Self-immolative polydisulfides and their use as nanoparticles for drug delivery systems

Over the last few decades, nanotechnology has established to be a promising field in medicine. A remaining dominant challenge in today's pharmacotherapy is the limited selectivity of active pharmaceutical ingredients and associated undesirable side effects. Controlled drug release can be promoted by smart drug delivery systems, which release embedded API primarily depending on specific stimuli. Consequently, also the microenvironment of tumor tissue can be used advantageously. Dithiothreitol (DTT) based self-immolative polydisulfides were synthesized that preferentially respond to pathologically increased glutathione (GSH) concentrations, as found in solid tumors. The synthesis with different degrees of polymerisation was investigated as well as the synthesis of a copolymer consisting of dithiothreitol and butanedithiol (BDT). Toxicity tests were carried out on pure polymers and their degradation products. The ability to degrade was examined at pathological and physiological glutathione concentrations in order to test the suitability of the polymer as a matrix for nanoparticulate carrier systems. In addition, the processability of one polymer into nanoparticles was investigated as well as the degradation behaviour with glutathione.

Unveiling Trends: Nanoscale Materials Shaping Emerging Biomedical Applications

The realm of biomedical materials continues to evolve rapidly, driven by innovative research across interdisciplinary domains. Leveraging big data from the CAS Content Collection, this study employs quantitative analysis through natural language processing (NLP) to identify six emerging areas within nanoscale materials for biomedical applications. These areas encompass self-healing, bioelectronic, programmable, lipid-based, protein-based, and antibacterial materials. Our Nano Focus delves into the multifaceted utilization of nanoscale materials in these domains, spanning from augmenting physical and electronic properties for interfacing with human tissue to facilitating intricate functionalities like programmable drug delivery.

Thermal-/pH-triggered hollow mesoporous carbon nanocarrier for NIR-responsive drug release

Intelligent drug-delivery systems are considered one of the most important techniques for improving cancer treatment using existing over-the-counter medicines. However, metallic materials are always accompanied by metabolism problems, whereas chemotherapy produces several side effects in humans. Carbon-based materials exhibit exceptional features such as bio-affinity and bio-degradability. Herein, hollow mesoporous carbon nanoparticles (HMCs) are reported as effective nanocarriers of anti-cancer small drug molecules. Near IR (NIR) sources, which can penetrate most organs, induce thermal effects via non-invasive pathways. NIR radiation not only provides thermal therapy but also is compatible with temperature-sensitive coated responsive polymer shells. The template method was used to synthesize HMCs with size 200 ± 50 nm, under various conditions, to obtain suitably sized and hollow structures for liver-cancer treatment. Additional pH/thermal-bi-responsive poly(N-isopropylacrylamide) (PNIPAM) shells were further coated onto the HMCs to produce multiple shells that could trigger swelling motions in PNIPAM@HMCs, as confirmed via small-angle X-ray scattering (SAXS). NIR results demonstrated an extreme increase to the ∆T of 8.7 and 14.2 °C for HMC and PNIPAM@HMCs, respectively. The SAXS spectra analyzed using SasView simulations demonstrated the multi-shell structures of synthesized HMCs and the release mechanism of PNIPAM@HMCs. Based on the model simulation of SAXS, the different rates of polymer swelling indicated the core shrinkage (229.7 to 134.2 Å) and shell expansion (324.3 to 514.3 Å) at 37 °C and 42 °C, respectively. In addition, the first-order, Higuchi, Korsmeyer-Peppas, and Weibull mathematical models were used to verify the drug-release kinetics, and the model with the highest R² value was considered most suitable for further application. This paper presents the first SAXS study on PNIPAM@HMCs release kinetics and related mechanisms. This phenomenon indicates NIR-induced PNIPAM@HMCs as an effective strategy for cancer treatment via doxorubicin release.

Natural Biopolymers as Smart Coating Materials of Mesoporous Silica Nanoparticles for Drug Delivery

In recent years, the functionalization of mesoporous silica nanoparticles (MSNs) with different types of responsive pore gatekeepers have shown great potential for the formulation of drug delivery systems (DDS) with minimal premature leakage and site-specific controlled release. New nanotechnological approaches have been developed with the objective of utilizing natural biopolymers as smart materials in drug delivery applications. Natural biopolymers are sensitive to various physicochemical and biological stimuli and are endowed with intrinsic biodegradability, biocompatibility, and low immunogenicity. Their use as biocompatible smart coatings has extensively been investigated in the last few years. This review summarizes the MSNs coating procedures with natural polysaccharides and protein-based biopolymers, focusing on their application as responsive materials to endogenous stimuli. Biopolymer-coated MSNs, which conjugate the nanocarrier features of mesoporous silica with the biocompatibility and controlled delivery provided by natural coatings, have shown promising therapeutic outcomes and the potential to emerge as valuable candidates for the selective treatment of various diseases.

