Enhanced porosity and permeability of three-dimensional alginate scaffolds via acoustic microstreaming induced by low-intensity pulsed ultrasound

•An in-depth understanding of the mechanism involved in the ultrasound enhanced porosity and permeability of scaffolds.•Scaffolds' microstructure are observed by combining scanning electron microscopy and confocal imaging.•Passive cavitation detection is carried out to verify whether the inertial and/or stable cavitation is happening.•Green fluorescent protein observation is used to assay the variation of porosity and permeability of 3-D scaffolds.

The shear stress resulting from the microstreaming induced by low-intensity pulsed ultrasound (LIPUS) has been often used to improve the permeability of cell membrane or porous engineering scaffolds. In the present study, three-dimensional (3-D) scaffold culture systems were constituted to simulate the in vivo microenvironment, providing benefits for cell growth. In order to investigate the mechanism underlying the enhanced porosity and permeability of the 3-D alginate scaffolds by using LIPUS with varied acoustic intensities, two quantitative imaging techniques (i.e. scanning electron microscopy, and laser con-focal imaging) were used to evaluate the porosity and permeability of the 3-D alginate scaffolds. The results suggested that the porosity and permeability of the scaffolds were enhanced by the microbubble-induced microstreaming, and increased with the increasing LIPUS driving intensity. Furthermore, the cell proliferation assessments verified that HeLa cell grew better in the treated 3-D alginate scaffolds, since the LIPUS exposures can improve the scaffold porosity and permeability, leading to better cell growth space and nutrition supply.