Degradability and Clearance of Silicon, Organosilica, Silsesquioxane, Silica Mixed Oxide, and Mesoporous Silica Nanoparticles

Anti-Infective Application of Graphene-Like Silicon Nanosheets via Membrane Destruction

The increasing problem of bacterial resistance to the currently effective antibiotics has resulted in the need for increasingly potent therapeutics to eradicate pathogenic microorganisms. 2D nanomaterials (2D NMs) have unique physical and chemical properties that make them attractive candidates for biomedical applications. Recently, the application of 2D NMs as antibacterial agents has attracted significant attention. Herein, a novel 2D graphene-like silicon nanosheet (GS NS) antimicrobial agent is fabricated from pristine silicon crystals by ultrasonication, which results in a highly exfoliated planar morphology and a significantly larger surface area as compared with bulk silicon. The GS NSs exhibit remarkable in vitro broad-spectrum bactericidal activity against Gram (-) Escherichia coli and Gram (+) Staphylococcus aureus because of a close interaction with the bacteria, which leads to highly efficient membrane destruction. The in vivo studies demonstrate that the local administration of GS NSs effectively mitigates implant-related infection by reducing the bacterial burden of the extracted samples and accelerating the remission of local inflammation. Based on these encouraging results, GS NSs are expected to be a useful new member of the 2D NMs family, with the potential of effectively killing pathogenic bacteria in clinical applications.

Anti‐Infective Application of Graphene‐Like Silicon Nanosheets via Membrane Destruction

The increasing problem of bacterial resistance to the currently effective antibiotics has resulted in the need for increasingly potent therapeutics to eradicate pathogenic microorganisms. 2D nanomaterials (2D NMs) have unique physical and chemical properties that make them attractive candidates for biomedical applications. Recently, the application of 2D NMs as antibacterial agents has attracted significant attention. Herein, a novel 2D graphene‐like silicon nanosheet (GS NS) antimicrobial agent is fabricated from pristine silicon crystals by ultrasonication, which results in a highly exfoliated planar morphology and a significantly larger surface area as compared with bulk silicon. The GS NSs exhibit remarkable in vitro broad‐spectrum bactericidal activity against Gram (−) Escherichia coli and Gram (+) Staphylococcus aureus because of a close interaction with the bacteria, which leads to highly efficient membrane destruction. The in vivo studies demonstrate that the local administration of GS NSs effectively mitigates implant‐related infection by reducing the bacterial burden of the extracted samples and accelerating the remission of local inflammation. Based on these encouraging results, GS NSs are expected to be a useful new member of the 2D NMs family, with the potential of effectively killing pathogenic bacteria in clinical applications.

New Advances in In Vivo Applications of Gated Mesoporous Silica as Drug Delivery Nanocarriers

One appealing concept in the field of hybrid materials is related to the design of gated materials. These materials are prepared in such a way that the release of chemical or biochemical species from voids of porous supports to a solution is triggered upon the application of external stimuli. Such gated materials are mainly composed of two subunits: i) a porous inorganic scaffold in which a cargo is stored, and ii) certain molecular or supramolecular entities, grafted onto the external surface, that can control mass transport from the interior of the pores. On the basis of this concept, a large number of examples are developed in the past ten years. A comprehensive overview of gated materials used in drug delivery applications in in vivo models from 2016 to date is thus given here.

A Tumor Microenvironment-Responsive Biodegradable Mesoporous Nanosystem for Anti-Inflammation and Cancer Theranostics

A nanoplatform that integrates diagnostic and therapeutic functions with intrinsic tumor microenvironment-responsive biodegradability is highly desired. Herein, a biodegradable nanotheranostic agent based on hollow mesoporous organosilica nanoparticles (HMONs), followed by encapsulating of heat shock protein 90 (Hsp 90) inhibitor is described. Then, the pore-engineering including gating with bovine serum albumin-iridium oxide nanoparticles (BSA-IrO₂ ) and conjugation of polyethylene glycol (PEG) is conducted to yield 17AAG@HMONs-BSA-IrO₂ -PEG (AHBIP) nanotheranostics for multimode computed tomography (CT)/photoacoustic (PA) imaging-guided photodynamic therapy (PDT) and low-temperature photothermal therapy (PTT). Such nanoplatforms show extraordinary photothermal conversion efficiency, high cargo loading (35.4% for 17AAG), and stimuli-responsive release of 17AAG for inhibition of Hsp90, which induces cell apoptosis at low-temperatures (≈41 °C). Also, the IrO₂ simultaneously endows the nanotheranostics with catalytic activity in triggering the decomposition of H₂ O₂ into O₂ and thus reducing the tumor hypoxia, as well as protecting normal tissues against H₂ O₂ -induced inflammation. AHBIP shows good photocatalysis activity for PDT as a result of the generation of superoxide anion by laser irradiation. The resulting AHBIP-mediated synergistic PTT/PDT offers an outstanding therapeutic outcome both in vitro and in vivo. Overall, the incorporation of the BSA-IrO₂ and biodegradable HMONs into one nanoplatform has great potential for clinical applications.

Biodegradable Inorganic Nanoparticles for Cancer Theranostics: Insights into the Degradation Behavior

Inorganic nanoparticles as a versatile nanoplatform have been broadly applied in the diagnosis and treatment of cancers due to their inherent superior physicochemical properties (including magnetic, thermal, optical, and catalytic performance) and excellent functions (e.g., imaging, targeted delivery, and controlled release of drugs) through surface functional modification or ingredient dopant. However, in practical biological applications, inorganic nanomaterials are relatively difficult to degrade and excrete, which induces a long residence time in living organisms and thus may cause adverse effects, such as inflammation and tissue cysts. Therefore, the development of biodegradable inorganic nanomaterials is of great significance for their biomedical application. This Review will focus on the recent advances of degradable inorganic nanoparticles for cancer theranostics with highlight on the degradation mechanism, aiming to offer an in-depth understanding of degradation behavior and related biomedical applications. Finally, key challenges and guidelines will be discussed to explore biodegradable inorganic nanomaterials with minimized toxicity issues, facilitating their potential clinical translation in cancer diagnosis and treatment.

