Optically traceable PLGA-silica nanoparticles for cell-triggered doxorubicin delivery.

Fluorescent silica nanoparticles with a polymer shell of poly (D, L-lactide-co-glycolide) (PLGA) can provide traceable cell-triggered delivery of the anticancer drug doxorubicin (DOX), protecting the cargo while in transit and releasing it only intracellularly. PLGA with 50:50 lactide:glycolide ratio was grown by surface-initiated ring-opening polymerization (ROP) from silica nanoparticles of ca. 50 nm diameter, doped with a perylenediimide (PDI) fluorescent dye anchored to the silica structure. After loading DOX, release from the core-shell particles was evaluated in solution at physiological pH (7.4), and in human breast cancer cells (MCF-7) after internalization. The hybrid silica-PLGA nanoparticles can accommodate a large cargo of DOX, and the release in solution (PBS) due to PLGA hydrolysis is negligible for at least 72 h. However, once internalized in MCF-7 cells, the nanoparticles release the DOX cargo by degradation of the PLGA. Accumulation of DOX in the nucleus causes cell apoptosis, with the drug-loaded nanoparticles found to be as potent as free DOX. Our fluorescently traceable hybrid silica-PLGA nanoparticles with cell-triggered cargo release offer excellent prospects for the controlled delivery of anticancer drugs, protecting the cargo while in transit and efficiently releasing the drug once inside the cell.

Drug Delivery from PCL/Chitosan Multilayer Coatings for Metallic Implants.

Implant-related infections, mainly caused by Staphylococcus aureus, are a major health concern. Treatment is challenging due to multi-resistant strains and the ability of S. aureus to adhere and form biofilms on bone and implant surfaces. The present work involved the preparation and evaluation of a novel dual polymeric film coating on stainless steel. Chitosan and polycaprolactone (PCL) multilayers, loaded with poly(methyl methacrylate) (PMMA) microspheres encapsulating vancomycin or daptomycin, produced by the dip-coating technique, allowed local antibiotic-controlled delivery for the treatment of implant-related infections. Enhanced adhesion of the film to the metal substrate surface was achieved by mechanical abrasion of its surface. Studies have shown that for both drugs the release occurs by diffusion, but the release profile depends on the type of drug (daptomycin or vancomycin), the pH of the solution, and whether the drug is freestanding (directly incorporated into the films) or encapsulated in PMMA microspheres. Daptomycin freestanding films reached 90% release after 1 day at pH 7.4 and 4 days at pH 5.5. In comparison, films with daptomycin encapsulated microspheres reached 90% release after 2 h at pH 5.5 and 2 days at pH 7.4. Vancomycin encapsulated and freestanding films showed a similar behavior reaching 90% release after 20 h of release at pH 5.5 and 2 and 3 days, respectively, at pH 7.4. Furthermore, daptomycin-loaded films showed activity (assessed by agar diffusion assays) against sensitive (ATCC 25923) and clinically isolated (MRSA) S. aureus strains.

Cellulose acetate fibres loaded with daptomycin for metal implant coatings.

Multifunctional polymeric coatings containing drug delivery vehicles can play a key role in preventing/reducing biofilm formation on implant surfaces. Their requirements are biocompatibility, good adhesion, and controllable drug release. Although cellulose acetate (CA) films and membranes are widely studied for scaffolding, their applications as a protective coating and drug delivery vehicle for metal implants are scarce. The reason is that adhesion to stainless steel (SS) substrates is non-trivial. Grinding SS substrates enhances the adhesion of dip-coated CA films while the adhesion of electrospun CA membranes is improved by an electrosprayed chitosan intermediate layer. PMMA microcapsules containing daptomycin have been successfully incorporated into CA films and fibres. The released drug concentration of 3 × 10-3 mg/mL after 120 min was confirmed from the peak luminescence intensity under UV radiation of simulated body fluid (SBF) after immersion of the fibres.

Mesoporous Silica Nanoparticles Modified inside and out for ON:OFF pH-Modulated Cargo Release.

