Multiwall carbon nanotubes as MRI contrast agents for tracking stem cells

Emerging Graphitic Carbon Nitride-based Nanobiomaterials for Biological Applications

Graphitic carbon nitride (g-CN) based nanostructures are distinctive materials with unique compositional, structural, optical, and electronic properties with exceptional band structure, moderate surface area, and exceptional thermal and chemical stability. Because of these properties, g-CN based nanomaterials have shown promising applications and higher performance in the biological avenue. This review covers the state-of-the-art synthetic strategies used for the preparation of the materials, the basic structure, and a panorama of different optimization strategies leading to improved physicochemical properties responsible for the biological application. The following sections include the recent progress in the use of g-CN based nanobiomaterials for biosensors, bioimaging, photodynamic therapy, drug delivery, chemotherapy, and the antimicrobial segment. Furthermore, we have summarized the role and evaluation of biosafety and biocompatibility of the material. Finally, the unresolved issues, plausible challenges, current status, and future perspectives for the development and design of g-CN have been summarized and are expected to promote a clinical path for the medical sector and human well-being.

Engineered Protein-Iron Oxide Hybrid Biomaterial for MRI-traceable Drug Encapsulation

Labeled protein-based biomaterials have become a popular for various biomedical applications such as tissue-engineered, therapeutic, or diagnostic scaffolds. Labeling of protein biomaterials, including with ultrasmall super-paramagnetic iron oxide (USPIO) nanoparticles, has enabled a wide variety of imaging techniques. These USPIO-based biomaterials are widely studied in magnetic resonance imaging (MRI), thermotherapy, and magnetically-driven drug delivery which provide a method for direct and non-invasive monitoring of implants or drug delivery agents. Where most developments have been made using polymers or collagen hydrogels, shown here is the use of a rationally designed protein as the building block for a meso-scale fiber. While USPIOs have been chemically conjugated to antibodies, glycoproteins, and tissue-engineered scaffolds for targeting or improved biocompatibility and stability, these constructs have predominantly served as diagnostic agents and often involve harsh conditions for USPIO synthesis. Here, we present an engineered protein-iron oxide hybrid material comprised of an azide-functionalized coiled-coil protein with small molecule binding capacity conjugated via bioorthogonal azide-alkyne cycloaddition to an alkyne-bearing iron oxide templating peptide, CMms6, for USPIO biomineralization under mild conditions. The coiled-coil protein, dubbed Q, has been previously shown to form nanofibers and, upon small molecule binding, further assembles into mesofibers via encapsulation and aggregation. The resulting hybrid material is capable of doxorubicin encapsulation as well as sensitive T₂*-weighted MRI darkening for strong imaging capability that is uniquely derived from a coiled-coil protein.

Design and Synthesis of Luminescent Lanthanide-Based Bimodal Nanoprobes for Dual Magnetic Resonance (MR) and Optical Imaging

Current biomedical imaging techniques are crucial for the diagnosis of various diseases. Each imaging technique uses specific probes that, although each one has its own merits, do not encompass all the functionalities required for comprehensive imaging (sensitivity, non-invasiveness, etc.). Bimodal imaging methods are therefore rapidly becoming an important topic in advanced healthcare. This bimodality can be achieved by successive image acquisitions involving different and independent probes, one for each mode, with the risk of artifacts. It can be also achieved simultaneously by using a single probe combining a complete set of physical and chemical characteristics, in order to record complementary views of the same biological object at the same time. In this scenario, and focusing on bimodal magnetic resonance imaging (MRI) and optical imaging (OI), probes can be engineered by the attachment, more or less covalently, of a contrast agent (CA) to an organic or inorganic dye, or by designing single objects containing both the optical emitter and MRI-active dipole. If in the first type of system, there is frequent concern that at some point the dye may dissociate from the magnetic dipole, it may not in the second type. This review aims to present a summary of current activity relating to this kind of dual probes, with a special emphasis on lanthanide-based luminescent nano-objects.

