Skin Research and Technology 2014; 20: 270–273 Printed in Singapore All rights reserved doi: 10.1111/srt.12115
© 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Skin Research and Technology
Entrance and propagation pattern of high-frequency electrical currents in biological tissues as applied to fractional skin rejuvenation using penetrating electrodes A. Taheri1, P. Mansoori2, L. F. Sandoval1, S. R. Feldman1,2,3, P. M. Williford1 and D. Pearce1 1 Department of Dermatology, Center for Dermatology Research, Wake Forest School of Medicine, Winston-Salem, NC, USA, Department of Pathology, Wake Forest School of Medicine, Winston-Salem, NC, USA and 3Department of Public Health Sciences, Wake Forest School of Medicine, Winston-Salem, NC, USA
2
Background: Fractional resurfacing of the skin using radiofrequency devices has been used for collagen remodeling and rejuvenation. Objectives: To determine how radiofrequency current enters and propagates through tissue, and the pattern of the resulting effect. Materials and Methods: An electrosurgical device with a 0.4 MHz frequency output was used as the source of radiofrequency current. Current was applied via a metallic needle introduced into a large piece of cow liver, with different amounts of energy delivered at multiple points. Cross-sections of the liver were then studied for tissue effect. Results: Thermal coagulation of tissue started from the tip of the electrode. With higher energy, a rim of coagulated tissue formed around the entire length of the needle. This rim of coagulated tissue was thicker around the tip of the electrode.
Conclusion: Radiofrequency currents have a tendency to move toward the center of the bulk of tissue. When an electrode of a fractional radiofrequency device enters the skin, maximum heating effect will be around the tip of the electrode in the dermis. This phenomenon can preserve epidermis from injury during dermal heating, reducing post-procedural skin surface side effects seen with many skin rejuvenation procedures.
FREQUENCY electrical currents, also called radiofrequency currents or radiofrequency energy, have been used for decades in electrosurgery. More recently, these currents have been applied to skin rejuvenation procedures. Fractional heating of the dermis using radiofrequency devices and penetrating electrodes has been used for collagen remodeling, skin tightening, and wrinkle reduction (1–4). Radiofrequency-based fractional devices deliver a high-frequency alternating electrical current in radiofrequency range (usually 0.3–5 MHz) to the skin via an array of penetrating multi-electrode-pins. This results in heating of the areas, which are directly targeted by the electrodes, leaving intact or slightly effected zones in between the targeted areas (1–4). The preserved tissue serves as a pool of cells that promote rapid wound healing. Laser-based fractional resurfacing produces greater tissue injury, and as a result, more
post-procedural side effects on the skin surface (epidermis) than in the deep dermis (5, 6). However, patterns of propagation of radio frequency energy through biological tissues and depth of its maximum effect have not been studied comprehensively. The aim of this study was to determine how a radiofrequency current enters and propagates through biologic tissue and the resulting tissue effect.
H
270
IGH
Key words: skin – rejuvenation – radiofrequency – fractional – tissue – injury – electrical – current – high-frequency
Ó 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Accepted for publication 19 October 2013
Methods In an in vitro study, we simulated in large scale a fractional radiofrequency skin rejuvenation electrode. An electrosurgical devise with a 0.4 MHz frequency output in continuous (cutting) mode was used as the source of radiofrequency current. A two-centimeter-long, thin, metallic needle with low electrical resistance was used to apply the current to a piece of cow liver larger than 10 9 10 9 7 cm in size. The
Electrical currents in tissues
needle was introduced into the liver at multiple points and different amounts of energy were delivered at each point while keeping the needle stationary. Cross-sections of liver, sliced parallel to the electrode, were then prepared and studied. The temperature of the liver, including the center, was maintained at room temperature for the entirety of the study. This study was performed in two stages. In stage 1, the return electrode was placed underneath the liver (i) or alongside the liver (ii), at a distance from the needle (Fig. 1). For stage 2, the return electrode was put on the top of the liver. A hole (≤1 cm or ≥2.5 cm) was made in the center of the return electrode and the needle electrode was passed through the center of the hole (Fig. 1).
liver near the return electrode. With higher energy, a rim of coagulated tissue formed along the entire length of the needle; however, this rim was thicker on the surface of the liver near the return electrode (Fig. 3).
