Raman Spectroscopy: A Tool for Tissue Engineering - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 425

cells. Raman spectroscopy therefore offers tissue engineers a highly sensitive
tool for the spatial and temporal comparison of engineered tissue to native
tissue [9].
Raman spectral mapping of TE constructs, may also, when combined with
optical imaging techniques (e.g. scanning electron microscopy (SEM)) [55] re-
veal if the heterogeneity or homogeneity of ECM formed is associated with
particular scaffold features. Furthermore, Raman spectroscopic monitoring of
the variation between tissue constructs (developed using the same TE manu-
facturing processes) may be important for obtaining the necessary regulatory
approval for clinical studies. Similarly, non-invasive Raman spectral analysis
could potentially be used to “batch test” or “screen” TE constructs prior to
implantation, to both validate the correct ECM formation and detect rogue
spectral signatures, such as undifferentiated stem cells (which could lead to
tumour formation).

18.4.2 Current Examples of Raman Spectroscopy as a Tool
for Tissue Engineering

Raman spectroscopy can be used for live, in situ, temporal studies on the de-
velopment of bone-like mineral (bone nodules) in vitro in response to a variety
of biomaterials/scaffolds, growth factors, hormones, environmental conditions
(e.g. oxygen pressure, substrate stiffness) and from a variety of cell sources
(e.g. stem cells, FOBs or adult osteoblasts). Furthermore, Raman spectroscopy
enables a detailed biochemical comparison between the TE bone-like nodules
formed and native bone tissue. Bone formation by osteoblasts (OB) is a dy-
namic process, involving the differentiation of progenitor cells, ECM produc-
tion, mineralisation and subsequent tissue remodelling.
Considerable spectral similarities between the Raman spectra of TE bone
nodules and native bone nodules exist ( R =0 . 99 for mean spectrum of
MOBs compared to mean bone spectrum), including prominent mineral vi-
brations and matrix peaks characteristic of collagenous proteins (Fig. 18.4).
However, despite these similar biomolecular signatures, univariate and multi-
variate spectral analyses revealed distinct biochemical differences in both the
mineral and matrix environments. Biochemical differences between TE bone
and native bone may be of particular importance as small changes in the min-
eral environment in humans have been linked to diseases such as osteoporosis
[56]. Spectral mapping of the developing bone nodules also enables spatial
imaging of biochemicals (e.g. PO 3 −

4 ) and/or biochemical ratios (e.g. mineral
(PO 3 4 ) to matrix (amide I)) in bone nodules (Fig. 18.4 [57]). Spectral map-
ping thereby allows insights into bone nodule structure during development
and can reveal biochemical heterogeneities (Fig. 18.4).
The direct accessibility of the skin, the critical clinical need for effective
skin regeneration technologies and the huge commercial interest in cosmetic
skin products has stimulated a number of skin-based Raman spectroscopic