Electromechanical Reshaping of Face, Neck and Auricular Cartilages: A Scoping Review

Abstract

Electromechanical Reshaping (EMR) has emerged as a novel modality to reshape the cartilage of face and neck in a minimally invasive manner. This scoping review focusses on assessing the efficacy and potential of EMR in clinical utility. Studies were collected and analyzed by two authors. PubMed, Scopus, and Springer were searched for databases from January 2000 to April 2024. Studies encompassing peer-reviewed original research articles on EMR in cartilage tissues, experimented in-vivo or ex-vivo were included. The data examined were mechanism of action, dosimetry, safety parameters, physical and chemical parameters, and electrode geometry. After screening 235 articles by de-duplication and by following inclusion and exclusion criteria, 27 articles were included in the review. The full-text articles were completely analyzed, the articles emphasized EMR in cartilage in-vivo or ex-vivo animal models. It was evident that EMR has less interference with tissue injury and has the potential to reshape the cartilage non-invasively when compared to other reshaping methods. Further studies are required for clinical validation and compatibility. EMR presents potential as a minimally invasive cartilage reshaping technique with favorable efficacy and safety profiles but requires optimization in dosimetry, electrode geometry and other parameters. Extensive clinical studies involving human subjects are essential for long-term validation and clinical readiness.

Introduction

Cartilaginous structures in the face and neck regions serve as the framework for the upper airway and contribute significantly to the aesthetic features of the face. Generally, to rectify deformities or injuries in face, head and neck cartilage, often septoplasty, otoplasty, and cosmetic reconstructive surgery was needed [1]. Wherein traditional techniques, such as carving, suturing, or morselizing, are employed for this purpose. It also causes damage to the tissue by reducing viability and causing other complications [2].Alternative methods have emerged, aiming to modify cartilage's mechanical properties and shape typically involving laser [3–5] or radiofrequency [6–8] technology to generate heat, denature or accelerate stress relaxation in collagenous tissues, while these alternatives have shown promise, they also have limitations, including the potential for thermal tissue damage [4, 5]. Electromechanical Reshaping (EMR) utilizes a Direct current (DC) leads to an electric field being applied to the tissue specimen under mechanical stress, resulting in permanent cartilage reshaping. Unlike laser and radiofrequency, EMR involves non-thermal mechanism of reshaping. EMR operates through an electrochemical process, with localized oxidation–reduction reactions occurring in the areas of stress concentration within the tissue matrix, thereby altering the mechanical properties of cartilage. Moreover, the degree of reshaping, as indicated by the bend angle, was directly proportional to the applied voltage and the duration of application [9, 10]. Simple electrochemical tests have revealed that EMR-induced tissue remodeling was fundamentally a chemical process based on the generation of highly localized pH gradients within cartilage when subjected to mechanical stress [11]. This temporary alteration through EMR along with controlled electric potential enables surgeons to reshape cartilage with precision and minimal damage, offering a promising avenue for enhancing surgical outcomes and patient experiences in reconstructive and cosmetic surgery [12]. Numerous studies have highlighted the potential impact of EMR in various treatments, including tracheal stenosis, septal cartilage correction, and otoplasty correction [9, 13, 14]. While these individual studies have shed light on the benefits of EMR, a review was needed to explore EMR’s clinical usage, safety, and process parameters. Such review would also aid in identifying opportunities of further investigation and development helping in the translation of the technology for clinical practice.

Methodology

Research Question

Considering the insights from existing literatures, how EMR was safe and efficient in cartilage reshaping in face and neck? Can it be translated to clinical utility?

Preliminary Search

The scoping review was performed based on the guidelines of Preferred Reporting Items for Systematic Reviews extension for Scoping Reviews (PRISMA-ScR). An extensive search of PubMed, Scopus and Springer was conducted most recently in April 2024. No limits like article type, publication date or language limits were placed during the search. Our research questions were developed using the PICOTS model (Table 1).

Table 1.

