Table 1.

Confounding factors existing in topographic cell culture devices that impede the establishment of high-quality topographic cell responses database.

Steps	Confounding factors derived from cell culture device	Example
Structure Generation	1. Structural inconsistency in a surface	Random topographic structures generated by surface roughening [37].
	2. Inconsistent physical properties	Inconsistent stiffness between control and topographies [38].
	3. Additional bioactive chemicals	Fluorine residual on the topographic structure after hydrofluoric acid treatment [39].
Cell Culture Application	1. Physicochemical instability during sterilization	Autoclaving sterilization process probably causes alteration of surface properties of titanium nanotube [13].
	2. Physicochemical instability during immersion	During immersion, the topographies on biodegradable materials, such as PLGA, might deform due to swelling or degradation [40].
	3. Moveable or non-fixable during immersion	Due to the low density, some cell culture devices, such as collagen membranes, cannot keep immobility in the culture medium.
	4. Cytotoxicity	Many toxic reagents might be introduced during the fabrication process, such as the etching process in the photolithography method.
Cell Response Analysis	1. Disturbed signal transmission and collection during the morphological assay	The opaqueness of some metal-made cell culture devices hinders the cell density and cell status assessment before cell response detection.
	2. Non-fixable during cell adhesion force assay	During hydrodynamic shear assay by shear force [41], the force may not be normally applied to cells on non-fixable substrates.
	3. Structural change during wound-healing assay	During wound-healing assay, physical scratch using pipette tip [28] might destroy the topographic structures.
	4. Interference with transmittance during absorbance test	Some topographic substrates change the transmission of visible light [[42], [43]], thus interfering with the detection of absorbance in CCK-8 or MTT assays.
	5. Interference with mRNA or protein extraction	The topographic substrates may react to the mRNA or protein extraction reagent, thus causing the degradation of samples [14].
	6. Interference with the relative quantification of mRNA or protein expression	Topographic substrates can regulate cytoskeletal dynamic [31] so that may influence the expression of some housekeeping genes, such as β-actin or α-tubulin, of which the constant expression in other cases was helpful to correct sample loading deviation in RT-qPCR or WB.