Application Of Mesoporous Silica Nanoparticles Research Articles

Physiochemical, Rheological, and Oxidative Aging Characteristics of Asphalt Binder in the Presence of Mesoporous Silica Nanoparticles

Physiochemical and rheological properties of asphalt binder are known to directly relate to asphalt pavement performance as it relates to fatigue and low temperature cracking. While other performance criteria such as rutting is also affected by binder properties, the latter is known to be also very sensitive to aggregate skeleton and mixture gradation. To enhance pavement performance, asphalt industry has commonly used various modifiers to improve binder rheological properties both before and after it is exposed to oxidative aging. Among those additives are polymers, ground tire rubber, as well as several organic and inorganic fillers. Inorganic fillers such as nano-clay and silica fume showed to be promising candidates to enhance asphalt rheology and aging behavior. Such enhancements are typically attributed to the presence of silicate platelet and silica particles. Accordingly, this paper investigates the merits of application of mesoporous silica nanoparticles in this paper referred to as nano-silica as an asphalt binder additive to enhance binder rheological properties and oxidative aging resistance. To do so, different percentages of nano-silica were added to neat asphalt binder. Asphalt binder was then exposed to short-term oxidative aging using a rolling thin film oven (RTFO). To study the distribution of nano-silica in binder as well as the change in the chemical, rheological, and morphological properties of asphalt binders due to the addition of nano-silica, the scanning electron microscopy (SEM), Superpave tests, and Fourier transform infrared spectroscopy (FTIR) were conducted. It was found that introduction of nano-silica to asphalt binder can improve the rheological properties and oxidative aging resistance of asphalt binder.

Functionalization of mesoporous silica nanoparticles with a cell-penetrating peptide to target mammalian sperm in vitro.

This study aimed to investigate the effects of actively targeting mesoporous silica nanoparticles (MSNPs) toward mammalian sperm with a cell-penetrating peptide (C105Y), with subsequent analysis of binding rates and nano-safety profiles. Boar sperm were exposed in vitro to C105Y-functionalized MSNPs or free C105Y, in a series of increasing doses for up to 2 h, followed by the evaluation of sperm motility, kinematic parameters, acrosome morphology, MSNP-sperm binding and cell fluorescence levels. C105Y-functionalized MSNPs preserved their biocompatibility with sperm, and exhibited an approximately fourfold increase in affinity toward gametes, compared with unmodified MSNPs, during the early stages of incubation. Our findings support the application of MSNPs and active targeting to sperm as valuable tools for reproductive biology.

NMR Study of BA/FBA Cocrystal Confined Within Mesoporous Silica Nanoparticles Employing Thermal Solid Phase Transformation

In this work, we report drug-loading procedure based on the solid state thermal transformation of a physical mixture of two ingredients: mesoporous silica nanoparticles (MSN) and an organic cocrystal. This procedure, known as the melting method, allows loading of the guest species into the host pores with high yield and an equimolar ratio of both components of the cocrystal. The study was carried out with commercial MSNs (MCM-41 and SBA-15) and a cocrystal consisting of equimolar amounts of benzoic acid (BA) and fluorinated benzoic acid (FBA). The BA/FBA sample was obtained by grinding crystalline acids. The structural constraints and molecular dynamics of BA/FBA in the crystal lattice were characterized employing 19F magic angle spinning (MAS), 13C MAS, 1H very fast (VF) MAS with sample rotation at 60 kHz, 2D NMR, 19F–19F BABA, and 1H–19F HETCOR correlations. We conclude that the system is very rigid with short distances between intermolecular aromatic layers. In contrast, BA/FBA loaded into MCM-41 and SBA-15 is very mobile in a broad range of temperatures. The structure and molecular dynamics of the guest assembly trapped in the MSN pores was established by 1H MAS, 19F MAS, 1H–19F HOESY MAS and 19F T2′ relaxation time measurements as well as 2H MAS. We conclude that the filling factor for the melting method, defined as the ratio of BA/FBA to MSN (weight to weight), is much higher compared to those for commonly used wet procedures. These results show new perspectives for future applications of MSNs as carriers of pharmaceutical cocrystals.