Antibiotic delivery from bone-targeted mesoporous silica nanoparticles for the treatment of osteomyelitis caused by methicillin-resistant Staphylococcus aureus

Osteomyelitis is a hard-to-treat infection of the bone and bone marrow that is mainly caused by Staphylococcus aureus, with an increasing incidence of methicillin-resistant S. aureus (MRSA). Owing to the aggressiveness of these bacteria in colonizing and destroying the bone, systemic antibiotic treatments fail to eradicate the infection. Instead, it normally entails surgery to remove the dead or infected bone. In this work, we report bone-targeted mesoporous silica nanoparticles for the treatment of osteomyelitis. The nanoparticles have been engineered with a functional gelatine/colistin coating able to hamper premature release from the mesopores while effectively disaggregating the bacterial biofilm. Because antibiotic resistance is a global emergency, we have designed two sets of identical nanoparticles, carrying each of them a clinically relevant antibiotic, that have demonstrated to have synergistic effect. The bone-targeted nanoparticles have been thoroughly evaluated in vitro and in vivo, obtaining a notable reduction of the amount of bacteria in the bone in just 24 h after only one dose, and paving the way for localized, nanoparticle-mediated treatment of MRSA-caused osteomyelitis. STATEMENT OF SIGNIFICANCE: In this work, we propose the use of bone-targeted mesoporous silica nanoparticles to address S. aureus-caused osteomyelitis that render synergistic therapeutic effect via multidrug delivery. Because the bacterial biofilm is responsible for an aggressive surgical approach and prolonged antibiotic treatment, the nanoparticles have been functionalized with a functional coating able to both disaggregate the biofilm, hamper premature antibiotic release and protect the intact bone. These engineered nanoparticles are able to effectively target bone tissue both in vitro and in vivo, showing high biocompatibility and elevated antibacterial effect.

Engineering mesoporous silica nanoparticles for drug delivery: where are we after two decades?

The present review details a chronological description of the events that took place during the development of mesoporous materials, their different synthetic routes and their use as drug delivery systems. The outstanding textural properties of these materials quickly inspired their translation to the nanoscale dimension leading to mesoporous silica nanoparticles (MSNs). The different aspects of introducing pharmaceutical agents into the pores of these nanocarriers, together with their possible biodistribution and clearance routes, would be described here. The development of smart nanocarriers that are able to release a high local concentration of the therapeutic cargo on-demand after the application of certain stimuli would be reviewed here, together with their ability to deliver the therapeutic cargo to precise locations in the body. The huge progress in the design and development of MSNs for biomedical applications, including the potential treatment of different diseases, during the last 20 years will be collated here, together with the required work that still needs to be done to achieve the clinical translation of these materials. This review was conceived to stand out from past reports since it aims to tell the story of the development of mesoporous materials and their use as drug delivery systems by some of the story makers, who could be considered to be among the pioneers in this area.

Arabic gum plus colistin coated moxifloxacin-loaded nanoparticles for the treatment of bone infection caused by Escherichia coli

Osteomyelitis is an inflammatory process of bone and bone marrow that may even lead to patient death. Even though this disease is mainly caused by Gram-positive organisms, the proportion of bone infections caused by Gram-negative bacteria, such as Escherichia coli, has significantly increased in recent years. In this work, mesoporous silica nanoparticles have been employed as platform to engineer a nanomedicine able to eradicate E. coli- related bone infections. For that purpose, the nanoparticles have been loaded with moxifloxacin and further functionalized with Arabic gum and colistin (AG+CO-coated MX-loaded MSNs). The nanosystem demonstrated high affinity toward E. coli biofilm matrix, thanks to AG coating, and marked antibacterial effect because of the bactericidal effect of moxifloxacin and the disaggregating effect of colistin. AG+CO-coated MX-loaded MSNs were able to eradicate the infection developed on a trabecular bone in vitro and showed pronounced antibacterial efficacy in vivo against an osteomyelitis provoked by E. coli. Furthermore, AG+CO-coated MX-loaded MSNs were shown to be essentially non-cytotoxic with only slight effect on cell proliferation and mild hepatotoxicity, which might be attributed to the nature of both antibiotics. In view of these results, these nanoparticles may be considered as a promising treatment for bone infections caused by enterobacteria, such as E. coli, and introduce a general strategy against bone infections based on the implementation of antibiotics with different but complementary activity into a single nanocarrier. STATEMENT OF SIGNIFICANCE: In this work, we propose a methodology to address E.coli bone infections by using moxifloxacin-loaded mesoporous silica nanoparticles coated with Arabic gum containing colistin (AG+CO-coated MX-loaded MSNs). The in vitro evaluation of this nanosystem demonstrated high affinity toward E. coli biofilm matrix thanks to the Arabic gum coating, a disaggregating and antibacterial effect of colistin, and a remarkable antibiofilm action because of the bactericidal ability of moxifloxacin and colistin. This anti-E. coli capacity of AG+CO-coated MX-loaded MSNs was brought out in an in vivo rabbit model of osteomyelitis where the nanosystem was able to eradicate more than 90% of the bacterial load within the infected bone.

