Enzyme-activated intracellular drug delivery with tubule clay nanoformulation

Features of Anisotropic Drug Delivery Systems

Natural materials are anisotropic. Delivery systems occurring in nature, such as viruses, blood cells, pollen, and many others, do have anisotropy, while delivery systems made artificially are mostly isotropic. There is apparent complexity in engineering anisotropic particles or capsules with micron and submicron sizes. Nevertheless, some promising examples of how to fabricate particles with anisotropic shapes or having anisotropic chemical and/or physical properties are developed. Anisotropy of particles, once they face biological systems, influences their behavior. Internalization by the cells, flow in the bloodstream, biodistribution over organs and tissues, directed release, and toxicity of particles regardless of the same chemistry are all reported to be factors of anisotropy of delivery systems. Here, the current methods are reviewed to introduce anisotropy to particles or capsules, including loading with various therapeutic cargo, variable physical properties primarily by anisotropic magnetic properties, controlling directional motion, and making Janus particles. The advantages of combining different anisotropy in one entity for delivery and common problems and limitations for fabrication are under discussion.

Recent advances in natural nanoclay for diagnosis and therapy of cancer: A review

Cancer is still one of the deadliest diseases, and diagnosing and treating it effectively remains difficult. As a result, advancements in earlier detection and better therapies are urgently needed. Conventional chemotherapy induces chemoresistance, has non-specific toxicity, and has a meager efficacy. Natural materials like nanosized clay mineral formations of various shapes (platy, tubular, spherical, and fibrous) with tunable physicochemical, morphological, and structural features serve as potential templates for these. As multifunctional biocompatible nanocarriers with numerous applications in cancer research, diagnosis, and therapy, their submicron size, individual morphology, high specific surface area, enhanced adsorption ability, cation exchange capacity, and multilayered organization of 0.7-1 nm thick single sheets have attracted significant interest. Kaolinite, halloysite, montmorillonite, laponite, bentonite, sepiolite, palygorskite, and allophane are the most typical nanoclay minerals explored for cancer. These multilayered minerals can function as nanocarriers to effectively carry a variety of anticancer medications to the tumor site and improve their stability, dispersibility, sustained release, and transport. Proteins and DNA/RNA can be transported using nanoclays with positive and negative surfaces. The platform for phototherapeutic agents can be nanoclays. Clays with bio-functionality have been developed using various surface engineering techniques, which could help treat cancer. The promise of nanoclays as distinctive crystalline materials with applications in cancer research, diagnostics, and therapy are examined in this review.

Hierarchical Composite Scaffold with Deferoxamine Delivery System to Promote Bone Regeneration via Optimizing Angiogenesis

A bone defect refers to the loss of bone tissue caused by trauma or lesion. Bone defects result in high morbidity and deformity rates worldwide. Autologous bone grafting has been widely applied in clinics as the gold standard of treatment; however, it has limitations. Hence, bone tissue engineering has been proposed and developed as a novel therapeutic strategy for treating bone defects. Rapid and effective vascularization is essential for bone regeneration. In this study, a hierarchical composite scaffold with deferoxamine (DFO) delivery system, DFO@GMs-pDA/PCL-HNTs (DGPN), is developed, focusing on vascularized bone regeneration. The hierarchical structure of DGPN imitates the microstructure of natural bone and interacts with the local extracellular matrix, facilitating cell adhesion and proliferation. The addition of 1 wt% of halloysite nanotubes (HNTs) improves the material properties. Hydrophilic and functional groups conferred by polydopamine (pDA) modifications strengthen the scaffold bioactivity. Gelatin microspheres (GMs) protect the pharmacological activity of DFO, achieving local application and sustained release for 7 days. DFO effectively promotes angiogenesis by activating the signaling pathway of hypoxia inducible factor-1 α. In addition, DFO synergizes with HNTs to promote osteogenic differentiation and matrix mineralization. These results indicate that DGPN promotes bone regeneration and accelerates cranial defect healing.

Assessment of synthesized chitosan/halloysite nanocarrier modified by carbon nanotube for pH-sensitive delivery of curcumin to cancerous media

Constructing a system to carry medicine for more effective remedy of cancer has been a leading challenge, as the number of cancer cases continues to increase. In this present research, a curcumin-loaded chitosan/halloysite/carbon nanotube nanomixture was fabricated by means of water/oil/water emulsification method. The drug loading efficiency (DL) and entrapment efficiency (EE), as a result, reached 42 % and 88 %, respectively and FTIR and XRD analysis confirmed the bonding between the drug and nanocarrier. Morphological observation through FE-SEM and characterization through DLS analysis demonstrated that the average size of nanoparticles is 267.37 nm. Assessment of release within 96 h in pH 7.4 and 5.4 showed sustained release. For more investigation, release data was analyzed by diverse kinetic models to understand the mechanism in the release procedure. An MTT assay was also carried out, and the results illustrated apoptosis induction on MCF-7 cells and exhibited ameliorated cytotoxicity of the drug-loaded nanocomposite compared to the free curcumin. These findings suggest that the unique pH-responsive chitosan/halloysite/carbon nanotube nanocomposite might make a good option for drug delivery systems, particularly for the cancer treatment.

Functionally modified halloysite nanotubes for personalized bioapplications

Halloysite nanotubes (HNTs) are naturally aluminosilicate clay minerals that have the benefits of large surface areas, high mechanical properties, easy functionalization, and high biocompatibility, HNTs have been developed as multifunctional nanoplatforms for various bioapplications. Although some reviews have summarized the properties and bioapplications of HNTs, it remains unclear how to functionalize the modifications of HNTs for their personalized bioapplications. In this review, based on the physicochemical properties of HNTs, we summarized the methods of functionalized modifications (surface modification and structure modification) on HNTs. Also, we highlighted their personalized bioapplications (anti-bacterial, anti-inflammatory, wound healing, cancer theranostics, bone regenerative, and biosensing) by stressing on the main roles of HNTs. Finally, we provide perspectives on the future of functionalized modifications of HNTs for docking specific biological applications.

