Bone-Like Mineral and Organically Modified Bone-Like Mineral Coatings - Biological and Biomedical Coatings: Processing and Characterization - page 12

TABLE 1.5
Commonly Used SBF Treatment Applications

Application SBFTreatment Reference

Metals 1. 5× SBF for 24 h at 37°C

2. 5× mSBF for 24 h at 50°C

Barrere et al. 2003

1. 5× SBF for 24 h at 37°C
2. 5× mSBF for 48 h at 50°C

Habibovic et al. 2005

Ceramics 1. SBF 4 days at 37°C Liu, Ding, and Chu 2004

PLGA films 1. 2× mSBF at 37°C Luong et al. 2006

PLGA scaffolds 1. 4× mSBF for 12 h at 37°C

2. SBF change every 6 h
3. 2× mSBF for 108 h at 37°C
4. SBF change every 8 h

Segvich, Luong, and Kohn 2008;
Segvich et al. 2008

Source: Ong et al., in Thin Calcium Phosphate Coatings for Medical Implants, Leon and Jansen

(eds.), Springer, pp. 175-198, 2009. With permission.

resulting in the formation of an apatite coating on the substrate. In the absence of this ther-
modynamically favorable situation, homogeneous precipitation can occur (Bunker et al.
1994). The thickness, morphology, and composition of the BLM formed are dependent on
several factors, such as the incubation time and temperature, ionic concentration, composi-
tion, and pH of SBF and method of surface functionalization. For example, apatite formed
from SBFs with low ionic products is more crystalline compared to apatite formed from
SBFs with higher ionic products. Also, the Ca/P ratios of BLM vary inversely with SBF
solution ionic activity—higher ionic products lead to lower Ca/P ratios (Shin, Jayasuriya,
and Kohn 2007).
Characterization of biomimetic apatite to quantify and understand its properties can
be achieved using several methods (Figure 1.1). Fourier transform infrared spectroscopy
(FTIR) is useful in determining chemical composition by measuring carbonate and phos-
phate band intensities and ratios, and presence of any organic constituents. X-ray diffrac-
tion (XRD) and transmission electron diffraction (TED) allow the measurement of the
lattice parameters of the crystallographic peaks and thereby assess the degree of crystal-
linity. Scanning electron microscopy (SEM) can be used to observe surface morphology
and, when used along with energy dispersive x-ray spectrometry (EDX), can provide a
qualitative measure of elemental composition. N-SEM, which is another form of SEM, can
be used to characterize surface morphology with high natural contrast but at the cost of
resolution. Microcomputed tomography (µCT) generates images of 3-D mineralized scaf-
folds from which total mineral content, volumetric mineral density, and distribution of
mineral can be quantified (Segvich, Luong, and Kohn 2008).
The use of SBF to prepare apatite coatings on prosthetic metal and ceramic implants
has been extended to soft resorbable materials used in bone tissue engineering to create a
new class of osteoconductive biomaterials. Since biomimetic apatite precipitation occurs at
ambient temperatures, it is possible to coat temperature-sensitive scaffold materials such
as polymers with a layer of uniform mineral. The use of processing techniques based on
biomineralization also allows the incorporation of biologically active molecules such as
growth factors, proteins, and nucleic acids into the mineral layer without any loss of bioac-
tivity due to high temperatures (Segvich et al. 2008; Luong et al. 2006; Luong, McFalls, and
Kohn 2009). Moreover, since porosity is important for tissue infiltration and vasculariza-
tion to induce biological fixation, polymer scaffolds can be coated with a spatially uniform