Nature-inspired innovation: Alginic-kojic acid material for sustainable antibacterial and carbon dioxide fixation

The current environmental consciousness of the world's population encourages researchers to work on new materials that are environmentally benign and able to display the appropriate features for the needed application. To develop high-performing, inexpensive eco-materials, scientists have frequently turned to nature, attempting to mimic its processes' excellent performance at a reasonable price. In this regard, we decided to focus on alginic acid (AA), a polysaccharide widely found in brown algae, and kojic acid (KA), a chelating agent fungi produces. This study proposes rapidly synthesizing a sustainable, biocompatible material (AK) based on AA and KA, employing chlorokojic acid (CKA). The material has a dual function: antibacterial activity on both Gram-positive and Gram-negative bacteria, without any cytotoxic action on human cells in vitro, and catalytic ability to convert CO2 into cyclic carbonates at atmospheric pressure, without solvents, with high yields, and without the use of metals. Furthermore, the material's insolubility in organic solvents allows it to be easily separated from the reaction product and reused for other catalytic cycles. Both applications have a key role in the medical and environmental fields, combating the outbreak of infections and providing an innovative methodology to fix the CO2 on specific substrates.

Micropatterning of biologically derived surfaces with functional clay nanotubes

Micropatterning of biological surfaces performed via assembly of nano-blocks is an efficient design method for functional materials with complex organic-inorganic architecture. Halloysite clay nanotubes with high aspect ratios and empty lumens have attracted widespread interest for aligned biocompatible composite production. Here, we give our vision of advances in interfacial self-assembly techniques for these natural nanotubes. Highly ordered micropatterns of halloysite, such as coffee rings, regular strips, and concentric circles, can be obtained through high-temperature evaporation-induced self-assembly in a confined space and shear-force brush-induced orientation. Assembly of these clay nanotubes on biological surfaces, including the coating of human or animal hair, wool, and cotton, was generalized with the indication of common features. Halloysite-coated microfibers promise new approaches in cotton and hair dyeing, medical hemostasis, and flame-retardant tissue applications. An interfacial halloysite assembly on oil microdroplets (Pickering emulsion) and its core-shell structure (functionalization with quantum dots) was described in comparison with microfiber nanoclay coatings. In addition to being abundantly available in nature, halloysite is also biosafe, which makes its spontaneous surface micropatterning prospective for high-performance materials, and it is a promising technique with potential for an industrial scale-up.

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.

Augmentin loaded functionalized halloysite nanotubes: A sustainable emerging nanocarriers for biomedical applications

Clay minerals such as Halloysite nanotubes (HNTs), abundantly available green nanomaterial, exhibit a significant advantage in biomedical applications such as drug delivery, antibacterial and antimicrobials, tissue engineering or regeneration, etc. Because of the mesoporous structure and high absorbability, HNTs exhibit great potential as a nanocarrier in drug delivery applications. The sulfuric acid treatment enhances the surface area of the HNTs and thereby improves their drug-loading capacity by enlarging their lumen space/inner diameter. In the present investigation, based on the literature that supports the efficacy of drug loading after acid treatment, a dual treatment was performed to functionalize the HNTs surface. First, the HNTs were etched and functionalized using sulfuric acid. The acid-functionalized HNTs underwent another treatment using (3-aminopropyl) triethoxysilane (APTES) to better interact the drug molecules with the HNTs surfaces for efficient drug loading. Augmentin, a potential drug molecule of the penicillin group, was used for HNTs loading, and their antibacterial properties, cytotoxicity, and cumulative drug release (%) were evaluated. Different characterization techniques, such as X-ray diffractometer (XRD) and Fourier Transform Infra-Red (FT-IR), confirm the loading of Augmentin to the APTES@Acid HNTs. TEM images confirm the effective loading of the drug molecule with the HNTs. The drug encapsulation efficiency shows 40.89%, as confirmed by the Thermogravimetric Analysis (TGA). Also, the Augmentin-loaded APTES@Acid HNTs exhibited good antibacterial properties against E. coli and S. aureus and low cytotoxicity, as confirmed by the MTT assay. The drug release studies confirmed the sustainable release of Augmentin from the APTES@Acid HNTs. Hence, the treated HNTs can be considered as a potential nanocarrier for effectively delivering Augmentin and promoting enhanced therapeutic benefits.

