Magnetic Targeting System Research Articles

A multiphysics model of magnetic hydrogel under a moving magnet for targeted drug delivery

A remarkable characteristics of magnetic hydrogel is its ability to dramatically alter its morphology and location in a remote way. Herein, a three-dimensional (3D) multiphysics model is presented to study the motion and deformation of the drug-loaded magnetic hydrogel in a moving fluid under an varying magnetic field created by a moving magnet. The magneto-chemo-hydro-mechanical model allows for nonlinear finite deformation, and the governing equations are formulated by balances of mass and forces. The constitutive relations are achieved via the second law of thermodynamics. In particular, the fluid-structure interaction is considered between the magnetic hydrogel and its surrounding fluid. After validation with theoretical works, the movable and deformable behaviors of the magnetic hydrogel are then studied under varying magnetic velocity, hydrogel radius, magnetic field strength, and fluid flow velocity. Results show that the slower moving magnet, the larger hydrogel radius and the flow velocity can shorten the time for the hydrogel to reach the channel outlet. In addition, the magnetic targeting system is obtained for transporting the drug-loaded hydrogel to the specific site through controlling the magnet velocity and the maximum magnetic field strength. The present multiphysics model may provide theoretical guidance in design and optimization of magnetic hydrogel-based drug targeting system.

Regenerative capacity of bone marrow stem cells with or without superparamagnetic iron oxide nanoparticles after facial nerve degeneration: A narrative review

Facial palsy can be defined as a kind of paralysis affecting facial muscles. It is termed Bell’s palsy if it is unilateral. It may occur due to trauma to the facial nerve, infections as herpes zoster, neoplastic lesions, or unknown cause. It may be also associated with metabolic and systemic diseases as hypertension, toxicity, amyloidosis, alcoholism, auto-immune diseases and diabetes mellitus. Mesenchymal stem cells (MSCs) are multipotent adult stromal cells that have many benefits as an evolving treatment modality. Bone marrow stem cells (BMSCs) divide progressively in culture, and differentiate into neurons exclusively with use of a simple protocol. Most ongoing preclinical and clinical cell treatment modalities composed of local or systemic transplantation of stem or progenitor cells. In addition, they depend on the migration and retention of transplanted cells at insult areas. Nevertheless, one of the main obstacles against this modality is how to detect the fate and exact location of these cells inside the body, and how to maintain the cells at this specific site. Magnetic targeting systems, which depends on cells labelled by magnetic carriers, have been assessed as a more efficient technique for stem cell delivery to target sites. These systems depend on loading stem cells with magnetic nanoparticles and attracting them to the exact intended area within the body by placing an external magnetic field. Superparamagnetic iron oxide nanoparticles (SPIONs) have been introduced in the last few years as a rising applicant of nanoparticles in a vast variety of medical fields as magnetic separation, drug delivery, magnetic resonance imaging (MRI) and magnetic hyperthermia. In addition, applications of SPIONs, as a site-specific drug carrier, diagnostic agent and stem cell delivery agent, receive most attention of researchers in that field. In this review, up-to-date information about Magnetic targeting of degenerated facial nerve by BMSCs labelled with SPIONs may suggest its capacity of better regeneration than injection of BMSCs alone.

Magnetization‐Switchable Implant System to Target Delivery of Stem Cell‐Loaded Bioactive Polymeric Microcarriers

Various magnetic microcarrier systems capable of transporting cells to target lesions are developed for therapeutic agent-based tissue regeneration. However, the need for bioactive molecules and cells, the potential toxicity of the microcarrier, and the large volume and limited workspace of the magnetic targeting device remain challenging issues associated with microcarrier systems. Here, a multifunctional magnetic implant system is presented for targeted delivery, secure fixation, and induced differentiation of stem cells. This magnetic implant system consists of a biomaterial-based microcarrier containing bioactive molecules, a portable magnet array device, and a biocompatible paramagnetic implant. Among biomedical applications, the magnetic implant system is developed for knee cartilage repair. The various functions of these components are verified through in vitro, phantom, and ex vivo tests. As a result, a single microcarrier can load ≈1.52 ng of transforming growth factor β (TGF-β1) and 3.3 × 103 of stem cells and stimulate chondrogenic differentiation without extra bioactive molecule administration. Additionally, the implant system demonstrates high targeting efficiency (over 90%) of the microcarriers in a knee phantom and ex vivo pig knee joint. The results show that this implant system, which overcomes the limitations of the existing magnetic targeting system, represents an important advancement in the field.

