Preparation And Characterization Of Injectable In-situ Regenerated Silk Hydrogels

The in-situ formation of injectable silk fibroin hydrogels(SFG) have potentialadvantages over various biomaterials due to the minimal invasiveness duringapplication. Biomaterials need to gel rapidly under physiological conditions afterinjection. In the current paper, a novel way to accelerate Bombyx mori silk gelationusing cationic surfactants (quaternary ammonium salts) and anionic surfactants (sulfates)such as Sodium Dodecyl Sulfate (SDS) and Sodium Alcohol Ether Sulphate (AES) asgelling agents, is reported. The effect of the above two categories of surfactants on thestructure and properties of hydrogels was studied. And the corresponding mechanismsof in-situ fibroin gelation were also explored.Anionic surfactant (sulfates) can shorten silk gelation time, which is directly relatedto the length of their hydrocarbon chains. Surfactants with short hydrocarbon chains (﹤8) had no significant role in gelation, but with the extension of hydrocarbon chains, thecorresponding SF gelation time has the tendency of reduction. The mechanism ofSDS-induced rapid gelation was determined. And the structure and properties such asmechanics, degradation, and drug delivery were also characterized. The releasebehaviors of doxorubicin (Dox) hydrochloride, as a model drug, in SDS/SFG andAES/SFG, show the same characteristics that the release rate at the late stage (10～38d)remained stable substantially, and was slower than that at early period (1～10d). Basedon these results, it is concluded that the Dox-loaded compound silk gel represents ainjectable sustained-release system.Using quaternary ammonium salts (QAS) as gel accelerators, silk fibroin aqueoussolutions were induced to gel rapidly. The formation mechanism and properties such asstructure and thermal stability of QAS-induced silk gel were characterized by means ofX-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy(SEM), differential thermal analysis (DTA) and circular dichroism (CD) measurements.The results show that QAS-induced silk gelation is accompanied by the formation of β-sheets. With the observation of SEM, the internal morphology of gel exhibited aporous three-dimensional network structure. In vitro degradation and DTA analysisrevealed that QAS-induced fibroin gel was not quite stable and disintegrated moreeasily in the enzyme solution. Also, QAS is amorphous or metastable crystal state insilk gel and thus easy to release and diffuse. The antibacterial test in vitro suggested thatQAS/SFG showed distinctly antibacterial activities against both Gram-positive andGram-negative bacteria. In-situ antimicrobial silk hydrogel is expected to be used for asurgical dressing.