Highly efficient pH-modulated cargo release was achieved with a new hybrid nanocarrier composed of a mesoporous silica core with functionalized pores and a grafted pH-responsive crosslinked polymer shell of 2-(diisopropylamino)ethyl methacrylate (pKa ≈ 6.5). The retention/release performance of the system was optimized by a novel approach using selective functionalization of the silica pores to tune the carrier-cargo interaction and by tunning the amount of grafted polymer. The system features excellent retention of cationic cargo at low pH and a burst release at higher pH. This results from the expanded-collapsed conformation transition of the pH-responsive polymer shell and the simultaneous change in the interaction between the cargo and the polymer shell and the modified pore walls. At low pH, the electrostatic interaction of the cationic cargo with the protonated amine groups of the extended polymer shell retains the cargo, resulting in very low leakage (OFF state). At high pH, the electrostatic interaction with the cargo is lost (due to deprotonation of the polymer amine groups), and the polymer shell collapses, squeezing out the cargo in a burst release (ON state). Pore functionalization in combination with the stimuli-responsive polymer shell is a very promising strategy to design high-performance ON:OFF smart hybrid nanocarriers for stimuli-actuated cargo release, with great potential for application in the controlled release of drugs and other biologically active agents.

GelMA/bioactive silica nanocomposite bioinks for stem cell osteogenic differentiation.

Leveraging 3D bioprinting for processing stem cell-laden biomaterials has unlocked a tremendous potential for fabricating living 3D constructs for bone tissue engineering. Even though several bioinks developed to date display suitable physicochemical properties for stem cell seeding and proliferation, they generally lack the nanosized minerals present in native bone bioarchitecture. To enable the bottom-up fabrication of biomimetic 3D constructs for bioinstructing stem cells pro-osteogenic differentiation, herein we developed multi-bioactive nanocomposite bioinks that combine the organic and inorganic building blocks of bone. For the organic component gelatin methacrylate (GelMA), a photocrosslinkable denaturated collagen derivative used for 3D bioprinting was selected due to its rheological properties display of cell adhesion moieties to which bone tissue precursors such as human bone marrow derived mesenchymal stem cells (hBM-MSCs) can attach to. The inorganic building block was formulated by incorporating mesoporous silica nanoparticles functionalized with calcium, phosphate and dexamethasone (MSNCaPDex), which previously proven to induce osteogenic differentiation. The newly formulated photocrosslinkable nanocomposite GelMA bioink incorporating MSNCaPDex nanoparticles and laden with hBM-MSCs was successfully processed into a 3D bioprintable construct with structural fidelity, and well dispersed nanoparticles throughout the hydrogel matrix. These nanocomposite constructs could induce the deposition of apatitein vitro, thus showing attractive bioactivity properties. Viability and differentiation studies showed that hBM-MSCs remained viable and exhibited osteogenic differentiation biomarkers when incorporated in GelMA/MSNCaPDex constructs and without requiring further biochemical, nor mechanical stimuli. Overall, our nanocomposite bioink has demonstrated excellent processability via extrusion bioprinting into osteogenic constructs with potential application in bone tissue repair and regeneration.

Efficient Single-Dose Induction of Osteogenic Differentiation of Stem Cells Using Multi-Bioactive Hybrid Nanocarriers.

Bone regeneration requires the presence of specific factors to induce the differentiation of stem cells into osteoblasts. These factors induce osteogenesis by stimulating the expression of bone-related proteins, bone cell proliferation and differentiation. Herein, bioactive mesoporous silica nanoparticles are doped with calcium and phosphate ions while the porous network is loaded with dexamethasone (MSN-CaPDex). The bioactive MSN-CaPDex nanocarriers are prepared without affecting the narrow size distribution, pore structure, and morphology of the MSNs, while incorporating multi-stimuli, complementary ionic/biochemical bioactive mediators. The bioactive nanocarriers induce osteogenic differentiation of human bone marrow mesenchymal stem cells (hBM-MSCs) after a single-dose administration, and without the need for further soluble osteogenic factors, in contrast to the standard continuous stimulation provided by osteogenic medium. The hBM-MSCs exhibit several biomarkers of osteogenic differentiation, including alkaline phosphatase peaking at early time points, secretion of osteopontin and osteocalcin, and deposition of a calcium-rich matrix. Overall, by inducing the osteogenic differentiation of stem cells with a single-dose administration and without requiring repeated osteogenic supplementation, the newly synthesized multi-bioactive hybrid nanocarrier shows great potential for bone tissue engineering applications.

Grafting with RAFT-gRAFT Strategies to Prepare Hybrid Nanocarriers with Core-shell Architecture.