Discussion
In stage 1, thermal coagulation of the tissue started from the tip of the electrode. With higher energy, a rim of coagulated tissue formed along the entire length of the needle; however, this rim was thicker around the tip of the electrode (Fig. 2). In stage 2, when a return electrode with a hole ≥2.5 cm in diameter was put on the top of the liver and the electrode was passed through the hole, the results were similar to stage 1 with the coagulated rim thicker around the electrode tip (Fig. 2). However, when using a return electrode with a hole ≤1 cm in diameter on the top of the liver, coagulation started from the surface (top) of the
In a long conductor with a small diameterto-length ratio, such as a metal wire, highfrequency electrical currents tend to move on the surface of the conductor, avoiding the center, a phenomenon called ‘skin effect’ (7). There are conflicting reports on the pattern of propagation of alternating electrical currents in biological tissues (8). Our study showed that in a piece of liver, which is not a good conductor and does not have a small diameter-to-length ratio for passing the current, the pattern of movement and propagation of electrical currents is not similar to metallic wires. Instead, the current propagated toward the center of the bulk of the tissue rather than moving toward the surface. High-frequency electrical currents tend to use the path of least resistance in biological tissues with large diameter-to-length ratios (8). It is likely that in liver tissue, the path of least resistance is the path toward the center of the bulk of tissue. Stage 2 provided evidence to support this theory, showing movement of current toward the return electrode when the active and return electrodes were placed near each other. Considering results of our study, we may conclude that when an electrode of a fractional
Fig. 1. Left: Stage 1. The return electrode was placed at a distance from the needle. Right: Stage 2. The return electrode was put on the top of the liver. A hole was made in the center of the return electrode and the needle electrode was passed through the center of the hole.
Fig. 2. Left. Stage 1: Coagulation started from the tip of the electrode (top left). With higher energy, a rim of coagulated tissue formed around the needle in its all length; however, this rim was thicker around the tip of the electrode (bottom left). In stage 2, when a return electrode with a 2.5 cm hole was used, results were similar to stage 1. Right. Stage 1: Pattern of coagulation at different energy levels.
Results
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Fig. 3. Stage 2: When a return electrode with 0.8 cm hole was used, coagulation started from the surface near the return electrode. With higher energy, a rim of coagulated tissue formed around the needle in its all length; however, this rim was thicker on the surface of the liver near the return electrode.
radiofrequency device enters the skin, maximum heating effect will be around the tip of the electrode in dermis. This phenomenon can preserve the epidermis during dermal heating and reduce the risk of post-procedural side effects including post-inflammatory dyspigmentation. By insulating the proximal end of the penetrating electrode, and allowing only the distal end to come in contact with the deeper dermis, the epidermis will escape injury more efficiently during heating of the dermis (9). Compared with laser-based fractional resurfacing devices that provide more tissue injury (effects and also greater post-procedural side effects) on the skin surface (epidermis) than in the deep dermis, radiofrequency devices may be a better option when the goal is collagen remodeling, skin tightening, and wrinkle reduction (5, 6). Easier post-operative care, shorter downtime, and lower risk of dyspigmentation are expected when the epidermis remains intact during such rejuvenation procedures (5, 6). A monopolar single-electrode device was used in this study. Most available fractional resurfacing devices, however, use multi-electrode-pins. Whether propagation of currents and the tissue results of multi-electrode devices
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are the same as a mono-electrode device was not explored. Fractional resurfacing devices that use bipolar mode are also available. In bipolar mode, active electrodes are near each other and as a result, the current probably uses the nearest path, similar to stage 2 of this study. Therefore, in bipolar devices, we would not expect the current to have a tendency for propagation in deeper tissues unless the penetrating electrodes are insulated on the proximal end (10). Hence, monopolar devices may be better choices than bipolar devices for targeting the dermis while sparing the epidermis. Another limitation of this study is the use of liver as the biologic tissue. In contrast to a large piece of liver that is a relatively homogenous tissue, human skin consists of three layers, with dermis having less electrical resistance than epidermis and subcutaneous fat(11). Therefore, we cannot predict how closely propagation patterns in human skin would resemble the patterns found in liver tissue. It is likely that lower electrical resistance of the dermis compared with epidermis contributes more to the propagation of the current into the dermis while avoiding epidermis.
