(11f) Bioeffects of Ultrasound Stimulation

Bioreactors play a critical role, providing controlled environments for reproducible, accurate application of specific regimes of mechanical forces to three dimensional (3D) tissue substitutes. Bioreactors based on rotation and compression are primarily used to generate tissue-engineered cartilage. Our research group is focused on the design and development of a novel ultrasound (US)-aided bioreactor that provides different regimes of stimulation to engineered tissues and aids in generating tissue-engineered neocartilage. When biological materials are exposed to US, the US related non-thermal and thermal mechanisms can impact or in certain cases act as the causative agent for the observed bioeffects, namely, proliferation, viability and cell-specific processes. Our ongoing research has documented the ability of US stimulation (5.0 MHz, 31-sec/application) to impact the proliferative and biosynthetic activity of chondrocytes seeded in 3D matrices. The focus of this work is to better understand the biophysical effects of the adopted US stimulation regimen and to delineate the contribution of ultrasound-induced thermal and non-thermal mechanisms on the observed cellular effects. US stimulation was not observed to induce any noticeable changes in the temperatures in the medium or in the vicinity of the cell. No increase in the levels of reactive oxygen species were noted upon US stimulation and levels similar to control, non-stimulated cells were observed. US stimulation was observed to temporarily influence the nuclear thermal denaturation profiles, which were assessed by dynamic scanning calorimetric analyses. Independently, US was also observed to impact the chromatic condensation as measured by staining with DAPI and confocal microscopy. These collective results allude to the acoustic pressure as the causative agent in mediating the observed effects upon US stimulation.