Magnetic Targeting Systems for Endo-Bronchoscope Diagnosis and Intramedullary-Nail Surgery: A Review

Nowadays, magnetic targeting systems are developed for clinical/surgical applications, such as treatment of carotid artery aneurysm, endo-bronchoscopic diagnosis for lung-cancer tumors, colonoscopic diagnosis for colon-cancer tumors, and intramedullary interlocking-nail surgery. Based on clinical requirements, the targeting systems specific for above endo-bronchoscopic diagnosis and nail surgery are urgently needed and thus rapidly developed. Moreover, because the systems have similar magnetic configurations and use similar magnetic targeting principles, the systems can be reviewed together. Endo-bronchoscopic diagnosis is a new clinical-proved method for doctors to diagnose lung-cancer tumors/lesions. However, in the diagnosis, targeting the endo-bronchoscope to tumors/lesions must be repeated many times and thereby is inconsistent. Thus, diagnosis-yield decreases and diagnosis-duration increases. To address this issue, researchers developed novel magnetic targeting systems to more accurately and rapidly target the endo-bronchoscope, i.e., increase yield and save time. The systems are categorized to magnetic-sensors based and magnetic-materials based targeting systems. Representative systems are reviewed (design, targeting principles, test methods, results, and features are highlighted) in this paper. Intramedullary interlocking-nail surgery is a standard clinical-method for fractured-bones. In the surgery, 2D X-ray imaging system is a conventional most-used method to target distal screw-hole of the nail for fractured-bones fixing. However, patients are over-exposed under X-ray radiation. To solve this problem, researchers presented innovative magnetic targeting systems to target the screw-hole without any X-ray radiation. Same as above-section, the systems are divided to magnetic-sensors based and magnetic-materials based targeting systems. Representative systems and corresponding design, targeting principles, test methods, results, and features are reviewed in this paper.

Magnetic Targeting of HU-MSCs in the Treatment of Glucocorticoid-Associated Osteonecrosis of the Femoral Head Through Akt/Bcl2/Bad/Caspase-3 Pathway.

PurposeOsteonecrosis of the femoral head (ONFH) is a chronic and irreversible disease that eventually develops into a joint collapse and results in joint dysfunction. Early intervention and treatment are essential for preserving the joints and avoiding hip replacement. In this study, a system of human umbilical mesenchymal stem cells-supermagnetic iron oxide nanoparticles (NPs) @polydopamine (SCIOPs) was constructed. The magnetic targeting system gathers in the lesion area, inhibits the apoptosis of bone cells, enhances osteogenic effect, and effectively treats ONFH under external magnetic field.Materials and MethodsThe supermagnetic iron oxide NPs @polydopamine (SPION@PDA NPs) were characterized by transmission electron microscopy and zeta potential, respectively. The effects of SPION@PDA NPs on the viability, proliferation, and differentiation of stem cells were detected by the CCK8 method, flow cytometry, and staining, respectively. The serum inflammatory indicators were detected by Luminex method. The bone mass of the femoral head was analyzed by micro computed tomography. The expression of apoptosis and osteoblast-related cytokines was detected by Western blotting. The osteogenesis of the femoral head was detected by histological and immunohistochemical sections.ResultsThe SCIOPs decreased the pro-inflammatory factors, and the micro CT showed that the bone repair of the femoral head was enhanced after treatment. The hematoxylin and eosin sections also showed an increase in the osteogenesis in the femoral head. Western blotting results showed and increased expression of anti-apoptotic proteins Akt and Bcl-2, decreased expression of apoptotic proteins caspase-3 and Bad, and increased expression of osteogenic proteins Runx-2 and Osterix in the femoral head.ConclusionUnder the effect of magnetic field and homing ability of stem cells, SCIOPs inhibited the apoptosis of osteoblasts, improved the proliferation ability of osteoblasts, and promoted bone repair in the femoral head through the Akt/Bcl-2/Bad/caspase-3 signaling pathway, thereby optimizing the tissue repair ability.

Tale of Two Magnets: An Advanced Magnetic Targeting System.

