Biomedical Engineering Reference
In-Depth Information
seen by the increased carbon and nitrogen concentrations (Table 3), and also evidenced by
the N 1s spectrum (Fig 6, b) being similar to the one observed for bacterial cell walls (Leone
et al., 2006).
XPS investigation of fast-frozen biomaterial samples, conditioned in original α-MEM
medium (without serum), shows that equilibrium is reached at the interface within only 1
day (Mladenovic, et al., 2010). Corresponding interfacial chemical compositions are given in
Table 4.
Surface composition (Atomic %) of biomaterials in original α-MEM after 1 day of equilibration
Photoelectron line
α-MEM
Algipore
Bio-Oss
45S5
C 1s
Organic
14.72
35.99
8.33
43.05
Surface carbonate
0.92
2.6
1.5
2.11
O 1s
70.48
34.82
68.56
38.96
N 1s
1.94
3.38
-
2.79
Ca 2p
-
5.7
9.74
0.58
P 2p
-
4.69
7.02
0.16
Si 2p
-
-
-
0.17
F 1s
-
-
-
-
K 2p
0.24
0.46
0.06
0.34
Na 1s
5.8
5.62
3.08
5.04
Cl 2p
5.91
6.76
1.71
6.8
Atomic ratio Na/Cl
0.98 : 1
0.83 : 1
1.8 : 1
0.74 : 1
Table 4. Surface composition of biomaterials in α-MEM after 1 day of equilibration.
The Bio-Oss - α-MEM medium interface does not show any adsorption of organic
components from the biological medium therefore similar in composition to the initial (dry)
surface, except for the contributions from water and Na
+
and Cl
-
ions from the solution. An
excess of sodium over chloride, providing the atomic ratio Na/Cl 1.8:1, indicates negative
charge of the Bio-Oss particles' surface. Assuming the Bio-Oss is similar to hydroxyapatite
(HAP), the isoelectric point of the biomaterial can be expected to have a pH value close to
8.1 (Bengtsson, et al., 2009). Therefore, the surface in α-MEM solution has to be substantially
neutral with the atomic ratio Na/Cl close to one. The observed excess of sodium ions may
indicate a re-adsorption of the phosphate-related solution species, like HPO
4
2-
, producing
outer-sphere coordination sites for the Na
+
. Such occurrences were confirmed for synthetic
HAP by the solution analysis and surface complexation modeling (Bengtsson, et al., 2009).
Additional adsorption of hydro phosphate ions is indirectly observed by a decrease in the
atomic ratio Ca/P at the Bio-Oss - α-MEM medium interface, compared to that at the dry
surface.
The interfacial composition of both Algipore and 45S5 is dominated by water, sodium and
chloride, and adsorbed organic molecules. The amino acids are the key players in the
adsorbed layer, as evident by N 1s spectra (Fig. 6, c and 7, c) which similar to that of the
