Three dimensional macroporous architectures and aerogels built of carbon nanotubes and/or graphene: synthesis and applications.

Carbon nanotubes and graphene are some of the most intensively explored carbon allotropes in materials science. This interest mainly resides in their unique properties with electrical conductivities as high as 10(4) S cm(-1), thermal conductivities as high as 5000 W m(-1) K and superior mechanical properties with elastic moduli on the order of 1 TPa for both of them. The possibility to translate the individual properties of these monodimensional (e.g. carbon nanotubes) and bidimensional (e.g. graphene) building units into two-dimensional free-standing thick and thin films has paved the way for using these allotropes in a number of applications (including photocatalysis, electrochemistry, electronics and optoelectronics, among others) as well as for the preparation of biological and chemical sensors. More recently and while recognizing the tremendous interest of these two-dimensional structures, researchers are noticing that the performance of certain devices can experience a significant enhancement by the use of three-dimensional architectures and/or aerogels because of the increase of active material per projected area. This is obviously the case as long as the nanometre-sized building units remain accessible so that the concept of hierarchical three-dimensional organization is critical to guarantee the mass transport and, as consequence, performance enhancement. Thus, this review aims to describe the different synthetic processes used for preparation of these three-dimensional architectures and/or aerogels containing either any or both allotropes, and the different fields of application in which the particular structure of these materials provided a significant enhancement in the efficacy as compared to their two-dimensional analogues or even opened the path to novel applications. The unprecedented compilation of information from both CNT- and graphene-based three-dimensional architectures and/or aerogels in a single revision is also of interest because it allows a straightforward comparison between the particular features provided by each allotrope.

Divergent approach to nanoscale glycomicelles and photo-responsive supramolecular glycogels. Implications for drug delivery and photoswitching lectin affinity.

The field of stimuli-responsive supramolecular biomaterials has rapidly advanced in recent years, with potential applications in diverse areas such as cancer theranostics, tissue engineering, and catalysis. However, designing molecular materials that exhibit predetermined hierarchical self-assembly to control the size, morphology, surface chemistry, and responsiveness of the final nanostructures remains a significant challenge. In this study, we present a divergent synthetic approach for the fabrication of spherical micelles and functional 1D-glyconanotube-based photoresponsive gels from structurally related diazobenzene/diacetylene glycolipids. The resulting nanostructures were characterized using NMR, TEM, and SEM, confirming the formation of spherical and tubular nanostructures in both the gel and solution states. Upon UV irradiation, a reversible gel-sol transition was observed, resulting from the photoswitching of the azobenzene unit from the stretched trans form to the compact, metastable cis form. Our gels were shown to enable spatio-temporal control of the adhesion and release of the lectin Concanavalin A, demonstrating potential use as regenerable biomaterials to fight against infections with toxins and pathogens. Additionally, our micelles and gels were evaluated as nanocontainers for loading and controlled release of hydrophobic dyes and antitumoural agents, suggesting their possible use as smart theranostic drug delivery systems.

In situ precipitation of amorphous calcium phosphate and ciprofloxacin crystals during the formation of chitosan hydrogels and its application for drug delivery purposes.

The immobilization of more than one single substance within the structure of a biocompatible polymer provides multifunctional biomaterials with attractive and enhanced properties. In the context of bone tissue engineering, it could be of great interest to synthesize a biomaterial that simultaneously contains amorphous calcium phosphate (ACP), to favor calcium and phosphate precipitation and promote osteogenesis, and an antibiotic such as ciprofloxacin (CFX) that can, eventually, avoid infections resulting after surgical scaffold implantation. However, the co-immobilization of multiple substances is by no means a trivial issue because of the enhanced number of interactions that can take place. One of the main issues is controlling not only the diverse solid forms that individual substances can eventually adopt, but also the forces responsible for the self-organization of the individual components. The latter determines whether phase-separated structures or conjugated architectures are obtained and, consequently, may dramatically affect their functionality. Herein, we have observed-by SEM, TEM, and solid-state NMR-that enzymatically-assisted coprecipitation of ACP and CFX resulted in phase-separated structures. Thus, CFX crystals showed identical morphology to that obtained in the absence of ACP, but the size was smaller. Neither the size nor the morphology of ACP exhibited significant differences whether precipitated with or without CFX, but, in the former case, ACP was stabilized over a wider range of pH and temperature. Finally, by using this methodology and the ice segregation induced self-assembly process (ISISA), we have successfully co-immobilized ACP and CFX in chitosan-based scaffolds. Interestingly, the presence of ACP exerted significant control on the CFX release from these materials.

