Biomedical Engineering Reference
In-Depth Information
Bioceramics
Applications
Reactivity
Inert
Resorbable
Bioactive
Substrate
for tissue
engineering
Substitution
Al
2
O
3
ZrO
2
Carbons
Sintered HA
CaAl
2
O
4
Si
3
N
4
SiC
HA, HCA
Bioglasses
Glass-ceramics:
A-W, Ceravital
Particle size,
crystal size,
porosity
CaSO
4
Coral-CaCO
3
:
aragonite
Ca-phosphates:
a
-TCP
b
-TCP
OCP
DCPA
DCPD
TetCP
HA:10
m
m
also with: ZnO,
Al
2
O
3
, Fe
2
O
3
,-
Coatings
Fillers
Small
pieces
HA: hydroxyapatite
HCA: hydroxycarbonate apatite
A-W: apatite - wollastonite
TCP: tricalcium phosphate
OCP: octacalcium phosphate
DCPA: dicalcium phosphate anhydrous
DCPD: dicalcium phosphate dihydrate
TetCP: Tetracalcium phosphate monoxide
Powder
Monolith
7.3
Main first and second generation bioceramics and their clinical
applications.
when they are synthesised by a sol-gel method.
8
Moreover, some glass
compositions that are considered to be bioactive can be completely resorbed
when used as particulates under a certain size limit, for instance, 90 mm
for Bioglass
®
45S5.
6
analogous examples can be found among crystalline
ceramics. For instance, the
in vivo
reactivity of hydroxyapatite (HA) can
range from almost bioinert, when highly sintered like dense monoliths,
9
to
resorbable, when used in powdered form, passing by the bioactive character
generally attributed to Ha.
10
When some glass compositions presenting the highest levels of bioactivity
were investigated, it was found that they were able to bond to hard and
soft tissues, whereas other bioactive materials only bond to hard tissues. to
explain these differences in reactivity in 1994 Hench defined two classes
of bioactivity: class a, osteoproductive and class B, osteoconductive.
11
the
first one, takes place when material obtains extracellular and intracellular
responses, whereas in the second one only an extracellular response is
obtained. it was explained that the ions released from these bioactive glasses,
in particulate form, stimulated regeneration of living tissues mediated by
genes. these osteoproductive glasses were considered to be third generation
bioceramics
6
and are the basis of actual research efforts looking for new
biomaterials that intend to stimulate a cellular response. nowadays, research
efforts are concentrated on porous second generation bioceramics and new
advanced bioceramics. in these materials, ceramic plays the role of scaffold
of cells and substances with biological activity (growth factors, hormones…)
