Needle Electrode-Based Electromechanical Reshaping of Cartilage

Abstract

Electromechanical reshaping (EMR) of cartilage provides an alternative to the classic surgical techniques of modifying the shape of facial cartilages. The original embodiment of EMR required surface electrodes to be in direct contact with the entire cartilage region being reshaped. This study evaluates the feasibility of using needle electrode systems for EMR of facial cartilage and evaluates the relationships between electrode configuration, voltage, and application time in effecting shape change. Flat rabbit nasal septal cartilage specimens were deformed by a jig into a 90° bend, while a constant electric voltage was applied to needle electrodes that were inserted into the cartilage. The electrode configuration, voltage (0–7.5 V), and application time (1–9 min) were varied systematically to create the most effective shape change. Electric current and temperature were measured during voltage application, and the resulting specimen shape was assessed in terms of retained bend angle. In order to demonstrate the clinical feasibility of EMR, the most effective and practical settings from the septal cartilage experimentation were used to reshape intact rabbit and pig ears ex vivo. Cell viability of the cartilage after EMR was determined using confocal microscopy in conjunction with a live/dead assay. Overall, cartilage reshaping increased with increased voltage and increased application time. For all electrode configurations and application times tested, heat generation was negligible (<1 °C) up to 6 V. At 6 V, with the most effective electrode configuration, the bend angle began to significantly increase after 2 min of application time and began to plateau above 5 min. As a function of voltage at 2 min of application time, significant reshaping occurred at and above 5 V, with no significant increase in the bend angle between 6 and 7.5 V. In conclusion, electromechanical reshaping of cartilage grafts and intact ears can be effectively performed with negligible temperature elevation and spatially limited cell injury using needle electrodes.

Changes in the Tangent Modulus of Rabbit Septal and Auricular Cartilage Following Electromechanical Reshaping

“…Due to the thinness of this rabbit cartilage, the effects of the opposite polarities could not be separately determined using flat electrodes in this study. Clinically, needle electrodes, rather than the surface electrodes used, are the most minimally invasive means of applying EMR, minimizing any threats to chondrocyte viability [25]. Mechanical studies involving needle electrodes have yet to be performed.…”

The influence of electric charge transferred during electro-mechanical reshaping on mechanical behavior of cartilage

“…The degree of the shape change increases with increase in applied voltage or/and voltage application time until the reshaped graft conforms to geometry of reshaping apparatus [4][5][6]. At the same time, reshaping degree is directly related to electric charge transferred in the electric circuit during voltage application, confirming electro-chemical mechanism of EMR [6].…”

“…At the same time, reshaping degree is directly related to electric charge transferred in the electric circuit during voltage application, confirming electro-chemical mechanism of EMR [6]. Figure 1: EMR of septal cartilage grafts: a) and c) reshaping of porcine cartilage into semicylindrical shape using gold surface electrodes [4], b) and d) reshaping of rabbit cartilage into 90 degree bend using platinum needle electrodes [5].…”

“…EMR of flat cartilage grafts into semi-cylindrical or acute angular shapes have been demonstrated using surface and needle electrodes ( Figure 1) [4,5]. The degree of the shape change increases with increase in applied voltage or/and voltage application time until the reshaped graft conforms to geometry of reshaping apparatus [4][5][6].…”

“…Corrections of septal deviation and reshaping of protuberant ears have been performed using fiber-delivered laser light as a heat source. Another non-surgical cartilage reshaping technique is electromechanical reshaping of cartilage (EMR) [4,5]. It relies on application of low-level electric voltage to mechanically deformed cartilage.…”