Our contributions to applications of mesoporous silica nanoparticles

Our contributions to mesoporous silica materials in the field of biomedicine are reported in this article. This perspective article represents our work in the basics of the material, preparing different ranges of mesoporous silica nanoparticles with different diameters and with varied pore sizes. We demonstrated the high loading capacity of these materials. Additionally, the possibility of functionalizing both internal and external surface with different organic or inorganic moieties allowed the development of stimuli-responsive features which allowed a proper control on the administered dose. In addition, we have demonstrated that these carriers are not toxic, and we have also ensured that the load reaches its destination without affecting healthy tissues. STATEMENT OF SIGNIFICANCE: This paper presents my personal opinion and background on a hot topic as mesoporous silica nanoparticles for drug delivery. To this aim it provides a comprehensive and historical overview on the innovative contributions of my research group to this rapidly expanding field of research.

Chronology of Global Success: 20 Years of Prof Vallet-Regí Solving Questions

Twenty years ago, a group of bold scientists led by Prof Vallet-Regí suggested for the first time the use of mesoporous materials as potential drug delivery systems. Without knowing it; these pioneers unleashed the beast of creativity around the world because that original idea has been the inspiration of hundreds of scientific groups for the design of many versatile delivery systems based on mesoporous materials. Because the dream is not the destination, it is the journey, the present review aims to summarise the chain of events that catapulted a small and young research team from the grassroots of academia to the elite of the Biomedical Engineering field.

Nanoantibiotics Based in Mesoporous Silica Nanoparticles: New Formulations for Bacterial Infection Treatment

This review focuses on the design of mesoporous silica nanoparticles for infection treatment. Written within a general context of contributions in the field, this manuscript highlights the major scientific achievements accomplished by professor Vallet-Regí's research group in the field of silica-based mesoporous materials for drug delivery. The aim is to bring out her pivotal role on the envisage of a new era of nanoantibiotics by using a deep knowledge on mesoporous materials as drug delivery systems and by applying cutting-edge technologies to design and engineer advanced nanoweapons to fight infection. This review has been divided in two main sections: the first part overviews the influence of the textural and chemical properties of silica-based mesoporous materials on the loading and release of antibiotic molecules, depending on the host-guest interactions. Furthermore, this section also remarks on the potential of molecular modelling in the design and comprehension of the performance of these release systems. The second part describes the more recent advances in the use of mesoporous silica nanoparticles as versatile nanoplatforms for the development of novel targeted and stimuli-responsive antimicrobial nanoformulations for future application in personalized infection therapies.

Chemically fueled materials with a self-immolative mechanism: transient materials with a fast on/off response

There is an increasing demand for transient materials with a predefined lifetime like self-erasing temporary electronic circuits or transient biomedical implants. Chemically fueled materials are an example of such materials; they emerge in response to chemical fuel, and autonomously decay as they deplete it. However, these materials suffer from a slow, typically first order decay profile. That means that over the course of the material's lifetime, its properties continuously change until it is fully decayed. Materials that have a sharp on-off response are self-immolative ones. These degrade rapidly after an external trigger through a self-amplifying decay mechanism. However, self-immolative materials are not autonomous; they require a trigger. We introduce here materials with the best of both, i.e., materials based on chemically fueled emulsions that are also self-immolative. The material has a lifetime that can be predefined, after which it autonomously and rapidly degrades. We showcase the new material class with self-expiring labels and drug-delivery platforms with a controllable burst-release.