Antibacterial Dental Composites with Chlorhexidine and Mesoporous Silica

One of the leading causes for the failure of dental composite restorations is secondary caries. Effectively inhibiting cariogenic biofilms and reducing secondary caries could extend the service life of composite restorations. Dental composites releasing antibacterial agents such as chlorhexidine (CHX) have shown biofilm-inhibitory efficacy, but they usually have poor physical and mechanical properties. Herein, we present a study of a new method to encapsulate and release CHX from dental composite using mesoporous silica nanoparticles (MSNs). SBA-15 MSNs were synthesized according to a reported procedure. CHX (62.9 wt%) was encapsulated into dried MSN from 0.3 M CHX ethanol solution. The dental composites containing 0% (control), 3%, 5%, and 6.3% CHX or the same amounts of CHX entrapped in MSN (denoted as CHX@MSN) were fabricated with methacrylate monomers and silanized glass fillers (CHX or CHX@MSN + glass filler particle = 70 wt%). The monomer mixture consisted of bisphenol A glycidyl methacrylate (BisGMA), hexanediol dimethacrylate (HDDMA), ethoxylated bisphenol A dimethacrylate (EBPADMA), and urethane dimethacrylates (UEDMA) at a weight ratio of 40:30:20:10. The composites were tested for CHX release and recharge, flexural strength and modulus (at 24 hr and 1 mo), surface roughness, in vitro wear, and antibacterial activity against Streptococcus mutans and Lactobacillus casei (in both planktonic growth and biofilm formation). The results showed that the composites with CHX@MSN largely retained mechanical properties and smooth surfaces and showed controlled release of CHX over a long time. In contrast, the composites with directly mixed CHX showed reduced mechanical properties, rough surfaces, and burst release of CHX in a short time. The composites with CHX either directly mixed or in MSN showed strong inhibition to S. mutans and L. casei. This research has demonstrated the successful application of MSNs as a novel nanotechnology in dental materials to inhibit oral biofilm without sacrificing materials’ mechanical properties and surface integrity.

Mesoporous Silica Nanoparticle Nanocarriers: Biofunctionality and Biocompatibility

The study of ordered mesoporous silica materials has exploded since their discovery by Mobil researchers 20 years ago. The ability to make uniformly sized, porous, and dispersible nanoparticles using colloidal chemistry and evaporation-induced self-assembly has led to many applications of mesoporous silica nanoparticles (MSNPs) as "nanocarriers" for delivery of drugs and other cargos to cells. The exceptionally high surface area of MSNPs, often exceeding 1000 m²/g, and the ability to independently modify pore size and surface chemistry, enables the loading of diverse cargos and cargo combinations at levels exceeding those of other common drug delivery carriers such as liposomes or polymer conjugates. This is because noncovalent electrostatic, hydrogen-bonding, and van der Waals interactions of the cargo with the MSNP internal surface cause preferential adsorption of cargo to the MSNP, allowing loading capacities to surpass the solubility limit of a solution or that achievable by osmotic gradient loading. The ability to independently modify the MSNP surface and interior makes possible engineered biofunctionality and biocompatibility. In this Account, we detail our recent efforts to develop MSNPs as biocompatible nanocarriers (Figure 1 ) that simultaneously display multiple functions including (1) high visibility/contrast in multiple imaging modalities, (2) dispersibility, (3) binding specificity to a particular target tissue or cell type, (4) ability to load and deliver large concentrations of diverse cargos, and (5) triggered or controlled release of cargo. Toward function 1, we chemically conjugated fluorescent dyes or incorporated magnetic nanoparticles to enable in vivo optical or magnetic resonance imaging. For function 2, we have made MSNPs with polymer coatings, charged groups, or supported lipid bilayers, which decrease aggregation and improve stability in saline solutions. For functions 3 and 4, we have enhanced passive bioaccumulation via the enhanced permeability and retention effect by modifying the MSNP surfaces with positively charged polymers. We have also chemically attached ligands to MSNPs that selectively bind to receptors overexpressed in cancer cells. We have used encapsulation of MSNPs within reconfigurable supported lipid bilayers to develop new classes of responsive nanocarriers that actively interact with the target cell. Toward function 4, we exploit the high surface area and tailorable surface chemistry of MSNPs to retain hydrophobic drugs. Finally, for function 5, we have engineered dynamic behaviors by incorporating molecular machines within or at the entrances of MSNP pores and by using ligands, polymers, or lipid bilayers. These provide a means to seal-in and retain cargo and to direct MSNP interactions with and internalization by target cells. Application of MSNPs as nanocarriers requires biocompatibility and low toxicity. Here the intrinsic porosity of the MSNP surface reduces the extent of hydrogen bonding or electrostatic interactions with cell membranes as does surface coating with polymers or lipid bilayers. Furthermore, the high surface area and low extent of condensation of the MSNP siloxane framework promote a high rate of dissolution into soluble silicic acid species, which are found to be nontoxic. Potential toxicity is further mitigated by the high drug capacity of MSNPs, which greatly reduces needed dosages compared with other nanocarriers. We anticipate that future generations of MSNPs incorporating molecular machines and encapsulated by membrane-like lipid bilayers will achieve a new level of controlled cellular interactions.