Phase behavior of elastin-like synthetic recombinamers in deep eutectic solvents.

Deep eutectic solvents promoted the stabilization of the collapsed state of elastin-like recombinamers - and the subsequent formation of aggregates - upon the loss of the structural water molecules involved in hydrophobic hydration. Cryo-etch scanning electron microscopy allowed the observation of these aggregates in neat deep eutectic solvents. The suppression of the lower critical solution temperature transition, observed by differential scanning calorimetry and dynamic light scattering, confirmed the presence of the elastin-like recombinamers in their collapsed state. Actually, the transition from the collapsed to the expanded state was suppressed even after moderate aqueous dilution - for water contents ranging from nil to ca. 45 wt % - and it was only recovered upon further addition of water - above 50 wt %. These features revealed the preferred stabilization of the collapsed state in not only neat deep eutectic solvents but also partially hydrated deep eutectic solvents. We consider that the capability to trigger the lower critical solution temperature transition by partial hydration of deep eutectic solvent may open interesting perspectives for nano(bio)technological applications of elastin-like recombinamers.

Broad-Spectrum Antimicrobial ZnMintPc Encapsulated in Magnetic-Nanocomposites with Graphene Oxide/MWCNTs Based on Bimodal Action of Photodynamic and Photothermal Effects.

Microbial diseases have been declared one of the main threats to humanity, which is why, in recent years, great interest has been generated in the development of nanocomposites with antimicrobial capacity. The present work studied two magnetic nanocomposites based on graphene oxide (GO) and multiwall carbon nanotubes (MWCNTs). The synthesis of these magnetic nanocomposites consisted of three phases: first, the synthesis of iron magnetic nanoparticles (MNPs), second, the adsorption of the photosensitizer menthol-Zinc phthalocyanine (ZnMintPc) into MWCNTs and GO, and the third phase, encapsulation in poly (N-vinylcaprolactam-co-poly(ethylene glycol diacrylate)) poly (VCL-co-PEGDA) polymer VCL/PEGDA a biocompatible hydrogel, to obtain the magnetic nanocomposites VCL/PEGDA-MNPs-MWCNTs-ZnMintPc and VCL/PEGDA-MNPs-GO-ZnMintPc. In vitro studies were carried out using Escherichia coli and Staphylococcus aureus bacteria and the Candida albicans yeast based on the Photodynamic/Photothermal (PTT/PDT) effect. This research describes the nanocomposites' optical, morphological, magnetic, and photophysical characteristics and their application as antimicrobial agents. The antimicrobial effect of magnetics nanocomposites was evaluated based on the PDT/PTT effect. For this purpose, doses of 65 mW·cm-2 with 630 nm light were used. The VCL/PEGDA-MNPs-GO-ZnMintPc nanocomposite eliminated E. coli and S. aureus colonies, while the VCL/PEGDA-MNPs-MWCNTs-ZnMintPc nanocomposite was able to kill the three types of microorganisms. Consequently, the latter is considered a broad-spectrum antimicrobial agent in PDT and PTT.

Clinical Trials of Thermosensitive Nanomaterials: An Overview.