Polymeric Membranes Doped with Halloysite Nanotubes Imaged using Proton Microbeam Microscopy

Polymeric membranes are useful tools for water filtration processes, with their performance strongly dependent on the presence of hydrophilic dopants. In this study, polyaniline (PANI)-capped aluminosilicate (halloysite) nanotubes (HNTs) are dispersed into polyether sulfone (PES), with concentrations ranging from 0.5 to 1.5 wt%, to modify the properties of the PES membrane. Both undoped and HNT-doped PES membranes are investigated in terms of wettability (static and time-dependent contact angle), permeance, mechanical resistance, and morphology (using scanning electron microscopy (SEM)). The higher water permeance observed for the PES membranes incorporating PANI-capped HNTs is, finally, assessed and discussed vis-à-vis the real distribution of HNTs. Indeed, the imaging and characterization in terms of composition, spatial arrangement, and counting of HNTs embedded within the polymeric matrix are demonstrated using non-destructive Micro Particle Induced X-ray Emission (µ-PIXE) and Scanning Transmission Ion Microscopy (STIM) techniques. This approach not only exhibits the unique ability to detect/highlight the distribution of HNTs incorporated throughout the whole thickness of polymer membranes and provide volumetric morphological information consistent with SEM imaging, but also overcomes the limits of the most common analytical techniques exploiting electron probes. These aspects are comprehensively discussed in terms of practical analysis advantages.

Polyurethane-Based Nanocomposites for Regenerative Therapies of Cancer Skin Surgery with Low Inflammatory Potential to Healthy Fibroblasts and Keratinocytes In Vitro

Nanocomposites based on thermoplastic polyurethanes (TPUs) filled with halloysite nanotubes (HNTs) were studied for their physicochemical and biological properties. Nanocomposites containing halloysite nanotube filler contents of 1 and 2% (E+1 and E+2), respectively, were obtained by extrusion. The newly formed E+1 and E+2 nanomaterials exhibited better flexibility and similar thermal properties compared to neat polyurethane. The use of atomic force microscopy (AFM) and differential scanning calorimetry (DSC) thermogram analysis showed that the distribution of halloysite nanotubes in the polymer matrix is more evenly dispersed in the E+1 nanomaterial, where the grains in the E+2 nanomaterial have a greater tendency to form agglomerates. Mechanical tests have shown that nanocomposites with the addition of HNT are characterized by a higher stress at break and elongation at break compared to neat TPU. The results of cytotoxicity tests suggest that the nanocomposite materials express lower toxicity to normal HaCaT and NHDF than to cancer Me45 cells. Further studies showed that the tested materials induced the expression of proinflammatory interleukins IL6 and IL8 in normal cells, but their overexpression in the cancer cell line resulted in cytostatic effects and proliferation reduction. Such a conclusion suggests the possible application of tested materials for regenerative therapies in cancer surgeries.

Tubular nanomaterials for bone tissue engineering

Nanomaterial composition, morphology, and mechanical performance are critical parameters for tissue engineering. Within this rapidly expanding space, tubular nanomaterials (TNs), including carbon nanotubes (CNTs), titanium oxide nanotubes (TNTs), halloysite nanotubes (HNTs), silica nanotubes (SiNTs), and hydroxyapatite nanotubes (HANTs) have shown significant potential across a broad range of applications due to their high surface area, versatile surface chemistry, well-defined mechanical properties, excellent biocompatibility, and monodispersity. These include drug delivery vectors, imaging contrast agents, and scaffolds for bone tissue engineering. This review is centered on the recent developments in TN-based biomaterials for structural tissue engineering, with a strong focus on bone tissue regeneration. It includes a detailed literature review on TN-based orthopedic coatings for metallic implants and composite scaffolds to enhance in vivo bone regeneration.

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.

Contribution of halloysite as nanotubular clay mineral on mechanism and adsorption rate of Cd(II) onto nanocomposites alginate-halloysite

In this work nanocomposites based on alginate (Alg) and halloysite as a nanotubular clay (Hy) were developed. Characterization techniques reveal that Hy/Alg nanocomposites are cation exchangers with predominantly negative charge density and good thermal stability. The adsorption equilibrium of Cd(II) in aqueous solution onto Hy/Alg nanocomposites revealed that by increasing the mass of halloysite in the nanocomposite, the adsorption capacity diminished significantly due to the halloysite-alginate interactions. Maximum adsorption capacities of 8, 65, 88, and 132 mg/g of Cd(II) were obtained for samples Hy, Hy/Alg 50%, Hy/Alg 95%, and Alg, respectively. In addition, the adsorption equilibrium of Cd(II) on the Hy/Alg bionanocomposites was affected by the pH and temperature of the solution, demonstrating the presence of electrostatic interactions during adsorption and that this is an exothermic process. The controlling mechanism of adsorption was cation exchange influenced by electrostatic forces. The Cd(II) adsorption rate studies were interpreted by the diffusion-permeation model and reveal that the presence of Hy in the structure of the nanocomposites enhances the permeation coefficient, that is, the adsorption rate was increased. The values of the permeation coefficient varied from 1.95 × 10^-7 to 8.50 × 10^-7 cm²/s for Hy/Alg 50% and from 1.70 × 10^-7 to 3.55 × 10^-7 cm²/s for Hy/Alg 95%.

