ORIGINAL ARTICLE EXPERIMENTAL/SPECIAL TOPICS

The Skin-Tightening Effects of 1,444-nm Nd:YAG Laseron Human Skin: An In Vivo Study

Kyung Hee Min • Ji Hoon Kim • Hyo Jin Park •

Heung Soo Chung • Chan Yeong Heo

Received: 17 December 2013 / Accepted: 31 March 2014 / Published online: 2 May 2014! Springer Science+Business Media New York and International Society of Aesthetic Plastic Surgery 2014

AbstractBackground The 1,444-nm Nd:YAG laser was developedto improve the removal of fat cells and to affect the

underlying dermis with the aim of skin tightening. We

conducted this study to evaluate whether this laser iseffective in tightening the skin and causing histological

alterations to dermal collagen fibers, fibroblasts, muco-

polysaccharides, and elastin.Methods In a 38-year-old patient who was scheduled to

undergo elective abdominoplasty, we subdermally per-

formed laser-assisted treatment with the 1,444-nmNd:YAG laser using different power settings over periods

of 3 months and 1 month and prior to surgery. Postopera-

tively, we evaluated the skin-tightening effect throughhistopathologic examination.

Results On histopathology examination, the thickness of

the dermis had gradually increased following the 3-monthtreatment with laser irradiation. In the treatment groups on

the abdomen, the collagen fibers were arranged in a more

parallel pattern and became denser than those in the control

group. Likewise, fibroblast proliferation and the levels ofmucopolysaccharides and elastin were higher in the treat-

ment groups than in the control group.

Conclusions The 1,444-nm Nd:YAG laser was effectivein promoting the remodeling of the dermis and the regen-

eration of collagen fibers. As such, the 1,444-nm Nd:YAG

laser could be used for skin tightening in addition to itsfunction in lipolysis.

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assign a level of evidence to each submission to whichEvidence-Based Medicine rankings are applicable. This

excludes Review Articles, Book Reviews, and manuscripts

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Keywords 1,444-nm Nd:YAG laser ! Laser lipolysis !Dermis

Introduction

Body contouring is one of the areas of expertise in the field

of plastic surgery. Various methods are used for fatreduction, including surgical lipectomy and less invasive

approaches (e.g., liposuction techniques). Some widely

used liposuction techniques include suction-assisted lipo-suction (SAL), ultrasound-assisted liposuction (UAL),

power-assisted liposuction (PAL), and laser-assisted lipo-

suction (LAL) [1]. To date, efforts have been made toidentify alternative methods and new tools that not only

can reduce the downtime, operative fatigue, and bleeding

K. H. MinDepartment of Plastic and Reconstructive Surgery, EuljiUniversity School of Medicine, Eulji General Hospital, Seoul,South Korea

J. H. Kim ! C. Y. Heo (&)Department of Plastic and Reconstructive Surgery, SeoulNational University Bundang Hospital, 300, Gumi-dong,Bundang-gu, Seongnam-si, Gyeonggi-do 463-707, Republic ofKoreae-mail: lionheo@snu.ac.kr

H. J. ParkDepartment of Pathology, Seoul National University BundangHospital, Gyeonggi, South Korea

H. S. ChungMidam Plastic Aesthetic Surgery Clinic, Seoul, South Korea

123

Aesth Plast Surg (2014) 38:585–591

DOI 10.1007/s00266-014-0316-4

associated with these procedures, but also promote skin

contraction [2].In laser-assisted liposuction, the energy is delivered

through a thin cannula and is then converted to thermal

energy within the subcutaneous layer, where adipocytesabsorb the energy. This eventually leads to the apoptosis

and necrosis of adipocytes. Concurrently, it is possible to

induce skin tightening through collagen remodeling byheating the subdermal and dermal tissues [3, 4].

The Nd:YAG (neodymium:yttrium-aluminum-garnet)and diode lasers are both lipolytic lasers that are currently

used in clinical settings. First described in 1994, Nd:YAG

laser lipolysis is currently one of the most popular laser-assisted lipoplasty methods in the world [5].