Smart gating porous particles as new carriers for drug delivery

The design of smart drug delivery carriers has recently attracted great attention in the biomedical field. Smart carriers can specifically respond to physical and chemical changes in their environment, such as temperature, photoirradiation, ultrasound, magnetic field, pH, redox species, and biomolecules. This review summarizes recent advances in the integration of porous particles and stimuli-responsive gatekeepers for effective drug delivery. Their unique structural properties play an important role in facilitating the diffusion of drug molecules and cell attachment. Various techniques for fabricating porous materials, with their major advantages and limitations, are summarized. Smart gatekeepers provide advanced functions such as "open-close" switching by functionalized stimuli-responsive polymers on a particle's pores. These controlled delivery systems enable drugs to be targeted at specific rates, time programs, and sites of the human body. The gate structures, gating mechanisms, and controlled release mechanisms of each trigger are detailed. Current ongoing research and future trends in targeted drug delivery, tissue engineering, and regenerative medicine applications are highlighted.

Smart Cargo Delivery System based on Mesoporous Nanoparticles for Bone Disease Diagnosis and Treatment

Bone diseases constitute a major issue for modern societies as a consequence of progressive aging. Advantages such as open mesoporous channel, high specific surface area, ease of surface modification, and multifunctional integration are the driving forces for the application of mesoporous nanoparticles (MNs) in bone disease diagnosis and treatment. To achieve better therapeutic effects, it is necessary to understand the properties of MNs and cargo delivery mechanisms, which are the foundation and key in the design of MNs. The main types and characteristics of MNs for bone regeneration, such as mesoporous silica (mSiO2 ), mesoporous hydroxyapatite (mHAP), mesoporous calcium phosphates (mCaPs) are introduced. Additionally, the relationship between the cargo release mechanisms and bone regeneration of MNs-based nanocarriers is elucidated in detail. Particularly, MNs-based smart cargo transport strategies such as sustained cargo release, stimuli-responsive (e.g., pH, photo, ultrasound, and multi-stimuli) controllable delivery, and specific bone-targeted therapy for bone disease diagnosis and treatment are analyzed and discussed in depth. Lastly, the conclusions and outlook about the design and development of MNs-based cargo delivery systems in diagnosis and treatment for bone tissue engineering are provided to inspire new ideas and attract researchers' attention from multidisciplinary areas spanning chemistry, materials science, and biomedicine.

Designing Mesoporous Silica Nanoparticles to Overcome Biological Barriers by Incorporating Targeting and Endosomal Escape

The several biological barriers that nanoparticles might encounter when administered to a patient constitute the major bottleneck of nanoparticle-mediated tumor drug delivery, preventing their successful translation into the clinic and reducing their therapeutic profile. In this work, mesoporous silica nanoparticles have been employed as a platform to engineer a versatile nanomedicine able to address such barriers, achieving (a) excessive premature drug release control, (b) accumulation in tumor tissues, (c) selective internalization in tumoral cells, and (d) endosomal escape. The nanoparticles have been decorated with a self-immolative redox-responsive linker to prevent excessive premature release, to which a versatile and polyvalent peptide that is able to recognize tumoral cells and induce the delivery of the nanoparticles to the cytoplasm via endosomal escape has been grafted. The excellent biological performance of the carrier has been demonstrated using 2D and 3D in vitro cell cultures and a tumor-bearing chicken embryo model, demonstrating in all cases high biocompatibility and cytotoxic effect, efficient endosomal escape and tumor penetration, and accumulation in tumors grown on the chorioallantoic membrane of chicken embryos.

Post-polymerization ‘click’ end-capping of polyglyoxylate self-immolative polymers

Post-polymerization CuAAC reactions are used to ‘click’ stimuli-cleavable triazole end-caps onto self-immolative poly(ethyl glyoxylate).

Mesoporous Silica Nanoparticles for Targeting Subcellular Organelles

Current chemotherapy treatments lack great selectivity towards tumoral cells, which leads to nonspecific drug distribution and subsequent side effects. In this regard, the use of nanoparticles able to encapsulate and release therapeutic agents has attracted growing attention. In this sense, mesoporous silica nanoparticles (MSNs) have been widely employed as drug carriers owing to their exquisite physico-chemical properties. Because MSNs present a surface full of silanol groups, they can be easily functionalized to endow the nanoparticles with many different functionalities, including the introduction of moieties with affinity for the cell membrane or relevant compartments within the cell, thus increasing the efficacy of the treatments. This review manuscript will provide the state-of-the-art on MSNs functionalized for targeting subcellular compartments, focusing on the cytoplasm, the mitochondria, and the nucleus.