Curcumin loaded Ag-TiO2-halloysite nanotubes platform for combined chemo-photodynamic therapy treatment of cancer cells

The use of naturally occurring anticancer materials in combination with doped metal oxide has emerged as one of the most promising ways for improving anticancer treatment efficacy. In this study, the anticancer potential of curcumin-loaded Ag-TiO2-halloysite nanotubes (curcumin-loaded Ag-TiO2-HNTs) was examined. Ag-TiO2-HNTs with different wt% of Ag-TiO2 were synthesized and characterized using XRD, TGA, FT-IR, UV-Vis spectroscopy, and SEM-EDX. The XRD results revealed the presence of crystalline TiO2. However, the presence of Ag was detected through the SEM-EDX analysis. Cyclic voltammetry measurements suggested the enhancement of the release of ROS from TiO2 upon deposition with Ag. FT-IR and TGA analysis confirmed the successful loading of curcumin inside the nanotubes of the halloysite. In vitro drug released studies revealed the release of approximately 80-99% curcumin within 48 hours. Kinetic model studies revealed that the release of curcumin from HNT and Ag-TiO2-HNT followed the first-order and Higuchi models, respectively. The light irradiated curcumin-loaded Ag-TiO2-HNTs samples exhibited considerable anticancer potential as compared to the free curcumin, irradiated Ag-TiO2 NPs samples, and unirradiated curcumin loaded Ag-TiO2-HNTs samples. The obtained results revealed that combined chemo- and photodynamic therapy using curcumin-loaded Ag-TiO2-HNTs nanomaterial has the potential as an effective anticancer treatment method.

In Vitro Binding and Release Mechanisms of Doxorubicin from Nanoclays

Nanoclays have been developed as drug delivery systems, but their mechanisms of DOX delivery are unclear. Herein, unmodified nanoclays (halloysite, kaolinite, montmorillonite) were comprehensively studied on their in vitro binding and release mechanisms of DOX from both experimental and theoretical aspects. These nanoclays with high loading capacity (>50%) and encapsulation efficiency capacity (>90%) of DOX are attributed to the exposed hydroxyl groups and the Lewis base sites on the surfaces. Density functional theory calculations also confirmed that DOX is preferentially adsorbed on the Al-OH surfaces while adsorption on Si-O surfaces is limited. Besides this, the pH-responsive profiles of DOX release from nanoclays are related to the protonation of negatively charged nanoclays in weakly acidic solutions that makes it easier to dissociate with positively charged DOX. The in-depth mechanistic method in this work is widely applicable and demonstrates that nanoclays can be used as efficient nanocarriers for more biomedical applications.

Hierarchical Fe2O3 hexagonal nanoplatelets anchored on SnO2 nanofibers for high-performance asymmetric supercapacitor device

Metal oxide heterostructures have gained huge attention in the energy storage applications due to their outstanding properties compared to pristine metal oxides. Herein, magnetic Fe₂O₃@SnO₂ heterostructures were synthesized by the sol-gel electrospinning method at calcination temperatures of 450 and 600 °C. XRD line profile analysis indicated that fraction of tetragonal tin oxide phase compared to rhombohedral hematite was enhanced by increasing calcination temperature. FESEM images revealed that hexagonal nanoplatelets of Fe₂O₃ were hierarchically anchored on SnO₂ hollow nanofibers. Optical band gap of heterogeneous structures was increased from 2.06 to 2.40 eV by calcination process. Vibrating sample magnetometer analysis demonstrated that increasing calcination temperature of the samples reduces saturation magnetization from 2.32 to 0.92 emu g^-1. The Fe₂O₃@SnO₂-450 and Fe₂O₃@SnO₂-600 nanofibers as active materials coated onto Ni foams (NF) and their electrochemical performance were evaluated in three and two-electrode configurations in 3 M KOH electrolyte solution. Fe₂O₃@SnO₂-600/NF electrode exhibits a high specific capacitance of 562.3 F g^-1 at a current density of 1 A g^-1 and good cycling stability with 92.8% capacitance retention at a high current density of 10 A g^-1 after 3000 cycles in three-electrode system. The assembled Fe₂O₃@SnO₂-600//activated carbon asymmetric supercapacitor device delivers a maximum energy density of 50.2 Wh kg^-1 at a power density of 650 W kg^-1. The results display that the Fe₂O₃@SnO₂-600 can be a promising electrode material in supercapacitor applications.

