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 copiar

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

Autoria SCIMAGO INSTITUTIONS RANKINGS

Resumo

Nanotubos de haloisita (NTH) são nanoargilas de silicato de alumínio com estrutura naturalmente tubular. Eles são biocompatíveis e apresentam viabilidade como carreador de moléculas biologicamente ativas devido ao seu espaço interno na estrutura tubular. Neste artigo as principais características dos NTH e a obtenção de nanocompósitos poliméricos com NTH, e suas potenciais aplicações para o aperfeiçoamento das propriedades mecânicas dos polímeros e como carreador de substâncias hidrofílicas e lipofílicas são revisadas. Revisam-se os trabalhos recentes publicados sobre nanocompósitos poliméricos com NTH e apresenta-se o promissor emprego desses sistemas como carreadores, devido à sua capacidade de sustentar a liberação de fármacos em escala nanométrica, adequados para aplicação na área farmacêutica e biomédica, apresentando baixa citotoxicidade e promovendo a liberação controlada de fármacos.

Palavras-chave:
nanoargila; bionanocompósitos; funcionalização; liberação sustentada de fármacos; nanotecnologia

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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