Ion release from hydroxyapatite and substituted hydroxyapatites in different immersion liquids: in vitro experiments and theoretical modelling study

Abstract

Multi-substituted hydroxyapatites (ms-HAPs) are currently gaining more consideration owing to their multifunctional properties and biomimetic structure, owning thus an enhanced biological potential in orthopaedic and dental applications. In this study, nano-hydroxyapatite (HAP) substituted with multiple cations (Sr 2+ , Mg 2+ and Zn 2+ ) for Ca 2+ and anion ( Si O 4 4 − ) for P O 4 3 − and OH − , specifically HAPc-5%Sr and HAPc-10%Sr (where HAPc is HAP-1.5%Mg–0.2%Zn–0.2%Si), both lyophilized non-calcined and lyophilized calcined, were evaluated for their in vitro ions release. These nanomaterials were characterized by scanning electron microscopy, field emission-scanning electron microscopy and energy-dispersive X-ray, as well as by atomic force microscope images and by surface specific areas and porosity. Further, the release of cations and of phosphate anions were assessed from nano-HAP and ms-HAPs, both in water and in simulated body fluid, in static and simulated dynamic conditions, using inductively coupled plasma optical emission spectrometry. The release profiles were analysed and the influence of experimental conditions was determined for each of the six nanomaterials and for various periods of time. The pH of the samples soaked in the immersion liquids was also measured. The ion release mechanism was theoretically investigated using the Korsmeyer–Peppas model. The results indicated a mechanism principally based on diffusion and dissolution, with possible contribution of ion exchange. The surface of ms-HAP nanoparticles is more susceptible to dissolution into immersion liquids owing to the lattice strain provoked by simultaneous multi-substitution in HAP structure. According to the findings, it is rational to suggest that both materials HAPc-5%Sr and HAPc-10%Sr are bioactive and can be potential candidates in bone tissue regeneration.

Physical-Chemical and Biological Properties of Novel Resin-Based Composites for Dental Applications

“…However, the information on ion release from hydroxyapatite required studying this issue to be sure that all tested llers are safe against probiotic bacteria that are present in the gastrointestinal tract and may be exposed to ions released e.g. in the oral cavity [32].…”

A Comparative EPR Study of Non-Substituted and Mg-Substituted Hydroxyapatite Behaviour in Model Media and during Accelerated Ageing

“…For example, Andrés et al showed that the degradation rate of Mg substituted HAP in PBS, PBS with lysozyme, and acetate buffer increases with increasing Mg content [18]. The surface of multi-substituted HAP nanoparticles (Mg, Zn, Sr, Si-HAP and Mg, Zn, Si-HAP) was shown to be more susceptible to dissolution in SBF (simulated body fluid) and water due to the lattice strain provoked by the simultaneous multi-substitution of ions in the structure of HAP [19]. However, to date, no data on the changes in the local structure of Mg-substituted HAP during exposure to different media has been published.…”

“…On the other hand, gamma radiation induces defects or free radicals in the material with a different nature and structure, which depend on the composition and the synthesis conditions of the samples. In addition, they can present different behaviour in physiological solutions [19]. Furthermore, due to the importance of the shelf-life of the material for biomedical applications and storage conditions, the accelerated ageing method is used.…”

Biomimetic Composite Coatings for Activation of Titanium Implant Surfaces: Methodological Approach and In Vivo Enhanced Osseointegration

“…Furthermore, the bioactive performance of bioceramic materials was improved by substituting various elements that are essential for bone regeneration, such as Mg, Zn or Si [20][21][22][23][24][25][26], into the HAP lattice, resulting in multi-substituted HAP (ms-HAP) bioceramics. The interest in this substitution originated from the well-established role of these elements in bone regeneration [27,28].…”