PICOTS table representing the Population, Intervention, Comparison, Outcome and Time of the study design

PICOTS Table
Population	Subjects with conditions that needs reshaping of cartilages in Face and Neck
Intervention	Electromechanical Reshaping as a non-invasive, outpatient method to reshape cartilage
Comparison	None
Outcomes	1. Investigating the efficacy of EMR for clinical usage 2. Assessing the safety of treatment with EMR 3. Understanding the electrical, mechanical, chemical, and biological parameters of EMR in correlation with safe and efficient reshaping of cartilage 4. Identify relevant areas that require further research to bridge the gaps for clinical utility 5. Assess the readiness of the technology for clinical utility
Timing	From the inception of respective databases until 19th of March 2023
Study Designs	Mechanism explorative studies, safety assessment studies, Ex-vivo animal studies, in-vivo animal studies, and validation studies

Search Strategy

Articles were searched in PubMed, Scopus and Springer from January 2000 to April 2024. A search of literature was conducted in 2024 with the following fields on the advanced search bar: (Electromechanical AND Reshaping AND Cartilage). Totally 235 results were obtained. The collected articles were de-duplicated using SR Accelerator software. The titles and abstract were screened to identify terms and keywords of interest related to the scope of study in EMR-based cartilage reshaping. Very limited resources were available on EMR. The articles were considered for literature review after filtering through the inclusion and exclusion criteria.

Eligibility and Exclusion Criteria

Inclusion Criteria

Peer-reviewed English manuscripts on EMR of cartilage tissues, using animal models (rabbits, porcine) and ex-vivo experiments on nasal septum, auricular, costal, and tracheal cartilages. Articles on EMR competency and preliminary work are also included.

Exclusion Criteria

Studies unrelated to EMR of cartilage tissues, non-invasive interventions, books, book chapters, oral presentations, and non-research articles.

Data items and Synthesis of Results

Data included authors, year, title, type of electrode, type of specimen, study type, animal models, Physical, chemical and biological parameters. Studies were grouped according to the inclusion and exclusion criteria. Results were analyzed for the relevance of electrode geometry, tissue injury, dosimetry, pH and mechanical findings. The efficacy of the EMR was defined as the ability to reshape cartilage with minimal tissue injury whereas the potential for clinical utility was defined by the safety and technology readiness.

Results

Study Selection

Our search resulted in 235 articles. References were downloaded from the database, screened for duplicates manually and reconfirmed with SR Accelerator. After deduplication 135 citations were identified. With the careful screening of title and abstracts, 105 citations were excluded, and 35 full-text articles were assessed for eligibility. Of these, 27 articles were identified to be relevant and included in the scoping review (Fig. 1). All the included articles are peer reviewed English language journals with experimental results of EMR on cartilage tissues in either ex-vivo specimens or in-vivo animal models and evaluated safety, efficacy, mechanism and other relevant parameters (Table 3).

Fig. 1.

Flowchart representing the study identification and screening as prescribed by PRISMA extension for scoping review (PRISMA-SCR)

Table 3.

Master table representing all the included articles obtained from the PubMed, Springer and Scopus

