Introduction

 As a leading cause of mortality worldwide, tens of millions of people suffer from various cancers each year and the number is still ever-increasing.  \cite{Ormel2018,Sung2021,Bray2021}Due to its high fatality rate in later stages, timely treatment is strongly suggested once malignant cancer is detected. Compared to other standard treatment modalities (e.g., chemotherapy and radiotherapy) that might cause severe side effects,\cite{Miller2019,Barazzuol2020,kong2018}radiofrequency ablation (RFA) is regarded as a promising minimally invasive cancer treatment with relatively gentle side effects and has been widely used for years,\cite{Ni2005,Kok2020} particularly for small sized ones (radius smaller than 3 cm). During RFA treatments, a key point lies in the generation of ideal RFA lesions that cover specific areas/volumes where target tissues exist. For large areal and highly efficient ablations, intensive efforts have been made for the development of new devices, such as expandable multi-tined electrodes and perfusion electrodes\cite{Chang2010,Tins2006,Gulesserian2006,Ihara2016,Ni2000,Nguyen2017,Kettenbach2003,Burdío2007,Topp2004}. Although these devices can effectively ablate the target tissue either by increasing the surficial area of electrode (e.g., expandable multi-tined electrodes) or by cooling the overheated surface of electrode (e.g., perfusion electrode), the shape of RFA lesions are almost same and cannot be adjusted for target tissues that are irregularly shaped.\cite{Chen2017,torrents-barrena2020,Golston1992,Mazurowski2017} They usually end up with unnecessarily excessive ablation and often brings irreversible damage to the organs’ functions. Therefore, in the clinical practice, conformal RFA lesions is desired since it can shorten the time that patients take to recover and improve their live quality, especially for the organs, e.g., kidney, that have limited capability to regenerate after injury.\cite{Chou2014}
To satisfy the diverse morphologic demanded in RFA lesions, several groups proposed various designs. Among them, the most influential strategy is to utilize multiple electrodes.\cite{Takaki2013,Laeseke2006,Ritz2006,Peng2011} The multiple electrodes strategy, which distinguishes from multi-tined electrode strategy, simultaneously insert several electrodes into the body, and a pre-programmed alternative current is then used to energize the electrodes. The deployment of these electrodes can be delicately designed to better conform to the target tissues and avoid some unnecessary injuries of other organs. However, the classic single polar electrode, as well as the bipolar electrode, usually leads to multiple insertions into the body and increase the pain of patients. \cite{Takaki2013,Laeseke2006,Ritz2006,Peng2011} What’s more, the precise deployment of these electrodes is complex and the electrodes have to be supported by other tools to ensure the correct relative position.\cite{Ritz2006,Peng2011} Hence, an operationally simple RFA device is urgently needed to achieve on-demand conformal ablation of diverse shaped target tissues in a highly efficient way.
Herein, we present an individually-controlled multi-tined expandable electrode for on-demand conformal RFA of target tissues, Figure 2A. Our electrode is designed with three tines (sub-electrodes), each of which consisting of an active cannulas and pre-curved stylet. The independent tunability and following interactions of stylets and cannulas enable our electrode to morph diverse shapes, and therefore the trajectory of individual sub-electrodes can be predicted according to the expanded length. Combined with rational energy control, various morphing shapes can result in diverse sizes and shapes of RFA lesions, Figure 1B. The ex vivo irregular RFA lesions ablated by our electrode is more conformal than that ablated by a commercial one. Ultrasound-guided experiments further validate that our proposed electrode can change the morphologic appearance (diverse ablation volumes in different shapes) of RFA lesions to match the target tissue on demand.