Doctor of Philosophy (PhD)
Molecular Genetics & Cell Biology
Rotator cuff tendon injuries often occur at the tendon-to-bone interface (i.e., enthesis) area with a high prevalence for the elderly population. In addition, regeneration of the gradient structure of the enthesis is still a significant clinical challenge. Our studies aim to identify the histological, molecular, and biomechanical alterations of the rotator cuff enthesis with maturation and aging, and develop a novel therapeutic method using three-dimensional (3D) bioprinting technique to regenerate a functional enthesis. Striking variations of the entheses were observed both histologically and biomechanically during the maturation process. The histological features did not show many differences at the insertion site during the aging process. However, the biomechanical properties showed a decreasing trend in nanoindentation testing and a significantly increased failure stress in tensile testing during the aging process. The proteomics analysis detected dramatic differences in protein contents during maturation process but minor changes during aging process. For the rotator cuff defect regeneration, we first developed a new strategy by combining a 3D printed scaffold with cell-laden collagen-fibrin hydrogels. We further improved the scaffold design to generate biomimetic multilayered scaffolds with 3D bioprinted pre-differentiated autologous adipose-derived mesenchymal stem cells (ADMSCs). The hydrogel-based bioinks offered high cell viability and proliferative capability for rabbit ADMSCs. The hydrogels with pre-differentiated or undifferentiated rabbit ADMSCs were 3D bioprinted into zonal-specific constructs to mimic the structure of the enthesis. The in vivo studies demonstrated that the scaffold with spatially differentiated autologous ADMSCs had a superior histological score and improved collagen organization when compared to acellular scaffolds and similar T2 value as the normal interface tissue. The biomechanical characterizations demonstrated that multilayered scaffolds improved the mechanical properties of the enthesis after reconstruction, but the incorporation of autologous ADMSCs showed limited contribution at 12 weeks after rotator cuff reconstruction surgery. Our studies demonstrated: (1) significant alterations of the enthesis composition and structure occurred during the maturation process, and whereas aging process had less impact in the mouse model; (2) a 3D bioprinting-based strategy with the application of autologous ADMSCs was generated to reconstruct massive rotator cuff tendon tears.
Jiang, Xiping, "The Rotator Cuff Tendon-to-Bone Interface: Maturation, Aging, and 3D Bioprinting for Regeneration" (2021). Theses & Dissertations. 586.