diff --git a/neurocollage/collage.py b/neurocollage/collage.py
index c9d5071..0fc4f56 100644
--- a/neurocollage/collage.py
+++ b/neurocollage/collage.py
@@ -455,7 +455,7 @@ def plot_3d_collage(
     centerline,
     sample=10,
     filename=None,
-    show=False,
+    show=True,
 ):
     """Plot 3d collage with trimesh."""
     mesh_helper = MeshHelper(atlas_path, region, hemisphere)
@@ -470,9 +470,13 @@ def plot_3d_collage(
             mesh_path = Path(atlas_path["structure"]).parent / boundary["path"]
             if mesh_path.is_dir():
                 for _mesh_path in mesh_path.iterdir():
-                    boundary_meshes.append(trimesh.load_mesh(_mesh_path))
+                    _mesh = trimesh.load_mesh(_mesh_path)
+                    _mesh.visual.face_colors = [100, 100, 100, 100]
+                    boundary_meshes.append(_mesh)
             else:
-                boundary_meshes.append(trimesh.load_mesh(mesh_path))
+                _mesh = trimesh.load_mesh(mesh_path)
+                _mesh.visual.face_colors = [100, 100, 100, 100]
+                boundary_meshes.append(_mesh)
 
     data = boundary_meshes + plane_data + cell_data + centerline_data
     mesh_helper.render(data=data, filename=filename)
diff --git a/neurocollage/mesh_helper.py b/neurocollage/mesh_helper.py
index e3ee1e5..8abf9ba 100644
--- a/neurocollage/mesh_helper.py
+++ b/neurocollage/mesh_helper.py
@@ -1,4 +1,5 @@
 """3D collage module."""
+
 from copy import deepcopy
 
 import matplotlib
@@ -35,7 +36,6 @@ def __init__(self, atlas_path, region, hemisphere=None):
         self.hemisphere = hemisphere
 
         self._layer_annotation = None
-        self._boundary_mask = None
         self._depths = None
 
     @property
@@ -98,38 +98,18 @@ def get_pia_mesh(self, cutoff=3):
         data[data > cutoff * np.mean(abs(self.depths.voxel_dimensions))] = 0
         data[np.isnan(data)] = 0
 
-        mesh = self._get_mesh(VoxelGrid(data), self.boundary_mask)
+        mesh = self._get_mesh(VoxelGrid(data))
         mesh.visual.face_colors = [0, 0, 255, 100]
         return mesh
 
-    @staticmethod
-    def _get_mesh(vg, mask=None):
-        """Get a mesh."""
+    def _get_mesh(self, vg):
+        """Get a mesh within a region."""
         mesh = vg.marching_cubes
-        if mask is not None:
-            tri_indices = vg.points_to_indices(mesh.triangles_center)
-            mesh.update_faces(~mask[tuple(tri_indices.T)])
+        mask = VoxelGrid(self.annotation.raw).matrix
+        tri_indices = vg.points_to_indices(mesh.triangles_center)
+        mesh.update_faces(mask[tuple(tri_indices.T)])
         return mesh
 
-    @property
-    def boundary_mask(self):
-        """Get a mask of inner and boundary voxel of a region."""
-        if self._boundary_mask is None:
-            m = VoxelGrid(self.annotation.raw).matrix
-            outer_vg = VoxelGrid(self.annotation.raw)
-            outer_vg.encoding.data[m == 0] = -1000
-            outer_vg.encoding.data[m > 0] = 0
-            d1 = outer_vg.matrix
-            d2 = outer_vg.matrix
-            d1[:-1] += d2[1:]
-            d1[1:] += d2[:-1]
-            d1[:, :-1] += d2[:, 1:]
-            d1[:, 1:] += d2[:, :-1]
-            d1[:, :, :-1] += d2[:, :, 1:]
-            d1[:, :, 1:] += d2[:, :, :-1]
-            self._boundary_mask = d1 > 0
-        return self._boundary_mask
-
     def get_layer_meshes(self, alpha=0.5, colors=None):
         """Get layer meshes."""
         if colors is None:
@@ -140,7 +120,7 @@ def get_layer_meshes(self, alpha=0.5, colors=None):
                 data = self.annotation.raw
                 vg = VoxelGrid(data)
                 vg.encoding.data[data != layer] = False
-                mesh = self._get_mesh(vg, self.boundary_mask)
+                mesh = self._get_mesh(vg)
                 color = [int(255 * v) for v in matplotlib.colors.to_rgb(colors[i - 1])]
                 color.append(255 * alpha)
                 mesh.visual.face_colors = color
diff --git a/neurocollage/planes.py b/neurocollage/planes.py
index e5b16f8..bb87ed7 100644
--- a/neurocollage/planes.py
+++ b/neurocollage/planes.py
@@ -64,9 +64,12 @@ def slice_n_cells(cells, n_cells, random_state=0):
 
     sampled_cells = []
     for mtype in cells.mtype.unique():
-        samples = cells[cells.mtype == mtype].sample(
-            n=min(n_cells, len(cells[cells.mtype == mtype])), random_state=random_state
-        )
+        if n_cells > 1:
+            samples = cells[cells.mtype == mtype].sample(
+                n=min(n_cells, len(cells[cells.mtype == mtype])), random_state=random_state
+            )
+        if n_cells < 1:
+            samples = cells[cells.mtype == mtype].sample(frac=n_cells, random_state=random_state)
         sampled_cells.append(samples)
 
     if len(sampled_cells) > 0:
diff --git a/neurocollage/planes_utils/planes.py b/neurocollage/planes_utils/planes.py
index 8827ac7..e378139 100644
--- a/neurocollage/planes_utils/planes.py
+++ b/neurocollage/planes_utils/planes.py
@@ -492,9 +492,7 @@ def _smoothing(path, ctrl_point_count=10):
     curve.ctrlpts = _split_path(path, ctrl_point_count).tolist()
     # Auto-generate knot vector
     curve.knotvector = utilities.generate_knot_vector(curve.degree, curve.ctrlpts_size)
-    print(curve.knotvector)
     curve.delta = 0.01
-
     step_count = 100
     steps = np.linspace(0, 1, step_count, endpoint=True)
     return np.asarray(curve.evaluate_list(steps))
diff --git a/neurocollage/utils.py b/neurocollage/utils.py
index 0988bdc..0f97b62 100644
--- a/neurocollage/utils.py
+++ b/neurocollage/utils.py
@@ -32,5 +32,5 @@ def _trans(p):
     # pylint: disable=cell-var-from-loop
     def trans(p):
         return p + df.loc[gid, ["x", "y", "z"]].to_numpy().T
-
-    return m.transform(trans)
+    p = m.transform(trans)
+    return p