Poly‐L‐Arginine Grafted Silica Mesoporous Nanoparticles for Enhanced Cellular Uptake and their Application in DNA Delivery and Controlled Drug Release

Mesoporous silica nanoparticles (MSNs), that are capable of delivering gene and drugs to organisms in an effective and selective way have attracted much attention lately for its potential in the treatment of cancer. However, the successful application of MSNs for delivery of plasmid DNA or drugs requires surface modification of the silica with positively charged functional groups so that it binds to the negatively charged nucleic acids and also helps it penetrate through the cell membrane. We report for the first time the synthesis of a hybrid MSN where the cell penetrating cationic polypeptide poly‐L‐arginine synthesized by NCA polymerization is grafted onto the external surface of MSN using click chemistry. These poly‐L‐arginine grafted MSNs show low cytotoxity (85% cell viability at 100 μg/mL MSN concentration) and high cellular uptake by both HeLa and A549 (>90%). The poly‐L‐arginine grafted MSNs were used effectively to deliver mCherry DNA plasmid into cells leading to expression of the protein mCherry inside the cells (transfection efficiency 60%). In contrast, poly‐L‐arginine grafted non‐porous silica nanoparticles were unable to express the protein mCherry inside the cells although their uptake into the cells was as efficient as with poly‐L‐arginine grafted MSNs. We also show preliminary results to demonstrate that these hybrid MSNs can be used as a delivery vehicle for the anticancer drug Doxorubicin towards cancerous cells HeLa and A549. The biocompatibility of poly‐L‐arginine and its cell penetrating ability are expected to make these MSN conjugates very useful carriers for the delivery of genes and drugs into cancer cells.

Theranostic applications of mesoporous silica nanoparticles and their organic/inorganic hybrids.

Mesoporous silica nanoparticles (MSNs), with their intrinsically large and easily functionalized surface areas and pore volumes, are particularly well-suited to efficient conveyance of a wide variety of therapeutic agents. When combined with other organic/inorganic nanomaterials, the resultant organic/inorganic-MSN hybrids demonstrate unique synergies and even greater versatility. In this paper, we describe the current status and future prospects of MSNs and organic/inorganic-MSN hybrids for combined therapeutic and diagnostic - theranostic - biomedical applications.

Stabilization of RNA through Absorption by Functionalized Mesoporous Silicate Nanospheres

The potential for encapsulating RNA within tunable, semi-permeable structures for storage and transportation purposes offers an interesting approach to the reduction of stringent storage requirements that often hamper the field application of genetic analysis methods. In this study, we assessed the potential for application of functionalized, porous silicate sorbents in maintaining nucleic acid integrity. Mesoporous silica nanoparticles (MSNs) with and without incorporated stabilizing reagents were used to encapsulate triosephosphate isomerase mRNA of Arabidopsis thaliana. The absorption, elution, and the long-term stability of the RNA were monitored by using quantitative real-time RT-PCR. The results indicate that adsorbed RNA can be eluted from the sorbents using simple buffers and employed directly for downstream molecular diagnostic assays without any further processing. RNA integrity can be maintained for extended time periods under refrigeration temperatures in the presence of covalently immobilized stabilizing compounds. This study provides initial evidence of the potential for application of MSNs in transportation and storage. They may also have utility in sample collection and processing in restrictive environments.

