Vascular calcification is an important pathological condition associated with increased risk of cardiovascular mortality. Hydroxyapatite (HA) found in such deposits is the same polymorph of calcium (Ca) found in bone, indicating calcification may involve mechanisms akin to bone formation. Vascular smooth muscle cells (Vsmcs) have been shown to undergo phenotypic change to osteoblast-like cells. However, the mechanisms underlying this phenotypic change are unclear, and whether the stimulus to become osteogenic is a result of loss of mineralization inhibitors or early mineral deposits is not known. Our aim in this study is to identify mechanisms and signal-transduction pathways that cause differentiation of Vsmcs into osteoblast-like cells in the presence of HA. We first characterized vascular origin of Vsmcs by studying the expression of smooth muscle cell markers: myosin heavy chain (MHC) and smooth muscle actin (SMA) along with SM22α at both mRNA and protein levels. Vsmcs grown on HA exhibited progressive change in cellular morphology at 3-, 7- and 14 day time points. Culturing of Vsmcs on HA discs resulted in decrease in media calcium and increased expression of calcium sensing receptor (CaSR) on Vsmcs resulting upregulation of intracellular CaSR signaling leading to increased BMP-2 secretion. BMP-2 pathway mediated differentiation of Vsmcs to osteoblast-like cells shown by expression of osteogenic markers like runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), and alkaline phosphatase (ALP) at mRNA and protein levels. Blocking CaSR by NPS-2143 reduced BMP-2 secretion and blocking the BMP-2 pathway by LDN-193189, a BMP inhibitor, modulated expression of osteogenic markers confirming their role in osteogenesis of Vsmcs.
Polysilazane-based coatings were prepared on dense and porous substrates by dip-coating. Both the pure, liquid polymer and polymer solutions in cyclohexane were investigated. Relevant properties of the coating solutions, including rheological properties and surface tension, were determined and used to predict the resulting layer thickness as a function of dip-coating parameters on dense borosilicate glass substrates. A good correlation between existing model (Landau and Levich) and experiment was found for the pure polymer. In the presence of a solvent, evaporation phenomena led to a predicted coating thickness that is much less than the experimental value for all dip coating withdrawal spends. The introduction of a correction factor was found to adequately describe the deviation. In case of porous substrates, the coating thickness could not be predicted using the model due to infiltration of the base structure, resulting in an interpenetrating ceramic composite layer after pyrolytic conversion of the preceramic polymer compound. When preparing polymer-derived ceramic films on porous base materials, e.g. for membrane applications, this phenomenon has to be taken into account.
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