Currently, we are facing increasing demand to develop efficient systems for the detection and treatment of diseases that can realistically improve distinct aspects of healthcare in our society. Sensitive nanomaterials that respond to environmental stimuli can play an important role in this task. In this manuscript, we review the clinical trials carried out to date on thermosensitive nanomaterials, including all those clinical trials in hybrid nanomaterials that respond to other stimuli (e.g., magnetic, infrared radiation, and ultrasound). Specifically, we discuss their use in diagnosis and treatment of different diseases. At present, none of the existing trials focused on diagnosis take advantage of the thermosensitive characteristics of these nanoparticles. Indeed, almost all clinical trials consulted explore the use of Ferumoxytol as a current imaging test enhancer. However, the thermal property is being further exploited in the field of disease treatment, especially for the delivery of antitumor drugs. In this regard, ThermoDox®, based on lysolipid thermally sensitive liposome technology to encapsulate doxorubicin (DOX), is the flagship drug. In this review, we have evidenced the discrepancy existing between the number of published papers in thermosensitive nanomaterials and their clinical use, which could be due to the relative novelty of this area of research; more time is needed to validate it through clinical trials. We have no doubt that in the coming years there will be an explosion of clinical trials related to thermosensitive nanomaterials that will surely help to improve current treatments and, above all, will impact on patients' quality of life and life expectancy.

Emulsion templated scaffolds that include gelatin and glycosaminoglycans.

Gelatin is one of the most commonly used biopolymer for creating cellular scaffolds due to its innocuous nature. To create stable gelatin scaffolds at physiological temperature (37 degrees C), chemical cross-linking is a necessary step. In a previous paper (Biomacromolecules 2006, 7, 3059-3068), cross-linking was carried out by either radical polymerization of the methacrylated derivative of gelatin (GMA) or through the formation of isopeptide bonds catalyzed by transglutaminase. The method of scaffold production was based on emulsion templating in which an organic phase is dispersed in the form of discrete droplets into a continuous aqueous solution of the biopolymer. Both kinds of scaffolds were tested as culture medium for hepatocytes. It turned out that the enzymatic cross-linked scaffold performed superiorily in this respect, even though it was mechanically less stable than the GMA scaffold. In the present paper, in an attempt to improve the biocompatibility of the GMA-based scaffold, biopolymers present in the extracellular matrix (ECM) were included in scaffold formulation, namely, chondroitin sulfate and hyaluronic acid. These biopolymers were derivatized with methacrylic moieties to undergo radical polymerization together with GMA. The morphology of the scaffolds was tuned to some extent by varying the volume fraction of the internal phase and to a larger extent by inducing a controlled destabilization of the precursor emulsion through the use of additives. In this way, scaffolds with 44% of the void volume attributable to voids with a diameter exceeding 60 microm and with 79% of the interconnect area attributable to interconnects with a diameter exceeding 20 microm in diameter could be successfully synthesized. To test whether the inclusion of ECM components into scaffold formulation resolves in an improvement of their biocompatibility with respect to GMA scaffolds, hepatocytes were seeded on both kinds of scaffolds and cell viability and function assays were carried out and compared.

Thermo-Sensitive Nanomaterials: Recent Advance in Synthesis and Biomedical Applications.

Progress in nanotechnology has enabled us to open many new fronts in biomedical research by exploiting the peculiar properties of materials at the nanoscale. The thermal sensitivity of certain materials is a highly valuable property because it can be exploited in many promising applications, such as thermo-sensitive drug or gene delivery systems, thermotherapy, thermal biosensors, imaging, and diagnosis. This review focuses on recent advances in thermo-sensitive nanomaterials of interest in biomedical applications. We provide an overview of the different kinds of thermoresponsive nanomaterials, discussing their potential and the physical mechanisms behind their thermal response. We thoroughly review their applications in biomedicine and finally discuss the current challenges and future perspectives of thermal therapies.

Ice as a Green-Structure-Directing Agent in the Synthesis of Macroporous MWCNTs and Chondroitin Sulphate Composites.

