## 2 Wound Healing
### Challenges and Promising Dressings  
Nowadays, new strategies for wound care are studied in order to reduce inpatient costs and provide an effective healing process and long-term relief [29]. When in contact with a chronic wound, the goal of any chronic wound dressing is to control the infection if present, through antimicrobial agents, but the biomaterial should also have proper mechanical properties, be biocompatible and non-toxic, remove excess exudates, be easily removed without causing trauma, create a proper moisture balance in order to accelerate the healing, provide a matrix for cell migration, and stimulate extracellular matrix deposition. However, there is no perfect wound dressing that embraces all necessary requirements. The effectiveness of a given dressing depends on the type of the wound, wound history, the applied treatment to date, and the frequency of the dressing change. All these parameters must be assessed. Wound dressings are classified according to the interaction with the wound--passive/inert dressings (immediately available for acute wounds) and bioactive/interactive dressings (bioactive compounds are incorporated to promote wound healing and protect wounds from infections) [9]. There are different types of wound dressings, such as hydrocolloids, films, foams, sponges, membranes, alignates, nanofibers, or hydrogels [30; 31]. All these distinct dressings have different properties that make them appropriate for a particular type of wound. Hydrocolloids are constituted by hydrophilic polymers (colloid particles) dispersed in water. As occlusive and moderate absorptive dressings, hydrocolloids are suitable for both acute and chronic wounds. However, some hydrocolloids can be difficult to remove and cytotoxic. Thus, this type of dressing is not ideal for infected wounds and for diabetic foot ulcers [32; 33]. Foams are non-adherent, easy to remove, and highly absorbent dressings that are able to provide a moist environment to the wound. As hydrocolloids, foams are appropriate for the treatment of granulated wounds with a mild to moderate exudate once the granulation tissue is maintained, and the epithelialization is improved [34]. Hydrogels can also be applied in granulated/epithelializing wounds and in wounds with eschar, as in the case of Vigilion(r) (Bard Home Health Ltd., Berkley Heights, NJ, USA). On the other hand, hydrogels are unsuitable for highly exuding wounds due to a possible maceration [35; 36]. Hydrogels are three-dimensional, cross-linked polymeric networks with a huge capacity to store high amounts of water. Non-adherence, high exudates capacity, biocompatibility, easy removal, healing properties, and low cost are considered as advantages of hydrogels in wound care. Nonetheless, their weak mechanical properties and their poor bacterial barrier represent some disadvantages of hydrogels [37; 38]. Recently, to avoid the formation of fluid pocketsthat enable the proliferation of bacteria, easy powders able to create in situ hydrogels have been suggested for wound care. Under physiological conditions, the powder can transform into a gel form by different mechanisms, including ionic cross-linkage, temperature modulation, and pH change, without the necessity to use external gelling agents. As advantages, in situ gelling system can cover some limitations of performed gels. This system provides easily dropped preparations and enables a more efficient and focused application in the wound site. An in situ gel-forming system composed of Pycnogenol(r) (Horphag Research Ltd., Switzerland, UK), a food supplement rich in phenolic compounds used for various medical purposes was evaluated in terms of wound healing activity. Results revealed that Pycnogenol loaded in situ gel exhibited remarkable wound healing activity and showed a significant effect on angiogenesis, granulation tissue thickness, and epidermal and dermal regeneration [39]. Sponges used as wound dressings have high porosity and are excellent dressing to maintain a moist environment at the wound site.