Table 2.

Methods for studying cancer cells mechanics and mechanical properties of cancer cells reported in the literature

Methods	Induced force		Advantages	Disadvantages	Applications				References
					Case study	Major observations	Typical values
							Cancer cells	Normal cells
Atomic force microscopy (AFM)	Partial of cell	10−7–10−11N	1) High resolution; 2) Low forces with minimal disruption; 3) Three dimensional surface profile.	1) Can be used only for cells that adhered to a substrate; 2) Relatively slow scanning rate; 3)Mechanical contact may lead to cellular response.	Stiffness of metastatic cancer cells from lung, breast and pancreas [67]	Stiffness of metastatic cancer cells is more than 70% softer than the benign cells	Lung: 0.56±0.09kPa; Breast: 0.50±0.08kPa; Pancreas: 0.54±0.08kPa;	Lung: 2.10±0.79kPa; Breast: 1.93±0.50kPa; Pancreas: 0.54±0.12kPa;	[67,68,257]
					Stiffness and adhesion forces of metastatic cancer cells and benign mesothelial cells [68]	Metastatic tumour cells are more than 80% softer than benign cells and surface adhesion is ∼33% less than normal cells.	Stiffness: 0.38±0.20kPa; Adhesion force: 34.2±5.3pN.	Stiffness: 2.53±1.30kPa; Adhesion force: 51.1±15.2pN.
Magnetic twisting cytometry (MTC)	Partial of cell	10−10–10−12N	Probe the single cell with very small deformations and over wide ranges of time scale and amplitude.	1) The bead localization on the cell is random; 2) The induced bead rotation and displacement are strongly dependent on the bead attachment angle.	The effects of tubeimoside I (TBMS I) on human hepatoma (HepG2) cells[131]	The stiffness of HepG2 cells decreased consistently with the increased concentration of TBMS I exposure. In addition, the HepG2 cells responded to TBMS I much faster than the normal liver (L-02) cells.	Stiffness (HepG2): 0.44±0.01 Pa/nm; Respond time: 73s.	Stiffness(L-02): 0.88±0.04 Pa/nm, Respond time: 109s.	[131,143,257]
Cytoindentation	Partial of cell	10−7–10−9N	1) Simple modelling of the viscoelastic behaviour of the cells; 2) Detection of differences in cell mechanics; 3) The probe is large to measure bulk cellular properties.	The response may depend significantly on the precise probing location.	The elasticity of benign (MCF-10A) and cancerous (MCF-7) human breast epithelial cells [12]	Apparent Young's modulus of malignant (MCF-7) cells significantly decreased, (1.4–1.8 times) than that of non-malignant (MCF-10A) cells at physiological temperature (37°C), and their apparent Young's modulus increased with loading rate.	–	–	[12,144,257]
Microplate stretcher	Single cell	10−7–10−9N	Sufficient to induce significant deformation of an entire cell.	1) Time consuming; 2) Low throughput; 3) Can only be applied to extremely well adhering cells.	Elastic response and energy dissipation under repeated tensile loading of epithelial pancreatic cancer cells [146]	The elastic modulus of Panc-1 pancreatic cancer cells decreased after treatment with SPC.	Before SPC: 28.8 ± 2.6 mN m−1. After SPC: 16.3 ± 1.1 mN m−1.	–	[145,146,257]
Micropipette aspiration(MA)	Single cell	10−7N- 10−10N	1) Allows for real time correlation of pressure and whole cell deformation; 2) High accuracy; 3) Aspiration pressure can be maintained over a specified duration.	Analytical or computational models are often necessary to derive material properties and the underlying assumptions may at times be difficult to validate.	Viscoelastic properties of human hepatocytes and hepatocellular carcinoma (HCC) cells[132]	HCC cells have higherelastic coefficients but not viscous coefficients compared to than hepatocytes.	Hepatocellular carcinoma (HCC): K1=103.6±12.6N.m−2; K2=42.5±10.4N.m−2; μ=4.5±1.9Pa.s.	Hepatocytes: Kl=87.5±12.1N.m−2; K2=33.3±10.3N.m−2; μ=5.9±3.0Pa.s.	[132,147,148, 156,257]
Laser/optical tweezers(OT)	Single cell	10−11–10−14N	A focused laser beam allows precise bead manipulation in all directions.	1) Force level is limited to induce larger deformation; 2) Larger force would require higher laser power that could excessively heat the cell.	Elasticity of myeloblasts (62–71 CD33+CD34+cells and 57–63 CD33+CD34-cells) from AML patients[150]	The induced deformation of CD33+CD+cells is greater than CD33+CD34-cells under the same stretching force.	The elastic area compressibility modulus, kα= 1.40±0.71 N/m (CD33+CD34-).	The elastic area compressibility modulus, kα= 0.25±0.15 N/m (CD33+CD34+).	[168–171, 267]
