I am trying to apply an image brush to a Triangle in WPF without success. What am i doing wrong?

This is my attempt:

    Dim ModelTri As New MeshGeometry3D
    ModelTri.Positions.Add(New Point3D(0, 0, 0))
    ModelTri.Positions.Add(New Point3D(100, 0, 0))
    ModelTri.Positions.Add(New Point3D(100, 100, 0))

    Dim MeshTri As New MeshGeometry3D
    MeshTri.TriangleIndices.Add(0)
    MeshTri.TriangleIndices.Add(1)
    MeshTri.TriangleIndices.Add(2)

    'Texture
    Dim TexturePoints As New PointCollection
    TexturePoints.Add(New Point(100, 0))
    TexturePoints.Add(New Point(0, 100))
    TexturePoints.Add(New Point(100, 100))
    MeshTri.TextureCoordinates = TexturePoints

    'Image Brush
    Dim imgBrush As New ImageBrush()
    imgBrush.ImageSource = New BitmapImage(New Uri("Mercury.jpg", UriKind.Relative))
    imgBrush.Stretch = Stretch.Fill
    imgBrush.TileMode = TileMode.Tile
    imgBrush.SetValue(NameProperty, "imgBrush")
    Dim Mat As Material
    Dim DMaterial As New DiffuseMaterial
    DMaterial.Brush = imgBrush

    Dim Bind As New Binding("imgBrush")
    Bind.Source = imgBrush
    BindingOperations.SetBinding(DMaterial, BindingGroupProperty, Bind)

    'This doesnt work
    Mat = DMaterial

    'This works
    'Mat = New DiffuseMaterial(New SolidColorBrush(Colors.Khaki))

    Dim triangleModel As GeometryModel3D = New GeometryModel3D(ModelTri, Mat)

    Dim model As New ModelVisual3D()
    model.Content = triangleModel

    Viewport.Children.Add(model)