I assume thus is old code as u can found in the example page of dotspatial, see documentation
'Declare a new feature set
Dim fs As New FeatureSet()
fs.FillAttributes()
'Pass in the file path for the standard shapefile that will be opened
FeatureSet.Open(Me.txtPadFileNaam.Text & MaatregelPunten & "_maatregelpunten" & ".shp")
'An IFeatureSet that contains the factory that will buffer the feature set
Dim [iF] As IFeatureSet = fs.Buffer(MaatregelPunten * (Me.TrackBarStaafjeUitklapFactor.Value) / 600, True)
'Saves the buffered feature set as a new file.
[iF].SaveAs(sfilename2, True)
Me.myVenster.AddLayer(sfilename2)