Biomedical Engineering Reference
In-Depth Information
ingrowth quantitatively and qualitatively speaking, when compared to the
BCP/Bi and BCP/Lu implanted materials [61].
Improved visualisation is necessary when bone defects are fi lled. The BCP/Ba
composite has given promising results for developping a radiopaque, resorbable,
injectable bone substitute designed for MIS, particularly in spine surgery for
vertebroplasty.
4.4.4 BCP for Resorbable Osteosynthesis
Following a loss of osseous substance of tumoral or traumatic origin, it is often
necessary to restore the osseous structure associating osteosynthesis and bone
substitute. However a second operation is required to remove the osteosynthesis
after wound healing, otherwise the osteosynthesis (such as titanium or Peek) will
remain in place defi nitively. Resorbable osteosynthesis has been developed using
resorbable polymers for many years [62-64]. Resorption control and higher
osteogenic properties have improved using a combination of calcium phosphate
granules, generally b-Tricalcium phosphate. PL DLLA polymers are resorbable
by means of hydrolysis but are not well controlled over time. After six months, the
hydrolysis appears in all the samples and suddenly the mechanical properties
disappear. This uncontrolled process can appear in six or twelve months, often
before bone ingrowth healing and mechanical stability have been attained. For
osteosynthesis, better control of mechanical stability is required and thus pro-
mote bone ingrowth at the expense of the implant.
The advantage of a composite with PL DLLA and PCa is that it is possible to
control the hydrolysis over time, to maintain the initial mechanical properties
during bone ingrowth and then have long term mechanical properties from bone
ingrowth at the expense of the implant. The development of composites combin-
ing PL DLLA and PCa have proved from the use of interference screws that the
hydrolysis is controlled and delayed over time until wound healing. A recent
study [65,66] reported the resorption kinetics of a composite using PL DLLA
(Poly [L-Lactide-co-D, L-Lactide] acid) charged with PCa granules and the inter-
action with an injectable substitute such as MBCP gel. The injectable biomaterial
was non self hardening, the biomaterial consists of BCP granules associated with
a hydrosoluble polymer. The material was shown to be perfectly biocompatible
and potentially resorbable and, thanks to its initial plasticity, it assumes the shape
of the bone defects very easily, eliminating the need to shape the material to ad-
just it to the implantation site. MBCP gel has no mechanical properties and must
be associated with osteosynthesis during the bone ingrowth process. However,
bone cells are able to invade the spaces liberated by the disappearance of the
polymer carrier. Bone ingrowth takes place all around the granules and at the
expense of the resorption of the BCP granules. In time, mechanical properties
could be observed due to the presence of the newly-formed bone [17,67-69].
Moreover, the three-dimensional structure of the network favourably infl uenced
recruitment, cellular differentiation, angiogenesis and the formation of bone
tissue.
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