For i As Integer = 0 To listbox1.Items.Count - 1
   Dim content As New System.Text.StringBuilder(listbox1.Items(i).ToString)
 
   For c As Integer = content.Length - 1 To 0 Step -1
       If Char.IsControl(content(c)) Then content.Remove(c, 1)
   Next c
 
   listbox1.Items(i) = content.ToString
Next i