Gradient Redox-Responsive and Two-Stage Rocket-Mimetic Drug Delivery System for Improved Tumor Accumulation and Safe Chemotherapy

Recent drug delivery nanosystems for cancer treatment still suffer from the poor tumor accumulation and low therapeutic efficacy due to the complex in vivo biological barriers. To resolve these problems, in this work, a novel gradient redox-responsive and two-stage rocket-mimetic drug nanocarrier is designed and constructed for improved tumor accumulation and safe chemotherapy. The nanocarrier is constructed on the basis of the disulfide-doped organosilica-micellar hybrid nanoparticles and the following dual-functional modification with disulfide-bonded polyethylene glycol (PEG) and amido-bonded polyethylenimine (PEI). First, prolonged circulation duration in the bloodstream is guaranteed due to the shielding of the outer PEG chains. Once the nanocarrier accumulates at the tumoral extracellular microenvironment with low glutathione (GSH) concentrations, the first-stage redox-responsive behavior with the separation of PEG and the exposure of PEI is triggered, leading to the improved tumor accumulation and cellular internalization. Furthermore, with their endocytosis by tumor cells, a high concentration of GSH induces the second-stage redox-responsiveness with the degradation of silsesquioxane framework and the release of the encapsulated drugs. As a result, the rocket-mimetic drug carrier displays longer circulation duration in the bloodstream, higher tumor accumulation capability, and improved antitumor efficacy (which is 2.5 times higher than that with inseparable PEG). It is envisioned that the rocket-mimetic strategy can provide new solutions for improving tumor accumulation and safety of nanocarriers in further cancer chemotherapy.

One-pot synthesis of chlorhexidine-templated biodegradable mesoporous organosilica nanoantiseptics

Chlorhexidine (CHX) is a widely used antiseptic in various infection control practices. In this work, we have developed biodegradable mesoporous organosilica nanoparticles (MONs) through a one-pot synthesis by employing CHX as a bifunctional agent that not any acts as a cationic template to form the structure of mesopores but also serves as a broad-spectrum antiseptic. The resulting CHX@MONs exhibit a relatively high CHX content and glutathione (GSH)-responsive release of CHX via a matrix-degradation-controlled mechanism, leading to comparable antibacterial effects with CHX on both Escherichia coli and Staphylococcus aureus. Furthermore, the effective antibacterial concentration of CHX@MONs shows less cytotoxicity toward normal cells. Our findings will help increase the use of CHX as an antiseptic agent, especially for responsive drug release upon bacterial infection.

Nanoparticles characterization using the CAM assay

The current chapter highlights the use of chorioallantoic membrane (CAM) of fertilized chicken egg for the characterization of nanoparticles applied in cancer nanomedicine. The CAM assay represents a promising alternative to mouse models in term of costs, ease of use, rapidity and ethical issues in particular for the screening of nanoformulations. Hence, the features of nanoparticles including blood retention, biocompatibility, active targeting or tumor accumulation, angiogenic activity, drug delivery and tumor elimination might be simply evaluated via the CAM model. In particular, in this model, embryo organs and morphology, CAM vasculature and blood cells, transplanted tumors on CAM were typically monitored and used for the evaluation of the nanomaterials. With the above advantages, the CAM assay, as highly valuable in vivo model, could be used regularly in pharmaceutical industries.

A. Ali L, Nguyen C, Becerro Nieto AI, Francolon N, Oliveiro E, Boyer D, Mahiou R, Raehm L, Gary-Bobo M, Durand JO, Charnay C. Encapsulation of Upconversion Nanoparticles in Periodic Mesoporous Organosilicas

(1) Background: Nanomedicine has recently emerged as a promising field, particularly for cancer theranostics. In this context, nanoparticles designed for imaging and therapeutic applications are of interest. We, therefore, studied the encapsulation of upconverting nanoparticles in mesoporous organosilica nanoparticles. Indeed, mesoporous organosilica nanoparticles have been shown to be very efficient for drug delivery, and upconverting nanoparticles are interesting for near-infrared and X-ray computed tomography imaging, depending on the matrix used. (2) Methods: Two different upconverting-based nanoparticles were synthesized with Yb3+-Er3+ as the upconverting system and NaYF4 or BaLuF5 as the matrix. The encapsulation of these nanoparticles was studied through the sol-gel procedure with bis(triethoxysilyl)ethylene and bis(triethoxysilyl)ethane in the presence of CTAB. (3) Results: with bis(triethoxysilyl)ethylene, BaLuF5: Yb3+-Er3+, nanoparticles were not encapsulated, but anchored on the surface of the obtained mesoporous nanorods BaLuF5: Yb3+-Er3+@Ethylene. With bis(triethoxysilyl)ethane, BaLuF5: Yb3+-Er3+ and NaYF4: Yb3+-Er3+nanoparticles were encapsulated in the mesoporous cubic structure leading to BaLuF5: Yb3+-Er3+@Ethane and NaYF4: Yb3+-Er3+@Ethane, respectively. (4) Conclusions: upconversion nanoparticles were located on the surface of mesoporous nanorods obtained by hydrolysis polycondensation of bis(triethoxysilyl)ethylene, whereas encapsulation occurred with bis(triethoxysilyl)ethane. The later nanoparticles NaYF4: Yb3+-Er3+@Ethane or BaLuF5: Yb3+-Er3+@Ethane were promising for applications with cancer cell imaging or X-ray-computed tomography respectively.

Biodegradable Mesoporous Silica Nanocarrier Bearing Angiogenic QK Peptide and Dexamethasone for Accelerating Angiogenesis in Bone Regeneration

In the repair of large segmental bone defects, bone tissue is often unable to heal due to the destruction of the vascular network near the wound site. An ideal bone repair material should have both angiogenic and osteogenic capabilities. To achieve this goal, we used biodegradable mesoporous silica nanoparticles (MSNs) as a delivery vehicle for dexamethasone (DEX), a small-molecule drug that induces osteogenic differentiation. Subsequently, chitosan was covalently modified onto the surface of the nanoparticles by glycidoxypropyltrimethoxysilane (GPTMS) to construct nanoparticulate delivery systems (DEX@chi-MSNs) that induce osteoblast formation. The QK peptide, which mimics the α-helical structure of vascular endothelial growth factor (VEGF) binding to the receptor, was adsorbed to the surface of chitosan-modified MSNs nanoparticles (QK@chi-MSNs) to render them with angiogenic ability. The QK@chi-MSNs can promote the formation of the tubular structure of human umbilical vein endothelial cells (HUVECs) and angiogenesis in vivo, as demonstrated by a chicken embryo chorioallantoic test (CAM) and subcutaneous embedding test. The DEX@chi-MSNs can improve alkaline phosphatase (ALP) activity, mineralized nodule formation, and the expression of osteogenic-related genes and proteins by BMSCs. Furthermore, the ability of bone repair and angiogenesis was evaluated in a critical size skull defect model in rats by using nanocarriers loaded with both DEX and QK (QK/DEX@chi-MSNs). The results of computed tomography (CT) scan, histological examination, and immunofluorescence staining indicated that QK/DEX@chi-MSNs can promote bone formation and angiogenesis in vivo, which has broad application prospects in bone tissue engineering.

