The dissemination of primary solid tumor cells to distant organs, termed metastasis, is a major cause of cancer-related deaths. Circulating tumor cells (CTCs), which can exist as individual cells or multicellular clusters, travel through the bloodstream. Their isolation from liquid biopsy samples is increasingly recognized as a valuable tool for diagnosis, prognosis, and treatment guidance for cancer patients. Current isolation methods typically rely on biomarkers like epithelial cell adhesion molecule (EpCAM) and utilize technologies such as magnetic beads or microfluidic chips. However, these methods face limitations due to tumor heterogeneity. Furthermore, tumor cells that transfer into CTCs often undergo epithelial-to-mesenchymal transition, gaining invasive characteristics while losing epithelial markers. As a result, these cells are difficult to detect using EpCAM-based methods. Label-free microscale isolation technologies tackle the limitations of biomarker-based methods by leveraging the distinctive physical properties of CTCs, such as their size, electrical charge, viscoelasticity, and deformability that contrast them from normal blood cells. This review evaluates primary label-free isolation methods, including deterministic lateral displacement, microfiltration, acoustophoresis, and dielectrophoresis, and whether they can offer a deeper insight into tumor heterogeneity and the dynamics of cancer progression and treatment. Additionally, it highlights automated platforms for high-throughput CTC isolation and analysis.

Organ-on-a-chip (OoC) devices require the precise control of various media. This is mostly done using several fluid control components, which are much larger than the typical OoC device and connected through fluidic tubing, i.e., the fluidic system is not integrated, which inhibits the system’s portability. Here, we explore the limits of fluidic system integration using off-the-shelf fluidic control components. A flow control configuration is proposed that uses a vacuum to generate a fluctuation-free flow and minimizes the number of components used in the system. 3D printing is used to fabricate a custom-designed platform box for mounting the chosen smallest footprint components. It provides flexibility in arranging the various components to create experiment-specific systems. A demonstrator system is realized for lung-on-a-chip experiments. The 3D-printed platform box is 290 mm long, 240 mm wide and 37 mm tall. After integrating all the components, it weighs 4.8 kg. The system comprises of a switch valve, flow and pressure controllers, and a vacuum pump to control the diverse media flows. The system generates liquid flow rates ranging from 1.5 μ Lmin ^{- 1} to 68 μ Lmin ^{- 1} in the cell chambers, and a cyclic vacuum of 280 mbar below atmospheric pressure with 0.5 Hz frequency in the side channels to induce mechanical strain on the cells-substrate. The components are modular for easy exchange. The battery operated platform box can be mounted on either upright or inverted microscopes and fits in a standard incubator. Overall, it is shown that a compact integrated and portable fluidic system for OoC experiments can be constructed using off-the-shelf components. For further down-scaling, the fluidic control components, like the pump, switch valves, and flow controllers, require significant miniaturization while having a wide flow rate range with high resolution.

Reciprocating piezoelectric micropumps enable miniaturization in microfluidics for lab-on-a-chip applications such as organs-on-chips (OoC). However, achieving a steady flow when using these micropumps is a significant challenge because of flow ripples in the displaced liquid, especially at low frequencies or low flow rates (<50 µL/min). Although dampers are widely used for reducing ripples in a flow, their efficiency depends on the driving frequency of the pump. Here, we investigated multi-phase rectification as an approach to minimize ripples at low flow rates by connecting piezoelectric micropumps in parallel. The efficiency in ripple reduction was evaluated with an increasing number (n) of pumps connected in parallel, each actuated by an alternating voltage waveform with a phase difference of 2π/n (called multi-phase rectification) at a chosen frequency. We introduce a fluidic ripple factor ((Formula presented.)), which is the ratio of the root mean square ((Formula presented.)) value of the fluctuations present in the rectified output to the average fluctuation-free value of the discharge flow, as a metric to express the quality of the flow. The fluidic ripple factor was reduced by more than 90% by using three-phase rectification when compared to one-phase rectification in the 2–60 μL/min flow rate range. Analytical equations to estimate the fluidic ripple factor for a chosen number of pumps connected in parallel are presented, and we experimentally confirmed up to four pumps. The analysis shown can be used to design a frequency-independent multi-phase fluid rectifier to the desired ripple level in a flow for reciprocating pumps.

