Preparation And Application Of Drug-loaded Silk Fibroin Nanospheres

Natural animal silks, mainly from Bombyx mori silkworm, have been in practically used by human beings for centuries because of its unique luster, fineness, and mechanical properties. In recent years, extensive studies have been carried on the biomedical application of regenerated silk fibroin (RSF), which is the main component of silk protein.Regenerated silk fibroin (RSF) contains 18 kinds of amino acid residues arranged in unique sequence, which forms alternating hydrophobic and hydrophilic blocks just like those seen in amphiphilic block co-polymers. These hydrophobic blocks consist of highly conserved sequence repeats as GAGAGS and less conserved repeats as GAGAGX (where X is either V or Y); while the hydrophilic parts are non-repetitive and shorter than those hydrophobic repeats. RSF can be water soluble by adopting random coil and/or helical conformation, but becomes water insoluble if it takes a conformation transition top-sheet induced by the change of the environment, such as the addition of organic solvents, the increase of temperature, and the variation of pH value. We applied two self-assembly methods to prepare drug-loaded RSF nanospheres for a future application such as lymphatic chemotherapy.Based on a simple and mild method for the preparation of silk fibroin nanospheres with controllable size we developed previously, anti-cancer drug paclitaxel (PTX)-loaded silk fibroin nanospheres ranging from 270 to 520 nm were produced accordingly. The drug loading, encapsulation efficiency and released property of PTX-loaded silk fibroin nanospheres are depended on the silk fibroin concentration and initial PTX loading capacity. The maximum drug loading is about 6.9% and the release time of such a kind of nanospheres is over 9 days. The release time of PTX-loaded silk fibroin nanospheres can be as long as 2 weeks when the drug loading is about 3%. All these results imply that such a kind of biomacromolecule based anti-cancer drug nanocarrier has a great potential for chemotherapy in clinical applications.Electrospray technique, derived from the elctrospin technique, is a promising method used for production of controlled size and controlled physical property polymer particles. In order to solve the problem of loading hydrophilic drug, specially designed equipment was used to co-axial electrospray and both RSF solution and drug solution were supplied from the inner and outer nozzle respectively. We applied elctrospray technique to well disperse RSF molecules in alcohol solvent, such as ethanol and methanol, and at a meanwhile obtained the needed nanospheres through controlling the RSF concentration, types of alcohols, electrical voltage, receipt distance and flow rate. Finally anti-cancer drug GEM-loaded silk fibroin nanospheres ranging from 150 to 200 nm were produced. By comprehensive consideration of RSF concentration, drug solution concentration and flow rate ratio nanospheres with drug loading over 10% was obtained which is relatively high among the biomacromolecule carriers. Compared with the other methods, the co-axial electrospraying technique is a effective method to improve drug loading which can be over than 90%.