Biocompatibility of Mesoporous Silica Nanoparticles

In this review, recent reports on the biocompatibility of mesoporous silica nanoparticles (MSNs) are reviewed, with special emphasis being paid to the correlations between MSNs' structural and compositional features and their biological effects on various cells and tissues. First, the different synthetic routes used to produce the most common types of MSNs and the various methods employed to functionalize their surfaces are discussed. This is, however, done only briefly because of the focus of the review being the biocompatibility of the materials. Similarly, the biological applications of MSNs in areas such as drug and gene delivery, biocatalysis, bioimaging, and biosensing are briefly introduced. Many examples have also been mentioned about the biological applications of MSNs while discussing the materials' biocompatibility. The cytotoxicity of different types of MSNs and the effects of their various structural characteristics on their biological activities, which are the focus of this review, are then described in detail. In addition, synthetic strategies developed to reduce or eliminate any possible negative biological effects associated with MSNs or to improve their biocompatibility, as necessary, are illustrated. At the same time, recent reports on the interactions between MSNs and various in vivo or in vitro biological systems, plus our opinions and remarks on what the future may hold for this field, are included.

Nanoparticles in Targeted Cancer Therapy: Mesoporous Silica Nanoparticles Entering Preclinical Development Stage

Nanotechnology may help overcome persisting limitations of current cancer treatment and thus contribute to the creation of more effective, safer and more affordable therapies. While some nanotechnology-based drug delivery systems are already being marketed and others are in clinical trial, most still remain in the preclinical development stage. Mesoporous silica nanoparticles have been highlighted as an interesting drug delivery platform, due to their flexibility and high drug load potential. Although numerous reports demonstrate sophisticated drug delivery mechanisms in vitro, the therapeutic benefit of these systems for in vivo applications have been under continuous debate. This has been due to nontranslatable conditions used in the in vitro studies, as well as contradictory conclusions drawn from preclinical (in vivo) studies. However, recent studies have indicated that the encouraging cellular studies could in fact be repeated also in vivo. Here, we report on these recent advances regarding therapeutic efficacy, targeting and safety issues related to the application of mesoporous silica nanoparticles in cancer therapy.

Ultrastable, Redispersible, Small, and Highly Organomodified Mesoporous Silica Nanotherapeutics

Practical biomedical application of mesoporous silica nanoparticles is limited by poor particle dispersity and stability due to serious irreversible aggregation in biological media. To solve this problem, hydrothermally treated mesoporous silica nanoparticles of small size with dual-organosilane (hydrophilic and hydrophobic silane) surface modification have been synthesized. These highly organomodified mesoporous silica nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, N(2) adsorption-desorption, dynamic light scattering, zeta potential, and solid-state (29)Si NMR, and they prove to be very stable in simulated body fluid at physiological temperature. Additionally, they can be dried to a powdered solid and easily redispersed in biological media, maintaining their small size for a period of at least 15 days. Furthermore, this preparation method can be expanded to synthesize redispersible fluorescent and magnetic mesoporous silica nanoparticles. The highly stable and redispersible mesoporous silica NPs show minimal toxicity during in vitro cellular assays. Most importantly, two types of doxorubicin, water-soluble doxorubicin and poorly water-soluble doxorubicin, can be loaded into these highly stable mesoporous silica nanoparticles, and these drug-loaded nanoparticles can also be well-redispersed in aqueous solution. Enhanced cytotoxicity to cervical cancer (HeLa) cells was found upon treatment with water-soluble doxorubicin-loaded nanoparticles compared to free water-soluble doxorubicin. These results suggest that highly stable, redispersible, and small mesoporous silica nanoparticles are promising agents for in vivo biomedical applications.

Targeted anticancer prodrug with mesoporous silica nanoparticles as vehicles

A targeted anticancer prodrug system was fabricated with 180 nm mesoporous silicananoparticles (MSNs) as carriers. The anticancer drug doxorubicin (DOX) wasconjugated to the particles through an acid-sensitive carboxylic hydrazone linker whichis cleavable under acidic conditions. Moreover, folic acid (FA) was covalentlyconjugated to the particle surface as the targeting ligand for folate receptors (FRs)overexpressed in some cancer cells. The in vitro release profiles of DOX from theMSN-based prodrug systems showed a strong dependence on the environmentalpH values. The fluorescent dye FITC was incorporated in the MSNs so as totrace the cellular uptake on a fluorescence microscope. Cellular uptakes by HeLa,A549 and L929 cell lines were tested for FA-conjugated MSNs and plain MSNsrespectively, and a much more efficient uptake by FR-positive cancer cells (HeLa)can be achieved by conjugation of folic acid onto the particles because of thefolate-receptor-mediated endocytosis. The cytotoxicities for the FA-conjugated MSNprodrug, the plain MSN prodrug and free DOX against three cell lines were determined,and the result indicates that the FA-conjugated MSN prodrug exhibits highercytotoxicity to FR-positive cells, and reduced cytotoxicity to FR-negative cells. Thus,with 180 nm MSNs as the carriers for the prodrug system, good drug loading,selective targeting and sustained release of drug molecules within targeted cancercells can be realized. This study may provide useful insights for designing andimproving the applicability of MSNs in targeted anticancer prodrug systems.

