Prospects and Pits on the Path of Biomimetics: The Case of Tooth Enamel

Abstract

This review presents a discourse on challenges in understanding and imitating the process of amelogenesis in vitro on the molecular scale. In light of the analysis of imitation of the growth of dental enamel, it also impends on the prospects and potential drawbacks of the biomimetic approach in general. As the formation of enamel proceeds with the protein matrix guiding the crystal growth, while at the same time conducting its own degradation and removal, it is argued that three aspects of amelogenesis need to be induced in parallel: a) crystal growth; b) protein assembly; c) proteolytic degradation. A particular emphasis is therefore placed on ensuring conditions for proteolysis-coupled protein-guided crystallization to occur. Discussed are structural and functional properties of the protein species involved in amelogenesis, mainly amelogenin and enamelysin, the main protein and the protease of the developing enamel matrix, respectively. A model of enamel growth based on controlled delivery of constituent ions or crystalline or amorphous building blocks by means of amelogenin is proposed. The importance of high viscosity of the enamel matrix and a more intricate role that water may play in such a gelatinous medium are also touched upon. The tendency of amelogenin to self-assemble into fibrous and rod-shaped morphologies is considered as potentially important in explaining the formation of elongated apatite crystals. The idea that a preassembling protein matrix serves as a template for the uniaxial growth of apatite crystals in enamel is finally challenged with the one based on co-assembly of the protein and the mineral phases.

Dynamic Light Scattering Based Microelectrophoresis: Main Prospects and Limitations

“…Convenient for following the adsorption of species onto dispersed particles of interest, ζ potential analyses have also recently been used to detect binding of amelogenin nanospheres onto apatite crystals under various conditions [75] and correspondingly improve the understanding of the mechanism of amelogenesis, a biomineralization process during which a finely structured protein gel directs the growth of hierarchically ordered enamel crystals, the hardest material in the vertebrate body. [76] Finally, the brain itself, as a whole, has a specific ζ potential, which implies that the extracellular translational motion is governed by electrokinetic effects under this naturally occurring electric field in addition to diffusion and tissue tortuosity. [77] …”

Amelogenin as a promoter of nucleation and crystal growth of apatite

“…Secondly, its microstructure is dominated by parallel rods [1,2], composed of bundles of 40-60 nm wide apatite crystals with the aspect ratio of up to 1:10 4 . And thirdly, it is the most mineralized tissue in the human body, comprising 96-98 wt% of the mineral phase, apatite, which is best described by the stoichiometric formula (Ca,Z) 10 (PO 4 ,Y) 6 (OH,X) 2 , where Z¼Na + , Mg 2 + , K + , Sr 2 + , etc., Y ¼CO 3 2 À , HPO 4 2 À and X¼Cl À , F À . The microstructural and morphological difference of apatite crystals in enamel compared to those present in bone and dentin have suggested that the mechanism of formation of apatite crystals in enamel may be markedly different from the organic-template-based one associated with collagenous hard tissues, such as bone or dentin [3].…”

The role of hydroxyl channel in defining selected physicochemical peculiarities exhibited by hydroxyapatite

“…This is illustrated in Fig.1, where two HAp crystals of geological origin are shown: one with the exposed (001) face by cutting and the other one with diagonal (011) and (101) faces instead of (001), the result of the sole directional growth of (001). An example among apatites of biomineral origin comes from the tooth enamel, where HAp grows almost uniaxially in the [001] direction, leading to the comparatively minor presence of basal, (001) faces in comparison with the prismatic, (hk0) ones in the final crystal forms 74 . The growth of HAp platelets (30 × 20 × 2 nm 75 ) in bone, however, proceeds in a very different manner.…”