Insights on the Dynamic Innovative Tumor Targeted-Nanoparticles-Based Drug Delivery Systems Activation Techniques

Anti-cancer conventional chemotherapeutic drugs novel formula progress, nowadays, uses nano technology for targeted drug delivery, specifically tailored to overcome therapeutic agents' delivery challenges. Polymer drug delivery systems (DDS) play a crucial role in minimizing off-target side effects arising when using standard cytotoxic drugs. Using nano-formula for targeted localized action, permits using larger effective cytotoxic doses on a single special spot, that can seriously cause harm if it was administered systemically. Therefore, various nanoparticles (NPs) specifically have attached groups for targeting capabilities, not seen in bulk materials, which then need activation. In this review, we will present a simple innovative, illustrative, in a cartoon-way, enumeration of NP anti-cancer drug targeting delivery system activation-types. Area(s) covered in this review are the mechanisms of various NP activation techniques.

Nano-Clays for Cancer Therapy: State-of-the Art and Future Perspectives

To date, cancer continues to be one of the deadliest diseases. Current therapies are often ineffective, leading to the urgency to develop new therapeutic strategies to improve treatments. Conventional chemotherapeutics are characterized by a reduced therapeutic efficacy, as well as them being responsible for important undesirable side effects linked to their non-specific toxicity. In this context, natural nanomaterials such as clayey mineral nanostructures of various shapes (flat, tubular, spherical and fibrous) with adjustable physico-chemical and morphological characteristics are emerging as systems with extraordinary potential for the delivery of different therapeutic agents to tumor sites. Thanks to their submicron size, high specific surface area, high adsorption capacity, chemical inertia and multilayer organization of 0.7 to 1 nm-thick sheets, they have aroused considerable interest among the scientific community as nano systems that are highly biocompatible in cancer therapy. In oncology, the nano-clays usually studied are halloysite, bentonite, laponite, kaolinite, montmorillonite and sepiolite. These are multilayered minerals that can act as nanocarriers (with a drug load generally between 1 and 10% by weight) for improved stabilization, efficient transport and the sustained and controlled release of a wide variety of anticancer agents. In particular, halloysite, montmorillonite and kaolinite are used to improve the dissolution of therapeutic agents and to delay and/or direct their release. In this review, we will examine and expose to the scientific community the extraordinary potential of nano-clays as unique crystalline systems in the treatment of cancer.

Nanoclays in medicine: a new frontier of an ancient medical practice

Clays have been used as early as 2500 BC in human civilization for medicinal purposes. The ease of availability, biocompatibility, and versatility of these unique charged 2D structures abundantly available in nature have enabled the extensive applications of clays in human history. Recent advances in the use of clays in nanostructures and as components of polymer clay nanocomposites have exponentially expanded the use of clays in medicine. This review covers the details of structures and biomedical applications of several common clays, including montmorillonite, LAPONITE®, kaolinite, and halloysite. Here we describe the applications of these clays in wound dressings as hemostatic agents in drug delivery of drugs for cancer and other diseases and tissue engineering. Also reviewed are recent experimental and modeling studies that elucidate the impact of clay structures on cellular processes and cell adhesion processes. Various mechanisms of clay-mediated bioactivity, including protein localization, modulation of cell adhesion, biomineralization, and the potential of clay nanoparticles to impact cell differentiation, are presented. We also review the current developments in understanding the impact of clays on cellular responses. This review also elucidates new emerging areas of use of nanoclays in osteogenesis and the development of in vitro models of bone metastasis of cancer.

Evaluation of intracellular distribution of folate functionalized silica nanoparticles using fluorescence and hyperspectral enhanced dark field microscopy

Using nanoparticles as carriers for drug delivery systems has become a widely applied strategy in therapeutics and diagnostics. However, the pattern of their intracellular distribution is yet to be clarified. Here we present an in vitro study on the incorporation of mesoporous silica nanoparticles conjugated with folate and loaded with a cytotoxic drug, Irinotecan. The nanoparticles count and distribution within the cell frame were evaluated by means of enhanced dark field microscopy combined with hyperspectral imagery and 3D reconstructions from double-labeled fluorescent samples. An original post-processing procedure was developed to emphasize the nanoparticles' localization in 3D reconstruction of cellular compartments. By these means, it has been shown that the conjugation of mesoporous silica nanoparticles with folate increases the efficiency of nanoparticles entering the cell and their preferential localization in the close vicinity of the nucleus. As revealed by metabolic viability assays, the nanoparticles functionalized with folate enhance the cytotoxic efficiency of Irinotecan.

The emergence of nanoporous materials in lung cancer therapy

Lung cancer is one of the most common cancers, affecting more than 2.1 million people across the globe every year. A very high occurrence and mortality rate of lung cancer have prompted active research in this area with both conventional and novel forms of therapies including the use of nanomaterials based drug delivery agents. Specifically, the unique physico-chemical and biological properties of porous nanomaterials have gained significant momentum as drug delivery agents for delivering a combination of drugs or merging diagnosis with targeted therapy for cancer treatment. This review focuses on the emergence of nano-porous materials for drug delivery in lung cancer. The review analyses the currently used nanoporous materials, including inorganic, organic and hybrid porous materials for delivering drugs for various types of therapies, including chemo, radio and phototherapy. It also analyses the selected research on stimuli-responsive nanoporous materials for drug delivery in lung cancer before summarizing the various findings and projecting the future of emerging trends. This review provides a strong foundation for the current status of the research on nanoporous materials, their limitations and the potential for improving their design to overcome the unique challenges of delivering drugs for the treatment of lung cancer.

