Mesoporous organosilicas with thiol functionalised pores: multifunctional dendrimers as sacrificial building block and template

The synthesis of multifunctional poly(amidoamine) (PAMAM)-based dendrimers containing a cleavable disulfide linker within each arm of the dendrimer, together with condensable triethoxysilyl groups on the periphery of the dendrimer, is described. The dendrimers were mixed with 1,4-bis(triethoxysilyl)benzene and subsequently transformed into silsesquioxane gels or periodic mesoporous organosilicas (PMOs) to generate materials with dendrimers covalently embedded within the interior of the silsesquioxane networks. Subsequent treatment of the gels with dithiothreitol enabled the core of the dendrimers to be selectively cleaved at the disulfide site, thus generating thiol functions localised within the pores. The effect of different dendrimer generations on the reactivity of the pendant thiol functions was probed by impregnation with gold salts, which were reduced to obtain gold nanoparticles within the pore networks of the gels and PMOs. The gels yielded polydisperse gold nanoparticles (2 to 70 nm) with dimensions modulated by the generation of the dendrimer, together with well-defined gold/thiolate clusters with Au⋯S distances of 2.3 Å. Such clusters were also observed in the PMO system, together with monodispersed gold nanoparticles with diameters comparable to that of the organised pores in the PMO. The role of surface functionalisation in controlling the formation of gold clusters and/or nanoparticles is discussed.

Dendritic Polymers as Promising Additives for the Manufacturing of Hybrid Organoceramic Nanocomposites with Ameliorated Properties Suitable for an Extensive Diversity of Applications

As the field of nanoscience is rapidly evolving, interest in novel, upgraded nanomaterials with combinatory features is also inevitably increasing. Hybrid composites, offer simple, budget-conscious and environmental-friendly solutions that can cater multiple needs at the same time and be applicable in many nanotechnology-related and interdisciplinary studies. The physicochemical idiocrasies of dendritic polymers have inspired their implementation as sorbents, active ingredient carriers and templates for complex composites. Ceramics are distinguished for their mechanical superiority and absorption potential that render them ideal substrates for separation and catalysis technologies. The integration of dendritic compounds to these inorganic hosts can be achieved through chemical attachment of the organic moiety onto functionalized surfaces, impregnation and absorption inside the pores, conventional sol-gel reactions or via biomimetic mediation of dendritic matrices, inducing the formation of usually spherical hybrid nanoparticles. Alternatively, dendritic polymers can propagate from ceramic scaffolds. All these variants are covered in detail. Optimization techniques as well as established and prospected applications are also presented.

Fundamentals and recent progress relating to the fabrication, functionalization and characterization of mesostructured materials using diverse synthetic methodologies

Since 1990 and the invention of the very first generation of ordered mesoporous silica materials, several innovative methodologies have been applied to synthesize, characterize, and modify silica/non-silica mesoporous materials. The growth of the mesoporous materials field has generated significant environmental and economic advantages compared to various other industrial developments. According to the literature, there are several key synthesis approaches and parameters that can affect the structural, textural and morphological characteristics of mesoporous materials. To date, huge attempts have been made to maximize the activities and selectivities of these materials through either the in situ or post-synthesis functionalization of the large interior surface areas and internal mesostructured frameworks in the presence of specific organic/inorganic components. However, the main challenge is to provide good control over the incorporation and distribution of multiple guest components within the mesostructured hosts. Mesostructured materials have received great attention for various applications, such as being used in electronics, medicine, photocatalysis, catalyst supports, catalysis, absorbers, sensors, gas separation, etc. In the current paper, several recent developments have been highlighted and reviewed regarding the fabrication and characterization of siliceous/non-siliceous mesoporous materials via various synthetic approaches. Furthermore, the availability of diverse functionalization methods has been reviewed to provide comprehensive approaches for synthesizing new generations of suitably modified mesoporous materials with superior structural, physicochemical, and textural characteristics.

