Concept: Strontium carbonate
Directed nucleation and growth by balancing local supersaturation and substrate/nucleus lattice mismatch
- Proceedings of the National Academy of Sciences of the United States of America
- Published 2 months ago
Controlling nucleation and growth is crucial in biological and artificial mineralization and self-assembly processes. The nucleation barrier is determined by the chemistry of the interfaces at which crystallization occurs and local supersaturation. Although chemically tailored substrates and lattice mismatches are routinely used to modify energy landscape at the substrate/nucleus interface and thereby steer heterogeneous nucleation, strategies to combine this with control over local supersaturations have remained virtually unexplored. Here we demonstrate simultaneous control over both parameters to direct the positioning and growth direction of mineralizing compounds on preselected polymorphic substrates. We exploit the polymorphic nature of calcium carbonate (CaCO3) to locally manipulate the carbonate concentration and lattice mismatch between the nucleus and substrate, such that barium carbonate (BaCO3) and strontium carbonate (SrCO3) nucleate only on specific CaCO3polymorphs. Based on this approach we position different materials and shapes on predetermined CaCO3polymorphs in sequential steps, and guide the growth direction using locally created supersaturations. These results shed light on nature’s remarkable mineralization capabilities and outline fabrication strategies for advanced materials, such as ceramics, photonic structures, and semiconductors.
We report the interfacial reaction-driven formation of micro/nanostructured strontium carbonate (SrCO3) biomorphs with subcelluar topographical features on strontium zinc silicate (Sr2ZnSi2O7) biomedical coatings, and explore their potential use in bone tissue engineering. The resulting SrCO3 crystals build a well-integrated scaffold surface that not only prevents burst release of ions from the coating but also presents a nanotopographic feature similar to cellular filopodia. The surface with biomorphic crystals enhances osteoblast adhesion, upregulates ALP activity and increases collagen production, highlighting the potential of the silica-carbonate biomorphs for tissue regeneration.
We introduce giant liposomes to investigate phase transformations in picoliter volumes. Precipitation of calcium carbonate in the confinement of DPPC liposomes leads to dramatic stabilization of amorphous calcium carbonate (ACC). In contrast, amorphous strontium carbonate (ASC) is a transient species, and BaCO3 precipitation leads directly to the formation of crystalline witherite.
Aim of this study was to evaluate two different approaches to obtain strontium-modified calcium phosphate bone cements (SrCPC) 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 strontium(II) source, it was introduced into a hydroxyapatite forming cement by either 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 (ToF-SIMS) and energy dispersive X-ray spectroscopy (EDX). Setting time of CPC and A-type cements was in the range of 6.5-7.5 min and increased for substitution-type cements (12.5-13.0 min). Set cements had an open porosity between 26 and 42%. Compressive strength was found to increase from 29 MPa up to 90% in substituted S-type cements (58 MPa). 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.