TABLE 1.

Summary of pros and cons of perfusion devices at the macro, milli, and micro scale.

	Pros	Cons
Macro scale	Model bone porous microarchitecture Simulate mechanical properties of bone tissue Presence of convective flow to ensure the mixing of culture medium around the 3D cellularized scaffolds allowing for better nutrient/oxygen transport than static cultures	Limited medium transport inside the scaffold causing:  • formation of a dense superficial cell layer on the surface  • low supply of nutrients and oxygen to cells in the centre of the scaffolds  • necrotic area at the core of the construct  • uneven distribution of fluid shear stress, resulting in impaired       mineralization in the inner part of the scaffolds Fail to model paracrine communication, cell-cell interaction, cell-ECM interaction at the microscale level
Milli scale	Model bone porous microarchitecture Simulate mechanical properties of bone tissue Medium perfusion through the scaffold Accurately mimic the effect of interstitial fluid flow Wide range of mechanical loadings to be applied Possibility to model osteogenesis	Fail to model paracrine communication, cell-cell interaction, cell-ECM interaction at the microscale level No simultaneous application of biophysical and biochemical stimuli Fail to model complex biological phenomena that take place at the microscale, as angiogenesis and mechanotransduction Low resolution live imaging
Micro scale	High resolution live imaging Reproducibility Accurately mimic the effect of interstitial fluid flow Simulate mechanical stress at microscale level Possibility to model paracrine communication, cell-cell interaction, cell-ECM interaction Possibility to combine multiple biochemical and biophysical stimuli to model complex biological phenomena (i.e., osteogenesis, mechanotransduction, angiogenesis) Reduction of the amount of reagents and cells Small number of cells allow insertion patient tissue biopsies, or cells isolated from biopsies, that are available in small quantities	Fail to mimic bone microarchitecture Fail to mimic mechanical properties of bone tissue Small range of materials available for in gel 3D cultures (i.e. injectable thermoresponsive hydrogels) Too simplistic in representing organ complexity due to small cell number