Several interstitial laser systems have been developed,

with wavelengths of 1,064, 1,320, and 1,444 nm [6–8]. Todate, it has been shown that a micropulsed 1,444-nm

Nd:YAG laser is highly effective in contouring the body and

face. A wavelength of 1,444-nm is inherently safe in laser-assisted lipolysis because of the higher degree of duality of

absorption by fat and water, which results in low thermal

diffusion to the tissue adjacent to the target area. From atheoretical standpoint, it has been suggested that a wave-

length of 1,444-nm can also be used more effectively for

laser-assisted lipolysis because its affinity to fat is more thanten times greater than that of a 1,064-nm equivalent [6].

In a previous study, we observed that a 1,444-nm

Nd:YAG laser induced dermal tissue remodeling in in vivoguinea pig models [9]. We expect that a skin-tightening

effect would be observed with clinical use of a 1,444-nm

Nd:YAG laser. Based on our previous animal study, weconducted the present study to evaluate, using histological

analysis, whether the 1,444-nm Nd:YAG laser would be

effective in achieving skin tightening.

Materials and Methods

A 38-year-old patient who was scheduled for electiveabdominoplasty gave informed consent for laser-assisted

treatment using the 1,444-nm Nd:YAG laser (Accu-

SculptTM, Lutronic Co., Goyang, Republic of Korea)

Fig. 1 Nine 4 9 4-cm areas were designed on the abdominal skin at 1-cm intervals and their borders were marked with tattoos

Fig. 2 Two entry points were incised at the lower border. Thecannula was then passed in a fan-shaped manner at 2-cm/s velocity

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followed by biopsy of skin samples collected during sub-

sequent abdominoplasty. Approval for the use of humantissues was granted by the Institutional Review Board at the

Seoul National University Bundang Hospital. Nine 4 9 4-

cm areas were designed on the abdominal skin with 1 cmbetween them and their borders were marked with tattoos

(Fig. 1). With the patient under mild sedation and local

anesthesia using 1 % lidocaine with a 1:200,000 epinephrinesolution, we subdermally performed laser-assisted treatment

using the 1,444-nm Nd:YAG laser (polyimide-coated,600-lm optic fiber, 200 mJ, 20–40 Hz) at different power

settings. Control (no power treatment), 4 W (200 mJ, 20 Hz)

and 40 J/cm2 (total energy = 640 J), and 8 W (200 mJ,40 Hz) and 20 J/cm2 (total energy = 320 J) were used

during a 3-month period, a 1-month period, and prior to the

scheduled abdominoplasty. Two entry points were incised atthe lower border. The cannula was then passed in a fan-

shaped manner with 2-cm/s velocity (Fig. 2).

Histopathologic Examination

Following standard abdominoplasty, excised skin from thelower abdomen was cut based on the marked squares and

the samples were placed in aqueous 10 % neutral buffered

formalin and then submitted for histological evaluation.The skin-tightening effect was evaluated by analyzing the

dermal thickness, collagen organization, fibroblast prolif-

eration, and the levels of mucopolysaccharides and elastin.More specifically, the tissue samples were stained with

hematoxylin and eosin for evaluation of dermal thickness

and fibroblast proliferation. Masson-trichrome stain wasused for evaluation of collagen organization. Toluidine

blue and Verhoeff’s stains were used for evaluation of the

levels of mucopolysaccharides and elastin.For evaluating collagen organization, all stained slides

were arranged according to the order of the density of col-

lagen fibers, from loose (grade 1) to dense (grade 3). Theproliferation of fibroblasts was assessed by counting the

number of fibroblasts in a high-power field (4009). The level

of mucopolysaccharides was shown by the degree of bluestaining; all stained slides were arranged according to the

degree of blue staining exhibited, from grade 1 to grade 3.

The level of elastin was used to evaluate the elastin contents,as shown by dark black strands. All stained slides were

arranged according to the extent of dark black strands they

displayed, from grade 1 to grade 3. All the histopathologicfindings were independently reviewed by an experienced

pathologist in a blinded setting [9].

Statistical Analysis

A one-way analysis of variance (ANOVA) test wasused to compare differences among the groups. The

repeated-measures analysis of variance (RMANOVA) test

was used to assess the differences over time in each group.Statistical significance was accepted for p values of\0.05.