Architectural design of core-shell nanotube systems based on aluminosilicate clay

A nanoarchitectural approach to the design of functional nanomaterials based on natural aluminosilicate nanotubes and their catalysis, and practical applications are described in this paper. We focused on the buildup of hybrid core-shell systems with metallic or organic molecules encased in aluminosilicate walls, and nanotube templates for structured silica and zeolite preparation. The basis for such an architectural design is a unique Al₂O₃/SiO₂ dual chemistry of 50 nm diameter halloysite tubes. Their structure and site dependent properties are well combined with biocompatibility, environmental safety, and abundant availability, which makes the described functional systems scalable for industrial applications. In these organic/ceramic hetero systems, we outline drug, dye and chemical inhibitor loading inside the clay nanotubes, accomplished with their silane or amphiphile molecule surface modifications. For metal-ceramic tubule composites, we detailed the encapsulation of 2-5 nm Au, Ru, Pt, and Ag particles, Ni and Co oxides, NiMo, and quantum dots of CdZn sulfides into the lumens or their attachment at the outside surface. These metal-clay core-shell nanosystems show high catalytic efficiency with increased mechanical and temperature stabilities. The combination of halloysite nanotubes with mesoporous MCM-41 silica allowed for a synergetic enhancement of catalysis properties. Finally, we outlined the clay nanotubes' self-assembly into organized arrays with orientation and ordering similar to nematic liquid crystals, and these systems are applicable for life-related applications, such as petroleum spill bioremediation, antimicrobial protection, wound healing, and human hair coloring.

Nanohydrogels: Advanced Polymeric Nanomaterials in the Era of Nanotechnology for Robust Functionalization and Cumulative Applications

In the era of nanotechnology, the synthesis of nanomaterials for advanced applications has grown enormously. Effective therapeutics and functionalization of effective drugs using nano-vehicles are considered highly productive and selectively necessary. Polymeric nanomaterials have shown their impact and influential role in this process. Polymeric nanomaterials in molecular science are well facilitated due to their low cytotoxic behavior, robust functionalization, and practical approach towards in vitro and in vivo therapeutics. This review highlights a brief discussion on recent techniques used in nanohydrogel designs, biomedical applications, and the applied role of nanohydrogels in the construction of advanced therapeutics. We reviewed recent studies on nanohydrogels for their wide applications in building strategies for advantageously controlled biological applications. The classification of polymers is based on their sources of origin. Nanohydrogel studies are based on their polymeric types and their endorsed utilization for reported applications. Nanotechnology has developed significantly in the past decades. The novel and active role of nano biomaterials with amplified aspects are consistently being studied to minimize the deleterious practices and side effects. Here, we put forth challenges and discuss the outlook regarding the role of nanohydrogels, with future perspectives on delivering constructive strategies and overcoming the critical objectives in nanotherapeutic systems.

Sustainability in Heritage Wood Conservation: Challenges and Directions for Future Research

Conserving the world’s cultural and natural heritage is considered a key contributor to achieving the targets set out in the United Nation’s Sustainable Development Goals, yet how much attention do we pay to the methods we use to conserve and protect this heritage? With a specific focus on wooden objects of cultural heritage, this review discusses the current state-of-the-art in heritage conservation in terms of sustainability, sustainable alternatives to currently used consolidants, and new research directions that could lead to more sustainable consolidants in the future. Within each stage a thorough discussion of the synthesis mechanisms and/or extraction protocols, particularly for bio-based resources is provided, evaluating resource usage and environmental impact. This is intended to give the reader a better understanding of the overall sustainability of each different approach and better evaluate consolidant choices for a more sustainable approach. The challenges facing the development of sustainable consolidants and recent research that is likely to lead to highly sustainable new consolidant strategies in the future are also discussed. This review aims to contribute to the ongoing discussion of sustainable conservation and highlight the role that consolidants play in truly sustainable heritage conservation.

Forskolin-Loaded Halloysite Nanotubes as Osteoconductive Additive for the Biopolymer Tissue Engineering Scaffolds

Here we report the use of forskolin-modified halloysite nanotubes (HNTs) as a dopant for biopolymer porous hydrogel scaffolds to impart osteoinductive properties. Forskolin is a labdane diterpenoid isolated from the Indian Coleus plant. This small molecule is widely used as a supplement in molecular biology for cell differentiation. It has been reported in some earlier publications that forskolin can activate osteodifferentiation process by cyclic adenosine monophosphate (c-AMP) signalling activation in stem cells. In presented study it was demonstrated that forskolin release from halloysite-doped scaffolds induced the osteodifferentiation of equine mesenchymal stem cells (MSCs) in vitro without addition of any specific growth factors. The reinforcement of mechanical properties of cells and intercellular space during the osteodifferentiation was demonstrated using atomic force microscopy (AFM). These clay-doped scaffolds may find applications to accelerate the regeneration of horse bone defects by inducing the processes of osteodifferentiation of endogenous MSCs.

Probing Antimicrobial Halloysite/Biopolymer Composites with Electron Microscopy: Advantages and Limitations

Halloysite is a tubular clay nanomaterial of the kaolin group with a characteristic feature of oppositely charged outer and inner surfaces, allowing its selective spatial modification. The natural origin and specific properties of halloysite make it a potent material for inclusion in biopolymer composites with polysaccharides, nucleic acids and proteins. The applications of halloysite/biopolymer composites range from drug delivery and tissue engineering to food packaging and the creation of stable enzyme-based catalysts. Another important application field for the halloysite complexes with biopolymers is surface coatings resistant to formation of microbial biofilms (elaborated communities of various microorganisms attached to biotic or abiotic surfaces and embedded in an extracellular polymeric matrix). Within biofilms, the microorganisms are protected from the action of antibiotics, engendering the problem of hard-to-treat recurrent infectious diseases. The clay/biopolymer composites can be characterized by a number of methods, including dynamic light scattering, thermo gravimetric analysis, Fourier-transform infrared spectroscopy as well as a range of microscopic techniques. However, most of the above methods provide general information about a bulk sample. In contrast, the combination of electron microscopy with energy-dispersive X-ray spectroscopy allows assessment of the appearance and composition of biopolymeric coatings on individual nanotubes or the distribution of the nanotubes in biopolymeric matrices. In this review, recent contributions of electron microscopy to the studies of halloysite/biopolymer composites are reviewed along with the challenges and perspectives in the field.

