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Gelled Calcium Polyphosphate Matrices Delay Antibiotic Release
S.C. Schofield1,
B. Berno2,
M. Langman1,3,
G. Hall1 and
M.J. Filiaggi1,3,*
1 Department of Applied Oral Sciences, Faculty of Dentistry, Dalhousie University, 5981 University Avenue, Halifax, Nova Scotia B3H 3J5, Canada;
2 The Atlantic Region Magnetic Resonance Centre, Dalhousie University; and
3 School of Biomedical Engineering, Dalhousie University
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Figure 2. Raman spectra of five-hour-gelled calcium polyphosphate matrices before elution. A blank five-hour-gelled disk (A) and a corresponding cefuroxime-loaded disk (B) showed characteristic peaks for a linear polyphosphate (704 and 1170 cm–1) (Jager and Heyns, 1998) and cefuroxime (1482 and 1600 cm–1), with no apparent interaction (no peak shifts) evident with antibiotic incorporation or compared with the starting compounds (not shown). Note that elevated "noise" or background levels seen between 2500 and 1400 cm–1 in the blank disk spectrum could not be adequately resolved with the available background subtraction software. Non-gelled and 24-hour-gelled disks did not have spectra significantly different from those of the five-hour-gelled disks and, thus, are not shown (n = 1).
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Figure 3. Solution 31P NMR spectra are shown of the amorphous calcium polyphosphate (A), and five-hour-gelled disks with cefuroxime incorporated before (B) and after the elution study (D), and five-hour-gelled disks without cefuroxime incorporated before (C) and after the elution study (E). No significant peak shifts can be seen between the amorphous calcium polyphosphate (A) and the five-hour-gelled disks before the elution study, either with (B) or without (D) cefuroxime incorporation. A chemical phase shift at ~ 1–2 ppm corresponds to an orthophosphate group having no bridging oxygen atoms (Q0), whereas the peak at ~ –9.5 ppm describes a terminal phosphate group with only 1 oxygen atom bridging to a neighboring tetrahedral (Q1). An internal phosphate tetrahedral bond involving 2 bridging oxygen atoms (Q2) is representative of either linear polyphosphate chains (~ –20 ppm) or of metaphosphate ringed structures (~ –22 ppm). Dramatic spectral changes are observed in the post-elution calcium polyphosphate matrices (C&E), showing very few internal phosphate bonds. Spectra of non-gelled and 24-hour-gelled disks did not significantly differ from those of the five-hour-gelled disks and, thus, are not shown (n = 1).
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Figure 4. Average phosphate chain lengths of the calcium polyphosphate matrices are shown for all 3 parameters (24-hour-gelled, five-hour-gelled, and non-gelled disks) and amorphous calcium polyphosphate, as calculated from the 31P NMR spectra by a peak area method (see text). No differences were seen between the cefuroxime-loaded matrices and their blank counterparts for any parameter, before or after the elution study. The gelling process changed the average phosphate chain length, such that a longer gelling time caused more phosphate chain lysis. All of the disks after the seven-day elution study revealed pyrophosphates (2 phosphates bonded together) in the calcium polyphosphate matrices, another indication of matrix degradation throughout the elution process (n = 1).
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Journal of Dental Research, Vol. 85, No. 7,
643-647 (2006)
DOI: 10.1177/154405910608500712
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), and five-hour-gelled disks (
). Cefuroxime release shown as a percent of the total antibiotic incorporated into the calcium polyphosphate disks (A), and the rate of cefuroxime release (mg/hr) at 13 time-points over the 7 days (B). Calcium release as a percent of the total available in the calcium polyphosphate matrix (C), and the rate of calcium release (mg/hr) at individual time-points (D), along with phosphate release as a percent of the total available in the calcium polyphosphate matrix (E), and the rate of phosphate release (mg/hr) at individual time-points (F) describe the matrix degradation of the calcium polyphosphate disks. Change in pH over time from the collected 7-mL samples was tracked (G). Cumulative release of cefuroxime (mg) is shown for the first 4 days (H) of the elution study, to highlight the linear portion of the 24- and five-hour-gelled curves. All samples for each time-point are presented as mean ± standard error (n = 14); blank samples (n = 2) did not significantly differ from their gelled and non-gelled equivalents and, thus, were not included in graphs C through G.