Naturally Derived Proteins As Sacrificial Templates For Synthesis Of Hollow Silica Materials With Controlled Morphology And Their Potential Applications

Silica is the principle component in the cell wall of diatom and shows stable chemical properties,non-toxic and excellent biocompatibility.The morphology of silica has great influence on its applications in biomedical and chemical fields.Hollow silica materials could support immobilization of therapeutic substances such as drugs,genes and biological growth factors because of their low density,unique hollow structure and much larger specific surface areas.Hollow structures can greatly improve the loading efficiency of drugs.Moreover,hollow silica exhibits good stability in aqueous solution,which affords its applications in chemical fields,such as catalyst supports and selective separation and detection of toxic metal ions.Numerous methods are available for preparation of hollow silica materials at present.A template route is preferable in the synthesis of hollow silica materials as the hollow structure is well directed by the template and can be facilely tuned by adjusting the structural parameters of templates.Several types of templates are available,including carbon nanotubes,anodic alumina,and calcium carbonate.Unfortunately,some problems still exist,such as expensive cost and less active functional groups.Recent researches have indicated that natural proteins are good template for preparation of hollow silica materials as they are biocompatible,safety,reliability,easy availability in large quantity and contain a large number of functional groups.Collagen nanofibers are good template to produce silica tubes as they contain a large number of amino and carboxyl groups.However,collagen is normally too expensive to be suitable for a large-scale production of silica tubes.Gelatin is the degraded product of collagen protein and has many advantages of low-cost,large-scale availability and excellent biocompatibility.Recently,the utilization of gelatin as sacrificial template for synthesis of silica tubes has not been addressed.Silk fibroin?SF?is one of the main structural components in the natural silk fibers and shows good biocompatibility and biodegradability.More importantly,SF exhibits good aqueous stability due to its unique?-sheet crystalline structure.In this work,natural proteins?gelatin,silk fibroin?were developed to address several problems currently existing.Natural proteins containing significant amounts of functional groups,such as-COOH and-NH₂,were employed as novel sacrificed templates for the synthesis of various hollow silica materials via a sol-gel route with a subsequent calcination process.The possible formation mechanisms have been proposed,and the applications in drug delivery and catalyst carrier have been evaluated.The main research contents and obtained results can be summarized as follows.?1?Synthesis and applications of silica tubes prepared using gelatin as novel sacrificed template.Silica tubes were prepared using the gelatin fibers as novel sacrificed template via a sol-gel route with a subsequent calcination process.FT-IR spectrum showed that the siloxane bonds?Si-O-Si?were involved in the silica tubes.SEM observations showed that the silica tubes had an average diameter of 742±82 nm with a hollow cavity of 513±68 nm.Electrospun gelatin fibers can be employed as template for synthesis of silica tubes.Gelatin possesses high affinity to silicate species and the reaction condition is mild.After soaked in the solution of tetracycline hydrochloride?TH,one of the representative antibiotics?as model drug,the silica tubes favored the adsorption of TH.A sustained release behavior of TH was observed as the TH-loaded silica tubes were soaked in the phosphate buffer saline and the resultant silica tubes could be used as good carriers of hydrophilic drug TH.The released TH was biologically active to strongly inhibit the growth of bacterial of Escherichia coli and the antibacterial rate for TH-loaded silica tubes was 100%at 24 h of culturing.?2?Naturally derived silk fibroin-gelatin composites as novel sacrificial template for synthesis of silica tubes and their applications.Electrospun silk fibroin-gelatin composite fibers,to improve the aqueous stability of gelatin fibers,were employed as novel sacrificial template for synthesis of silica tubes and the in vitro biocompatibility of silica tubes were performed.The stability of composite fibers and silica tubes was much better than that of gelatin fibers as template due to the presence of silk fibroin.Silk fibroin-gelatin composite fibers can replace collagen as good template and exhibit the same excellent template effect.TEM observation showed that the diameter of silica tubes could be controlled from 225±11 nm to 470±9 nm by tuning the silk fibroin-gelatin weight ratio from 1.25 to 2.After incubation with the osteoblast MG63 cells,silica tubes?0–200?g/m L?had no significant cytotoxicity and presented excellent biocompatibility.Furthermore,the resultant silica tubes showed high encapsulation efficiency of TH.?3?Silk fibroin as sacrificial template for facile synthesis of novel porous silica tubes and Au-decorated silica tubes.SF fibers,to explore the influence of SF on the morphology of silica tubes,were employed as single sacrificial template for synthesis of silica tubes and Au-decorated silica tubes with cage-like porous morphology via the sol-gel route and calcination.SEM and TEM observations indicated that the resultant silica tubes presented cage-like morphology and porous hollow structure with the controllable pore size from139±11 nm to 209±64 nm.The formation of the pore structure should be mainly attributed to the self-assembly,packing and fusion of the silica nanospheres,while the formation of the hollow structure should be assigned to the template role of SF fibers.Furthermore,it was found that porous silica tubes can be used as scaffold to immobilize the Au NPs and Au NPs were distributed evenly.The resultant porous Au-decorated silica tubes showed photo-catalytic activity for conversion of 4-nitrophneol to 4-aminophenol.?4?Silk fibroin as sacrificial template for synthesis of hollow silica spheres and their functionalization.SF-based biomaterials show good aqueous stability due to the unique?-sheet structure.The structures of silica tubes could be well controlled by the template of SF fibers or SF-based composite fibers.To expand the applications of SF,thus,the hollow silica spheres were synthesized using SF spheres as single sacrificial template via a sol-gel route.TEM observation showed that silica spheres had a hollow cavity and a porous shell.After exposure to Hela cells,MTT assay indicated that silica spheres were in vitro biocompatible.And it was found that silica spheres not only supported adsorption of TH with adsorption efficiency of 17.4%,but also exhibited a sustained release behavior for TH.The TH-loaded silica spheres showed antibacterial property to inhibit the growth of two representative bacteria:Escherichia coli and Staphylococcus aureus,indicating that the released TH was biologically active.In addition,near infrared?NIR?sensitive silica-GNR spheres were synthesized with SF spheres as template.Under the irradiation of808 nm NIR light,the temperature of the suspension of silica-GNR spheres was increased from 25°C to 48.6°C,indicating that the silica-GNR spheres were NIR-sensitive and showed the photo-thermal activity.