Study of Uptake Mechanisms of Halloysite Nanotubes in Different Cell Lines

Purpose

Halloysite nanotubes (HNTs) are a natural aluminosilicate clay with a chemical formula of Al₂Si₂O₅(OH)₄×nH₂O and a hollow tubular structure. Due to their peculiar structure, HNTs can play an important role as a drug carrier system. Currently, the mechanism by which HNTs are internalized into living cells, and what is the transport pathway, is still unclear. Therefore, this study aimed at establishing the in vitro mechanism by which halloysite nanotubes could be internalized, using phagocytic and non-phagocytic cell lines as models.

Methods

The HNT/CURBO hybrid system, where a fluorescent probe (CURBO) is confined in the HNT lumen, has been used as a model to study the transport pathway mechanisms of HNTs. The cytocompatibility of HNT/CURBO on cell lines model was investigated by MTS assay. In order to identify the internalization pathway involved in the cellular uptake, we performed various endocytosis-inhibiting studies, and we used fluorescence microscopy to verify the nanomaterial internalization by cells. We evaluated the haemolytic effect of HNT/CURBO placed in contact with human red blood cells (HRBCs), by reading the absorbance value of the supernatant at 570 nm.

Results

The HNT/CURBO is highly biocompatible and does not have an appreciable haemolytic effect. The results of the inhibition tests have shown that the internalization process of nanotubes occurs in an energy-dependent manner in both the investigated cell lines, although they have different characteristics. In particular, in non-phagocytic cells, clathrin-dependent and independent endocytosis are involved. In phagocytic cells, in addition to phagocytosis and clathrin-dependent endocytosis, microtubules also participate in the halloysite cellular trafficking. Upon internalization by cells, HNT/CURBO is localized in the cytoplasmic area, particularly in the perinuclear region.

Conclusion

Understanding the cellular transport pathways of HNTs can help in the rational design of novel drug delivery systems and can be of great value for their applications in biotechnology.

Dark-field/hyperspectral microscopy for detecting nanoscale particles in environmental nanotoxicology research

Nanoscale contaminants (including engineered nanoparticles and nanoplastics) pose a significant threat to organisms and environment. Rapid and non-destructive detection and identification of nanosized materials in cells, tissues and organisms is still challenging, although a number of conventional methods exist. These approaches for nanoparticles imaging and characterisation both inside the cytoplasm and on the cell or tissue outer surfaces, such as electron or scanning probe microscopies, are unquestionably potent tools, having excellent resolution and supplemented with chemical analysis capabilities. However, imaging and detection of nanomaterials in situ, in wet unfixed and even live samples, such as living isolated cells, microorganisms, protozoans and miniature invertebrates using electron microscopy is practically impossible, because of the elaborate sample preparation requiring chemical fixation, contrast staining, matrix embedding and exposure into vacuum. Atomic force microscopy, in several cases, can be used for imaging and mechanical analysis of live cells and organisms under ambient conditions, however this technique allows for investigation of surfaces. Therefore, a different approach allowing for imaging and differentiation of nanoscale particles in wet samples is required. Dark-field microscopy as an optical microscopy technique has been popular among researchers, mostly for imaging relatively large specimens. In recent years, the so-called "enhanced dark field" microscopy based on using higher numerical aperture light condensers and variable numerical aperture objectives has emegred, which allows for imaging of nanoscale particles (starting from 5 nm nanospheres) using almost conventional optical microscopy methodology. Hyperspectral imaging can turn a dark-field optical microscope into a powerful chemical characterisation tool. As a result, this technique is becoming popular in environmental nanotoxicology studies. In this Review Article we introduce the reader into the methodology of enhanced dark-field and dark-field-based hyperspectral microscopy, covering the most important advances in this rapidly-expanding area of environmental nanotoxicology.

Preclinical developments of natural-occurring halloysite clay nanotubes in cancer therapeutics

The natural world holds useful resources that can be exploited to design effective therapeutic approaches. Ready-to-use tubular nanoclays, such as halloysite clay nanotubes (HNTs), are widely available, cost-effective, and sustainable submicron crystalline materials that have been showing great potential towards chronic multifactorial and malignant diseases, standing out as a promising anticancer nanotherapeutic strategy. Currently, several preclinical studies have reported the application of HNTs in cancer research, diagnosis, monitoring, and therapeutics. This groundbreaking review highlights the preclinical knowledge hitherto collected concerning the application of HNTs towards cancer therapy. Despite their reproducibility issues, HNTs were used as nanoarchitectonic platforms for the delivery of conventional chemotherapeutic, natural-occurring, biopharmaceutical, and phototherapeutic anticancer agents in a wide range of in vitro and in vivo solid cancer models. Overall, in different types of cancer mice models, the intratumoral and intravenous administration of HNTs-based nanoplatforms induced tumor growth inhibition without causing significant toxic effects. Such evidence raises a relevant question: does the therapeutic benefit of the parenteral administration of HNTs in cancer outweigh their potential toxicological risk? To answer this question further long-term absorption-distribution-metabolism-excretion studies in healthy and cancer animal models need to be performed. In cancer therapeutics, HNTs are envisaged as promising platforms for cancer multi-agent therapy, enabling the combination of different therapeutic modalities. Furthermore, HNTs might constitute suitable nanotheranostic platforms. Nevertheless, to confirm the potential and safety of the application of HNTs as nanodelivery systems for cancer therapy, it is necessary to perform in-depth in vivo pharmacokinetics and pharmacodynamic studies to further the translation to clinical trials.