Authors & reference	Title	Objectives	Type of Electrode	Dosimetry Optimized/evaluated	Type of specimen	Animal Details	Study Type (In-vivo/Ex-vivo)	Parameters evaluated	Sample size	Numbers of electrode	Geometry
Ho, K. 2003 [9]	Electromechanical Reshaping of Septal Cartilage	Electromechanical reshaping of tissue by applying Direct Current (DC)	Aluminum electrodes	0–3 V for 5 min	Nasal Septal Cartilage	Porcine	Ex-vivo	Evaluation of Electromechanical Reshaping in nasal septal cartilage	NA	2	NA
Ho, K. 2003 [15]	Effect on Electrode Composition on Electromechanical Cartilage Reshaping	Determining the dependence of shape change on electrode composition during electroformation using DC current	Aluminum electrode and gold electrode	0–6 min under constant voltages of 2 V for aluminum, 5 V for Gold	Nasal Septum Cartilage	Porcine	Ex-vivo	Shape retention depending on the voltage and duration	NA	2	semicircular electrodes
Protsenko, Dmitriy 2006 [10]	Stress relaxation in porcine septal cartilage during electromechanical reshaping: mechanical and electrical responses	Determining underlying physical mechanisms responsible for shape change in deformed facial cartilage specimens exposed to electric field	Aluminum electrodes	2, 4, 6 and 9 V for 5 min	Nasal Septal Cartilage	Porcine	Ex-vivo	Reshaping parameters (angle, time and voltage),	n = 207	2	semicircular electrodes
Wu, E.C. 2009 [12]	Electromechanical reshaping of rabbit	Demonstrating the use of a six-	Platinum needle	0, 1, 2, 4, 6, 8 V for 2	Nasal Septum	New Zealand	Ex-vivo	Effect of cartilage thickness on bend	n = 13 (0 V); 8 (1 V),	18	6 arrays of 3 rows
	septal cartilage: A six needle electrode geometric configuration	electrode needle-based geometric configuration for cartilage reshaping	electrode	minutes	Cartilage	White rabbit		angle, current measurement, electrode arrangement and polarity, tissue effects	7 (2 V), 8 (4 V), 10 (6 V), 8 (8 V)
Manuel, Cyrus T 2010 [16]	Needle electrode-based electromechanical reshaping of cartilage	EMR in cartilage grafts and intact ears can be performed with negligible temperature elevation and limited cell injury using needle electrodes	Platinum needle electrodes	0–10 V for 1–9 min	Nasal Septal Cartilage (New Zealand White rabbit), Ear (Porcine)	New Zealand White rabbit and Porcine	Ex-vivo	Live dead cell assay and clinical feasibility	n = 200	8	4 arrays of 2 rows
Protsenko, Dmitry 2011 [17]	Survival of chondrocytes in rabbit septal cartilage after electromechanical reshaping	Determining the short and long-term viability of chondrocytes after EMR in cartilage grafts maintained in tissue culture	Aluminum electrodes	0, 3, 4, 5 & 6 V for 1, 2 & 3 min	Nasal Septal Cartilage	New Zealand White rabbit	Ex-vivo	Chondrocyte viability by live dead assay	NA	2	semi-cylindrical aluminum electrodes
Manuel, Cyrus 2010 [18]	Monitoring of electrical current in rabbit and porcine cartilage tissue during electromechanical reshaping	Evaluating the relationship between the voltage applied, the electrical current measured during EMR with platinum needles, and reshaping	Platinum needle electrode	0–7.5 V for 1–9 min	Septal and auricular cartilage (New Zealand White rabbit) auricular and costal	New Zealand White rabbit and Porcine	Ex-vivo	Chemical kinetics of EMR		2,4,6,8	needle electrode
Chen, Heather 2010 [19]	Using optical coherence tomography to monitor effects of electromechanical reshaping in septal cartilage	Application of Optical Coherence Tomography to examine structural changes in cartilage during EMR	Platinum needle electrode	6 V for 3 min	Nasal Septal Cartilage	New Zealand White rabbit	Ex-vivo	OCT imaging at different stages	30 mm × 10 mm × 1 mm	2	NA
Karimi, Koohyar 2010 [20]	Comparison of bend angle measurements in fresh cryopreserved cartilage specimens after electromechanical reshaping	Using a unique method to cryopreserve septal cartilage for EMR studies	Platinum needle electrode	2 V & 6 V for 2 min	Nasal Septal Cartilage	New Zealand White rabbit	Ex-vivo	Bend angle with cryopreserved samples	20 ± 1 × 12 ± 0.5 × 0.8 ± 0.1 mm	6	Needle electrode
Wu, E.C. 2011 [21]	Needle-electrode-based electromechanical reshaping of rabbit septal cartilage: A systematic evaluation	Evaluation of the effect of voltage and application time on specimen shape change using needle electrode	Platinum needle electrode	0–8 V for 1–4 min	Nasal Septal Cartilage (20mm × 8mm × 1mm)	New Zealand White rabbit	Ex-vivo	Electric Field configuration of applied voltage, number of electrodes, geometric configuration electrodes	n = 200	6	3 rows 2 array
Manuel, C.T. 2011 [22]	Electromechanical reshaping of costal cartilage grafts: A new surgical treatment modality	Determining the effect of EMR voltage and time on the shape change of costal cartilage grafts	Platinum needle electrode	3–7 V for 1–5 min	Costal cartilage	Porcine	Ex-vivo	Analysis of bend angles in costal cartilage	n = 1	6	NA
Wu, E.C. 2011 [23]	pH-dependent mechanisms of electromechanical cartilage reshaping	Elucidating pH-related changes using phenol red during EMR	Platinum needle electrode	8 V for 2 min under different pH rehydration	Nasal Septum Cartilage	New Zealand White rabbit	Ex-vivo	Extent of local pH & color change, pH indicator application time, Rehydration	NA	18	6 arrays of 3 rows
Protsenko, D.E. 2011 [24]	The influence of electric charge transferred during electro-mechanical reshaping on mechanical behavior of cartilage	Investigating the correlation between the electric charge transferred during EMR and equilibrium elastic modulus	Flat platinum electrode	0–8 V for 1–4 min	Nasal Septum Cartilage	Porcine	Ex-vivo	Numerical implementation of triphasic theory, equilibrium reaction force calculation, shape change	15 × 5 × 2 mm2	2	flat platinum electrodes
Lim, A 2011 [25]	Changes in the tangent modulus of rabbit septal and auricular cartilage following electromechanical reshaping	Optimizing EMR application parameters and understanding various side effects	Flat platinum electrode	2, 3, 4, 6, or 8 V for three minutes (ear), 2, 4, 5, 6, or 8 V for two minutes (Septum)	Ear and Nasal septal cartilage	New Zealand White rabbit	Ex-vivo	Voltage application observation, cartilage tangent modulus	Auricular (n = 75), Septal (n = 52)	2	flat platinum electrodes
