MR elastography for evaluating regeneration of tissue-engineered cartilage in an ectopic mouse model

Purpose The purpose of the present study was to apply noninvasive methods for monitoring regeneration and mechanical properties of tissue-engineered cartilage in vivo at different growth stages using MR elastography (MRE). Methods Three types of scaffolds, including silk, collagen, and gelatin seeded by human mesenchymal stem cells, were implanted subcutaneously in mice and imaged at 9.4T where the shear stiffness and transverse MR relaxation time (T₂) were measured for the regenerating constructs for 8 wk. An MRE phase contrast spin echo-based sequence was used for collecting MRE images. At the conclusion of the in vivo study, constructs were excised and transcript levels of cartilage-specific genes were quantitated using reverse-transcription polymerase chain reaction. Results Tissue-engineered constructs showed a cartilage-like construct with progressive tissue formation characterized by increase in shear stiffness and decrease in T₂ that can be correlated with increased cartilage transcript levels including aggrecan, type II collagen, and cartilage oligomeric matrix protein after 8 wk of in vivo culture. Conclusion Altogether, the outcome of this research demonstrates the feasibility of MRE and MRI for noninvasive monitoring of engineered cartilage construct's growth after implantation and provides noninvasive biomarkers for regeneration, which may be translated into treatment of tissue defects.