Table 1.

List of advantages and potential pitfalls of various micro- and nanoengineered tools, and possible solutions to avoid them.

Tools	Advantages	Potential Pitfalls and Limitations	Solutions for the Specific Pitfalls	Complexity of Solutions
Microfluidics Gradient Generators	Arbitrary shape of gradients [17, 25] Combinatorial gradients of multiple species [30] Gradients of soluble [25], insoluble [75], gaseous [22], and mechanical [43, 58] factors Temporal control of the shape of gradients [34]	Pneumatic valve controls can quickly become unmanageable with increasing complexity	Keep number of conditions limited	++
			Automate pneumatic valve control [34]	++++
		Absorption of biochemicals due to high surface area to volume ratio	Check for absorption profile of biochemical factor in pdms [71]	++++
Long term differentiation assays with perfusion	Combinatorial combinations of various factors [13] High throughput perturbations and observations Screening over large dose responses [19, 32] Precise temporal control of dosage and combinations [34] Combination of mechanical, physical and biochemical factors [30]	Shear stress	Use H-chip designs to avoid direct flow of fluid over cells	++
			Dampen flow by specialized perfusion[24, 26]	+++
			Culture cells in protected etched channels or microwells[25, 63]	++
		Loss of autocrine paracrine signaling[62]	Maintain pulsatile flow with long periods (5–6 hours) with no flow [24]	++++
			Use no flow conditions, and culture cells in high throughput microwells with media replenishment every 6–12 hours [46, 76]	+++
Co-culture	2 or more cell types can be cultured with arbitrary interaction profiles Consistent culture of spheroid cultures	Sophisticated requirements for temporal control[49]		+++++
Control of shear and rigidity	Precise spatial and temporal control of shear Integration of biochemical gradients and shear gradients	Difficult to ascertain effect on cell viability by shear alone [60]	Ex-chip control always suggested with comparable cell density and media	++
	Combination of spatial mechanical rigidity gradient with biochemical gradients	Temporal control of rigidity difficult and require sophisticated set ups[59]		+++++
Control of topography	Highly precise mimicking of substrate topography Biodegradable and biocompatible polymers Spatial gradients of topography Ease of culture and experimentations	Expensive to fabricate [77–79]	CFL [80] and electrospinning[60] are cheaper but difficult to fabricate	+++++
		Small surface area prohibiting biochemical experiments [70]	Use CFL substrata from commercial or expert laboratories to minimize optimizations	+
		3D control not available in all topographical features	Electrospinning allows 3D control. CFL allows 2.5D control	++