Bone-Like Mineral and Organically Modified Bone-Like Mineral Coatings - Biological and Biomedical Coatings: Processing and Characterization - page 22

biological response. Adsorption, being largely a surface phenomenon and characterized
by weak binding forces and burst release, is not useful in producing spatial distributions
and/or gradients of biomolecules. Coprecipitation involves adding the protein into the
saturated calcium-phosphate solution, resulting in a heterogeneous matrix consisting of
both mineral and protein being simultaneously precipitated onto the substrate. It is pos-
sible to distribute single or multiple molecules over sections or the entire thickness of the
coating by varying the time periods of mineralization and coprecipitation, thus producing
gradients of bioactive molecules within the biomaterial (Luong et al. 2006) (Figure 1.5).
Further, since the precipitation occurs at ambient temperatures, loss in biological activity
of the protein can be minimized.

Effect of Protein Addition on BLM Formation

Bovine serum albumin (BSA) is often used as a model protein to understand the influence
of proteins on mineral nucleation and growth. Addition of BSA to SBF causes a delay in
the mineral nucleation and growth, indicating that BSA inhibits these processes (Luong

Top of
mineral layer
(external
surface)

Preliminary
mineral

Top layer
of mineral
(no FITC)

Preliminary
mineral

Bottom of film
(below
mineral layer)

(d) 3-day min.
2-day cop.,
1-day min.

(b) 3-day min.,
3-day ads.

(c) 3-day min.,
3-day cop.

(a) 6-day cop.

FIGURE 1.5
Images through the thickness of the mineral layer containing FITC-labeled BSA taken using confocal micros-
copy. Spatial distribution of the protein through the thickness of the mineral layer is exhibited for the follow-
ing incorporation techniques: (a) 6-day coprecipitation, (b) 3-day mineralization, 3-day adsorption, (c) 3-day
mineralization, 3-day coprecipitation, (d) 3-day mineralization, 2-day coprecipitation, 1-day mineralization.
Fluorescence can be seen where coprecipitation or adsorption has occurred. Control over the spatial distribu-
tion of the protein is shown by the presence of fluorescence through the thickness of the mineral for the differ-
ent coprecipitation groups. (Reprinted from Luong et al., Biomaterials, 27(7), 1175-1186, 2006, with permission
from Elsevier.)