Recent Advances on Drug-Loaded Mesenchymal Stem Cells With Anti-neoplastic Agents for Targeted Treatment of Cancer

Mesenchymal stem cells (MSCs), as an undifferentiated group of adult multipotent cells, have remarkable antitumor features that bring them up as a novel choice to treat cancers. MSCs are capable of altering the behavior of cells in the tumor microenvironment, inducing an anti-inflammatory effect in tumor cells, inhibiting tumor angiogenesis, and preventing metastasis. Besides, MSCs can induce apoptosis and inhibit the proliferation of tumor cells. The ability of MSCs to be loaded with chemotherapeutic drugs and release them in the site of primary and metastatic neoplasms makes them a preferable choice as targeted drug delivery procedure. Targeted drug delivery minimizes unexpected side effects of chemotherapeutic drugs and improves clinical outcomes. This review focuses on recent advances on innate antineoplastic features of MSCs and the effect of chemotherapeutic drugs on viability, proliferation, and the regenerative capacity of various kinds of MSCs. It also discusses the efficacy and mechanisms of drug loading and releasing procedures along with in vivo and in vitro preclinical outcomes of antineoplastic effects of primed MSCs for clinical prospection.

Multimodal Decorations of Mesoporous Silica Nanoparticles for Improved Cancer Therapy

The presence of leaky vasculature and the lack of lymphatic drainage of small structures by the solid tumors formulate nanoparticles as promising delivery vehicles in cancer therapy. In particular, among various nanoparticles, the mesoporous silica nanoparticles (MSN) exhibit numerous outstanding features, including mechanical thermal and chemical stability, huge surface area and ordered porous interior to store different anti-cancer therapeutics with high loading capacity and tunable release mechanisms. Furthermore, one can easily decorate the surface of MSN by attaching ligands for active targeting specifically to the cancer region exploiting overexpressed receptors. The controlled release of drugs to the disease site without any leakage to healthy tissues can be achieved by employing environment responsive gatekeepers for the end-capping of MSN. To achieve precise cancer chemotherapy, the most desired delivery system should possess high loading efficiency, site-specificity and capacity of controlled release. In this review we will focus on multimodal decorations of MSN, which is the most demanding ongoing approach related to MSN application in cancer therapy. Herein, we will report about the recently tried efforts for multimodal modifications of MSN, exploiting both the active targeting and stimuli responsive behavior simultaneously, along with individual targeted delivery and stimuli responsive cancer therapy using MSN.

Hybrid Injectable Sol-Gel Systems Based on Thermo-Sensitive Polyurethane Hydrogels Carrying pH-Sensitive Mesoporous Silica Nanoparticles for the Controlled and Triggered Release of Therapeutic Agents

Injectable therapeutic formulations locally releasing their cargo with tunable kinetics in response to external biochemical/physical cues are gaining interest in the scientific community, with the aim to overcome the cons of traditional administration routes. In this work, we proposed an alternative solution to this challenging goal by combining thermo-sensitive hydrogels based on custom-made amphiphilic poly(ether urethane)s (PEUs) and mesoporous silica nanoparticles coated with a self-immolative polymer sensitive to acid pH (MSN-CS-SIP). By exploiting PEU chemical versatility, Boc-protected amino groups were introduced as PEU building block (PEU-Boc), which were then subjected to a deprotection reaction to expose pendant primary amines along the polymer backbone (PEU-NH2, 3E18 -NH2/gPEU-NH2) with the aim to accelerate system response to external acid pH environment. Then, thermo-sensitive hydrogels were designed (15% w/v) showing fast gelation in physiological conditions (approximately 5 min), while no significant changes in gelation temperature and kinetics were induced by the Boc-deprotection. Conversely, free amines in PEU-NH2 effectively enhanced and accelerated acid pH transfer (pH 5) through hydrogel thickness (PEU-Boc and PEU-NH2 gels covered approximately 42 and 52% of the pH delta between their initial pH and the pH of the surrounding buffer within 30 min incubation, respectively). MSN-CS-SIP carrying a fluorescent cargo as model drug (MSN-CS-SIP-Ru) were then encapsulated within the hydrogels with no significant effects on their thermo-sensitivity. Injectability and in situ gelation at 37°C were demonstrated ex vivo through sub-cutaneous injection in rodents. Moreover, MSN-CS-SIP-Ru-loaded gels turned out to be detectable through the skin by IVIS imaging. Cargo acid pH-triggered delivery from PEU-Boc and PEU-NH2 gels was finally demonstrated through drug release tests in neutral and acid pH environments (in acid pH environment approximately 2-fold higher cargo release). Additionally, acid-triggered payload release from PEU-NH2 gels was significantly higher compared to PEU-Boc systems at 3 and 4 days incubation. The herein designed hybrid injectable formulations could thus represent a significant step forward in the development of multi-stimuli sensitive drug carriers. Indeed, being able to adapt their behavior in response to biochemical cues from the surrounding physio-pathological environment, these formulations can effectively trigger the release of their payload according to therapeutic needs.