Structural Alteration, Hydration Stability, Heavy Metal Removal Efficiency, and Montmorillonite Porosity Fate by Coupling the Soil Solution pH and a Thermal Gradient

Clay minerals are considered as a promising material in the context of geological barrier for the confinement of radioactive and industrial waste. Understanding the usefulness of the smectite mineral, in this approach, remains insufficient. The deep investigation about structural response/changes, hydrate stability, cation exchange process, permeability, and heavy metal/radionuclide adsorption/removal efficiency under external constraints is needed. To explore the structural alteration, the hydration stability, and the evolution of montmorillonite porosity under a first order of external applied constraints coupling, a reference Na-rich montmorillonite specimen is used as a starting material, and three exchangeable heavy metal cations (Ba2+, Cu2+, and Co2+) have been selected. The applied constraint coupling is realized at laboratory scale and assured by simultaneously varying of the soil solution pH and the thermal gradient. The evaluation of the mineral fraction response is established by correlation of quantitative XRD analysis results, thermal analysis, and porosity measurements. The quantitative XRD analysis allows rebuilding of the theoretical model describing the interlamellar space (IS) configurations/damages, structural heterogeneity degrees, and hydrous stability. Obtained results show a dominant interstratified hydration character, for all studied complexes, attributed to a new IS organization versus the applied constraint strength. Furthermore, all samples exhibit a heterogeneous hydration behavior traduced by the coexistence of different layers of type population within the crystallite. Additionally, the theoretical XRD profile decomposition allowed us to prove link between the domination of the segregated stacking layers mode against the constraint strength. Thermal analysis allowed us to develop theoretical models describing the decrease of the water molecule amounts as a function of the increase in temperature and soil solution pH. Moreover, a specific hydration footprint response and an interstratification mapping are assigned for each corresponding stress degrees. The evolution of montmorillonite porosity is determined by adsorption measurement, based on Brunauer, Emmett, and Teller (BET) and Barrett-Joyner-Halenda (BJH) pore size distribution analyses which confirms for all samples, the exfoliation process, and the mesopore diameter rise by increasing the constraint intensity.

Mechanical Properties and Antibacterial Effect on Mono-Strain of Streptococcus mutans of Orthodontic Cements Reinforced with Chlorhexidine-Modified Nanotubes

Recently, several studies have introduced nanotechnology into the area of dental materials with the aim of improving their properties. The objective of this study is to determine the antibacterial and mechanical properties of type I glass ionomers reinforced with halloysite nanotubes modified with 2% chlorhexidine at concentrations of 5% and 10% relative to the total weight of the powder used to construct each sample. Regarding antibacterial effect, 200 samples were established and distributed into four experimental groups and six control groups (4 +ve and 2 -ve), with 20 samples each. The mechanical properties were evaluated in 270 samples, assessing microhardness (30 samples), compressive strength (120 samples), and setting time (120 samples). The groups were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy, and the antibacterial activity of the ionomers was evaluated on Streptococcus mutans for 24 h. The control and positive control groups showed no antibacterial effect, while the experimental group with 5% concentration showed a zone of growth inhibition between 11.35 mm and 11.45 mm, and the group with 10% concentration showed a zone of growth inhibition between 12.50 mm and 13.20 mm. Statistical differences were observed between the experimental groups with 5% and 10% nanotubes. Regarding the mechanical properties, microhardness, and setting time, no statistical difference was found when compared with control groups, while compressive strength showed higher significant values, with ionomers modified with 10% concentration of nanotubes resulting in better compressive strength values. The incorporation of nanotubes at concentrations of 5% and 10% effectively inhibited the presence of S. mutans, particularly when the dose-response relationship was taken into account, with the advantage of maintaining and improving their mechanical properties.

Amine-Functionalized Natural Halloysite Nanotubes Supported Metallic (Pd, Au, Ag) Nanoparticles and Their Catalytic Performance for Dehydrogenation of Formic Acid

In today’s age of resource scarcity, the low-cost development and utilization of renewable energy, e.g., hydrogen energy, have attracted much attention in the world. In this work, cheap natural halloysite nanotubes (HNTs) were modified with γ-aminopropyltriethoxysilane (APTES), and the functionalized HNTs were used as to support metal (Pd, Au, Ag) catalysts for dehydrogenation of formic acid (DFA). The supports and fabricated catalysts were characterized with ICP, FT-IR, XRD, XPS and TEM. The functional groups facilitate the anchoring of metal particles to the supports, which brings about the high dispersion of metallic particles in catalysts. The catalysts show high activity against DFA and exhibit selectivity of 100% toward H2 at room temperature or less. The interactions between active centers and supports were investigated by evaluation and comparison of the catalytic performances of Pd/NH2-HNTs, PdAg/NH2-HNTs and PdAu/NH2-HNTs for DFA.