Hydrolytic surface erosion of mesoporous silica nanoparticles for efficient intracellular delivery of cytochrome c

Delivery of apoptosis-associated proteins is an attractive approach to treat cancer, but their large molecular sizes and membrane-impermeability require the use of a suitable delivery carrier. As a versatile drug carrier, mesoporous silica nanoparticles (MSNs) have been utilized to transport a variety of therapeutic molecules. However, the use of MSNs for protein delivery has been limited because their conventionally obtainable pore size (ca. 2-3 nm in diameter) is too small to load large-sized biomolecular cargos. In this article, we present surface erosion of MSNs by hydrolytic degradation as a new strategy to obtain a mesoporous colloidal carrier for effective delivery of a bulky apoptosis-inducible protein, cytochrome c (CYT). A series of physicochemical properties of particles were analyzed before and after the hydrolytic surface erosion of pristine small-pored MSNs and the subsequent CYT loading. The results showed that hydrolytic degradation of MSNs imparts beneficial structural features for CYT loading and release, i.e., enlarged pores (up to ~10 nm in diameter) and roughened surface texture, leading to significantly enhanced intracellular delivery of CYT over conventional small-pored MSNs. The present results may offer a useful insight into silica degradability for tuning the internal/external surface characteristics of MSN-based colloidal particles to open a wide range of biomedical applications.

A Responsive Mesoporous Silica Nanoparticle Platform for Magnetic Resonance Imaging-Guided High-Intensity Focused Ultrasound-Stimulated Cargo Delivery with Controllable Location, Time, and Dose

Magnetic resonance imaging (MRI) is an essential modality for clinical diagnosis, and MRI-guided high-intensity focused ultrasound (MRgHIFU) is a powerful technology for targeted therapy. Clinical applications of MRgHIFU primarily utilize hyperthermia and ablation to treat cancerous tissue, but for drug delivery applications thermal damage is undesirable. A biofriendly MRgHIFU-responsive mesoporous silica nanoparticle (MSN) platform that is stimulated within a physiological safe temperature range has been developed, reducing the possibility of thermal damage to the surrounding healthy tissues. Biocompatible polyethylene glycol (PEG) was employed to cap the pores of MSNs, and the release of cargo molecules by HIFU occurs without substantial temperature increase (∼4 °C). To visualize by MRI and measure the stimulated delivery in situ, a U.S. Food and Drug Administration (FDA)-approved gadolinium-based contrast agent, gadopentetate dimeglumine (Gd(DTPA)^2-), was used as the imageable cargo. Taking advantage of the three-dimensional (3-D) imaging and targeting capabilities of MRgHIFU, the release of Gd(DTPA)^2- stimulated by HIFU was pinpointed at the HIFU focal point in 3-D space in a tissue-mimicking gel phantom. The amount of Gd(DTPA)^2- released was controlled by HIFU stimulation times and power levels. A positive correlation between the amount of Gd(DTPA)^2- released and T₁ was found. The MRgHIFU-stimulated cargo release was further imaged in a sample of ex vivo animal tissue. With this technology, the biodistribution of the nanocarriers can be tracked and the MRgHIFU-stimulated cargo release can be pinpointed, opening up an opportunity for future image-guided theranostic applications.

Nanoantibiotics: A Novel Rational Approach to Antibiotic Resistant Infections

Background:

The main drawbacks for using conventional antimicrobial agents are the development of multiple drug resistance due to the use of high concentrations of antibiotics for extended periods. This vicious cycle often generates complications of persistent infections, and intolerable antibiotic toxicity. The problem is that while all new discovered antimicrobials are effective and promising, they remain as only short-term solutions to the overall challenge of drug-resistant bacteria.

Objective:

Recently, nanoantibiotics (nAbts) have been of tremendous interest in overcoming the drug resistance developed by several pathogenic microorganisms against most of the commonly used antibiotics. Compared with free antibiotic at the same concentration, drug delivered via a nanoparticle carrier has a much more prominent inhibitory effect on bacterial growth, and drug toxicity, along with prolonged drug release. Additionally, multiple drugs or antimicrobials can be packaged within the same smart polymer which can be designed with stimuli-responsive linkers. These stimuli-responsive nAbts open up the possibility of creating multipurpose and targeted antimicrobials. Biofilm formation still remains the leading cause of conventional antibiotic treatment failure. In contrast to conventional antibiotics nAbts easily penetrate into the biofilm, and selectively target biofilm matrix constituents through the introduction of bacteria specific ligands. In this context, various nanoparticles can be stabilized and functionalized with conventional antibiotics. These composites have a largely enhanced bactericidal efficiency compared to the free antibiotic.

Conclusion:

Nanoparticle-based carriers deliver antibiotics with better biofilm penetration and lower toxicity, thus combating bacterial resistance. However, the successful adaptation of nanoformulations to clinical practice involves a detailed assessment of their safety profiles and potential immunotoxicity.

