Halloysite nanotubes-polymeric nanocomposites: characteristics, modifications and controlled drug delivery approaches

Ferrari, P. C.; Araujo, F. F.; Pianaro, S. A.

doi:10.1590/0366-69132017633682167

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Articles • Cerâmica 63 (368) • Oct-Dec 2017 • https://doi.org/10.1590/0366-69132017633682167 copy

Halloysite nanotubes-polymeric nanocomposites: characteristics, modifications and controlled drug delivery approaches

Nanocompósitos poliméricos com nanotubos de haloisita: características, modificações e atuação como sistemas de liberação controlada de fármacos

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Halloysite nanotubes (HNTs) are aluminosilicate nanoclay mineral which have a hollow tubular structure and occurs naturally. They are biocompatible and viable carrier for inclusion of biologically active molecules due to the empty space inside the tubular structure. In this article, the HNTs main characteristics, and the HNTs-polymeric nanocomposite formation and their potential application as improvement of the mechanical performance of polymers and entrapment of hydrophilic and lipophilic substances are summarized. Recent works covering the increment of HNTs-polymeric nanocomposites and presenting promising employment of these systems as nanosized carrier, being suitable for pharmaceutical and biomedical applications, based on earlier evidence in literature of its nature to sustain the release of loaded drugs, presenting low cytotoxicity, and providing evidence for controlled drug delivery are reviewed.

Keywords:
nanoclay; bio-nanocomposites; functionalization; sustained drug release; nanotechnology

Table I Main physical and chemical characteristics of halloysite nanotubes (HNTs).

HNTs characteristic	Value	Comment	Reference
Elastic modulus	230-340 GPa		²²22 M. Liu, Z. Jia, D. Jia, C. Zhou, Prog. Polym. Sci. 39 (2014) 1498.
Mean particle size	50-400 nm	143 nm to 5 wt% aqueous solution	⁴4 S. Del Buffa, M. Bonini, F. Ridi, M. Severi, P. Losi , S. Volpi, T.A. Kayal, G. Soldani, P. Baglioni, J. Colloid Interface Sci. 448 (2015) 501. ^{), (} ⁵5 P. Pasbakhsh, G.J. Churchman, J.L. Keeling, Appl. Clay Sci. 74 (2013) 47.
BET surface area	20.0-100.0 m².g^-1		²²22 M. Liu, Z. Jia, D. Jia, C. Zhou, Prog. Polym. Sci. 39 (2014) 1498.
Lumen space	10.7-39%		²²22 M. Liu, Z. Jia, D. Jia, C. Zhou, Prog. Polym. Sci. 39 (2014) 1498.
Inner diameter	10-40 nm		²³23 Y. Joo, J.H. Sim, Y. Jeon, S.U. Lee, D. Sohn, Chem. Commun. 49 (2013) 4519.
External diameter	40-60 nm		³3 Y.M. Lvov, W. Wang, L. Zhang, R. Fakhrullin, Adv. Mater. 28 (2016) 1227.
Density	2.14-2.59 g.cm^-3	Low, compared to other fillers, such as talc, calcite CaCO3, montmorillonite and kaolinite	²²22 M. Liu, Z. Jia, D. Jia, C. Zhou, Prog. Polym. Sci. 39 (2014) 1498.
Pores space	14-46.8%		²⁴24 G. Tari, I. Bobos, C.S.F. Gomes, J.M.F. Ferreira, J. Colloid Interface Sci. 210 (1999) 360.
Cation exchange capacity	Dehydrated HNTs: 5-10 meq/100 g		²⁵25 R.E. Grim, Clay mineralogy, McGraw-Hill, New York (1953).
Cation exchange capacity	Hydrated HNTs: 40-50 meq/100 g
Surface charge	Negative outer - siloxanes and silanols/aluminols	Predominantly negative over physiologically pH range (>2)	²¹21 R. Kamble, M. Ghag, S. Gaikawad, B.K. Panda, J. Adv. Sci. Res. 3 (2012) 25. ^{), (} ²⁴24 G. Tari, I. Bobos, C.S.F. Gomes, J.M.F. Ferreira, J. Colloid Interface Sci. 210 (1999) 360.
Surface charge	Positive inner - aluminols	Predominantly negative over physiologically pH range (>2)

Table II Examples of purification, modification and functionalization process of halloysite nanotubes (HNTs).

