Bio-macromolecular assembly machine for human limb lengthening

Abstract

Growth plate (GP) is the critical cartilaginous structure for longitudinal bone growth. Herein, employing high-resolution analytical techniques, we explore the intricate mechanisms that govern the polarized mineralization patterns within GP. The GP-epiphysis interface displays a sharp transition in tissue modulus, acting as a "protective shell" for the underlying GP, whereas the GP-metaphysis interface exhibits a gradual modulus increase, enabling efficient load redistribution to metaphysis. The unique mechanical environments at these two interfaces contribute to polarized CaP mineralization patterns, which are regulated by a complex protein-based molecular machinery. The mineralization inhibitors SPP1 and AHSG enriched at the GP-epiphysis interface could act as a line of defence against mineralization. When these two proteins coexisted with the mineralization-promoting ENPP1 and ALPL at the GP-metaphysis interface, a sequential event of precise nucleation and programmable assembly of CaP minerals occur, forming "mineralization waves" to guide bone elongation. By replicating such specific macromolecular environment at GP-metaphysis interface, a hypertable amorphous calcium phosphate (ACP) phase is well-retained in vitro, demonstrating the possibility for precise and gentle control of ACP-hydroxyapatite (HAp) transformation under physiological conditions. Our study defines a novel concept of "mineralization waves" that govern the velocity and amplitude of GP-guided mineralization process.