Targeted drug delivery is a promising application of microrobots owing to the capability of the microrobots to access nearly every region of the human body through the circulatory system. Research on microrobots over the past few decades has enabled substantial advances in the design of both the untethered microrobots swimming in a biofluid and the related mechanisms to carry and release therapeutic agents in a controlled manner. This paper presents a comprehensive review of the technological state of the art in untethered microrobots for targeted drug delivery applications. First, the in vivo microrobot locomotion techniques are discussed with respect of the different types of actuation energy sources such as magnetic fields, motile microorganisms, acoustic waves, and chemical reaction, outlining the respective advantages and major limitations. Subsequently, recent progress in various technologies of microrobot-driven targeted drug delivery is surveyed deliberating on the corresponding drug manipulation mechanisms: magnetically driven, motile microorganisms-driven, acoustic-aided, and stimuli-responsive hydrogels-aided. Although most studies on microrobot-driven targeted drug delivery were carried out in vitro, few among them successfully demonstrated in vivo operations in living animals. In the concluding section, current challenges and future perspectives of the microrobot-driven targeted drug delivery technology are discussed.

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TUI for failed MUS demonstrated a low cure rate but high patient satisfaction, and the procedure was minimally invasive with no significant complications.

• ADC from DW-MRI can help assess prostate cancer aggressiveness in potential AS candidates. • There was a closed correlation between higher ADC values and insignificant prostate cancer. • The absence of lesions on DWI/DWI can help select potential AS candidates.