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マルチフィジックスシミュレーションによる非破壊美容処置の設計

CoolSculpting® and CoolTone® are separate noninvasive medical aesthetic procedures designed to eliminate targeted subcutaneous fat and strengthen muscles, respectively. Allergan Aesthetics is using heat transfer and electromagnetics simulation to enhance these processes.


By Rachel Keatley
March 2021

In the 1970s, it was observed that an infant can develop dimples in their cheeks after eating popsicles. Why? When exposed to the cold treat, some of the infant's fat cells would die, causing a small indent to form (Ref. 1). Decades later, this phenomenon, known as "popsicle panniculitis", helped inspire the foundation of a noninvasive fat reduction treatment: CoolSculpting®. Invented by Dr. Dieter Manstein and Dr. Rox Anderson of Harvard Medical School, CoolSculpting® targets and kills fat cells without damaging the surrounding tissue using a fat-freezing method known as cryolipolysis.

Joel Jimenez Lozano, PhD, a senior scientist at Allergan Aesthetics, an AbbVie company, helps design CoolSculpting® technology. "This procedure cools treated fat cells to prespecified temperatures with an applicator. These fat cells crystallize, then die through apoptosis. The dead fat cells are gradually removed by our own body's natural processes," says Jimenez Lozano. With minimal to no downtime required postprocedure, CoolSculpting® has become a highly sought fat elimination treatment in recent years. The procedure is cleared by the FDA for the treatment of various body areas, including the abdomen, back, flanks, thighs, and upper arms, as well as under the chin and jawline.

More recently, Allergan Aesthetics developed another procedure to add to its roster: CoolTone®, a nonsurgical body contouring procedure designed to help strengthen and tone muscles with magnetic muscle stimulation. Currently, this treatment is FDA cleared to treat abdomen, thigh, and gluteal muscles.

To design optimized applicators for the CoolSculpting® treatment and to gain a deeper understanding of the magnetic phenomena involved in the CoolTone® procedure, Jimenez Lozano and his team are using simulation.

Freezing Fat with Plates and Cups

In the early years of the CoolSculpting® technology, a patient's tissue and fat cells would be subjected to cold temperatures for 60 minutes with parallel cooling plate technology. These applicators would hold the tissue in place with vacuum suction. Although the cooling plates functioned properly, customers wanted better results and shorter treatment times.

"Now, we offer a cup-shaped applicator design, which provides efficient heat extraction from the treatment area when using the CoolSculpting® system," said Jimenez Lozano. The cooling cup applicators are metallic, use thermoelectric cooling technology, and come in different sizes. "The cups were designed so that clinicians can cool the whole fat bulge, not just the fat between the parallel plates."

Figure 1. The CoolSculpting® Elite System is composed of a portable control unit with a user interface (left) and has different cup applicator sizes for use (right).

In addition to providing patients with a more comfortable procedure, the cup applicators have reduced the treatment time from 60 to 35 minutes. For body areas where a clinician cannot draw tissue into a vacuum cup, such as the lateral thighs, a 3-panel flat applicator is available for use. Prior to the fabrication of these improved applicators, Jimenez Lozano and his team analyzed their designs with heat transfer simulation.

Enhancing CoolSculpting® Technology with Heat Transfer Simulation

In order to design optimized cooling cup applicators, it is important to understand how a patient's tissue interacts with these cups at various temperatures. However, measuring this interaction in real life can be uncomfortable for patients. Simulation can help avoid this issue. In his work, Jimenez Lozano studies tissue temperatures and their transient changes during the CoolSculpting® treatment. He aims to enhance the performance of the CoolSculpting® cooling cups, while preserving their safety. With the COMSOL Multiphysics® simulation software and add-on Heat Transfer Module, he models the cooling cups and tissue interactions during the CoolSculpting® treatment.

Figure 2. A simulation of the temperature distribution in tissue during the CoolSculpting® treatment.

In order to validate his models, Jimenez Lozano uses clinical data. "Once you validate a model, you are more comfortable making predictions about your designs," said Jimenez Lozano. "The extent of cryolipolytic injured fat tissue assessed by the temperatures reached in our tissue model agreed with our human histological measurements" (Ref. 2).

