Injectable, Hierarchically Degraded Bioactive Scaffold for Bone Regeneration.

Bioactive materials play vital roles in the repair of critical bone defects. However, bone tissue engineering and regenerative medicine are still challenged by the need to repair bone defects evenly and completely. In this study, we functionally simulated the natural creeping substitution process of autologous bone repair by constructing an injectable, hierarchically degradable bioactive scaffold with a composite hydrogel, decalcified bone matrix (DBM) particles, and bone morphogenetic protein 2. This composite scaffold exhibited superior mechanical properties. The scaffold promoted cell proliferation and osteogenic differentiation through multiple signaling pathways. The hierarchical degradation rates of the crosslinked hydrogel and DBM particles accelerated tissue ingrowth and bone formation with a naturally woven bone-like structure in vivo. In the rat calvarial critical defect repair model, the composite scaffold provided even and complete repair of the entire defect area while also integrating the new and host bone effectively. Our results indicate that this injectable, hierarchically degradable bioactive scaffold promotes bone regeneration and provides a promising strategy for evenly and completely repairing the bone defects.

Spheroid Formation Enhances the Regenerative Capacity of Nucleus Pulposus Cells via Regulating N-CDH and ITGß1 Interaction.

Background: Nucleus pulposus (NP) degeneration is the core pathological change of intervertebral disc (IVD) degenerative diseases, but currently, no effective therapy is available. With the rapid development of biomaterials and tissue engineering in recent years, biomaterial-assisted cell transplantation becomes a promising therapy for IVD degeneration. However, the application is severely limited by the weak biological characteristics of NP cells (NPCs), such as a moderate proliferation ability, weak self-renewal capacity, and minimal extracellular matrix (ECM) synthesis capacity, caused by the current inappropriate cell seeding or grafting methods. Methods: Here, we developed a three-dimensional (3D) spheroidizing culture method to construct NPC spheroids and investigated repair and regeneration potential of these spheroids in vitro and in vivo. The in vitro biological characteristics (including cell viability and proliferation), and in vivo functions (including anti-degeneration potential and ability to induce tissue repair) of NPC spheroids and monolayer-cultured NPCs were compared. Furthermore, an RNA-seq-based transcriptome analysis and a series of function experiments were performed to elucidate the potential mechanisms of their differences that were involved in the tissue regeneration process. Results: NPC spheroids exhibited obviously superior self-renewal and ECM synthesis capacities compared to monolayers of NPCs in vitro. In vivo, NPC spheroids generated more functional ECM components, primarily aggrecan (ACAN) and collagen type II (Col2), and markedly promoted NP regeneration in the disc degeneration model induced by partial NP excision. Additionally, the biological characteristics and functions of NPC spheroids were to some extent regulated by the interaction of N-cadherin (N-CDH) and Integrinß1 (ITGß1), two key mechanosensing ECM-receptors expressed on NPCs. Conclusions: The NPC spheroidizing culture method is beneficial for cell renewal and the generation of functional ECM in NP tissue. The molecular mechanism involved in this regeneration process is closely associated with the regulation of the N-CDH and ITGß1 interaction-mediated ECM homeostesis. Moreover, the strategy of hydrogel-assisted NPC spheroids transplantation may potentially be used in the future treatment of IVD degeneration.