Objective: This paper aims to provide a comprehensive review of the changing role of transforming growth factor-b (TGF-b) signaling in intervertebral disc (IVD) health and disease. Methods: A comprehensive literature search was performed using PubMed terms 'TGF-b' and 'IVD'. Results: TGF-b signaling is necessary for the development and growth of IVD, and can play a protective role in the restoration of IVD tissues by stimulating matrix synthesis, inhibiting matrix catabolism, inflammatory response and cell loss. However, excessive activation of TGF-b signaling is detrimental to the IVD, and inhibition of the aberrant TGF-b signaling can delay IVD degeneration. Conclusions: Activation of TGF-b signaling has a promising treatment prospect for IVD degeneration, while excessive activation of TGF-b signaling may contribute to the progression of IVD degeneration. Studies aimed at elucidating the changing role of TGF-b signaling in IVD at different pathophysiological stages and its specific molecular mechanisms are needed, and these studies will contribute to safe and effective TGF-b signaling-based treatments for IVD degeneration.

A graphene-like hexagonal aluminum nitride monolayer (g-AlN) is a promising nanoscale optoelectronic material. We investigate its mechanical stability and properties using first-principles plane-wave calculations based on density-functional theory, and find that it is mechanically stable under various strain directions and loads. g-AlN can sustain larger uniaxial and smaller biaxial strains than g-BN before it ruptures. The third, fourth, and fifth-order elastic constants are essential for accurately modeling the mechanical properties under strains larger than 0.02, 0.06, and 0.12 respectively. The second-order elastic constants, including in-plane stiffness, are predicted to monotonically increase with pressure while the Poisson ratio monotonically decreases with increasing pressure. g-AlN's tunable sound velocities have promising applications in nano waveguides and surface acoustic wave sensors.

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