Electromechanical reshaping (EMR) of cartilage has been suggested as an alternative to the classical surgical techniques
of modifying the shape of facial cartilages. The method is based on exposure of mechanically deformed cartilaginous
tissue to a low level electric field. Electro-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 balance 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 electric charge transferred during EMR and equilibrium elastic
modulus.
We used a finite element model based on the triphasic theory of cartilage mechanical properties to study how electric
charges transferred in the electro-chemical reactions in cartilage can change its mechanical responses to step
displacements in unconfined compression. The concentrations of the ions, the strain field and the fluid and ion velocities
within the specimen subject to an applied mechanical deformation were estimated and apparent elastic modulus (the ratio
of the equilibrium axial stress to the axial strain) was calculated as a function of transferred charge. The results from
numerical calculations showed that the apparent elastic modulus decreases with increase in electric charge transfer. To
compare numerical model with experimental observation we measured elastic modulus of cartilage as a function of
electric charge transferred in electric circuit during EMR. Good correlation between experimental and theoretical data
suggests that electric charge disbalance is responsible for alteration of cartilage mechanical properties.
Electromechanical reshaping of cartilage is a novel modality that has significant clinical applications in otolaryngology
and plastic surgery. Although EMR dosimetry has been extensively studied, little is known about the mechanisms of
EMR, of which local tissue pH changes is believed to play a role. In this study, rabbit nasal septal cartilage is subject to a
number of experiments aimed at elucidating pH-related changes using phenol red. The lateral extent and magnitude of
pH change as well as factors that impact pH change are studied. Increasing voltage and application appear to increase the
area and intensity of color change. With parameters known to produce thermal tissue injury, a transitional zone likely
representing a confluence of acid-base products is noted in the region around the bend axis. Furthermore, rehydration
and pH indicator application time do not appear to play a role in the quality of pH change. These simple experiments
may provide insight into the role of pH changes in EMR that may allow correlation of dosimetry to tissue damage,
further optimizing the clinical potential of EMR.
Electro Mechanical Reshaping (EMR) with platinum needle electrodes has been recently developed to shape cartilage
without conventional cut and suture surgery. This study investigates the relationship between the voltage applied, the
electrical current measured during EMR, and the resulting shape. Monitoring the electrical current provides information
to model the electro-chemistry, which will aid in determining the onset of shape stabilization. Porcine costal grafts,
rabbit auricular, and porcine auricular tissue were bent into a 90° angle using a moulage. Platinum needle electrodes
were then placed in contact with the cartilage and a constant voltage was applied for a set time. The electrical current
was measured during the process and total charge transferred was calculated. The cartilage specimen was then removed
from the jig and photographed after one minute in order to determine the resulting bend angle. Results show that a higher
current in tissue is produced with increasing applied voltage. Each current trace is unique and is dependent on tissue
thickness and inter-electrode distances. Understanding the electrical current process ultimately leads to optimizing EMR
and feedback control. Voltage, for example, could be varied in real-time during EMR to produce a constant chemical
reaction rate and potentially reduce total tissue dehydration in contact with electrodes. In conclusion, electric current
traces provide information about chemical kinetics during EMR that depend on exposure settings, and monitoring these
traces is an important step in optimizing the reshaping process.
Electromechanical reshaping (EMR) of cartilage is a promising noninvasive technique with potential for broad
application in reconstructive surgery. EMR involves applying direct current electrical fields to localized stress regions
and initiating a series of oxidation-reduction reactions, thus effecting a shape change. Previous EMR studies have
focused on macroscopic structural measurements of the shape change effect or monitoring of electrical current flow.
Only limited investigation of structural changes in the tissue at the histologic level have been performed, and not in real
time. This study is the first to use optical coherence tomography (OCT) to examine structural changes in cartilage during
EMR. Two platinum needle electrodes were inserted into fixed rectangular rabbit nasal septal cartilage specimens. The
spectral domain OCT probe was then positioned above the section of cartilage in which the anode needle was inserted. A
constant voltage of 6V was applied for 3 minutes, and images were obtained (8 frames/second). OCT was also performed
in specimens undergoing dehydration under ambient conditions and during pH changes produced by the addition of HCl,
as both processes accompany EMR. The OCT data identified distinct findings among the three conditions, suggesting
that EMR causes a much greater degree of reshaping on a molecular level than dehydration or a change in pH alone.
OCT provides a means to gauge structural changes in the tissue matrix during EMR. The application of OCT to image
the EMR process will add to our understanding of the mechanisms of action involved and potentially facilitate
optimization of this process.
Grafts obtained from peripheral regions of costal cartilage have an inherent tendency to warp over time. Laser
irradiation provides a potential method to control the warping process, thus yielding stable grafts for facial reconstructive
surgery. In our current study, we propose a simple and well-fitting model that numerically describes the degree of
warping of laser irradiated costal cartilage grafts. Using a Nd:YAG laser (λ=1.32μm) at various exposure settings, grafts
harvested from the peripheral regions of porcine costal cartilage were irradiated. The resulting graft geometry was
objectively fitted to a curve using a quadratic regression model. The coefficient of determination (R2) demonstrated a
very strong fit for all grafts modeled. A quadratic regression is simple to perform and results in a single numerical value
that appropriately describes the degree of cartilage warping. Our proposed model is valuable in assessing the effect of
laser irradiation on the warping process of costal cartilage.
Cryopreservation of cartilage has been investigated for decades and is currently an established protocol. However, the
reliability and applicability of cartilage cryopreservation for the use in electromechanical reshaping (EMR) has not been
studied exclusively. A system to cryopreserve large numbers of tissue specimens provides a steady source of cartilage of
similar quality for experimentation at later dates. This will reduce error that may arise from different cartilage stock, and
has the potential to maximize efficiency under time constraints. Our study utilizes a unique methodology to cryopreserve
septal cartilage for use in EMR studies. Rabbit septal cartilage specimens were harvested and standardized to 20 x 8 x 1
mm, and placed in one of three solutions (normal saline, PBS, 10% DMSO in PBS) for four hours in a cold storage room
at 4 degrees Celsius. Then, each cartilage specimen was vacuumed and sealed in an anti-frost plastic bag and stored in a
freezer at -80 degrees Celsius for 1 to 3 weeks duration. EMR was performed using 2 and 6 volts for 2 minutes
application time. Bend angle measurements of the cryopreserved cartilage specimens were compared to bend angles of
fresh cartilage which underwent EMR using the same parameters. Results demonstrate that normal saline, phosphate
buffered saline (PBS), and PBS with DMSO were effective in cryopreservation, and indicated no significant differences
in bend angle measurements when compared to no cryopreservation. Our methodology to cryopreserve cartilage
specimens provides a successful approach for use in conducting large-scale EMR studies.
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