Since 1990 and the invention of the very first generation of ordered mesoporous silica materials, several innovative methodologies have been applied to synthesize, characterize, and modify silica/non-silica mesoporous materials.

Dendrimer-Encapsulated Pd Nanoparticles, Immobilized in Silica Pores, as Catalysts for Selective Hydrogenation of Unsaturated Compounds

Heterogeneous Pd-containing nanocatalysts, based on poly (propylene imine) dendrimers immobilized in silica pores and networks, obtained by co-hydrolysis in situ, have been synthesized and examined in the hydrogenation of various unsaturated compounds. The catalyst activity and selectivity were found to strongly depend on the carrier structure as well as on the substrate electron and geometric features. Thus, mesoporous catalyst, synthesized in presence of both polymeric template and tetraethoxysilane, revealed the maximum activity in the hydrogenation of various styrenes, including bulky and rigid stilbene and its isomers, reaching TOF values of about 230000 h-1. Other mesoporous catalyst, synthesized in the presence of polymeric template, but without addition of Si(OEt)4, provided the trans-cyclooctene formation with the selectivity of 90-95 %, appearing as similar to homogeneous dendrimer-based catalysts. Microporous catalyst, obtained only on the presence of Si(OEt)4, while dendrimer molecules acting as both anchored ligands and template, demonstrated the maximum activity in the hydrogenation of terminal linear alkynes and conjugated dienes, reaching TOF values up to 400000 h-1. Herein the total selectivity on alkene in the case of terminal alkynes and conjugated dienes reached 95-99 % even at hydrogen pressure of 30 atm. The catalysts synthesized can be easily isolated from reaction products and recycled without significant loss of activity.

Mesoporous silica nanoparticles decorated with polycationic dendrimers for infection treatment

This work aims to provide an effective and novel solution for the treatment of infection by using nanovehicles loaded with antibiotics capable of penetrating the bacterial wall, thus increasing the antimicrobial effectiveness. These nanosystems, named "nanoantibiotics", are composed of mesoporous silica nanoparticles (MSNs), which act as nanocarriers of an antimicrobial agent (levofloxacin, LEVO) localized inside the mesopores. To provide the nanosystem of bacterial membrane interaction capability, a polycationic dendrimer, concretely the poly(propyleneimine) dendrimer of third generation (G3), was covalently grafted to the external surface of the LEVO-loaded MSNs. After physicochemical characterization of this nanoantibiotic, the release kinetics of LEVO and the antimicrobial efficacy of each released dosage were evaluated. Besides, internalization studies of the MSNs functionalized with the G3 dendrimer were carried out, showing a high penetrability throughout Gram-negative bacterial membranes. This work evidences that the synergistic combination of polycationic dendrimers as bacterial membrane permeabilization agents with LEVO-loaded MSNs triggers an efficient antimicrobial effect on Gram-negative bacterial biofilm. These positive results open up very promising expectations for their potential application in new infection therapies.

STATEMENT OF SIGNIFICANCE

Seeking new alternatives to current available treatments of bacterial infections represents a great challenge in nanomedicine. This work reports the design and optimization of a new class of antimicrobial agent, named "nanoantibiotic", based on mesoporous silica nanoparticles (MSNs) decorated with polypropyleneimine dendrimers of third generation (G3) and loaded with levofloxacin (LEVO) antibiotic. The covalently grafting of these G3 dendrimers to MSNs allows an effective internalization in Gram-negative bacteria. Furthermore, the LEVO loaded into the mesoporous cavities is released in a sustained manner at effective antimicrobial dosages. The novelty and originality of this manuscript relies on proving that the synergistic combination of bacteria-targeting and antimicrobial agents into a unique nanosystem provokes a remarkable antimicrobial effect against bacterial biofilm.

Adsorption properties of pyridylphenylene dendrimers

Sorption and surface properties study of the first three generations of polypyridylphenylene dendrimers.

