Biomedical Engineering Reference
In-Depth Information
24 h. The test starts after 24 h hydration. The test probe accuracy was 0.01 mm. Values below
0.05 mm per 24 h solution impinging are judged as acid resistant.
Determination of Ca and Al in the solution during the hydration process of the Ca-
aluminate based material was performed using atomic absorption spectrometry (Liu et al
2002). Standard solutions of different concentrations of Ca and Al were prepared according
to the manual. Samples were prepared with a size of 10mm x 2mm height using a wet-press
method, corresponding to a surface area of 224 mm
2
. The test pieces were placed in plastic
bottles in inorganic saliva solution of pH 7. The amount of liquid was 10 ml in each bottle.
The temperature selected was 37
o
C. The inorganic saliva solution contained calcium
chloride, magnesium chloride, sodium chloride, a phosphate buffer, hydro-carbonate and
citric acid. The Ca-content in the saliva solution corresponded to 68 ppm. 1 ml solution was
removed at 1, 7 and 28 days for analyses, and saliva was exchanged at 1, 7 and 28 days after
every measurement. For the 28 days test additional samples were also taken 1 h after new
solution was added.
Measurement of pH development during hydration of the material was conducted using a
standard pH-meter. Samples were prepared according to the procedure for atomic
absorption described above. The pH-testing was conducted in two separate ways. First the
samples were immersed in saliva solution (pH =7) at 37
o
C, and pH was measured
continually over the whole experiment period (Test 1). 1 ml solution was removed at 1, 7, 14
and 28 days for pH measurement. The second type of measurement comprised immersion
in 10 ml saliva solution at 37
o
C, where the saliva was exchanged at 1, 7, 14 and 28 days. pH
was measured at the time of observation and also after one hour in new saliva (data within
brackets), Test 2.
Specimens at different setting stages were subjected to cytotoxicity testing by using primary
cultures of human oral fibroblasts. A tissue culture insert retaining tested materials was
assembled into a 12-well plate above the fibroblast monolayers. The cytotoxicity was
determined by MTT reduction assay after various curing times. Specimens were set and
hydrated at 37
o
C for different periods of time, i.e. 0, 5, 30, 60 min, 24 h and 1 week and were
then placed on tissue culture netwell for a cytotoxicity test. Both acute (1 and 24 h) and long
term (1 week) in vitro toxicity tests were conducted with MTT assay.
3.1.1 Biocompatibility including bioactivity of Ca-aluminate bioceramics
Biocompatibility evaluation
Summarized below are the results from several biocompatibility and bioactivity studies
(Engqvist 2004, 2005, Faris 2006) where Ca-aluminate is used as a biomaterial in orthopaedic
and dental applications.
In vitro
bioactivity studies show apatite formation on the surface of
the Ca-aluminate materials exposed to phosphate buffer solution, an example shown in
Figure 2 below.
Corrosion resistance
No height reduction at all was observed for two tested Ca-aluminate materials. Thus,
according to the acid corrosion test, Ca-aluminate materials are judged as stable materials.
The total absence of material loss, measured as height reduction in the acid corrosion test, is
related to the general basic nature of the material, with possibility of neutralization of the
acid in the contact zone - especially in the earlier stage of the hydration process.
