| Glaucoma is currently one of the three major causes of vision loss in the world,and its main treatment is to reduce intraocular pressure through anterior segment administration.Based on the complex physiological structure of the eye,the bioavailability of traditional eye drops in the eye is less than 7%,so it is difficult to meet the needs of long-term drug administration for glaucoma.Therefore,a new type of ocular drug delivery system which can improve the compliance of patients and the bioavailability of ocular drug delivery needs to be developed and applied.On the basis of the previous research of the laboratory research group,acid treatment was used to activate medical montmorillonite(MMt).The cationic drug Betaolol hydrochloride(BH)was intercalated into the interlayer domain of activated montmorillonite by ion exchange mechanism to obtain a new potential drug carrier drug-loaded montmorillonite(MMt-BH).Then the MMt-BH is inserted it into bio-adhesive material chitosan(CS)combined with hyaluronic acid(HA),which can bind to CD44 receptor of corneal epithelium,and then wrapped polyacrylic resin(ED)membrane to prepare charged shift nanoparticles(MMt-BH-HA/CS-ED NPs).The freeze-drying process,physical and chemical properties,in vitro drug release mechanism,microstructure characterization,safety,anterior corneal retention and pharmacokinetics of MMt-BH-HA/CS-ED NPs were evaluated.The MMt-BH-HA/CS-ED NPs nano-suspension prepared by ion crosslink-solvent volatilization method is light blue and has Tyndall effect.The average particle size is 778.90±60.88 nm and the Zeta potential is 21.28±1.11 m V.The p H value and osmotic pressure are in accordance with the regulations of the 2020 edition of Chinese Pharmacopoeia.It is worth noting that the entrapment efficiency and drug loading rate of MMt-BH-HA/CS-ED NPs are 85.40±0.20%and 15.92±0.26%,respectively,indicating that MMt-BH-HA/CS-ED NPs can load more drugs than the previously prepared nanoparticles(such as solid lipid nanoparticles,liposomes and simple ED nanoparticles)to meet the requirements of clinical application.The in vitro release result showed that MMt-BH-HA/CS-ED NPs could slowly release the drug up to 12 h with less than 40%of the release amount within 0.5 h(no sudden release)and more than 80%of the cumulative release rate,which was better than that of BH-HA/CS-ED NPs.In addition,theoretically,the lower surface tension and contact angle of MMt-BH-HA/CS-ED NPs should have made it spread to the eye surface more rapidly,but the study shows that the diffusion time of cornea in vitro is much longer than that of BH aqueous solution.Combined with rheological experiments,MMt-BH-HA/CS-ED NPs has higher initial viscosity to prolong the anterior corneal retention time in resting state.On the other hand,the excellent properties of the pseudoplastic fluid with shear thinning make the viscosity decrease during the blink without irritation.TEM scanning showed that MMt-BH-HA/CS-ED NPs was spherical with smooth surface,dark middle color and nearly transparent outer ring,which was consistent with the shell-core structure of hyaluronic acid/chitosan nanoparticles outer ED film.XRD showed that after the drug was successfully intercalated into MMt,the interlayer spacing increased from1.2370 nm to 1.8906 nm.In the narrow spectrum of Cl2p of XPS,BH has a strong diffraction peak of Cl2p at the binding energy of 197.5 e V,while MMt-BH has no characteristic peak,indicating that the drug was successfully loaded by ion exchange mechanism instead of Na~+between montmorillonite layers.According to the combination of XPS,XRD and FI-IR,MMt-BH was more loaded into the depths of the MMt-BH-HA/CS-ED NPs instead of absorbing on the surface.According to the safety evaluation(hemolysis test,corneal hydration value test and Draize test)of the preparation,MMt-BH-HA/CS-ED NPs has no obvious irritation.In the fluorescence tracer experiment,the anterior corneal retention time of MMt-BH-HA/CS-ED NPs was 4.57 times longer than that of BH aqueous solution.It is reported that the tear film is renewed once in 43-62min.Combined with the metabolic kinetics of tear film,the drug concentration of BH solution is lower than the detection limit after 2 hours,but the tear drug concentration of MMt-BH-HA/CS-ED NPs group can be released continuously to 6 hours.This phenomenon can be attributed to the micro-interaction between positively charged MMt-BH-HA/CS-ED NPs and negatively charged lacrimal film mucin:the hydrogel reticular structure formed by mucin in tear film is negatively charged and has a certain mesh size.The negatively charged polysaccharide part of the protein-polysaccharide complex outside the corneal epithelial cells will extend into the tear film,and the flow time of the sugar calyx structure is as long as 6-12 hours.The hydrogel-type meshwork formed by mucins in the tear film has a better trapping effect on nanoparticles of suitable particle size.The negatively charged polysaccharides attached to the surface of corneal epithelial cells extend into the tear film and formed a glycocalyx structure that resembled a vine.After local administration,MMt-BH-HA/CS-ED NPs with too large or small particle sizes were easily washed away by tear aqueous turnover,whereas MMt-BH-HA/CS-ED NPs of suitable particle size were capable of micro-interaction with negatively charged mucins in tears due to their positive charge,changing the drug clearance from tear aqueous turnover to mucous turnover,thus prolonging their precorneal retention time significantly.For route B,firstly,the outermost wrapped ED membrane of MMt-BH-HA/CS-ED NPs absorbed water and swelled to form the pores,which allowed water and some cations in the tear to enter the inner core through the pores,and the drug on/in the montmorillonite was separated by ion exchanged and released from the pores together with the drug encapsulated in the inner core HA-CS.Then,the inner core HA chains continuously absorbed water and swelled,making the positively charged MMt-BH-HA/CS-ED NPs became larger and gradually sunk into the negatively charged mucin mesh and glycocalyx structures in the tear film under the driving force of their own gravity,resulting in charge interaction and retention so as not to be removed by the normal physiological action of the ocular surface.Next,water absorption and swelling of the inner core continuously happened until the volume expanded to a certain extent,it broke the outer membrane of the ED,exposing the negatively charged inner core nanoparticles MMt-BH-HA/CS NPs wrapped inside.This transition from the original positively charged to the new negatively charged stage would change the interaction with the negatively charged mucin vine structure from the original opposite-charge attraction to the homogeneous-charge repulsion,thus freeing the MMt-BH-HA/CS NPs from mucin vine entanglement.Finally,the water-absorbing and swelling MMt-BH-HA/CS NPs would expose the HA and CS molecular chains,further sunk to the corneal epithelial surface and targeted to the corneal epithelial CD44receptors,thus further prolonging the retention of nanoparticles in front of the cornea due to the targeting interaction effect between HA and CD44. |
PDF Full Text Request