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

Abstract

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.

In‐depth analysis of pH‐dependent mechanisms of electromechanical reshaping of rabbit nasal septal cartilage

“…Contemporary understanding of cartilage tissue behavior under mechanical stress is largely based on Lai's triphasic theory, which states that the biomechanical properties of cartilage tissue are dependent on fixed charge density (e.g., proteoglycans), the stiffness of the collagen matrix, and interstitial ionic content . EMR, which essentially transforms deformed cartilage tissue into an electrochemical cell, is postulated to directly affect interstitial ionic content, where the ions are free‐flowing within a fluid medium . Thus, acid–base products (hydroxyl ion at the cathode and hydrogen ion at the anode) formed at the tissue–electrode interface diffuse through the interstitial fluid as its ionic concentration changes over time with the overlying electric field, resulting in areas lateral to and between arrays of electrodes in which pH indicator may be applied to detect the presence of acid–base products.…”

“…22 EMR, which essentially transforms deformed cartilage tissue into an electrochemical cell, is postulated to directly affect interstitial ionic content, where the ions are freeflowing within a fluid medium. 23 Thus, acid-base products (hydroxyl ion at the cathode and hydrogen ion at the anode) formed at the tissue-electrode interface diffuse through the interstitial fluid as its ionic concentration changes over time with the overlying electric field, resulting in areas lateral to and between arrays of electrodes in which pH indicator may be applied to detect the presence of acid-base products.…”

Ex Vivo Electromechanical Reshaping of Costal Cartilage in the New Zealand White Rabbit Model

“…12,13 The electric field, created in the vicinity of needle electrodes, initiates local redox reactions that produce relaxation of the internal stress without thermogenic denaturation of the tissue. 13–17 …”

“…12,13 The electric field, created in the vicinity of needle electrodes, initiates local redox reactions that produce relaxation of the internal stress without thermogenic denaturation of the tissue. [13][14][15][16][17] EMR has been examined ex vivo in porcine costal cartilage tissue producing successful reshaping results. 12 This study aimed to determine the optimal EMR parame-ters for shape change and cell viability in the ex vivo rabbit costal cartilage model for auricular reconstruction, as this is the first step required before proceeding to in vivo animal studies.…”

“…Low amplitude electric voltage is applied to needle electrodes strategically inserted into locations of stress concentration in mechanically deformed specimens . The electric field, created in the vicinity of needle electrodes, initiates local redox reactions that produce relaxation of the internal stress without thermogenic denaturation of the tissue …”