Development of Self-Assembled Organothiol-Based Nanolithography Templates for Biomimetic Synthesis of Calcium Phosphate on Amyloid-Like Amelogenin Nanoribbons

Tooth enamel is the hardest tissue in the body mainly due to the intricate interwoven structure of highly organized apatite filaments that form it. It has been theorized that unidirectionally aligned (co-aligned) amyloid-like amelogenin nanoribbons (Amel NR) guide the formation of apatite by providing an energetically and stereochemically favorable scaffold for nucleation and transformation of amorphous calcium phosphate (ACP) precursor to hydroxyapatite (HAP). To understand the efficacy with which protein structures direct the nucleation of ACP and the subsequent transformation to HAP, studies have been carried out to quantitatively analyze the nucleation of ACP by self-assembled NRs of the full-length protein as well as varying sequences of peptides made up of protein subsegments responsible for self-assembly and ACP binding. Supramolecular block-copolymer templates with alternating hydrophilic and hydrophobic regions were also used to direct the self-assembly of amelogenin-derived peptide nanoribbons having discrete, spatially separated domains. These domains in turn templated the mineralization of filamentous and plate-shaped calcium phosphate. To create more versatile templates, we are using AFM-based nanolithography to create highly modifiable nanopatterns of novel organothiol monolayers self-assembled on Muscovite Mica. By using AFM probes, we perform Nanografting on monolayers of hydrophobic organothiols on Mica in predetermined patterns and backfill the patterns with hydrophilic thiols. The proposed system is similar to the block-copolymer system in its basic function, but with the capability of modifying the design on-the-fly to study the effects of geometry. While similar thiol systems on metal substrates (like nearly-atomically flat Au substrates) have been extensively studied and are even now used for a multitude of applications, the proposed system offers significantly better reproducibility, reusability, and affordability. Although the proposed system has been developed for the use of templating the growth of Amel NRs, it has the potential to be employed for a variety of other applications by modifying the surface chemistry of the Organothiol headgroups. Additionally, since Mica is the preferred substrate for the study of many soft matter systems, it provides the possibility of the direct study of many of these systems, eliminating the need for the modification of the parent molecule to enable its binding to the substrate. Monolayers of long chain alkanethiols (like the ones used on gold substrates) with average roughness ≈0.2nm have already been achieved with extremely adaptable grafting pattern thicknesses ranging from 50 nm-200 nm. By manipulating the spacing and dimensions of the 2D-patterns, as well as the composition of the mineralizing solution, we seek to find understand the controls the of scaffold geometry on nucleation and growth rates of the ACP precursor domains, as well as their transformation to HAP. Understanding how manipulating the scaffold geometry affects the fidelity of guided mineralization will move us closer towards the biomimetic synthesis of enamel-like materials.