Oligo(l-glutamic acids) in Calcium Phosphate Precipitation: Mechanism of Delayed Phase Transformation

Proteins and their mimics that contain negatively charged sequences are important in natural and biomimetic mineralization. The mechanism by which these sequences affect calcium phosphate mineralization is not well understood. Here, peptides containing different numbers of repeat units of contiguous glutamic acid residues, oligo(l-glutamic acid)_n (n = 3, 7, 8, 10), were investigated with regards to the mechanism in delaying the crystallization of amorphous calcium phosphate (ACP) while holding the amount of carboxylic acid groups in solution constant. Increasing peptide chain length increases the stability of ACP at a certain total amount of carboxylic acid groups in solution. This effect is shown to be due to stronger binding as well as binding to more calcium ions per peptide by the longer oligopeptides compared to the shorter ones. It is proposed that these associations delay the structural rearrangement of calcium ions and the dehydration of ACP, which are required for the crystallization of hydroxyapatite. The initial nucleation and the local structure of ACP, however, do not vary with chain length. This second part of a two-part series provides an improved mechanistic understanding of how organic additives, especially those with contiguous acidic amino acid sequences, modulate the kinetics of calcium phosphate precipitation and phase transformation.

Oligo(l-glutamic acids) in Calcium Phosphate Precipitation: Chain Length Effect

The understanding of calcium phosphate precipitation is of major interest in different fields of science, including medicine, biomaterials, and physical chemistry. The presence of additive biomacromolecules has been known to influence various stages of the precipitation process from nucleation to crystal growth. In the current work, well-defined sequences of short, negatively charged peptides, oligo(l-glutamic acids), were utilized as a model, inspired by contiguous sequences of acidic amino acids in natural biomineralization proteins. The precipitate morphology and phases, the element time profile in solution and in the precipitates, as well as the kinetics during the precipitation process were analyzed to explain the effect of these short peptides on calcium phosphate precipitation. The results show that peptides can delay the phase transformation of an amorphous precursor phase to hydroxyapatite and that there is an optimal chain length for this effect at a given concentration of peptide. This study is the first part of a two-part series and is followed by a subsequent work to reveal the mechanism by which these short peptides influence the calcium phosphate precipitation.

Anionic Polymer Brushes for Biomimetic Calcium Phosphate Mineralization-A Surface with Application Potential in Biomaterials

This article describes the synthesis of anionic polymer brushes and their mineralization with calcium phosphate. The brushes are based on poly(3-sulfopropyl methacrylate potassium salt) providing a highly charged polymer brush surface. Homogeneous brushes with reproducible thicknesses are obtained via surface-initiated atom transfer radical polymerization. Mineralization with doubly concentrated simulated body fluid yields polymer/inorganic hybrid films containing AB-Type carbonated hydroxyapatite (CHAP), a material resembling the inorganic component of bone. Moreover, growth experiments using Dictyostelium discoideum amoebae demonstrate that the mineral-free and the mineral-containing polymer brushes have a good biocompatibility suggesting their use as biocompatible surfaces in implantology or related fields.

EDTA and NTA Effectively Tune the Mineralization of Calcium Phosphate from Bulk Aqueous Solution

This study describes the effects of nitrilotriacetic acid (NTA) and ethylenediaminotetraacetic acid (EDTA) on the mineralization of calcium phosphate from bulk aqueous solution. Mineralization was performed between pH 6 and 9 and with NTA or EDTA concentrations of 0, 5, 10, and 15 mM. X-ray diffraction and infrared spectroscopy show that at low pH, mainly brushite precipitates and at higher pH, mostly hydroxyapatite forms. Both additives alter the morphology of the precipitates. Without additive, brushite precipitates as large plates. With NTA, the morphology changes to an unusual rod-like shape. With EDTA, the edges of the particles are rounded and disk-like particles form. Conductivity and pH measurements suggest that the final products form through several intermediate steps.

A Dendritic Amphiphile for Efficient Control of Biomimetic Calcium Phosphate Mineralization

The phase behavior of a dendritic amphiphile containing a Newkome-type dendron as the hydrophilic moiety and a cholesterol unit as the hydrophobic segment is investigated at the air-liquid interface. The amphiphile forms stable monomolecular films at the air-liquid interface on different subphases. Furthermore, the mineralization of calcium phosphate beneath the monolayer at different calcium and phosphate concentrations versus mineralization time shows that at low calcium and phosphate concentrations needles form, whereas flakes and spheres dominate at higher concentrations. Energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and electron diffraction confirm the formation of calcium phosphate. High-resolution transmission electron microscopy and electron diffraction confirm the predominant formation of octacalcium phosphate and hydroxyapatite. The data also indicate that the final products form via a complex multistep reaction, including an association step, where nano-needles aggregate into larger flake-like objects.

Recombinant DNA technology and click chemistry: a powerful combination for generating a hybrid elastin-like-statherin hydrogel to control calcium phosphate mineralization

Understanding the mechanisms responsible for generating different phases and morphologies of calcium phosphate by elastin-like recombinamers is supreme for bioengineering of advanced multifunctional materials. The generation of such multifunctional hybrid materials depends on the properties of their counterparts and the way in which they are assembled. The success of this assembly depends on the different approaches used, such as recombinant DNA technology and click chemistry. In the present work, an elastin-like recombinamer bearing lysine amino acids distributed along the recombinamer chain has been cross-linked via Huisgen [2 + 3] cycloaddition. The recombinamer contains the SNA15 peptide domains inspired by salivary statherin, a peptide epitope known to specifically bind to and nucleate calcium phosphate. The benefit of using click chemistry is that the hybrid elastin-like-statherin recombinamers cross-link without losing their fibrillar structure. Mineralization of the resulting hybrid elastin-like-statherin recombinamer hydrogels with calcium phosphate is described. Thus, two different hydroxyapatite morphologies (cauliflower- and plate-like) have been formed. Overall, this study shows that crosslinking elastin-like recombinamers leads to interesting matrix materials for the generation of calcium phosphate composites with potential applications as biomaterials.

Facile synthesis of scandium fluoride oriented single-crystalline rods and urchin-like structures by a gas–solution interface technique

ScF₃ rod-like oriented crystals and urchin-like structures were synthesized at the gas–solution interface for the first time.

ZnO nanorods assembled with different porphyrins – size-tunable hybrid particles

We present a fundamental study on ZnO nanorod–porphyrin assembly formation in solution, providing the key to novel tunable hybrid assemblies with potential in solar energy conversion.

Formation of calcium phosphate nanostructures under the influence of self-assembling hybrid elastin-like-statherin recombinamers

The self-assembly properties of elastin-like-statherin recombinamers have great influence on calcium phosphate mineralization.