Page 397 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

374 BIOMATERIALS

: carbonate
: phosphate

Absorbance 2000 1900 1800 1700 1600 1500 1400 900850

2.00 SBF
1.75 SBF
1.50 SBF
1.25 SBF
1.00 SBF
0.75 SBF
Control
2200 2000 1800 1600 1400 1200 1000 800 600 400
–1
Wave number (cm )
FIGURE 15.9 FTIR spectra of the mineralized pore surfaces of 85:15 PLGA scaffolds incubated in simulated body
fluids (SBF) of varying ionic activity products (IP) for 16 days. Inset = bands within the boxes stacked and enlarged to
better show changes in CO 2− . Band intensities of phosphate and carbonate increased with increasing IP. [From Shin
3
et al. (2007), with permission.]
15.4.2 Inorganic/Organic Hybrid Biomimetics
Advancements in understanding biomineralization have also resulted in the synthesis of mineral-
organic hybrids, consisting of bonelike apatites combined with inductive factors, to control cell pro-
liferation, differentiation, and bone formation (Murphy et al., 2000b; Luong et al., 2006; Segvich et al.,
2008a; Liu et al., 2001). The method of combining inorganic mineral with organic factors can
influence the resultant release profile, and therefore influence the biological response of cells. The
most basic method of incorporating proteins into ceramics is adsorption, where the factor is loosely
bound to the ceramic surface by submersion or pipetting. A second way of incorporating protein with
apatite is to create microcarriers that allow HA crystals to form in the presence of protein or allow
protein to adsorb to the HA (Ijntema et al., 1994; Barroug and Glimcher, 2002; Matsumoto et al., 2004).
A third method of protein incorporation is coprecipitation, in which protein is added to SBF and
becomes incorporated into bonelike apatite during calcium-phosphate precipitation. Organic/inorganic
hybrids show promise in combining the osteoconductive properties provided by the apatite with the
osteoinductive potential provided by growth factors, DNA, and peptides.
Through coprecipitation, BMP-2 has been incorporated into biomimetic coatings deposited on
titanium, and biological activity has been retained (Liu et al., 2004). Biomolecules can be incorpo-
rated at different stages of calcium-phosphate nucleation and growth (Fig. 15.10) (Luong et al.,
2006; Azevedo et al., 2005), enabling spatial localization of the biomolecule through the apatite
thickness, and allowing the controlled release of the biomolecule. With spatial localization, there is
also the potential for delivery of multiple biomolecules.