Importance of Nano Medicine and New Drug Therapies for Cancer

Cancer is one of the deadly diseases leading to approximately 7.6 million deaths worldwide, with the mortality rate of 13%, and the number of deaths is expected to increase to 13.1 million within the next 10 years. In controlled drug delivery systems (DDS), the drug is transported to the desired location. Thus, the influence of drugs on vital tissues and undesirable side effects can be minimised. Additionally, DDS protects the drug from rapid degradation or clearance and enhances drug concentration in target tissues, and therefore, minimise the required dose of drug. This modern form of therapy is particularly important when there is a discrepancy between the dose and concentration of a drug. Cell-specific targeting can be achieved by attaching drugs to individually designed carriers. Recent developments in nanotechnology have shown that nanoparticles (particles with diameter < 100 nm in at least one dimension) have great potential as drug carriers. Because of their small size, these nanostructures exhibit unique physicochemical and biological properties that make them a favourable material for biomedical applications. Therefore, in this review, we aimed to describe the importance and types of nanomedicines and efficient ways in which new drug delivery systems for the treatment of cancer can be developed.

Antibody-Functionalized Halloysite Nanotubes for Targeting Bacterial Cells

Halloysite nanotubes (HNTs) are naturally occurring tubular clay particles which have emerged in recent years as a promising nanomaterial for numerous applications. Specifically, HNTs’ large pore volume and high specific surface area in combination with their biocompatibility make them ideal nanocarriers for bioactive compounds. This research aims to design and synthesize functionalized HNTs, which could selectively bind to target bacterial cells in suspension. Such a system can allow us to treat target cells within a challenging heterogeneous population, such as contaminated ecosystems or gut flora. HNTs functionalization is achieved by immobilizing specific antibodies onto the nanotube surface. The synthetic route is realized by the following subsequent steps: acidic etching of the HNTs, silanization of reactive surface hydroxyls, conjugation of protein A, and oriented immobilization of the antibody. HNT functionalization is studied by a set of analytical techniques including attenuated total reflectance Fourier-transform infrared spectroscopy, zeta potential measurements, thermal gravimetric analysis, scanning and transmission electron microscopy, as well as fluorescence microscopy. The selective binding of the functionalized HNTs to their target bacteria is observed upon incubation with live homogenous and heterogeneous cultures using fluorescence microscopy and high-throughput flow cytometry. Plate count and live/dead staining experiments demonstrate the biocompatibility of the antibody-HNT hybrid with its target bacteria. The suggested HNT-based smart carrier constitutes a generic platform for targeted delivery that could be selectively tailored against any microorganism by facile antibody adjustment.

Recent advances in the design of inorganic and nano-clay particles for the treatment of brain disorders

Inorganic materials, in particular nanoclays and silica nanoparticles, have attracted enormous attention due to their versatile and tuneable properties, making them ideal candidates for a wide range of biomedical applications, such as drug delivery. This review aims at overviewing recent developments of inorganic nanoparticles (like porous or mesoporous silica particles) and different nano-clay materials (like montmorillonite, laponites or halloysite nanotubes) employed for overcoming the blood brain barrier (BBB) in the treatment and therapy of major brain diseases such as Alzheimer's, Parkinson's, glioma or amyotrophic lateral sclerosis. Recent strategies of crossing the BBB through invasive and not invasive administration routes by using different types of nanoparticles compared to nano-clays and inorganic particles are overviewed.

Halloysite nanotubes - the nano-bio interface

The numerous biological applications of nanoparticles in general and nano-clays in particular are rooted in understanding and harnessing their dynamic nano-bio interface. Among clays, the intrinsically-mesoporous halloysite nanotubes (HNTs) have emerged in recent years as promising nanomaterials. The diverse interactions of these nanotubes with living cells, encompassing electrostatic, van der Waals, and ion exchange, along with cellular response, are crucial in determining the behaviour of HNTs in biological systems. Thus, rational engineering of the nanotube properties allows for vast applications ranging from bacteria encapsulation for bioremediation, through algae flocculation for aquaculture, to intracellular drug delivery. This review summarizes the many aspects of the nano-bio interface of HNTs with different cell types (bacteria, algae and fungi, and mammalian cells), highlighting biocompatibility/bio-adverse properties, interaction mechanisms, and the latest cutting-edge technologies.

Past, Present and Future Perspectives on Halloysite Clay Minerals

Halloysite nanotubes (HNTs), clay minerals belonging to the kaolin groups, are emerging nanomaterials which have attracted the attention of the scientific community due to their interesting features, such as low-cost, availability and biocompatibility. In addition, their large surface area and tubular structure have led to HNTs' application in different industrial purposes. This review reports a comprehensive overview of the historical background of HNT utilization in the last 20 years. In particular it will focus on the functionalization of the surfaces, both supramolecular and covalent, following applications in several fields, including biomedicine, environmental science and catalysis.

Cellular Analysis and Chemotherapeutic Potential of a Bi-Functionalized Halloysite Nanotube

The surface of halloysite nanotubes (HNTs) was bifunctionalized with two ligands—folic acid and a fluorochrome. In tandem, this combination should selectively target cancer cells and provide a means for imaging the nanoparticle. Modified bi-functionalized HNTs (bi-HNTs) were then doped with the anti-cancer drug methotrexate. bi-HNTs were characterized and subjected to in vitro tests to assess cellular growth and changes in cellular behavior in three cell lines—colon cancer, osteosarcoma, and a pre-osteoblast cell line (MC3T3-E1). Cell viability, proliferation, and cell uptake efficiency were assessed. The bi-HNTs showed cytocompatibility at a wide range of concentrations. Compared with regular-sized HNTs, reduced HNTs (~6 microns) were taken up by cells in more significant amounts, but increased cytotoxicity lead to apoptosis. Multi-photon images confirmed the intracellular location of bi-HNTs, and the method of cell entry was mainly through caveolae-mediated endocytosis. The bi-HNTs showed a high drug loading efficiency with methotrexate and a prolonged period of release. Most importantly, bi-HNTs were designed as a drug carrier to target cancer cells specifically, and imaging data shows that non-cancerous cells were unaffected after exposure to MTX-doped bi-HNTs. All data provide support for our nanoparticle design as a mechanism to selectively target cancer cells and significantly reduce the side-effects caused by off-targeting of anti-cancer drugs.