RETRACTED: In vitro and in vivo evaluation of degradation, toxicity, biodistribution, and clearance of silica nanoparticles as a function of size, porosity, density, and composition

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the corresponding author. Subsequent to the publication of the article Journal of Controlled Release 311–312 (2019) 1–15, in follow up studies in 2021, the corresponding author's lab members noticed significant discrepancies in reproducibility of some of the results reported in this manuscript. A detailed investigation in the lab was launched, and by retrieving the raw data available at the core facility pertaining to this manuscript, the following discrepancies were discovered that provide the basis for this retraction. These discrepancies have been reported to the University of Utah Research Integrity and Compliance Office by the corresponding author. The co-authors have been made aware of these discrepancies and of the decision of the corresponding author to retract. The corresponding author believes that the subject matter of this article, detailed analysis of the degradation of silica nanoparticles as a function of their physicochemical properties in relevant biological media in vitro, and in vivo, is significant. For successful utility of these particles in drug delivery applications their detailed biological fate needs to be examined. The significant discrepancies and lack of reproducibility of the reported data however is very unfortunate and the author hopes that this does not cast a doubt on the need for more detailed examination of the biological fate of silica nanoparticles in the future for their successful application in controlled release. In Vitro Data (Fig. 3) • Actual dissolution reaction volume was 2.5mL (confirmed by reviewing the lab notebook of the first author during the investigation) vs 3.5mL reported in the manuscript. • Sample volume was not used in the calculation to convert Inductively Coupled Plasma Mass Spectrometry (ICPMS) data to mg of silicon retrieved which is needed to calculate % degradation (needed to multiply data by 0.1 due to 0.1mL sample volumes). • Our investigation revealed a 20% “matrix effect with fluids” was communicated by ICPMS core facility person to the first author that was not addressed in the manuscript. • All data is different when calculating % degradation, not just by a factor of 10 due to not calculating for the 100ml sample volume. • Raw data during our investigation after publication, obtained from ICPMS facility, and not noted in the lab notebook, for day 28 of simulated lysosomal fluid (SLF) reveals n=1 and no data points for Stober100. In the manuscript however, error bars are shown for all particles at this time point and for the data for Stober100. Intracellular Degradation (Fig. 5) • Extremely high background with control causing negative % degradation for Disulfide Meso 100 from retrieved ICPMS data from core facility after publication, but manuscript shows ~1.25% degradation. • All other calculated % degradation based on retrieved data from ICPMS facility during the investigation after publication, do not match reported data in the paper. • Paper claims n=6, but raw data received from ICPMS facility during investigation (after publication) is clearly n=3. In Vivo Degradation (Fig. 6) ICPMS data retrieved during the investigation after publication for control mice showed extremely high background, and probably were not used in the calculations reported in this manuscript because it would have led to negative silicon contents for a few samples. Urine ICPMS data from the core facility was not available during investigation after publication, and cannot be retrieved from the first author's lab notebook. Hence its validity cannot be ascertained. There may be other discrepancies in the manuscript that have gone unnoticed. However, the Editor-in-Chief agrees that the above is significant enough to warrant retraction of the manuscript.

Mesoporous Silica Nanoparticles Trigger Liver and Kidney Injury and Fibrosis Via Altering TLR4/NF-κB, JAK2/STAT3 and Nrf2/HO-1 Signaling in Rats

Mesoporous silica nanoparticles (MSNs) represent a promising inorganic platform for multiple biomedical applications. Previous studies have reported MSNs-induced hepatic and renal toxicity; however, the toxic mechanism remains unclear. This study aimed to investigate MSNs-induced hepatic and nephrotoxicity and test the hypothesis that altered TLR4/MyD88/NF-κB, JAK2/STAT3, and Nrf2/ARE/HO-1 signaling pathways mediate oxidative stress, inflammation, and fibrosis induced by MSNs. Rats were administered 25, 50, 100, and 200 mg/kg MSNs for 30 days, and samples were collected for analyses. MSNs induced functional and histologic alterations, increased the levels of reactive oxygen species (ROS), lipid peroxidation and nitric oxide, suppressed antioxidants, and Nrf2/HO-1 signaling in the liver and kidney of rats. MSNs up-regulated the expression of liver and kidney TLR4, MyD88, NF-κB p65, and caspase-3 and increased serum pro-inflammatory cytokines. In addition, MSNs activated the JAK2/STAT3 signaling pathway, down-regulated peroxisome proliferator activated receptor gamma (PPARγ), and promoted fibrosis evidenced by the increased collagen expression and deposition. In conclusion, this study conferred novel information on the role of ROS and deregulated TLR4/MyD88/NF-κB, JAK2/STAT3, PPARγ, and Nrf2/ARE/HO-1 signaling pathways in MSNs hepatic and nephrotoxicity. These findings provide experimental evidence for further studies employing genetic and pharmacological strategies to evaluate the safety of MSNs for their use in nanomedicine.

Fluorescent Silicon Nanorods-Based Nanotheranostic Agents for Multimodal Imaging-Guided Photothermal Therapy

The utilization of diagnosis to guide/aid therapy procedures has shown great prospects in the era of personalized medicine along with the recognition of tumor heterogeneity and complexity. Herein, a kind of multifunctional silicon-based nanostructure, i.e., gold nanoparticles-decorated fluorescent silicon nanorods (Au@SiNRs), is fabricated and exploited for tumor-targeted multimodal imaging-guided photothermal therapy. In particular, the prepared Au@SiNRs feature high photothermal conversion efficiency (~ 43.9%) and strong photothermal stability (photothermal performance stays constant after five-cycle NIR laser irradiation), making them high-performance agents for simultaneously photoacoustic and infrared thermal imaging. The Au@SiNRs are readily modified with targeting peptide ligands, enabling an enhanced tumor accumulation with a high value of ~ 8.74% ID g-1. Taking advantages of these unique merits, the Au@SiNRs are superbly suitable for specifically ablating tumors in vivo without appreciable toxicity under the guidance of multimodal imaging. Typically, all the mice treated with the Au@SiNRs remain alive, and no distinct tumor recurrence is observed during 60-day investigation.

Oral Curcumin via Hydrophobic Porous Silicon Carrier: Preparation, Characterization, and Toxicological Evaluation In Vivo

Curcumin has antioxidant, anti-inflammatory, antimicrobial, and anticarcinogenic activities. However, the clinical application of curcumin has been restricted by the poor water solubility and low bioavailability of this molecule. In this work, hydrophobic porous silicon (pSi) particles were prepared by electrochemical etching method and grafted with the different hydrophobic groups on their surfaces. The loading efficiency of curcumin in pSi has been investigated. The properties of pSi particles have been characterized by scanning electron microscopy (SEM) and Fourier transform-infrared spectroscopy (FTIR). The highest loading efficiency of curcumin can be obtained with pSi surface modified with the octadecyl silane group. The release properties of curcumin in hydrophobic pSi have been researched in vitro and in vivo. The curcumin in the hydrophobic pSi surface keeps a high antioxidant bioactivity. The toxicological evaluation of the hydrophobic pSi particles indicates they have a high in vivo biocompatibility within the observed dose ranges. The hydrophobic pSi particles could provide an effective and controlled release delivery carrier for curcumin, which may provide a new tool platform for the further development of curcumin.

