Superparamagnetic iron oxide (SPIO) labeling efficiency and subsequent MRI tracking of native cell populations pertinent to pulmonary heart valve tissue engineering studies

Abstract

The intimal and medial linings of the pulmonary artery consist largely of vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs), respectively. The migration of these cell types to a potential tissue-engineered pulmonary valve (TEPV) implant process is therefore of interest in understanding the valve remodeling process. Visualization and cell tracking by MRI, which employs hypointense contrast achievable through the use of superparamagnetic iron oxide (SPIO) microparticles to label cells, provides a method in which this can be studied. We investigated the SPIO labeling efficiency of human VECs and VSMCs, and used two- and three-dimensional gradient echo sequences to track the migration of these cells in agar gel constructs. Protamine sulfate (4.5 µg/mL) was used to enhance SPIO uptake and was found to have no influence on cell viability or proliferation. MRI experiments were initially performed using a 9.4-T scanner. The results demonstrated that the spatial positions of hypointense spots were relatively unchanged over 12 days. Subsequent MR experiments performed at 7 T demonstrated that three-dimensional imaging provided the best spatial resolution to assess cell fate. R(2)* maps were bright in SPIO cell-encapsulated gels in comparison with unlabeled counterparts. Signal voids were ruled out as hypointense regions owing to the smooth exponential decay of T(2)* in these voxels. As a next step, we intend to use the SPIO cell labeling and MR protocols established in this study to assess whether hemodynamic stresses will alter the vascular cell migratory patterns. These studies will shed light on the mechanisms of vascular remodeling after TEPV implantation.

A Novel Bioreactor for Mechanobiological Studies of Engineered Heart Valve Tissue Formation Under Pulmonary Arterial Physiological Flow Conditions

“…Finally, a U-shaped flow chamber design was chosen over a straight tube section to allow the device to fit within a standard cell culture incubator. Detailed flow characteristics in the chamber such as the velocity field and fluid-induced shear stresses on the housed [12,18] Previously established to be up to 6 dynes/cm2 for fluid shear stress [25] and ~ 1.2 Hz (72 beats/min) for flexure and stretch Longitudinal noninvasive tracking of cells will provide insights on cell migratory activity within scaffold environment [57] Physiological pulsatile flow waveforms may be most biomimetic but prescribing more straightforward flow conditions, including square oscillatory waveforms and time-averaged steady flow should be possible since from a mechanobiology viewpoint, the specific roles of individual or combined stress states, as well as relatively simpler versus more complex flow environments (e.g., fully forward flow versus a combination of forward and oscillatory flow) can be identified in a systematic manner. The tubing requirement will maintain a sterile environment specimens were evaluated through moving boundary CFD simula tions (see Sec.…”

“…of the device with plastic equivalents made this novel FSF bioreactor adaptable for use in an MRI instrument. We were able to previously demonstrate that specimens inside the chamber could be successfully imaged by MRI [57], Although the results herein focus on steady pump flow condi tions, we note that the pump could be programmed to generate pulsatile flow waveforms if necessary. Other innovative design features, such as the removable sample holder (Fig.…”

Bone marrow mesenchymal stem cells for tissue engineered pulmonary valves (TEPV)

“…One option is to transfect cells with a reporter gene before valve implantation [92] and subsequently track the cells with positron emission tomography camera [93]. This can also be accomplished via visualization and cell tracking by MRI [94][95]. It is important to assess and quantify matrix elements such as collagen, elastin and glycosaminoglycans following transplantation.…”

Visual bone marrow mesenchymal stem cell transplantation in the repair of spinal cord injury

“…Superparamagnetic iron oxide (SPIO) nanoparticles can efficiently label cells, endowing sufficient magnetism for remote manipulation by external magnetic fields (Kyrtatos et al, 2009;Vaněček et al, 2012). In addition, superparamagnetic iron oxide is a non-invasive contrast agent that has been developed for magnetic resonance imaging (Andreas et al, 2012;Wang et al, 2013b), and enables the tracking of labeled cells in vivo (Hu et al, 2012a;Ramaswamy et al, 2012). Thus, this technique provides a method for the non-invasive monitoring of the efficiency of cell transplantation procedures.…”