Formation of Hydroxyapatite via Transformation of Amorphous Calcium Phosphate in the Presence of Alginate Additives

Abstract

Hydroxyapatite (HA) is the primary mineral of vertebral tooth and bone tissue, thus, it is often incorporated into synthetic composite materials designed for hard tissue engineering applications.Understanding the formation mechanisms of apatitic minerals and the effects of matrix molecules during mineralization is vitally important to instruct the design of synthetic biomaterials. Here we explore the mechanism of HA formation via an amorphous calcium phosphate (ACP) precursor and the effects of alginate-based additives on the reaction progression. We found that in additive-2 free experiments the solution speciation was dominated by the classical formation of ion pairs prior to the emergence of an ACP phase, which was then followed by a transformation to HA. In the presence of alginate-based additives, ACP formation was retarded by several orders of magnitude due to kinetic hinderance and possible stabilization of intermediates, depending on the functionality of the molecules. ACP lifetime was also prolonged in the presence of additives and this stabilizing effect was associated with the surface adsorption capacity of the additives which suggests a solvent-mediated transformation mechanism. When additives with G-units were introduced in the system, the final precipitates were composed of a mixture of octacalcium phosphate (OCP) and HA via effective suppression of HA formation. Our results demonstrate that compositional variations in the additive molecules strongly influence mineralization pathways.

Nucleation of Brushite and Hydroxyapatite from Amorphous Calcium Phosphate Phases Revealed by Dynamic In Situ Raman Spectroscopy

“…Moreover, calcium phosphates find wide medical and industrial applications in dentistry, orthopedics, reconstructive surgery, food additives, fertilizers, and water depollution (1)(2)(3)(4)(5)(6). The formation of calcium phosphates and the interactions and associations of these minerals with organic macromolecules have been widely investigated under in vivo and in vitro conditions in the last decades (7-10) in order to identify the nature of first primary precipitating particles, their lifetime and their chemical transformation into other minerals in aqueous media (11)(12)(13)(14)(15)(16)(17)(18)(19)(20). For example, the formation of hydroxyapatite nanocrystals (Ca10(PO4)6(OH)2) under biotic or abiotic conditions involves the early formation of a transient amorphous calcium phosphate phase (ACP) (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26).…”

“…The formation of calcium phosphates and the interactions and associations of these minerals with organic macromolecules have been widely investigated under in vivo and in vitro conditions in the last decades (7-10) in order to identify the nature of first primary precipitating particles, their lifetime and their chemical transformation into other minerals in aqueous media (11)(12)(13)(14)(15)(16)(17)(18)(19)(20). For example, the formation of hydroxyapatite nanocrystals (Ca10(PO4)6(OH)2) under biotic or abiotic conditions involves the early formation of a transient amorphous calcium phosphate phase (ACP) (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26). This phase may either (1) transform directly by a solid-state transformation, (2) dissolve and reprecipitate to produce nanocrystalline hydroxyapatite, or (3) nucleate inside other amorphous phases (e.g.…”

“…Therefore, a convincing temporal and/or spatial characterization of phosphate formation in natural or synthetic samples is still lacking (e.g. 5,8,15,[27][28] despite the use of sophisticated time-resolved measurements and simulations performed in the last two decades, such as in situ X-ray absorption (XAS), in situ small/wide-angle X-ray scattering (SAXS/WAXS), electron transmission microscopy (Cryo-TEM or liquid-cell TEM), atomic force microscopy (liquid-cell AFM) and ab initio numerical simulations based on the density functional theory (e.g. 1, 12-13, 19, 25-27, 29-30).…”

Antibacterial graphene‐based hydroxyapatite/chitosan coating with gentamicin for potential applications in bone tissue engineering

“…The prospective solution represents the combination of biopolymer matrix and bioceramics, for example, hydroxyapatite‐based composite coatings with natural or synthetic polymers (Qu, Fu, Han, & Sun, 2019). The most commonly used natural polymers are collagen (Tiplea et al, 2017), gelatin (Maji & Dasgupta, 2019), alginate (Ucar et al, 2019), and chitosan (Januariyasa, Ana, & Yusuf, 2020; Maji & Dasgupta, 2019; Yadav, Rhee, Park, & Hui, 2014). Synthetic polymers that are most often used in bone tissue engineering are poly(lactide‐co‐glycolide) (PLGA) (Guo, Du, Wang, Cai, & Yang, 2020), polycaprolactone (PCL) (Liu et al, 2020), poly(vinyl alcohol) (PVA) (Januariyasa et al, 2020), poly(glycolic acid) (PGA) (Takahashi, Yamaguchi, Tanimoto, Yao‐Umezawa, & Kasai, 2015), poly(lactic acid) (PLA) (Behera, Sivanjineyulu, Chang, & Chiu, 2018; Zhang et al, 2020).…”

Advanced Materials Based on Nanosized Hydroxyapatite

“…In the presence of guluronate-unit (G-unit) additives, the final precipitates were composed of a mixture of octacalcium phosphate and HAP. The work helps to understand the complex biomineralization processes in the presence of multiple components [ 74 ]. Sans et al [ 75 ] developed a robust method based on hydrothermal methods but without using any additive, only using organic solvent to produces pure and crystalline HAP with a controlled shape and size.…”