gure 1D). The measured hydrodynamic diameter of the RNV encapsulating different
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gure 1D). The measured hydrodynamic diameter of the RNV encapsulating different hydrophilic reagents is around 140 nm, and the polydispersity index (PDI) is smaller than 0.25 by dynamic light scattering (DLS) (Table 1). RNV loaded with different hydrophilic reagents shows marginal differences in size and PDI. The surface charges of the RNV encapsulating different reagents can be influenced by the contents. Briefly, the positively charged DOTAP may diffuse to the outer lipid layer, resulting in the positive surface charge of RNV when encapsulating calcein and rhodamine B. However, for fabrication of RNV encapsulating siRNA, the negatively charged siRNA will interact with the DOTAP, thus limiting the diffusion of DOTAP and resulting in the negative surface charge of RNV (Supporting Information). The entrapment efficiencies of three hydrophilic reagents into the RNV are almost 90% (Table 1), approximately 1.5 times
Table 1: Size (d), zeta potential (3), polydispersity index (PDI) and entrapment efficiency (EE) of RNVs loaded with different reagents. RNV/[reagent] Z-AVE EE [96] d [nml RNVIrhodamine 130.614.10 4.11.76 0.221 t0.027 89.68 1.47 RNVIcalcein] RNV[Dox/siMDR 136.43.814 -14.2+3.25 0.2220.017 91.234.5 [al Z-AVE mean particle size. [b] Details can be found in the Supporting Information. 49.82.815 11.20.35 0.1320.018 90.66+0.27Explanation / Answer
Rigid nanovesicles (RNV) are hallow structured vesicles which enables them to load hydrophilic drug candidates within the hallow structure. RNV are prepared by different techniques and once dispersed in physiological medium (saline, PBS buffer or blood), RNV diffuses into the medium. These particles or vesicles are always in Brownian motion. Wheen light is passed through the slution, these vesicles scatter light and it is dependent on Brownian motion of the vesicles. Based on the scattering of light, researchers calculate size of the vesicles which is known as hydrodynamic radius. This is not actual size of the vesicles rather size of the vesicles in the solution.
Hydrodynamic radius is of atmost importance in drug delivery as it has impact on immune system. Smaller the radius, less provoking of immune system. And all the vesicles prepared should pose uniform or almost uniform hydrodynamic size which is measured using polydispersity index (PDI). It is estimated that PDI value less than 0.3 is highly uniform (monodisperse) in size.
Surface charge or zeta potential is again plays a significant role in drug delivery. Surface charge is a measure of surface potenial of the vesicles. More the surface potenital (either positive or negative) less will be the agglumerization of the particles due to charge repulsion. Hence it is expected that vesicles should pose higher zeta value. Herein, DOTAP is a cationic lipid which is extensively used to prepare cationic liposomes. These lipids face outer layer of the liposome and contribute positive charge to the vesicles. Hence particles are well seperated over period of time without agglumerating. Encapsulating SiRNA which is a short interfering RNA (negatively charged) into the RNV leads to coupling of SiRNA with DOTAP due to opposite charges. This leads to prevention of diffusion of DOTAP towards the outer layer of the vesicles and hence limiting positive charge of the vesicles.
Finally entrapment efficiency is a measure of how much amount of drug that has been incorporated within the vesicles with respect to the total amount of drug used while preparation of the vesicles. These vesicles have incorporated upto 90% of the total drug within the vesicles. That means 10% of the drug remained outside the vesicles i.e., in the preparation medium.
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