Abstract
Biomineralization templated by organic molecules to produce inorganic-organic nanocomposites is a fascinating example of nature using bottom-up strategies at nanoscale to accomplish highly ordered multifunctional materials. One such nanocomposite is bone, composed primarily of hydroxyapatite (HA) nanocrystals that are embedded within collagen fibrils with their c-axes arranged roughly parallel to the long axis of the fibrils. Here we discern the ultra-structure of biomimetic mineralized collagen fibrils (MCFs) as consisting of bundles of subfibrils with approximately 10 nm diameter; each one with an organic-inorganic core-shell structure. Through an amorphous calcium phosphate precursor phase the HA nanocrystals were specifically grown along the longitudinal direction of the collagen microfibrils and encapsulated them within the crystal lattice. They intercalated throughout the collagen fibrils such that the mineral phase surrounded the surface of collagen microfibrils forming an interdigitated network. It appears that this arrangement of collagen microfibrils in collagen fibrils is responsible for the observed ultrastructure. Such a subfibrillar nanostructure in MCFs was identified in both synthetic and natural bone, suggesting this is the basic building block of collagen-based hard tissues. Insights into the ultrastructure of mineralized collagen fibrils have the potential to advance our understanding on the biomineralization principles and the relationship between bone’s structure and mechanical properties, including fracture toughness mechanisms. We anticipate that these principles from biological systems can be applied to the rational design of new nanocomposites with improved performance.
Highlights
Bone represents one of the most intriguing hierarchical nanocomposite structures found in nature, which is optimized to achieve an outstanding mechanical performance [1,2]
The self-assembled collagen fibrils mineralized by a polymer-induced liquid-precursor (PILP) mineralization solution containing poly-L-aspartic acid as the process-directing agent, CaCl2 and K2HPO4 in tris-buffered saline for up to 14 days resulted in mineralized matricees with 48 wt% of mineral content, as we reported previously [23]
It was displayed as clusters of short filaments where nearby clusters tended to converge together. These clusters contained mineral which expanded the width of the fibrils. This observation is in agreement with that from cryo-transmission electron microscope (TEM) study, where electron-dense needle-like minerals appeared and collagen fibrils were deformed during the early mineralization stage [18]
Summary
Bone represents one of the most intriguing hierarchical nanocomposite structures found in nature, which is optimized to achieve an outstanding mechanical performance [1,2]. In the last two decades, notable advances have been made to replicate the most fundamental level of bone structure, the interpenetrating collagen-hydroxyapatite nanocomposite These studies have demonstrated that calcium phosphate minerals can successfully infiltrate into collagen fibrils in a way that HA nanocrystals are aligned preferentially with their c-axes parallel to the longitudinal axis of the fibril, resembling what has been observed for bone [12,15,19]. Such a biomimetic bone mineralization has been achieved through infiltration of an amorphous precursor phase into collagen fibrils with the assistance of acidic polyelectrolytes and crystalization upon phase transformation, i.e. the polymer-induced liquid-precursor (PILP) process [12]. Based on those findings we further propose here a model of the subfibrillar texture of bone that will aid to explore the correlation between its ultrastructure and mechanical properties
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call