如何从MDI父窗体中的MDIClient组件中删除3d边框(凹陷)？

Protected Overrides Sub WndProc(ByRef m As Message)
    If m.Msg = &H85 Then ' WM_NCPAINT
        Dim hDC As IntPtr = GetWindowDC(m.HWnd)
        If hDC.ToInt32() <> 0 Then
            Using graphics As Graphics = Graphics.FromHdc(hDC)
                Dim rect As Rectangle = Me.ClientRectangle
                rect.Inflate(-1, -1)
                graphics.DrawRectangle(Pens.Black, rect)
            End Using
            ReleaseDC(m.HWnd, hDC)
        End If
    Else
        MyBase.WndProc(m)
    End If
End Sub