Recent advancement in polymer/halloysite nanotube nanocomposites for biomedical applications

Halloysite nanotubes (HNTs) have recently been the subject of extensive research as a reinforcing filler. HNT is a natural nanoclay, non-toxic and biocompatible, hence, applicable in biomedical fields. This review focuses on the mechanical, thermal, and functional properties of polymer nanocomposites with HNT as a reinforcing agent from an experimental and theoretical perspective. In addition, this review also highlights the recent applications of polymer/HNT nanocomposites in the biomedical fields.

Halloysite Nanotubes: Smart Nanomaterials in Catalysis

The use of clay minerals as catalyst is renowned since ancient times. Among the different clays used for catalytic purposes, halloysite nanotubes (HNTs) represent valuable resources for industrial applications. This special tubular clay possesses high stability and biocompatibility, resistance against organic solvents, and most importantly be available in large amounts at a low cost. Therefore, HNTs can be efficiently used as catalysts themselves or supports for metal nanoparticles in several catalytic processes. This review reports a comprehensive overview of the relevant advances in the use of halloysite in catalysis, focusing the attention on the last five years.

Development of polymer-based multifunctional composite particles of protease and peroxidase activities

A hybrid material (SL-PPN-HEP-HRP) of dual enzyme function was prepared by co-immobilization of papain (PPN) and horseradish peroxidase (HRP) on sulphate latex (SL) microspheres using heparin (HEP) polyelectrolyte as a building block in the sequential adsorption method. The doses of PPN, HEP and HRP were optimized in each step of the preparation process to achieve high functional and colloidal stability. The enzymes and the polyelectrolyte strongly adsorbed on the oppositely charged surfaces via electrostatic forces, and enzyme leakage was not observed from the hybrid material, as confirmed by colorimetric protein tests and microscopy measurements. It was found that the polyelectrolyte acted as a separator between PPN and HRP to prevent hydrolytic attack on the latter enzyme, which otherwise prevents the joint use of these important biocatalysts. Excellent colloidal stability was obtained for the SL-PPN-HEP-HRP composite and the embedded PPN and HRP showed remarkable protease and peroxidase activities, respectively, at least until five days after preparation. The present results offer a promising approach to develop biocatalytic systems of dual function, which are often required in manufacturing processes in the food industry, where the colloidal stability of such multifunctional materials is a key parameter to achieve remarkable efficiency.

Toxicological Evaluations in Macrophages and Mice Acutely and Chronically Exposed to Halloysite Clay Nanotubes Functionalized with Polystyrene

Halloysite clay nanotubes (HNTs) have been proposed as highly biocompatible for several biomedical applications. Various polymers have been used to functionalize HNTs, but scarce information exists about polystyrene for this purpose. This work evaluated polystyrene-functionalized HNTs (FHNTs) by comparing its effects with non-FHNTs and innocuous talc powder on in vitro and in vivo models. Monocyte-derived human or murine macrophages and the RAW 264.7 cell line were treated with 0.01, 0.1, 1, and 100 μg mL^-1 FHNTs, HNTs, or talc to evaluate the cytotoxic and cytokine response. Our results show that nanoclays did not cause cytotoxic damage to macrophages. Only the 100 μg mL^-1 concentration induced slight proinflammatory cytokine production at short exposure, followed by an anti-inflammatory response that increases over time. CD1 mice treated with a single dose of 1, 2.5, or 5 mg Kg^-1 of FHNTs or HNTs by oral and inhalation routes caused aluminum accumulation in the kidneys and lungs, without bodily signs of distress or histopathological changes in any treated mice, evaluated at 48 h and 30 days post-treatment. Nanoclay administration simultaneously by four different parenteral routes (20 mg Kg^-1) or the combination of administration routes (parenteral + oral or parenteral + inhalation; 25 mg Kg^-1) showed accumulation on the injection site and slight surrounding inflammation 30 days post-treatment. CD1 mice chronically exposed to HNTs or FHNTs in the bedding material (ca 1 mg) throughout the parental generation and two successive inbred generations for 8 months did not cause any inflammatory process or damage to the abdominal organs and the reproductive system of the mice of any of the generations, did not affect the number of newborn mice and their survival, and did not induce congenital malformations in the offspring. FHNTs showed a slightly less effect than HNTs in all experiments, suggesting that functionalization makes them less cytotoxic. Doses of up to 25 mg Kg^-1 by different administration routes and permanent exposure to 1 mg of HNTs or FHNTs for 8 months seem safe for CD1 mice. Our in vivo and in vitro results indicate that nanoclays are highly biocompatible, supporting their possible safe use for future biomedical and general-purpose applications.

