Preparation And Evaluation Of Nanostructured Lipid Carriers-Based Local Microenvironmental Stimulating Response Eye Drops

Dexamethasone?DEX?,one of the corticosteroid hormone with anti-inflammatory and immunosuppressive effects,has a certain effect on secondary macular edema diseases.However,a difficulty of intraocular barrier in the administration of posterior segment limits the treatment of posterior segment diseases.Except that the minimally invasive implant can achieve an effective therapy,but it is easy to create side effects such as postoperative complications because of its own traumatic implant.And the systemic or topical route are difficult to achieve effective therapeutic concentration in the posterior segment of the eye.Based on this,in order to avoid the side effects caused by the implantation route and the toxic side effects of hormonal drugs,we use a non-invasive method of topical administration to reduce the number of doses,increase the retention time of drugs,and promote the drug through the intraocular barrier to improve the drug bioavailability in the eye.The drug delivery system of nanostructured lipid carriers-based local microenvironmental stimulating response eye drops was designed to provide intraocular adaptability and feasibility through evaluating the physicochemical properties,in vitro release,intraocular elimination behavior and pharmacokinetics of different nanostructured lipid carriers-based responsive gel.The main contents and results are as follows:1.The environmental stimulating response material was used as a gel matrix carrier.Under non-physiological and physiological conditions,the drug delivery system of pH-responsive in situ gel?pH-ISG?,thermosensitive in situ gel?T-ISG?and ion-responsive in situ gel?ion-ISG?,can form solution-gel phase transition,were successfully prepared.The curve results of gelling sensitiveness show that the degree of gelling sensitiveness is:T-ISG>pH-ISG>ion-ISG.Under physiological conditions,the viscosity index is ranked as:T-ISG>pH-ISG>ion-ISG.The nanostructured lipid carriers?NLCs?were prepared by high pressure homogenization method,and the NLCs were dispersed in different responsive in situ gels.The HPLC analysis results of the nanostructured lipid carriers-based responsive gel?NSG?showed that the linear relationship,specificity,precision,recovery,stability and content determination of all formulations accord with the analytical requirements in the range of 1.004¹00.4?g·mL^-1.The methods of differential scanning calorimetry?DSC?and fourier transform infrared spectrometer?FTIR?have been used to show that the drug in NSG exist in an amorphous state,and the drug may interact with lipid carrier or gel matrix by a hydrogen bonding force.2.Nanostructured lipid carriers-based pH-responsive gel?pH-NSG?and nanostructured lipid carriers-based thermosensitive gel?T-NSG?were prepared by cold-melt method,and hot-melt method for nanostructured lipid carriers-based ion-responsive gel?ion-NSG?.Under non-physiological conditions,the NSGs,was light blue after being diluted with a certain proportion of water,have a appearance color of milky white and good fluidity.The results of TEM showed that the morphology of each formulation was round and uniform,and there was almost no adhesion between the particles,which was similar to the particle size measured by laser particle size analyzer.The median diameters of pH-NSG,T-NSG and ion-NSG measured by laser particle size analyzer were 209.67±10.58 nm,184.03±1.60 nm and 185.87±5.89nm,respectively.The?-potential values of pH-NSG,T-NSG and ion-NSG were in the range of-20^-40 mV.Thus,the particle size and?-potential of pH-NSG,T-NSG and ion-NSG were in accordance with the requirements of ophthalmic preparations.Additionally,compared with pH-NSG and ion-NSG,T-NSG has the highest gel strength,hardness and cohesion in the gel state.The adhesion work of T-NSG?1922.95 mN·sec?was 1.44 and 1.58 times of pH-NSG and ion-NSG,respectively,indicating that T-NSG has better gel strength and bioadhesion.Moreover,the results of dynamic rheological showed that T-NSG and pH-NSG exhibited Newtonian fluid and pseudoplastic fluid under non-physiological and physiological conditions,respectively,while ion-NSG was only pseudoplastic fluid.The phase transition temperature of T-NSG is 33.2°C,while