Modification	Application	Method and substances applied	Reference
HNTs purification	Dispersion-centrifugation-drying technique	10 wt% water suspension with heating to 60 °C	⁵5 P. Pasbakhsh, G.J. Churchman, J.L. Keeling, Appl. Clay Sci. 74 (2013) 47. ^{), (} ³⁸38 M.L. Jackson, Soil chemistry analysis: advanced course, Madison, Wisconsin (1956).
HNTs purification	H₂O₂ to remove organic impurities	H₂O₂ aqueous solution (30%)	³⁹39 S. Zeng, C. Reyes, J. Liu, P.A. Rodgers, S.H. Wentworth, L. Sun, Appl. Polym. 55 (2014) 6519.
Covalent functionalization	Reduction of the polarity; shielding of the hydroxyl groups; inclusion of hydrocarbons; creation of functional groups	Grafting silanes via condensation between the hydrolyzed silanes and the surface hydroxyl groups of the HNTs	⁴⁰40 M. Poikelispää, A. Das, W. Dierkes, J. Vuorinen, J. App. Polym. Sci. 127 (2013) 4688.
	Increase the interfacial adhesion of the HNTs	γ-glycidoxypropyltrimethoxysilane; 3-(trimethoxysilyl)propyl methacrylate	⁷7 S. Zhong, C. Zhou, X. Zhang, H. Zhou, H. Li, X. Zhu, Y. Wang, J. Hazard Mater. 276 (2014) 58. ^{), (} ²²22 M. Liu, Z. Jia, D. Jia, C. Zhou, Prog. Polym. Sci. 39 (2014) 1498.
	Surface modifier (introduce double bonds onto the surface of HNTs to form sites for polymerization)	3-methacryloxypropyltrimethoxysilane; poly(2-hydroxyethyl methacrylate); poly(2-hydroxyl ethyl methacrylate-b-methyl methacrylate)	⁴¹41 C. Zhou, H. Li, H. Zhou, H. Wang, P. Yang, S. Zhong, J. Sep. Sci. 38 (2015) 1365.
	Enhance biocompatibility of several nanomaterials	3-Aminopropyltriethoxysilane	⁴4 S. Del Buffa, M. Bonini, F. Ridi, M. Severi, P. Losi , S. Volpi, T.A. Kayal, G. Soldani, P. Baglioni, J. Colloid Interface Sci. 448 (2015) 501. ^{), (} ³⁵35 T.Y. Cheang, B. Tang, A.E. Xu, G.Q. Chang, Z.J. Hu, W.L. He, Z.H. Xing, J.B. Xu, M. Wang, S.M. Wang, Int. J. Nanomed. 7 (2012) 1061.
	Improve dispersion in polymers (intercalation and interaction of lumen space inside HNTs)	γ-methacryloxypropyl trimethoxysilane	⁵5 P. Pasbakhsh, G.J. Churchman, J.L. Keeling, Appl. Clay Sci. 74 (2013) 47.
	Enhance the negative charge or become neutral HNTs surface	Cationic and anionic surfactants: sodium dodecanoate and decyl trimethyl ammonium bromide	³³33 M.J. Mitchell, C.A. Castellanos, M.R. King, Biomaterials 56 (2015) 179.
Covalently grafting phosphonic acid	Change morphology of nanotubes to nanoplatelets: increase the basal spacing from 7.2 to 15.1 Å	Phenyl phosphonic acid	⁴²42 J.L. Guimarães, P. Peralta-Zamora, F. Wypych, J. Colloid Interface Sci. 206 (1998) 281. ^{), (} ⁴³43 Y. Tang, S. Deng, L. Ye, C. Yang, Q. Yuan, J. Zhang, C. Zhao, Compos. Part A 42 (2011) 345.
Covalently grafting phosphonic acid	Remove the air from nanotubes lumen - drug loading	Octadecyl phosphonic acid: bond to the alumina sites at the tube lumen but not the outer siloxane surface	³¹31 W.O. Yah, A. Takahara, Y.M. Lvov, J. Am. Chem. Soc. 134 (2012) 1853.
Non-covalent functionalization
Alkali treatment	Low concentration NaOH: to maximize the density of hydroxyl groups on silica; increase the dispersibility of HNTs in polar solvents	NaOH react with the tetrahedral silicate to create silanol (Si-OH) groups	³⁹39 S. Zeng, C. Reyes, J. Liu, P.A. Rodgers, S.H. Wentworth, L. Sun, Appl. Polym. 55 (2014) 6519. ^{), (} ⁴⁴44 Q. Wang, J. Zhang, A. Wang, App. Surf. Sci. 287 (2013) 54.
Acid activation	Disaggregation of HNTs: elimination of mineral impurities and inner layers dissolution; replacement of interlayer cations by protons; better exposure of the external adsorption sites	H₂SO₄	⁴⁵45 E. Abdullayev, A. Joshi, W.B. Wei, Y.F. Zhao, Y.M. Lvov, ACS Nano 6 (2012) 7216. ^{), (} ⁴⁶46 D. Banaś, A. Kubala-Kukuś, J. Braziewicz, U. Majewska, M. Pajek, J. Wudarczyk-Moćko, K. Czech, M. Garnuszek, P. Słomkiewicz, B. Szczepanik, Radiat. Phys. Chem. 93 (2013) 129.
Acid and heat activation	Dehydroxylation of the structural aluminol groups: decrease of the adsorption capacity for cationic drug; HNTs becomes amorphous	Structural rearrangement: changes in the pore structure and surface properties; remove the physically bounded water	¹⁸18 Q. Wang, J. Zhang, Y. Zheng, A. Wang, Colloids Surf. B 113 (2014) 51.

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