Microfluidic device for continuous deformability based separation of circulating tumor cells

Circulating tumor cells have been implicated as potential seeds of cancer metastasis and have strong prognostic and diagnostic value in cancer therapy. The primary challenge in CTC characterization is their extreme rarity in circulation relative to leukocytes. Conventional strategies employ CTC immunoenrichment that is highly selective but may fail to enrich for CTCs with poor antigen expression. However, CTCs exhibit unique morphological characteristics that distinguish them from leukocytes and deformability-based sorting mechanisms represent a compelling label-free CTC enrichment strategy. Our group previously reported the microfluidic ratchet mechanism capable of highly selective deformability based cell separation without clogging. Here, we developed a continuous version of this process that obviates the need for microvalves and operate with dramatically increased throughput. Implementation of the microfluidic ratchet consists of a matrix of funnel constrictions with microchannels for flow control. The openings of the funnel constrictions are gradually reduced from the bottom row to the top row. Cells enter at the bottom-left of the funnel matrix and are driven by a rightward flow simultaneously as a vertical oscillatory flow. Each cell traverses through the funnel matrix in a step-wise diagonal path until reaching a limiting funnel size. CTCs are the least deformable cells and reach their limiting funnel size relatively quickly. Leukocytes are more deformable and travel to a smaller funnel region. Finally, erythrocytes are extremely deformable and exit through the top row. We evaluated the selectivity of this mechanism using UM-UC13 bladder cancer cells doped into whole blood from healthy donors. UM-UC13 cells were enriched by ~10⁴ relative to leukocytes, with ~90% capture efficiency, and thus demonstrate significantly greater selectivity than separation based solely on size. We used the microfluidic ratchet device to enumerate CTCs from 58 samples with 52 patients with castrate resistant prostate cancer, in parallel with CellSearch, and 6 healthy control samples. The CTC capture rate is significantly higher for our device, which detected ≥5 CTCs in 67.3% of patients with an average count of 256, while the CellSearch system detected ≥5 CTCs in 40.4% of patients with an average count of 74.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat