Raman Microscopy and Imaging: Applications to Skin Pharmacology and Wound Healing - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 371

lipophilicity of the acetate presumably permits intercalation within the well-
ordered region of the SC.
Tracking the formation of the bioactive material ( -TH in this case) from

its acetate pre-cursor is an important demonstration of the power of confocal
Raman microscopy. To develop an analytical approach to track the in situ hy-
drolysis, we observe (Fig. 15.7c) that

α

-TAc has a strong feature at 560 cm − 1
and weaker bands at 582 and 591 cm − 1 , while

α

α -TH exhibits a strong fea-

ture at 590 cm − 1 558 cm − 1 . Thus the area ratio

I (590) /I (560), with the denominator metric including both the 558 (

and a weaker feature at ∼

α -TH)

and 560 ( -TAc) bands, provides a useful measure of the hydrolysis. The area

ratio of the high-frequency half of the 590 cm − 1 to the band at 558 / 560 cm − 1
was used to track hydrolysis. This procedure reduces interference from the
582 cm − 1 feature of

α

-TAc.
A calibration curve tracking mixtures comprised of the two pure compo-
nents mixed in various proportions is shown in Fig. 15.9a. A ratio map of
the same parameter from a skin sample to which

α

-TAc has been added is
imaged in Fig. 15.9b. As is evident from a comparison of the image with the
calibration curve, most of the

α

-TAc remains un-hydrolyzed. Values of the
ratio range mostly from 0.12 to 0.25 and reveal (from the calibration plot
in Fig. 15.9a) little or no hydrolysis. In a few regions of the viable epider-
mis, the ratios are slightly elevated (

α

0 . 25-0 . 30). It is noted that the Raman
marker bands deep in skin are weak, possibly leading to significant errors in
the estimate of the extent of hydrolysis. Data from deeper regions ( > 30

∼

m)
in the sample have therefore been removed from the image. In addition, the
scattering coecients of the two species may differ in skin compared with the
mixtures used for calibration. Nevertheless, the ability to estimate (at least
semiquantitatively) the extent of hydrolysis in different spatial regions is a
potentially useful advance.

μ

15.3.3 Wound Healing

Introduction

The response of the human body to wounding leads to rapid sealing of the site,
prevention of infection, and organization of a complex spatially and tempo-
rally coordinated response to initiate healing of the injured tissue. For recent
reviews, see Gurtner et al. [38] and Coulombe [39]. Cutaneous wounds lead
to disruption of the epidermis and dermis resulting in the loss and damage
of epithelial cells and connective tissue. Wound closure involves two main
cellular mechanisms, re-epithelialization and contraction of connective tissue.
Re-epithelialization of skin wounds begins within a few hours following in-
jury [40]. At the edge of the wound, keratinocytes become activated, start to
proliferate, and migrate to cover the site. The migration becomes significant
within the first 2 days and is carried out by a layer of epidermal cells known
as the migrating epithelial tongue [41]. The process is essentially complete