Copolyamide-Clay Nanotube Polymer Composite Nanofiber Membranes: Preparation, Characterization and Its Asymmetric Wettability Driven Oil/Water Emulsion Separation towards Sewage Remediation

To address the problem of ever-increasing oily wastewater management, due to its directional liquid transport property, membranes with asymmetric wettability can be effectively used for emulsion separation. This study reports the synthesis of electrospun polymer-clay nanocomposite nanofibers, using co-polyamide polymer (COPA) and halloysite nanotubes (HA) as filler. The influence of clay content on the morphological, thermal and dielectric properties of the polymer composite nanofiber was investigated comprehensively to address the material characteristics of the developed system. The surface structure analysis and contact angle measurements of the electrospun composite nanofibers confirms the change in surface roughness and wettability when the fillers are added to the polymer. The porosity of the composite electrospun nanofiber membrane was found to be 85% with an oil adsorption capacity of 97% and water permeability of 6265 L/m2 h. Furthermore, the asymmetric wettability-driven oil/water emulsion separation abilities of the as-synthesized membranes shows that the separation efficiency of the composite fiber membrane is 10% improved compared to that of the neat fiber membrane, with improved separation time.

Halloysite Nanoclay with High Content of Sulfonic Acid-Based Ionic Liquid: A Novel Catalyst for the Synthesis of Tetrahydrobenzo[b]pyrans

One of the main drawbacks of supported ionic liquids is their low loading and consequently, low activity of the resultant catalysts. To furnish a solution to this issue, a novel heterocyclic ligand with multi imine sites was introduced on the surface of amino-functionalized halloysite support via successive reactions with 2,4,6-trichloro-1,3,5-triazine and 2-aminopyrimidine. Subsequently, the imine sites were transformed to sulfonic acid-based ionic liquids via reaction with 1,4-butanesultone. Using this strategy, high loading of ionic liquid was loaded on halloysite nanoclay. The supported ionic liquid was then characterized with XRD, SEM, TEM, EDS, FTIR, BET, TGA and elemental mapping analysis and utilized as a metal-free Brønsted acid catalyst for promoting one-pot reaction of aldehydes, dimedone and malononitrile to furnish tetrahydrobenzo[b]pyrans. The catalytic tests confirmed high performance of the catalyst. Moreover, the catalyst was stable upon recycling.

Surface modified halloysite nanotubes with different lumen diameters as drug carriers for cancer therapy

Paclitaxel (PTX) is successfully loaded by surface modification of distearoyl phosphoethanolamine (DSPE) on halloysite nanotubes (HNTs) with different inner lumen diameters. Drug loading of DSPE-HNTs-PTX attains 18.44% of DSPE content with a nearly complete release (near 100%) achieved. The anticancer efficacy (cell viability less than 52%) of DSPE-HNTs₁₅-PTX increased and is attributed to the lower interfacial energy both inside and outside the tubes that improves tube loading.

Influence of the Halloysite Nanotube (HNT) Addition on Selected Mechanical and Biological Properties of Thermoplastic Polyurethane

Halloysite nanotube (HNT) additions to the thermoplastic polyurethane (TPU) system were thoroughly evaluated in this study. The resultant composites have been designed for future personalized intervertebral disc implant applications, which requires additional technology to obtain the appropriate geometry unique to each patient. These requirements can be fulfilled using 3D printing. In this work, a technology was developed to produce filaments for fused deposition modeling (FDM). Nanocomposites were prepared using variable HNT content (1, 2, and 3 wt.%). The nanostructure of the resultant composites was confirmed using scanning transmission electron microscopy (STEM). Mechanical tests were used to measure the tensile modulus, stress, and elongation the composites and TPU matrix. Nanocomposites with 2% HNT content were able to withstand 26% increased stress and 50% increased elongation compared to pure TPU before fracturing in addition to a 13% reduction in the friction coefficient. A MTT cytotoxicity assay confirmed the cytotoxicity of all tested materials against human epidermal keratinocyte cells (HaCaT).

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.

Injectable chitosan-quince seed gum hydrogels encapsulated with curcumin loaded-halloysite nanotubes designed for tissue engineering application