Oxygen Functional Groups on MWCNT Surface as Critical Factor Boosting T2 Relaxation Rate of Water Protons: Towards Improved CNT-Based Contrast Agents

PURPOSE

Salicyl (Sal) - among other oxygen functionalities - multi-walled carbon nanotubes (MWCNTs) and their nanohybrids are investigated as promising contrast agents (CA) in magnetic resonance imaging (MRI) or drug delivery platforms, due to their unique properties. The preliminary results and the literature reports were the motivation to endow high r2 relaxivities, excellent dispersibility in water, and biocompatibility to superparamagnetic MWCNTs nanohybrids. It was hypothesized that these goals could be achieved by, not described in the literature yet, two-stage oxygen functionalization of MWCNTs.

RESULTS

Two structurally different MWCNT materials differing in diameters (44 and 12 nm) and the iron content (4.7% and 0.5%) are studied toward the functionalization effect on the T2 relaxometric properties. MWCNT oxidation is typically the first step of functionalization resulting in "first generation" oxygen functional groups (OFGs) on the surface. Until now, the impact of OFGs on the relaxivity of MWCNT was not truly recognized, but this study sheds light on this issue. By follow-up functionalization of oxidized MWCNT with 4-azidosalicylic acid through [2+1] cycloaddition of the corresponding nitrene, "second generation" of oxygen functional groups is grafted onto the nanohybrid, ie, Sal functionality.

CONCLUSION

The introduced OFGs are responsible for an almost 30% increase in the relaxivity, which leads to remarkable r2 relaxivity of 951 mM-1s-1 (419 (mg/mL)-1s-1), the unprecedented value reported to date for this class of CAs. Also, the resulting nanohybrids express low cytotoxicity and superb diffusion after subcutaneous injection to a mouse.

Influence of Oxidation Degree of Graphene Oxide on Its Nuclear Relaxivity and Contrast in MRI

Graphene oxide (GO) serves as a versatile platform for various applications, with the oxygen content of GO playing an important role in governing its properties. In the present study, different GO types covering a wide range of oxidation degree were prepared using our newly developed two-step method involving ball milling of graphite followed by its oxidation to GO. In addition to the variations in their physicochemical properties, the different GO types exhibited differences in proton relaxivity due to their paramagnetic nature. Nuclear magnetic resonance spectroscopy studies showed that the degree of oxidation of GO perturbs its nuclear relaxation properties and, together with intercalated Mn2+ ions, provides large contrast variation in magnetic resonance imaging (MRI). The study for the first time reveals that the surface chemistry of GO affects its relaxivity and opens up new avenues for developing tunable GO-based contrast agents in magnetic resonance imaging for diagnostics and therapies.

Carbon nanotubes: An effective platform for biomedical electronics

Cylindrical fullerenes (or carbon nanotubes (CNTs)) have been extensively investigated as potential sensor platforms due to effective and practical manipulation of their physical and chemical properties by functionalization/doping with chemical groups suitable for novel nanocarrier systems. CNTs play a significant role in biomedical applications due to rapid development of synthetic methods, structural integration, surface area-controlled heteroatom doping, and electrical conductivity. This review article comprehensively summarized recent trends in biomedical science and technologies utilizing a promising nanomaterial of CNTs in disease diagnosis and therapeutics, based on their biocompatibility and significance in drug delivery, implants, and bio imaging. Biocompatibility of CNTs is essential for designing effective and practical electronic applications in the biomedical field particularly due to their growing potential in the delivery of anticancer agents. Furthermore, functionalized CNTs have been shown to exhibit advanced electrochemical properties, responsible for functioning of numerous oxidase and dehydrogenase based amperometric biosensors. Finally, faster signal transduction by CNTs allows charge transfer between underlying electrode and redox centres of biomolecules (enzymes).

