Depth-dependent ratcheting strains of young and adult articular cartilages by experiments and predictions

Abstract

Background Ratcheting strain is produced due to the repeated accumulation of compressive strain in cartilage and may be a precursor to osteoarthritis. The aim of this study was to investigate the ratcheting behaviors of young and adult articular cartilages under cyclic compression by experiments and theoretical predictions. Methods A series of uniaxial cyclic compression tests were conducted for young and adult cartilage, and the effects of different loading conditions on their ratcheting behaviors were probed. A theoretical ratcheting model was constructed and applied to predict the ratcheting strains of young and adult cartilages with different loading conditions. Results Ratcheting strains of young and adult cartilages rapidly increased at the initial stage, followed by a slower increase in subsequent stages. The strain accumulation value and its rate for young cartilage were greater than them for adult cartilage. The ratcheting strains of the two groups of cartilage samples decreased with increasing stress rate, while they increased with increasing stress amplitude. As the stress amplitude increased, the gap between the ratcheting strains of young and adult cartilages increased gradually. The ratcheting strains of young and adult cartilages decreased along the cartilage depth from the surface to the deep layer. The ratcheting strains of different layers increased with the compressive cycle, and the difference among the three layers was noticeable. Additionally, the theoretical predictions agreed with the experimental data. Conclusions Overall, the ratcheting behavior of articular cartilage is affected by the degree of articular cartilage maturation.

Biomimetic and mechanically supportive 3D printed scaffolds for cartilage and osteochondral tissue engineering using photopolymers and digital light processing

“…Results showed a non-linear elastic response, similar to native cartilage [71]. However, unlike native cartilage, which has a viscous response to compressive loading and subsequent deformation accumulation [72], loading curves traced suggest no plastic deformation or pillar failure. Future work will need to include a more comprehensive evaluation of the viscoelastic nature of the bilayer design as well as more comprehensive life cycle and fatigue testing of the structures.…”

“…The bilayer structural design represents a unified system with controllable variation in crosslink density to enhance integration and mechanical properties through the structure design, which is formed from a single resin formulation that is afforded by DLPbased printing. In contrast, a frequently employed methodology in FDM printing, is the use of multiple materials and/or extrusion heads to achieve different mechanical properties [72,73]. However, this approach can result in delamination, due to variations in properties between materials that can lead to points of failure [74].…”

“…alginate) laden with pre-defined cells (i.e. chondrocytes and osteoblasts) [72,73] into a stiffer structure (e.g. PCL structure) or using bioprinting methods to incorporate MSCs in bioinks with specific biochemical cues incorporated [77,78].…”