The influence of Sr and H3PO4 concentration on the hydration of SrCaHA bone cement

Crystallisation of phosphates revisited: a multi-step formation process for SrHPO4

SrHPO4 is used in a multitude of applications, including biomedicine, catalysts, luminescent materials, and batteries. However, the performance of these materials depends on the ability to control the formation and transformation of strontium phosphates. This work focuses on the application of in situ and ex situ measurements, including synchrotron-based X-ray diffraction (XRD) analysis, luminescence of Ce3+ and Eu3+ dopants, light transmission, reflectance, and thermogravimetry to track structural changes in SrHPO4 under different experimental conditions. Ex situ analysis of aliquots revealed favourable crystallisation of β-SrHPO4 through the formation of Sr6H3(PO4)5·2H2O as an intermediate. Furthermore, in situ analysis showed that the reaction mechanism evolves via the initial formation of amorphous strontium phosphate and Sr5(PO4)3OH, which subsequently transforms to γ-SrHPO4. Analysis of the luminescence properties of the lanthanide dopants provided insights into the coordination environments of the substituted Sr2+ sites.

Toughening of Bioceramic Composites for Bone Regeneration

Bioceramics are widely considered as elective materials for the regeneration of bone tissue, due to their compositional mimicry with bone inorganic components. However, they are intrinsically brittle, which limits their capability to sustain multiple biomechanical loads, especially in the case of load-bearing bone districts. In the last decades, intense research has been dedicated to combining processes to enhance both the strength and toughness of bioceramics, leading to bioceramic composite scaffolds. This review summarizes the recent approaches to this purpose, particularly those addressed to limiting the propagation of cracks to prevent the sudden mechanical failure of bioceramic composites.

A Novel Fast-Setting Strontium-Containing Hydroxyapatite Bone Cement With a Simple Binary Powder System

In recent years, strontium-substituted calcium phosphate bone cement (Sr-CPC) has attracted more and more attentions in the field of bone tissue repair due to its comprehensive advantages of both traditional CPC and Sr ions. In this study, a crucial Sr-containing α-Ca_{3 - x} Sr _x (PO₄)₂ salt has been synthesized using a simplified one-step method at lower synthesis temperature. A novel Sr-CPC has been developed based on the simple binary Sr-containing α-Ca_{3 - x} Sr _x (PO₄)₂/Ca₄(PO₄)₂O cement powder. The physicochemical properties and hydration mechanism of this Sr-CPC at various Sr contents were intensively investigated. The setting product of this Sr-CPC after a set for 72 h is a single-phase Sr-containing hydroxyapatite, and its compressive strength slightly decreased and its setting time extended with the increase of Sr content. The hydration process included the initial formation of the medium product CaHPO₄⋅2H₂O (30 min∼1 h), the following complete hydration of Ca₄(PO₄)₂O and the initially formed CaHPO₄⋅2H₂O (2∼6 h), and the final self-setting of α-Ca_{3 - x} Sr _x (PO₄)₂ (6 h∼). The compressive strength of Sr-CPC, which was closely related to the transformation rate of Sr-containing hydroxyapatite, tended to increase with the extension of hydration time. In addition, Sr-CPC possessed favorable cytocompatibility and the effect of Sr ions on cytocompatibility of Sr-CPC was not obvious at low Sr contents. The present study suggests α-Ca_{3 - x} Sr _x (PO₄)₂ is a kind of vital Sr-containing salt source which is useful to develop some novel Sr-containing biomaterials. In addition, the new Sr-containing cement system based on this simple binary α-Ca_{3 - x} Sr _x (PO₄)₂/Ca₄(PO₄)₂O cement powder displayed an attractive clinical application potential in orthopedics.

A novel and easy-to-prepare strontium(II) modified calcium phosphate bone cement with enhanced mechanical properties

The aim of this study was to evaluate two different approaches to obtaining strontium-modified calcium phosphate bone cements (SrCPCs) without elaborate synthesis of Sr-containing calcium phosphate species as cement precursors that could release biologically effective doses of Sr(2+) and thus could improve the healing of osteoporotic bone defects. Using strontium carbonate as a strontium(II) source, it was introduced into a hydroxyapatite-forming cement either by the addition of SrCO3 to an α-tricalcium phosphate-based cement precursor mixture (A-type) or by substitution of CaCO3 by SrCO3 during precursor composition (S-type). The cements, obtained after setting in a water-saturated atmosphere, contained up to 2.2at.% strontium in different distribution patterns as determined by time-of-flight secondary ion mass spectrometry and energy-dispersive X-ray spectroscopy. The setting time of CPC and A-type cements was in the range of 6.5-7.5min and increased for substitution-type cements (12.5-13.0min). Set cements had an open porosity between 26 and 42%. Compressive strength was found to increase from 29MPa up to 90% in substituted S-type cements (58MPa). SrCPC samples released between 0.45 and 1.53mgg(-1) Sr(2+) within 21days and showed increased radiopacity. Based on these findings, the SrCPC developed in this study could be beneficial for the treatment of defects of systemically impaired (e.g. osteoporotic) bone.