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.

No abstract

No abstract

a b s t r a c tThis paper presents a tunable liquid iris based on electromagnetic actuation for miniature cameras in mobile devices such as smart phones and pads. To investigate the effect of a magnetic field on a ferrofluid, contact angle modification and transportation of a sessile ferrofluid droplet are tested using a neodymium magnet and an electric coil. The variation in the contact angle of the ferrofluid droplet is 21.3 • for the neodymium magnet and 18.1 • for the electric coil. In addition, transportation of the ferrofluid droplet is also demonstrated using the neodymium magnet and the electric coil. As a proof of concept, a pretest of a tunable iris operated by electromagnetic actuation is conducted by using a hollow cylinder cell. Initially, the ferrofluid is in a relaxed state, so the cylinder cell shows the largest aperture (4.06 mm). When an electric current is applied to an electric coil wound around the outside of the cylinder cell, the ferrofluid, which is initially placed in the hydrophobic sidewall inside the cylinder cell, is actuated and pulled to the center. The aperture diameter under the applied current is modified from 4.06 mm at 0 A to 3.21 mm at 2.0 A. Finally, a tunable iris, consisting of two connected circular microchannels, is realized using MEMS technology. The iris size is 9 mm × 9 mm × 2 mm, and the aperture diameter can be varied from 1.72 mm at 0 A to 1.09 mm at 2.6 A. The response times of the iris for actuation and relaxation are measured by a high-speed camera and found to be 250 ms and 450 ms, respectively.

No abstract