Results

The postoperative course after the laser treatments wasuneventful except for mild erythema and bruising, both of

which resolved within a few days.

Dermal Thickness

One month and 3 months after the laser treatment, the

treatment groups showed significantly greater dermal

thickness compared to the control group. After 1 month oflaser treatment, the 8 W, 20 J/cm2 group showed signifi-

cantly greater dermal thickness than the 4 W, 40 J/cm2

group. Dermal thickness also increased significantly overtime in the treatment groups (Fig. 3).

Immediately after laser treatment, the dermis could have

been thickened due to swelling and hyalinization of dermalcollagen fibers. After that, the increase in dermal thickness

was due to dermal remodeling in treatment groups. On the

other hand, the dermal thickness of the control groupdecreased to its previous thickness.

Histologic Findings

For collagen organization, the grades in the treatment groups

were higher than that of the control group, but not to the levelof significance. One month after laser treatment using a set-

ting of 4 W and 40 J/cm2, dense collagen bundles were found

to be rearranged parallel to the direction of skin (Fig. 4).One month and 3 months after the laser treatment, the

fibroblast numbers in the treatment groups were signifi-

cantly higher than those in the control group. In the treat-ment groups, the number of fibroblasts was higher 1 month

after the laser treatment and thereafter slightly decreased or

maintained, nonsignificantly (Fig. 5). The mucopolysac-charide levels of the treatment groups were nonsignifi-

cantly higher than those of the control group 1 and

3 months after the laser treatment. Across all groups, themucopolysaccharide levels were increased 1 month after

laser treatment and thereafter they slightly but nonsignifi-

cantly decreased. One month after laser treatment using asetting of 4 W and 40 J/cm2, a greater number of blue-

stained mucopolysaccharides were seen in the dermis

(Fig. 6). The elastin levels of the treatment groups werenonsignificantly higher than those of the control group,

both immediately and 1 month after laser treatment. In the

treatment groups, the elastin level increased 1 month afterthe laser treatment and thereafter slightly decreased, at a

Aesth Plast Surg (2014) 38:585–591 587

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nonsignificant level. One month after laser treatment using

a setting of 4 W and 40 J/cm2, a greater number of darkblack stranded elastin could be seen in the dermis (Fig. 7).

Discussion

A wide variety of surgical and medical interventions havebeen reported for use in fat reduction, including ultrasound,

vibration, carbon dioxide injection, and mesotherapy for

the prevention of associated complications, in addition tothe traditional liposuction and lipectomy [10]. With its

advent, many authors have reported laser-assisted lipolysis

to be of great advantage compared to the traditional lipo-suction procedure. Katz et al. [11] suggest that skin laxity

might worsen following the use of conventional types of

liposuction. With the use of laser-assisted lipolysis,

however, skin laxity may be successfully treated. The main

advantages of laser-assisted lipolysis include less bleedingand pain, minimal damage to tissue, an earlier recovery,

and dermal tightening [12].

In laser-assisted lipolysis, heat is generated by laserabsorption by chromophores. This eventually leads to lysis

of the adipocyte membranes and dermal collagen [13, 14].

In an earlier study, Ichikawa et al. [10] used a pulsed1,064-nm Nd:YAG laser to irradiate freshly excised human

skin to remove the subcutaneous fat. They then histopa-

thologically demonstrated that this method was effectivefor the destruction of human fat tissue. Following the use of

the 1,064-nm Nd:YAG laser for submental liposuction,

Goldman [15] proposed that it might be effective for thetreatment of local lipodystrophy. He also noted that this

method was effective for cellular lysis and neocollagen

synthesis. McBean and Katz [7] conducted a clinical study

Fig. 3 Dermal thickness(*p \ 0.05)

Fig. 4 Left Collagen organization (grade) (*p \ 0.05). Right One month after laser treatment using a setting of 4 W and 40 J/cm2, densecollagen bundles were found to be rearranged parallel to the direction of skin

588 Aesth Plast Surg (2014) 38:585–591

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using a combination of a 1,064-nm laser and a 1,320-nm

laser. These authors showed that this method caused skin

shrinkage, which suggests another benefit of laser-assistedlipolysis. Compared with the other wavelengths that are

currently used for laser-assisted lipolysis (e.g., 1,064 and

1,320 nm), the 1,444-nm Nd:YAG laser offers numerousadvantages because of its greater specificity to subcutane-

ous fat and tissue water. Its greater selectivity provides

both an improved efficiency and a greater thermal con-finement (i.e., energy is relatively more localized to the

intended source), which are extremely important features

that make it possible to safely use this technology forsubregional facial contouring [8].