Badran, K. 2013 [26]	Ex-vivo electromechanical reshaping of costal cartilage in the New Zealand white rabbit model	Determining the parameters of EMR for shape change and cell viability in New Zealand White rabbit costal cartilage	Platinum needle electrode	2 V–2 min, 3 V–2 min, 3 V–3 min, 4 V for 3 min	Costal and auricular cartilage	New Zealand White rabbit	Ex-vivo	Shape change and Cell viability	New Zealand White rabbit rib cartilage (n = 12), Porcine auricular cartilage (n = 21)	4
Oliaei, S. 2013 [27]	In-vivo electromechanical reshaping of ear cartilage in a rabbit model: A minimally invasive approach for otoplasty	Reporting the study of in -vivo EMR of ear model of New Zealand White rabbit cartilage	Platinum needle electrode	5 V for 4 min	Ear	New Zealand White rabbit	In-vivo	Histological analysis, mechanical response measurement	n = 10	19 platinum needles	4 rows of 19 apertures
Yau, A.Y.Y. 2014 [28]	In-vivo needle-based electromechanical reshaping of pinnae New Zealand white rabbit model	Demonstration of EMR in shape change of in-vivo intact pinnae of an animal model to show shape change and cell injury is proportional to increase in dosimetry	Platinum needle electrode (20 pairs, 2mm apart)	4 V–4 min, 4 V–5 min, 5 V–3 min, 5 V–4 min, 6 V–2 min, 6 V–3 min	Pinnae—Ear	New Zealand White rabbit	In-vivo	Histology and cell viability—live dead cell assay	n = 35 (5nos in each group of dosimetry)	20 pairs	6 arrays
Gandy, J.R. 2014 [29]	Modular component assembly approach to microtia reconstruction	Illustrating a Modular Component Assembly (MCA) approach that minimizes the experimental challenges with microtia repair and reduces the amount of cartilage to a single rib	Platinum coated electrode	5 V–3 min	Rib	Porcine	Ex-vivo	Tissue viability using confocal microscopy, Scaffold feasibility for clinical use,	n = 1	4 pairs	cylindrical cork mandrel
Kuan, E.C. 2014 [30]	In-depth analysis of pH-dependent mechanisms of electromechanical reshaping of rabbit nasal septal cartilage	Characterization of local tissue pH changes after EMR and its correlation with tissue damage and shape change	Platinum needle electrode	Controls (0 V, 2 min), Shape change (4 V, 4 min; 6 V, 1, 2, 4 min; 8 V, 1 min, Tissue damage (8 V, 4, 5 min; 10 V, 4, 5 min)	Nasal Septal cartilage	New Zealand White rabbit	Ex-vivo	Diffusion of redox products, total charge transfer, pH change	n = 52	3 platinum electrodes	in Array
Lauren E. Tracy, 2014 [31]	The Effect of pH on Rabbit Septal Cartilage Shape Change: Exploring the Mechanism of Electromechanical Tissue Reshaping	Examining the isolated effect of protonation (pH) on cartilage shape change	NA	pH of 3, 7 & 11 for 15 min each	Nasal Septal cartilage	New Zealand White rabbit	Ex-vivo	Shape change based of different pH levels	n = 153	NA	NA
Manuel, C.T. 2015 [32]	Optimal electromechanical reshaping of the auricular ear and long-term outcomes in an in-vivo rabbit model	Long-term outcomes of a more refined EMR voltage and time settings for reshaping New Zealand White rabbit auricle	Platinum needle electrode	(4 V–4 min, 4 V–5 min, 5 V–4 min, 5 V–3 min	Pinnae–Ear	New Zealand White rabbit	In-vivo	mechanical evaluation & Shape change, histologic evaluation, chondrocyte viability,	n = 14 (7nos each group)	20	Pairs
Kim, S. 2015 [33]	Handheld-Level Electromechanical Cartilage Reshaping Device	Handheld-level multichannel EMR cartilage device and evaluation of its feasibility in an outpatient setting	Platinum needle electrodes	5–8 V for 1–7 min	Rib–costal cartilage	Porcine	Ex-vivo	Shape change, current flow, thermograph, and cell viability assays using confocal microscopy	n = 10	6 pairs	NA
Hussain, S. 2015 [34]	Electromechanical reshaping of ex-vivo porcine trachea	Demonstrating the feasibility of EMR as a potentially minimally invasive procedure to alter the tracheal structure	Platinum needle electrode	3–5 V for 2–3 min	Tracheal ring	Porcine	Ex-vivo	Live dead assay, shape retention and analysis using digital imaging	n = 8 for each parameter, n = 10 for control	2 pairs	NA
Badran, K.W. 2015 [35]	Long-term in-vivo electromechanical reshaping for auricular reconstruction in the New Zealand white rabbit model	Demonstrating the dosimetry effect of EMR on cartilage shape change, structural integrity, cellular viability and graft remodeling in an in-vivo long term animal model	Platinum needle electrode	4–6 V for three minutes, survival duration of 6th & 12th week	Porcine costal graft cartilage and New Zealand White rabbit auricular cartilage	Porcine and New Zealand White rabbit	In-vivo	Histological analysis, cell viability assays and shape change	n = 1	4 needles	NA
Hunter, B.M. 2016 [11]	Controlled-Potential Electromechanical Reshaping of Cartilage	Indication of electrochemical generation of localized, low pH gradients within tissue after EMR	Platinum needle electrode	5 V	Nasal Septum, auricular and costal cartilage	New Zealand White rabbit	Ex-vivo	EMR and pH restoration for reduced tissue injury	NA	6	NA
Hong, S.J. 2016 [36]	Monitoring of Biological Changes in Electromechanical Reshaping of Cartilage Using Imaging Modalities	Validating non-thermal damage by EMR and observing post-EMR structural changes using several imaging modalities	Platinum needle electrode	3–6 V for 6 min	Nasal Septal Cartilage	New Zealand White rabbit	Ex-vivo	Imaging modalities (Thermograph, Optical Coherence Tomography-OCT and SEM)	for thermograph(n = 4), for structural changes each group (n = 5). Cartilage size (23 mm × 6 mm × 0.5/1/1.5 mm)	6	6 arrays
Lim, A. 2016 [37]	Methods for evaluating changes in cartilage stiffness following electromechanical reshaping	Validating cartilage stiffness before and after EMR of both septal and auricular cartilage over the range of dosimetries	Platinum needle electrode	2–8 V for 2 min in septal cartilage and 3 min for auricular cartilage	Nasal Septum and Auricular cartilage	New Zealand White rabbit	In-vivo	Young’s modulus	NA	2	Flat electrodes

