Biomedical Engineering Reference
In-Depth Information
l
1
Ra
z x dx
()
(1)
0
where
zx
absolute ordinate value inside the elementary measuring length, with
l = lp
,
and
lp
elementary length in
x
direction (on average line) used for identification of
unevenesses characterizing profile under evaluation,
R
z
the height of roughness acc. to 10 points as the measure of the range of roughness
values in the profile. It is generally determined as the mean of 5 single measuring lengths of
the roughness profile it corresponds to the mean peak-to-valley height,
Rt
- the total height of the primary roughness profile defined as the difference between
height of the highest profile peak and the depth of the lowest profile valley of the respective
profile within the evaluation length
ln
(
l = ln
).
A computerized HOMMEL TESTER T800 system of Hommelwerke GmbH for roughness
measurement was used for the study of surface roughness. The comparison of roughness
studies results after both conventional electropolishing (EP) and magnetoelectropolishing
(MEP) were carried out on the Ti samples.
Surface roughness measurements on CP Ti Grade 2 samples were performed both on wires
and plates after standard electropolishing (EP), and magnetoelectropolishing (MEP), with
mechanically abrasive polishing (MP) samples serving as a reference. Comparison of the
R
z
,
R
z
ISO
,
Rt
, and
Ra
results obtained after MP, EP, and MEP are presented in Fig. 2.
Dependent
on the treatment proposed, a decreasing surface roughness is observed with MEP roughness
being the least (Figs. 2a,b,c).
The maximum height of scale limited surface
Sz
is the sum of the largest peak height value
and the largest pit depth value within a definition area. The arithmetic mean height
Sa
is the
arithmetic mean of the absolute of the height within a definition area
()
1
Sa
z x y
(,)
dxdy
(2)
A
with
A
being the definition area (Standard ISO 25178-2, 2008).
The interferometric roughness studies were performed on CP Ti Grade 2 strips after MP, EP,
and MEP (Fig. 3). The obtained results are even more pronounced with detailed data given
in Table 1. Even if
Sa
surface roughness parameter measured after EP is very low (of 88%) in
comparison with
Sa
after MP, this parameter of Ti sample surface after MEP is still reduced
over 12%.
Our previous studies performed on MP, EP, and MEP sample surfaces of different
metallic biomaterials indicated decreasing roughness, evaluated both by 2D standard
roughness measurements (
Ra
,
R
z
,
Rt
), as well as 3D interferometry measurements (
Sa
,
Sz
),
(Hryniewicz & Rokosz, 2009) as well as presented in our works elsewhere (Hryniewicz &
Rokicki, 2007; (2) Hryniewicz & Rokicki, 2007; Hryniewicz et al., 2007). Consequently,
regarding reduction in hydrogenation, the results obtained by SIMS are in agreement with
the sample surface roughness data concerning their mode of treatment (Hryniewicz et al.,
2011).
Some of the studies on surface roughness performed by other technique (Atomic Force
Microscopy, AFM) on Nitinol (Fig. 4) also confirm improvement of MEP treated samples
against EP ones (Rokicki et al., 2008; Hryniewicz & Rokicki, 2008).