Mesoporous Organosilica Hollow Nanoparticles: Synthesis and Applications

Hollow periodic mesoporous organosilicas (PMOs) with molecularly homogeneous organic functional groups in the inorganic pore walls are attracting more and more attention due to the high surface areas, tunable pore sizes, low densities, large cavities in the center, permeable thin shells, and versatile organic-inorganic hybrid frameworks, which make them promising in a variety of applications including adsorption, catalysis, drug delivery, and nanotheranostics. Herein, recent advances in the synthesis of hollow PMO nanoparticles with various organic moieties are summarized, and the mechanism and new insights of synthesis approaches, including hard-core templating methods, liquid-interface assembly methods, and the interfacial reassembly and transformation strategy are discussed in-depth. Meanwhile, the design principles, properties, and synthetic strategies for some smart hollow architectures such as multishelled hollow PMOs, yolk-shell structured PMOs, and nonspherical hollow PMOs are discussed. Moreover, the typical applications of hollow PMO nanomaterials as nanoreactors for chemical transformations and nanoplatforms for biomedicine are summarized. Finally, the challenges and prospects for the future development of hollow PMOs are described.

Nonspherical Nanoparticle Shape Stability Is Affected by Complex Manufacturing Aspects: Its Implications for Drug Delivery and Targeting

The shape of nanoparticles is known recently as an important design parameter influencing considerably the fate of nanoparticles with and in biological systems. Several manufacturing techniques to generate nonspherical nanoparticles as well as studies on in vitro and in vivo effects thereof have been described. However, nonspherical nanoparticle shape stability in physiological-related conditions and the impact of formulation parameters on nonspherical nanoparticle resistance still need to be investigated. To address these issues, different nanoparticle fabrication methods using biodegradable polymers are explored to produce nonspherical nanoparticles via the prevailing film-stretching method. In addition, systematic comparisons to other nanoparticle systems prepared by different manufacturing techniques and less biodegradable materials (but still commonly utilized for drug delivery and targeting) are conducted. The study evinces that the strong interplay from multiple nanoparticle properties (i.e., internal structure, Young's modulus, surface roughness, liquefaction temperature [glass transition (T_g ) or melting (T_m )], porosity, and surface hydrophobicity) is present. It is not possible to predict the nonsphericity longevity by merely one or two factor(s). The most influential features in preserving the nonsphericity of nanoparticles are existence of internal structure and low surface hydrophobicity (i.e., surface-free energy (SFE) > ≈55 mN m^-1 , material-water interfacial tension <6 mN m^-1 ), especially if the nanoparticles are soft (<1 GPa), rough (R_rms > 10 nm), porous (>1 m² g^-1 ), and in possession of low bulk liquefaction temperature (<100 °C). Interestingly, low surface hydrophobicity of nanoparticles can be obtained indirectly by the significant presence of residual stabilizers. Therefore, it is strongly suggested that nonsphericity of particle systems is highly dependent on surface chemistry but cannot be appraised separately from other factors. These results and reviews allot valuable guidelines for the design and manufacturing of nonspherical nanoparticles having adequate shape stability, thereby appropriate with their usage purposes. Furthermore, they can assist in understanding and explaining the possible mechanisms of nonspherical nanoparticles effectivity loss and distinctive material behavior at the nanoscale.

Nanomaterials meet zebrafish: Toxicity evaluation and drug delivery applications

With the rapid development of engineered nanomaterials for various applications, in vivo toxicological studies for evaluating the potential hazardous effects of nanomaterials on environmental and human safety are in urgent need. Zebrafish has long been considered as the "gold standard" for biosafety assessments of chemicals and pollutants due to its high fecundity, cost-effectiveness, well-characterized developmental stages, optical transparency, and so forth. Thus, zebrafish holds great potential for high-throughput nanotoxicity screening. In this review, we summarize the in vivo toxicological profiles of different nanomaterials, including Ag nanoparticles (NPs), CuO NPs, silica NPs, polymeric NPs, quantum dots, nanoscale metal-organic frameworks, etc, in zebrafish and focus on how the physicochemical properties (e.g., size, surface charge, and surface chemistry) of these nanomaterials influence their biosafety. In addition, we also report the recent advances of the in vivo delivery of nanopharmaceuticals using zebrafish as the model organism for therapeutic assessment, biodistribution tracking, and the controlled release of loaded drugs. Limitations and special considerations of zebrafish model are also discussed. Overall, zebrafish is expected to serve as a high-throughput screening platform for nanotoxicity and drug delivery assessment, which may instruct the design of safe nanomaterials and more effective nanomedicines.

Biodegradable, pH-Sensitive Hollow Mesoporous Organosilica Nanoparticle (HMON) with Controlled Release of Pirfenidone and Ultrasound-Target-Microbubble-Destruction (UTMD) for Pancreatic Cancer Treatment

The dense extracellular matrix (ECM) and hypovascular networks were often found in solid pancreatic tumors form an impenetrable barrier, leading to limited uptake of chemotherapeutics and thus undesirable treatment outcomes.

Methods: A biodegradable nanoplatform based on hollow mesoporous organosilica nanoparticle (HMON) was designed as an effective delivery system for pirfenidone (PFD) to overcome the challenges in pancreatic tumor treatment. By varying pH producing a mildly acidic environment to emulate tumor cells, results in cleavage of the acetal bond between HMON nanoparticle and gating molecular, gemcitabine (Gem), enabling its controlled release.

Results: The in vitro and in vivo immunocytochemistry evaluations demonstrated an excellent ECM regulation efficacy of the nanoplatform and therefore the improved penetration of drug into the cells. The technique employed was especially enhanced when mediated with ultrasound target microbubble destruction (UTMD). Evaluations culminated with pancreatic cancer bearing mice and demonstrated therapeutic efficacy, good biodegradability, and negligible systemic toxicity.

Conclusion: the designed Gem gated biodegradable nanosystem is expected to provide an alternative way of improving antitumor efficacy by down-regulation of ECM levels and offers a passive-targeted therapy for pancreatic cancer treatment.

