Local control of magnetic microbubble behavior by magnetic field and pulsed ultrasound

The localization of magnetic microbubbles (MMBs) to a target site has been shown to be essential to their efficacy in therapeutic applications such as targeted drug delivery and gene therapy. In this work, the MMBs' dynamic equations of vibration, horizontal and vertical motion in a fluid-filled tube, subject to a magneto-acoustic complex field, are established by Lagrange method. The responses and capture efficiency under three ultrasonic pulses waveform in a magnetic field are numerically analyzed. The regulation effects of the external field are observed by experiments. The results show that the transport behavior is influenced by bubble size, original position, liquid flow rate, tube diameter, parameters of acoustic and magnetic field. For the same acoustic parameters, square wave pulse can make stronger vibrate compared with cosine wave and sawtooth wave, which pushes MMBs closer to the magnet. In addition, high frequency and large amplitude pulse are benefit to translation, and increasing the cycle number in a single pulse can also promote translation. In practical applications, variable parameters such as bubble speed and magnet length can be used to improve the capture efficiency. The observations of high-speed camera are consistent with the prediction of theoretical model, which indicates the model is mostly correct.