Limits...
Visualising phase change in a brushite-based calcium phosphate ceramic

View Article: PubMed Central - PubMed

ABSTRACT

The resorption of brushite-based bone cements has been shown to be highly unpredictable, with strong dependence on a number of conditions. One of the major factors is phase transformation, with change to more stable phases such as hydroxyapatite affecting the rate of resorption. Despite its importance, the analysis of phase transformation has been largely undertaken using methods that only detect crystalline composition and give no information on the spatial distribution of the phases. In this study confocal Raman microscopy was used to map cross-sections of brushite cylinders aged in Phosphate Buffered Saline, Foetal Bovine Serum, Dulbecco’s – Minimum Essential Medium (with and without serum). Image maps showed the importance of ageing medium on the phase composition throughout the ceramic structure. When aged without serum, there was dissolution of the brushite phase concomitant to the deposition of octacalcium phosphate (OCP) around the periphery of the sample. The deposition of OCP was detectable within five days and reduced the rate of brushite dissolution from the material. The use of serum, even at a concentration of 10vol% prevented phase transformation. This paper demonstrates the value of confocal Raman microscopy in monitoring phase change in biocements; it also demonstrates the problems with assessing material degradation in non-serum containing media.

No MeSH data available.


Related in: MedlinePlus

Raman image formation from a day 50 sample showing spectra taking from the centre and outside of the cross section, showing the relative intensities of the main peaks associated with each phase.Each peak was mapped to the specimen showing the distribution of brushite, TCP and OCP over the cross section. Scale bar 1000 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5015027&req=5

f1: Raman image formation from a day 50 sample showing spectra taking from the centre and outside of the cross section, showing the relative intensities of the main peaks associated with each phase.Each peak was mapped to the specimen showing the distribution of brushite, TCP and OCP over the cross section. Scale bar 1000 μm.

Mentions: CRM mapping was performed on cylinders that were aged for 10 days in each media using a 785 nm laser. Calcium phosphate phases were identified based on Raman spectral peak locations previously reported in the literature15 (Table 1.). The P-O stretching mode (v1) of the PO4 group which has a unique peak shift for brushite (985 cm−1), octacalcium phosphate (OCP, Ca8H2(PO4)6.5H2O) (958 cm−1), and TCP (970 cm−1) was used as the main reference peak for each CaP phase. Spectra at the centre and edge of a cylinder aged for 50 days in PBS are shown in Fig. 1. A −5 cm−1 shift in the peak location was observed for samples aged in DMEM and FBS based media. Prior to image formation datasets were filtered to remove cosmic rays, baseline corrected, and normalised. Due to the close proximity of the peaks (~12 cm−1) relative to the spectral resolution of the grating (~3.5 cm−1) and their FWHM (~10 cm−1), a significant overlap was present which would give rise to misleading results as constructive interference increased the apparent intensity of weaker or non-present peaks. A classical least squares regression was performed to fit an individual Gaussian to each peak in the region for image mapping calculations to be taken from. It should be noted that intensity values were produced to be consistent across phases for each sample mapping but not between every data set.


Visualising phase change in a brushite-based calcium phosphate ceramic
Raman image formation from a day 50 sample showing spectra taking from the centre and outside of the cross section, showing the relative intensities of the main peaks associated with each phase.Each peak was mapped to the specimen showing the distribution of brushite, TCP and OCP over the cross section. Scale bar 1000 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5015027&req=5

f1: Raman image formation from a day 50 sample showing spectra taking from the centre and outside of the cross section, showing the relative intensities of the main peaks associated with each phase.Each peak was mapped to the specimen showing the distribution of brushite, TCP and OCP over the cross section. Scale bar 1000 μm.
Mentions: CRM mapping was performed on cylinders that were aged for 10 days in each media using a 785 nm laser. Calcium phosphate phases were identified based on Raman spectral peak locations previously reported in the literature15 (Table 1.). The P-O stretching mode (v1) of the PO4 group which has a unique peak shift for brushite (985 cm−1), octacalcium phosphate (OCP, Ca8H2(PO4)6.5H2O) (958 cm−1), and TCP (970 cm−1) was used as the main reference peak for each CaP phase. Spectra at the centre and edge of a cylinder aged for 50 days in PBS are shown in Fig. 1. A −5 cm−1 shift in the peak location was observed for samples aged in DMEM and FBS based media. Prior to image formation datasets were filtered to remove cosmic rays, baseline corrected, and normalised. Due to the close proximity of the peaks (~12 cm−1) relative to the spectral resolution of the grating (~3.5 cm−1) and their FWHM (~10 cm−1), a significant overlap was present which would give rise to misleading results as constructive interference increased the apparent intensity of weaker or non-present peaks. A classical least squares regression was performed to fit an individual Gaussian to each peak in the region for image mapping calculations to be taken from. It should be noted that intensity values were produced to be consistent across phases for each sample mapping but not between every data set.

View Article: PubMed Central - PubMed

ABSTRACT

The resorption of brushite-based bone cements has been shown to be highly unpredictable, with strong dependence on a number of conditions. One of the major factors is phase transformation, with change to more stable phases such as hydroxyapatite affecting the rate of resorption. Despite its importance, the analysis of phase transformation has been largely undertaken using methods that only detect crystalline composition and give no information on the spatial distribution of the phases. In this study confocal Raman microscopy was used to map cross-sections of brushite cylinders aged in Phosphate Buffered Saline, Foetal Bovine Serum, Dulbecco’s – Minimum Essential Medium (with and without serum). Image maps showed the importance of ageing medium on the phase composition throughout the ceramic structure. When aged without serum, there was dissolution of the brushite phase concomitant to the deposition of octacalcium phosphate (OCP) around the periphery of the sample. The deposition of OCP was detectable within five days and reduced the rate of brushite dissolution from the material. The use of serum, even at a concentration of 10vol% prevented phase transformation. This paper demonstrates the value of confocal Raman microscopy in monitoring phase change in biocements; it also demonstrates the problems with assessing material degradation in non-serum containing media.

No MeSH data available.


Related in: MedlinePlus