Characteristics of the Included Studies

27 studies were included according to the eligibility criteria. Of the included studies, 81% reported ex-vivo cartilage experiments, and 19% reported in-vivo animal model validations. Of these, 59% of studies reported experiments in septal cartilages, whereas 26% reported experiments in auricular cartilages and the remaining were in tracheal and costal cartilages (Table 2). Studies included in the review assessed reshaping efficiency, safety and other parameters in different cartilage tissues and animal models (Table 3).

Table 2.

The characteristics of the included studies based on the samples used and data represented

Characteristics of included studies (n = 27)	n	Round off (%)
Studies reporting Septal Cartilage	15	55
NZW Rabbit	10	37
Porcine	5	19
Studies reporting Auricular Cartilage	7	26
NZW Rabbit	5	19
Porcine	2	7
Studies Reporting other (Tracheal or Costal) Cartilage tissues	5	19
Studies reporting In-vivo animal models	4	15
NZW Rabbit	4	15
Porcine	0	0
Both	0	0
Studies evaluated dosimetry	25	93
Studies evaluated safety parameters	15	56
Studies assessed Mechanical parameters	5	19
Studies reporting longevity data	2	7
Studies reporting Needle electrodes	20	74
Studies reporting Flat electrodes	5	19
Studies reporting temperature	3	11

