Abstract
In this work, we investigated the effects of the vacuum pumping on both the loading efficiencies and the release kinetics of halloysite nanotubes filled with drug molecules dissolved in ethanol. As model drugs, salicylic acid and sodium diclofenac were selected. For comparison, the loading of the drug molecules was conducted on platy kaolinite to explore the key role of the hollow tubular morphology on the filling mechanism of halloysite. The effects of the pressure conditions used in the loading protocol were interpreted and discussed on the basis of the thermodynamic results provided by Knudsen thermogravimetry, which demonstrated the ethanol confinement inside the halloysite cavity. Several techniques (TEM, FTIR spectroscopy, DLS and zeta-potential experiments) were employed to characterize the drug filled nanoclays. Besides, release kinetics of the drugs were studied and interpreted according to the loading mechanism. This work represents a further step for the development of nanotubular carriers with tunable release feature based on the loading protocol and drug localization into the carrier.Graphic abstractThe filling efficiency of halloysite nanotubes is enhanced by the reduction of the pressure conditions used in the loading protocol.
Highlights
In the very last decades, we observed a growing interest of the scientific community in the study of clays, which were employed in numerous applications
The pressure conditions induced a relevant effect on the loading efficiency of halloysite nanotubes (HNTs)
The successful loading of salicylic acid into the nanotubes was confirmed by Fourier transform infrared (FTIR) spectroscopy, which evidenced the presence of the characteristic signals of the drug in the HNTs/Salicylic acid (SA) hybrids
Summary
In the very last decades, we observed a growing interest of the scientific community in the study of clays, which were employed in numerous applications. Halloysite nanotubes can be loaded with negatively charged active species, such as biological molecules, anti-corrosion compounds and antioxidants that can be protected inside the inner lumen of the nanotubes [39,40,41] This one is a very important property, which endows the preparation of new smart nanocontainers for loading, storage and sustained release of chemical agents [42,43,44,45]. We moved forward by investigating the confinement effect of an organic solvent, namely ethanol, to understand its influence on the loading mechanism, on the drug localization within the clay and on the releasing kinetics This seems to be the most important aspect for all the applications we discussed above, concerning the use of halloysite as controlled and tunable delivery system
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