Conclusion High-frequency electrical currents have a tendency to propagate toward the center of the bulk of tissue. In contrast to fractionated lasers, with fractionated radiofrequency devices, greater injury can be targeted at the dermis, preserving the epidermis, and producing less post-procedural skin surface side effects.
Funding The Center for Dermatology Research is supported by an unrestricted educational grant from Galderma Laboratories, L.P.
Conflict of interest Drs. Taheri, Mansoori, Sandoval, Williford, and Pearce have no conflicts to disclose. Steven R Feldman is a consultant and speaker for Abbott Labs, Amgen, BiogenIdec, Bristol Myers Squibb, Galderma, Genentech, GlaxoSmithKline, Janssen, Photomedex, Stiefel, and Warner Chilcott. Steven R Feldman has received grants from 3M, Abbott Labs, Amgen, Astellas,
Electrical currents in tissues
Aventis Pharmaceuticals, BiogenIdec, Bristol Myers Squibb, Galderma, Coria, Genentech, GlaxoSmithKline, Janssen, Novartis, Ortho Pharmaceuticals, Pharmaderm, Photomedex,
References 1. Hantash BM, Ubeid AA, Chang H, Kafi R, Renton B. Bipolar fractional radiofrequency treatment induces neoelastogenesis and neocollagenesis. Lasers Surg Med 2009; 41: 1–9. 2. Hruza G, Taub AF, Collier SL, Mulholland SR. Skin rejuvenation and wrinkle reduction using a fractional radiofrequency system. J Drugs Dermatol 2009; 8: 259–265. 3. Lee HS, Lee DH, Won CH, Chang HW, Kwon HH, Kim KH, Chung JH. Fractional rejuvenation using a novel bipolar radiofrequency system in Asian skin. Dermatol Surg 2011; 37: 1611–1619. 4. Seo KY, Yoon MS, Kim DH, Lee HJ. Skin rejuvenation by microneedle fractional radiofrequency treatment in Asian skin; clinical and histological analysis. Lasers Surg Med 2012; 44: 631–636. 5. Brightman L, Goldman MP, Taub AF. Sublative rejuvenation: experi-
6.
7. 8.
9.
Roche Dermatology, Stiefel, and Warner Chilcott. Steven R Feldman has received stock options from Photomedex.
ence with a new fractional radiofrequency system for skin rejuvenation and repair. J Drugs Dermatol 2009; 8(11 Suppl): s9–s13. Peterson JD, Palm MD, Kiripolsky MG, Guiha IC, Goldman MP. Evaluation of the effect of fractional laser with radiofrequency and fractionated radiofrequency on the improvement of acne scars. Dermatol Surg 2011; 37: 1260–1267. Miranda EN. A simple model for understanding the skin effect. Int J Elect Enging Educ 1999; 36: 31–36. Christie RV, Binger CA. An experimental study of diathermy: IV. Evidence for the penetration of high frequency currents through the living body. J Exp Med 1927; 46: 715–734. Hantash BM, Renton B, Berkowitz RL, Stridde BC, Newman J. Pilot clinical study of a novel minimally invasive bipolar microneedle radiofrequency device. Lasers Surg Med 2009; 41: 87–95.
