Biomedical Engineering Reference
In-Depth Information
18.2.4.1 Mercury Porosimetry Case Studies
Mercury porosimetry has been used in many dental materials' research applications including to elu-
cidate the efficacy of copolymer of polylactic/polyglycolic acid at promoting bone healing and new
bone formation in post-extraction sockets
[51]
, measure the porosity of dental luting cements
[52]
,
and to determine the porosity and pore size distribution of demineralized dentin
[53]
.
In the latter work a mercury porosimeter (Micromeritics Autopore IV, Micromeritics, Georgia,
USA) was used to measure porosity in demineralized dentin. In restorative dentistry, to obtain an effi-
cient infiltration of superficially demineralized dentin, designed porosity is required. In order to have
the highest porosity, pretreatment of dentin can be performed and mercury porosimetry can be used
to evaluate the effect of different pretreatments on demineralized dentin. In the work of Vennat et al.
[53]
, after weighing the assembly including penetrometer, mercury, and sample (to obtain the sample
volume using the porosimeter as a pycnometer), pressures of between 0.20 and 200 MPa were applied.
Measurements of intruded volume of mercury versus applied pressure were obtained, and the
pressures were converted into pore sizes using the Washburn equation. The higher intrusion pres-
sure of 200 MPa corresponded to a pore diameter around 0.01 μm.
Figure 18.9
shows the incremen-
tal porosity versus pore size obtained for demineralized lyophilized-treated and hexamethyldisilazane
(HMDS)-dried dentin specimens. The findings of this work indicated that freeze-drying with lyophili-
zation drying technique was more reliable than the HMDS drying with less shrinkage and less overall
internal binding of collagen fibers. The results showed two types of pores corresponding either to
tubules and microbranches or to inter-fibrillar spaces created by demineralization. Global porosity
varied from 59% for the HMDS-dried samples to 70% for the freeze-dried samples.
18.3
MEASUREMENT OF COMPOSITION OF NANOSTRUCTURES
18.3.1
Energy Dispersive X-Ray Spectroscopy
EDS is one of the most common spectroscopy techniques used as SEMs from the 1960s, which have
been commonly equipped with this chemical analytical device
[54,55]
. In this technique, electro-
magnetic radiation is bombarded into a material surface which causes electrons from inner atomic
shells to be ejected and subsequently filled with electrons from higher energy levels. Electromagnetic
radiation used to excite the sample is usually a focused high energy stream of electrons, protons, or
X-rays. In a typical SEM, a stream of electrons is used. Electron transitions from the higher energy
shells to lower energy shells causes X-rays to be emitted. A detector of SiLi or more commonly now
a silicon drift detector is used to collect and count the number of X-rays emitted at each energy level.
The energy level characterizes the element from which the X-ray was emitted while the count of the
number of X-rays with this energy level is used to characterize the amount of the element that is
present. A typical spectrum presents the count of the X-rays versus the energy level of the X-rays.
New EDS systems come pre-calibrated to allow automatic detection and quantification of the ele-
ments present within the sample.
Care must be taken when interpreting EDS results. For example, wrong elements can often be
detected where energy levels emitted from different elements overlap. X-rays can be generated from
K, L, or M energy-level shells in a typical element. Therefore, overlapping of energy levels detected
can occur, e.g., when Ti and Ba (Ti-K
α
and Ba-L), or Mn and Fe (Mn-K
β
and Fe-K
α
), or Mn and Cr
(Mn-K
α
and Cr-K
β
) are present. Some knowledge of the sample elemental chemistry or knowledge
