Ultra‐small‐angle X‐ray scattering–X‐ray photon correlation spectroscopy studies of incipient structural changes in amorphous calcium phosphate‐based dental composites

Abstract

The local structural changes in amorphous calcium phosphate (ACP) based dental composites were studied under isothermal conditions using both static, bulk measurement techniques and a recently developed methodology based on combined ultra-small angle X-ray scattering – X-ray photon correlation spectroscopy (USAXS-XPCS), which permits a dynamic approach. While results from conventional bulk measurements do not show clear signs of structural change, USAXS-XPCS results reveal unambiguous evidence for local structural variations on a similar time scale to that of water loss in the ACP fillers. A thermal-expansion based simulation indicates that thermal behavior alone does not account for the observed dynamics. Together, these results suggest that changes in the water content of ACP affect the composite morphology due to changes in ACP structure that occur without an amorphous-to-crystalline conversion. It is also noted that biomedical materials research could benefit greatly from USAXS-XPCS, a dynamic approach.

Structural and dynamical studies of acid-mediated conversion in amorphous-calcium-phosphate based dental composites

“…We attribute the first, smaller population to the primary particles and the second, larger population to the aggregation of the primary particles. These results are consistent with the findings of a wide range of in vivo and in vitro ACP studies [12, 16, 17, 47, 48]. Additionally, with assistance from the contrast parameters in Table 2 , we found that the total scattering volume fraction of the ACP was about 0.26 ± 0.04, which yields a mass fraction of ACP at 0.37 ± 0.04.…”

“…We have previously established that for this type of ACP filled dental composite bulk characterization methods are not adequately sensitive to detect the local and subtle structural changes in the amorphous fillers [48]. XPCS, on the other hand, is an interferometric technique based on monochromatic coherent X-rays.…”

“…[44, 48] These maps, shown in Figure 3 , were analyzed with data acquired at HCl concentrations of 0.07 M, 0.10 M, 0.25 M, and 0.75 M, respectively. The corresponding pH values of the HCl are 1.15, 1, 0.60, and 0.13, respectively.…”

“…Clearly, the overall scattering intensity increases with acid immersion time across all of the measured scattering angle range. It is likely that some of this may be due to ingress of Cl − ions into the composite during the acid immersion, where a connected porosity pathway is suggested based on TGA measurements of the same composites [48]. What is also observed is a progressive emergence of 3 broad peaks in the diffraction pattern.…”

Airbrushed Composite Polymer Zr-ACP Nanofiber Scaffolds with Improved Cell Penetration for Bone Tissue Regeneration

“…33,34 The composite polymer nanofibers were produced using a two-step process: (a) mixing Zr-ACP powder with solvent and polymer and (b) airbrushing the composite onto TCPS discs.…”