Marianne E. Mertens

Nanoparticles for imaging: top or flop?

Nanoparticles are frequently suggested as diagnostic agents. However, except for iron oxide nanoparticles, diagnostic nanoparticles have been barely incorporated into clinical use so far. This is predominantly due to difficulties in achieving acceptable pharmacokinetic properties and reproducible particle uniformity as well as to concerns about toxicity, biodegradation, and elimination. Reasonable indications for the clinical utilization of nanoparticles should consider their biologic behavior. For example, many nanoparticles are taken up by macrophages and accumulate in macrophage-rich tissues. Thus, they can be used to provide contrast in liver, spleen, lymph nodes, and inflammatory lesions (eg, atherosclerotic plaques). Furthermore, cells can be efficiently labeled with nanoparticles, enabling the localization of implanted (stem) cells and tissue-engineered grafts as well as in vivo migration studies of cells. The potential of using nanoparticles for molecular imaging is compromised because their pharmacokinetic properties are difficult to control. Ideal targets for nanoparticles are localized on the endothelial luminal surface, whereas targeted nanoparticle delivery to extravascular structures is often limited and difficult to separate from an underlying enhanced permeability and retention (EPR) effect. The majority of clinically used nanoparticle-based drug delivery systems are based on the EPR effect, and, for their more personalized use, imaging markers can be incorporated to monitor biodistribution, target site accumulation, drug release, and treatment efficacy. In conclusion, although nanoparticles are not always the right choice for molecular imaging (because smaller or larger molecules might provide more specific information), there are other diagnostic and theranostic applications for which nanoparticles hold substantial clinical potential.

Theranostic Systems and Strategies for Monitoring Nanomedicine-Mediated Drug Targeting

Nanomedicine formulations are considered to be superior to standard low-molecular-weight drugs because of an increased drug accumulation at the pathological site and a decreased localization to healthy non-target tissues, together leading to an improved balance between the efficacy and the toxicity of (chemo-) therapeutic interventions. To better understand and further improve nanomedicine-mediated drug targeting, it is important to design systems and strategies which are able to provide real-time feedback on the localization, the release and the therapeutic efficacy of these formulations. The advances made over the past few years with regard to the development of novel imaging agents and techniques have provided a broad basis for the design of theranostic nanomedicine materials, i.e. multicomponent carrier constructs in which drugs and imaging agents are combined, and which can be used to address issues related to drug localization, drug release and drug efficacy. Here, we summarize several recent efforts in this regard, and we show that theranostic systems and strategies hold significant potential for monitoring and improving nanomedicine-mediated drug targeting.

Enhanced In Vitro and In Vivo Cellular Imaging with Green Tea Coated Water-Soluble Iron Oxide Nanocrystals

Fully green and facile redox chemistry involving reduction of colloidal iron hydroxide (Fe(OH)3) through green tea (GT) polyphenols produced water-soluble Fe3O4 nanocrystals coated with GT extracts namely epigallocatechin gallate (EGCG) and epicatechin (EC). Electron donating polyphenols stoichiometrically reduced Fe(3+) ions into Fe(2+) ions resulting in the formation of magnetite (Fe3O4) nanoparticles and corresponding oxidized products (semiquinones and quinones) that simultaneously served as efficient surface chelators for the Fe3O4 nanoparticles making them dispersible and stable in water, PBS, and cell culture medium for extended time periods. As-formed iron oxide nanoparticles (2.5-6 nm) displayed high crystallinity and saturation magnetization as well as high relaxivity ratios manifested in strong contrast enhancement observed in T2-weighted images. Potential of green tea-coated superparamagnetic iron oxide nanocrystals (SPIONs) as superior negative contrast agents was confirmed by in vitro and in vivo experiments. Primary human macrophages (J774A.1) and colon cancer cells (CT26) were chosen to assess cytotoxicity and cellular uptake of GT-, EGCGq-, and ECq-coated Fe3O4 nanoparticles, which showed high uptake efficiencies by J774A.1 and CT26 cells without any additional transfection agent. Furthermore, the in vivo accumulation characteristics of GT-coated Fe3O4 nanoparticles were similar to those observed in clinical studies of SPIONs with comparable accumulation in epidermoid cancer-xenograft bearing mice. Given their promising transport and uptake characteristics and new surface chemistry, GT-SPIONs conjugates can be applied for multimodal imaging and therapeutic applications by anchoring further functionalities.