10. Berube D, Renton B, Hantash BM. A predictive model of minimally invasive bipolar fractional radiofrequency skin treatment. Lasers Surg Med 2009; 41: 473–478. 11. Miklavcic D, Pavcelj N, Hart F. Electric properties of tissues. Wiley encyclopedia of biomedical engineering. Hoboken: John Wiley & Sons, Inc., 2006. Address: A. Taheri Department of Dermatology Wake Forest School of Medicine 4618 Country Club Road Winston-Salem NC 27104 USA Tel: +1 336 716 1763 Fax: +1 336 716 7732 e-mail: [email protected]
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© 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Skin Research and Technology
Entrance and propagation pattern of high-frequency electrical currents in biological tissues as applied to fractional skin rejuvenation using penetrating electrodes A. Taheri1, P. Mansoori2, L. F. Sandoval1, S. R. Feldman1,2,3, P. M. Williford1 and D. Pearce1 1 Department of Dermatology, Center for Dermatology Research, Wake Forest School of Medicine, Winston-Salem, NC, USA, Department of Pathology, Wake Forest School of Medicine, Winston-Salem, NC, USA and 3Department of Public Health Sciences, Wake Forest School of Medicine, Winston-Salem, NC, USA
2
Background: Fractional resurfacing of the skin using radiofrequency devices has been used for collagen remodeling and rejuvenation. Objectives: To determine how radiofrequency current enters and propagates through tissue, and the pattern of the resulting effect. Materials and Methods: An electrosurgical device with a 0.4 MHz frequency output was used as the source of radiofrequency current. Current was applied via a metallic needle introduced into a large piece of cow liver, with different amounts of energy delivered at multiple points. Cross-sections of the liver were then studied for tissue effect. Results: Thermal coagulation of tissue started from the tip of the electrode. With higher energy, a rim of coagulated tissue formed around the entire length of the needle. This rim of coagulated tissue was thicker around the tip of the electrode.
Conclusion: Radiofrequency currents have a tendency to move toward the center of the bulk of tissue. When an electrode of a fractional radiofrequency device enters the skin, maximum heating effect will be around the tip of the electrode in the dermis. This phenomenon can preserve epidermis from injury during dermal heating, reducing post-procedural skin surface side effects seen with many skin rejuvenation procedures.
FREQUENCY electrical currents, also called radiofrequency currents or radiofrequency energy, have been used for decades in electrosurgery. More recently, these currents have been applied to skin rejuvenation procedures. Fractional heating of the dermis using radiofrequency devices and penetrating electrodes has been used for collagen remodeling, skin tightening, and wrinkle reduction (1–4). Radiofrequency-based fractional devices deliver a high-frequency alternating electrical current in radiofrequency range (usually 0.3–5 MHz) to the skin via an array of penetrating multi-electrode-pins. This results in heating of the areas, which are directly targeted by the electrodes, leaving intact or slightly effected zones in between the targeted areas (1–4). The preserved tissue serves as a pool of cells that promote rapid wound healing. Laser-based fractional resurfacing produces greater tissue injury, and as a result, more
post-procedural side effects on the skin surface (epidermis) than in the deep dermis (5, 6). However, patterns of propagation of radio frequency energy through biological tissues and depth of its maximum effect have not been studied comprehensively. The aim of this study was to determine how a radiofrequency current enters and propagates through biologic tissue and the resulting tissue effect.
H
270
IGH
Key words: skin – rejuvenation – radiofrequency – fractional – tissue – injury – electrical – current – high-frequency
Ó 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Accepted for publication 19 October 2013
Methods In an in vitro study, we simulated in large scale a fractional radiofrequency skin rejuvenation electrode. An electrosurgical devise with a 0.4 MHz frequency output in continuous (cutting) mode was used as the source of radiofrequency current. A two-centimeter-long, thin, metallic needle with low electrical resistance was used to apply the current to a piece of cow liver larger than 10 9 10 9 7 cm in size. The
Electrical currents in tissues
needle was introduced into the liver at multiple points and different amounts of energy were delivered at each point while keeping the needle stationary. Cross-sections of liver, sliced parallel to the electrode, were then prepared and studied. The temperature of the liver, including the center, was maintained at room temperature for the entirety of the study. This study was performed in two stages. In stage 1, the return electrode was placed underneath the liver (i) or alongside the liver (ii), at a distance from the needle (Fig. 1). For stage 2, the return electrode was put on the top of the liver. A hole (≤1 cm or ≥2.5 cm) was made in the center of the return electrode and the needle electrode was passed through the center of the hole (Fig. 1).
liver near the return electrode. With higher energy, a rim of coagulated tissue formed along the entire length of the needle; however, this rim was thicker on the surface of the liver near the return electrode (Fig. 3).
