Raman Spectroscopy of Bone and Cartilage - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 347

focusing light onto the periosteal surface using microprobes fitted with low
numerical aperture objectives. In this case, the laser light would penetrate
through several lamellae. The lamellae themselves have staggered orientation
[37]. This property, together with depolarization by light scattering, makes it
dicult or impossible to observe polarization effects under these experimental
conditions.

14.5 Genetic Defects and Genetic Modifications

Morris and coworkers have investigated early mineralization in mouse cal-
varia subjected to periodic loading to model craniosynostosis, a birth defect
in which the calvarial sutures fuse prematurely. Raman imaging was used to
study the composition, relative amounts, and locations of mineral and matrix
components in murine fetal calvarial sections [38]. The results are summa-
rized in Fig. 14.4. The same mineral composition was found in the control-
and force-induced tissue. Addition of fibroblast growth factor-2 (fgf2) was
found to increase the rate of mineralization without causing a change in min-
eral composition [6, 39, 40]. However, accelerating mineralization did result
in a less ordered mineral structure.
In a subsequent study mineralization in cultured fetal murine calvarial sec-
tions was followed for up to 72 h [7]. Transient octacalcium phosphate (OCP)
or OCP-like intermediates were observed and converted to CA over periods
of a few hours. Increased levels of OCP were found in sutures undergoing
fgf2-induced accelerated mineralization. These results supported the transient
precursor mineralization mechanism, which had been hypothesized but not
previously observed [41, 42].
Kozloff and coworkers reported changes in mineralization for the Brtl
mouse, a model of Sillence type IV osteogenesis imperfecta in which glycine-
349 is replaced by cysteine in one or both α 1 chains of matrix collagen [43].
They found no differences in crystallinity (inverse band width of phosphate ν 1

between wild type and the heterozygous brtl mouse). Mineral/matrix ratios
were different.

14.6 Biomechanical Studies

The first studies relating damage to bone chemistry focused on mineral
changes that occurred near sites of mechanical deformation. While these
changes were initially interpreted as phase changes[21, 44-46], other workers
have interpreted similar changes as increases or decreases in mineral lattice
strain as the applied load is change [47, 48]. This interpretation is consis-
tent with Raman studies of bone powder at high (up to 4 GPa) hydrostatic
loading [49]. In this case band shifts are completely reversible when the tissue
is unloaded (Fig. 14.4).