Mesoporous Silica Nanoparticles as Drug Delivery Systems for Targeted Inhibition of Notch Signaling in Cancer

Notch signaling, a key regulator of stem cells, is frequently overactivated in cancer. It is often linked to aggressive forms of cancer, evading standard treatment highlighting Notch as an exciting therapeutic target. Notch is in principle "druggable" by γ-secretase inhibitors (GSIs), inhibitory peptides and antibodies, but clinical use of Notch inhibitors is restricted by severe side effects and there is a demand for alternative cancer-targeted therapy. Here, we present a novel approach, using imagable mesoporous silica nanoparticles (MSNPs) as vehicles for targeted delivery of GSIs to block Notch signaling. Drug-loaded particles conjugated to targeting ligands induced cell-specific inhibition of Notch activity in vitro and exhibited enhanced tumor retainment with significantly improved Notch inhibition and therapeutic outcome in vivo. Oral administration of GSI-MSNPs controlled Notch activity in intestinal stem cells further supporting the in vivo applicability of MSNPs for GSI delivery. MSNPs showed tumor accumulation and targeting after systemic administration. MSNPs were biocompatible, and particles not retained within the tumors, were degraded and eliminated mainly by renal excretion. The data highlights MSNPs as an attractive platform for targeted drug delivery of anticancer drugs with otherwise restricted clinical application, and as interesting constituents in the quest for more refined Notch therapies.

Mesoporous silica nanoparticles for bioadsorption, enzyme immobilisation, and delivery carriers

Mesoporous silica nanoparticles (MSNs) provide a non-invasive and biocompatible delivery platform for a broad range of applications in therapeutics, pharmaceuticals and diagnosis. The creation of smart, stimuli-responsive systems that respond to subtle changes in the local cellular environment are likely to yield long term solutions to many of the current drug/gene/DNA/RNA delivery problems. In addition, MSNs have proven to be promising supports for enzyme immobilisation, enabling the enzymes to retain their activity, affording them greater potential for wide applications in biocatalysis and energy. This review provides a comprehensive summary of the advances made in the last decade and a future outlook on possible applications of MSNs as nanocontainers for storage and delivery of biomolecules. We discuss some of the important factors affecting the adsorption and release of biomolecules in MSNs and review of the cytotoxicity aspects of such nanomaterials. The review also highlights some promising work on enzyme immobilisation using mesoporous silica nanoparticles.

Mesoporous silica nanoparticle based nano drug delivery systems: synthesis, controlled drug release and delivery, pharmacokinetics and biocompatibility

The biomedical applications of mesoporous silica nanoparticles (MSNs) as efficient drug delivery carriers have attracted great attention in the last decade. The structure, morphology, size, and surface properties of MSNs have been found to be facilely tunable for the purposes of drug loading, controlled drug release and delivery, and multifuctionalization. Meanwhile, the biosafety and in vivo drug efficiency of MSN-based nano drug delivery systems (nano-DDSs), involving biocompatibility (including cytotoxicity, blood and tissue compatibility) and pharmacokinetics (including biodistribution, biodegradation, retention, excretion, blood circulation) are also drawing increasing attention because of their clinical application prospects. Herein, we review the most recent research progresses on the synthesis, controlled drug release and delivery, pharmacokinetics and biocompatibility of MSNs.