Influence of the Surface Functionalization on the Fate and Performance of Mesoporous Silica Nanoparticles

Mesoporous silica nanoparticles have been broadly applied as drug delivery systems owing to their exquisite features, such as excellent textural properties or biocompatibility. However, there are various biological barriers that prevent their proper translation into the clinic, including: (1) lack of selectivity toward tumor tissues, (2) lack of selectivity for tumoral cells and (3) endosomal sequestration of the particles upon internalization. In addition, their open porous structure may lead to premature drug release, consequently affecting healthy tissues and decreasing the efficacy of the treatment. First, this review will provide a comprehensive and systematic overview of the different approximations that have been implemented into mesoporous silica nanoparticles to overcome each of such biological barriers. Afterward, the potential premature and non-specific drug release from these mesoporous nanocarriers will be addressed by introducing the concept of stimuli-responsive gatekeepers, which endow the particles with on-demand and localized drug delivery.

Engineered pH-Responsive Mesoporous Carbon Nanoparticles for Drug Delivery

In this work, two types of mesoporous carbon particles with different morphology, size, and pore structure have been functionalized with a self-immolative polymer sensitive to changes in pH and tested as drug nanocarriers. It is shown that their textural properties allow significantly higher loading capacity compared to typical mesoporous silica nanoparticles. In vial release experiments of a model Ru dye at pH 7.4 and 5 confirm the pH-responsiveness of the hybrid systems, showing that only small amounts of the cargo are released at physiological pH, whereas at slightly acidic pH (e.g., that of lysosomes), self-immolation takes place and a significant amount of the cargo is released. Cytotoxicity studies using human osteosarcoma cells show that the hybrid nanocarriers are not cytotoxic by themselves but induce significant cell growth inhibition when loaded with a chemotherapeutic drug such as doxorubicin. In preparation of an in vivo application, in vial responsiveness of the hybrid system to short-term pH-triggering is confirmed. The consecutive in vivo study shows no substantial cargo release over a period of 96 h under physiological pH conditions. Short-term exposure to acidic pH releases an experimental fluorescent cargo during and continuously after the triggering period over 72 h.

Ultrasound-Activated Nanomaterials for Therapeutics

Ultrasound has attracted much attention in recent years as an external stimulus capable of activating different types of nanomaterials for therapeutic application. One of the characteristics that makes ultrasound an especially appealing triggering stimulus for nanomedicine is its capacity to be non-invasively applied in a focused manner at deep regions of the body. Combining ultrasound with nanoparticles, different biological effects can be achieved. In this work, an overview of the four main types of inducible responses will be provided: inducing drug release, producing ultrasound-derived biological effects, modifying nanoparticle biodistribution and developing theranostic agents. Several examples of each one of these applications are presented here to illustrate the key concepts underlying recent developments in the discipline.

Mesoporous Silica Nanoparticles for the Treatment of Complex Bone Diseases: Bone Cancer, Bone Infection and Osteoporosis

Bone diseases, such as bone cancer, bone infection and osteoporosis, constitute a major issue for modern societies as a consequence of their progressive ageing. Even though these pathologies can be currently treated in the clinic, some of those treatments present drawbacks that may lead to severe complications. For instance, chemotherapy lacks great tumor tissue selectivity, affecting healthy and diseased tissues. In addition, the inappropriate use of antimicrobials is leading to the appearance of drug-resistant bacteria and persistent biofilms, rendering current antibiotics useless. Furthermore, current antiosteoporotic treatments present many side effects as a consequence of their poor bioavailability and the need to use higher doses. In view of the existing evidence, the encapsulation and selective delivery to the diseased tissues of the different therapeutic compounds seem highly convenient. In this sense, silica-based mesoporous nanoparticles offer great loading capacity within their pores, the possibility of modifying the surface to target the particles to the malignant areas and great biocompatibility. This manuscript is intended to be a comprehensive review of the available literature on complex bone diseases treated with silica-based mesoporous nanoparticles-the further development of which and eventual translation into the clinic could bring significant benefits for our future society.

Self-immolative polymers in biomedicine

Biomedical use cases for self-immolative polymers.

