Team:METU-Gene/Gelatin Sponge

It is believed that, epidermal growth factor (EGF) stimulates the growth of keratinocytes in vivo, and therefore plays an important role in the process of wound healing that depends on mitosis and migration of keratinocytes. Rhinewald and Green showed, in vitro that in the presence of growth factors, higher percentage of cells leave the resting state, enter and remain in the mitotic cycle. Assuming a similar effect of EGF on epidermal cells in vivo, the primary mechanism of enhanced wound healing is most likely due to increased proliferation of epidermal cells.

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.

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.

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.

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.

[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.