Leveraging the Photothermal Effect for Cosmetic Applications

The photothermal effect is a phenomenon in which matter absorbs light energy and converts it into heat. This process can be leveraged to enable the application of light for biological applications, especially for otherwise benign light with wavelengths in the “optical window” regime of the electromagnetic spectrum between 700-900 nm that can penetrate deeply into tissue. The objective of this dissertation work was to apply and adapt the photothermal effect in the context of cosmetic surgery in a safe and effective manner to aid in fat removal during liposuction. This thesis begins with a discussion of an area in which the photothermal effect has been applied extensively in biology, specifically, for the eradication of cancer, called photothermal therapy. Materials used for this application, known as photothermal agents, are briefly introduced. Light-matter interactions, including a variation of the photothermal effect called selective photothermolysis, are discussed in detail. Chapter One introduces an example where the photothermal effect was observed to be the key underlying mechanism enabling the release of encapsulated payloads from inherently non-light responsive polymer particles in the context of drug delivery. In Chapter Two, starting from basic engineering principles, specifically the heat equation, the photothermal effect is derived and mathematically modeled. Subsequently, the ability to achieve selective and confined photothermal heating in a target pigmented region was tested in a physical model involving a thermoresponsive polymer as an indicator to allow for simple visualization. After successful demonstration of these concepts, parameters such as photothermal agent concentration and manner of light exposure were optimized, and subsequent studies were performed in an ex vivo porcine tissue, in an in vivo porcine model, and finally, in an ex vivo human adipose tissue liposuction model. This work culminated in a single-blind study in human adipose tissue comparing photothermally assisted liposuction (dubbed NanoLipo), to a control involving saline injection and near infrared light laser-assisted liposuction absent gold nanoparticles. The results achieved in this work demonstrate the significant potential of this promising technology in making a clinical impact

Gold Nanoparticle-assisted Selective Photothermolysis of Adipose Tissue (NanoLipo)

Background: Conventional suction-assisted lipectomy (SAL) often results in contour irregularity. Selective photothermal heating of adipose tissue by polymer-coated gold nanorods energized by an external near-infrared exposure at 800 nm is introduced in this work to facilitate fat removal. Methods: The effects of NanoLipo were examined in food-grade porcine abdominal tissue (skin, fat, and fascia) by histology. The efficacy of NanoLipo was compared with that of conventional SAL in vivo in Yucatan mini pigs by quantification of removed subcutaneous tissue and fatty acids and ultrasound measurement of adipose layer thickness. Results: NanoLipo led to the appearance of disruptions in adipose tissue that were not apparent in control groups in ex vivo samples. NanoLipo allowed removal of more subcutaneous tissue (~33% vs ~25% of removed material, P < 0.05) and approximately twice as much free fatty acids (~60% vs ~30% of removed tissue, P < 0.05) in comparison with conventional SAL. Most importantly, NanoLipo led to a greater decrease in adipose layer thickness at 1 month post surgery (P < 0.001). Conclusions: NanoLipo facilitates removal of a greater quantity of fat and requires less suction time (4 vs 10 minutes) than conventional SAL. As the safety of poly(ethylene-glycol)-coated gold nanorods is well-established, a clinical trial is currently being organized

Near-Infrared-Induced Heating of Confined Water in Polymeric Particles for Efficient Payload Release

Near-infrared (NIR) light-triggered release from polymeric capsules could make a major impact on biological research by enabling remote and spatio­temporal control over the release of encapsulated cargo. The few existing mechanisms for NIR-triggered release have not been widely applied because they require custom synthesis of designer polymers, high-powered lasers to drive inefficient two-photon processes, and/or coencapsulation of bulky inorganic particles. In search of a simpler mechanism, we found that exposure to laser light resonant with the vibrational absorption of water (980 nm) in the NIR region can induce release of payloads encapsulated in particles made from inherently non-photo-responsive polymers. We hypothesize that confined water pockets present in hydrated polymer particles absorb electromagnetic energy and transfer it to the polymer matrix, inducing a thermal phase change. In this study, we show that this simple and highly universal strategy enables instantaneous and controlled release of payloads in aqueous environments as well as in living cells using both pulsed and continuous wavelength lasers without significant heating of the surrounding aqueous solution