In silico study on probing atomistic insights into structural stability and tensile properties of Fe-doped hydroxyapatite single crystals

Abstract

Hydroxyapatite (HA, Ca10PO4(OH)2) is a widely explored material in the experimental domain of biomaterials science, because of its resemblance with natural bone minerals. Specifically, in the bioceramic community, HA doped with multivalent cations (e.g., Mg2+, Fe2+, Sr2+, etc.) has been extensively investigated in the last few decades. Experimental research largely established the critical role of dopant content on mechanical and biocompatibility properties. The plethora of experimental measurements of mechanical response on doped HA is based on compression or indentation testing of polycrystalline materials. Such measurements, and more importantly the computational predictions of mechanical properties of single crystalline (doped) HA are scarce. On that premise, the present study aims to build atomistic models of Fe2+-doped HA with varying Fe content (10, 20, 30, and 40 mol%) and to explore their uniaxial tensile response, by means of molecular dynamics (MD) simulation. In the equilibrated unit cell structures, Ca(1) sites were found to be energetically favourable for Fe2+ substitution. The local distribution of Fe2+ ions significantly affects the atomic partial charge distribution and chemical symmetry surrounding the functional groups, and such signatures are found in the MD analyzed IR spectra. The significant decrease in the intensity of the IR bands found in the Fe-doped HA together with band splitting, because of the symmetry changes in the crystal structure. Another important objective of this work is to computationally predict the mechanical response of doped HA in their single crystal format. An interesting observation is that the elastic anisotropy of undoped HA was not compromised with Fe-doping. Tensile strength (TS) is systematically reduced in doped HA with Fe2+ dopant content and a decrease in TS with temperature can be attributed to the increased thermal agitation of atoms at elevated temperatures. The physics of the tensile response was rationalized in terms of the strain dependent changes in covalent/ionic bond framework (Ca–P distance, P–O bond strain, O–P–O angular strain, O–H bond distance). Further, the dynamic changes in covalent bond network were energetically analyzed by calculating the changes in O–H and P–O bond vibrational energy. Summarizing, the current work establishes our foundational understanding of the atomistic phenomena involved in the structural stability and tensile response of Fe-doped HA single crystals.

A Study of the Peculiarities of the Formation of a Hybrid Interface Based on Polydopamine between Dental Tissues and Dental Composites, Using IR and Raman Microspectroscopy, at the Submicron Level

“…At the same time, a number of works devoted to theoretical and experimental studies of vibrational spectra of calcium phosphates, which are typical of natural enamel apatite, indicate that in different calcium phosphate nanostructures, depending on the stoichiometry and local atomic environment, vibrational frequencies can be observed, attributed to P-O bonds [56,[74][75][76] It should be noted that the splitting of the main phosphate band ν 3 PO 4 in IR spectra is often associated with the substitution of calcium atoms in the crystal lattice by external ions. In this case, a characteristic feature is the appearance of a band in the IR spectra in the region of 1095 cm −1 , assigned to the Ca-O-P bond [81], which is also observed in our experimental spectrum.…”

Hierarchical and reconfigurable interfibrous interface of bioinspired Bouligand structure enabled by moderate orderliness

“…The FTIR spectra calculations of simulated molecular models with different tensile strain and spatial orientation angles were conducted using LAMMPS code package and an available Python code ( 47 , 51 , 52 ). The LAMMPS was used to compute the net dipole moment of the system.…”

Magnetic Hydroxyapatite Nanoparticles in Regenerative Medicine and Nanomedicine

“…Such ionic doping/substitutions alter the thermodynamic stability of the HA crystal as well as its bulk and surface properties while retaining its lattice structure. Several studies have explored the synthesis of variously doped HA nanoparticles to obtain materials with enhanced biologic abilities [ 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 ]. On the other hand, the doping of HA with magnetic ions (such as Fe) has gained considerable attention as a switching system to remotely control and tune the regenerative process, for its ability to become superparamagnetic under the application of static magnetic field, as well as acting as a contrast agent for magnetic resonance imaging (MRI) [ 97 ] and a heat mediator for hyperthermia-based anti-cancer therapies when an alternating magnetic field is applied [ 98 , 99 ].…”