Polyaminoacids in Biomimetic Collagen Mineralization: Roles of Isomerization and Disorder in Polyaspartic and Polyglutamic Acids

Abstract

The extracellular matrix of hard connective tissues is composed primarily of mineralized collagen fibrils. Acidic noncollagenous proteins play important roles in mediating mineralization of collagen. Polyaspartate, a homopolymer substitute for such proteins, has been used extensively in in vitro models to produce biomimetic mineralized collagen. Polyglutamate behaves differently in mineralization models, despite its chemical similarity. We show that polyaspartate is a 350 times more effective inhibitor of solution precipitation of hydroxyapatite than polyglutamate. Supersaturated CaP solutions stabilized with polyaspartic acid produce collagen with aligned intrafibrillar mineral, while solutions containing polyglutamate lead to the formation of unaligned mineral clusters on the fibril surface. Molecular analysis showed that the commercial polyaspartic acid contains substantial isomerization, unlike polyglutamic acid. Hence, the secondary structure of polyaspartic acid is more disordered than that of polyglutamic acid. The increased flexibility of the polyaspartic acid chain may explain its potency as an inhibitor of solution crystallization and a mediator of intrafibrillar collagen mineralization.

Multifunctional Nanomachinery for Enhancement of Bone Healing

“…Spontaneously self‐assembly of RNA into intrinsically disordered RNA‐ACP tertiary structures also enable these flexible RNA molecules to bind more efficiently with cation ions or mineral nanoparticles. [ 27 ] These external mineral nanoparticles protect the RNA molecules from degradation and increase their stability (Figure S10, Supporting Information). Stable RNA could also be detected on the surface of collagen fibrils during the late stage of mineralization (Figure S11, Supporting Information).…”

Influence of Biomimetically Mineralized Collagen Scaffolds on Bone Cell Proliferation and Immune Activation

“…In order to achieve intrafibrillar mineralization, i.e., deposition of minerals within the gap zone of collagen fibrils, which occurs in the native bone tissue, it is necessary to simulate the natural process of collagen mineralization. In the natural process, the mineral component is interconnected with collagen molecules through non-collagenous proteins, i.e., osteocalcin, osteopontin and bone sialoprotein, which are generally highly negatively charged due to the abundance of acidic amino acids in their molecules [ 24 ]; for a review, see [ 10 , 11 ]). This phenomenon inspired the development of the polymer-induced liquid precursor (PILP) process, where the mineralization of collagen in ionic solutions is facilitated by the presence of various anionic polymers, such as poly-L-aspartic acid, poly-L-glutamic acid, polyvinylphosphonic acid and polyacrylic acid ([ 24 ]; for a review, see [ 10 , 11 ]).…”

“…In the natural process, the mineral component is interconnected with collagen molecules through non-collagenous proteins, i.e., osteocalcin, osteopontin and bone sialoprotein, which are generally highly negatively charged due to the abundance of acidic amino acids in their molecules [ 24 ]; for a review, see [ 10 , 11 ]). This phenomenon inspired the development of the polymer-induced liquid precursor (PILP) process, where the mineralization of collagen in ionic solutions is facilitated by the presence of various anionic polymers, such as poly-L-aspartic acid, poly-L-glutamic acid, polyvinylphosphonic acid and polyacrylic acid ([ 24 ]; for a review, see [ 10 , 11 ]). Additionally, other negatively charged compounds, such as citric acid [ 47 ], sericin [ 69 ], carboxymethyl chitosan [ 30 ], and also fluid shear stress, generated, e.g., by dynamic cell culture systems [ 11 ], have been shown to have a positive effect on intrafibrillar collagen mineralization.…”

“…The mineral component has been incorporated into the collagen scaffolds by two main procedures, i.e., by admixing mineral micro- or nanoparticles into the collagen matrix [ 8 , 9 , 10 , 11 , 12 ] or by a spontaneous process referred to as biomimetic mineralization. Biomimetic mineralization includes “classical” incubation of the scaffolds in a simulated body fluid (SBF) or in other related fluids containing calcium, phosphate and other ions [ 9 , 23 ] or a more sophisticated, bioinspired polymer-induced liquid precursor (PILP) process, in which the mineralization of collagen in ionic solutions is facilitated by the presence of various anionic polymers that mimic negatively charged non-collagenous proteins in the native bone tissue [ 24 ]; for a review, see [ 10 , 11 , 25 ]. Biomimetic mineralization of the collagen matrix can also be realized directly by cells, e.g., by dental pulp stem cells [ 26 ] or even by osteosarcoma-derived line cells, such as osteoblast-like Saos-2 cells [ 27 ].…”

Self-assembly behavior and sustained drug release properties of amphiphilic poly(amino acid)s

“…14 Poly(amino acid)s have structures similar to those of proteins and show good compatibility with cells, tissues and other biological components. [15][16][17] The biocompatibility, biodegradability and selfassembly behavior of poly(amino acid)s make them have a very wide application prospect in controlled drug release systems. 18 In addition, poly(amino acid)s exhibit different characteristics from ordinary macromolecules due to the existence of secondary structures (a-helix and b-fold).…”