Silk Fibroin As A Carrier For Controlled Release Of Fragrance

Fragrances have effects of sedation,health care,sterilization and deodorization.With the improvement of our life quality,fragrances are being used more and more in daily lives.Common fragrances are mostly alcohols,alkenes,aldehydes,ketones and esters,with low boiling points and unsaturated bonds,which are volatile and prone to oxidative degradation reactions.All these shortcomings limit the applications of fragrances.Silk fibroin(termed silk thereafter)is a naturally derived protein.Silk is non-toxic and non-irritating,which has not only excellent physical and chemical properties,but also great biocompatibility and biodegradability.Studies have shown that silk fibroin as a drug carrier material can effectively stabilize bioactive molecules and control drug release.In the present work,silk fibroin microspheres loaded with three fragrances(citral,beta-ionone and myrcene)were prepared by controlling the interaction between fragrances and silk fibroin.The morphology and size distribution were characterized by scanning electron microscopy(SEM)and dynamic light scattering(DLS).It was found that particle size could be controlled by changing the concentration of silk fibroin solution.The secondary structure and crystalline structure of fragrance-loaded silk microspheres were analyzed by FT-IR and XRD.The results showed that fragrance promoted the formation of ?-sheet structure in silk microspheres,and Silk II crystal structure could be found in the citral-loaded silk microspheres.DSC and TGA analyses showed that the thermal stability of the fragrance embedded in silk microspheres was significantly improved.Under the same conditions,silk microspheres exhibited the highest loading of citral(25.93%)among three fragrances,followed by beta-ionone with a loading of 11.56%,and myrcene with a loading of 0.96%.Fragrance-loaded silk microspheres with different sizes were then used to treat cotton fabrics.It was found that the amount of microspheres attached to the fabric were particle size dependent,with less than 1 ?m particles 2-5 times of those with sizes of 3-18 ?m.There was 50-80% fragrance remained on the aromatic fabric after one washing,indicating a great washing durability of the treated fabric.The treated fabric was placed in ovens set at different temperatures and fragrance release rates were determined by measuring the amount of fragrance remained in the fabric.At 60?,the release of fragrance embedded in silk microspheres lasted 9-15 hours,which was remarkably longer than pure fragrance and fragrance/polyethylene glycol mixture(1-3 hours).At 37?,the release time of fragrance in silk microspheres was 29-74 hours,while only 4-6 hours for the pure fragrance and fragrance/polyethylene glycol mixture.At room temperature,the release time of fragrance in silk microspheres was 103-134 hours,much longer than the 12-20 hours for the pure fragrance and fragrance/polyethylene glycol mixture.In summary,silk as a carrier of volatile fragrance could embed and stabilize fragrance and extend its release time 5-11 times compared to pure fragrance at room temperature.Fragrance-loaded silk microspheres can be widely used in textile finishing,cosmetic and food industry in the future.