Mesoporous Silica Nanoparticles for Intracellular Controlled Drug Delivery

The application of nanotechnology in the field of drug delivery has attracted much attention in the latest decades. Recent breakthroughs on the morphology control and surface functionalization of inorganic-based delivery vehicles, such as mesoporous silica nanoparticles (MSNs), have brought new possibilities to this burgeoning area of research. The ability to functionalize the surface of mesoporous-silica-based nanocarriers with stimuli-responsive groups, nanoparticles, polymers, and proteins that work as caps and gatekeepers for controlled release of various cargos is just one of the exciting results reported in the literature that highlights MSNs as a promising platform for various biotechnological and biomedical applications. This review focuses on the most recent progresses in the application of MSNs for intracellular drug delivery. The latest research on the pathways of entry into live mammalian and plant cells together with intracellular trafficking are described. One of the main areas of interest in this field is the development of site-specific drug delivery vehicles; the contribution of MSNs toward this topic is also summarized. In addition, the current research progress on the biocompatibility of this material in vitro and in vivo is discussed. Finally, the latest breakthroughs for intracellular controlled drug release using stimuli-responsive mesoporous-silica-based systems are described.

Towards multifunctional, targeted drug delivery systems using mesoporous silica nanoparticles – opportunities & challenges

One of the big challenges of medicine today is to deliver drugs specifically to defected cells. Nanoparticulate drug carriers have the potential to answer to this call, as nanoparticles can cross physiological barriers and access different tissues, and also be provided in a targetable form aimed at enhancing cell specificity of the carrier. Recent developments within material science and strong collaborative efforts crossing disciplinary borders have highlighted the potential of mesoporous silica nanoparticles (MSNs) for such targeted drug delivery. Here we outline recent advances which in this sense push MSNs to the forefront of drug delivery development. Relatively straightforward inside-out tuning of the vehicles, high flexibility, and potential for sophisticated release mechanisms make these nanostructures promising candidates for targeted drug delivery such as 'smart' cancer therapies. Moreover, due to the large surface area and the controllable surface functionality of MSNs, they can be controllably loaded with large amounts of drugs and coupled to homing molecules to facilitate active targeting, simultaneously carrying traceable (fluorescent or magnetically active) modalities, also making them highly interesting as theragnostic agents. However, the increased relative surface area and small size, and flexible surface functionalization which is beneficially exploited in nanomedicine, consequently also includes potential risks in their interactions with biological systems. Therefore, we also discuss some safety issues regarding MSNs and highlight how different features of the drug delivery platform influence their behaviour in a biological setting. Addressing these burning questions will facilitate the application of MSNs in nanomedicine.

Focus on The Advances in Nanomedicine Symposium, 233Rd National Meeting of The American Chemical Society, 2006

Nanomedicine – a concept that encompasses the myriad of applications of nanotechnology toward the betterment of human health – has become as inclusive as nanotechnology itself. Nevertheless, this term describes both conveniently and aptly the current efforts to develop nanoscale materials and metrologies for biomedical purposes, with staunch investments made by government agencies and increasing attention being paid to issues of regulatory concern. To the reader, it will be no surprise that nanomedicine has been making rapid advancements on numerous fronts, several of which were featured in a dedicated symposium last September at the 233rd National Meeting of the American Chemical Society in San Francisco (CA, USA). Included among the recent nanomedical advances that were discussed during the meeting are nanoengineered materials for drug delivery, functionalized nanoparticles for imaging and therapy, organic and inorganic nanostructures with applications in tissue engineering and nanoscale substrates and devices for ex vivo biomedical diagnostics. This issue of Nanomedicine features several reviews and a research article that highlight some of the exciting research presented in San Francisco last year. A topical review by Victor Lin and colleagues discusses recent applications of mesoporous silica nanoparticles as vehicles for drug, gene and neurotransmitter delivery applications. The authors believe that many new and exciting applications of these novel materials will soon be realized. Wafa’ Al-Majal and Kostas Kostarelos provide an updated perspective on liposome-encapsulated particles (e.g., quantum dots, small iron oxide nanoparticles and silica and polystyrene nanoparticles) as hybrid nanostructures. Liposomes can make nanoparticles biocompatible and offer a clinically proven (having been in clinical use for over 10 years), versatile platform for the further extension of nanoparticle use in medicine. This review illustrates specific benefits of liposome use in biomedical applications. Vincent Rotello and colleagues review the use of functionalized gold nanoparticles as adjuvants for gene and drug delivery. These particles have unique dimensions and tunable functionalities, which make them particularly promising candidates for drug-delivery applications.