With the information gained from the simulations, Allergan Aesthetics was able to improve the designs of their applicators, in turn cutting down on their treatment times. The improved technology can be found in medical spas, dermatology offices, and plastic surgery practices around the world.

CoolTone® Technology

The use of simulation at Allergan Aesthetics does not stop with CoolSculpting® technology. Jimenez Lozano and his team also use it for optimization of the recently developed CoolTone® system.

Figure 3. The CoolTone® system is composed of a portable control unit with a touchscreen display and two applicators (left). A closeup view of a CoolTone® applicator (right).

"It is not about fat, it is about muscle," Jimenez Lozano says to describe the noninvasive CoolTone® procedure. "CoolTone® produces an electromagnetic field that interacts with the targeted tissue. It induces an electrical current on the muscle, which produces muscle contractions and can eventually strengthen, tone, and firm the muscle."

Figure 4. A simulation showcasing a peak magnetic field (curved lines) and an induced electric field in the abdominal muscles during the CoolTone® treatment (left). An anatomical CAD model, featuring a CoolTone® applicator (right). CAD models can be analyzed in COMSOL Multiphysics® with the add-on CAD Import Module.

In order to get a deeper understanding of the physics behind electromagnetic muscle stimulation and the effects electric currents have on tissue, the team uses electromagnetics simulation. "To really know how the magnetic field interacts in the tissue, you have to model it," said Jimenez Lozano. When modeling the muscles, abdomen, and skin, the research team uses realistic, anatomically accurate geometries. Overall, these simulations improve the understanding of applicator components and their electromagnetic performance to target muscle groups.

Democratizing Simulation

At Allergan Aesthetics, Jimenez Lozano and his team use simulation applications to showcase their heat transfer and electromagnetics simulation work to internal specialists and nonspecialists alike. Apps are built with the Application Builder in COMSOL Multiphysics®. "Communicating with somebody who does not use COMSOL® in their work is easier with apps," said Jimenez Lozano.

Figure 5. A simulation application designed by Jimenez Lozano to investigate tissue temperatures at different parameters during the CoolSculpting® treatment.

For instance, when showing a nonspecialist a simulation application of a CoolSculpting® applicator cooling cup, it is easy for Jimenez Lozano to quickly demonstrate how changing certain parameters, like the treatment time or temperature of the cups, will affect the outcome of the procedure. Allergan engineers also use apps to present their work at conferences, and in some cases, provide supporting data for regulatory agency submissions.

The Future of the Cosmetic Procedure Industry

As for the future, Allergan Aesthetics plans to continue to work on new products and to improve the understanding of device function and device–tissue interaction.

In the United States, over 16.3 million minimally invasive and/or noninvasive cosmetic procedures were performed in 2019 — a number that has more than tripled over the past two decades (Ref. 3). Jimenez Lozano believes noninvasive procedures will continue to grow in popularity thanks to their ability to nonsurgically target and treat specific areas on the body with short recovery times.

Acknowledgements

Joel Jimenez Lozano would like to thank all whose engineering work, research, and support contributed to the development of the technology presented in this article. In addition, Jimenez Lozano would like to extend a special thank you to George Frangineas, executive director of the Advanced Development team at Allergan Aesthetics; Linda Pham, PhD; Peter Yee; Like Zeng, PhD; and Andrew Wong, Paul Allan, and Tuan Mai, members of the Advanced Development team.

References

  1. Epstein and M. Oren, "Popsicle Panniculitis", The New England Journal of Medicine, vol. 282, 17, pp. 966–7, 1970.
  2. Jimenez Lozano, J., Assessment of Subcutaneous fat injury, depth of injury and temperature threshold after cryolipolysis, Lasers in Surgery and Medicine, Vol. 51, S30, Abstracts 39th ASLMS Conference, February 2019.
  3. "Plastic Surgery Statistics Report", American Society of Plastic Surgeons®, 2019.

COOLSCULPTING® and COOLTONE® are trademarks of Zeltiq Aesthetics, Inc., an AbbVie Company.