Compressive mechanical modulation alters the viability of growth plate chondrocytes in vitro

The aim of this study was to investigate the effect of compressive modulation parameters (mode, magnitude, duration, as well as frequency and amplitude for cyclic modulation) on the viability of growth plate chondrocytes. Swine ulnar growth plate explants (n = 60) were randomly distributed among 10 groups: baseline (n = 1 × 6); culture control (n = 1 × 6); static (n = 3 × 6); and dynamic (n = 5 × 6). Static and dynamic samples were modulated in vitro using a bioreactor. Different compression magnitudes (0.1 MPa or 0.2 MPa), durations (12 h or 24 h), frequencies (0.1 Hz or 1.0 Hz), and amplitudes (30% or 100%) were investigated. Viability was assessed by automatic quantification of number of live/dead cells from confocal images of Live/Dead labeled tissues. Chondrocyte viability was found to be dependent on compression magnitude, duration, frequency, and amplitude in a way that increasing each parameter decreased viability in certain zones of growth plate. More specifically, proliferative and hypertrophic chondrocytes were found to be more sensitive to the applied compression. This study provides an in vitro protocol for studying the effects of compressive modulation on biomechanical and biological responses of growth plate explants, which will be useful in finding efficient and non-detrimental parameters for mechanical modulation of bone growth exploited in scoliosis fusionless treatments.