Biomedical Engineering Reference
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Fig. 3 Sample autocorrelation curves obtained using fluorescence correlation spectroscopy
(FCS). Calcium phosphosilicate particles were characterized at pH 4 and pH 7 and free Cy3 at pH
4. Dissolved particles (pH 4) resemble behavior of free dye at pH 4 verifying calcium phospho-
silicate particle dissolution and dye release as shown in Fig. 4 (Reproduced from Morgan ( 2008 ).
With permission)
This pH dependent release mechanism was studied by Morgan et al . and
Muddana et al . for the calcium phosphosilicate nanocomposite particles (CPSNPs)
(Morgan 2008 ; Muddana 2009 ). Using fluorescence correlation spectroscopy
(FCS) the solution-phase behavior of the particles was studied in DPBS (Dulbecco's
phosphate buffered saline) at pH 7 and pH 4 to mimic the pH of mature endosomes
(Morgan 2008 ; Muddana 2009 ). The drop in pH causes dissociation of calcium
phosphate into its constituent ions and serves as a release mechanism for the pay-
load encapsulated within the particle. As shown in Fig. 3 , the sample autocorrela-
tion curve at pH 4 resembles that of free Cy3 dye molecules, indicating particle
dissolution and dye release. The change in the hydrodynamic diameter and the dif-
fusion coefficient of the particles as a function of pH for the CPSNPs is depicted in
Fig. 4 (Morgan 2008 ). The hydrodynamic diameter data verify that the particles at
pH 4 resemble the behavior of the free dye with respect to both hydrodynamic
diameter and diffusion coefficient (Morgan 2008 ). The pH dependent solubility
paired with the biocompatibility of the material system render calcium phosphate
delivery systems promising alternatives to conventional treatments (Altınoğlu 2009,
2008 ; Morgan 2008 ; Adair 2010 ; Li 2010 ).
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