Stimuli-responsive polymer materials are used in smart nanocarriers to provide the stimuli-actuated mechanical and chemical changes that modulate cargo delivery. To take full advantage of the potential of stimuli-responsive polymers for controlled delivery applications, these have been grafted to the surface of mesoporous silica particles (MSNs), which are mechanically robust, have very large surface areas and available pore volumes, uniform and tunable pore sizes and a large diversity of surface functionalization options. Here, we explore the impact of different RAFT-based grafting strategies on the amount of a pH-responsive polymer incorporated in the shell of MSNs. Using a "grafting to" (gRAFT-to) approach we studied the effect of polymer chain size on the amount of polymer in the shell. This was compared with the results obtained with a "grafting from" (gRAFT-from) approach, which yield slightly better polymer incorporation values. These two traditional grafting methods yield relatively limited amounts of polymer incorporation, due to steric hindrance between free chains in "grafting to" and to termination reactions between growing chains in "grafting from." To increase the amount of polymer in the nanocarrier shell, we developed two strategies to improve the "grafting from" process. In the first, we added a cross-linking agent (gRAFT-cross) to limit the mobility of the growing polymer and thus decrease termination reactions at the MSN surface. On the second, we tested a hybrid grafting process (gRAFT-hybrid) where we added MSNs functionalized with chain transfer agent to the reaction media containing monomer and growing free polymer chains. Our results show that both modifications yield a significative increase in the amount of grafted polymer.

Silica nanocarriers with user-defined precise diameters by controlled template self-assembly.

Mesoporous silica nanoparticles (MSNs) feature ideal structural properties and surface chemistry for use as nanocarriers of molecules, polymers and biomolecules in cutting-edge applications. One important challenge remaining in their preparation is the ability to tune their diameter in the range of a few tens of nanometers, with narrow size dispersity, preferably using a simple, sustainable and scalable synthetic process. This work presents a fully controllable low-temperature and purely aqueous sol-gel method to prepare MSNs with user-defined diameters from 15 nm to 80 nm and narrow size dispersity. The method also allows modification of the pore structure and offers the possibility of incorporating a luminescent species in the silica network for optical traceability. Control was achieved by tuning the colloidal stability of the assembly of cylindrical micelles that template the MSN synthesis. Using CTAB cylindrical micelles as template and sodium hydroxide (NaOH) as catalyst, precise diameter control was achieved either by changing the pH (that controls micelle surface charge) or by adding salt at constant pH (to tune the ionic strength and charge screening). This new sustainable MSN synthesis method provides full control over the nanoparticle diameters and can be used as a platform for the application of MSNs with user-defined sizes in different fields.

Bioactive silica nanoparticles with calcium and phosphate for single dose osteogenic differentiation.

The differentiation of adult stem cells is usually performed in vitro, by exposing them to specific factors. Alternatively, one can use nanocarriers containing such factors, to be internalized by the cells. In this work we have reduce the size of those carriers to the nanoscale, developing bioactive silica nanoparticles with diameters under 100 nm, containing calcium and phosphate ions (SiNPs-CaP). These ions, once released inside adult stem cells, induce bone cell proliferation and differentiation, and stimulate the expression of bone-related proteins in a single dose administration. The SiNPs-CaP nanomaterials were prepared through a sol-gel approach, and the ions added with a post-synthesis functionalization method. The synthesized SiNPs-CaP have narrow size distribution, good colloidal stability, and show high levels of ion incorporation. Furthermore, the SiNPs-CaP have good cytocompatibility and promote the osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSC), with alkaline phosphatase, osteopontin and osteocalcin production levels comparable to the ones obtained in standard osteogenic medium. The novel bioactive SiNPs-CaP are synthesized in a simple and fast manner and show the ability to promote osteogenic differentiation after a single dose administration, independently from external osteogenic inducers, showing great potential as carriers in bone tissue engineering applications.

Hybrid Mesoporous Nanoparticles for pH-Actuated Controlled Release.

Among a variety of inorganic-based nanomaterials, mesoporous silica nanoparticles (MSNs) have several attractive features for application as a delivery system, due to their high surface areas, large pore volumes, uniform and tunable pore sizes, high mechanical stability, and a great diversity of surface functionalization options. We developed novel hybrid MSNs composed of a mesoporous silica nanostructure core and a pH-responsive polymer shell. The polymer shell was prepared by RAFT polymerization of 2-(diisopropylamino)ethyl methacrylate (pKa ~6.5), using a hybrid grafting approach. The hybrid nanoparticles have diameters of ca. 100 nm at pH < 6.5 and ca. 60 nm at pH > 6.5. An excellent control of cargo release is achieved by the combined effect of electrostatic interaction of the cargo with the charged silica and the extended cationic polymer chains at low pH, and the reduction of electrostatic attraction with a simultaneous collapse of the polymer chains to a globular conformation at higher pH. The system presents a very low (almost null) release rate at acidic pH values and a large release rate at basic pH, resulting from the squeezing-out effect of the coil-to-globule transition in the polymer shell.

Multifunctional Platform Based on Electroactive Polymers and Silica Nanoparticles for Tissue Engineering Applications.

