The effect of polyaspartate chain length on mediating biomimetic remineralization of collagenous tissues

Abstract

Formation of hydroxyapatite (HAP) within collagen fibrils, as found in bone, dentine and cementum, is thought to be mediated by proteins rich in aspartate (Asp) and glutamate such as osteopontin and bone sialoprotein, respectively. Indeed polyaspartate ( pAsp), a homopolymer analogue of such proteins, has been shown to induce intrafibrillar mineralization of collagen from solutions of calcium and phosphate that are supersaturated with respect to HAP. To elucidate the role of pAsp in mineralization of collagen, we explored the effect of pAsp chain length on in vitro HAP deposition in demineralized mouse periodontal tissue sections. Through characterization of both tissue sections and mineralizing solution, we show that chain length contributes to the effectiveness of pAsp in mediating intrafibrillar mineralization. This function appears to be associated with inhibition of otherwise kinetically favoured crystallization in the bulk solution, which allows for intrafibrillar crystallization, though this does not preclude the possibility of a more active role for pAsp in addition. Inhibition of crystallization in solution by pAsp occurs by slowing the growth of amorphous calcium phosphate and stabilization of this phase, rather than by sequestration of Ca 2þ ions. These results suggest that the length of Asp-rich sequences of mineralizing proteins may be essential to their function, and could also be useful in optimization of mineralized tissue replacement synthesis.

Influence of Calcium Binding on Conformations and Motions of Anionic Polyamino Acids. Effect of Side Chain Length

“…Polyelectrolytes, such as anionic poly(amino acids), are widely used in diverse applications including water treatment and purification [ 1 ], anticorrosion agents [ 2 ], drug delivery [ 3 , 4 , 5 , 6 ] and tissue engineering [ 7 , 8 , 9 , 10 , 11 ]. Biodegradable and biocompatible anionic poly(amino acids) are attractive due to their comparative cheapness and ease of high-volume manufacturing.…”

“…For example, poly-(α- l aspartic acid) (PASA) and poly-(α- l glutamic acid) (PGA) are commonly used to guide nucleation and crystal growth in calcium containing minerals [ 8 , 12 , 13 ]. PASA and PGA have successfully been used in the regulation of mineralization in organic matrices in the synthesis of scaffolds for bone tissue [ 8 , 9 , 10 ]; anionic poly(amino acids) (both PASA and PGA) and short peptides can be grafted onto surfaces to increase mineralization [ 14 , 15 , 16 ]. On the other hand, in some cases, anionic poly(amino acids) are used for the opposite purpose, that is, to inhibit calcification [ 17 , 18 , 19 ].…”

Biomineralization of Collagen-Based Materials for Hard Tissue Repair

“…Overall, the establishment of Gibbs-Donnan equilibrium suggested that both short-range electrostatic forces driven by charge distribution and long-range osmosis driven by osmotic pressure between the extrafibrillar and intrafibrillar water compartments are responsible for collagen mineralization. The work provided significant insight of the effect of driving forces on ACP infiltration and for the first time disclosed the crucial role of osmotic forces in collagen mineralization [ 75 , 81 , 82 ]. It opened a new pathway in explaining collagen mineralization mechanisms.…”

The Significance and Utilisation of Biomimetic and Bioinspired Strategies in the Field of Biomedical Material Engineering: The Case of Calcium Phosphat—Protein Template Constructs

“…Conversely, other reports suggested that collagen does provide a heterogenous nucleation template without the need of NCPs via electrostatic interactions between apatite and COL [37]. The carboxylic groups (-COO − ) of glutamic (Glu), aspartic (Asp), and glucuronic (Glc) acid sidechains attract and bind two Ca 2+ ions from solution and further attract PO 4 3− ions so as to form a connective CaP network with consequential nucleation [38,39]. A large number of NCPs and phosphorylated modifications thereof [40,41] are strongly involved in the matrix vesicle-mediated mineralisation process and play essential roles in the regulation of bone biomineralisation, such as via the initiation of the formation of ACP, apatite nucleation, and crystal growth, as well as via inhibition [42].…”