Carbon Nano-Allotrope/Magnetic Nanoparticle Hybrid Nanomaterials as T2 Contrast Agents for Magnetic Resonance Imaging Applications

Magnetic resonance imaging (MRI) is the most powerful tool for deep penetration and high-quality 3D imaging of tissues with anatomical details. However, the sensitivity of the MRI technique is not as good as that of the radioactive or optical imaging methods. Carbon-based nanomaterials have attracted significant attention in biomaterial research in recent decades due to their unique physical properties, versatile functionalization chemistry, as well as excellent biological compatibility. Researchers have employed various carbon nano-allotropes to develop hybrid MRI contrast agents for improved sensitivity. This review summarizes the new research progresses in carbon-based hybrid MRI contrast agents, especially those reported in the past five years. The review will only focus on T2-weighted MRI agents and will be categorized by the different carbon allotrope types and magnetic components. Considering the strong trend in recent bio-nanotechnology research towards multifunctional diagnosis and therapy, carbon-based MRI contrast agents integrated with other imaging modalities or therapeutic functions are also covered.

The Potential of Nanotechnology in Medically Assisted Reproduction

Reproductive medicine is a field of science which searches for new alternatives not only to help couples achieve pregnancy and preserve fertility, but also to diagnose and treat diseases which can impair the normal operation of the reproductive tract. Assisted reproductive technology (ART) is a set of methodologies applied to cases related to infertility. Despite being highly practiced worldwide, ART presents some challenges, which still require special attention. Nanotechnology, as a tool for reproductive medicine, has been considered to help overcome some of those impairments. Over recent years, nanotechnology approaches applied to reproductive medicine have provided strategies to improve diagnosis and increase specificity and sensitivity. For in vitro embryo production, studies in non-human models have been used to deliver molecules to gametes and embryos. The exploration of nanotechnology for ART would bring great advances. In this way, experiments in non-human models to test the development and safety of new protocols using nanomaterials are very important for informing potential future employment in humans. This paper presents recent developments in nanotechnology regarding impairments still faced by ART: ovary stimulation, multiple pregnancy, and genetic disorders. New perspectives for further use of nanotechnology in reproductive medicine studies are also discussed.

Interactions of the innate immune system with carbon nanotubes

The therapeutic application of nanomaterials requires that they are biocompatible and can reach the desired target. The innate immune system is likely to be the first defence machinery that would recognise the nanomaterials as 'non-self'. A number of studies have addressed the issue of how carbon nanotubes (CNTs) interact with phagocytic cells and their surface receptors that can impact on their intracellular processing and subsequent immune response. In addition, soluble innate immune factors also get involved in the recognition and clearance of CNTs. The interaction of CNTs with the complement system, the most potent and versatile innate immune mechanism, has shed interesting light on how complement activation on the surface of CNTs can modulate their phagocytosis and effector cytokine response. The charge or altered molecular pattern on the surface of CNTs due to functionalization and derivatization can also dictate the level of complement activation and subsequent inflammatory response. It is becoming evident that complement deposition may facilitate phagocytic uptake of CNTs through receptor routes that leads to dampening of pro-inflammatory response by complement-receptor bearing macrophages and B cells. Thus, recombinant complement regulators decorated on the CNT surface can constructively influence the therapeutic strategies involving CNTs and other nanoparticles.