Anti-biofilm activity of garlic extract loaded nanoparticles

The emergence and widespread distribution of multi-drug resistant bacteria are considered as a major public health concern. The inabilities to curb severe infections due to antibiotic resistance have increased healthcare costs as well as patient morbidity and mortality. Bacterial biofilms formed by drug-resistant bacteria add additional challenges to treatment. This study describes a solgel based nanoparticle system loaded with garlic extract (GE-np) that exhibits: i) slow and sustained release of garlic components; ii) stabilization of the active components; and iii) significant enhancement of antimicrobial and antibiofilm activity relative to the free garlic extract. Also, GE-np were efficient in penetrating and disrupting the well-established methicillin-resistant Staphylococcus aureus (MRSA) biofilms. Overall, the study suggests that GE-np might be a promising candidate for the treatment of chronic infections due to biofilm forming drug-resistant bacteria.

Targeted acetylcholinesterase-responsive drug carriers with long duration of drug action and reduced hepatotoxicity

PURPOSE

Acetylcholinesterase (AChE) plays a critical role in the transmission of nerve impulse at the cholinergic synapses. Design and synthesis of AChE inhibitors that increase the cholinergic transmission by blocking the degradation of acetylcholine can serve as a strategy for the treatment of AChE-associated disease. Herein, an operational targeted drug delivery platform based on AChE-responsive system has been presented by combining the unique properties of enzyme-controlled mesoporous silica nanoparticles (MSN) with clinical-used AChE inhibitor.

METHODS

Functionalized MSNs were synthesized by liquid phase method and characterized by using different analytical methods. The biocompatibility and cytotoxicity of MSNs were determined by hemolysis experiment and MTT assay, respectively. Comparison of AChE activity between drug-loading system and inhibitor was developed with kits and by ELISA method. The efficacy of drug-loaded nanocarriers was investigated in a mouse model.

RESULTS

Compared with AChE inhibitor itself, the inhibition efficiency of this drug delivery system was strongly dependent on the concentration of AChE. Only AChE with high concentration could cause the opening of pores in the MSN, leading to the controlled release of AChE inhibitor in disease condition. Critically, the drug delivery system can not only exhibit long duration of drug action on AChE inhibition but also reduce the hepatotoxicity in vivo.

CONCLUSION

In summary, AChE-responsive drug release systems have been far less explored. Our results would shed lights on the design of enzyme controlled-release multifunctional system for enzyme-associated disease treatment.

Reduction of Nanoparticle Load in Cells by Mitosis but Not Exocytosis

The long-term fate of biomedically relevant nanoparticles (NPs) at the single cell level after uptake is not fully understood yet. We report that lysosomal exocytosis of NPs is not a mechanism to reduce the particle load. Biopersistent NPs such as nonporous silica and gold remain in cells for a prolonged time. The only reduction of the intracellular NP number is observed via cell division, e.g., mitosis. Additionally, NP distribution after cell division is observed to be asymmetrical, likely due to the inhomogeneous location and distribution of the NP-loaded intracellular vesicles in the mother cells. These findings are important for biomedical and hazard studies as the NP load per cell can vary significantly. Furthermore, we highlight the possibility of biopersistent NP accumulation over time within the mononuclear phagocyte system.

Intracellular Trafficking Network and Autophagy of PHBHHx Nanoparticles and their Implications for Drug Delivery

3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBHHx), which is naturally generated by biodegradable polyhydroxyalkanoates synthesized by bacteria, is an attractive material for drug delivery due to its controllable physical properties, non-toxicity, environmental friendliness, degradable properties and good biocompatibility. However, the intracellular trafficking network pathways, especially the autophagy mechanism of PHBHHx nanoparticles (NPs), have rarely been investigated. In this paper, we successfully prepared the NPs used solvent displacement method and investigated the autophagy pathways and other intracellular trafficking mechanisms based on NPs with the assistance of Rab proteins. We found that NPs were internalized in cells mainly via clathrin endocytosis and caveolin endocytosis. Beside the classical pathways, we discovered two new pathways: the micropinocytosis early endosome (EEs)-micropinocytosis-lysosome pathway and the EEs-liposome-lysosome pathway. NPs were delivered to cells through endocytosis recycling vesicles and GLUT4 exocytosis vesicles. Similar to other nanoparticles, NPs also induced intracellular autophagy and were then degraded via endolysosomal pathways. 3-MA and CQ were used as autophagy inhibitors to avoid the degradation of NPs through lysosomes by blocking endolysosomal pathways. Tumor volumes and weights were significantly decreased when autophagy inhibitors and chemical drugs packaged in NPs were cooperatively used.

PEGylated rhenium nanoclusters: a degradable metal photothermal nanoagent for cancer therapy

A common issue of functional nanoagents for potential clinical translation is whether they are biodegradable or renal clearable. Previous studies have widely explored noble metal nanoparticles (Au and Pd) as the first generation of photothermal nanoagents for cancer therapy, but all of the reported noble metal nanoparticles are non-degradable. On the other hand, rhenium (Re), one of the noble and precious metals with a high atomic number (Z = 75), has been mainly utilized as a jet superalloy or chemical catalyst, but the biological characteristics and activity of Re nanoparticles have never been evaluated until now. To address these issues, here we report a simple and scalable liquid-reduction strategy to synthesize PEGylated Re nanoclusters, which exhibit intrinsically high photothermal conversion efficacy (33.0%) and high X-ray attenuation (21.2 HU mL mg-1), resulting in excellent photothermal ablation (100% tumor elimination) and higher CT enhancement (15.9 HU mL mg-1 for commercial iopromide in clinics). Impressively, biocompatible Re nanoclusters can degrade into renal clearable ReO4 - ions after exposure to H2O2, and thus achieve much higher renal clearance efficiency than conventional gold nanoparticles. This work reveals the potential of theranostic application of metallic Re nanoclusters with both biodegradation and renal clearance properties and provides insights into the design of degradable metallic platforms with high clinical prospects.

Photocracking Silica: Tuning the Plasmonic Photothermal Degradation of Mesoporous Silica Encapsulating Gold Nanoparticles for Cargo Release

The degradation of bionanomaterials is essential for medical applications of nanoformulations, but most inorganic-based delivery agents do not biodegrade at controllable rates. In this contribution, we describe the controllable plasmonic photocracking of gold@silica nanoparticles by tuning the power and wavelength of the laser irradiation, or by tuning the size of the encapsulated gold cores. Particles were literally broken to pieces or dissolved from the inside out upon laser excitation of the plasmonic cores. The photothermal cracking of silica, probably analogous to thermal fracturing in glass, was then harnessed to release cargo molecules from gold@silica@polycaprolactone nanovectors. This unique and controllable plasmonic photodegradation has implications for nanomedicine, photopatterning, and sensing applications.