FMN-coated fluorescent USPIO for cell labeling and non-invasive MR imaging in tissue engineering

Non-invasive magnetic resonance imaging (MRI) is gaining significant attention in the field of tissue engineering, since it can provide valuable information on in vitro production parameters and in vivo performance. It can e.g. be used to monitor the morphology, location and function of the regenerated tissue, the integrity, remodeling and resorption of the scaffold, and the fate of the implanted cells. Since cells are not visible using conventional MR techniques, ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles are routinely employed to label and monitor the cells embedded in tissue-engineered implants. We here set out to optimize cell labeling procedures with regard to labeling efficiency, biocompatibility and in vitro validation during bioreactor cultivation, using flavin mononucleotide (FMN)-coated fluorescent USPIO (FLUSPIO). Efficient FLUSPIO uptake is demonstrated in three different cell lines, applying relatively short incubation times and low labeling concentrations. FLUSPIO-labeled cells were successfully employed to visualize collagen scaffolds and tissue-engineered vascular grafts. Besides promoting safe and efficient cell uptake, an exquisite property of the non-polymeric FMN-coating is that it renders the USPIO fluorescent, providing a means for in vitro, in vivo and ex vivo validation via fluorescence microscopy and fluorescence reflectance imaging (FRI). FLUSPIO cell labeling is consequently considered to be a suitable tool for theranostic tissue engineering purposes.

Magnetic resonance imaging in zirconia‐based dental implantology

OBJECTIVES X-ray-based planning and post-implantation assessment of titanium implants is the commonly accepted standard to date. However, new implant materials such as zirconia (ZrO2 ) have become available, and magnetic resonance imaging may be a valuable alternative with these implants. The present in vitro study investigated artifacts produced by titanium and zirconia implants in magnetic resonance imaging (MRI) and assessed the accuracy of pre-implant planning and post-implantation assessment comparing MRI to standard X-ray-based imaging modalities: Orthopantomogram (OPT), cone beam (CBCT), and computed tomography (CT). MATERIALS AND METHODS Twelve porcine mandibles were prepared and scanned (MRI, OPT, CBCT, μCT), and bone height above the nerve canal was measured. Specimens were implanted with either two titanium or zirconia implants and rescanned to investigate the influence of implant materials on post-implantation assessment. MRI and μCT artifacts were quantified with implants embedded in gelatin phantoms and porcine specimens. RESULTS Compared with CBCT set as standard, μCT, OPT, and MRI showed similar accuracy in pre-op bone height measurements. Post-implantation, while titanium implants induced a strong B0 -field distortion resulting in extensive signal voids, zirconia implants were clearly depictable with only minor distortions. CONCLUSIONS Excellent contrast, limited artifacts, radiation-free and accurate implant assessment may indicate that MRI is a valuable imaging alternative for zirconia-based implant dentistry.

Nondestructive monitoring of tissue-engineered constructs

Abstract Tissue engineering as a multidisciplinary field enables the development of living substitutes to replace, maintain, or restore diseased tissue and organs. Since the term was introduced in medicine in 1987, tissue engineering strategies have experienced significant progress. However, up to now, only a few substitutes were able to overcome the gap from bench to bedside and have been successfully approved for clinical use. Substantial donor variability makes it difficult to predict the quality of tissue-engineered constructs. It is essential to collect sufficient data to ensure that poor or immature constructs are not implanted into patients. The fulfillment of certain quality requirements, such as mechanical and structural properties, is crucial for a successful implantation. There is a clear need for new nondestructive and real-time online monitoring and evaluation methods for tissue-engineered constructs, which are applicable on the biomaterial, tissue, cellular, and subcellular levels. This paper reviews current established nondestructive techniques for implant monitoring including biochemical methods and noninvasive imaging.

Non-invasive Imaging of Tissue-Engineered Vascular Endothelium with Iron Oxide Nanoparticles

J. Frese, L. Hrdlicka, M. E. Mertens, L. Rongen, S. Koch, P. Schuster, V.N. Gesché, T. Lammers, P. Mela, F. Kiessling, S. Jockenhoevel Department of Tissue Engineering & Textile Implants, Institute of Applied Medical Engineering, RWTH Aachen University, Aachen, Germany, frese@hia.rwth-aachen.de Department of Experimental Molecular Imaging, RWTH-Aachen University, Aachen, Germany, Department of Tissue Engineering & Textile Implants, Institut für Textiltechnik, RWTH Aachen University, Aachen Germany

Fluorinated Polyurethane Scaffolds for 19F Magnetic Resonance Imaging

Polymers are increasingly employed in implant materials. To reduce the incidence of complications, which in the case of vascular grafts include incorrect placement and restenosis, materials are needed which allow for image-guided implantation, as well as for accurate and efficient postoperative implant imaging. We here describe amorphous fluorinated polymers based on thermoplastic polyurethane (19F-TPU), and show that are useful starting materials for developing tissue-engineered vascular grafts which can be detected using 19F MRI.

Generation and imaging of patient customized implants

Personalized medicine is the development of individual solutions and therapies tailored to the specific disease pattern of a patient. To enable patient customized medical solutions 40 partners of the Aachen Research Cluster “innovation medical technology in.nrw” are investigating a new generation of biomedical devices and systems. The subproject Patim addresses non-invasive monitoring techniques to observe dynamic changes in tissue engineered cardiovascular implants.