The incorporation of multi-walled carbon nanotubes (MWCNTs) into chondroitin sulphate-based scaffolds and the effect on the structural, mechanical, conductive, and thermal properties of the resulting scaffolds is investigated. Three-dimensional hierarchical materials are prepared upon the application of the ice segregation-induced self-assembly (ISISA) process. The use of ice as structure-directing agents avoids chemicals typically used for this purpose (e.g., surfactants, block copolymers, etc.), hence, emphasising the green features of this soft-templating approach. We determine the critical parameters that control the morphology of the scaffolds formed upon ice-templating (i.e., MWCNTs type, freezing conditions, polymer and MWCNT concentration). MWCNTs are surface functionalized by acidic treatment. MWCNT functionalization is characterized by Raman, Fourier transfer infrared (FTIR) and X-ray Photoelectron (XPS) spectroscopies. Scanning electron microscopy (SEM) analysis and porosity studies reveal that MWCNT content modifies the morphology of the macroporous structure, which decreases by increasing MWCNT concentration. Differences in scaffold morphology should be translated into their conductivity and mechanical properties. As a general trend, the Young's modulus and the electrical conductivity of the scaffolds increase with the MWCNT content. Preliminary biocompatibility tests with human osteoblast-like cells also reveal the capability of these structures to support cell growth.

Mammalian cell cryopreservation by using liquid marbles.

Liquid marbles (LMs) are nonsticky droplets covered by micro- or nanometrically scaled particles and obtained by simply rolling small amounts of a liquid in a very hydrophobic powder. Since pioneer work by Aussillous and Quéré, a wide palette of hydrophobic materials for the preparation of LMs, as well as potential applications, have been reported. Because of the bioinspired origin of this concept, the applicability of LMs in biomedicine is gaining increasing attention, with remarkable advances in their use as microbioreactors for blood typing, drug screening, and tumor growth, among others. Herein, we explore the novel use of LMs as a biotechnological tool for the cryopreservation of mammalian cells as an alternative to conventional methods, which typically require the use of cryopreservant agents that commonly associate with some degree of cell toxicity. Murine L929 fibroblasts, a reference cell line for cytotoxicity studies, and poly(tetrafluoroethylene), a hydrophobic polymer widely used in cardiovascular surgery, were selected for the preparation of the cell-containing LMs. Our results reveal that there is a safe range of droplet volumes and cell densities that can be successfully used to cryopreserve mammalian cell lines and recover them after thawing without significantly affecting major cellular parameters such as adhesion, morphology, viability, proliferation, and cell cycle. We envision that progress in the exploration of cell-containing LMs could also open their impact as microreactors for the miniaturization of cytotoxicity procedures of drugs and materials in which powerful tools for cell evaluation such as flow cytometry could be used because of the elevated amount of cells handled.

Chondroitin sulphate-based 3D scaffolds containing MWCNTs for nervous tissue repair.

Nervous tissue lesions are an important social concern due to their increasing prevalence and their high sanitary costs. Their treatment still remains a challenge because of the reduced ability of nervous tissue to regenerate, its intrinsic structural and functional complexity and the rapid formation of fibroglial scars inhibiting neural repair. Herein, we show that 3D porous scaffolds made of chondroitin sulphate (CS), a major regulatory component of the nervous tissue, and multi-walled carbon nanotubes (MWCNTs) are selective substrates for the formation of a viable and neuron-enriched network with a transitory low glial content. Scaffolds have been fabricated by using the ice segregation-induced self-assembly technique and cultured with embryonic neural progenitor cells. Cell adhesion, morphology, viability, neuron/glial differentiation, calcium signaling dynamics, and mitochondrial activity have been studied over time on the scaffolds and compared to appropriate 2D control substrates. Our results indicate the formation of viable cultures enriched in neuron cells for up to 20 days, with ability to display calcium transients and active mitochondria, even in the absence of poly-D-lysine coating. A synergistic neural-permissive signaling from both the scaffold structure and its components (i.e., MWCNTs and CS) is suggested as the major responsible factor for these findings. We anticipate that these scaffolds may serve nerve regeneration if implanted in the acute phase after injury, as it is during the first stages of graft implantation when the most critical sequence of phenomena takes place to drive either nervous regeneration or fibroglial scar formation. The temporary glial inhibition found may be, indeed, beneficial for promoting the formation of neuron-enriched circuits at early phases while guaranteeing posterior glial integration to support longer-term neuron survival and activity.

Chitosan scaffolds containing calcium phosphate salts and rhBMP-2: in vitro and in vivo testing for bone tissue regeneration.

