Formulation of silk sericin loaded in niosomes and evaluation of biological activities

Abstract

The process of extraction of sericin from silkworm, Bombyx mori Linn (Nang-noi Sisaket 1), was investigated for the appropriate method for silk sericin extraction. Method I which was preformed by using a high temperature and pressure degumming technique, yielded silk sericin with a significantly higher superoxide scavenging and antityrosinase activities than method II (p < 0.05). In addition, the optimized spraying condition was estimated using response surface methodology. The effect of two process parameters, inlet temperature and cocoon concentration solution on yield and moisture content was studied. A face centered design showed a linear model fitted for %yield and a quadratic model for %moisture content (p < 0.05). The optimum region by overlay plot was carried out using the best condition to evaluate the repeatability of the spray-drying technique. The observed means obtained for %yield and %moisture content were in range of the prediction intervals at 95% confidence level as, 11.64±0.62% and 6.38±0.23%, respectively. The result clearly showed that the model fitted the experimental data well. The properties of silk sericin spray dried powder were determined. The protein content of silk sericin was 21.83±1.71% (w/w). The scavenging activities of sericin against DPPH and superoxide free radicals exhibited the EC₅₀ values of 0.82 and 0.43 mg/ml, respectively. The antityrosinase activity of sericin exhibited an EC₅₀ value of 0.40 mg/ml. Consequently, niosomes loaded with 1.0% weight by volume silk sericin could be prepared by reverse phase evaporation technique. Niosomes could be achieved by four formulations using Span 20, Span 40, Span 60 and Span 80 with surfactant: cholesterol ratio of 1:1 and with Solulan® C-24 as a stabilizer. Vesicular sizes of all formulations determined by photon correlation spectroscopy technique were between 181-341 nanometers. Entrapment efficiency of all niosomes formulation was between 84.22-93.88%. All of silk sericin loaeded in niosomes formulations have biological activities. Vesicular size showed a larger mean size at 4 °C for 12 weeks. The percentage of silk sericin in niosomes that composed of Span 40 and Span 60 were non-significantly decreased at 4 °C for 8 weeks (p> 0.05). The in vitro permeation using newborn abdorminal porcine skin as skin model revealed that niosomes loaded with sericin could enhance the skin penetration of sericin through pig skin as compared with sericin solution. The result demonstrated that niosomes could enhance the delivery of sericin through skin. The permeability coefficient of sericin loaded niosome formulations were between 0.0043-0.0051 cm/h.