Preparation Of Drug-loaded Porous Gelatin Microspheres

Due to good biocompatibility and special physical and chemical properties,gelatin is widely used as a potent biomaterial for preparation of microspheres.Gelatin microsphere has been applied in the areas of pesticide delivery;however,the smaller surface area and less active sites of the gelatin microspherelimit its application.Porous gelatin microspheres thus show good application prospect as a pesticide carrier because of its larger specific surface area.Etching method is the common method for preparing porous microspheres,but it will reduce surface polar groups and decrease the loading capacity.Chitin is a kind of environment-friendly renewable natural polymer materials,and the major components of fungal cell wall and insects and other arthropod exoskeletons.Chitin is attracting many attentions because of its excellent mechanical property.Therefore,in order to establish a porous gelatin microspheres drug delivery system with high loading capacity,good environmental stability and ecological friendliness.the CaCO₃etching method and chitin composite method were explored.The drug loading performance and mechanical properties of porous gelatin microspheres were evaluated.（1）Preparation and optimization of gelatin microspheres:Emulsification crosslinking method was adopted.The optimal preparation conditions were as follows:500rpm,water/oil ratio 2:10,and emulsifier Span80.The gelatin microspheres prepared showed better spherical appearance under SEM and electron microscope,and the size distribution is 210.64±32.53μm.（2）Preparation and optimization of CaCO₃etched porous gelatin microspheres:Three different particle sizes of CaCO₃（40nm,300nm and micron）were used to prepare porous gelatin microspheres and the preparation conditions were optimized.For directly adding300nm CaCO₃to prepare etched porous gelatin microspheres,20%CaCO₃added amount had the best effect.For the porous gelatin microspheres prepared by directly adding 40nm CaCO₃,ethanol disperse CaCO₃should be added,and the volume ratio of ethanol to gelatin solution is1:15,which is the best addition amount.Micron-sized CaCO₃was obtained through the reaction of Na₂CO₃and CaCl₂,and the molecular size was determined to be about 2300 nm.The optimized preparation conditions were as follows:Na₂CO₃was first added to the gelatin solution,then CaCl₂was added.The reaction time was 20 min,and the microspheres were prepared with complete spherical shape and the most uniform surface pores.FT-IR characterization proved that the gelatin microspheres were cross-linked successfully.The mercury injection data indicates that the addition of CaCO₃with different particle sizes can cause the different pore sizes distribution in porous microspheres,so as to control the pore size.Using rhodamine B as the model drug,the loading and distribution of the drug on the porous microspheres was simulated.Under the laser confocal microscope,the fluorescence of rhodamine B was distributed in the interior of the porous microspheres,while the fluorescence of unetched microspheres was distributed on the surface of the microspheres.The loading capacity of three kinds of porous microspheres prepared by etching method was studied,and the following results were obtained:the best thiamethoxam drug loading and encapsulation rate were shown by etching the porous microspheres with 40nm CaCO₃,which were 80.44 mg/g and 67.04%,resppectively.The final drug release rate of both theetched porous microspheres and the unetched porous microspheres could both reach 100%,showing the phenomenon of drug slow release.However,the maximum drug loading of berberine hydrochloride for CaCO₃etching porous microspheres is only 8.11 mg/g,and the encapsulation efficiency is only 4.18%.（3）Preparation of and optimization chitin-gelatin composite porous microspheres:The composite microspheres were obtained by repeated freeze-thaw dissolution of chitin in Na OH/urea aqueous solution and cross-linking with the gelatin composite emulsion.The microspheres were smaller than 100μm in size.The surface of the composite microspheres of chitin gelatin was observed under tungsten filament electron microscope,and the microspheres after crushing also showed a reticulate porous structure.Infrared spectrum proved that gelatin and chitin composite successfully and intramolecular hydrogen bonds were formed.The thermal stability of chitin gelatin composite microspheres was better than that of gelatin microspheres.Berberine hydrochloride was chose as model drug.The optimized loading conditions were determined as:the ratio of berberine hydrochlorideand chitin gelatin composite microspheres was 1:5.and when chitin:gelatin microspheres=3:10,the drug loading capacity was the best and reached 105.08±3.69 mg/g,which is 12.97 times higher than CaCO₃etching porous microspheres.Chitin gelatin composite microspheres began to release drugs after 8 hours,and then entered the slow release stage.5 days post release,the release amount reached more than 81%,showing the composite carrier has good sustained drug release property.In this paper,a drug-loading system of porous gelatin microspheres based on calcium carbonate etching and chitin inclusion was established.Thiamethoxam and berberine hydrochloride were used as model drugs to evaluate the drug-loading performance of the two systems,which provided a reference for the development of drug-loading system with high load,good environmental stability and ecological friendliness.