Using Magnetic Resonance Microscopy to Assess the Osteogenesis in Porous Hydrogels
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0984-MM15-09
Using Magnetic Resonance Microscopy to Assess the Osteogenesis in Porous Hydrogels Prasanna Mishra, Mahrokh Dadsetan, Srinivasan Rajagopalan, Theresa E. Hefferan, Michael J. Yaszemski, and Slobodan I. Macura Mayo Foundation, Rochester, MN, 55905
ABSTRACT Hydrogels are multi-functional and can be used as scaffolds in bone tissue engineering. The pore architecture of the scaffolds is a significant factor in bone cell function. In this work, oligo (poly (ethylene glycol) fumarate) (OPF) hydrogel is used in the fabrication of porous scaffolds, and the effect of hydrogel porosity on bone formation is evaluated using an in vitro bone marrow stromal cell model. The porous hydrogels consist of copious amounts of water (90% or more by volume), and their structure is very similar to soft tissues. The characterization of porosity and interconnectivity in a typical OPF hydrogel scaffold and the bone formation inside the scaffold are assessed using magnetic resonance microscopy (MRM) techniques and are shown to be very useful in micro structural studies of such water rich materials. A Bruker Avance 7 Tesla (proton 300 MHz) spectrometer equipped with a Micro Imaging 2.5 accessory is used in these studies. By optimizing the acquisition parameters such as relaxation recovery time (TR), echo time (TE), pulse flip angle (TA), and using solvent relaxation-enhancing media, the pores and bone formations are clearly observed at an in-plane resolution of 29 µm/ pixel in various scaffold materials. Analysis of our MRM images shows that the pores are highly interconnected and the porosity computed from the images correlate quite well with the experimental porosity parameters such as porogen size and percentage. In addition, the quantitative alkaline phosphatase activity, alizarin red staining as marker of osteoblastic differentiation, and the mineralization capacity of marrow stromal cells are in good agreement with the bone formation seen in the MRM images. INTRODUCTION Biomaterials are preeminent for their usefulness. For such materials to help in the growth of cells that finally leads to the desired tissue formation such as bone, a compatible medium that can also be a scaffold for the cells to grow is highly desirable. Hydrogels have copious amount of water in them and water can be highly conducive to cell growth. Further, the porosity and interconnectivity in such structured hydrogels can be a good scaffold for the cells to grow. MRM as a non-invasive investigative tool 1-3 proves invaluable as it can image the water construct inside the hydrogels thus showing the pore architecture of scaffolds at a very high spatial resolution. In this work, the porosity and interconnectivity of micro porous OPF hydrogels are assessed using magnetic resonance microscopy techniques. We investigate how the morphological features of the OPF hydrogels affect the marrow stromal cell (MSC) adhesion and the phenotypic function expression. We find the magnetic resonance microscopy to be a very useful tool in the study of the mineralization of ma
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