Microfluidic organs-on-chips (OoCs) technology has emerged as the trend for in vitro functional modeling of organs in recent years. Simplifying the complexities of the human organs under controlled perfusion of required fluids paves the way for accurate prediction of human organ functionalities and their response to interventions like exposure to drugs. However, in the state-of-the-art OoC, the existing methods to control fluids use external bulky peripheral components and systems much larger than the chips used in experiments. A new generation of compact microfluidic flow control systems is needed to overcome this challenge. This study first presents a structured classification of OoC devices according to their types and microfluidic complexities. Next, we suggest three fundamental fluid flow control mechanisms and define component configurations for different levels of OoC complexity for each respective mechanism. Finally, we propose an architecture integrating modular microfluidic flow control components and OoC devices on a single platform. We emphasize the need for miniaturization of flow control components to achieve portability, minimize sample usage, minimize dead volume, improve the flowing time of fluids to the OoC cell chamber, and enable long-duration experiments.

Piezoelectric micropumps enable miniaturization in microfluidics for lab-on-a-chip applications such as Organs-on-chips (OoC). However, achieving a steady flow with these micropumps is a significant challenge because of the reciprocating motion of the displacing component. Although dampers are widely preferred for reducing ripples, they are not efficient at low flow rates. Here, we propose a phased-actuation of piezoelectric micropumps connected in parallel and a damper to minimize ripples at low flow rates. We are able to reduce ripples by 80% with our proposed configuration compared to a micropump-only configuration between 10-50 μl/min flow rate range.

Microvalves are important flow-control devices in many standalone and integrated microfluidic applications. Polydimethylsiloxane (PDMS)-based pneumatic microvalves are commonly used but they generally require large peripheral connections that decrease portability. There are many alternatives found in the literature that use Si-based microvalves, but variants that can throttle even moderate pressures (1) tend to be bulky (cm-range) or consume high power. This paper details the development of a low-power, normally-open piezoelectric microvalve to control flows with a maximum driving pressure of 1, but also retain a small effective form-factor of 5x5x1.8. A novel combination of rapid prototyping methods like stereolithography and laser-cutting have been used to realize this device. The maximum displacement of the fabricated piezoelectric microactuator was measured to be 8.5 at 150. The fabricated microvalve has a flow range of 0–90 at 1 inlet pressure. When fully closed, a leakage of 0.8 open-flow was observed with a power-consumption of 37.5. A flow resolution of 0.2— De-ionized (DI) water was measured at 0.5 pressure.

Being one of the major pillars of liquid biopsy, isolation and characterization of circulating tumor cells (CTCs) during cancer management provides critical information on the evolution of cancer and has great potential to increase the success of therapies. In this article, we define a novel strategy to effectively enrich CTCs from whole blood based on size, utilizing a spiral microfluidic channel embedded with a hydrofoil structure at the downstream of the spiral channel. The hydrofoil increases the distance between the streams of CTCs and peripheral blood cells, which are already distributed about two focal axes by the spiral channel, thereby improving the resolution of the separation. Analytical validation of the system has been carried out using Michigan Cancer Foundation-7 (MCF7) breast cancer cell lines spiked into blood samples from healthy donors, and the performance of the system in terms of white blood cell (WBC) depletion, CTC recovery rate and cell viability has been shown in single or two-step process: by passing the sample once or twice through the microfluidic chip. Single step process yielded high recovery (77.1%), viable (84.7%) CTCs. When the collected cell suspension is re-processed by the same chip, recovery decreases to 65.5%, while the WBC depletion increases to 88.3%, improving the purity. Cell viability of >80% was preserved after two-step process. The novel microfluidic chip is a good candidate for CTC isolation applications requiring high recovery rate and viability, including functional downstream analyses for variety of cancer types.

Microvalves are important flow-control components in many standalone and integrated microfluidic circuits. Although there is a large body of work regarding
microvalves, there is still a need for an easyto-fabricate, small-footprint, low-power device that can control both liquids and gases at moderate pressures. This paper details the development of a piezoelectric microvalve compatible with both liquids and gases with a maximum driving pressure of 1 bar. A novel combination of accessible methods like 3D-printing and lasercutting has been used to realize this device. The device has a flow range of 0 - 90 μL min−1 at 1 bar inlet pressure. When fully closed, a leakage of 0.8% open-flow was measured with a power consumption of 37.5 μW.