Nanoparticles to Knockdown Osteoporosis-Related Gene and Promote Osteogenic Marker Expression for Osteoporosis Treatment

Osteoporosis is the most common disease involving bone degeneration. Current clinical treatments are not able to offer a satisfying curative effect, so the development of effective treatments is desired. Gene silencing through siRNA delivery has gained great attention as a potential treatment in bone diseases. SOST gene inhibits the Wnt signaling pathway reducing osteoblast differentiation. Consequently, silencing SOST genes with a specific siRNA could be a potential option to treat osteoporosis. Generally, siRNAs have a very short half-life and poor transfection capacity, so an effective carrier is needed. In particular, mesoporous silica nanoparticles (MSNs) have attracted great attention for intracellular delivery of nucleic acids. We took advantage of their high loading capacity to further load the pores with osteostatin, an osteogenic peptide. In this study, we developed a system based on MSNs coated with poly(ethylenimine), which can effectively deliver SOST siRNA and osteostatin inside cells, with the consequent augmentation of osteogenic markers with a synergistic effect. This established the potential utility of MSNs to co-deliver both biomolecules to promote bone formation, this being a potential alternative to treat osteoporosis.

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.

Bioceramics: from bone substitutes to nanoparticles for drug delivery

Since the second half of the 20th century, bioceramics are used for bone repair and regeneration. Inspired by bones and teeth, and aimed at mimicking their structure and composition, several artificial bioceramics were developed for biomedical applications. And nowadays, in the 21st century, with the increasing prominence of nanoscience and nanotechnology, certain bioceramics are being used to build smart drug delivery systems, among other applications. This minireview will mainly describe both tendencies through the research work carried out by the research team of María Vallet-Regí.

Ultrasound responsive mesoporous silica nanoparticles for biomedical applications

Nanotechnology, which has already revolutionised many technological areas, is expected to transform life sciences. In this sense, nanomedicine could address some of the most important limitations of conventional medicine. In general, nanomedicine includes three major objectives: (1) trap and protect a great amount of therapeutic agents; (2) carry them to the specific site of disease avoiding any leakage; and (3) release on-demand high local concentrations of therapeutic agents. This feature article will make special emphasis on mesoporous silica nanoparticles that release their therapeutic cargo in response to ultrasound.

A l-glutamate-responsive delivery system based on enzyme-controlled self-immolative arylboronate-gated nanoparticles

Janus Au–mesoporous silica nanoparticles functionalized withl-glutamate oxidase and self-immolative arylboronate as al-glutamate-responsive delivery system.

Multi-stimuli responsive trigger for temporally controlled depolymerization of self-immolative polymers

The design and development of a multi-stimuli trigger enables temporal control over trigger cleavage and subsequent depolymerization of self-immolative polymer.

Hybrid Mesoporous Nanocarriers Act by Processing Logic Tasks: Toward the Design of Nanobots Capable of Reading Information from the Environment

Here, we present the design of smart nanodevices capable of reading molecular information from the environment and acting accordingly by processing Boolean logic tasks. As proof of concept, we prepared Au-mesoporous silica (MS) nanoparticles functionalized with the enzyme glucose dehydrogenase (GDH) on the Au surface and with supramolecular nanovalves as caps on the MS surface, which is loaded with a cargo (dye or drug). The nanodevice acts as an AND logic gate and reads information from the solution (presence of glucose and nicotinamide adenine dinucleotide (NAD⁺)), which results in cargo release. We show the possibility of coimmobilizing GDH and the enzyme urease on nanoparticles to mimic an INHIBIT logic gate, in which the AND gate is switched off by the presence of urea. We also show that such nanodevices can deliver cytotoxic drugs in cancer cells by recognizing intracellular NAD⁺ and the presence of glucose.

Hybrid Polyester Self-Immolative Polymer Nanoparticles for Controlled Drug Release

Delivery systems have been developed to address problematic properties of drugs, but the specific release of drugs at their targets is still a challenge. Polymers that depolymerize end-to-end in response to the cleavage of stimuli-responsive end-caps from their termini, commonly referred to as self-immolative polymers, offer high sensitivity to stimuli and have potential for the development of new high-performance delivery systems. In this work, we prepared hybrid particles composed of varying ratios of self-immolative poly(ethyl glyoxylate) (PEtG) and slowly degrading poly(d,l-lactic acid) (PLA). These systems were designed to provide a dual release mechanism consisting of a rapid burst release of drug from the PEtG domains and a slower release from the PLA domains. Using end-caps responsive to UV light and reducing thiols, it was found that triggered particles exhibited partial degradation, as indicated by a reduction in their dynamic light-scattering count rate that depended on the PEtG:PLA ratio. The particles were also shown to release the hydrophobic dye Nile red and the drug celecoxib in a manner that depended on triggering and the PEtG:PLA ratio. In vitro toxicity assays showed an effect of the stimuli on the toxicity of the celecoxib-loaded particles but also suggested it would be ideal to replace the sodium cholate surfactant that was used in the particle synthesis procedure in order to reduce the background toxicity of the delivery system. Overall, these hybrid systems show promise for tuning and controlling the release of drugs in response to stimuli.

