Presidential Greeting - American Society for Laser Medicine and ...

6 American Society for Laser Medicine and Surgery Abstracts
activate regeneration processes resulting in new tissue growth
and therefore in some alteration of cartilage shape obtained
immediately after laser procedure, the results obtained are of
importance to forecast the stability of laser reshaping procedure.
#15
FLUID CHARACTERIZATION OF A NOVEL
HOLLOW-CORE MICRONEEDLE DESIGN
Robert Hood, Mehmet Kosoglu, Matthew Parker,
Christopher Rylander
Virginia Tech, Blacksburg, VA
Background: Microneedles have been successfully utilized to
deliver small fluid volumes for many different applications. We
are investigating a novel hollow-core microneedle design that will
permit co-localized, simultaneous light and fluid delivery.
Successful skin penetration of similar microneedle designs has
been previously demonstrated by our group. The potential
applications for such a device range from cosmetic fat reshaping to
targeted destruction of tumors. The primary objective of this study
was to determine the optimal microneedle parameters for fluid
flow.
Study: Microneedles with tip diameters varying between 15 and
90 mm were fabricated via a custom melt-draw apparatus from
capillary tubing (150 mm inner diameter) capable of co-delivering
light and fluids. A series of experiments characterizing the
capillary tubing’s fluid resistance were conducted by measuring
the volumetric flow rate of water through the tubing at constant
pressures ranging from 10 to 90 psi. Following accurate
characterization of tubing resistance, additional experiments
investigating the flow resistance of different microneedle
geometries were conducted.
Results: The first set of experiments determined that fluid flow in
tubing lengths longer than 50 mm adhered highly to Poiseuille’s
Law in the range of pressures investigated (10–90 psi). For
lengths < 50 mm, turbulent effects in the flow caused Poiseuille’s
Law to under-predict the fluid resistance. In either laminar or
turbulent flow regimes, the flow rate increased significantly as
tubing length decreased. Increased microneedle resistance was
correlated with small tip diameter, shorter needle length, and
bending in the needle bore.
Conclusion: This study sought to determine the best geometry
balancing minimal invasiveness and low flow resistance in a novel
hollow-core microneedle design. The experiments indicated that
the optimal design involves having a microneedle with a
completely straight bore, length between 0.5 and 0.8 mm, and tip
diameter between 40 and 60 mm preceded by the shortest tubing
length possible. The next developmental step will involve
determining the best geometries for incorporation of light delivery
in addition to fluid flow.
#16
USING TRIPHASIC THEORY TO EVALUATE
CARTILAGE MECHANICAL RESPONSE TO
LASER RESHAPING
Dmitry Protsenko, Brian Wong
Beckman Laser Institute and Medical Clinic,
University of California, Irvine, CA
Background: Laser cartilage reshaping (LCR) has been
suggested as an alternative to the classical surgical techniques of
modifying the shape of facial features. The method is based on
exposure of mechanically deformed cartilaginous tissue to a laser
heating. Bio-chemical reactions within the tissue lead to reduction
of internal stress, and establishment of a new equilibrium shape.
The same reactions offset the electric charge, osmotic and
hydraulic balances between collagen and proteoglycan matrix and
interstitial fluid responsible for maintenance of cartilage
mechanical properties. The objective of this study was to
investigate correlation between the temperature rise during LCR
and cartilage mechanical behavior.
Study: We used a finite element model based on the modified
triphasic theory to study how internal temperature field
generated in the laser heating of cartilage can modulate its
mechanical responses to step displacements in unconfined and
confined compression. The native concentrations of the ions,
collagen matrix stiffness and the fluid and ion velocities within the
specimen were estimated from compression and stress relaxation
experiments.
Results: The results from finite element calculations
demonstrated apparent stress increase during heating due to
thermal expansion. Generally, stress relaxation following the
heating accelerates with increase in temperature and irradiation
time. To compare numerical model with experimental observation
we measured stress evolution in cartilage during and after lasers
heating.
Conclusion: Good correlation between experimental and
theoretical data (R < 0.9) confirms contribution of thermal
expansion to stress evolution and suggests softening of collagen
matrix as a major mechanism of stress relaxation.
#17
COMPARISON OF THERMAL AND MECHANICAL
CHARACTERISTICS DURING TISSUE ABLATION
OF Er:YAG, Er,Cr:YSGG AND CO2 IN THE
MICROSECOND TO MILLISECONDS PULSE
RANGE IN VIEW OF SOFT TISSUE APPLICATIONS
IN SURGERY
Rudolf Verdaasdonk, Vladimir Lemberg, Albert
Veen van der, Stefan Been, Dmitri Boutoussov,
Werner Landgraf
VU University Medical Center, Amsterdam, Netherlands;
Optomix, Santa Clara, CA; University Medical Center Utrecht,
Utrecht, Netherlands; Biolase, Irvine, CA; Biolase Floss, Germany
Background: Erbium lasers are being used successfully in
dentistry for hard tissue ablation. In dermatology, Erbium laser
dermabrasion has been replaced with fractional techniques
mainly with CO2 lasers. Due to the precise and controlled
ablation, Erbium lasers might be considered as alternatives for
fractional applications as well as for microsurgery in, for example,
ENT, reconstruction and neurosurgery. In this study, the ablation
effect of several Erbium lasers was examined in relation to pulse
duration, wavelength and fiber delivery system.
Study: Three Erbium based laser modalities, Er:YSGG at
2.78 mm, pulse 60 or 700 microseconds and Er:YAG at 2.94 mm
60 microseconds delivered through 200 and 400 mm diameter silica
tips were compared during the ablation of phantom tissue
(polyacrylamide gel 90% water content) at pulse energies from 10
to 100 mJ. High speed and thermal Schlieren imaging techniques
were applied to visualize the mechanical and thermal effects.
Results: The differences in ablation depth were significant as
well as the thermal residual in relation to pulse length. The
ablation at 2.94 mm was around 25% more effective compared to
2.78 mm with less thermal residual. There was minimal difference