Type of Document Dissertation Author Kosoglu, Mehmet Alpaslan Author's Email Address email@example.com 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
Date of Defense 2011-10-19 Availability unrestricted AbstractShallow 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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