Magnetic targeting strategies employ external magnet fields to manipulate magnetic nanoparticles (MNPs) remotely, aiming to enhance their accumulation and penetration in vivo, which have received increasing attention in drug-delivery systems over the past decades. However, this approach has not yet been successful in translational clinical studies, largely due to the low efficacy and uncontrollable distribution of MNPs. The standard magnetic targeting strategy uses a single magnet and, thus, suffers from rapid drop-off of the magnetic field and field gradient with increasing distance away from the magnet surface. As a result, magnetic targeting of MNPs is often limited to superficial regions of interest. As reported in this issue of ACS Nano, Andrew Tsourkas and his colleagues showed that a two-magnet configuration can solve this dilemma by introducing a constant field gradient between the magnets for advanced magnetic targeting. The custom-built two-magnet device evidenced greatly enhanced accumulation and penetration of MNPs in a solid tumor model, shedding new light on future design considerations of magnetic targeting systems.

Computational simulation of electromagnetic fields on human targets for magnetic targeting applications.

In the last few years, the use of nanoparticles for therapeutic applications has attracted the interest of many scientists, who are looking for effective methods to target nanoparticles linked to drugs directly to the diseased organs. Among them, magnetic targeting consists of magnetic systems (magnets or coils) which can impress high gradient magnetic fields and then magnetic forces on the magnetic nanoparticles. Despite some studies have reported an effective improvement in drug delivery by using this technique, there is still a paucity of studies able to quantify and explain the experimental results. In this scenario, "in silico" models allow to analyze and compare different magnetic targeting systems in their ability to generate the required magnetic field gradient for specific human targets.In this paper we then evaluated, by means of computational electromagnetics techniques, the attitude of various ad-hoc designed magnetic systems in targeting the heart tissues of differently aged human anatomical models.

Optimization of Deformable Magnetic-Sensitive Hydrogel-Based Targeting System in Suspension Fluid for Site-Specific Drug Delivery.

For optimization of the targeting performance of the magnetic hydrogel subject to the magneto-chemo-hydro-mechanical coupled stimuli, a multiphysics model for a suspension fluid flow in a blood vessel is developed, in which a deformable magnetic-sensitive hydrogel-based drug targeting system moves with fluid. In this model, the fluid-structure interaction of the movable and deformable magnetic hydrogel with surrounding fluid flow is characterized through the fully coupled arbitrary Lagrangian-Eulerian algorithm. Moreover, the four physicochemical responsive mechanisms are considered, including hydrogel magnetization, solvent diffusion, fluid flow, and nonlinear large deformation. After the present model is examined by the experimental data in open literature, the transient behaviors of the motion and deformation of the magnetic hydrogel are investigated in suspension flow. It is found that the higher flow velocity and/or the larger hydrogel size accelerate the movement of the hydrogel, while the smaller hydrogel size contributes to the larger swelling ratio. Furthermore, the performance of the magnetic targeting system is optimized for delivering the drug-loaded hydrogel to the desired site by tuning the maximum magnetic field strength, the maximum inlet flow velocity, and the magnet position. Therefore, it is confirmed that the present optimizable magnetic hydrogel-based drug targeting system via the multiphysics model may provide a promising efficient platform for site-specific drug delivery.

Effects of static magnetic fields on natural or magnetized mesenchymal stromal cells: Repercussions for magnetic targeting

The magnetic targeting (MT) technique improves delivery of mesenchymal stromal cells (MSCs) to target sites. However, the moderate-intensity static magnetic fields (SMF) used for MT may exert adverse effects on MSCs. Thus, we aimed to evaluate the effects of SMF on MSCs in vitro. Cells were initially magnetized using citrate-coated magnetite nanoparticles. Then, control and magnetized MSCs were transferred to an in vitro MT system and exposed to 0.3–0.45 Tesla SMFs. MSC viability, morphology, ultrastructure, proliferation rates, differentiation, and immunomodulation were evaluated after 24 and 48 hours of exposure. MSCs temporarily lost viability and exhibited ultrastructural changes after exposure to SMFs, regardless of magnetization. Moreover, exposure to SMF reduced magnetized MSC proliferation rates. Nevertheless, MSCs remained functional (i.e., capable of differentiating, secreting repair mediators, and modulating alveolar macrophage phenotype). Thus, the experimental protocol tested in this experiment can be applied in future in vivo MT studies.

Cell Magnetic Targeting System for Repair of Severe Chronic Osteochondral Defect in a Rabbit Model.

