Electromechanical reshaping (EMR) of facial cartilage has recently been developed as an alternative to classic surgical techniques to alter cartilage shape. This study focuses on determining the underlying physical mechanisms responsible for shape change (stress relaxation) in mechanically deformed facial cartilage specimens exposed to constant electric fields. Flat porcine nasal septal cartilage specimens were deformed by an aluminum jig into semicylindrical shapes while a constant electric voltage was applied to the concave and convex surfaces of the specimen. Mechanical stress, electric current and resistance were measured during voltage application. Specimen shape retention was measured as retained bend angle. Total electric charge transferred in the electric circuit was calculated from the electric current measurement. Electrical resistance, transferred charge and the bend angle increase with increase in voltage application time until bend angle reaches maximum value determined by the jig geometry. Then, the bend angle decreases and electrical parameters nearly saturate. The time dependent behavior of electric current was analyzed using the Cottrell equation. The observed changes in electric current suggest that during the initial 1-2 min of EMR nonlinear diffusion determines electro-chemical reaction rates, which are then followed by a linear diffusion dominated process. Close correlation between alteration of cartilage mechanical state and change in its electrical properties suggest that an electro-chemical reaction is the dominant mechanism behind EMR.

Electromechanical reshaping (EMR) has been recently described as an alternative method for reshaping facial cartilage without the need for incisions or sutures. This study focuses on determining the short- and long-term viability of chondrocytes following EMR in cartilage grafts maintained in tissue culture. Flat rabbit nasal septal cartilage specimens were bent into semi-cylindrical shapes by an aluminum jig while a constant electric voltage was applied across the concave and convex surfaces. After EMR, specimens were maintained in culture media for 64 days. Over this time period, specimens were serially biopsied and then stained with a fluorescent live–dead assay system and imaged using laser scanning confocal microscopy. In addition, the fraction of viable chondrocytes was measured, correlated with voltage, voltage application time, electric field configuration, and examined serially. The fraction of viable chondrocytes decreased with voltage and application time. High local electric field intensity and proximity to the positive electrode also focally reduced chondrocyte viability. The density of viable chondrocytes decreased over time and reached a steady state after 2–4 weeks. Viable cells were concentrated within the central region of the specimen. Approximately 20% of original chondrocytes remained viable after reshaping with optimal voltage and application time parameters and compared favorably with conventional surgical shape change techniques such as morselization.

The critical transition temperature region was determined by the sharp increase in bend angle at consecutive times of immersion at the same temperature. This range was determined to be 59-68 degrees C and 62-68 degrees C for porcine and rabbit cartilage, respectively. Similar transition zones for dosimetry occurred below 20.4 W/cm2 during cartilage irradiation in both species.