MRI method for labeling and imaging decellularized extracellular matrix scaffolds for tissue engineering.

PURPOSE: To develop a facile method for labeling and imaging decellularized extracellular matrix (dECM) scaffolds intended for regenerating 3D tissues. METHODS: A small molecule manganese porphyrin, MnPNH2 , was synthesized and used to label dECM scaffolds made from porcine bladder and trachea and murine whole lungs. The labeling protocol was optimized on bladder dECM, and imaging on a 3T clinical scanner was performed to assess reductions in T1 and T2 relaxation times. In vivo MRI was performed on dECM injected in the rat dorsum to verify sensitivity of detection. Toxicity assays for cell viability, metabolism, and proliferation were performed on human umbilical vein endothelial cells. The incorporation of MnPNH2 and its long-term retention in dECM were assessed on transmission electron microscopy and ultraviolet absorbance of eluted MnPNH2 over time. RESULTS: All tissues, including thick whole 3D organs, were uniformly labeled and demonstrated high signal-to-noise on MRI. A nearly 10-fold reduction in T1 was consistently obtained at a labeling dose of 0.4 mM, and even 0.2 mM provided sufficient contrast in vivo and ex vivo. No toxicity was observed up to 0.4 mM, the maximum tested. Binding studies suggested nonspecific association, and retention studies in the labeled whole decellularized lungs revealed less than 20% MnPNH2 loss over 30 days, the majority occurring in the first 3 days after labeling. CONCLUSION: The proposed labeling method is the first report for visualizing dECM on MRI and has the potential for long-term monitoring and optimization of dECM-based organ tissue engineering.

One-Step Labeling of Collagen Hydrogels with Polydopamine and Manganese Porphyrin for Non-Invasive Scaffold Tracking on Magnetic Resonance Imaging.

Biomaterial scaffolds are the cornerstone to supporting 3D tissue growth. Optimized scaffold design is critical to successful regeneration, and this optimization requires accurate knowledge of the scaffold's interaction with living tissue in the dynamic in vivo milieu. Unfortunately, non-invasive methods that can probe scaffolds in the intact living subject are largely underexplored, with imaging-based assessment relying on either imaging cells seeded on the scaffold or imaging scaffolds that have been chemically altered. In this work, the authors develop a broadly applicable magnetic resonance imaging (MRI) method to image scaffolds directly. A positive-contrast "bright" manganese porphyrin (MnP) agent for labeling scaffolds is used to achieve high sensitivity and specificity, and polydopamine, a biologically derived universal adhesive, is employed for adhering the MnP. The technique was optimized in vitro on a prototypic collagen gel, and in vivo assessment was performed in rats. The results demonstrate superior in vivo scaffold visualization and the potential for quantitative tracking of degradation over time. Designed with ease of synthesis in mind and general applicability for the continuing expansion of available biomaterials, the proposed method will allow tissue engineers to assess and fine-tune the in vivo behavior of their scaffolds for optimal regeneration.