Biomedical Engineering Reference
In-Depth Information
and bioresorbability phenomena are fine examples of chemical
reactivity and calcium orthophosphates (both non-substituted and
ion-substituted ones) fall into these two categories of bioceramics
[4-7, 39, 40, 45, 49-54, 77, 531, 589-591]. A bioactive material will
dissolve slightly but promote formation of a surface layer of biological
apatite before interfacing directly with the tissue at the atomic
level, that result in formation of a direct chemical bonds to bones.
Such an implant provides a good stabilization for materials that are
subject to mechanical loading. A bioresorbable material will dissolve
over time (regardless of the mechanism leading to the material
removal) and allow a newly formed tissue to grow into any surface
irregularities but may not necessarily interface directly with the
material. Consequently, the functions of bioresorbable materials are
to participate in dynamic processes of formation and re-absorption
occurring in bone tissues; thus, bioresorbable materials are used as
scaffolds or filling spacers allowing to the tissues their infiltration
and substitution [50, 194, 295, 593-595].
Interestingly, but a distinction between the bioactive and
bioresorbable bioceramics might be associated with a structural
factor only. For example, bioceramics made from non-porous,
dense and highly crystalline HA behaves as a bioinert (but a
bioactive) material and is retained in an organism for at least 5-7
years without noticeable changes (Fig. 4.2 bottom), while a highly
porous bioceramics of the same composition can be resorbed
approximately within a year. Furthermore, submicron-sized HA
powders are biodegraded even faster than the highly porous HA
scaffolds. Other examples of bioresorbable materials include porous
bioceramic scaffolds made of BCP (which is an intimate mixture of
either β-TCP + HA [111-126] or α-TCP + HA [8-12]) or bone grafts
(dense or porous) made of CDHA [152], TCP [411, 596, 597] and/
or ACP [462, 598]. One must stress that recently the concepts of
bioactive and bioresorbable materials have converged and bioactive
materials are made bioresorbable, while bioresorbable materials are
made bioactive [599].
experiments an inflammatory
reaction was observed after implantation of calcium orthophosphate
bioceramics [600-602], the general conclusion on using calcium
orthophosphates with Ca/P ionic ratio within 1.0-1.7 is that
all types of implants (bioceramics of various porosities and
structures, powders or granules) are not only nontoxic but also
Although in certain
in vivo
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