pH-NSG and ion-NSG were not affected by temperature.At the same time,the complex viscosity of all NSG decreases with the increase of angular frequency,which was beneficial to the formulation spreading well on the surface of the eye.3.The infiltration behavior,release kinetics and gel dissolution situation of the NSG and ISG were preliminarily evaluated through the studies of excising corneal permeability,in vitro release and in vitro dissolution tests.The results of excising corneal permeability showed that both pH-NSG and ion-NSG belonged to the first-order release model,and T-NSG belonged to the Ritger-Peppas release model.The order of the apparent permeability coefficient(P_app)and the steady state flow(J_ss)were from large to small:pH-NSG>ion-NSG>T-NSG>TobraDex>Aqueous solution.It was speculated that drug release was affected by high gel strength and strong bioadhesiveness of T-NSG,resulting in slow drug release.The P_apppp and J_sss values of NSGs were large than TobraDex and aqueous solutions,indicating that the gel formulation increased the retention time and contact tightly with the cornea,as well as greater drug absorption on the cornea.Moreover,the in vitro release results showed that the release rate of T-NSG was the slowest with a more pronounced sustained release effect,and the results were similar to the results of excising corneal permeability.Meanwhile,the relationship between the dissolution situation and drug release was investigated by a membrane-free dissolution model.The results showed that the drugs in pH-NSG and T-NSG were mainly released by diffusion and dissolution,while ion-NSG was mainly released in a diffusion manner.4.The experiments of elimination through tears of rabbit pre-corneal and in vivo microdialysis pharmacokinetic were investigated.The results of elimination kinetics showed that the MRT of pH-NSG was increased by 2.31 times compared with TobraDex or nanoparticles,the ion-NSG was increased by 1.34 times compared with pH-NSG,and T-NSG increased by nearly 1.02 times when compared with ion-NSG,indicating that T-NSG had stronger bioadhesion and was beneficial for enhancing the retention time in the eye.Additionally,the results of in vitro microdialysis test showed that the CMA probe was more suitable for dialysis sampling of dexamethasone,and it was determined that 0.5?L·mL^-11 was the perfusion flow rate,5?g·mL^-11 was the perfusion concentration,and the normal saline was the perfusion medium.Under these conditions,the recovery rate?RR?was similar to loss recovery rate?RL?,which was close to 60%.The RR and RL of CMA probe within 8h was stable and reliable.However,the in vivo recovery rate was62.06±2.23%,which was similar to the in vitro recovery rate.The results of intraocular aqueous humor pharmacokinetic showed that T-NSG had the highest C_max,AUC_0?8,MRT,T_1/2/2 and T_maxax when compared with other formulation,which was beneficial to form the drug stores in the eye,indicating T-NSG has the better responsive characteristics and most obvious effect in overcoming the corneal barrier,prolonging the residence time and improving the ocular bioavailability.In this study,we evaluated and compared the physical and chemical properties,corneal permeability,in vitro release,elimination kinetics and microdialysis aqueous pharmacokinetic of different responsive gels.The results showed that compared with pH-NSG and ion-NSG,T-NSG was more suitable for topical intraocular administration,which can be stored in a solution state and transited in a gel state in the intraocular temperature with easily to spread on the ocular surface.The delivery system of composite drug carriers increases the solubility of the poorly soluble dexamethasone,improves the bioadhesion and wettability of the preparations on the cornea by using materials with good bioadhesiveness and compatibility.This system can reduce the number of administrations and the toxic side effects of corticosteroids,thereby prolonging the retention time of the drug on the cornea,dilating the tight cells of the corneal epithelium,and transporting the drug to the posterior segment of the eye through the ocular barrier to achieve the treatment of the posterior segment diseases.Actually,it can provide a valuable reference for the development of topical non-invasive delivery systems.