The goal of tissue engineering is to assemble functional constructs that restore, maintain, or improve damaged tissues or organs. Hydrogels formed with natural polymers display high potential in artificial scaffolds for tissue repair as they can resemble the extracellular matrices. Thus, the aim of this study was to design nanocomposite hydrogels of chitosan/oxidized-modified quince seed gum/curcumin-loaded in halloysite nanotubes (CS/OX-QSG/CUR-HNTs) for tissue engineering applications. The produced hydrogels were analyzed for thermal stability, degradation, swelling ratio, gelling time and mechanical properties. The results showed that with increasing content of OX-QSG, thermal stability, swelling ratio, and degradation rate of hydrogels were improved. Notably, the optimal CS/OX-QSG hydrogel with ratio of 25:75 exhibited rapid gelation behavior (<50 s) and improved compressive strength (3.96 ± 0.64 MPa), representing the suitable hydrogel for application in tissue engineering. The MTT test showed that these hydrogels were non-toxic and any reduction or stop of NIH-3 T3 cells growth wasn't observed over time. In addition, CS/OX-QSG 25:75 hydrogels containing CUR-HNTs with 10 and 30% content was significantly (P < 0.05) enhanced cell growth and proliferation (around 150%). Obtained results illustrated that CS/OX-QSG hydrogels with ratio of 25:75 and the content of 30% CUR-HNTs can be an effective scaffold for application in tissue engineering.

Surface modified novel magnetically tuned halloysite functionalized sulfonic acid: synthesis, characterization and catalytic activity

The present work demonstrates the synthesis of magnetically tuned halloysite solid acid, the physiochemical properties of which are thoroughly studied using different characterization techniques and has been successfully used for the synthesis of bisamides and 4H-pyrans.

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.

Creating Structured Hydrogel Microenvironments for Regulating Stem Cell Differentiation

The development of distinct biomimetic microenvironments for regulating stem cell behavior and bioengineering human tissues and disease models requires a solid understanding of cell-substrate interactions, adhesion, and its role in directing cell behavior, and other physico-chemical cues that drive cell behavior. In the past decade, innovative developments in chemistry, materials science, microfabrication, and associated technologies have given us the ability to manipulate the stem cell microenvironment with greater precision and, further, to monitor effector impacts on stem cells, both spatially and temporally. The influence of biomaterials and the 3D microenvironment's physical and biochemical properties on mesenchymal stem cell proliferation, differentiation, and matrix production are the focus of this review chapter. Mechanisms and materials, principally hydrogel and hydrogel composites for bone and cartilage repair that create "cell-supportive" and "instructive" biomaterials, are emphasized. We begin by providing an overview of stem cells, their unique properties, and their challenges in regenerative medicine. An overview of current fabrication strategies for creating instructive substrates is then reviewed with a focused discussion of selected fabrication methods with an emphasis on bioprinting as a critical tool in creating novel stem cell-based biomaterials. We conclude with a critical assessment of the current state of the field and offer our view on the promises and potential pitfalls of the approaches discussed.

Polyurethane/Nanosilver-Doped Halloysite Nanocomposites: Thermal, Mechanical Properties, and Antibacterial Properties

In this study, the researchers successfully embellished the surface of halloysite (Ag/HNTs) with silver using halloysite, silver nitrate (AgNO₃), and polyvinylpyrrolidone (PVP). The researchers then prepared polyurethane that contained pyridine ring by using 4,4′-diphenylmethane diisocyanate (MDI) and polytetramethylene glycol (PTMG) as the hard chain segment and the soft chain segment of polyurethane (PU), as well as 2,6-pyridinedimethanol (2,6-PDM) as the chain extension agent. This was followed by the preparation of Ag/HNTs/PUs nanocomposite thin films, achieved by mixing Ag/HNTs with different ratios into polyurethane that contains pyridine ring. First, the Ag/HNTs powders were analyzed using energy-dispersive X-ray spectroscopy, X-ray diffraction, and transmission electron microscopy. Subsequently, Fourier-transform infrared spectroscopy was used to examine the dispersibility of Ag/HNTs in PU, whereas the thermal stability and the viscoelasticity of Ag/HNTs/PU were examined using thermal gravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. When the mechanical properties of Ag/HNTs/PU were tested using a universal strength tester, the results indicated a maximum increase of 109.5% in tensile strength. The researchers then examined the surface roughness and the hydrophobic ability of the Ag/HNTs/PU thin films by using atomic force microscopy and water contact angle. Lastly, antibacterial testing on Escherichia coli revealed that when the additive of Ag/HNTs reached 2.0 wt%, 99.3% of the E. coli were eliminated. These results indicated that the addition of Ag/HNTs into PU could enhance the thermal stability, mechanical properties, and antibacterial properties of PU, implying the potential of Ag/HNTs-02 as biomedicine material.

Nanocontainers for drug delivery systems: A review of Halloysite nanotubes and their properties

Halloysite nanotubes (HNTs) are known as inexpensive and available nanomaterials that are rich in functionality, environmentally benign, and also safe and easy to process. As well, good particle size (i.e. nanoscale) and perfect tubular microstructures of these materials make them to be used extensively as drug carriers. Also, the unique physical and chemical properties of their internal and external surfaces are the greatest priority for the drug encapsulation controlling and releasing. In this review, is tried to emphasis on the main properties of HNTs to manage and develop effective drug delivery tools in the biomedical and pharmaceutical fields.