The aim of this study was to investigate a cell delivery system for repair of severe chronic osteochondral defects using magnetically labeled mesenchymal stem cells (m-MSCs), with the aid of an external magnetic device, through the accumulation of a small number of m-MSCs into a desired area and to detect the suitable number of autologous m-MSCs needed for repair of the defect. Twenty-six male Japanese white rabbits aged 6 months were used. An osteochondral defect was created bilaterally at the weight-bearing surface of the medial femoral condyle of the rabbits' knees (3 mm diameter; 4 mm depth). At 4 weeks after creation of the defect, autogenic transplantation of the m-MSCs into the defect area was performed, followed by 10-min exposure to an external magnetic device, where animals were divided into four groups: high (1 × 10(6) m-MSCs), medium (2 × 10(5) m-MSCs), low (4 × 10(4) m-MSCs), and control (PBS injection). At 4 and 12 weeks posttransplantation of m-MSCs, repaired tissue was assessed histologically using the Fortier score with toluidine blue staining. Transplantation of a low number of m-MSCs was not enough to improve osteogenesis and chondrogenesis, but the medium and high groups improved repair of the chronic defect with chondrogenic tissues and showed histologically significantly better results than the control and low groups. The use of a magnetic targeting system for delivering m-MSCs has the potential to overcome the clinical hurdles for repair of the severe chronic osteochondral defect. Furthermore, this system is predicted to produce good clinical outcomes for humans, not only to repair osteochondral defects but also to repair a variety of damaged tissues.

Note: Magnetic targeting for enhancement of the activation efficiency of G protein-coupled receptor with a two-pair coil system.

Insufficient contact of drug with target cells is a primary reason for limited efficiency of G protein-coupled receptor activation. To overcome this limitation, a simple approach based on magnetic targeting for enhancing drug delivery towards the cell surfaces using magnetic nanoparticles and a two-pair coil system consisting of Helmholtz and Maxwell coils was reported. As a proof of the concept, comparative experiments on G protein-coupled receptor activation process were carried out and results show that the efficiency of G protein-coupled receptor activation can be increased about 6 times in the experiments with the aid of the proposed magnetic targeting system.

Effects of Magnetically Guided, SPIO-Labeled, and Neurotrophin-3 Gene-Modified Bone Mesenchymal Stem Cells in a Rat Model of Spinal Cord Injury.

Despite advances in our understanding of spinal cord injury (SCI) mechanisms, there are still no effective treatment approaches to restore functionality. Although many studies have demonstrated that transplanting NT3 gene-transfected bone marrow-derived mesenchymal stem cells (BMSCs) is an effective approach to treat SCI, the approach is often low efficient in the delivery of engrafted BMSCs to the site of injury. In this study, we investigated the therapeutic effects of magnetic targeting of NT3 gene-transfected BMSCs via lumbar puncture in a rat model of SCI. With the aid of a magnetic targeting cells delivery system, we can not only deliver the engrafted BMSCs to the site of injury more efficiently, but also perform cells imaging in vivo using MR. In addition, we also found that this composite strategy could significantly improve functional recovery and nerve regeneration compared to transplanting NT3 gene-transfected BMSCs without magnetic targeting system. Our results suggest that this composite strategy could be promising for clinical applications.

Design of site-directed magnetic targeting system in acute spinal cord injury.

Effective repair immediately after spinal cord injury can improve the prognosis of the patient. Injection of membrane resealing nanomaterial is one of the most promising technique to repair the membrane. In order to improve the retention rate of membrane repair material at injury site, membrane resealing nanomaterial can be combined with magnetic nanoparticle and magnetic targeting system. In this paper, a special site directed magnetic targeting system, which contain a C-shaped permanent magnet and a ferromagnetic needle, was constructed. Simulation was conducted to analyze the influence of the shape of needle on the magnetic field to provide magnetic force large enough to make the magnetic particles stay at the target site. Results showed that the appearance of ferromagnetic needle raised both the strength and the gradient of magnetic field at the target site. Moreover, with similar apex angles, longer needles with larger diameters can produced lager magnetic field, but smaller needles has better focal area at the small injury site in spinal cord injury. These results provide a basis for design and fabrication of ferromagnetic needles when the targeting system is applied in future experiments.

In Vivo Kinetics of Mesenchymal Stem Cells Transplanted into the Knee Joint in a Rat Model Using a Novel Magnetic Method of Localization.

