Amorphous 1-D nanowires of calcium phosphate/pyrophosphate: A demonstration of oriented self-growth of amorphous minerals

Metastable Calcium Phosphate Cluster-Involved Mineralization Process Regulated by a Dual Biomolecule System Toward the Application in Dentinal Tubules Occlusion

Dentin hypersensitivity caused by the exposure of dentinal tubules is affecting a significant portion of the population. With promising prospects, the biomimetic mineralization materials used in treating dentin hypersensitivity are expected to possess a metastable characteristic, for which they can easily penetrate the tubules and the surrounding tissues, but then occlude them via a transformation of size and phase immediately. Herein, this study develops a metastable calcium phosphate cluster (MCPC)-involved mineralization process, which is regulated by dual biological macromolecules: bovine serum albumin (BSA) and poly-L-lysine (PLL). BSA functions to stabilize the primary calcium phosphate clusters; PLL further tunes the cluster's evolution (toward larger and crystalline particles) into a metastable fashion, and meanwhile inhibits the local bacteria. Upon treatments, the system generates amorphous MCPC with ultrasmall size (1-2 nm); then they enter the deep dentinal tubules, subsequently aggregate and crystalline into immobile larger particles, which finally seal the exposed dentinal tubules. The effective occlusion of dentinal tubules as well as significant antibacterial performance are confirmed both in vivo and in vitro. This study has devised not only a regulatory approach for the evolution of mineralization-active clusters but also established an efficient method for managing dentin hypersensitivity.

From Ions to Crystals: A Comprehensive View of the Non-Classical Nucleation of Calcium Sulfate

The early stages of mineralization continue to be in the focus of intensive research due to their inherent importance for natural and engineered environments. While numerous observations have been reported for single steps in the pathways of various crystallizing phases in previous studies, the complexity of the underlying processes and their elusive character have left central questions unanswered in most cases. In the present work, we provide a detailed view on the nucleation of calcium sulfate mineralization-an abundant mineral with broad use in construction industry-in aqueous systems at ambient conditions. As experimental basis, a co-titration procedure with potentiometric, turbidimetric and conductometric detection was developed, allowing solution speciation and the formation of crystallization precursors to be monitored quantitatively as the level of nominal (super)saturation gradually increases. The nature and spatiotemporal evolution of these precursors was further elucidated by time-resolved small-angle X-ray scattering (SAXS) and analytical ultracentrifugation (AUC) experiments, complemented by cryogenic transmission electron microscopy (cryo-TEM) as a direct imaging technique. The results reveal how ions associate into nanometric primary species, which subsequently aggregate and develop anisotropic order by intrinsic structural reorganization. Our observations challenge the common understanding of fundamental notions such as the nucleation barrier or the meaning of supersaturation, with broad implications for mineralization phenomena in general and the formation of calcium sulfate in geochemical settings and industrial applications in particular.

Highly Stable Amorphous (Pyro)phosphate Aggregates: Pyrophosphate as a Carrier for Bioactive Ions and Drugs in Bone Repair Applications

Pyrophosphate is widely used as an iron supplement because of its excellent complexation and hydrolysis ability; however, there are few reports on the use of pyrophosphate in active ionophores for bone repair. In this research, we proposed a simple and efficient ultrasonic method to prepare magnesium-calcium (pyro)phosphate aggregates (AMCPs). Due to strong hydration, AMCPs maintain a stable amorphous form even at high temperatures (400 °C). By changing the molar ratio of calcium and magnesium ions, the content of calcium and magnesium ions can be customized. AMCPs had surface negativity and complexing ability that realized the controlled release of ions (Ca2+, Mg2+, and P) and drugs (such as doxorubicin) over a long period. Pyrophosphate gave it an excellent bacteriostatic effect. Increasingly released Mg2+ exhibited improved bioactivity though the content of Ca2+ decreased. While Mg2+ content was regulated to 15 wt %, it performed significantly enhanced stimulation on the proliferation, attachment, and differentiation (ALP activity, calcium nodules, and the related gene expression of osteogenesis) of mouse embryo osteoblast precursor cells (MC3T3-E1). Furthermore, the high content of Mg2+ also effectively promoted the proliferation, attachment, and migration of human umbilical vein endothelial cells (HUVECs) and the expression of angiogenic genes. In conclusion, pyrophosphate was an excellent carrier for bioactive ions, and the AMCPs we prepared had a variety of active functions for multiscenario bone repair applications.

Inorganic Pyrophosphate at Serum Concentration May Not Be Able to Inhibit Mineralization: A Study in Aqueous Solutions and Serum

The constituent ions of calcium phosphate in body fluids are in the supersaturated state and tend to form minerals physiologically or pathologically. Inorganic pyrophosphate (PPi) has been considered as one of the most important inhibitors against the formation of calcium phosphate minerals. However, serum PPi concentrations in humans are maintained at a level of several μmol/L, and its effectiveness and mechanism for mineralization inhibition remain ambiguous. Therefore, this work studied the mineralization process in an aqueous solution, explored the effective inhibitory concentration of PPi by titration, and characterized the species during the reactions. We find that PPi at a normal serum concentration does not inhibit mineralization significantly. Such a conclusion was further confirmed in the PPi-added serum. This work indicates that PPi may not be a major direct inhibitor of mineralization in serum and possibly functions via alternative mechanisms.