Optical stretcher	Single cell	10−9–10−11N	1) Cells can be suspended to eliminate mechanical contact; 2) Very small numbers of cells are required for distinction; 3) Relatively high throughput using a microfluidic channel.	1) Laser power should be controlled without damaging the cells; 2) Limitations may exist when probing stiffer cells.	Optical deformation (OD) of mouse fibroblasts and human breast epithelial cells [155]	Optical deformability of the SV-T2 cells is significantly increased compared to the BALB/3T3 cells; the cancerous MCF-7 cells are deformed more than the normal MCF-10 cells, and the metastatic modMCF-7 are deformed even more than the nonmetastatic MCF-7.	ODSV-T2 = 11.7±1.1 ODMCF-7 = 21.4±1.1; ODmodMCF-7 = 30.4±1.8.	ODBALB/3T3 = 8.4±1.0; ODMCF-10 = 10.5±0.8.	[153-156,257]
Shear flow	Cell populations	1–100Pa	Cone and plate rheometers allow precise control over the applied shear stress.	1) Difficult to visualize induced cellular deformations; 2) Small variations in the cell height and topology can cause local variations of shear stress.	Influence of shear flow on the adhesion of nonmetastatic (MCF-7) and highly metastatic (MDA-MB-435) cells[135]	Detachment of the nonmetastatic MCF-7 cell line decreased significantly while detachment of the highly metastatic MDA-MB-435 significantly increased after 15 hour exposure of a 15 dyn/cm2 shear stress.	Detachment (MCF-7) decreased from 44.0±4.6% to 12.1±3.7%; Detachment (MDA-MB-435) ncreased from 37.2±6.3% to 36.2±2.1%.	–	[135,257,258]
Microfluidic assay	Cell populations	–	1) High throughput; 2) Can mimic in vivo environment; 3) High accuracy; 4) Easy to fabricate and low cost.	Microfluidic channels need to be properly designed.	Deformability of benign breast epithelial cells (MCF-10A) and nonmetastatic tumour breast cells (MCF-7) [130].	Transit velocity is not significantly affected by cell type. MCF-10A cells were found to have longer entry time than MCF-7 cells of similar sizes, MCF-10A is stiffer than MCF-7 cells.	MCF-10A intry time: 1.698±0.201s; ilongation index: 1.231±0.01191; Transit velocity: 187.0±7.920μm/s.	MCF-7 Entry time: 0.433±0.045s; Elongation index 1.281±0.01505; Transit velocity: 177.3±9.836 μm/s.	[130,142,259]
Microfabricated post array	Single cell/Cell populations	10−7–10−9N	1) Force application is localized and can be measured with high resolution; 2) The geometry and stiffness of micropillars can be independently adjusted; 3)Can be applied for cell adhesion force, traction force and migration studies.	1) Substrate has a nontrivial topology that might affect cell adhesion and bias the measurements; 2) Substrate may cause active cell-substrate response.	Traction forces exerted by cancer cells [134]	Cancer cell exhibits a larger traction force than the normal cell by ∼20% for a HeLa cell and ∼50% for a L929 cell.	Traction forces of Hela cell: 2.84±0.49 μN and L929 cell: 3.48±0.46 μN.	Traction forces: 2.3210.16μN.	[86,134,141,257]
Nanoparticle-based techniques	Cell populations	–	It can provide insight into intracellular dynamics and structure, as well as into active transport processes.	1) Hard transferring of experimental observations to theoretical and phenomenological models; 2) Nonlinear effects.	ECM stiffness on the intracellular rheology of cancer cells [33].	In 3D matrices, the intracellular effective creep compliance of prostate cancer cells is shown to increase with increasing ECM stiffness, whereas modulating ECM stiffness does not significantly affect the intracellular mechanical state when cells are attached to 2D matrices.	–	–	[133,136-140,257]
	Partial of cell/Cell population	10−7 −10−9N	1) High spatially and resolved force with long duration and repeats. 2) Localized stimuli and cell population measurement are both achieved, which increases the throughput.	1) System is complex, which limits its real application; 2) Both cells and magnetic elements are needed to be patterned, and the alignment between them should be precisely controlled.	The influence of mechanical forces on single-cell behaviour [137].	Nanoparticle-induced tension generates filopodia asymmetry and bias metaphase-plate orientation of Hela cells.	–	–