SupraCells: Living Mammalian Cells Protected within Functional Modular Nanoparticle-Based Exoskeletons

Creating a synthetic exoskeleton from abiotic materials to protect delicate mammalian cells and impart them with new functionalities could revolutionize fields like cell-based sensing and create diverse new cellular phenotypes. Herein, the concept of "SupraCells," which are living mammalian cells encapsulated and protected within functional modular nanoparticle-based exoskeletons, is introduced. Exoskeletons are generated within seconds through immediate interparticle and cell/particle complexation that abolishes the macropinocytotic and endocytotic nanoparticle internalization pathways that occur without complexation. SupraCell formation is shown to be generalizable to wide classes of nanoparticles and various types of cells. It induces a spore-like state, wherein cells do not replicate or spread on surfaces but are endowed with extremophile properties, for example, resistance to osmotic stress, reactive oxygen species, pH, and UV exposure, along with abiotic properties like magnetism, conductivity, and multifluorescence. Upon decomplexation cells return to their normal replicative states. SupraCells represent a new class of living hybrid materials with a broad range of functionalities.

Mesoporous Silica-Based Materials with Bactericidal Properties

Bacterial infections are the main cause of chronic infections and even mortality. In fact, due to extensive use of antibiotics and, then, emergence of antibiotic resistance, treatment of such infections by conventional antibiotics has become a major concern worldwide. One of the promising strategies to treat infection diseases is the use of nanomaterials. Among them, mesoporous silica materials (MSMs) have attracted burgeoning attention due to high surface area, tunable pore/particle size, and easy surface functionalization. This review discusses how one can exploit capacities of MSMs to design and fabricate multifunctional/controllable drug delivery systems (DDSs) to combat bacterial infections. At first, the emergency of bacterial and biofilm resistance toward conventional antimicrobials is described and then how nanoparticles exert their toxic effects upon pathogenic cells is discussed. Next, the main aspects of MSMs (e.g., physicochemical properties, multifunctionality, and biosafety) which one should consider in the design of MSM-based DDSs against bacterial infections are introduced. Finally, a comprehensive analysis of all the papers published dealing with the use of MSMs for delivery of antibacterial chemicals (antimicrobial agents functionalized/adsorbed on mesoporous silica (MS), MS-loaded with antimicrobial agents, gated MS-loaded with antimicrobial agents, MS with metal-based nanoparticles, and MS-loaded with metal ions) is provided.

A hydrofluoric acid-free method to dissolve and quantify silica nanoparticles in aqueous and solid matrices

As the commercial use of synthetic amorphous silica nanomaterials (SiO2-NPs) increases, their effects on the environment and human health have still not been explored in detail. An often-insurmountable obstacle for SiO2-NP fate and hazard research is the challenging analytics of solid particulate silica species, which involves toxic and corrosive hydrofluoric acid (HF). We therefore developed and validated a set of simple hydrofluoric acid-free sample preparation methods for the quantification of amorphous SiO2 micro- and nanoparticles. To circumvent HF, we dissolved the SiO2-NPs by base-catalyzed hydrolysis at room temperature or under microwave irradiation using potassium hydroxide, replacing the stabilizing fluoride ions with OH-, and exploiting the stability of the orthosilicic acid monomer under a strongly basic pH. Inductively coupled plasma - optical emission spectroscopy (ICP-OES) or a colorimetric assay served to quantify silicon. The lowest KOH: SiO2 molar ratio to effectively dissolve and quantify SiO2-NPs was 1.2 for colloidal Stöber SiO2-NPs at a pH >12. Fumed SiO2-NPs (Aerosil®) or food grade SiO2 (E551) containing SiO2-NPs were degradable at higher KOH: SiO2 ratios >8000. Thus, hydrofluoric acid-free SiO2-NP digestion protocols based on KOH present an effective (recoveries of >84%), less hazardous, and easy to implement alternative to current methods.

Degradable and Thermosensitive Microgels Synthesized via Simultaneous Quaternization and Siloxane Condensation

Degradable and thermosensitive microgels were successfully prepared via simultaneous quaternization and siloxane condensation during surfactant-free emulsion polymerization, with N-vinylcaprolactam as the main monomer and 1-vinylimidazole (VIM) as the comonomer, in the presence of (3-bromopropyl)trimethoxysilane (BPTMOS). The formation mechanism of cross-linking network was attributed to the hydrolysis and condensation of the methoxysilyl groups of BPTMOS and the quaternization of imidazole moiety of VIM by the bromine group of BPTMOS, leading to the microgels. The microgels were spherical in shape with a narrow size distribution, stable in an acidic buffer solution, but degradable in neutral and alkaline solutions. The presence of quaternized imidazolium in the same chain segment of Si-O-Si cross-linking points promoted the decomposition of Si-O-Si bonds and hence the degradation of the microgels. The obtained microgels could load and release the model drug, doxorubicin. The size, thermosensitivity, stability, degradation rate, and drug release behavior of the resultant microgels could be tuned by controlling the cross-linking degree, chemical composition, and degradation medium.

Recent Studies on Fluorinated Silica Nanometer-Sized Particles

Since initially being reported, fluorinated silica nanometer-sized particles (F-SiNPs) have gained much interest in the scientific community, due to their unique properties. These properties, include, low surface energies, increased mechanical strength, thermal robustness, and chemical resistance, and are a direct result of the incorporation of fluorine with a nanometer-sized silica network. This review aims to summarize the synthetic methods that have, and are still, being utilized to prepare these specialized materials. Following this, applications for F-SiNPs, with an emphasis on recent examples, will be presented in further detail.

New insights towards mesoporous silica nanoparticles as a technological platform for chemotherapeutic drugs delivery

Mesoporous silica nanoparticles (MSNs) displays interesting properties for biomedical applications such as high chemical stability, large surface area and tunable pores diameters and volumes, allowing the incorporation of large amounts of drugs, protecting them from deactivation and degradation processes acting as an excellent nanoplatform for drug delivery. However, the functional MSNs do not present the ability to transport the therapeutics without any leakage until reach the targeted cells causing side effects. On the other hand, the hydroxyls groups available on MSNs surface allows the conjugation of specific molecules which can binds to the overexpressed Enhanced Growth Factor Receptor (EGFR) in many tumors, representing a potential strategy for the cancer treatment. Beyond that, the targeting molecules conjugate onto mesoporous surface increase its cell internalization and act as gatekeepers blocking the mesopores controlling the drug release. In this context, multifunctional MSNs emerge as stimuli-responsive controlled drug delivery systems (CDDS) to overcome drawbacks as low internalization, premature release before to reach the region of interest, several side effects and low effectiveness of the current treatments. This review presents an overview of MSNs fabrication methods and its properties that affects drug delivery as well as stimuli-responsive CDDS for cancer treatment.

