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</td>
<td>
Mitogenic effect of EGF requires continuous exposure of
target cells to EGF for a minimum 6-12 h.The stimulation of wound healing by EGF has been
confirmed by Laato et al. as growth of granulation tissue
in sponge implants used as inductive matrices.Buckley et al. reported that
sustained release of EGF from subcutaneous pellets accelerated
process of wound repair in rats, whereas daily
injections of EGF were much less effective.
</td>
</tr>
</table>
Layer Usage
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The half-life of EGF in the body is,
however, too short to exert the biological activity effectively
when applied via injection or in free form. It is
known that many proteases are activated in the injured
tissue and they easily decompose EGF in the wounded or
burned site of skin as soon as it is applied as an ointment
. Therefore, our biomaterial grade sponge has protease inhibitor feature. A porous and biodegradable matrix that would serve as
the host for the proliferating cells and would degrade
spontaneously without creating any adverse effects while
the tissue regenerates was planned to act as the underlying
dermal layer.Thus,with biodegredation of sponge,EGF and KGF will be able to pass through the layer easily.
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Discussion onto Material
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Polyurethane membranes were used as the external
layer because of their biocompatibility and hemocompatibility.
Besides they are highly elastomeric (extensible)
and permeable to gaseous substances. They create an
inert environment for the blood, control water and heat
transfer through the wound area, and prevent bacterial
invasion. They are mechanically strong and protect the
wound from the external effects.
Gelatin was chosen as the porous soft layer material.
Since it is practically more convenient than collagen and
known to have no antigenicity while collagen expresses
some in physiological conditions. Also, it is extremely
di$cult to prepare concentrated solutions of native collagen.
Furthermore, gelatin is far more economical than
collagen. The soft and porous gelatin sponges beneath
the polyurethane films would have direct contact with
the tissue and expected not to cause any damage to the
wound area. Because of their high absorptive capacity
they would prevent fluid accumulation. Therefore, excess
water (exudate composed of wound fluids) and cell debris
would be absorbed and retained inside the sponges. Tissue
ingrowth would take place in the matrix and the
regenerating wound tissue and implant would not be
separated. The sponge is biodegradable, therefore, it
would degrade and be replaced by the newly regenerated
tissue.
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Preparation of gelatin sponges and bilayer wound dressing
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Preparation of gelatin sponges : Aqueous gelatin solutions stirred at about 2000 rpm
for 30 min at room temperature and glutaraldehyde solutions
were added to form crosslinkings. Then the solutions
were poured into molds, frozen in liquid nitrogen
and freeze-dried for 24 h. The resultant sponges (thickness
ca. 1 cm) were exposed to UV for 1 h prior to in vivo
applications to achieve sterilization. These sponges were
labeled as GS.
Preparation of bilayer wound dressing : In the present study, bilayer wound dressing was constructed
in situ, at the wound site, by initially applying
the sponges and then covering with commercially available,
adhesive polyurethane, OpSite. However, in order
to see the adhesion of sponge onto polyurethane membranes;
some bilayer dressings were prepared by pouring
the foaming gelatin solution on polyurethane "lms prepared
in our laboratory. But these dressings were not
used in in vivo applications.
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References
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[1]Ulubayram K., Cakar A.N., Korkusuz P., Ertan C. and Hasirci N. “EGF containing gelatin-based wound dressings.” Biomaterials, accepted 22 September 2000.
[2]Rhinewald JG, Green H. Epidermal growth factor and the multiplication
of cultered human epidermal keratinocytes. Nature
1977;265:421.
[3]Laato M, Niinikoski J, Bardin B, Lebel L. Stimulation of wound
healing by epidermal growth factor: a dose dependent e!ect. Ann
Surg 1986;203:379}81.
[4]Buckley A, Davidson JM, Kamerath TBW, Woodward SC.
Sustained release of epidermal growth factor accelerates wound
repair, Proc Natl Acad Sci USA 1985;82:7340}4.
[5]Okumura K, Kiyohara Y, Komada F, Iwakawa S, Hirai M, Fuwa
T. Improvement in wound healing by epidermal growth factor
(EGF) Ointment. I. E!ect of nafamostat, gabexate, or gelatin on
stabilization anf e$cacy of EGF. Pharm Res 1990;7(12):1289}93.
[6]Hasirci N, Burke A. A novel polyurethane "lm for biomedical use.
J Bioac Comp Polym 1987;2:131}41.
[7]Ulubayram K, Hasirci N. Properties of plasma modi"ed
polyurethane surfaces. J Colloid Surf B: Biointeractions 1993;
1:261}9.
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