Multiwalled carbon nanotube hybrids as MRI contrast agents

Magnetic resonance imaging (MRI) is one of the most commonly used tomography techniques in medical diagnosis due to the non-invasive character, the high spatial resolution and the possibility of soft tissue imaging. Contrast agents, such as gadolinium complexes and superparamagnetic iron oxides, are administered to spotlight certain organs and their pathologies. Many new models have been proposed that reduce side effects and required doses of these already clinically approved contrast agents. These new candidates often possess additional functionalities, e.g., the possibility of bioactivation upon action of particular stimuli, thus serving as smart molecular probes, or the coupling with therapeutic agents and therefore combining both a diagnostic and therapeutic role. Nanomaterials have been found to be an excellent scaffold for contrast agents, among which carbon nanotubes offer vast possibilities. The morphology of multiwalled carbon nanotubes (MWCNTs), their magnetic and electronic properties, the possibility of different functionalization and the potential to penetrate cell membranes result in a unique and very attractive candidate for a new MRI contrast agent. In this review we describe the different issues connected with MWCNT hybrids designed for MRI contrast agents, i.e., their synthesis and magnetic and dispersion properties, as well as both in vitro and in vivo behavior, which is important for diagnostic purposes. An introduction to MRI contrast agent theory is elaborated here in order to point to the specific expectations regarding nanomaterials. Finally, we propose a promising, general model of MWCNTs as MRI contrast agent candidates based on the studies presented here and supported by appropriate theories.

Monitoring/Imaging and Regenerative Agents for Enhancing Tissue Engineering Characterization and Therapies

The past three decades have seen numerous advances in tissue engineering and regenerative medicine (TERM) therapies. However, despite the successes there is still much to be done before TERM therapies become commonplace in clinic. One of the main obstacles is the lack of knowledge regarding complex tissue engineering processes. Imaging strategies, in conjunction with exogenous contrast agents, can aid in this endeavor by assessing in vivo therapeutic progress. The ability to uncover real-time treatment progress will help shed light on the complex tissue engineering processes and lead to development of improved, adaptive treatments. More importantly, the utilized exogenous contrast agents can double as therapeutic agents. Proper use of these Monitoring/Imaging and Regenerative Agents (MIRAs) can help increase TERM therapy successes and allow for clinical translation. While other fields have exploited similar particles for combining diagnostics and therapy, MIRA research is still in its beginning stages with much of the current research being focused on imaging or therapeutic applications, separately. Advancing MIRA research will have numerous impacts on achieving clinical translations of TERM therapies. Therefore, it is our goal to highlight current MIRA progress and suggest future research that can lead to effective TERM treatments.

PEG–MWCNT/Fe hybrids as multi-modal contrast agents for MRI and optical imaging

This study examines the use of oxidized multi-walled carbon nanotube/iron (O-MWCNT/Fe) nanohybrids modified with polyethylene glycol (PEG) as multifunctional cellular imaging agents for magnetic resonance imaging (MRI) and fluorescence microscopy.

Colloidally stabilized magnetic carbon nanotubes providing MRI contrast in mouse liver tumors

The use of medical imaging contrast agents may lead to improved patient prognosis by potentially enabling an earlier detection of diseases and therefore an earlier initiation of treatments. In this study, we fabricated superparamagnetic iron oxide (SPIO) nanoparticles within the inner cavity of multiwalled carbon nanotubes (MWCNTs) for the first time; thereby ensuring high mechanical stability of the nanoparticles. A simple, but effective, self-assembled coating with RAFT diblock copolymers ensured the SPIO-MWCNTs have a high dispersion stability under physiological conditions. In vivo acute tolerance testing in mice showed a high tolerance dose up to 100 mg kg(-1). Most importantly, after administration of the material a 55% increase in tumor to liver contrast ratio was observed with in vivo MRI measurements compared to the preinjection image enhancing the detection of the tumor.

Carbon nanotubes for biomedical imaging: the recent advances

This article reviews the latest progresses regarding the applications of carbon nanotubes (CNTs), including single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs), as multifunctional nano-probes for biomedical imaging. Utilizing the intrinsic band-gap fluorescence of semi-conducting single-walled carbon nanotubes (SWNTs), fluorescence imaging in the near infrared II (NIR-II) region with enhanced tissue penetration and spatial resolution has shown great promise in recent years. Raman imaging based on the resonance Raman scattering of SWNTs has also been explored by a number of groups for in vitro and in vivo imaging of biological samples. The strong absorbance of CNTs in the NIR region can be used for photoacoustic imaging, and their photoacoustic signals can be dramatically enhanced by adding organic dyes, or coating with gold shells. Taking advantages of metal nanoparticle impurities attached to nanotubes, CNTs can also serve as a T2-contrast agent in magnetic resonance (MR) imaging. In addition, when labeled with radioactive isotopes, many groups have developed nuclear imaging with functionalized CNTs. Therefore CNTs are unique imaging probes with great potential in biomedical multimodal imaging.

