Biomedical Engineering Reference
In-Depth Information
(a)
100
80
60
40
20
0
25
50
75
Time (h)
(b)
4.0
×
10
−
2
3.0
2.0
1.0
0.0
10
−
6
10
−
4
10
−
2
DTT conc. (M)
FIGURE 9.2
The DTT-induced release profi les of vancomycin (
●
) and ATP (
▲
) from the CdS-capped MSN
system: (a) release percentage over time; (b) the DTT concentration-dependent releases. Released analyte
concentrations were measured with CdS-MSNs (2.3 mg) in pH 7.4 PBS buffers (0.8 mL) after 24 h of the
DTT additions. (Reprinted from Lai, C.Y. et al.,
J. Am. Chem. Soc.
, 125, 4451, 2003. © American Chemical
Society.)
molecules than the conventional mesoporous MCM-41 and MCM-48 and had sustained drug-
release properties. The researchers also prepared hollow mesoporous silica spheres (average diam-
eter of 300-400 nm) with pore channels penetrating from the outside to the inner hollow core
(Figures 9.3 and 9.4) [25]. The pH and salt-induced stimuli-responsive function was achieved by
polyelectrolyte multilayers (sodium polystyrene sulfonate (PSS) and polycation poly(allylamine
hydrochloride) (PAH)) with an average thickness of 14 nm. IBU was used for drug loading and
release experiments.
Figures 9.4a and 9.4b show transmission electron microscopy (TEM) micrographs of hollow mes-
oporous silica spheres with an average diameter of 300-400 nm. The hollow structure can be clearly
observed. Figure 9.4c shows a TEM micrograph of a hollow sphere after the adsorption of IBU mol-
ecules. No apparent difference can be observed after IBU loading. Figure 9.4d shows a TEM micro-
graph of an IBU-loaded sphere coated with PAH/PSS multilayers, with a thickness of around 14 nm.
Figure 9.5 shows the cumulative IBU release from the two systems in the release media of
pH 1.4 (a simulated gastric fl uid) and pH 8.0 (a simulated intestinal fl uid). Both systems showed
sustained-release properties, and the drug release rates from both the systems were similar in the
medium of pH 1.4. The amounts released from the two systems reached about 80% in 48 h. This
result implies that the PAH/PSS multilayers had open pathways in the release medium of pH 1.4 and
could not cap the openings of the mesoporous channels. When the pH value of the release medium