Numerous strategies that are currently used to regenerate bone depend on employing biocompatible materials exhibiting a scaffold structure. These scaffolds can be manufactured containing particular active compounds, such as hydroxyapatite precursors and/or different growth factors to enhance bone regeneration process. Herein, we have immobilized calcium phosphate salts (CPS) and bone morphogenetic protein 2 (BMP-2)--combined or alone--into chitosan scaffolds using ISISA process. We have analyzed whether the immobilized bone morphogenetic protein preserved its osteoinductive capability after manufacturing process as well as BMP-2 in vitro release kinetic. We have also studied both the in vitro and in vivo biocompatibility of the resulting scaffolds using a rabbit model. Results indicated that rhBMP-2 remained active in the scaffolds after the manufacturing process and that its release kinetic was different depending on the presence of CPS. In vitro and in vivo findings showed that cells grew more in scaffolds with both CPS and rhBMP-2 and that these scaffolds induced more bone formation in rabbit tibia. Thus chitosan scaffolds containing both CPS and rhBMP-2 were more osteoinductive than their counterparts alone indicating that could be useful for bone regeneration purposes, such as some applications in dentistry.

Different cell responses induced by exposure to maghemite nanoparticles.

Recent advances in nanotechnology have permitted the development of a wide repertoire of inorganic magnetic nanoparticles (NPs) with extensive promise for biomedical applications. Despite this remarkable potential, many questions still arise concerning the biocompatible nature of NPs when in contact with biological systems. Herein, we have investigated how controlled changes in the physicochemical properties of iron oxide NPs at their surface (i.e., surface charge and hydrodynamic size) affect, first, their interaction with cell media components and, subsequently, cell responses to NP exposure. For that purpose, we have prepared iron oxide NPs with three different coatings (i.e., dimercaptosuccinic acid - DMSA, (3-aminopropyl)triethoxysilane - APS and dextran) and explored the response of two different cell types, murine L929 fibroblasts and human Saos-2 osteoblasts, to their exposure. Interestingly, different cell responses were found depending on the NP concentration, surface charge and cell type. In this sense, neutral NPs, as those coated with dextran, induced negligible cell damage, as their cellular internalization was significantly reduced. In contrast, surface-charged NPs (i.e., those coated with DMSA and APS) caused significant cellular changes in viability, morphology and cell cycle under certain culture conditions, as a result of a more active cellular internalization. These results also revealed a particular cellular ability to detect and remember the original physicochemical properties of the NPs, despite the formation of a protein corona when incubated in culture media. Overall, conclusions from these studies are of crucial interest for future biomedical applications of iron oxide NPs.

Modulating the cytocompatibility of tridimensional carbon nanotube-based scaffolds.

Carbon nanotubes (CNTs) have lately attracted significant attention in the field of biomedicine. Although a wide repertoire of CNT-based composites has been explored as substrates for cell growth, the fabrication of 3D scaffolds has been more rarely accomplished. Additionally, concerns referred to CNT biocompatibility make their use in biomaterials still controversial. Herein we explore the interaction of three types of CNT-based 3D scaffolds - prepared with multi-walled CNTs and processed to show different architectural and morphological features at the microscale by using three different polymers (i.e., chitosan, chondroitin sulphate and gelatin) - with three types of mammalian cells displaying different sizes and adhesion patterns. Cell-material interaction has been assessed by studying cell viability, adhesion, morphology, and apoptosis. By means of time-lapse confocal laser scanning microscopy, we investigate, for the first time in CNT-based scaffolds, cell migration processes in real time. Scaffolds displaying both a pore size in range with that of cells and lower surface roughness reveal the highest viability values. In contrast, those with a smaller pore size and higher surface roughness account for the lowest cytocompatibility. Results from these studies benefit the fabrication of optimized biomaterials by varying scaffold-dependent parameters in accordance with those of target cells. Furthermore, they may serve to anticipate the response of other cell types sharing similar characteristics to those described herein when in contact with CNT-based scaffolds.