Engineered nanoparticle bio-conjugates toxicity screening: The xCELLigence cells viability impact

Introduction: The vast diverse products and applications of engineered nanoparticle bio-conjugates (ENPBCs) are increasing, and thus flooding the-markets. However, the data to support risk estimates of ENPBC are limited. While it is important to assess the potential benefits, acceptability and uptake, it is equally important to understand where ENPBCs safety is and how to expand and affirm consumer security concerns. Methods: Online articles were extracted from 2013 to 2016 that pragmatically used xCELLigence real-time cell analysis (RTCA) technology to describe the in-vitro toxicity of ENPBCs. The xCELLigence is a +noninvasive in vitro toxicity monitoring process that mimics exact continuous cellular bio-responses in real-time settings. On the other hand, articles were also extracted from 2008 to 2016 describing the in vivo animal models toxicity of ENPBCs with regards to safety outcomes. Results: Out of 32 of the 121 (26.4%) articles identified from the literature, 23 (71.9%) met the in-vitro xCELLigence and 9(28.1%) complied with the in vivo animal model toxicity inclusion criteria. Of the 23 articles, 4 of them (17.4%) had no size estimation of ENPBCs. The xCELLigence technology provided information on cell interactions, viability, and proliferation process. Eighty-three (19/23) of the in vitro xCELLigence technology studies described ENPBCs as nontoxic or partially nontoxic materials. The in vivo animal model provided further toxicity information where 1(1/9) of the in vivo animal model studies indicated potential animal toxicity while the remaining results recommended ENPPCs as potential candidates for drug therapy though with limited information on toxicity. Conclusion: The results showed that the bioimpacts of ENPBCs either at the in vitro or at in vivo animal model levels are still limited due to insufficient information and data. To keep pace with ENPBCs biomedical products and applications, in vitro, in vivo assays, clinical trials and long-term impacts are needed to validate their usability and uptake. Besides, more real-time ENPBCs-cell impact analyses using xCELLigence are needed to provide significant data and information for further in vivo testing.

Halloysite Nanotubes Coated by Chitosan for the Controlled Release of Khellin

In this work, we have developed a novel strategy to prepare hybrid nanostructures with controlled release properties towards khellin by exploiting the electrostatic interactions between chitosan and halloysite nanotubes (HNT). Firstly, khellin was loaded into the HNT lumen by the vacuum-assisted procedure. The drug confinement within the halloysite cavity has been proved by water contact angle experiments on the HNT/khellin tablets. Therefore, the loaded nanotubes were coated with chitosan as a consequence of the attractions between the cationic biopolymer and the halloysite outer surface, which is negatively charged in a wide pH range. The effect of the ionic strength of the aqueous medium on the coating efficiency of the clay nanotubes was investigated. The surface charge properties of HNT/khellin and chitosan/HNT/khellin nanomaterials were determined by ζ potential experiments, while their morphology was explored through Scanning Electron Microscopy (SEM). Water contact angle experiments were conducted to explore the influence of the chitosan coating on the hydrophilic/hydrophobic character of halloysite external surface. Thermogravimetry (TG) experiments were conducted to study the thermal behavior of the composite nanomaterials. The amounts of loaded khellin and coated chitosan in the hybrid nanostructures were estimated by a quantitative analysis of the TG curves. The release kinetics of khellin were studied in aqueous solvents at different pH conditions (acidic, neutral and basic) and the obtained data were analyzed by the Korsmeyer-Peppas model. The release properties were interpreted on the basis of the TG and ζ potential results. In conclusion, this study demonstrates that halloysite nanotubes wrapped by chitosan layers can be effective as drug delivery systems.

Facile Fabrication of Natural Polyelectrolyte-Nanoclay Composites: Halloysite Nanotubes, Nucleotides and DNA Study

Complexation of biopolymers with halloysite nanotubes (HNTs) can greatly affect their applicability as materials building blocks. Here we have performed a systematic investigation of fabrication of halloysite nanotubes complexes with nucleotides and genomic DNA. The binding of DNA and various nucleotide species (polyAU, UMP Na₂, ADP Na₃, dATP Na, AMP, uridine, ATP Mg) by halloysite nanotubes was tested using UV-spectroscopy. The study revealed that binding of different nucleotides to the nanoclay varied but was low both in the presence and absence of MgCl₂, while MgCl₂ facilitated significantly the binding of longer molecules such as DNA and polyAU. Modification of the nanotubes with DNA and nucleotide species was further confirmed by measurements of ζ-potentials. DNA-Mg-modified nanotubes were characterized using transmission electron (TEM), atomic force (AFM) and hyperspectral microscopies. Thermogravimetric analysis corroborated the sorption of DNA by the nanotubes, and the presence of DNA on the nanotube surface was indicated by changes in the surface adhesion force measured by AFM. DNA bound by halloysite in the presence of MgCl₂ could be partially released after addition of phosphate buffered saline. DNA binding and release from halloysite nanotubes was tested in the range of MgCl₂ concentrations (10–100 mM). Even low MgCl₂ concentrations significantly increased DNA sorption to halloysite, and the binding was leveled off at about 60 mM. DNA-Mg-modified halloysite nanotubes were used for obtaining a regular pattern on a glass surface by evaporation induced self-assembly process. The obtained spiral-like pattern was highly stable and resisted dissolution after water addition. Our results encompassing modification of non-toxic clay nanotubes with a natural polyanion DNA will find applications for construction of gene delivery vehicles and for halloysite self-assembly on various surfaces (such as skin or hair).

Stimuli-Responsive Biomaterials for Vaccines and Immunotherapeutic Applications

The immune system is the key target for vaccines and immunotherapeutic approaches aimed at blunting infectious diseases, cancer, autoimmunity, and implant rejection. However, systemwide immunomodulation is undesirable due to the severe side effects that typically accompany such strategies. In order to circumvent these undesired, harmful effects, scientists have turned to tailorable biomaterials that can achieve localized, potent release of immune-modulating agents. Specifically, "stimuli-responsive" biomaterials hold a strong promise for delivery of immunotherapeutic agents to the disease site or disease-relevant tissues with high spatial and temporal accuracy. This review provides an overview of stimuli-responsive biomaterials used for targeted immunomodulation. Stimuli-responsive or "environmentally responsive" materials are customized to specifically react to changes in pH, temperature, enzymes, redox environment, photo-stimulation, molecule-binding, magnetic fields, ultrasound-stimulation, and electric fields. Moreover, the latest generation of this class of materials incorporates elements that allow for response to multiple stimuli. These developments, and other stimuli-responsive materials that are on the horizon, are discussed in the context of controlling immune responses.

