**2. Mechanism of wound healing**

Wound healing is an extremely complex and dynamic process, which includes replacing of devitalized and missing cellular structures and tissue layers. It reflects in a set of biochemical events that integrate into an organized cascade of processes to repair the damaged tissue [5]. Immediately after injury, damaged vessels leak fluid, to which the body responds with haemostasis. Platelets start to aggregate in the wound bed and secrete multiple growth factors that contribute to an effective clot formation to hinder further loss of fluids from the defected area [6]. Simultaneously with the launch of haemostatic mechanisms, the inflammatory phase is induced as well [7]. It is characterized by local vasodilatation, platelet aggregation and phagocytosis, which together with the release of several cytokines, contribute to local inflammation of the wound site. Multiple chemokines, released by platelets, stimulate the immune and other cells (e.g. keratinocytes) to release growth factors and cytokines to regulate various signalling cascades that govern the inflammation and healing in general [8]. Macrophages and other immune cells are stimulated and they migrate towards the wound to dispose cell debris and fight invading bacteria during the wound healing. Angiogenesis occurs at this phase and new blood vessels transport essential nutrients to the wound bed [6]. The next phase in wound healing is the proliferative phase, which is characterized by granulation, wound contraction and epithelialisation. During granulation, fibroblasts form a bed of collagen, followed by the production of new capillaries [7]. During wound contraction, myofibroblasts decrease the size of the wound by gripping the wound edges and pulling them into the wound interior mechanisms that resemble that of smooth muscle cells. After completion of respective processes, unneeded cells undergo apoptosis (controlled cell death) [9]. Epithelialisation is initiated by keratinocytes proliferating and migrating across the wound site [8]. Fibroblasts are activated and differentiated into myofibroblasts that (either indirectly by production of cytokines or directly) regulate other cells to grow and form new epithelial tissue over the wound site. The final wound healing phase is the remodelling

**Figure 1.** Schematic depiction of distinct phases during wound healing.

phase, which is governed by the rearrangement of the newly formed extracellular matrix (ECM) using increasing amounts of type I collagen. The fibres of collagen rearrange their structures with increasing interfibrillar binding and diameter [10]. The aim of wound treatment can be therefore described as a therapy to either shorten the time required for healing or to minimize the undesired consequences, for example extensive scarring [11]. A general overview of the wound healing is shown in **Figure 1**.