Self-immolative polymers as novel pH-responsive gate keepers for drug delivery

A novel pH-sensitive nanocarrier based on mesoporous silica nanoparticles with self-immolative polymers blocking the pore openings is presented.

Integration of polymers in the pore space of mesoporous nanocarriers for drug delivery

The construction of carrier-polymer–drug hybrids in confined nanopore space is reviewed for advancing related drug delivery systems.

Selective topotecan delivery to cancer cells by targeted pH-sensitive mesoporous silica nanoparticles

Topotecan targeted pH-sensitive delivery system based in mesoporous silica nanoparticles coated with a multifunctional biopolymer coating for cancer therapy.

Mesoporous Silica Nanoparticles Decorated with Carbosilane Dendrons as New Non-viral Oligonucleotide Delivery Carriers

A novel nanosystem based on mesoporous silica nanoparticles covered with carbosilane dendrons grafted on the external surface of the nanoparticles is reported. This system is able to transport single-stranded oligonucleotide into cells, avoiding an electrostatic repulsion between the cell membrane and the negatively charged nucleic acids thanks to the cationic charge provided by the dendron coating under physiological conditions. Moreover, the presence of the highly ordered pore network inside the silica matrix would make possible to allocate other therapeutic agents within the mesopores with the aim of achieving a double delivery. First, carbosilane dendrons of second and third generation possessing ammonium or tertiary amine groups as peripheral functional groups were prepared. Hence, different strategies were tested in order to obtain their suitable grafting on the outer surface of the nanoparticles. As nucleic acid model, a single-stranded DNA oligonucleotide tagged with a fluorescent Cy3 moiety was used to evaluate the DNA adsorption capacity. The hybrid material functionalised with the third generation of a neutral dendron showed excellent DNA binding properties. Finally, the cytotoxicity as well as the capability to deliver DNA into cells, was tested in vitro by using a human osteoblast-like cell line, achieving good levels of internalisation of the vector DNA/carbosilane dendron-functionalised material without affecting the cellular viability.

The role of SBA-15 in drug delivery

In this review, preparation, characterization and application of various types of SBA-15 as drug delivery agents is investigated.

Angiogenesis in bone regeneration: tailored calcium release in hybrid fibrous scaffolds

In bone regeneration, silicon-based calcium phosphate glasses (Bioglasses) have been widely used since the 1970s. However, they dissolve very slowly because of their high amount of Si (SiO2 > 45%). Recently, our group has found that calcium ions released by the degradation of glasses in which the job of silicon is done by just 5% of TiO2 are effective angiogenic promoters, because of their stimulation of a cell-membrane calcium sensing receptor (CaSR). Based on this, other focused tests on angiogenesis have found that Bioglasses also have the potential to be angiogenic promoters even with high contents of silicon (80%); however, their slow degradation is still a problem, as the levels of silicon cannot be decreased any lower than 45%. In this work, we propose a new generation of hybrid organically modified glasses, ormoglasses, that enable the levels of silicon to be reduced, therefore speeding up the degradation process. Using electrospinning as a faithful way to mimic the extracellular matrix (ECM), we successfully produced hybrid fibrous mats with three different contents of Si (40, 52, and 70%), and thus three different calcium ion release rates, using an ormoglass-polycaprolactone blend approach. These mats offered a good platform to evaluate different calcium release rates as osteogenic promoters in an in vivo subcutaneous environment. Complementary data were collected to complement Ca(2+) release analysis, such as stiffness evaluation by AFM, ζ-potential, morphology evaluation by FESEM, proliferation and differentiation analysis, as well as in vivo subcutaneous implantations. Material and biological characterization suggested that compositions of organic/inorganic hybrid materials with a Si content equivalent to 40%, which were also those that released more calcium, were osteogenic. They also showed a greater ability to form blood vessels. These results suggest that Si-based ormoglasses can be considered an efficient tool for calcium release modulation, which could play a key role in the angiogenic promoting process.