We have developed a magnetic system for targeting cells in minimally invasive cell transplantation. Magnetically labeled MSCs (m-MSCs) with nanoscale iron particles can be guided into the desired region by magnetic force from an extracorporeal device. We reported that magnetic targeting of m-MSCs enhances cartilage repair in a mini-pig model. However, the detailed kinetics of these magnetically targeted m-MSCs remain unknown. For clinical use, this aspect should be clarified from a safety standpoint. We therefore investigated the spatial and temporal distribution of the fluorescently-labeled m-MSCs transplanted into the knee joint using in vivo fluorescence combined with three-dimensional computed tomographic imaging in a rat model. Although the intraarticularly injected m-MSCs were spread throughout the joint cavity in the absence of magnetic force, the magnetic force caused the injected m-MSCs to accumulate around the chondral lesion. Further examinations including ex vivo imaging, histological assessments and reverse transcription polymerase chain reaction revealed that transplanted MSCs were not present in any major organs after intraarticular administration, regardless of magnetic targeting. Our data suggest that m-MSCs can be accumulated efficiently into a chondral lesion using our magnetic targeting system, while none of the intraarticularly transplanted MSCs migrate to other major organs.

Encapsulation of magnetic nanoparticles in poly(methyl methacrylate) by miniemulsion and evaluation of hyperthermia in U87MG cells

Magnetic nanoparticles (MNPs) are promising materials for hyperthermia treatment and magnetic targeting systems. The objective of this work was to synthesize and characterize magnetic nanoparticles coated with oleic acid (MNPsOA) loaded with poly(methyl methacrylate) prepared by miniemulsion polymerization (MNPs-PMMA) and evaluate their cytotoxicity in murine fibroblast (L929) cells, blood biocompatibility (hemolysis assay) and hyperthermia (HPT) in human glioblastoma (U87MG) cells. The MNPs-PMMA nanoparticles presented average mean diameter of 99±1.9nm with a polydispersity index (PdI) of 0.13±0.15 and saturation magnetization (Ms) value of 34emu/g of iron oxide, as well as superparamagnetic proprieties. The MNPs-PMMA nanoparticles did not present cytotoxicity in murine fibroblast (L929) and U87MG cells. HPT assays were applied, demonstrating that AC magnetic field application (1MHz and 40Oe) for 3min or 6min reduced the viability cells by 75% and 52% respectively. Morphological analyses showed that U87MG cells treated with 0.1μgmL−1 of MNPs-PMMA nanoparticles shrank after AC magnetic field application for 6min, resulting in a region of hypoxia. Hemolysis assay showed that MNPs-PMMA nanoparticles presented high blood biocompatibility. Our results indicate that MNPs-PMMA nanoparticles obtained by miniemulsion polymerization have the potential to be used as carrier systems for HPT.

Preparation of γ-Fe2O3/SiO2-capsule composites capable of using as drug delivery and magnetic targeting system from hydrophobic iron acetylacetonate and hydrophilic SiO2-capsule

Series of nanocomposites with γ-Fe2O3 supported on SiO2-capsules were prepared by adsorption of hydrophobic iron acetylacetonate on the hydrophilic surface of SiO2-capsules in the evaporation process of the solvent and then calcination the complex at 450 °C. The adsorption and calcination conditions were studied and the resultant nanaoparticles were characterized by XRD, XRF and TEM in detail. The results indicated that γ-Fe2O3 loaded discontinuously but uniformly on the surface of SiO2-capsules at appropriate content. The specific surface area characterization and doxorubicin hydrochloride release shown although the surface area of the target composites decreased slightly, the nanoparticles still had large potential using as drug delivery and magnetic targeting system.

Enhancement of muscle repair using human mesenchymal stem cells with a magnetic targeting system in a subchronic muscle injury model

BackgroundA magnetic cell targeting system was previously developed to promote the accumulation of transplanted cells in sites of injury in order to effectively treat injured tissues. However, the optimum time of exposure to the magnetic field and the strength of the magnetic force have not yet been clarified. In this study, we investigated the optimum conditions of the magnetic force required to retain iron-labeled human mesenchymal stem cells (hMSCs) at the site of transplantation for muscle repair in a subchronic skeletal muscle injury nude rat model. MethodsFirst, the optimum strength and time of exposure to the magnetic force for cell retention at the transplantation site were investigated 2 days after cell transplantation (1 × 105 cells). Second, the degree of enhancement of muscle repair was investigated at 3 weeks after cell transplantation in the group treated without a magnetic force and two typical magnetic condition groups that exhibited different levels of cell integration in first part of the study. ResultsOn the basis of the results of the first investigation, it was concluded that a magnetic strength of 1.5 T and 10 min of exposure to the magnetic force were efficient conditions to induce the retention of transplanted cells at the site of transplantation. In the second study, the groups exposed to a 1.5-T magnetic field for 10 min demonstrated significant enhancement of muscle repair, both histologically and electromechanically. ConclusionsThis study identified the optimal conditions required to retain transplanted hMSCs at the site of transplantation using a magnetic targeting system. This study also showed that the restoration of subchronic muscle injuries can be enhanced by magnetically labeled hMSCs following the application of a magnetic force.

