THE MICRO MACROPOROUS BIPHASIC CALCIUM PHOSPHATE CONCEPT FOR BONE RECONSTRUCTION AND TISSUE ENGINEERING - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 105

ranging from 60/40 to 75/25 (Table 4.1), present similar macroporosity percent-
ages (50 to 60%), but microporosity percentages are very different, varying from
3% to 25%.
A low microporosity percentage and low surface area can result in lower
bioactivity and lower dissolution properties. Microporosity of at least 20% with a
specifi c surface area of more than 2 m 2 /g is required for optimal BCP effi cacy.
Ideally, pore size for a bioceramic material should be similar to that of bone.
It has been demonstrated that microporosity (diameter

< 10 μ m) allows body fl uid

circulation whereas macroporosity (diameter > 100 μ m) provides a scaffold for

bone - cell colonisation.
Signifi cant improvements in the method for introducing macroporosity/
microporosity have recently been developed in the production of micro-
macroporous BCP (MBCP2000®, Biomatlante, France) [32]. In this method,
CDA is mixed with a combination of selected particles of naphthalene and sugar.
After isostatic compaction, the CDA block is subjected to a specifi c process of
sublimation/calcination. The BCP obtained using the classic naphthalene poro-
gen (MBCP) compared to that using a mixture of porogens, naphthalene and
sugar (MBCP2000), resulted in differences in density, Specifi c Surface Area
(SSA) of the crystal, compression strength and total porosity (Table 4.2). The
permeability after incubation in bovine serum of MBCP2000 was twice as high as
that of MBCP, and MBCP2000 showed a 30% increase in absorption compared to
MBCP. The considerably higher permeability of MBCP2000 compared to MBCP
cannot be explained by any difference in total porosity but may be attributed to
differences in pore size, particularly mesopores.

4.3.2 Physical and Chemical Properties
As

-TCP is more soluble than HA [33], the extent of dissolution of BCP ceram-
ics of comparable macroporosity and particle size will depend on the HA/

β

- TCP
ratio: the higher the ratio, the lower the extent of dissolution [8,10,13]. The dis-
solution properties are also affected by the methods used in producing the BCPs:
whether from a single calcium-defi cient apatite phase (BCP1) or from a mechan-
ical mixture of two unsintered calcium phosphate preparations (BCP2): BCP2

β

TABLE 4.2.

Temperature sintering Duration Temperature step control

D1 1050 5 none

D2 1050 5 900 ° C, 3H

D3 1050 5 900 ° C, 3H

D4 1200 5 900 ° C, 12H

D5 1200 5 900 ° C, 12H

(Temperature rise, 5 °C/min; cooling rate; 1 °C/min). Continuous heating for BCP specimens D1 and
D5; programmed heating for D2, D3, and D4).