Synthesis and surface modification of mesoporous silica nanoparticles and its application as carriers for sustained drug delivery

High drug loading is one of the important issues in the drug delivery research, especially the drug delivery system by oral administration. If high drug loading carriers are utilized the times of drug intake could be significantly reduced. Accordingly in this study, ordered mesoporous SBA-15 modified with (3-aminopropyl) triethoxysilane (APTES) was used as a carrier for nonsteroidal anti-inflammatory drug and optimization of the loading process was done. SBA-15 silica material with rope-like morphology was synthesized and modified by post-synthesis method with APTES. The synthesized SBA-15 and modified SBA-15 were characterized by XRD, SEM, thermal analysis and FT-IR spectroscopy. Loading optimization experiments were performed by changing the factors affecting the drug loading, such as temperature, time, stirring rate, Ibuprofen/SBA-15 ratio. The results of drug delivery experiments showed that the surface modification of SBA-15 with amino groups significantly increases the drug loading and decreases the drug delivery rate.

Controlled 3D-coating of the pores of highly ordered mesoporous antiferromagnetic Co3O4 replicas with ferrimagnetic Fe(x)Co(3-x)O4 nanolayers

The controlled filling of the pores of highly ordered mesoporous antiferromagnetic Co3O4 replicas with ferrimagnetic FexCo3-xO4 nanolayers is presented as a proof-of-concept toward the integration of nanosized units in highly ordered, heterostructured 3D architectures. Antiferromagnetic (AFM) Co3O4 mesostructures are obtained as negative replicas of KIT-6 silica templates, which are subsequently coated with ferrimagnetic (FiM) FexCo3-xO4 nanolayers. The tuneable magnetic properties, with a large exchange bias and coercivity, arising from the FiM/AFM interface coupling, confirm the microstructure of this novel two-phase core-shell mesoporous material. The present work demonstrates that ordered functional mesoporous 3D-materials can be successfully infiltrated with other compounds exhibiting additional functionalities yielding highly tuneable, versatile, non-siliceous based nanocomposites.

Synthesis of hetero-polymer functionalized nanocarriers by combining surface-initiated ATRP and RAFT polymerization

Smart nanocarriers are created based on a bi-functional hetero-initiator for RAFT and ATRP technique, bi-functionalizing mesoporous silica nanoparticles with two polymer types. The pH-dependent behavior of PDEAEMA as the gatekeeper polymer is verified by electrokinetic measurements and a controlled release behavior is demonstrated using doxorubicin as the drug.

Structure and functionalization of mesoporous bioceramics for bone tissue regeneration and local drug delivery

This review article describes the importance of structure and functionalization in the performance of mesoporous silica bioceramics for bone tissue regeneration and local drug delivery purposes. Herein, we summarize the pivotal features of mesoporous bioactive glasses, also known as 'templated glasses' (TGs), which present chemical compositions similar to those of conventional bioactive sol-gel glasses and the added value of an ordered mesopore arrangement. An in-depth study concerning the possibility of tailoring the structural and textural characteristics of TGs at the nanometric scale and their influence on bioactive behaviour is discussed. The highly ordered mesoporous arrangement of cavities allows these materials to confine drugs to be subsequently released, acting as drug delivery devices. The functionalization of mesoporous silica walls has been revealed as the cornerstone in the performance of these materials as controlled release systems. The synergy between the improved bioactive behaviour and local sustained drug release capability of mesostructured materials makes them suitable to manufacture three-dimensional macroporous scaffolds for bone tissue engineering. Finally, this review tackles the possibility of covalently grafting different osteoinductive agents to the scaffold surface that act as attracting signals for bone cells to promote the bone regeneration process.

