A Mechanical Composite Spheres Analysis of Engineered Cartilage Dynamics

In the preparation of bioengineered reparative strategies for damaged or diseased tissues, the processes of biomaterial degradation and neotissue synthesis combine to affect the developing mechanical state of multiphase, composite engineered tissues. Here, cell-polymer constructs for engineered cartilage have been fabricated by seeding chondrocytes within three-dimensional scaffolds of biodegradable polymers. During culture, synthetic scaffolds degraded passively as the cells assembled an extracellular matrix (ECM) composed primarily of glycosaminoglycan and collagen. Biochemical and biomechanical assessment of the composite (cells, ECM, and polymer scaffold) were modeled at a unit-cell level to mathematically solve stress-strain relationships and thus construct elastic properties (⁠$n=4$ samples per seven time points). This approach employed a composite spheres, micromechanical analysis to determine bulk moduli of: (1) the cellular-ECM inclusion within the supporting scaffold structure; and (2) the cellular inclusion within its ECM. Results indicate a dependence of constituent volume fractions with culture time $(p<0.05)$⁠. Overall mean bulk moduli were variably influenced by culture, as noted for the cell-ECM inclusion (⁠$Kc‐m=29.7kPa$⁠, $p=0.1439$⁠), the cellular inclusion (⁠$Kc=5.5kPa$⁠, $p=0.0067$⁠), and its surrounding ECM (⁠$Km=373.9kPa$⁠, $p=0.0748$⁠), as well as the overall engineered construct (⁠$K=165.0kPa$⁠, $p=0.6899$⁠). This analytical technique provides a framework to describe the time-dependent contribution of cells, accumulating ECM, and a degrading scaffold affecting bioengineered construct mechanical properties.