Reshaping Efficacy and Dosimetry

Four in-vivo studies and 23 ex-vivo studies were conducted using EMR. 93% of the studies evaluated the reshaping efficacy of EMR by measuring the bend angle with varying dosimetry. Among 23 ex-vivo studies, EMR was performed on rabbit nasal, costal, and auricular cartilage in 14 studies, wherein the nine studies, porcine septal, auricular, and costal cartilages were used as specimens. 3 studies reported the use of semicircular electrodes and 5 studies used flat electrodes with respect to the jig. 74% of the studies reported the reshaping results with penetrating needle electrodes. In all the ex-vivo studies, the specimen was rehydrated in Phosphate-buffered saline for 15 min after EMR to restore the pH and rigidity of the cartilage [11, 38]. All included studies performed EMR immediately or within 24 h of sampling from animals to maintain tissue viability, but a study also supports the effectiveness of EMR even after cryopreservation [20]. Reshaping was efficient with voltage ranging between 1 and 9 V and duration between 1 and 9 min. It was evident from the studies that increasing the voltage and application time increased the shape retention but incurred loss of tissue viability with higher dosimetry. In one study, maximum bend angle of 125° was attained with minimal tissue injury at a dosimetry of 6 V for 3 min [39]. The dosimetry differs significantly with the type of cartilage tissue. In case of rabbit nasal septal cartilage, significant reshaping of more than 70° achieved at or above the dosimetry of 6 V for 2 min. Two studies reported that below 6 V, there was no significant reshaping of the cartilage [12, 16]. In the case of rabbit and porcine auricular, tracheal, or costal cartilage, efficient reshaping was achieved with dosimetry between 4 V for 4 min and 5 V for 5 min with more than 50% chondrocyte viability when compared to the conventional surgeries. Dosimetry 7 V or 8 V yielded the shape change exactly up to the mechanical deformation with significant chondrocyte loss [22, 27, 28, 32, 34, 40].

Safety

In the included studies, 56% of the studies assessed the safety by evaluating the morphological feature and cell viability through histopathological examination and Live/Dead assay respectively. Usually few chondrocytes present in the extracellular matrix, thereby maintaining homeostasis and repair processes. The inflammation due to chondrocyte trauma leads to fibrocartilaginous tissue production, resulting in scarring and loss of function [11]. Hence, it was crucial to maintain the viability of chondrocytes during EMR. For analysis of cartilage viability, live-dead imaging method was used. For the histological studies, the samples were stained with hematoxylin and eosin. All the studies reported the focal cell death in the needle insertion site, where the tissue injury was highly localized and comparable to conventional morselization [11, 17, 18, 25, 27–30, 35, 35]. The extent of tissue injury was observed 2 mm in the case of lower dosimetry in the range of 5 V and 5 mm in case of higher dosimetry in the range of 8 V [29, 33]. Cell death beyond 5 mm from the needle insertion site was not found in any study. It maintained a pattern that the tissue injury was more at the anode than the cathode, and the pH change during redox reactions was one of the reasons for tissue injury [30]. Histopathological evaluation reported discontinuous cartilage layer (0.3–0.8 mm) and neo-chondrogenesis at the needle insertion site [27]. The study also observed the fibrous tissue formation, ECM loss, empty cavities, and loss of smooth surface architecture with disrupted collagen fiber organization [30]. One study suggested that the viable perichondrium and chondrocytes surrounding needle insertion sites can potentially facilitate repopulating damaged regions with viable chondrocytes [18]. All four in-vivo studies performed in auricular cartilage in rabbits tolerated the reshaping process and survived with no local or systemic detrimental effects or complications. in-vivo studies did not report any infection, hematoma formation, hemorrhage, soft tissue necrosis or skin slough [27, 28, 32, 35]. Two studies reported the exudative crusts on the surface of the ears at the electrode insertion sites on day 1, but it fell off after a week. After the duration of the study in 3 and 6 months, two studies reported normal appearing skin and normal hair regrowth [32, 35].’