Optimized synthesis of luminescent silica nanoparticles by a direct micelle-assisted method

Silica nanoparticles (NPs) are versatile nanomaterials, which are safe with respect to biomedical applications, and therefore are highly investigated. The advantages of NPs include their ease of preparation, inexpensive starting materials and the possibility of functionalization or loading with various doping agents. However, the solubility of the doping agent(s) imposes constraints on the choice of the reaction system and hence limits the range of molecules that can be included in the interior of NPs. To overcome this problem, herein, we improved the current state of the art synthetic strategy based on Pluronic F127 by enabling the synthesis in the presence of large amounts of organic solvents. The new method enables the preparation of nanoparticles doped with large amounts of water-insoluble doping agents. To illustrate the applicability of the technology, we successfully incorporated a range of phosphorescent metalloporphyrins into the interior of NPs. The resulting phosphorescent nanoparticles may exhibit potential for biological oxygen sensing.

Near-Infrared-Triggered Photodynamic, Photothermal, and on Demand Chemotherapy by Multifunctional Upconversion Nanocomposite

In an attempt to integrate photodynamic therapy (PDT) with photothermal therapy and chemotherapy for enhanced anticancer activity, we have rationally synthesized a multifunctional upconversion nanoplatform using NaYF₄:Yb/Tm/Er/Fe nanoparticles (NPs) as the core and NaYbF₄:1% Tm as a shell. The as-synthesized core-shell upconversion (CSU) NPs exhibited diverse and enhanced photoluminescence emissions in a wide range (UV to NIR) consequent upon Fe³⁺ doping in the core and fabrication of an active shell. Subsequently, CSU was first decorated with titania NPs as photosensitizers. Next, the mesoporous silica (MS) shell loaded with doxorubicin (DOX) via a photocleavable Ru complex as the gating molecule was developed around titania-containing CSU. Finally, gold nanorods (GNRs) with localized surface plasmon resonance (LSPR) at 800 nm were incorporated around the MS layer to obtain the multifunctional nanoplatform. We demonstrated that the UV, blue, and NIR emissions from the CSU produced ROS-mediated PDT through titania activation, induced DOX release through photocleavage of the Ru complex, and generated hyperthermia by LSPR activity of GNRs, respectively, upon a single NIR excitation through FRET. The therapeutic efficacy was validated on HeLa cell lines in vitro by various microscopic and biochemical studies under a significantly milder NIR irradiation and lower dosage of the nanoplatforms, which have been further demonstrated as diagnostic nanoprobes for cell imaging.

Cumulative directional calcium gluing between phosphate and silicate: A facile, robust and biocompatible strategy for siRNA delivery by amine-free non-positive vector

For siRNA therapeutics, the use of positively charged amine-rich delivery vectors has been indispensable, but the amine-associated toxicological responses remain a clinical conundrum. Herein, we report a new strategy of harnessing a biocompatible, biodegradable and well-tolerated nanomaterial as an amine-free non-positive carrier for siRNA delivery. By employing mesoporous silica nanoparticles (MSNs) as a biocompatible vector, siRNA is loaded nonconventionally through calcium ion (Ca²⁺)-mediated interconnection (calcium gluing) between phosphates of siRNA and surface silicates of MSNs in a sequential, cumulative and directional way. The "one-pot" gluing process utilizing endogenously abundant Ca²⁺ ions offers a simple but robust means of siRNA loading on the non-positive bare surface of MSNs without the aid of multi-amine functionalization, and thus minimizes the risk of amine-associated cytotoxicity and immunogenicity while keeping the intrinsic biocompatibility of MSNs. As demonstrated with loading of an anticancer siRNA, this strategy allows stable in vivo delivery of siRNA for targeted gene silencing, and capitalizes on the unique structural versatility of MSNs by simultaneously delivering a pore-loaded chemodrug to synergistically enhance the treatment efficacy. Therefore, the Ca²⁺-glued MSNs as a general siRNA carrier platform provide a less toxic, less laborious and more utilitarian delivery tool for more effective and safer siRNA therapeutics.

Multimodal Polysilsesquioxane Nanoparticles for Combinatorial Therapy and Gene Delivery in Triple-Negative Breast Cancer

Multifunctional hybrid nanoparticles are being developed to carry a wide variety of therapeutic and imaging agents for multiple biomedical applications. Polysilsesquioxane (PSilQ) nanoparticles are a promising hybrid platform with numerous advantages to be used as a delivery system. In this report, we demonstrate the ability of a stimuli-responsive PSilQ-based platform to transport and deliver simultaneously protoporphyrin IX, curcumin, and RNA interference inducers inside human cells. This multimodal delivery system shows a synergistic performance for the combined phototherapy and chemotherapy of triple-negative breast cancer and can be used for efficient transfection of therapeutic nucleic acids. The current work represents the first report of using the PSilQ platform for the combined phototherapy and chemotherapy and gene delivery.

Advances in mesoporous silica nanoparticles for targeted stimuli-responsive drug delivery: an update

INTRODUCTION

Mesoporous silica nanoparticles (MSNs) are outstanding nanoplatforms for drug delivery. Herein, the most recent advances to turn MSN-based carriers into minimal side effect drug delivery agents are covered.

AREAS COVERED

This review summarizes the scientific advances dealing with MSNs for targeted and stimuli-responsive drug delivery since 2015. Delivery aspects to diseased tissues together with approaches to obtain smart MSNs able to respond to internal or external stimuli and their applications are here described. Special emphasis is done on the combination of two or more stimuli on the same nanoplatform and on combined drug therapy.

EXPERT OPINION

The use of MSNs in nanomedicine is a promising research field because they are outstanding platforms for treating different pathologies. This is possible thanks to their structural, chemical, physical and biological properties. However, there are certain issues that should be overcome to improve the suitability of MSNs for clinical applications. All materials must be properly characterized prior to their in vivo evaluation; furthermore, preclinical in vivo studies need to be standardized to demonstrate the MSNs clinical translation potential.