SSA-MOA: a novel CTC isolation platform using selective size amplification (SSA) and a multi-obstacle architecture (MOA) filter

Abstract

Circulating tumor cells (CTCs) have gained increasing attention as physicians and scientists learn more about the role these extraordinarily rare cells play in metastatic cancer. In developing CTC technology, the critical criteria are high recovery rates and high purity. Current isolation methods suffer from an inherent trade-off between these two goals. Moreover, ensuring minimal cell stress and robust reproducibility is also important for the clinical application of CTCs. In this paper, we introduce a novel CTC isolation technology using selective size amplification (SSA) for target cells and a multi-obstacle architecture (MOA) filter to overcome this trade-off, improving both recovery rate and purity. We also demonstrate SSA-MOA's advantages in minimizing cell deformation during filter transit, resulting in more stable and robust CTC isolation. In this technique, polymer microbeads conjugated with anti-epithelial cell adhesion molecules (anti-EpCAM) were used to selectively size-amplify MCF-7 breast cancer cells, definitively differentiating from the white blood cells (WBCs) by avoiding the size overlap that compromises other size selection methods. 3 μm was determined to be the optimal microbead diameter, not only for size discrimination but also in maximizing CTC surface coverage. A multi-obstacle architecture filter was fabricated using silicon-on-glass (SOG) technology-a first such application of this fabrication technique-to create a precise microfilter structure with a high aspect ratio. The filter was designed to minimize cell deformation as simulation results predicted that cells captured via this MOA filter would experience 22% less moving force than with a single-obstacle architecture. This was verified by experiments, as we observed reliable cell capture and reduced cell deformation, with a 92% average recovery rate and 351 peripheral blood leukocytes (PBL) per millilitre (average). We expect the SSA-MOA platform to optimize CTC recovery rates, purity, and stability, increasing the sensitivity and reliability of such tests, thereby potentially expanding the utilization of CTC technologies in the clinic.

Whole-blood sorting, enrichment and in situ immunolabeling of cellular subsets using acoustic microstreaming

“…Another promising category of microfluidic systems is "label-free", and they are able to sort blood cells based on their sizes using known techniques such as deterministic lateral displacement (DLD) 22,42 , inertial microfluidics 43 , and acoustophoresis 20,21,44 . However, recent developments in oncology have shown heterogeneity and great size overlap between rare cells such as CTCs and healthy WBCs 19,45 . Being able to separate blood cell sub-populations with fine resolution to define a size threshold that ensures~100% capture of targeted rare cells, and then identify the targeted cells within this concentrated population via gentle immunolabeling in situ is a powerful combination of techniques needed for liquid biopsy.…”

“…These technologies typically require pre-processed samples and cannot handle the physical properties and complex populations inherent in whole blood [6][7][8][9][10] . They are limited to either diluted 11,12 or lysed blood 13,14 , and in some cases, density based centrifugation to reduce blood complexity and cell-cell interaction [15][16][17][18][19][20][21] . The microfluidic cell sorting technologies that can handle whole blood, in general fall into two categories: label free sorting based on physical characteristics of the target cells or biomarker labeling.…”

Label-free isolation of circulating tumor cells in microfluidic devices: Current research and perspectives

“…A very efficient separation of the tumor cells was observed for a 5 lm gap. A microfluidic system using multi-obstacle architecture for size-dependent separation of CTCs has also been developed, 29 but in this case polymer microbeads conjugated with Membrane-based filtration is one of the first methods used for CTC enrichment and represents a relatively straightforward and low cost technique. The technique is based on the principle that malignant cells are larger than other blood cell populations.…”

Anti-Cancer Drug Assay for Micro-Ellipse Filters after Sensitively Capturing Circulating Tumor Cells

“…Many filters with high purity have been expored, microfluidic funnel rachets [5], microfluidic rachets [6] and a multi-obstacle architecture (MOA) filter [7]. Microposts are in the shape of square [8], rectangular [9] or weir-style [10].…”