This work presents a study of polymeric microdevices implemented by piezoelectric actuators to carry out processes of sorting/separation on flowing suspensions, acting as acoustic tweezers to extract separately target particles or cells. They provide a low-cost and label-free platform, exploiting the difference of size, density and compressibility. Their ability to perform isolation of tumor cells from white blood cells makes them strategic tools for medical applications such as early detection or future tools for monitoring personalized chemotherapy. Polymer-based microdevices implemented by ultrasounds have been developed to isolate these cells with an efficiency level up to 70%. This technology is currently being optimized to reach efficiencies higher than 90% for its clinical application.