Abstract
Synthetic nanostructured hybrid composites based on collagen and nanocrystalline apatites are interesting materials for the generation of scaffolds for bone tissue engineering. In this work, mineralized collagen fibrils were prepared in the presence of citrate and Eu3+. Citrate is an indispensable and essential structural/functional component of bone. Eu3+ endows the mineralized fibrils of the necessary luminescent features to be potentially employed as a diagnostic tool in biomedical applications. The assembly and mineralization of collagen were performed by the neutralization method, which consists in adding dropwise a Ca(OH)2 solution to a H3PO4 solution containing the dispersed type I collagen until neutralization. In the absence of citrate, the resultant collagen fibrils were mineralized with nanocrystalline apatites. When citrate was added in the titrant solution in a Citrate/Ca molar ratio of 2 or 1, it acted as an inhibitor of the transformation of amorphous calcium phosphate (ACP) to nanocrystalline apatite. The addition of Eu3+ and citrate in the same titrant solution lead to the formation of Eu3+–doped citrate–coated ACP/collagen fibrils. Interestingly, the relative luminescent intensity and luminescence lifetime of this latter composite were superior to those of Eu3+–doped apatite/collagen prepared in absence of citrate. The cytocompatibility tests, evaluated by the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) colorimetric assay in a dose–dependent manner on GTL–16 human gastric carcinoma cells, on MG–63 human osteosarcoma cells and on the m17.ASC, a spontaneously immortalized mouse mesenchymal stem cell clone from subcutaneous adipose tissue, show that, in general, all samples are highly cytocompatible.
Highlights
The hierarchically–structured architecture of human mineralized tissues such as bones and teeth has long fascinated scientists and engineers, and a considerable effort has been devoted to produce synthetic materials inspired from the natural ones [1]
The interaction between tropocollagen units leads to self–organization into fibrillar structures having a regular array of holes and overlap zones that can be observed by transmission electron microscopy (TEM) as a periodic banding pattern of 67 nm [7,8]
The results revealed by that adding citrate to the titrant Ca(OH)2 solution, the mineralized fibrils are basically constituted of amorphous calcium phosphate (ACP) or incipiently formed poorly crystalline apatite nanoparticles
Summary
The hierarchically–structured architecture of human mineralized tissues such as bones and teeth has long fascinated scientists and engineers, and a considerable effort has been devoted to produce synthetic materials inspired from the natural ones [1]. Crystals 2019, 9, 13 mineralized tissues is a big challenge for materials scientists because they are formed in vivo through biomineralization processes that involve cascades of complex events such as self–assembly, mineralization and self–organization [2]. The basic building block of bone tissue structure is a self–assembled collagen fibril (mainly type I collagen) mineralized with oriented apatite nanocrystals at both intrafibrillar and interfibrillar zones [3,4,5,6]. The collagen molecules self–assemble under physiological conditions into triple helical structures forming the so–called tropocollagen. The last results have shown that the use of citrate is an interesting and straightforward nature inspired strategy to control the chemical–physical features of the apatite for the development of improved nanoparticle–based biomaterials [20,21,22]
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