Magnetic targeting of human peripheral blood CD133+ cells for skeletal muscle regeneration.

Skeletal muscle injuries often leave lasting functional damage or pain. Muscle injuries are routinely treated conservatively, but the most effective treatment to promote the repair of injured muscles has not yet been established. Our previous report demonstrated that human peripheral blood-derived CD133(+) cell transplantation to rat skeletal muscle injury models inhibited fibrosis and enhanced myogenesis after injury. However, the acquisition of a sufficient number of cells remains the limitation for clinical application, as the CD133(+) population is rare in human blood. In this study, we applied a magnetic cell targeting system to accumulate transplanted cells in the muscle injury site and to enhance the regenerative effects of CD133(+) cell transplantation, focusing on the fact that CD133(+) cells are labeled with a magnetic bead for isolation. For the magnetic cell targeting, the magnet field generator was set up to adjust the peak of the magnetic gradient to the injury site of the tibialis anterior muscle, and 1×10(4) human peripheral blood CD133(+) cells were locally injected into the injury site. This cell number is 10% of that used in the previous study. In another group, the same number of CD133(+) cells was injected without magnetic force. The CD133(+) cells transplanted with the magnetic force were more accumulated in the muscle injury site compared with the CD133(+) cells transplanted without the magnetic force. In addition, the transplantation of CD133(+) cells under the magnetic control inhibited fibrous scar formation and promoted angiogenesis and myogenesis, and also upregulated the mRNA expression of myogenic transcription factors, including Pax7, MyoD1 and Myogenin. However, the transplantation of CD133(+) cells without the magnetic force failed to demonstrate these effects. Thus, our magnetic cell targeting system enables transplantation of a limited number of CD133(+) cells to promote the repair of skeletal muscle injury.

Is a Magnetic-Manual Targeting Device an Appealing Alternative for Distal Locking of Tibial Intramedullary Nails?

BackgroundIn order to enable a radiation-free, accurate and simple positioning of distal locking screws, a combined magnetic and manual targeting system has been developed by Sanatmetal®. Where a low-frequency magnetic field is initially used to detect the position of the first drill hole and three more holes can be found with a mechanical template.ObjectivesOur cadaver study was performed to evaluate the accuracy and efficiency of this device.Materials and MethodsIn two runs, 30 probands (group 1: 10 students; group 2: 10 residents; group 3: 10 attendings), none of who being familiar with the device, tested the radiation-free system using 60 intact cadaver tibias. Each proband performed the surgical procedure twice in succession.ResultsReferring to the first attempts, 9.6, 7.2 and 7.1 minutes were the time periods required to insert the four distal screws and the relevant values for the second attempts were 8.6, 6.3 and 6.2 minutes; in both cases revealing a significant difference between group 1 and 2 and group 1 and 3. Furthermore, the mean values within each group indicated a significant decrease of the test duration. Out of the 240 drillings, only one failure (group 1) occurred, representing an accuracy of 99.58 %. Of the probands, 90 % rated the targeting device better than the free-hand technique and 77 % at least attested a high user-friendliness.ConclusionsDue to our satisfactory test results, the brief training, the steep learning curve and the radiation-free technique the new device has to be considered an appealing alternative for distal locking.

Enhancement of bone formation in an experimental bony defect using ferumoxide-labelled mesenchymal stromal cells and a magnetic targeting system

We used interconnected porous calcium hydroxyapatite ceramic to bridge a rabbit ulnar defect. Two weeks after inducing the defect we percutaneously injected rabbit bone marrow-derived mesenchymal stromal cells labelled with ferumoxide. The contribution of an external magnetic targeting system to attract these cells into the ceramic and their effect on subsequent bone formation were evaluated. This technique significantly facilitated the infiltration of ferumoxide-labelled cells into ceramic and significantly contributed to the enhancement of bone formation even in the chronic phase. As such, it is potentially of clinical use to treat fractures, bone defects, delayed union and nonunion.