Incorporation of ion exchange functionalized-montmorillonite into solid lipid nanoparticles with low irritation enhances drug bioavailability for glaucoma treatment

Figures & data

Figure 1. The schematic illustration for the formation of Mt-BH-SLNs. Initial emulsion was obtained by subjecting organic phase containing the emulsifier and the internal aqueous phase containing Mt-BH with met-emulsion sonication. Solid lipid nanoparticles were prepared by injecting the initial emulsion into external aqueous phase with rapid stirring in an ice-water bath.

Figure 2. (a) The TEM of the Mt-BH-SLNs; (b) The appearance of Mt-BH-SLNs; (c) In vitro release of BH from Mt-BH-SLNs and BH solution. Studies performed in freshly prepared simulated tear fluid (STF) at 34 °C. Values are presented as the mean ± SD (n = 3).

Table 1. The stability of Mt-BH-SLNs at 4 °C and 25 °C (n = 3).

Time (d)	4 °C			25 °C
	Particle size (nm)	Zeta (mV)	PDI	Particle size (nm)	Zeta (mV)	PDI
0	149.5 ± 3.2	18.24 ± 1.2	0.185 ± 0.017	149.5 ± 2.2	18.14 ± 1.2	0.285 ± 0.045
10	152.2 ± 2.1	18.01 ± 0.4	0.182 ± 0.014	167.2 ± 1.1	17.01 ± 0.4	0.282 ± 0.033
20	151.5 ± 1.5	17.74 ± 1.7	0.186 ± 0.011	181.5 ± 1.2	16.04 ± 1.7	0.296 ± 0.026
30	150.3 ± 0.8	19.04 ± 0.9	0.184 ± 0.009	210.3 ± 2.8	17.17 ± 0.9	0.284 ± 0.015

Table 2. Mathematical models of regression for in vitro release profiles of Mt-BH-SLNs.

	Mt-BH-SLNs		BH solution
	Equation	r^2	Equation	r^2
Zero order	Y = 3.2649t + 31.4810	0.487	Y = 39.1331t + 42.7317	0.512
First order	In(100-Y) = −1.0712t + 4.0319	0.989	In(100-Y) = −3.9281t + 4.5899	0.986
Higuchi	Y = 16.21t^1/2 + 8.287	0.916	Y = 34.80$\sqrt{t}$+ 49.66	0.972
Weibull	In In[100/100-Y] = 0.5514t + 4.1441	0.975	In In [100/100-Y] = 0.5232t + 4.7034	0.999
Hixson-Crowell	(100-Y)^1/3 = −0.078t + 4.243	0.828	∛(100-Y) = −2.249t + 4.428	0.989
Ritger-Pappas	log Y = 0.2218log t + 1.5689	0.838	log Y = 0.2009log t + 1.9637	0.962
Korsmeyer-Peppas	Y = 52.401t^0.6641	0.9876	Y = 84.328t^0.6188	0.9976

Figure 3. (a) The absorption of trypan blue after exposure to formulations (Blank-SLNs, Mt-BH-SLNs and BH solution); (b) The viability of cells being exposed to different amount of BH solution, Mt-BH-SLNs and Blank-SLNs for 120 min. Values are presented as the mean ± SD (n = 3).

Table 3. Scatchard-plot equation and Rose Bengal binding constant values (K) of Mt-BH-SLNs, Acid-Mt-SLNs and Blank-SLNs.

Types of SLN	Scatchard-plot equation	K values
Mt-BH-SLNs	y = −75.206x + 2.008	75
Acid-Mt-SLNs	y = −87.06x + 2.2438	87
Blank-SLNs	y = −88.159x + 2.3465	88

Figure 4. (a) The process of interaction between Mt-BH-SLNs and mucin in ocular tear film. Tear film was composed of lipid layer, aqueous layer and mucin layer. Mt-BH-SLNs with opposite charge to mucin bind to it by electrostatic interaction. The hydrophilicity of Mt-BH-SLNs surface was improved due to the release of water-soluble BH to the nanoparticles surface. Mt-BH-SLNs with increased surface hydrophilicity could penetrate or dissolve in aqueous mucus, and ocular surface retention time could be prolonged; (b) Concentration of BH in rabbit aqueous humor at various time points after instillation of different formulations; (c) The microdialysis sampling technique of rabbit eye; (d) The pharmacological response (the decrease in IOP, △IOP) versus time profiles for BH solution and Mt-BH-SLNs; (e) The schematic drawing of IOP, which caused by blocked aqueous circulation and further damaged the optic nerve head.

Table 4. Pharmacokinetic parameters of BH in rabbit aqueous humor after instillation of different formulations.

Pharmacokinetic parameters	AUC0–t ( μg/mL^.min)	Tmax (h)	Cmax (μg/mL)	MRT0-t (h)
Mt-BH-SLNs	1086.96	2	6.99	2.841
BH solution	660.48	0.5	7.05	1.849