UC San Diego

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.