Cytocompatibility and Uptake of Halloysite Clay Nanotubes
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Abstract:
Halloysite is aluminosilicate clay with hollow tubular structure of 50 nm external diameter and 15 nm diameter lumen. Halloysite biocompatibility study is important for its potential applications in polymer composites, bone implants, controlled drug delivery, and for protective coating (e.g., anticorrosion or antimolding). Halloysite nanotubes were added to different cell cultures for toxicity tests. Its fluorescence functionalization by aminopropyltriethosilane (APTES) and with fluorescently labeled polyelectrolyte layers allowed following halloysite uptake by the cells with confocal laser scanning microscopy (CLSM). Quantitative Trypan blue and MTT measurements performed with two neoplastic cell lines model systems as a function of the nanotubes concentration and incubation time indicate that halloysite exhibits a high level of biocompatibility and very low cytotoxicity, rendering it a good candidate for household materials and medicine. A combination of transmission electron microscopy (TEM), scanning electron microscopy (SEM), and scanning force microscopy (SFM) imaging techniques have been employed to elucidate the structure of halloysite nanotubes.Keywords:
Halloysite
Biocompatibility
Trypan blue
In this study, the characteristics of halloysite subjected to silane coupling treatment as a reinforcing agent are investigated. Halloysite is one of the natural substances that is currently recognized as having a nanotubular structure. Halloysite nanotubes are 50 nm in diameter, 0.5-1 μm in length and 15 nm of inner diameter. Polyvinyl alcohol (PVA) which is a synthetic polymer with characteristics such as biodegradability and solubility in water was used as the matrix. The halloysite/PVA films were characterized by tensile test, scanning electron microscopy (SEM), and optical transmittance. The tensile strength of PVA/untreated halloysite film was decreased, but Young’s modulus was increased compared with neat PVA film. In addition, silane coupling treatment was performed on halloysite to improve the interfacial adhesion between PVA and halloysite. PVA/silane-treated-halloysite film had improved elongation compared with PVA/untreated-halloysite films. SEM images revealed the fracture mode and the distribution of halloysite inside the composites. When the halloysite content was low, a fracture surface formed by dimples originating at the halloysite sites was observed. On the other hand, when the halloysite content was high, brittle fracture occurred. In the case of high halloysite content, agglomeration of nanotubes was observed. The optical transmittances of PVA/silane-treated-halloysite films with 8 wt% halloysite were over 80%.
Halloysite
Polyvinyl Alcohol
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Halloysite
Mechanical strength
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Nanoclays have shown great potential in the field of controlled release. In particular, the cylindrical geometry and surface chemistry of halloysite nanotubes make them attractive for use as nanocarriers. Halloysite's tubular cavity can be filled with drug which later diffuses out of the lumen, enabling controlled release behavior over several hours. When halloysite is incorporated into polymer matrices, such as polyvinyl alcohol (PVOH) and poly(methyl methacrylate) (PMMA), release has been shown to be extended even further, on the order of days. In this chapter, the principles and mechanisms used in controlled release applications are presented, and recent studies of controlled release from halloysite nanotubes are reviewed. Particular attention is paid to two studies on the incorporation of tetracycline-loaded halloysite into polymer films to prepare monolithic controlled release systems. Factors affecting the release from halloysite are explored, particularly loading method and material properties.
Halloysite
Polyvinyl Alcohol
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