Ordered mesoporous polymer-silica hybrid nanoparticles as vehicles for the intracellular controlled release of macromolecules

A two-dimensional hexagonal ordered mesoporous polymer-silica hybrid nanoparticle (PSN) material was synthesized by polymerization of acrylate monomers on the surface of SBA-15 mesoporous silica nanoparticles. The structure of the PSN material was analyzed using a series of different techniques, including transmission electron microscopy, powder X-ray diffraction, and N(2) sorption analysis. These structurally ordered mesoporous polymer-silica hybrid nanoparticles were used for the controlled release of membrane-impermeable macromolecules inside eukaryotic cells. The cellular uptake efficiency and biocompatibility of PSN with human cervical cancer cells (HeLa) were investigated. Our results show that the inhibitory concentration (IC(50)) of PSN is very high (>100 μg/mL per million cells), while the median effective concentration for the uptake (EC(50)) of PSN is low (EC(50) = 4.4 μg/mL), indicating that PSNs are fairly biocompatible and easily up-taken in vitro. A membrane-impermeable macromolecule, 40 kDa FITC-Dextran, was loaded into the mesopores of PSNs at low pH. We demonstrated that the PSN material could indeed serve as a transmembrane carrier for the controlled release of FITC-Dextran at the pH level inside live HeLa cells. We believe that further developments of this PSN material will lead to a new generation of nanodevices for intracellular controlled delivery applications.

Quantum dot-antisense oligonucleotide conjugates for multifunctional gene transfection, mRNA regulation, and tracking of biological processes

It was demonstrated that oligonucleotides, independent of their base sequence and length, could effectively induce the cellular uptake of mercapto acid-capped CdTe QDs after the oligonucleotides were covalently attached on the surface of the QDs. Following these experimental observations, a conjugate composed of covalently linked anti-survivin antisense oligonucleotides (ASON) and CdTe QDs was designed and synthesized. Then, the survivin mRNA down-regulation and the apoptosis of HeLa cells induced by ASON were studied. Systematic experimental results revealed that CdTe-ASON could effectively induce the apoptosis of HeLa cells, while CdTe QDs offered the possibility to visualize the specific intracellular localization of the CdTe-ASON probes strongly associated with their biological functions.

Sol-gel silica-based biomaterials and bone tissue regeneration

The impact of bone diseases and trauma in developed and developing countries has increased significantly in the last decades. Bioactive glasses, especially silica-based materials, are called to play a fundamental role in this field due to their osteoconductive, osteoproductive and osteoinductive properties. In the last years, sol-gel processes and supramolecular chemistry of surfactants have been incorporated to the bioceramics field, allowing the porosity of bioglasses to be controlled at the nanometric scale. This advance has promoted a new generation of sol-gel bioactive glasses with applications such as drug delivery systems, as well as regenerative grafts with improved bioactive behaviour. Besides, the combination of silica-based glasses with organic components led to new organic-inorganic hybrid materials with improved mechanical properties. Finally, an effort has been made to organize at the macroscopic level the sol-gel glass preparation. This effort has resulted in new three-dimensional macroporous scaffolds, suitable to be used in tissue engineering techniques or as porous pieces to be implanted in situ. This review collects the most important advances in the field of silica glasses occurring in the last decade, which are called to play a lead role in the future of bone regenerative therapies.

Dendritic Macromolecules: New Possibilities for Advanced Bioceramics

Dendrimers are a relatively new class of molecules that display a variety of potentially useful architecture-induced properties. In this chapter, we firstly present a general description of this interesting class of macromolecules, making special emphasis in their current biomedical applications. The combination of dendrimers with ceramics, traditionally used in the biomedical field, provides synergistic features and functions to the resulting hybrid materials. After the dendrimers introduction, an overall description of mesoporous silicas, iron oxide nanoparticles and carbon nanotubes bioceramics, is presented. Finally, recent research examples of dendrimer-functionalized ceramics, both from the synthetic and biomedical applicative points of view, are reviewed.