Correlation of Parameters with Safety and Efficacy

There are physical, chemical, and biological parameters that correlate with the safety and efficacy of EMR. One study examined electrode composition, suggesting aluminum electrodes [15, 41], while 23 studies preferred platinum electrodes due to their biocompatibility, high conductivity, and reduced electrodeposition. 74% of the studies used needle electrodes to minimize tissue damage, while 19% employed surface electrodes, despite their potential for extensive electrochemical damage at the tissue-electrode interface and temperature rises exceeding 10 °C [25]. According to a study, the electrode needle should be inserted or placed into areas of cartilage with increased internal stress due to mechanical deformation and the cathode and anode must be at least 3 mm apart [18]. One study reported that the High voltage, high application time, reduced distance between electrodes and reduced distance between electrode arrays create a highly concentrated electric field, which in turn leads to reduced chondrocyte viability [12].

In some studies, temperature measurements were carried out with thermocouple or with FLIR (Forward Looking Infrared) cameras. 11% of the studies reported that at the optimal voltages and time application, the temperature elevation was as negligible as 1–2 °C [25, 36, 41]. One study reported that with the dosimetry of 8 V–2 min, the temperature elevated was as high as 40 °C using a flat platinum surface electrode [25]. Across multiple studies, it was evident that an increase in voltage leads to increase in temperature during EMR. In experiments where voltage was applied at 5 V, the peak temperature measured on pig’s costal cartilage reached 20.3 °C within 45 seconds [41]. Similarly, in electroforming at 5 V for 5 min, the surface temperature of aluminum and gold increased by about 1.8 °C and 8.2 °C, respectively [15]. Higher voltages lead to increased heating. For instance, at 20 V, a significant temperature rise occurred, correlating with elevated current levels. One study noted over a 100-fold increase in power, underscoring the influence of electrical parameters on temperature changes during electroforming [41]. At lower voltages (< 10 V), heat generation was minimal, with cartilage matrix resistance being a crucial factor. Compared to traditional thermal methods like radiofrequency and laser reshaping, EMR exhibits negligible heating effects. In an EMR experiment at 6 V, the temperature rose by only 2.6 °C, suggesting EMR functions more as an electroforming technique than a thermoforming one [36].

Monitoring of electrical parameters during EMR aids in optimizing the process. Three studies evaluated the current, charge transferred and resistance during the EMR Process [10, 24, 33]. A study found that applying 8 V for 3 min resulted in a maximum current of 460 mA and a maximum charge transferred of 5.5 kC. Thicker cartilage exhibited a higher peak electric current [33], and the magnitude of EMR was reported to be directly proportional to the amount of charge transferred into the tissue. Another study reported that cartilage resistance increases with increased voltage and time and correlates with the degree of shape change. At 6 V, maximum bend angle and resistance occur; beyond this, both decreases. Monitoring resistance feedback aids in assessing shape change [10].

One study evaluated the effect of charge transfer in the mechanical integrity and stiffness of cartilage in terms of elastic modulus and reaction force and suggested that the increased amount of charge transferred deploys the FCD (Fixed Charge Density) of the cartilage thereby the mechanical stiffness and load bearing capacity of the cartilage diminishes [24]. Cartilage mechanical properties saturate at high voltages and longer application times, impacting post-treatment outcomes. Studies report reduced tangent and Young’s modulus in EMR-treated samples [25, 29, 37]. But two in-vivo studies reported the elastic modulus, structural integrity and elastic recoiling of the EMR treated cartilage were not significantly different when compared with the control [27, 28]. Another study reported that the reaction force of the cartilage decreased during the EMR and saturated at one point, indicating the end of the reshaping process [10]. Two studies assessed structural properties by imaging with Optical Coherence Tomography (OCT) and Scanning Electron Microscopy (SEM) and reported the uneven shrinkage and irregular, loosely connected, damaged collagen fibers at the electrode insertion side [19, 36]. Two studies correlated cartilage pH with tissue injury, indicating that electrochemical reaction byproducts diffuse to form a transition zone, directly influencing injury severity, dosimetry, and charge transfer [23, 30].

Discussion

Summary of Findings

This scoping review identified 27 studies for evaluating the efficacy and safety of EMR as a novel modality or reshaping cartilages in the face and neck. The analysis of the included studies revealed that EMR has demonstrated promising efficacy in reshaping cartilage tissue by achieving significant bend angles. The optimal dosimetry for reshaping varied depending on the type of cartilage tissue, with voltages between 4V and 6V being identified as optimal for nasal, auricular, and tracheal cartilage [11, 12, 16, 28]. The significant difference in the dosimetry requirement for different tissue site may be due to the variation of composition in the hyaline and elastic cartilages, where hyaline contain more amount of Type II collagen and proteoglycans which in turn require more dosage of electric current for the efficient stress relaxation [42]. Overall findings suggest that EMR can effectively reshape cartilage with minimal tissue injury, making it a viable alternative to conventional techniques such as laser ablation, radiofrequency ablation or morselization [22, 27, 28, 32, 34].

