Hydrodynamic Cavitation on a Chip: A Tool to Detect Circulating Tumor Cells

Abstract

Circulating tumor cells (CTCs) are essential biomarkers for cancer diagnosis. Although various devices have been designed to detect, enumerate, and isolate CTCs from blood, some of these devices could have some drawbacks, such as the requirement of labeling, long process time, and high cost. Here, we present a microfluidic device based on the concept of “hydrodynamic cavitation-on-chip (HCOC)”, which can detect CTCs in the order of minutes. The working principle relies on the difference of the required inlet pressure for cavitation inception of working fluids when they pass through the microfluidic device. The interface among the solid/floating particles, liquid, and vapor phases plays an important role in the strength of the fluid to withstand the rupture and cavitation formation. To this end, four experimental groups, including the “cell culture medium”, “medium + Jurkat cells”, “medium + Jurkat cells + CTCs”, and “medium + CTCs”, were tested as a proof of concept with two sets of fabricated microfluidic chips with the same geometrical dimensions, in which one set contained structural sidewall roughness elements. Jurkat cells were used to mimic white blood cells, and MDA-MB-231 cells were spiked into the medium as CTCs. Accordingly, the group with CTCs led to detectable earlier cavitation inception. Additionally, the effect of the CTC concentration on cavitation inception and the effect of the presence of sidewall roughness elements on the earlier inception were evaluated. Furthermore, CTC detection tests were performed with cancer cell lines spiked in blood samples from healthy donors. The results showed that this approach, HCOC, could be a potential approach to detect the presence of CTCs based on cavitation phenomenon and offer a cheap, user-friendly, and rapid tool with no requirement for any biomarker or extensive films acting as a biosensor. This approach also possesses straightforward application procedures to be employed for detection of CTCs.

The integrated on-chip isolation and detection of circulating tumour cells

“…122) and detection limits as low as 2 cells per mL whole blood (Table 2). 117 The majority of CTC isolation methods in integrated platforms rely on immuno-affinity, 112,114,115,118,120,122 but others, based on cell deformability, 138 inertia force, 41 and size variance 158 have been documented. Integrated detection methods range from direct imaging of a transparent PDMS chip, often employing some derivative of immunofluorescent staining, to electrochemical detection using electrodes embedded within the platform.…”

“…114 Detection limits for optical means typically range from 1-50 cells per mL of whole blood, 41,56,115,116,118,120,121,139 with physical methods somewhat poorer. 138,158 4.1 Future directions in integrated CTC isolation & detection While scalable and potentially very cost-effective integrated platforms hold great promise for supporting high capture efficiency and sensitivities high enough to detect as low as 1 cell per mL, such methods are early in development and have yet to translate into clinical practice. Reducing the turnaround time to less than 1 hour per sample (rather than the ∼1/2 day typically associated with a CellSearch analysis) and substantially lowering cost and increasing reliability would enable the application of this currently prohibitively expensive technique to routine clinical practice.…”

“…Purely physical methods of CTC analysis/assaying remain rare, and are associated with relatively poor detection limits. 138,158 While the long-standing optical method of detection via IF imaging sensitive, 116,121 this comes with inherent time and throughput challenges, as discussed in section 3. 116,121 Simple forms of optical assay such as brightfield 142 or up-conversion luminescence imaging 118 can be chip-integrated offer reduced labour and time, but these do not offer any phenotypic or profiling information about the captured CTCs.…”

“…94,157 These do not employ immunorecognition agents or staining protocols and therefore have a rapid TAT when compared to methods that do (i.e., immediate detection with high-speed camera or pressure gauge). 138,158 Physical methods of CTC detection have been less frequently reported (integrated or otherwise), but one non-integrated example utilised specialised software to confirm CTC identity following isolation with CellSearch® based on size, nuclearcytoplasmic ratio, and elongation (i.e., cell morphology). 94 These technologies have not yet been widely adopted, however a few examples of physical CTC detection on integrated platforms are discussed below (section 3.2.3).…”

“…This was shown to be reduced when CTCs were present, despite the presence of Jurkat cells as models for healthy WBCs. 158 Pressure variation was explained by the heterogeneous nucleation theorem, whereby cells act as stream nucleation sites for the generation of bubbles in the liquid sample. While this offers a unique method of physical CTC detection, no metrics of platform performance (i.e., capture efficiency or purity) were published other than the detection limit.…”