Mechanical stimulation in 2D: A potent accelerator of matrix mineralization in ATDC5 chondrogenic cells

Matrix mineralization is a key process in endochondral ossification and cartilage maturation. While optimized biochemical protocols using ATDC5 chondrogenic cells have shortened mineralization timelines, the role of mechanical stimulation in enhancing this process remains underexplored. This study investigates whether dynamic mechanical stimulation in 2D monolayer cultures can accelerate mineralization and influence extracellular matrix (ECM) composition.

ATDC5 cells were cultured on PDMS membranes coated with collagen and subjected to cyclic tensile strain (12 % at 0.05 Hz for 1 h/day) using a uniaxial bioreactor over 5 days. The culture protocol included supplementation with β-glycerophosphate and ascorbic acid. Mineralization and ECM production were assessed at days 7, 17, and 23 using Alizarin Red and Alcian Blue staining. SEM/EDX confirmed calcium-phosphate deposition. A phenomenological finite element model was developed to correlate mechanical stimuli with hypertrophy using the osteogenic index.

Mechanical stimulation led to a 32 % increase in Alizarin Red staining compared to controls (P < 0.001), indicating faster mineralization. GAG production was reduced under mechanical loading (P < 0.05), consistent with early mineralization. SEM/EDX confirmed more uniform mineral deposition in stimulated samples. Morphologically, stimulated cells aligned along the loading axis and displayed a nearly 10-fold increase in hypertrophic cell area. The numerical model showed elevated osteogenic index values and stress peaks in the chondrocyte membrane under mechanical loading.

Dynamic tensile stimulation in 2D culture significantly accelerates ECM mineralization in ATDC5 cells. This effect appears to be mediated through enhanced chondrocyte hypertrophy and alignment of ECM components. The combined use of mechanical and biochemical cues provides a promising strategy for optimizing in vitro models of endochondral ossification and developing tissue engineering therapies.