METALLO-SOLID LIPID NANOPARTICLES AS COLLOIDAL TOOLS FOR MESO- MACROPOROUS SUPPORTED CATALYSTS

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Light-responsive MSN

Photoactive silica materials became also very useful in the control of drug delivery through light stimuli sensitive molecules. In general, they are grafted at the pore outlets and act as gatekeepers. In such kind of systems, the drug delivery is activated by external light and usually drug molecules do not have overlapped light absorption band with the gatekeeper molecules for the release efficiency.
In this context, Fujiwara et al. reported the first example of light stimuli-responsive mesoporous silica nanoparticles MCM-41, in which the loading, the storage and the release of model molecules (steroid cholestane, pyrene, phenanthrene and progesterone) were controlled by light.132 To do so, they functionalized MCM-41 materials with a photosensitive coumarin derivative, the 7-[(3-triethoxysilyl)propoxy]coumarin, either by post functionalized or co-condensation. Then, drug was loaded into modified MCM-41 by impregnation method. This material was irradiated under UV light (> 310nm for 30 min) in order to form the gatekeepers, namely the cyclobutane rings, which result from the photodimerization reaction between a pair of coumarin groups. Then, the drug was easily released since cyclobutane rings are photocleavable upon UV light irradiation (around 250 nm), as schemed in Figure 1.9.
Mesoporous silica nanoparticle modified with azobenzene moiety has also largely been investigated for their interesting photoreversibility property. As an example, Zink et al. reported light stimuli responsive MSN functionalized by azobenzene derivatives used as gatekeepers. They prepared two modified azobenzene molecules presenting trans-to-cis transition for post-synthesis functionalization of MCM-41 nanoparticles. The azobenzene derivative molecules were grafted inside the MCM-41 pores pointing straight along the channel like a thread when in the trans configuration. The latest conformation allowed loading Rhodamine B inside the MCM-41 porosity and either a pyrene-β-cyclodextrin or β-cyclodextrin molecule was chosen as sealing agent. The cargo porosity was opened under UV light irradiation at 351 nm, in which azobenzene derivative molecules adopt cis configuration.
In another work, Zink et al. coupled the photoisomerization property of the azobenzene derivative moiety with a pH-switchable pseudorotaxanes (curcurbit6uril (CB6)) rings encircling bisammonium derivative stalks) acting as nanovalves of the pores. Adding such a pH-responsive secondary gatekeepers at the outlet of mesopores could reduce drug leaking and also design dual-controllable MSN drug delivery system. The UV-irradiation at 448 nm provokes continuous photocommutation of azobenzene moiety from trans to cis configuration inside of the pore. Moreover, under basic pH ion-dipole interaction between CB6 rings and bisammonium derivative stalks are disrupted. Then the dissociation of the rings releases guest molecules as illustrated in Figure 1.10.133,134
Figure 1.10. Operation of dual-controlled nanoparticles. (a) Excitation with 448 nm light induces the dynamic wagging motion of the nanoimpellers, but the nanovalves remain shut and the contents are contained. (b) Addition of NaOH opens the nanovalves, but the static nanoimpellers are able to keep the contents contained. (c) Simultaneous excitation with 448 nm light and addition of NaOH cause the contents to be released.
In some applications needing photostimulation, the encapsulated drug is sensitive to light and it can be degraded, as it is the case for doxourubicin (DOX). Lin et al. developed MSN functionalized with aminopropyl groups protected by nitroveratyl function through a carbamate bond. When the carbamate linker is irradiated at 350 nm, Doxourubicin (DOX) loaded in MSN can be released. In fact, UV-light triggers the deprotection of amine groups, which become positively charged when the process is done in water, thus DOX molecules release is induced by electrostatic repulsion between the respective ammonium moieties. The mechanism was verified by zeta potential measurement that showed the increase of positive charge due to free amino group.135 Lin et al. also designed light-responsive MSN using gold nanoparticles as gatekeep136 to cap mesopores through a cleavable photolabile linker, named thioundecyl-tetraethyleneglycolester-onitrobenzylethyldimethyl ammonium bromide (TUNA) for intracellular drug delivery. Their system was tested for photoinduced intracellular controlled release of an anticancer drug, paclitaxel, inside of human fibroblast and liver cells. According to the results, endocytosis and drug release were efficient under irradiation (λ = 365nm), preventing zero burst release.

