Fig. S1: The drug release kinetics: (a) BL model for drug delivery in acidic buffer; (b) BL model for drug delivery in acidic buffer; (c) Higuchi model for drug delivery in acidic buffer; (d) Higuchi model for drug delivery in basic buffer; (e) KP model for drug delivery in acidic buffer and (f) BL model for drug delivery in basic buffer
Table S1: Goodness of fit (χ2) values of the microparticles
Sample / χ2 valuesGastric buffer / Intestinal buffer
BL model / Higuchi model / KP model / BL model / Higuchi model / KP model
BMSA / 0.000248 / 1.45956 / 0.009152 / 0.001485 / 0.390637 / 0.005513
MSOSA / 0.002249 / 0.457193 / 0.004958 / 0.003096 / 0.535867 / 0.005496
MOGSA / 0.002094 / 1.11012 / 0.007882 / 0.004709 / 1.83758 / 0.002215
BMMZ / 0.004478 / 1.86266 / 0.012232 / 0.003313 / 4.13119 / 0.022418
MSOMZ / 0.00177 / 1.08505 / 0.007711 / 0.002706 / 10.5961 / 0.018824
MOGMZ / 0.001696 / 0.345047 / 0.003418 / 0.03185 / 4.33606 / 0.05831
Swelling equilibrium and erosion studies
The swelling studies were conducted in aqueous buffers of pH 1.2 and 7.2.[1] Accurately weighed ~1 g of the dried microparticles was incubated in 50 ml of the buffer at 37 ± 1 °C. The weight of the microparticles was measured at regular intervals of time. % swelling of the microparticles(MPs) was calculated from the following equation: [2]
where,
Ww is the wet weight of the microparticles at time t.
Wd is the initial dry weight of the microparticles.
Erosion of the microparticles was checked simultaneously with swelling studies in both the buffers.
Fig. S2: % swelling of microparticles in (a) acidic buffer and (b) Phosphate buffer
Fig. S2 shows the % swelling of the microparticles in acidic and phosphate buffers. The equilibrium swelling was achieved in lesser time under acidic environment as compared to the basic environment. As per the previously reported literature, the Ca-alginate microparticles require ~1.0 h of time to attain equilibrium swelling, under both acidic and basic conditions, when prepared by internal/emulsification method [3-5]. In the current study, longer time was needed to attain equilibrium swelling. This may be associated with the presence of either sunflower oil or organogel within the microparticles. Under acidic conditions, the % swelling was highest for BM followed by MOG and MSO. On the other hand, the % swelling was similar in BM and MOG followed by MSO. The presence of sunflower oil within the microparticles has reduced the water absorption capacity of the microparticles. This may be due to the hydrophobic nature of sunflower oil. BM was a homogenous matrix of calcium alginate. Hence, the water absorption capacity was more. The % swelling of MOG was either similar or lesser than the % swelling of BM. But in either of the pH conditions, the % swelling of MOG was higher than MSO. This may be accounted to the fact that the organogels are made up of surfactant molecules, sunflower oil and water. The immersion of the MOG into the swelling media resulted in the accommodation of the water molecules within the organogel core of the microparticles. This resulted in the higher % swelling of MOG.
Under acidic conditions, the microparticles were found to be stable without losing their structural integrity even after 24 h of incubation. Under basic conditions, BM, MSO and MOG lost their structural integrities after 10h 14h and 18h, respectively. Entrapment of the organogel within the microparticles enhanced the stability of the microparticles. This may be due to the water holding capacity of the sorbitan ester based organogels [6]. This phenomenon might have delayed the erosion of the microparticles. Also, the strength of the microparticles is associated with the degree of cross-linking of the alginate molecules, which is dependent on the pH. A higher degree of crosslinking of alginate molecules by Ca2+ was achieved under acidic conditions as compared to neutral and basic conditions [7]. The higher stability of the microparticles under acidic conditions for longer duration may be explained by this phenomenon [8].
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