Effect of low-intensity pulsed ultrasound on osteogenic human mesenchymal stem cells commitment in a new bone scaffold

Purpose: Bone tissue engineering is helpful in finding alternatives to overcome surgery limitations. Bone growth and repair are under the control of biochemical and mechanical signals; therefore, in recent years several approaches to improve bone regeneration have been evaluated. Osteo-inductive biomaterials, stem cells, specific growth factors and biophysical stimuli are among those. The aim of the present study was to evaluate if low-intensity pulsed ultrasound stimulation (LIPUS) treatment would improve the colonization of an MgHA/Coll hybrid composite scaffold by human mesenchymal stem cells (hMSCs) and their osteogenic differentiation. LIPUS stimulation was applied to hMSCs cultured on MgHA/Coll hybrid composite scaffold in osteogenic medium, mimicking the microenvironment of a bone fracture. Methods: hMSCs were seeded on MgHA/Coll hybrid composite scaffold in an osteo-inductive medium and exposed to LIPUS treatment for 20 min/day for different experimental times (7 days, 14 days). The investigation was focused on (i) the improvement of hMSCs to colonize the MgHA/Coll hybrid composite scaffold by LIPUS, in terms of cell viability and ultrastructural analysis; (ii) the activation of MAPK/ERK, osteogenic (ALPL, COL1A1, BGLAP, SPP1) and angiogenetic (VEGF, IL8) pathways, through gene expression and protein release analysis, after LIPUS stimuli. Results: LIPUS exposure improved MgHA/Coll hybrid composite scaffold colonization and induced in vitro osteogenic differentiation of hMSCs seeded on the scaffold. Conclusions: This work shows that the combined use of new biomimetic osteo-inductive composite and LIPUS treatment could be a useful therapeutic approach in order to accelerate bone regeneration pathways.