Self-Setting Calcium Orthophosphate Formulations: Cements, Concretes, Pastes, and Putties - Calcium Orthophosphates: Applications in Nature, Biology and Medicine - page 485

succinic acid disodium salt solution, the initial setting times of the
cement were 19.4 ± 0.55 and 11.8 ± 0.45 min, respectively. These
setting times were much shorter than that of distilled water, 88.4 ±
0.55 min [260]. Biopex

®

is mixed with a spatula inside a syringe that
can be opened from the front. After mixing, the front part is closed,
a needle is inserted into this front part and the cement paste can be
manually injected [197, 198].
Several systematic studies on the influence of composition
and concentration of the liquids used in preparing of calcium
orthophosphate cements were performed as well [23, 227].
Unfortunately, the results appeared to be rather unclear. For example,
for several cements, mixing with sodium citrate or citric acid resulted
in some effects on the initial setting time [23, 228], while for other
cements the effect was insignificant [227]. Concentration increasing
of sodium citrate solution resulted in initial setting time increasing
[23, 227], although the injectability variations of the cement pastes
were inconsistent [23, 228].

5.4.3 Rheological Properties of the Self-setting

Formulations

Good injectability, adequate viscosity, and satisfactory cohesion are
required for the successful biomedical applications of the self-setting
calcium orthophosphate formulations [261, 262]. Injectability is an
ability of a paste to be extruded through a small hole of a long needle
(e.g., 2 mm diameter and 10 cm length) [263, 264] (other needles are

also applied [265, 266]); and for certain applications, injectability
is even a prerequisite. It is measured by the weight percentage of
the cement paste that could be injected without demixing from a
standard syringe by either a hand or a force of 100 N maximum (Fig.
5.3). Usually, injectability of a cement paste varies inversely with its
viscosity, the P/L ratio, as well as the time after starting the mixing
of liquid and powder [56, 264, 267]. Furthermore, injectability
is improved with smaller particle sizes, with shorter and larger
diameter cannula, as well as at smaller flow rates [263]. Moreover,
particle shape of the powder is also expected to have effects on
the injectability. Namely, powders with spherical shape or round
particles may contribute good injectability. Spherical powder itself
is easy to roll and thus good handling properties and injectability are