Recent Advance on Mesoporous Silica Nanoparticles-Based Controlled Release System: Intelligent Switches Open up New Horizon

Abstract

Mesoporous silica nanoparticle (MSN)-based intelligent transport systems have attracted many researchers' attention due to the characteristics of uniform pore and particle size distribution, good biocompatibility, high surface area, and versatile functionalization, which have led to their widespread application in diverse areas. In the past two decades, many kinds of smart controlled release systems were prepared with the development of brilliant nano-switches. This article reviews and discusses the advantages of MSN-based controlled release systems. Meanwhile, the switching mechanisms based on different types of stimulus response are systematically analyzed and summarized. Additionally, the application fields of these devices are further discussed. Obviously, the recent evolution of smart nano-switches promoted the upgrading of the controlled release system from the simple "separated" switch to the reversible, multifunctional, complicated logical switches and selective switches. Especially the free-blockage switches, which are based on hydrophobic/hydrophilic conversion, have been proposed and designed in the last two years. The prospects and directions of this research field are also briefly addressed, which could be better used to promote the further development of this field to meet the needs of mankind.

Keywords: controlled release; free-blockage switch; mesoporous materials; nano-switch; smart materials; stimulus response.

Figure 1

Schematic of the stimuli-responsive controlled release system (magnet-MSN) based on MSNs capped with Fe₃O₄ nanoparticles. Reproduced with permission from [23]. Copyright John Wiley and Sons, 2005.

Figure 2

Depiction of the assembly of the components to form nanovalves with the structural formulas of the bistable [2] rotaxanes 1⁴⁺ and 2⁴⁺, the three silane linkers a, b, and c used in this study, as well as the graphical representations of luminescent probe molecules and the possible positions (IN and OUT) of the linkers relative to the pore orifice. The pores are loaded when the valves are open and the probe molecules are trapped inside the pores when the valves are closed. The trapped molecules are released when the valves are reopened. The cycle can be repeated over and over again. Reproduced with permission from [28]. Copyright American Chemical Society, 2007.

Figure 3

Schematic illustration of pH-responsive nanogated ensemble based on gold-capped MSNs through acid-labile acetal linker. Reproduced with permission from [37]. Copyright American Chemical Society, 2010.

Figure 4

(a) Synthetic procedure for up-converting nanoparticles coated with a MSN outer layer. (b) The schematic of NIR light-triggered doxorubicin release by making use of the up-conversion property of UCNPs and trans-cis photoisomerization of azobenzene group molecules grafted on MSNs. Reproduced with permission from [62]. Copyright John Wiley and Sons, 2013.

Figure 5

Schematic illustration of the synthesis and operation of a magnet-responsive controlled release system, using ZnNCs encapsulated within MSNs. Reproduced with permission from [72]. Copyright American Chemical Society, 2010.

Figure 6

Schematic representation of the glucose-responsive MSN-based delivery system for controlled release of bioactive G-Ins and cAMP. Reproduced with permission from [79]. Copyright American Chemical Society, 2009.

Figure 7

Schematic representation of proton-fueled release of a drug from the pores of MSNs capped with i-motif DNA. Reproduced with permission from [84]. Copyright Oxford University Press, 2011.

Figure 8

(a) Scheme of preparation of DNA-modified MSNs. (1) 3-Aminopropyltriethoxy silane; (2) succinic anhydride and triethylamine; (3) N-hydroxy-succinimide (NHS), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-HCl (EDC), and NH₂-ended DNA strand 1; (4) cargo molecules, Rodamine B; (5) DNA 2-functionalized AuNPs. (b) The controlled release was modulated by the motor DNA’s conformation change which was driven by changing the pH value of the solution. (c) A schematic sketch of the hydrogen bonding between the protonated cytosines. Reproduced with permission from [85]. Copyright The Royal Society of Chemistry, 2011.

Figure 9

Graphical representation of operating supramolecular nanovalves from DB24C8/dialkylammonium-tethered porous silica particle MSNs. Reproduced with permission from [94]. Copyright American Chemical Society, 2006.

Figure 10

The release process of the dual-dye-loaded MSNs. The dual dyes were loaded into the MSNs separately by pH-controlled nanogates and UV-controlled nanovalves. This system can selectively release Eosin Yellowish (EY) upon UV irradiation (at pH 7.0) and Rhodamine B (RhB) at pH 3.5. Reproduced with permission from [98]. Copyright John Wiley and Sons, 2014.

Figure 11

Schematic illustration of a multi-responsive Au@MSN@Valve. Reproduced with permission from [105]. Copyright American Chemical Society, 2012.

Figure 12

Schematic for the preparation process of M-MSN–PNIPAAm. Reproduced with permission from [108]. Copyright John Wiley and Sons, 2014.