Studies On The Solid Lipid Nanoparticles Prepared By The Double Emulsion Method

Solid lipid nanoparticles (SLN) were first introduced at the beginning of the 1990s. Compared with the traditional drug delivery systems such as polymer nanoparticles, emulsions and liposome, SLN is the potential carriers for a number of drugs, owing to the sensitive targeting effect, high stability, low toxicity, and large-scale production.Double emulsion method is used to prepare SLN, and a systematic research on the physicochemical properties of SLN is carried out. Above all, the influences of the emulsifier, the amount and kind of lipid on the SLN particle size and the electrochemistry properties are studied. The effect of preparation process on the physicochemical properties of SLN is also invesgigated. Secondly, the position of bovine serum albumin (BSA) in the SLN and the impact of the SLN on the secondary structure of BSA are investigated when BSA is loaded into SLN as the model drug. Finally, the crystallization states of the SLN before and after containing puerarin are compared. It opens up a new way for the future study of SLN preparation method.Double emulsion method used for preparing SLN is based on the microemulsion method. In this paper, glyceryl monocaprate (MC) is used as the solid lipid, Span 80 as a hydrophobic emulsifier, and Tween 20 as a hydrophilic emulsifier. SLN can be successfully prepared by double emulsion methods via a two-step emulsification process.At the beginning of this dissertation, a series of ternary phase diagrams based on different kinds of lipid and emulsifier are constructed. Dynamic light scattering (DLS) and zeta potential method are used to investigate the influence of the lipid chain length and the emulsifier types on SLN. It is found that with the increasing of the lipid chain length, the region of microemulsion decreases; and as the emulsifier chain length increasing, the region of microemulsion increases. According to the critical accumulation parameter theory, it confirms that the variations of lipid and surfactants may lead to the change of the SLN size. In addition, the variation of particle zeta potentials can be explained by the surface energy and the theory of space stabilization.The basic physicochemical properties of SLN were affected by many factors during the preparation process. The ternary phase diagrams show that although the pH of the buffer solution has little effect on the W/O microemulsion region, the particle size and the value of zeta potential are greatly affected with the addition of electrolytes. The temperature makes an effect on the microemulsion region, but dose not affect the final shape of the SLN and the zeta potential. The dispersion degree is also an important factor on the basic properties of SLN.BSA, which is one kind of common hydrophilic proteins, is loaded into SLN with the double emulsion method. Several methods are applied to investigate the particle size, morphology, the position of BSA in SLN, and the influence of BSA on the loading process into SLN. It is observed that increasing the protein content leads to an increase in diameter and enhanced stability. Fluorescence spectroscopy confirms that the loaded position of BSA is the interface between the inner aqueous phase and the solid lipid phase. Both Fourier-transform infrared spectroscopy and circular dichroism spectra indicates that the secondary structure of the BSA is disrupted slightly. Ultimately, a drug-loaded model structure is proposed.The freeze-dried powders were used to detect the crystalline state of the lipid of SLN by mean of the differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The DSC spectrogram demonstrates that the crystallinity of the lipid in SLN prepared by double emulsion method is lower than that made by the microemulsion method. It can be explained that the mixture of the two different emulsifiers is not propitious to the crystallization of the lipid. The crystalline behavior of the lipid matrix is further disrupted after the addition of the puerarin, which can further weaken the crystallization of the lipid.