Magnetic-responsive MSN

Building mesoporous silica nanoparticles (MSN) that respond to the magnetic field has attracted a lot of attention for its potential applications. As drug delivery system, magnetic MSN could be guided to the desired site, and then removed after complete release using an external magnetic field. This strategy might be of interest for cancer targeting drugs, showing certain toxicity for organs, in order to reduce side effects. Beside of guiding the drug by magnetic field, magnetic MSN can be used for hyperthermia therapy.
For instance, superparamagnetic nanoparticles embedded MSN were already widely studied for both drug guide system and hyperthermia properties.139 However, biocompatibility and toxicity problems is always a limiting factor, thus only magnetite (Fe3O4) or maghemite (γ-Fe2O3) have been considered for biomedical applications. Though, up to date, more than 1700 publications (based on web of sciences) are dealing with magnetic MSN. However, in this chapter, we focus on some examples that marked a turning point in the biomedical field.
For the synthesis of magnetic MSN, various designs and strategies have been proposed.140,141 Core-shell structure with magnetic nanoparticle, proposed by Shi et al., has been considered as a basic model for magnetic MSN (Figure 1.11).142,143 Its potential medical applications were confirmed using ibuprofen as well.
Zhao et al. have extend core-shell model using several iron sources and also simplified synthesis methods (Figure 1.12).144,145 Besides of conventional drug molecules, DNA can be carried inside mesopores and delivered using magnetic field (Figure 1.13).146 Moreover, magnetic MSN have been extensively tested on in vivo cells in recent years.147 The results showed that a core-shell structure, in which metallic nanoparticles do not have direct contact with cellular culture, exhibiting an excellent biocompatibility.
Embedding magnetic nanoparticles into MSN has been also of interest for scientists.
Magnetic nanoparticles can be easily incorporated inside mesopores or on the matrix of silica.
Corriu et al. reported the synthesis of magnetic silica-based nanocomposites containing magnetite (Fe3O4) nanoparticles using internal anchored acetylacetonate groups as a ligand.148 Huang et al. demonstrated controlled and targeting ibuprofen release using magnetic γ-Fe2O3@MSN composites with different morphologies.
Adenosine triphosphate, ATP, can be used also as biological stimuli for controlled drug release. Indeed, mesopores capping is achieved by the complexation of Cu2+ between amino-functionnalized MSN and L-cysteine modified gold nanoparticles (AuNP) under low pH.154 ATP, which contains a more effective complexation site than single amino group, was shown to be a biological stimulus to detach gold nanoparticle from mesopores gates through Cu2+ complexation. In this investigation, low pH and ATP have been used as biological stimuli for drug release within either, the lysosome in case of low pH, and/or the cytosol that contains high concentration of ATP.
Using FDA-approved peptide drug protamine as coating agent of MSN is an effective way to make biological stimuli-responsive drug delivery system, demonstrated by Raichur et al.155 Indeed, like other coating agents, protamine can effectively protect the encapsulated drug from burst or undesired release. Coating is conducted on amino functionalized MSN using glutaraldehyde as coupling agent. In the presence of the enzyme such as trypsin that recognizes and cut arginine or lysine sites, the protamine coating can dissolve opening the mesopores and releasing the drug.

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Conclusion and perspectives

In this chapter, it is demonstrated that MSN have largely been employed to design efficient drug delivery systems, especially due to their high loading capacity, high stability and the ability to protect the guest molecules from various biochemical attacks. Indeed what encourages many research groups to design MSN drug carriers are the biocompatibility and biodegradability of these materials. In addition, MSN can offer a multitude of functionalization routes that allow decorating either the inner and/or the outer surface, with pH, thermal, light and magnetic stimuli responsive molecules, polymers, metallic nanoparticles and targeting ligands. The latest functionalization strategies have been tailored to control the drug delivery kinetic at the appropriate place with zero premature release together with preventing undesired side effects. For the moment, most in vitro studies have evaluated the cytotoxicity, the biocompatibility, biodegradability, the retention of MSN nanocarriers and the understanding of some cellular uptake mechanisms. However, toxicity and intracellular uptake results reported in the literature are specific to each drug delivery system. Moreover, the design of MSN drug carriers with simple and cost-effective way is still needed to demonstrate the potential of MSN as drug delivery systems or biosensors in therapeutic applications.

