diff --git a/src/compas_vol/microstructures/lattice.py b/src/compas_vol/microstructures/lattice.py
index 703fdf8..c83da5c 100644
--- a/src/compas_vol/microstructures/lattice.py
+++ b/src/compas_vol/microstructures/lattice.py
@@ -55,7 +55,7 @@ def frame(self, frame):
     @property
     def ltype(self):
         return self._ltype
-    
+
     @property
     def lattice_type(self):
         return self.ltype, self.typenames[self.ltype]
diff --git a/src/compas_vol/modifications/multishell.py b/src/compas_vol/modifications/multishell.py
index 9042ced..1cf5153 100644
--- a/src/compas_vol/modifications/multishell.py
+++ b/src/compas_vol/modifications/multishell.py
@@ -48,7 +48,7 @@ def get_distance_numpy(self, x, y, z):
     sh = MultiShell(u, 1.0, 2.5)
 
     x, y, z = np.ogrid[-15:15:60j, -15:15:60j, -15:15:60j]
-    dm = sh.get_distance_numpy(x,y,z)
+    dm = sh.get_distance_numpy(x, y, z)
     plt.imshow(dm[:, :, 20], cmap='RdBu')  # transpose because numpy indexing is 1)row 2) column instead of x y
     plt.show()
 
diff --git a/src/compas_vol/utilities/utils.py b/src/compas_vol/utilities/utils.py
index 87a9af9..513bfcd 100644
--- a/src/compas_vol/utilities/utils.py
+++ b/src/compas_vol/utilities/utils.py
@@ -173,6 +173,7 @@ def export_layer(distfield, resolution, level, filename='layerimage.png'):
 
     import numpy as np
     from skimage import io
+    # add support for marching squares > outline
 
     # x, y = np.ogrid[-10:10:resolution+0j, -10:10:resolution+0j]
     y, x = np.ogrid[-10:10:resolution*1j, -10:10:resolution*1j]