Poly(vinylidene fluoride) nanocomposites processed with different morphologies, such as porous and non-porous films and fibres, have been prepared with silica nanoparticles (SiNPs) of varying diameter (17, 100, 160 and 300 nm), which in turn have encapsulated perylenediimide (PDI), a fluorescent molecule. The structural, morphological, optical, thermal, and mechanical properties of the nanocomposites, with SiNP filler concentration up to 16 wt %, were evaluated. Furthermore, cytotoxicity and cell proliferation studies were performed. All SiNPs are negatively charged independently of the pH and more stable from pH 5 upwards. The introduction of SiNPs within the polymer matrix increases the contact angle independently of the nanoparticle diameter. Moreover, the smallest ones (17 nm) also improve the PVDF Young's modulus. The filler diameter, physico-chemical, thermal and mechanical properties of the polymer matrix were not significantly affected. Finally, the SiNPs' inclusion does not induce cytotoxicity in murine myoblasts (C2C12) after 72 h of contact and proliferation studies reveal that the prepared composites represent a suitable platform for tissue engineering applications, as they allow us to combine the biocompatibility and piezoelectricity of the polymer with the possible functionalization and drug encapsulation and release of the SiNP.

On the Structure of Amorphous Mesoporous Silica Nanoparticles by Aberration-Corrected STEM.

Mesoporous silica materials have demonstrated a vast spectrum of applications, stimulating an intensive field of study due to their potential use as nanocarriers. Nonetheless, when produced at the nanoscale, their structural characterization is hindered due to the re-arrangement of the pores. To address this issue, this work combines molecular dynamics simulations with electron microscopy computer simulations and experimental results to provide an insight into the structure of amorphous mesoporous silica nanoparticles. The amorphous silica model is prepared using a simple melt-quench molecular dynamics method, while the reconstruction of the mesoporous nanoparticles is carried out using a methodology to avoid false symmetry in the final model. Simulated scanning transmission electron microscopy images are compared with experimental images, revealing the existence of structural domains, created by the misalignment of the pores to compensate the surface tension of these spherical nanoparticles.

Artefact-free Evaluation of Metal Enhanced Fluorescence in Silica Coated Gold Nanoparticles.

Metal nanoparticles can either quench or enhance the emission of dyes in their vicinity, but the precise measurement and understanding of this effect is still hindered by experimental artifacts, especially for particles in colloidal dispersion. Here, we introduce a new methodology to correct the inner filter effect of the metal on the dye emission. To test the method, we developed new hybrid nanoparticles with a gold core and a silica shell of precise thickness (tuned from 7 to 13 nm), with a high quantum yield perylenediimide dye on the surface. This novel approach effectively avoids fluorescence quenching, allowing us to measure emission enhancements of 5 to 30 times, with no change on the dye fluorescence lifetime. Being able to measure the emission enhancement in dye-metal hybrid nanoparticles in dispersion, free from inner filter and quenching artifacts, offers excellent prospects to guide the development of more efficient fluorescent probes, sensors and photonic devices.

Functional Group Coverage and Conversion Quantification in Nanostructured Silica by 1H NMR.

Silica nanostructured materials are important in many fields, including catalysis, imaging, and drug delivery, mainly due to the versatility of surface functionalization that can bestow a huge variety of chemical and physical properties. With most applications requiring precise control over this surface modification, characterization of surface composition and reactivity have become of extreme importance. We present a novel approach to track silica surface modification and quantify functional group coverage using only solution NMR. We test the method using different types of silica nanoparticles and surface modifications, to show that after dissolving the silica matrix, the 1H NMR spectra can be resolved for every single component of the mixture. By using an internal standard, we are able to quantify the density of ligands and follow their sequential modification. Our work presents a fast, accurate, and straightforward method for surface characterization of silica nanostructures, using widely available NMR spectroscopy and small amounts of sample.

Impact of Molecular Organization on Exciton Diffusion in Photosensitive Single-Crystal Halogenated Perylenediimides Charge Transfer Interfaces.