Water-dispersible magnetic carbon nanotubes as T2-weighted MRI contrast agents

An efficient MRI T2-weighted contrast agent incorporating a potential liver targeting functionality was synthesized via the combination of superparamagnetic iron oxide (SPIO) nanoparticles with multiwalled carbon nanotubes (MWCNTs). Poly(diallyldimethylammonium chloride) (PDDA) was coated on the surface of acid treated MWCNTs via electrostatic interactions and SPIO nanoparticles modified with a potential targeting agent, lactose-glycine adduct (Lac-Gly), were subsequently immobilized on the surface of the PDDA-MWCNTs. A narrow magnetic hysteresis loop indicated that the product displayed superparamagnetism at room temperature which was further confirmed by ZFC (zero field cooling)/FC (field cooling) curves measured by SQUID. The multifunctional MWCNT-based magnetic nanocomposites showed low cytotoxicity in vitro to HEK293 and Huh7 cell lines. Enhanced T2 relaxivities were observed for the hybrid material (186 mM(-1) s(-1)) in comparison with the pure magnetic nanoparticles (92 mM(-1) s(-1)) due to the capacity of the MWCNTs to "carry" more nanoparticles as clusters. More importantly, after administration of the composite material to an in vivo liver cancer model in mice, a significant increase in tumor to liver contrast ratio (277%) was observed in T2 weighted magnetic resonance images.

Are carbon nanotubes a natural solution? Applications in biology and medicine

Carbon nanotubes and materials based on carbon nanotubes have many perceived applications in the field of biomedicine. Several highly promising examples have been highlighted in the literature, ranging from their use as growth substrates or tissue scaffolds to acting as intracellular transporters for various therapeutic and diagnostic agents. In addition, carbon nanotubes have a strong optical absorption in the near-infrared region (in which tissue is transparent), which enables their use for biological imaging applications and photothermal ablation of tumors. Although these advances are potentially game-changing, excitement must be tempered somewhat as several bottlenecks exist. Carbon nanotube-based technologies ultimately have to compete with and out-perform existing technologies in terms of performance and price. Moreover, issues have been highlighted relating to toxicity, which presents an obstacle for the transition from preclinical to clinical use. Although many studies have suggested that well-functionalized carbon nanotubes appear to be safe to the treated animals, mainly rodents, long-term toxicity issues remains to be elucidated. In this report, we systematically highlight some of the most promising biomedical application areas of carbon nanotubes and review the interaction of carbon nanotubes with cultured cells and living organisms with a particular focus on in vivo biodistribution and potential adverse health effects. To conclude, future challenges and prospects of carbon nanotubes for biomedical applications will be addressed.

Novel frontiers in ultra-structural and molecular MRI of the brain

PURPOSE OF REVIEW

Recent developments in the MRI of the brain continue to expand its use in basic and clinical neuroscience. This review highlights some areas of recent progress.

RECENT FINDINGS

Higher magnetic field strengths and improved signal detectors have allowed improved visualization of the various properties of the brain, facilitating the anatomical definition of function-specific areas and their connections. For example, by sensitizing the MRI signal to the magnetic susceptibility of tissue, it is starting to become possible to reveal the laminar structure of the cortex and identify millimeter-scale fiber bundles. Using exogenous contrast agents, and innovative ways to manipulate contrast, it is becoming possible to highlight specific fiber tracts and cell populations. These techniques are bringing us closer to understanding the evolutionary blueprint of the brain, improving the detection and characterization of disease, and help to guide treatment.

SUMMARY

Recent MRI techniques are leading to more detailed and more specific contrast in the study of the brain.