Measurement of LNT and calcium ion release from CSL-gel
The standard curve of LNT was determined by UV-vis spectrophotometry
(UV-vis, PGEN-ERAL) according to the method as described previously
(Xiang et al., 2019). The sustained-release ability and rate of CSL-gel
and SL-gel were tested according to the previous methods (Xiang et al.,
2019): Briefly, 50 pieces of CSL-gel or SL-gel were added into 10 mL of
deionized water (pH 5) at 20 °C and an UV−vis spectrophotometer was used
to measure the absorbance of LNT in solution at 24-336 h, respectively.
The same method was used to measure the cumulative release of calcium
ions and investigate the effects of different temperatures (Temperature:
10, 20, 30, 40, 50, and 60 °C, pH=5), different pH values (pH: 3.0, 5.0,
7.0, and 9.0, adjusted by Tris-HCl, at 20 °C), and different
concentrations of cations (The concentrations of NaCl solution were 0.1,
0.2, 0.4, and 0.8 mol/L, respectively, pH=5, at 20 °C) on the
sustained-release ability and rate of CSL-gel as well. The cumulative
release rate (CRR) of LNT was calculated according to formula 3. The
release kinetics of LNT from CSL-hydrogel and SL-hydrogel were analyzed
using Higuchi (Formula 4) and Korsmeyer−Peppas models (Formula 5)
(Korsmeyer R W, 1983).
CRR (%)
=\(\frac{\sum_{0}^{t}{C_{t}V_{\text{total}}}}{Q_{1}}\ \times 100\%\)(3)
Ct represents the release LNT concentration at time t,
Vtotal represents solution volume, and
Q1 represents the total quality of loaded LNT.
Higuchi model: Qt=\(\text{Kt}^{1/2}\) (4)
Korsmeyer-Peppas model: Qt=\(\text{Kt}^{n}\) (5)
Qt represents the cumulative release rate of LNT until
time t, K represents the kinetic constant, and n is an index that
reflects the following release mechanisms: Fickian diffusion (n
< 0.43), non-Fickian or anomalous diffusion (0.43 <
n < 0.85), and case II transport (n > 0.85).