Abstract
Electromechanical reshaping (EMR) provides a means of producing shape change in cartilage by initiating oxidation-reduction reactions in mechanically deformed specimens. This study evaluates the effect of voltage and application time on specimen shape change using needle electrodes. Rabbit septal cartilage specimens (20 x 8 x 1 mm, n = 200) were bent 90 degrees in a precision-machined plastic jig. Optimal electrode placement and the range of applied voltages were estimated using numerical modeling of the initial electric field within the cartilage sample. A geometric configuration of three platinum needle electrodes 2 mm apart from each other and inserted 6 mm from the bend axis on opposite ends was selected. One row of electrodes served as the anode and the other as the cathode. Constant voltage was applied at 1, 2, 4, 6, and 8 V for 1, 2, and 4 minutes, followed by rehydration in phosphate buffered saline. Samples were then removed from the jig and bend angle was measured. In accordance with previous studies, bend angle increased with increasing voltage and application time. Below a voltage threshold of 4 V, 4 minutes, no clinically significant reshaping was observed. The maximum bend angle obtained was 35.7 ± 1.7 º at 8 V, 4 minutes.
Highlights
Cartilage forms the framework for the upper airway and the structural aesthetic features of the face, and reshaping this tissue is necessary in reconstructive and aesthetic surgery in the head, neck, and upper airway
We have demonstrated that these electrochemical reactions, while complex, act synergistically to locally alter the chemical composition of cartilage resulting in relaxation of internal stress and subsequent stable shape change [12], [13]
This study aims to: 1) numerically estimate the initial electric field surrounding needle electrodes inserted into a cartilage specimen, and use this model to estimate the voltage levels needed to produce clinically significant shape change with minimal tissue injury; 2) systematically evaluate the dependence of the shape change on voltage and application time; and 3) identify voltage and application time thresholds for the onset and plateau region for the electromechanical reshaping (EMR) effect
Summary
Cartilage forms the framework for the upper airway and the structural aesthetic features of the face, and reshaping this tissue is necessary in reconstructive and aesthetic surgery in the head, neck, and upper airway. Traditional surgical techniques aimed at altering shape generally require incising and/or suturing cartilage to release or balance the intrinsic forces that resist sustained deformation [8]–[10]. An alternative to thermoforming methods relies on in situ redox reactions in the tissue matrix of mechanical deformed cartilage specimens using low-level dc voltages generating currents in the milliampere range [11]–[13]. This electromechanical reshaping (EMR) process exploits the properties of the cartilage as a charged polymer hydrogel. EMR at appropriate voltage levels produces a negligible temperature elevation suggesting that the shape change occurs without any contribution from resistive heating [13]
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