According to this review, the findings indicate that EMR exhibits a favorable safety profile. 15 studies including 4 in-vivo studies assessed safety through histopathological examination and cell viability assays.

Notably, the studies reported localized tissue injury only at the needle insertion sites, which was comparable to conventional morselization techniques [11, 18, 25, 27–30, 35]. This localized injury has no effect on the surrounding tissues, as evidenced by the survival of animals in in-vivo studies without adverse effects or complications [27, 28, 32, 35]. The review also highlighted the correlation of various physical, chemical, and biological parameters in the safety and efficacy of EMR. The choice of electrode composition and geometry are crucial since it determines the electric field distribution for reshaping. Platinum electrodes are preferred in the studies for their biocompatibility and high conductivity. Needle electrodes were found to minimize tissue damage and localize the effects of EMR effectively [25]. Monitoring electrical parameters, such as current and resistance, during the procedure can aid in achieving the personalization of EMR according to the cartilage properties. Additionally, EMR also proved to be a non-thermal dependent technique without any thermal damage [25, 36, 38]. The mechanical properties of reshaped cartilage are vital for maintaining functional integrity. While two ex-vivo studies reported a reduction in mechanical properties post-EMR, two in-vivo studies found no significant differences when compared to control cartilage [25, 27–29]. Two studies examined pH changes in cartilage due to electrochemical reactions, correlating with dosimetry, and tissue injury, highlighting pH monitoring as crucial [23, 30].

Limitations of the Current Review

This scoping review highlights insights into EMR but lacks coverage of other applications like non-invasive corneal curvature change. No meta-analysis was conducted due to a qualitative approach, and human studies were unavailable. The review couldn’t fully explore EMR’s effects on tendons and ligaments. Evidence on needle vs. flat electrodes' invasiveness was lacking. Standardizing EMR protocols was challenging due to parameter diversity.

Future Prospects & Research Directions

To explore its potential, comparative studies contrasting EMR with conventional surgery are imperative for understanding its benefits. Future research should refine EMR technology, optimize dosimetry, and enhance electrode designs for precision. Exploring EMR’s role in specific clinical scenarios like Septoplasty, Rhinoplasty, and Otoplasty was essential for tailoring it to diverse needs. EMR could provide a minimally invasive alternative for these procedures, potentially reducing complications and expanding treatment options. A thorough understanding of EMR’s effectiveness will drive its integration into surgical practices, advancing cartilage-based interventions.

Conclusion

EMR demonstrates promising efficacy in achieving significant bend angles and reshaping cartilage tissue, making it a potential alternative or adjunctive therapeutic procedure to conventional surgical interventions. EMR exhibits a favorable safety profile, characterized by localized tissue injury limited to the sites of electrode insertion, with no reported adverse effects or complications observed during in-vivo studies. The selection of appropriate electrode composition and geometry, as well as the meticulous monitoring of electrical parameters such as current, pH, and resistance are crucial factors that significantly influence the safety and efficacy of EMR. Further research should prioritize the implementation of animal trials followed by well-designed human trials to comprehensively evaluate the safety, efficacy, and long-term durability of EMR, particularly with consideration given to the anticipated variables during the translation of this technology from ex-vivo to in-vivo settings.

Author Contributions

Conceptualization: Harisharan Ramesh, Mohamed Jameer Basha Jahankir, Thilak Chakaravarthi, Amit Goyal. Methodology: Harisharan Ramesh, Mohamed Jameer Basha Jahankir. Formal Analysis and Investigation: Harisharan Ramesh, Mohamed Jameer Basha Jahankir, Amit Goyal. Writing—Original draft preparation: Harisharan Ramesh, Mohamed Jameer Basha Jahankir. Writing—review and editing: Vidhu Sharma, Amit Goyal. Supervision: Amit Goyal.

Funding

No funds, grants, or other support was received.

Declarations

Conflict of Interest

The authors declare that they have no conflict of interest concerning the publication of this manuscript.