Kaolinite group minerals: Applications in cancer diagnosis and treatment

The clay minerals are characterized as important minerals due to their specific properties. One of the most important groups of the clay minerals is the kaolinite's group minerals due to their morphology, availability and range of potential applications. Halloysite and kaolinite are investigated here for their pharmaceutical applications and especially for their potential in cancer treatment. This review study is focusing on the potential applications of the kaolinite's group minerals in cancer diagnosis and monitoring, cancer treatment, the avoidance of metastasis, and the relief of cancer pains. Anticancer drug-loaded formulations based on these minerals show high potential for the treatment of various types of cancer as they have been shown to exhibit high anticancer activity in cancer cell lines and cancer animal models, high biocompatibility, low side effects, and high drug bioavailability.

Smart Functionalization of Ceramic-Coated AZ31 Magnesium Alloy

Providing materials with smart functionalities such as self-healing properties is primarily a domain for organic materials, although their applicability is restricted to mild environments and loads because of poor thermal and mechanical properties. This work seeks to achieve the active functionalities obtained in organic materials but in ceramics, which are much more heat resistant and robust. Ceramic coatings were produced by plasma electrolytic oxidation (PEO), which is an environmentally friendly technique that offers an alternative to potentially carcinogenic treatments used widely in the automotive and aircraft industries to protect light alloys against corrosion. The active functionalization was achieved by incorporating corrosion inhibitors encapsulated into halloysite nanotubes (HNTs) into the PEO coatings. This allowed controlled release of active agents when detecting environmental pH changes associated with the corrosion initiation of the metal substrate. Three corrosion inhibitors-vanadate, molybdate salts, and 8-hydroxyquinoline (8-HQ)-were assessed within the PEO-HNT system and demonstrated considerable improvements in the corrosion resistance by decreasing the kinetics of both anodic and cathodic reactions. For immersion times up to 72 h, vanadate offered a consistently higher corrosion resistance, which was followed by molybdate, whereas the positive effect of 8-HQ was time-limited. The improvement in corrosion resistance was associated with the combined enhancement of the barrier and active protection properties of ceramic coatings. All coatings containing corrosion inhibitors were capable of providing self-healing to small scratches, whereas only vanadate could partially restore a more severe damage.

Selective Cytotoxic Activity of Prodigiosin@halloysite Nanoformulation

Prodigiosin, a bioactive secondary metabolite produced by Serratia marcescens, is an effective proapoptotic agent against various cancer cell lines, with little or no toxicity toward normal cells. The hydrophobicity of prodigiosin limits its use for medical and biotechnological applications, these limitations, however, can be overcome by using nanoscale drug carriers, resulting in promising formulations for target delivery systems with great potential for anticancer therapy. Here we report on prodigiosin-loaded halloysite-based nanoformulation and its effects on viability of malignant and non-malignant cells. We have found that prodigiosin-loaded halloysite nanotubes inhibit human epithelial colorectal adenocarcinoma (Caco-2) and human colon carcinoma (HCT116) cells proliferative activity. After treatment of Caco-2 cells with prodigiosin-loaded halloysite nanotubes, we have observed a disorganization of the F-actin structure. Comparison of this effects on malignant (Caco-2, HCT116) and non-malignant (MSC, HSF) cells suggests the selective cytotoxic and genotoxic activity of prodigiosin-HNTs nanoformulation.

Tagged Halloysite Nanotubes as a Carrier for Intercellular Delivery in Brain Microvascular Endothelium

Neurological disorders that are characterized by unpredictable seizures affect people of all ages. We proposed the use of nanocarriers such as halloysite nanotubes to penetrate the blood–brain barrier and effectively deliver the payload over an extended time period. These 50-nm diameter tubes are a natural biocompatible nanomaterial available in large quantities. We proved a prolonged gradual drug delivery mechanism by the nanotube encapsulating rhodamine isothiocyanate and then ionomycin into brain microvascular endothelial cells (BMVECs). Through delayed diffusion, the nanotubes effectively delivered the drug to the primary BMVECs without killing them, by binding and penetration in time periods of 1 to 24 h.

Naturally derived nano- and micro-drug delivery vehicles: halloysite, vaterite and nanocellulose

We discuss prospects for halloysite nanotubes, vaterite crystals and nanocellulose to enter the market of biomaterials for drug delivery and tissue engineering, and their potential for economically viable production from abundant natural sources.

Functional biohybrid materials based on halloysite, sepiolite and cellulose nanofibers for health applications

Biohybrid materials were prepared by co-assembling the three following components: nanotubular halloysite, microfibrous sepiolite, and cellulose nanofibers dispersed in water, in order to exploit the most salient features of each individual component and to render homogeneous, flexible, yet strong films. Indeed, the incorporation of halloysite improves the mechanical performance of the resulting hybrid nanopapers and the assembly of the three components modifies the surface features concerning wetting properties compared to pristine materials, so that the main characteristics of the resulting materials become tunable with regard to certain properties. Owing to their hierarchical porosity together with their diverse surface characteristics, these hybrids can be used in diverse biomedical/pharmaceutical applications. Herein, for instance, loading with two model drugs, salicylic acid and ibuprofen, allows controlled and sustained release as deduced from antimicrobial assays, opening a versatile path for developing other related organic-inorganic materials of potential interest in diverse application fields.

