Biomedical Engineering Reference
In-Depth Information
for the NaOH pretreated sample than for the as-received sample, indicating a much higher degree
of oxidation. The spectrum from AES includes a sequence of peaks with specific energy levels.
Reference energy peak bands from oxygen, belled O KLL, and titanium, labelled Ti LMM, can be
used to compare against peaks from other energy states. The O KLL peaks, for example, represent the
energy of the electrons ejected from the atoms due to the filling of the O 1s state (K shell) by an elec-
tron from the L shell coupled with the ejection of an electron from an L shell.
18.4
MEASUREMENT OF THE MECHANICAL PROPERTIES OF
NANOSTRUCTURES
18.4.1
Nanoscratch Testing
Micro-scratch testing is commonly performed to evaluate the adherence of surface coatings. In
one study, the adherence of functionally graded HA film on Si substrate and sputter-deposited film
with 62% crystallinity on glass substrate were determined using a CSM Microscratch Instrument
(MicroPhotonics, Irvine, CA, USA)
[69]
. Scratch tests were performed under a linearly increasing load,
from 0.01 to 3 N. The scratch length was set to 3 mm, and the scratch speed was set to 1 mm/min. A dia-
mond tip (20-μm tip diameter, Rockwell C geometry) was used for these tests. The scratch-tip diameter
has a strong influence on the maximum and mean Hertzian pressures. A load of 3 N applied to a circular
diamond tip of 20 μm diameter in contact with a flat HA coating surface results in a maximum Hertzian
pressure of 70 GPa. The commonly used 200 μm diamond tip would require a load of 300 N to reach the
same maximum Hertzian pressure.
Nanoscratch test work is performed similarly, in order to provide a representative measure of coat-
ing adhesion. The nanoscratch test may be useful to evaluate mineralized tissue adhesion properties
in titanium cultures. The adhesion of mineralized tissue to titanium and polystyrene was assessed
using the nanoscratch test by Butz et al.
[70]
. Osteoblastic cells derived from rat bone marrow were
cultured on polystyrene, titanium-coated polystyrene, and titanium disks with either a machined or
dual-acid-etched surface. Nanoscratch testing was performed (NST, CSEM Instruments, Neuchatel,
Switzerland) on mineralized tissue specimens after 28 days of culturing. The scratch path was moni-
tored by light microscopy until complete delamination of mineralized tissue from the substrate
occurred, and the required force was recorded as the critical load. Mean critical load values were
31 mN for polystyrene, 67 mN for titanium-coated polystyrene, 76 mN for machined titanium, and
107 mN for dual-acid-etched titanium surface. Culturing mineralized tissue on titanium, especially on
roughened surfaces, was seen to increase the tissue critical load.
18.4.2
Nanohardness Test
Nanohardness is a widely used technique for measuring the local stress, strain, modulus, and tough-
ness properties of dental materials
[71-73]
. This is a particularly relevant test for dental materials
as an understanding of the brittleness or stiffness an implant or bonding material is important for
its successful application. In the field of nanoindentation, the Berkovich tip has been widely used to
measure the mechanical properties of bulk materials and thin films. This indenter has a triangular-
shaped tip with the total included angle of 142.3° and half angle of 65.35°; this tip can only produce
a constant equivalent strain value during a test procedure. To measure the stress-strain response of