In an experimental study, Tark et al. [6] compared the

lipolytic effects of the 1,444-nm Nd:YAG laser with thoseof the 1,064-nm laser. They showed via histopathology that

there was marked reduction in the fat volume and an

increase in the number of oil vacuoles and giant cells fol-

lowing the use of the 1,444-nm Nd:YAG laser compared tothe 1064-nm one. In vitro experiments have also shown

that there were a greater number of oil vacuoles in human

fat following the use of the 1,444-nm laser [6].A clinical study was conducted by DiBernardo et al.

[16]. They reported that the appearance of cellulite in the

buttock and thigh was improved after a single treatmentwith a 1440-nm Nd:YAG laser with a novel side-firing

fiber during 6 months of follow-up and with minimal

adverse effects [16].Sasaki [17] conducted a clinical study using a 1,440-nm

Nd:YAG laser for treatment of grade II and III cellulite. That

study showed that results at 2 years demonstrated anincrease in the mean skin elasticity and the mean dermal

Fig. 6 Left The level of mucopolysaccharide (grade) (*p \ 0.05). Right One month after laser treatment using a setting of 4 W and 40 J/cm2, agreater number of blue-stained mucopolysaccharides were seen in the dermis

Fig. 5 The number offibroblasts in a high-power field(4009) (*p \ 0.05)

Aesth Plast Surg (2014) 38:585–591 589

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thickness. In the histology results, formation of new collagen

was also observed [17]. In our previous animal study, dermaltissue remodeling was observed in guinea pigs after irradi-

ation with the 1,444-nm Nd:YAG laser subdermally. Dermal

thickness increased with time in the treatment groups and inthe control group through 3 months. There were no signifi-

cant differences in dermal thickness between the groups. In

terms of collagen organization, fibroblast proliferation, andlevels of mucopolysaccharides and elastin, the treatment

groups showed higher results than those of the control group

overall [9]. In this study, fibroblast proliferation in thetreatment groups was significantly greater than that in the

control group. The levels of mucopolysaccharides and

elastin in the treatment groups were also higher than those inthe control group, but not to the level of significance. Like-

wise, the collagen in the dermis of the treatment groups wasdenser and had a greater parallel arrangement. Similar to the

results of the animal study, fibroblast proliferation and the

levels of mucopolysaccharides and elastin in the treatmentgroups were increased up to 1 month and thereafter

decreased, nonsignificantly. However, collagen organiza-

tion was not decreased after 3 months. Unlike in the animalstudy, the dermal thickness of the treatment groups was

greater than that in the control group and this significantly

increased over time.This result also showed that the use of a 1,444-nm

Nd:YAG laser promoted remodeling of the dermis.

This remodeling could be correlated with the wound-healing process, including extracellular matrix remodeling.

In the remodeling phase, the collagenous matrix becomes

organized into a thicker pattern by collagen cross-linking.Various growth factors that are released from the fat tissue

during lipolysis could induce dermal tissue remodeling

[18]. This could lead to a skin-tightening effect. Furtheranalysis of the gross changes in the skin (e.g., skin

elasticity) and more long-term analysis to confirm the skin-

tightening effect of the 1,444-nm Nd:YAG laser are rec-ommended. Likewise, comparative studies examining other

laser wavelengths are needed to confirm the superiority of

the 1,444-nm Nd:YAG laser.Despite the need for future research, there are early

indications that treatment with the 1444-nm Nd:YAG laser

could also be used for skin-tightening in addition to itswell-known indications for liposculpture of the face and

body.

Acknowledgments This research was supported by a grant fromLutronic Corporation, Republic of Korea.

Conflict of interest The authors declare that they have no conflictsof interest to disclose.

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