Discussion
In stage 1, thermal coagulation of the tissue started from the tip of the electrode. With higher energy, a rim of coagulated tissue formed along the entire length of the needle; however, this rim was thicker around the tip of the electrode (Fig. 2). In stage 2, when a return electrode with a hole ≥2.5 cm in diameter was put on the top of the liver and the electrode was passed through the hole, the results were similar to stage 1 with the coagulated rim thicker around the electrode tip (Fig. 2). However, when using a return electrode with a hole ≤1 cm in diameter on the top of the liver, coagulation started from the surface (top) of the
In a long conductor with a small diameterto-length ratio, such as a metal wire, highfrequency electrical currents tend to move on the surface of the conductor, avoiding the center, a phenomenon called ‘skin effect’ (7). There are conflicting reports on the pattern of propagation of alternating electrical currents in biological tissues (8). Our study showed that in a piece of liver, which is not a good conductor and does not have a small diameter-to-length ratio for passing the current, the pattern of movement and propagation of electrical currents is not similar to metallic wires. Instead, the current propagated toward the center of the bulk of the tissue rather than moving toward the surface. High-frequency electrical currents tend to use the path of least resistance in biological tissues with large diameter-to-length ratios (8). It is likely that in liver tissue, the path of least resistance is the path toward the center of the bulk of tissue. Stage 2 provided evidence to support this theory, showing movement of current toward the return electrode when the active and return electrodes were placed near each other. Considering results of our study, we may conclude that when an electrode of a fractional
Fig. 1. Left: Stage 1. The return electrode was placed at a distance from the needle. Right: Stage 2. The return electrode was put on the top of the liver. A hole was made in the center of the return electrode and the needle electrode was passed through the center of the hole.
Fig. 2. Left. Stage 1: Coagulation started from the tip of the electrode (top left). With higher energy, a rim of coagulated tissue formed around the needle in its all length; however, this rim was thicker around the tip of the electrode (bottom left). In stage 2, when a return electrode with a 2.5 cm hole was used, results were similar to stage 1. Right. Stage 1: Pattern of coagulation at different energy levels.
Results
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Taheri et al.
Fig. 3. Stage 2: When a return electrode with 0.8 cm hole was used, coagulation started from the surface near the return electrode. With higher energy, a rim of coagulated tissue formed around the needle in its all length; however, this rim was thicker on the surface of the liver near the return electrode.
radiofrequency device enters the skin, maximum heating effect will be around the tip of the electrode in dermis. This phenomenon can preserve the epidermis during dermal heating and reduce the risk of post-procedural side effects including post-inflammatory dyspigmentation. By insulating the proximal end of the penetrating electrode, and allowing only the distal end to come in contact with the deeper dermis, the epidermis will escape injury more efficiently during heating of the dermis (9). Compared with laser-based fractional resurfacing devices that provide more tissue injury (effects and also greater post-procedural side effects) on the skin surface (epidermis) than in the deep dermis, radiofrequency devices may be a better option when the goal is collagen remodeling, skin tightening, and wrinkle reduction (5, 6). Easier post-operative care, shorter downtime, and lower risk of dyspigmentation are expected when the epidermis remains intact during such rejuvenation procedures (5, 6). A monopolar single-electrode device was used in this study. Most available fractional resurfacing devices, however, use multi-electrode-pins. Whether propagation of currents and the tissue results of multi-electrode devices
272
are the same as a mono-electrode device was not explored. Fractional resurfacing devices that use bipolar mode are also available. In bipolar mode, active electrodes are near each other and as a result, the current probably uses the nearest path, similar to stage 2 of this study. Therefore, in bipolar devices, we would not expect the current to have a tendency for propagation in deeper tissues unless the penetrating electrodes are insulated on the proximal end (10). Hence, monopolar devices may be better choices than bipolar devices for targeting the dermis while sparing the epidermis. Another limitation of this study is the use of liver as the biologic tissue. In contrast to a large piece of liver that is a relatively homogenous tissue, human skin consists of three layers, with dermis having less electrical resistance than epidermis and subcutaneous fat(11). Therefore, we cannot predict how closely propagation patterns in human skin would resemble the patterns found in liver tissue. It is likely that lower electrical resistance of the dermis compared with epidermis contributes more to the propagation of the current into the dermis while avoiding epidermis.
