# Anti-Cancer Drug Screening with Microfluidic Technology
## 2 Monodrug Screening on a Microscale Sample
### Two-Dimensional Cell Cultures  
[PERSON] et al. described a microfluidic device consisting of multiple drug gradient generators to measure different cellular parameters in anti-cancer drug-induced apoptosis of human liver carcinoma HepG2 cells [36]. This platform consists of eight uniform structure units, and each unit has an upstream CGG and downstream parallel cell culture chambers. Their microscale cell culture arrays allow high-throughput screening in response to different doses of drugs with discrete concentration gradients. They also thoroughly evaluated other cellular responses such as nuclear size and membrane permeability. [PERSON] et al. reported a PDMS-based cell array consisting of 440 micromechanical traps to screen anti-cancer drugs in real-time [37]. In this kinetic on-chip assay, researchers investigated the staurosporine-induced tumor cell death over human promyelocytic leukaemia (HL60) and histiocytic leukaemia (U937) cell lines. Utilizing this platform realizes high-throughput screening and automated single-cell microarray cytometry with a smaller number of cells and eliminates the need for single-pass flow cytometer measurements. [PERSON] et al. developed a microfluidic chip to evaluate the cytotoxicity of two oxygen-dependent anti-cancer drugs (TPZ and Cisplatin) to A549 cells [38]. They tested a single drug dose under different oxygen tensions. [PERSON] et al. exploited a droplet-based microfluidic device for drug screening on cancer cell lines and cells separated from a human primary tumor [39]. All samples were tested on-chip against four anti-cancer drugs, namely bortezomib, epirubicin, cisplatin, and vorinostat, for five assay conditions based on sample input size and throughput requirement. This platform provides a rapid and low-input sample drug screening of potentially all types of cancer. Microwell chips are widely used to trap cells or tissue slices for drug screening. [PERSON] et al. described a micro-gap plate with 96 units arranged in the standard format of a 96-well plate to test the response of breast cancer cell lines (MCF7 and MDA-MB-231) and patient primary samples to two anti-cancer drugs, namely cisplatin and docetaxel [33]. Their presented design consisted of culture wells, micro-gaps, and microchannels. The small height of micro-gaps aided cell conservation during solution exchange. [PERSON] et al. engineered a multifunctional microfluidic device to estimate the activity-toxicity in a cell model simultaneously [40]. The optimum drug combination with maximum efficacy and minimal toxicity was predicted by adjusting different concentration ratios of three anti-cancer drugs, including dinatin, diosmetin, and cisplatin, on HEK293 cells. [PERSON] et al. developed a microfluidic platform for nanoparticle-based chemotherapeutic drug screening [41]. They used integrated microstructures in the cell chamber to enhance fluid mixing and drug-cell interaction. Several methotrexate-based treatments were tested over an osteosarcoma cell monolayer. This platform provides a  
Figure 1: Monodrug screening on a microscale sample: (**a**) a microwell platform to trap cells in 96-well plates. Reproduced from Ref. [33] under an open access Creative Common CC BY license. (**b**) Micropillar-microwell platform for alginate 3D cell culture (since the cell-containing micropillar chips lay onto the medium-containing microwell chips, replacing the growth media in this platform is easier than conventional hydrogel 3D cell cultures). Reproduced with permission from Ref. [34]. (**c**) An integrated microfluidic concentration gradient generator for mechanical stimulation and drug delivery. The device consists of two layers of PDMS with an integrated membrane sandwiched between the two layers. The device can generate four different concentrations of a drug and, at the same time, it can impose the adjustable shear stress and osmotic pressure gradients on the cultured cells. Reproduced from Ref. [23] under an open access Creative Common CC BY license.