Table of contents :

CHAPTER 1 – LITERATURE REVIEW 
1.1 SILICA RESPONDING TO CHALLENGES IN DRUG DELIVERY
1.1.1. POROUS MATERIALS
1.1.2. ADMINISTRATION ROUTES
1.2 NANOSTRUCTURED SILICA: SUITABLE MATRIX FOR LOADING AND RELEASE
1.3 STIMULI RESPONSIVE NANOSTRUCTURED SILICA MATERIALS
1.3.1 PH STIMULI-RESPONSIVE MSN
1.3.2 TEMPERATURE-RESPONSIVE MSN
1.3.3 REDOX-RESPONSIVE MSN
1.3.4 LIGHT-RESPONSIVE MSN
1.3.5 MAGNETIC-RESPONSIVE MSN
1.3.6 BIOLOGICAL STIMULI RESPONSIVE DRUG RELEASE
1.4 CONCLUSION AND PERSPECTIVES
CHAPTER 2 – DESIGNING STIMULI-RESPONSIVE NANO-STRUCTURED CARRIERS OF CURCUMIN 
PART 2.1. PH-CONTROLLED DELIVERY OF CURCUMIN FROM A COMPARTMENTALIZED SOLID LIPID NANOPARTICLE@MESOSTRUCTURED SILICA MATRIX 
2.1.1. INTRODUCTION
2.1.2. MATERIALS AND METHODS
2.1.3. RESULTS AND DISCUSSION
2.1.4. CONCLUSION
PART 2.2. CORE-SHELL MICROCAPSULES OF SOLID LIPID NANOPARTICLES AND MESOPOROUS SILICA FOR ENHANCED ORAL DELIVERY OF CURCUMIN
2.2.1. INTRODUCTION
2.2.2. MATERIALS AND METHODS
2.2.3. RESULTS AND DISCUSSION
2.2.4. CONCLUSION
PART 2.3. PH- AND GLUTATHIONE-RESPONSIVE RELEASE OF CURCUMIN FROM MESOPOROUS SILICA NANOPARTICLES COATED USING TANNIC ACID-FE(III) COMPLEX 
2.3.1. INTRODUCTION
2.3.2. MATERIALS AND METHODS
2.3.3. RESULTS AND DISCUSSION
2.3.4. CONCLUSION
CHAPTER 3 – MAGNETO-RESPONSIVE SILICA MATERIALS TEMPLATED WITH MAGNETORESPONSIVE SURFACTANTS
PART 3.1. SPIN CROSSOVER AS A PROBE OF VESICLE SELF-ASSEMBLY OBSERVED USING MAGNETORESPONSIVE SURFACTANTS 
3.1.1. INTRODUCTION
3.1.2. MATERIALS AND METHODS
3.1.3. RESULTS AND DISCUSSION
3.1.4. CONCLUSION
PART 3.2. NANOPARTICLE-FREE MAGNETIC MESOPOROUS SILICA WITH MAGNETO RESPONSIVE SURFACTANTS 
3.2.1. INTRODUCTION
3.2.2. MATERIALS AND METHODS
3.2.3. RESULTS AND DISCUSSION
3.2.4. CONCLUSION
PART 3.3. METALLO-SOLID LIPID NANOPARTICLES AS COLLOIDAL TOOLS FOR MESO- MACROPOROUS SUPPORTED CATALYSTS
3.3.1. INTRODUCTION
3.3.2. MATERIALS AND METHODS
3.3.3. RESULTS AND DISCUSSION
3.3.4. CONCLUSION
GENERAL CONCLUSION

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