Electromechanical reshaping (EMR) of cartilage is a novel technique that has significant potential for use in facial reconstructive surgery. EMR achieves permanent shape change by initiating electrochemical redox reactions in the vicinity of stress concentrations, thereby altering mechanical properties of tissue matrix. This study reports the use of a six electrode needle-based geometric configuration to reshape cartilage. Rectangular samples (24 x 12 x 1 mm) of rabbit nasal septal cartilages were bent at a right angle in a precision-machined reshaping jig. Two parallel arrays of three platinum needle electrodes were each inserted into cartilage along the bend at 3 mm from the bend line. One array served as an anode and the other as cathode. Constant voltage at 1, 2, 4, 6, and 8 volts was applied to the arrays for 2 minutes. The specimens were then removed from the jig and rehydrated for 15 minutes in phosphate buffered saline. Following rehydration, bend angles and thicknesses were measured. Bend angle increased with increasing voltage and application time. No statistically significant bending was observed below 6 volts for 2 minutes application time. Maximum bend angle of 33 ± 8 degrees or reshaping degree of 33% was observed at 8 volts applied for 2 minutes. Current flow was small (< 0.1 A) for each case. Sample thickness was 0.9 ± 0.2 mm. ANOVA analysis showed that cartilage thickness had no significant impact on the extent of reshaping at given voltage and application time. The six needle electrode geometric configuration conforms to the voltage-and time-dependent trends predicted by previous EMR studies. In the future, the reshaping properties of other geometric configurations will be explored.
Transforming decades' old methodology, electromechanical reshaping (EMR) may someday replace traditionally destructive surgical techniques with a less invasive means of cartilage reshaping for reconstructive and esthetic facial surgery. Electromechanical reshaping is essentially accomplished through the application of voltage to a mechanically deformed cartilage specimen. While the capacity of the method for effective reshaping has been consistently shown, its associated effects on cartilage mechanical properties are not fully comprehended. To begin to explore the mechanical effect of EMR on cartilage, the tangent moduli of EMR-treated rabbit septal and auricular cartilage were calculated and compared to matched control values. Between the two main EMR parameters, voltage and application time, the former was varied from 2-8 V and the latter held constant at 2 min for septal cartilage, 3 min for auricular cartilage. Flat platinum electrodes were used to apply voltage, maintaining the flatness of the specimens for more precise mechanical testing through a uniaxial tension test of constant strain rate 0.01 mm/s. Above 2 V, both septal and auricular cartilage demonstrated a slight reduction in stiffness, quantified by the tangent modulus. A thermal effect was observed above 5 V, a newly identified EMR application threshold to avoid the dangers associated with thermoforming cartilage. Optimizing EMR application parameters and understanding various side effects bridge the gap between EMR laboratory research and clinical use, and the knowledge acquired through this mechanical study may be one additional support for that bridge.
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