Mesoporous silica nanoparticles in nanomedicine applications

In the last few years mesoporous silica nanoparticles (MSNs) have gained the attention of the nanomedicine research community, especially for the potential treatment of cancer. Although this topic has been reviewed before, periodic updates on such a hot topic are necessary due to the dynamic character of this field. The reasons that make MSNs so attractive for designing controlled drug delivery systems lie beneath their physico-chemical stability, easy functionalisation, low toxicity and their great loading capacity of many different types of therapeutic agents. The present brief overview tries to cover some of the recent findings on stimuli-responsive mesoporous silica nanocarriers together with the efforts to design targeted nanosystems using that platform. The versatility of those smart nanocarriers has promoted them as very promising candidates to be used in the clinic in the near future to overcome some of the pitfalls of conventional medicine.

Lectin-conjugated pH-responsive mesoporous silica nanoparticles for targeted bone cancer treatment

A novel multifunctional nanodevice based in doxorubicin (DOX)-loaded mesoporous silica nanoparticles (MSNs) as nanoplatforms for the assembly of different building blocks has been developed for bone cancer treatment. These building blocks consists of: i) a polyacrylic acid (PAA) capping layer grafted to MSNs via an acid-cleavable acetal linker, to minimize premature cargo release and provide the nanosystem of pH-responsive drug delivery ability; and ii) a targeting ligand, the plant lectin concanavalin A (ConA), able to selectively recognize, bind and internalize owing to certain cell-surface glycans, such as sialic acids (SA), overexpressed in given tumor cells. This multifunctional nanosystem exhibits a noticeable higher internalization degree into human osteosarcoma cells (HOS), overexpressing SA, compared to healthy preosteoblast cells (MC3T3-E1). Moreover, the results indicate that small DOX loading (2.5 µg mL^-1) leads to almost 100% of osteosarcoma cell death in comparison with healthy bone cells, which significantly preserve their viability. Besides, this nanodevice has a cytotoxicity on tumor cells 8-fold higher than that caused by the free drug. These findings demonstrate that the synergistic combination of different building blocks into a unique nanoplatform increases antitumor effectiveness and decreases toxicity towards normal cells. This line of attack opens up new insights in targeted bone cancer therapy.

STATEMENT OF SIGNIFICANCE

The development of highly selective and efficient tumor-targeted smart drug delivery nanodevices remains a great challenge in nanomedicine. This work reports the design and optimization of a multifunctional nanosystem based on mesoporous silica nanoparticles (MSNs) featuring selectivity towards human osteosarcoma cells and pH-responsive antitumor drug delivery capability. The novelty and originality of this manuscript relies on proving that the synergistic assembly of different building blocks into a unique nanoplatform increases antitumor effectiveness and decreases toxicity towards healthy cells, which constitutes a new paradigm in targeted bone cancer therapy.

Mesoporous Silica Nanoparticles for Drug Delivery: Current Insights

This manuscript reviews the recent progress on mesoporous silica nanoparticles as drug delivery systems. Their intrinsic structural, textural and chemical features permit to design versatile multifunctional nanosystems with the capability to target the diseased tissue and release the cargo on demand upon exposition to internal or external stimuli. The degradation rate of these nanocarriers in diverse physiological fluids is overviewed obeying their significance for their potential translation towards clinical applications. To conclude, the balance between the benefits and downsides of this revolutionary nanotechnological tool is also discussed.

pH-Responsive Mesoporous Silica and Carbon Nanoparticles for Drug Delivery

The application of nanotechnology to medicine constitutes a major field of research nowadays. In particular, the use of mesoporous silica and carbon nanoparticles has attracted the attention of numerous researchers due to their unique properties, especially when applied to cancer treatment. Many strategies based on stimuli-responsive nanocarriers have been developed to control the drug release and avoid premature release. Here, we focus on the use of the subtle changes of pH between healthy and diseased areas along the body to trigger the release of the cargo. In this review, different approximations of pH-responsive systems are considered: those based on the use of the host-guest interactions between the nanocarriers and the drugs, those based on the hydrolysis of acid-labile bonds and those based on supramolecular structures acting as pore capping agents.