Nanostructures and Specific Properties - Nanostructural Bioceramics: Advances in Chemically Bonded Ceramics - page 65

cements are entering the market [17, 18]. Calcium salt-based
cements have many advantages for polymer materials; the absence
of organic monomers, lower exothermal curing reactions, a higher
degree of bioactivity, and for some of these materials bioresorption
over time are favourable factors.
Interest in the haemocompatibility of bone cement and
injectable ceramic pastes has increased because of claimed risks
for adverse coagulation as the material may enter the blood system
unexpectedly during injection into vertebral bodies, for example,
during vertebroplasty or kyphoplasty. The clotting behaviour of
some common bone substitute materials, which are used for or
are candidates for vertebroplasty and kyphoplasty are presented
below. The process that leads to thrombosis formation as blood
contacts an artificial surface depends on a range of factors coupled
to the material and its surface characteristics, the rheology, and the
biological aspects commencing with the initial protein adsorption
[19].
Below is presented an investigation of four orthopaedic cements:
a PMMA (traditional bone cement) and three calcium-based ceramic
cements, using a close-circuit Chandler loop model with the inner
surfaces of the poly(vinyl chloride) (PVC) tubing coated with
heparin. The model exposes the test materials to fresh human whole
blood. A special procedure was developed to evaluate solidifying
pastes in the Chandler loop model. This procedure covers a section
of the inner wall of the tubing with a thin layer of non-cured cement
paste. Thereafter the tubing is filled with fresh whole blood and the
loop is closed. The loop is rotated at 32 rpm in a 37°C water bath
for 60 minutes. The cements are curing in contact with the flowing
blood.
After incubation, the blood and the material surfaces were
investigated with special attention to clotting reactions. Blood
samples were collected and supplemented with ethylene-diamin-
tetra acid (EDTA) for cell count analysis. Blood from the loops was
centrifuged to generate plasma for analysis of the thrombin-anti-
thrombin (TAT) complex, C3a, and the terminal compact complex
(TCC) complement marker. It is concluded that the clotting behaviour
of the Ca-aluminate-based cement and the PMMA is considerably
lower than that of the calcium phosphate and sulphate materials
in these tests. More details about the test method are described in
Chapter 10.