Biomedical Engineering Reference
In-Depth Information
Figure 5. Dynamic compaction apparatus.
material. Heating is necessary to strengthen the material but unfortunately prevents mixing of
therapeutic agents with CaP before consolidation. To overcome this problem, therapeutic agents
have been loaded on CaP ceramics after consolidation by adsorption through electrostatic and
reversible bound simply by incubating the ceramic block in a solution containing the drug. In
addition, an innovative process, called “dynamic compaction”, to consolidate CaP powder with-
out the use of external heating, has recently been patented (Nantes University, patent n
°
0 666
764). In this process, compaction is achieved by a shock wave produced by piston impact on
the surface of CaP powders and subsequent consolidation by localized interparticle melting
42
(Fig. 5).
Pharmacokinetic Profile of Drug Released from CaP Ceramics
Drug release pattern from homogeneous drug-loaded solid matrix generally follows the
square root of time relationship:
43,44
M
t
= A M
o
[C
s
⋅
(D
i
ε
/
τ
) (2C
d
-
ε
C
s
)
t
]
1/2
K = A M
o
[C
s
⋅
(D
i
ε
/
τ
) (2C
d
-
ε
C
s
)]
1/2
where M
t
is the amount of drug released from the matrix at time
t
, K the Higuchi release
rate constant, M
o
the total amount of drug loaded, A the matrix surface area, D
i
the drug
diffusion coefficient, C
s
the drug solubility, C
d
the drug concentration,
τ
the matrix tortuosity,
and
ε
the matrix porosity. The linear pattern for the square root of time obtained with CaP
ceramic systems
5
indicates that initial release apparently involves a first-order diffusion-controlled
mechanism, as described by Higuchi et al.
44
However, this theoretical analysis of the release
rate of drugs dispersed in solid matrices concerns cases in which solid drug particles are dis-
persed in an homogeneous matrix. In this case, matrix acts as a diffusional support from which
drugs are released by the leaching action of penetrating solvent. This description does not seem
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