Halloysite Nanoclay/Biopolymers Composite Materials in Tissue Engineering

Biocompatible materials for the fabrication of tissue substitutes are crucially important in the advancement of modern medicinal biotechnology. These materials, to serve their function, should be similar in physical, chemical, biological, and structural properties to native tissues which they are aimed to mimic. The porosity of artificial scaffolds is essential for normal nutrient transmission to cells, gas diffusion, and cell attachment and proliferation. Nanoscale inorganic additives and dopants are widely used to improve the functional properties of the polymer materials for tissue engineering. Among these inorganic dopants, halloysite nanotubes are arguably the most perspective candidates because of their biocompatibility and functional properties allowing to enhance significantly the mechanical and chemical stability of tissue engineering scaffolds. Here, this vibrant field of biotechnology for regenerative medicine is overviewed.

Biomedical potential of clay nanotube formulations and their toxicity assessment

Introduction: Halloysite clay nanotubes (HNTs) are a naturally abundant and biocompatible aluminosilicate material with a structure able to encapsulate 10-20% of drugs. These features are attractive toward the clinical application in controlled drug delivery, tissue engineering and regenerative medicine. Areas covered: We describe the application of HNTs as a viable method for clinical purposes, particularly developing formulations for prophylaxis, diagnosis and therapeutics, having a special attention to these nanotubes bio-safety. HNTs may be used for pharmaceuticals, biopharmaceuticals, wound healing, bone regeneration, dental repair, hair surface engineering and biomimetic applications. Expert opinion: HNTs are a versatile, safe and biocompatible nanomaterial used for drug encapsulation for numerous clinical applications. The studies here reviewed confirm the HNTs biocompatibility, describing their low toxicity. Further developments will be made regarding the long-term efficacy of halloysite-based treatments in humans, concentrating mostly on topical applications.

Selective Antimicrobial Effects of Curcumin@Halloysite Nanoformulation: A Caenorhabditis elegans Study

Alterations in the normal gastrointestinal microbial community caused by unhealthy diet, environmental factors, and antibiotic overuse may severely affect human health and well-being. Novel antimicrobial drug formulations targeting pathogenic microflora while not affecting or even supporting symbiotic microflora are urgently needed. Here we report fabrication of a novel antimicrobial nanocontainer based on halloysite nanotubes loaded with curcumin and protected with a dextrin outer layer (HNTs+Curc/DX) and its effective use to suppress the overgrowth of pathogenic bacteria in Caenorhabditis elegans nematodes. Nanocontainers have been obtained using vacuum-facilitated loading of hydrophobic curcumin into halloysite lumens. We have applied UV-vis and infrared spectroscopy, thermogravimetry and microscopy to characterize the HNTs+Curc/DX nanocontainers. In experiments in vitro we found that HNTs+Curc/DX effectively suppressed the growth of Serratia marcescens cells, whereas Escherichia coli bacteria were not affected. We applied HNTs+Curc/DX nanocontainers to alleviate the S. marcescens infection in C. elegans nematodes in vivo. The nematodes ingest HNTs+Curc/DX at 4-6 ng per worm, which results in improvement of the nematodes' fertility and life expectancy. Remarkably, treatment of S. marcescens-infected nematodes with HNTs+Curc/DX nanocontainers completely restored the longevity, demonstrating the enhanced bioavailability of hydrophobic curcumin. We believe that our results reported here open new avenues for fabrication of effective antimicrobial nanoformulations based on hydrophobic drugs and clay nanotubes.

Nanoparticle Activation Methods in Cancer Treatment

In this review, we intend to highlight the progress which has been made in recent years around different types of smart activation nanosystems for cancer treatment. Conventional treatment methods, such as chemotherapy or radiotherapy, suffer from a lack of specific targeting and consequent off-target effects. This has led to the development of smart nanosystems which can effect specific regional and temporal activation. In this review, we will discuss the different methodologies which have been designed to permit activation at the tumour site. These can be divided into mechanisms which take advantage of the differences between healthy cells and cancer cells to trigger activation, and those which activate by a mechanism extrinsic to the cell or tumour environment.

Antimicrobial Applications of Clay Nanotube-Based Composites

Halloysite nanotubes with different outer surface/inner lumen chemistry (SiO₂/Al₂O₃) are natural objects with a 50 nm diameter hollow cylindrical structure, which are able to carry functional compounds both inside and outside. They are promising for biological applications where their drug loading capacity combined with a low toxicity ensures the safe interaction of these nanomaterials with living cells. In this paper, the antimicrobial properties of the clay nanotube-based composites are reviewed, including applications in microbe-resistant biocidal textile, paints, filters, and medical formulations (wound dressings, drug delivery systems, antiseptic sprays, and tissue engineering scaffolds). Though halloysite-based antimicrobial materials have been widely investigated, their application in medicine needs clinical studies. This review suggests the scalable antimicrobial nano/micro composites based on natural tubule clays and outlines research and development perspectives in the field.

Multifunctional Carrier Based on Halloysite/Laponite Hybrid Hydrogel for Kartogenin Delivery

A novel carrier system based on halloysite nanotubes (HNT), for the potential intraarticular delivery of kartogenin (KGN) by means laponite (Lap) hydrogel (HNT/KGN/Lap), is developed. The drug was first loaded into HNT, and the hybrid composite obtained was used as filler for laponite hydrogel. Both the filler and the hydrogel were thoroughly investigated by several techniques and the hydrogel morphology was imaged by transmission electron microscopy. Furthermore, the gelating ability of laponite in the presence of the filler and the rheological properties of the hybrid hydrogel were also investigated. The kinetic release of kartogenin from HNT and HNT/Lap hybrid hydrogel was studied both in physiological conditions and in ex vivo synovial fluid. In the last case, the kinetic results highlighted that HNT carrier can effectively release KGN in a sustained manner for at least 38 days. Finally, a preliminary biological assays showed that the HNT/KGN/Lap hybrid hydrogel did not exhibit any cytotoxic effect.

Layered composite based on halloysite and natural polymers: a carrier for the pH controlled release of drugs

We have prepared new biohybrid materials based on halloysite nanotubes and natural polymers (alginate and chitosan) for the controlled and sustained release of bioactive species.