Conclusion High-frequency electrical currents have a tendency to propagate toward the center of the bulk of tissue. In contrast to fractionated lasers, with fractionated radiofrequency devices, greater injury can be targeted at the dermis, preserving the epidermis, and producing less post-procedural skin surface side effects.
Funding The Center for Dermatology Research is supported by an unrestricted educational grant from Galderma Laboratories, L.P.
Conflict of interest Drs. Taheri, Mansoori, Sandoval, Williford, and Pearce have no conflicts to disclose. Steven R Feldman is a consultant and speaker for Abbott Labs, Amgen, BiogenIdec, Bristol Myers Squibb, Galderma, Genentech, GlaxoSmithKline, Janssen, Photomedex, Stiefel, and Warner Chilcott. Steven R Feldman has received grants from 3M, Abbott Labs, Amgen, Astellas,
Electrical currents in tissues
Aventis Pharmaceuticals, BiogenIdec, Bristol Myers Squibb, Galderma, Coria, Genentech, GlaxoSmithKline, Janssen, Novartis, Ortho Pharmaceuticals, Pharmaderm, Photomedex,
References 1. Hantash BM, Ubeid AA, Chang H, Kafi R, Renton B. Bipolar fractional radiofrequency treatment induces neoelastogenesis and neocollagenesis. Lasers Surg Med 2009; 41: 1–9. 2. Hruza G, Taub AF, Collier SL, Mulholland SR. Skin rejuvenation and wrinkle reduction using a fractional radiofrequency system. J Drugs Dermatol 2009; 8: 259–265. 3. Lee HS, Lee DH, Won CH, Chang HW, Kwon HH, Kim KH, Chung JH. Fractional rejuvenation using a novel bipolar radiofrequency system in Asian skin. Dermatol Surg 2011; 37: 1611–1619. 4. Seo KY, Yoon MS, Kim DH, Lee HJ. Skin rejuvenation by microneedle fractional radiofrequency treatment in Asian skin; clinical and histological analysis. Lasers Surg Med 2012; 44: 631–636. 5. Brightman L, Goldman MP, Taub AF. Sublative rejuvenation: experi-
6.
7. 8.
9.
Roche Dermatology, Stiefel, and Warner Chilcott. Steven R Feldman has received stock options from Photomedex.
ence with a new fractional radiofrequency system for skin rejuvenation and repair. J Drugs Dermatol 2009; 8(11 Suppl): s9–s13. Peterson JD, Palm MD, Kiripolsky MG, Guiha IC, Goldman MP. Evaluation of the effect of fractional laser with radiofrequency and fractionated radiofrequency on the improvement of acne scars. Dermatol Surg 2011; 37: 1260–1267. Miranda EN. A simple model for understanding the skin effect. Int J Elect Enging Educ 1999; 36: 31–36. Christie RV, Binger CA. An experimental study of diathermy: IV. Evidence for the penetration of high frequency currents through the living body. J Exp Med 1927; 46: 715–734. Hantash BM, Renton B, Berkowitz RL, Stridde BC, Newman J. Pilot clinical study of a novel minimally invasive bipolar microneedle radiofrequency device. Lasers Surg Med 2009; 41: 87–95.
10. Berube D, Renton B, Hantash BM. A predictive model of minimally invasive bipolar fractional radiofrequency skin treatment. Lasers Surg Med 2009; 41: 473–478. 11. Miklavcic D, Pavcelj N, Hart F. Electric properties of tissues. Wiley encyclopedia of biomedical engineering. Hoboken: John Wiley & Sons, Inc., 2006. Address: A. Taheri Department of Dermatology Wake Forest School of Medicine 4618 Country Club Road Winston-Salem NC 27104 USA Tel: +1 336 716 1763 Fax: +1 336 716 7732 e-mail: [email protected]
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