformity of red and 1,064 nm light delivery along

the microneedle axis. For equivalent total energy delivery, microneedles with smaller

diameters reduced carbonization in the adipose tissue experiments.

However, thin fiberoptic microneedles designed to minimize tissue disruption and

deliver diffuse therapeutic light are limited in their possible clinical application due to a

lack of mechanical strength. Fiberoptic microneedles have been embedded in an

elastomeric support medium (polydimethylsiloxane, PDMS) to mitigate this issue. The

critical buckling force of silica microneedles with 55, 70, and 110 microns diameters and 3

mm length were measured with and without the elastomeric support in place (N = 5).

Average increases in the mechanical strength for microneedles of 55, 70, and 110 microns

diameters were measured to be 610%, 290%, and 33%, respectively. Aided by

mechanical strengthening through an elastomeric support, microneedles with 55 microns

diameter were able to repeatedly penetrate ex vivo porcine skin.

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