Ultrastructure of the mineralized collagen fibril- the relationship between collagen microfibrils and hydroxyapatite nanocrystals
EMSL Project ID
46706
Abstract
Biomineralization processes templated by soluble organic additives producing inorganic-organic nanocomposites represents one of the most unique and fascinating features of nature using bottom-up strategies at the nano scale to accomplish highly adaptive and multifunctional materials. It provides many insights for the development of novel materials in biomaterials, nanotechnology, and engineering by extracting various design principles from the analysis of natural systems. One such nanocomposite is bone, consisting primarily of collagen and hydroxyapatite (HA) nanocrystals with intimate association, in which HA nanocrystals are basically embedded within the collagen fibrils, and their c-axes arranged roughly parallel to the long axis of fibril. In our research, we have been able to duplicate the fundamental nanometer level of bone structure using a polymer-induced liquid-precursor (PILP) process. The ultrastructure of the mineralized collagen fibrils were each composed of a bundle of subfibrillar structures (subfibrils) resembling the microfibrillar substructure of collage fibrils in natural bone upon which the mineral is templated. Those subfibrils were about 10-nm wide and 50 ~ 150 nm long. Moreover, the biomimetically mineralized fibrils exhibited analogous texture and hierarchical structure to natural bone. Because of the fluidic character of the amorphous mineral precursor phase in bone mineralization, we hypothesize that the nanocrystals of HA are 'molded' by growing within the confined nanoscopic compartments delineated by the interstitial space of the self-assembled collagen fibrils. If this interstitial space is based upon the collagen microfibril model, then it seems reasonable to speculate that the mineral would interpenetrate throughout and encapsulate the collagen microfibrils forming core-shell cylindrical shape of subfibrils. Even though it is possible to distinguish the core-shell cylindrical shape of subfibrils by TEM through mass/thickness contrast, the extremely small size feature of subfibrils (about 10 nm wide) and dense packing in the bundle makes the analysis of the ultrastructure of the mineralized fibril by electron microscopy limited.In this proposal, we suggest the use of atom-probe tomography (APT) to determine the three dimensional chemical tomography of the nanoscale collagen-hydroxyapatite subfibrillar structure in our synthesized nanocomposites, in which this model system can then be used for comparison to the nanostructure of mammalian bone. A recent study by Gordon et al. demonstrated that pulsed-laser APT can be used to analyze organic fibers (diameter of 5-10 nm) within a magnetite (Fe3O4) mineral matrix. Thus, it is reasonable to propose that pulsed-laser APT could be used to analyze the proposed core-shell subfibrils of hydroxyapatite (Ca10(PO4)6(OH)2) and collagen. Hydroxyapatite is composed of Ca and P and will be easily distinguished from collagen (C-based) during APT analysis.
This study will probe the concept of controlled crystal growth and hierarchical structure templated by organic matrix in hard tissues, as well as exemplify the ability of using APT for resolving structure and composition of hybrid nanocomposites in biological and synthetic materials. It will bring a new perspective to the mechanism of bone mineralization, provide a more realistic model of bone nanostructure, and help understand bone diseases caused by defects in composition and structure, such as osteogenesis imperfecta, osteoporosis, and osteolytic malignancies.
Project Details
Project type
Limited Scope
Start Date
2012-02-03
End Date
2012-04-04
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members