Biomedical Engineering Reference
In-Depth Information
citric or glycolic acids) to form a stable paste that can be directly
injected into a bone defect [584-589]. In literature, this type of
cement pastes is called “premixed calcium phosphate cements”
(occasionally referred to as PCPC) in which the paste remains stable
during storage and hardens only after placement into the defect.
The paste can be obtained of different consistencies, from low
viscosity ones to putty-like plastic pastes [122-124]. Setting occurs
in vivo
in a physiological
solution and results in CDHA formation. This approach eliminates
the powder-liquid mixing stage during surgery, which might
improve the cement performance. Besides, it allows shortening the
surgical time and the risk of operator-induced error is considerably
reduced. Unfortunately, the setting reaction of the premixed
formulations is difficult to control and the mechanical properties
of the hardened cements are poor. Besides, such formulations must
be protected from the environmental moisture during storage [590,
591]. Furthermore, little attention has been paid to the problem that
the presence of water impurities in the non-aqueous liquid and/or
the powdered solid can compromise the stability of the paste.
Earlier formulations of the premixed calcium orthophosphate
cements had a setting time of longer than 1 h and a low mechanical
strength [584]. Afterwards, improved formulations have been
developed. They exhibit a rapid setting when immersed in a
physiological solution, yielding a hardened ceramics with a higher
mechanical strength, approached the reported strengths of sintered
porous HA implants and cancellous bone [585-587]. Brushite-
forming premixed cement formulations have been introduced
as well [590, 592-594]; they are expected to have a shorter
setting time then the aforementioned apatite-forming premixed
cement formulations. Creation of premixed macroporous calcium
orthophosphate cement scaffolds reinforced by slow-dissolving
fibers (in other words, premixed macroporous concrete scaffolds)
is the latest achievement of this approach [326].
Other researchers invented cements in the form of two injectable
pastes that could be mixed together and injected at the time of
implantation (e.g., by a static twin-chambered mixer incorporated in
the injection cannula that allows injection of the paste immediately
after mixing) [593, 594]. A wide range of possibilities appears by
upon a contact with body fluids or
in vitro
Search WWH ::
Custom Search