The efficiency of organic photodetectors and optoelectronic devices is strongly limited by exciton diffusion, in particular for acceptor materials. Although mechanisms for exciton diffusion are well established, their correlation to molecular organization in real systems has received far less attention. In this report, organic single-crystals interfaces were probed with wavelength-dependent photocurrent spectroscopy and their crystal structure resolved using X-ray diffraction. All systems present a dynamic photoresponse, faster than 500 ms, up to 650 nm. A relationship between molecular organization and favorable exciton diffusion in substituted butyl-perylenediimides (PDIB) is established. This is demonstrated by a set of PDIBs with different intra- and interstack distances and short contacts and their impact on photoresponse. Given the short packing distances between PDIs cores along the same stacking direction (3.4-3.7 Å), and across parallel stacks (2.5 Å), singlet exciton in these PDIBs can follow both Förster and Dexter exciton diffusion, with the Dexter-type mechanism assuming special relevance for interstack exciton diffusion. Yet, the response is maximized in substituted PDIBs, where a 2D percolation network is formed through strong interstack contacts, allowing for PDIBs primary excitons to reach with great efficiency the splitting interface with crystalline rubrene. The importance of short contacts and molecular distances, which is often overlooked as a parameter to consider and optimize when choosing materials for excitonic devices, is emphasized.

Effect of Molecular Stacking on Exciton Diffusion in Crystalline Organic Semiconductors.

Exciton diffusion is at the heart of most organic optoelectronic devices' operation, and it is currently the most limiting factor to their achieving high efficiency. It is deeply related to molecular organization, as it depends on intermolecular distances and orbital overlap. However, there is no clear guideline for how to improve exciton diffusion with regard to molecular design and structure. Here, we use single-crystal charge-transfer interfaces to probe favorable exciton diffusion. Photoresponse measurements on interfaces between perylenediimides and rubrene show a higher photocurrent yield (+50%) and extended spectral coverage (+100 nm) when there is increased dimensionality of the percolation network and stronger orbital overlap. This is achieved by very short interstack distances in different directional axes, which favors exciton diffusion by a Dexter mechanism. Even if the core of the molecule shows strong deviation from planarity, the similar electrical resistance of the different systems, planar and nonplanar, shows that electronic transport is not compromised. These results highlight the impact of molecular organization in device performance and the necessity of optimizing it to take full advantage of the materials' properties.

Functional Films from Silica/Polymer Nanoparticles.

High performance functional coatings, based on hybrid organic/inorganic materials, are being developed to combine the polymer flexibility and ease of processing with the mechanical properties and versatility of inorganic materials. By incorporating silica nanoparticles (SiNPs) in the polymeric matrices, it is possible to obtain hybrid polymer films with increased tensile strength and impact resistance, without decreasing the flexural properties of the polymer matrix. The SiNPs can further be used as carriers to impart other functionalities (optical, etc.) to the hybrid films. By using polymer-coated SiNPs, it is possible to reduce particle aggregation in the films and, thus, achieve more homogeneous distributions of the inorganic components and, therefore, better properties. On the other hand, by coating polymer particles with silica, one can create hierarchically structured materials, for example to obtain superhydrophobic coatings. In this review, we will cover the latest developments in films prepared from hybrid polymer/silica functional systems.

Highly efficient singlet-singlet energy transfer in light-harvesting [60,70]fullerene-4-amino-1,8-naphthalimide dyads.

New C60 and C70 fullerene dyads formed with 4-amino-1,8-naphthalimide chromophores have been prepared by the Bingel cyclopropanation reaction. The resulting monoadducts were investigated with respect to their fluorescence properties (quantum yields and lifetimes) to unravel the role of the charge-transfer naphthalimide chromophore as a light-absorbing antenna and excited-singlet-state sensitizer of fullerenes. The underlying intramolecular singlet-singlet energy transfer (EnT) process was fully characterized and found to proceed quantitatively (Φ(EnT)≈1) for all dyads. Thus, these conjugates are of considerable interest for applications in which fullerene excited states have to be created and photonic energy loss should be minimized. In polar solvents (tetrahydrofuran and benzonitrile), fluorescence quenching of the fullerene by electron transfer from the ground-state aminonaphthalimide was postulated as an additional path.

Intrinsically fluorescent silica nanocontainers: a promising theranostic platform.

In this paper we describe the preparation of fluorescent mesoporous silica nanoparticles (MSNs) for traceable drug delivery systems. The nanoparticles were prepared following a sol-gel procedure, incorporating a modified perylenediimide dye in the silica structure. Transmission electron microscopy and scanning electron microscopy show that the nanoparticles are monodispersed, with a spheroid shape and a raspberry-type surface morphology. The hybrid MSNs are robust, maintaining the mesoporous structure after template removal, with a pore diameter above 2 nm. A polymer shell was synthesized from the external surface of the hybrid nanoparticles by atom transfer radical polymerization, showing temperature-switchable collapsed/expanded conformation control. The fluorescent properties of the perylenediimide dye incorporated in the MSN pore walls are intact, and internalization in HEK293 cells shows that the nanoparticles are efficiently dispersed in the cytosol. These results show that the mesoporous fluorescent hybrid nanoparticles are an excellent platform for development of a traceable drug delivery system.