Modulation of stability and mucoadhesive properties of chitosan microspheres for therapeutic gastric application.

Chitosan microspheres have been explored for pharmaceutical applications, namely as a drug delivery systems for Helicobacter pylori gastric infection treatment, due to their mucoadhesive capacity. In this study, a different application of chitosan microspheres is proposed aiming the creation of an H. pylori-binding system where, after oral administration, microspheres will capture and remove these bacteria from infected patients, taking advantage of their muco/bacterial adhesive process. However, mucoadhesion is influenced by the degree of crosslinking necessary to avoid microspheres dissolution in the acidic gastric environment. During this work, the effect of genipin crosslinking on the stability, size, charge and mucoadhesive properties of chitosan microspheres under acidic pH was studied. Chitosan microspheres with ∼170 µm were produced by ionotropic gelation and subsequently covalently crosslinked with genipin in different degrees. The crosslinking reaction was followed by infrared spectroscopy and time-lapse fluorescence microscopy, since we have demonstrated that the fluorescence intensity of chitosan microspheres increases with genipin chemical bonding to chitosan. Results showed that both the zeta potential and the swelling capacity of chitosan microspheres decrease with increasing crosslinking. When immersed in simulated gastric fluid (SGF) with pepsin for 7 days, chitosan microspheres crosslinked with 10mM of genipin for 1h did not dissolve and doubled their size to approximately 345 µm. Furthermore, they maintained their in vitro mucoadhesion to soluble gastric mucins at both pH tested (3.6 and 6.5) and presented an in vivo retention time of around 2h in the stomach of C57BL/6 mice.

Influence of dialkyne structure on the properties of new click-gels based on hyaluronic acid.

Hydrogels have been widely used in tissue engineering as a support for tissue formation and/or to deliver drug locally. A novel procedure for the in situ rapid chemical gelation of aqueous solutions of hyaluronan (HA) was employed. HA was functionalised with an arm bearing a terminal azido group (HAAA). When HAAA was mixed with a series of dialkyne reagents of different length, a 1,3-dipolar cycloaddition ("click-chemistry") reaction took place in the presence of catalytic amount of Cu(I) resulting in fast gelation at room temperature. The resulting gels were characterised in terms of degree of cross-linking by (1)H HR-MAS NMR. The kinetic of gelation and the determination of elastic moduli as well as the degree of swelling and the controlled release of a model drug, were studied as a function of chemical nature of the dialkyne group, catalyst concentration, HAAA concentration and temperature. All these variables allowed the swelling ratio and the extent of release of a drug, doxorubicin, entrapped within the gel, to be modulated. In all cases the kinetic of release reached the stationary state within 150 h. The height of the plateau was dependent on the overall (chemical and topological) degree of cross-linking.

Novel hydrogels via click chemistry: synthesis and potential biomedical applications.

A novel procedure for the in situ rapid chemical gelation of aqueous solutions of hyaluronan has been employed. In brief, water-soluble polysaccharide derivatives bearing side chains endowed with either azide or alkyne terminal functionality have been prepared. When the latter two types of derivatives are mixed together in aqueous solution they give rise to a 1,3-dipolar cycloaddition reaction resulting in fast gelation (in the presence of catalytic amounts of Cu(I)) at room temperature. Gel formation has been characterized rheologically and could also be followed qualitatively by means of IR spectroscopy. The resulting gels have been studied in terms of swelling properties and, in particular, NMR spectral features. Carrying out the gelation process in aqueous solutions of benzidamine and doxorubicin, respectively, the polysaccharide networks acted as drug reservoirs. The doxorubicin release resulted in well controllable acting upon the gels degree of cross-linking. Finally, formation of the click-gels using aqueous suspensions of Saccharomices cerevisiae yeast cells allowed the obtainment of scaffolds inside which cells were homogeneously distributed and smoothly adhered to the inner pores surfaces, according to SEM analysis. After 24 h about 60% of the entrapped cells exhibited proliferating activity. Click-gels prepared as detailed herein do have a number of positive features that make them, in perspective, materials of choice for drug release and tissue engineering manipulations.