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.