Enhancing skin epidermal stability - Biomaterials for Treating Skin Loss - page 132

enzymatic detachment is not required, cell surface proteins are not damaged and
therefore take and stability may be enhanced.
Laserskin ® has been under development since the early 1990s. However,
comparisons with other epithelial autografts, particularly in conjunction with
different dermal substitutes have not been conducted (Price et al ., 2006). Addi-
tionally, no studies on the long term stability or persistence of cultured cells
delivered on Laserskin ® have been carried out. Fibroblast-keratinocyte compos-
ite cultures using Laserskin ® have been grown in vitro at the air-liquid interface
and a wide range of target antigens have been examined in order to characterise
the cultured skin. There was formation of laminin-5 and collagen type VII,
which are the main components of the basal lamina. The fibroblasts seeded in
the dermal matrix adhered, proliferated and secreted the main extracellular
matrix (ECM) components collagen I, III and IV, fibronectin and laminin I
(Zacchi et al ., 1998).
Differentiation of keratinocytes cultured on Laserskin ® has been demon-
strated, with specific basal cytokeratins being only expressed in cells growing in
the perforations and in the basal layer. Structures resembling hemidesmosomes
were also evident in the cells in close contact with the Laserskin ® membrane
(Andreassi et al ., 1991). It was suggested by these authors that the cells growing
on the Laserskin ® were at a point preceding the formation of a true dermal-
epidermal junction (DEJ), unlike cell sheets grown on plastic. Initial
ultrastructural similarities to a basal layer were noted by Pianigiani et al . (1999)
in the region close to the Laserskin ® substrate although with time these cells
became keratinized. They also demonstrated that epidermal cells grown in vitro
on Laserskin ® developed a fully functional stratum corneum providing a physi-
ological barrier, reducing dehydration and thus improving the likelihood of
successful take and epidermal stability.
The stability of keratinocyte seeded Laserskin ® sheets may be enhanced by
alterations to the physical structure. The rate of hyaluronic acid resorption is
dependent on both the type of hyaluronic acid and the degree of esterification, with
100% esterified hyaluronic acid having a longer residence in tissues when com-
pared with partially esterified hyaluronic acid. Prolonged action of 100% compared
with 75% esterified hyaluronic acid may have promoted more angiogenic effects
(Price et al ., 2006) therefore both the presence and structure of hyaluronic acid are
likely to affect the stability of grafted epidermal elements. The hyaluronic acid
derivative used to prepare both the microperforated membrane and the non-woven
fabric are esters of hyaluronic acid. These esters have a percentage of esterification
of between 75 and 100%. By varying the percentage of esterification of the
hyaluronic acid esters used, it is possible to control the degradation kinetics of the
tissue support and, therefore, the length of time that the device can remain in situ .
Degradation (to 75%) times of 30 days for the 100% ester and 4 days for the 75%
ester were reported by Price et al . (2006). Owing to a fast rate of degradation of
Laserskin ® in the treatment of traumatic soft tissue injuries, an additional split