Physicochemical properties and micro-interaction between micro-nanoparticles and anterior corneal multilayer biological interface film for improving drug delivery efficacy: the transformation of tear film turnover mode

Figures & data

Figure 1. Schematic diagram of the preparation processes of MT-BHC MPs and MT-BHC SLNs.

Figure 2. Characterization of MT-BHC MPs and MT-BHC SLNs. A: SEM images of MT-BHC MPs (top) and MT-BHC SLNs (bottom); B: Cumulative drug release from MT-BHC MPs, MT-BHC SLNs, and BHC solution (mean ± SD, n = 3).

Table 1. Physicochemical characteristics of MT-BHC MPs and MT-BHC SLNs (data expressed as mean ± SD, n = 3).

	MT-BHC MPs	MT-BHC SLNs
Particle size	9.82 ± 3.56 µm	547.70 ± 2.37 nm
ZP	8.58 ± 0.57 mV	7.84 ± 0.94 mV
EE%	85.43 ± 1.27	83.52 ± 0.91
DL%	6.23 ± 0.07	4.55 ± 0.05
pH	6.19 ± 0.16	6.07 ± 0.11
Osmolarity	300 ± 3 mOsmol/kg	301 ± 2 mOsmol/kg

Figure 3. In vivo fluorescent tracing and physicochemical properties of BHC solution, MT-BHC SLNs, and MT-BHC MPs. A: Precorneal retention of the BHC solution, MT-BHC SLNs, and MT-BHC MPs eye drops using the fluorescence tracing method. No fluorescence was found after application of the BHC solution after 16 min, the MT-BHC SLNs after 45 min, and the MT-BHC MPs after 135 min. B: Surface tension and contact angle of the BHC solution, MT-BHC SLNs, and MT-BHC MPs eye drops. C: The spreading time of BHC solution, MT-BHC SLNs, and MT-BHC MPs eye drops on isolated rabbit cornea.

Table 2. Rheological behavior of MT-BHC SLNs and MT-BHC MPs eye drops (mean values ± SD, n = 3).

Sample	Power law equations	non-Newtonian index (n)	r^2	Fluid type
MT-BHC MPs	$\tau =0.037{\dot{\gamma }}^{0.747}$	0.747	0.9998	pseudoplastic fluid
MT-BHC SLNs	$\tau =0.006{\dot{\gamma }}^{0.755}$	0.755	0.9900	pseudoplastic fluid

Table 3. Scatchard-plot equation and Rose Bengal binding constant values (K) for MT-BHC MPs and MT-BHC SLNs.

Sample	Scatchard-plot equation	Binding constant (K)
MT-BHC MPs	y = –343.03x + 4.3809	343.03
MT-BHC SLNs	y = –84.849x + 1.645	84.849

Figure 4. Tear elimination pharmacokinetics and schematic diagram of transformation for tear film turnover pattern based micro-interactions. A: Tear drug concentration-time curves after topical application of 100 μL BHC solution, MT-BHC MPs, and MT-BHC SLNs eye drops to rabbit eyes (mean ± SD, n = 3). B: Schematic representation of the proposed micro-interactions of the BHC solution, MT-BHC MPs, and MT-BHC SLNs with the ocular surface after topical administration. (1) In the early stage, some free drug molecules from the BHC solution, large MT-BHC MPs and small MT-BHC SLNs remain on the ocular surface. (2) Positively charged MT-BHC MPs, and MT-BHC SLNs interact with negatively charged tear film mucins suggesting that particles are no longer eliminated by aqueous flow. (3) After penetrating the mucin layer, MT-BHC MPs with higher hydrophobicity interacted with the corneal epithelium to maintain longer retention.

Table 4. Date analysis of the tear elimination pharmacokinetics results.

	BHC solution	MT-BHC SLNs	MT-BHC MPs
Area under the Curve (AUC) ((μg·min/mL) ± SD)	1,762.0 ± 181.43	9,458.8 ± 536.21^****	22,323 ± 1179.8^****####

Mean values ± SD, n = 3 per group; ^* P< 0.05, ^** P< 0.01, ^*** P< 0.001, and ^**** P< 0.0001 vs. the BHC solution. ^# p< 0.05, ^## p< 0.01, ^### p< 0.001, and ^#### P<0.0001 vs. the MT-BHC SLNs.    

Figure 5. A: Rabbit chronic high intraocular pressure model. B: IOP-lowering effects of BHC solution, MT-BHC MPs and MT-BHC SLNs eye drops after topical administration (mean ± SD, n = 3).

Table 5. Date analysis of the IOP-lowering effects.

	BHC solution	MT-BHC SLNs	MT-BHC MPs
Area under the Curve(AUC) ((mmHg·h) ± SD)	78.36 ± 4.214	106.8 ± 3.422^**	194.8 ± 6.636^****^####

Mean values ± SD, n = 3 per group; ^*P< 0.05, ^** P< 0.01, ^*** P< 0.001, and ^**** P< 0.0001 vs. the BHC solution. ^# p< 0.05, ^## p< 0.01, ^### p< 0.001, and ^#### P<0.0001 vs. the MT-BHC SLNs. .

Table 6. Ocular irritation scores in rabbits (single and multiple administration, n = 3).

	Single dosing				Multiple dosing
	Saline	BHC aqueous solution	MT-BHC SLNs	MT-BHC MPs	Saline	BHC aqueous solution	MT-BHC SLNs	MT-BHC MPs
Cornea	0	0	0	0	0	0	0	0
Iris	0	0	0	0	0	0	0	0
Conjunctival congestion	0	0	0	0	0	1.67	0.67	0
Edema	0	0	0	0	0.33	0	0	0
Secretions	0	0	0	0	0	0.33	0.33	0.33
Total	0	0	0	0	0.33	2	1	0.33

Figure 6. Corneal and scleral tissue sections after repeated eye drop administration.

Table 7. Blink frequency after eye drop administration (data expressed as the mean values ± SD, n = 6).

Samples	Blink frequency (min^–1)
Saline	3 ± 2
BHC solution	7 ± 2
MT-BHC MPs	7 ± 3
MT-BHC SLNs	6 ± 2