Ion Specific Effects on the Stability of Halloysite Nanotube Colloids-Inorganic Salts versus Ionic Liquids

Charging and aggregation processes were studied in aqueous dispersions of halloysite nanotubes (HNTs) in the presence of monovalent inorganic electrolytes and ionic liquid (IL) constituents. The same type of co-ion (same sign of charge as HNT) was used in all systems, while the type of counterions (opposite sign of charge as HNT) was systematically varied. The affinity of the inorganic cations to the HNT surface influenced their destabilizing power leading to an increase in the critical coagulation concentration (CCC) of HNT dispersions in the Cs+ < K+ < Na+ order. This trend agrees with the classical Hofmeister series for negatively charged hydrophobic surfaces. For the IL cations, the CCCs increased in the order BMPY+ < BMPIP+ < BMPYR+ < BMIM+. An unexpectedly strong adsorption of BMPY+ cations on the HNT surface was observed giving rise to charge neutralization and reversal of the oppositely charged outer surface of HNT. The direct Hofmeister series was extended with these IL cations. The main aggregation mechanism was rationalized within the classical theory developed by Derjaguin, Landau, Verwey, and Overbeek, while ion specific effects resulted in remarkable variation in the CCC values. The results unambiguously proved that the hydration level of the surface and the counterions plays a crucial role in the formation of the ionic composition at the solid-liquid interface and consequently, in the colloidal stability of the HNT particles in both inorganic salt and IL solutions.

Electrophoretic Deposition of Gentamicin-Loaded ZnHNTs-Chitosan on Titanium

There is a need for titanium (Ti), an antimicrobial implant coating that provides sustained protection against bacterial infection. Chitosan (CS) coatings, combined with halloysite nanotubes (HNTs), are an attractive solution due to the inherent biocompatibility of halloysite, its ability to provide sustained drug release, and the antimicrobial properties of CS. In this study, the electrodeposition (EPD) method was used to coat titanium foil with CS blended with zinc-coated HNTs (ZnHNTs) and pre-loaded with the antibiotic gentamicin. The CS-ZnHNTs-gentamycin sulfate (GS) coatings were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and UV-visible spectroscopy. The coatings were further examined for their ability to sustain GS release, resist bacterial colonization and growth, and prevent biofilm formation. The CS-ZnHNTs-GS coatings were cytocompatible, exhibited significant antimicrobial properties, and supported pre-osteoblast cell proliferation. Hydroxyapatite also formed on the coatings after immersion in simulated body fluid. While the focus in this study was on zinc-coated HNTs doped into CS, our design offers tunability, as different metals can be coated onto the HNT surface and different drugs or growth factors loaded into the HNT lumen. Our results, and the potential for customization, suggest that these coatings have potential in the construction of an array of infection-resistant implant coatings.

3D printed antimicrobial PLA constructs functionalised with zinc- coated halloysite nanotubes-Ag-chitosan oligosaccharide lactate

The control and inhibition of microbial infection are of critical importance for patients undergoing dental or orthopedic surgery. A critical requirement is the prevention of bacterial growth, subsequent bacterial colonization of implant surfaces, and biofilm formation. Among biofilm-forming bacteria, S. aureus and S. epidermidis are the most common bacteria responsible for causing implant-related infections. The ability to produce customized and patient-specific antimicrobial treatments will significantly reduce infections leading to enhanced patient recovery. We propose that 3D-printed antimicrobial biomedical devices for on-demand infection prophylaxis and disease prevention are a rational solution for the prevention of infection. In this study, we modified 3D printed polylactic acid (PLA) constructs using an alkali treatment to increase hydrophilicity and functionalized the surface of the constructs using a suspension of Zinc/HNTs-Ag-Chitosan Oligosaccharide Lactate (ZnHNTs-Ag-COS). The morphologies of printed constructs were analyzed using Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDS), and chemical analysis by Fourier-transform infrared spectroscopy (FTIR). Assessment of the antimicrobial potential of our constructs was assessed using agar diffusion and biofilm assays. The surface of 3D printed PLA constructs were chemically modified to increase hydrophilicity and suspensions of COS-ZnHNTs-Ag were adsorbed on the construct surface. Surface adsorption of ZnHNTs-Ag-COS on PLA printed constructs was determined to be a function of relative pore size. Morphological surface characterization using SEM-EDS confirmed the presence of the suspension coatings on the constructs, and FTIR analysis confirmed the presence of COS-ZnHNTs-Ag in the coatings. The inhibition of bacterial growth was evaluated using the agar diffusion method. Results obtained confirmed the antimicrobial potential of the PLA constructs (which was a function of the Ag content in the material).