# Modifications of Wound Dressings with Bioactive Agents to Achieve Improved Pro-Healing Properties
## 2 Current Concepts in Wound Dressings
Films protect wounds against bacterial infections, enhance regeneration, and provide optimal oxygenation and moisture at the wound bed due to their good permeability to oxygen and water vapor. The main restriction in their use is their low absorption capacity, which excludes these biomaterials from the list of suitable dressings for exuding wounds [27]. In contrast, foams have high absorption capacity due to their highly porous structure and are dedicated to highly exuding wounds. The structure of the foam dressing is usually multi-layered, made of a porous polymeric (most often polyurethane) inset with an outer germ-resistant, waterproof, and anti-adhesive layer [31]. This type of wound  
Figure 2: The features of the ideal wound dressing. dressing is also recommended for granulating wounds or lower leg ulcers, but it is not suitable for dry and eschar wounds [15; 31]. A great variety of wound dressings are produced using a natural polysaccharide called chitosan. It can be processed into functional dressings, such as films, fibers, sponges, and hydrogels [3]. In view of important biological properties of the chitosan, such as biodegradation, biocompatibility [32; 33], antioxidant [34; 35; 36] and antimicrobial [37; 38] properties, non-toxicity [39; 40], and anti-cancer properties [41; 42], it is not surprising that chitosan is a frequently used compound for the production of various modern dressing materials. Nevertheless, its low solubility is a limiting factor that contributes to a growing interest when it comes to chemical modifications of this molecule [43]. Except chitosan, collagen is also frequently used in the production of wound dressings [44]. However, although it promotes wound healing, collagen-based materials are often permeable to external pathogens, limiting their clinical applications [20]. Cellulose has attracted considerable interest related to biomaterial production due to its suitable mechanical and physical properties. Moreover, it is characterized by biodegradability and low production cost, making it widely used for the fabrication of dressing materials [45]. Biomaterials for wound healing applications can be enriched with different bioactive compounds that can speed up the regeneration process. Bioactive dressings are aimed at delivering active substances (antibiotics, peptides, drugs, vitamins, growth factors etc.) to the wound environment to enhance the process of wound healing [46]. Interactive dressings directly interact with the wound bed promoting regeneration process. These interactions include removal of excessive exudate, providing a moist environment in the wound bed, and prevention of infections [47]. Importantly, interactive dressings are favorable for the re-epithelialization process due to better oxygen concentration and pH control [48]. All mentioned features of the dressings optimize the skin regeneration process. A short classification of the wound dressings is presented in Figure 3.  
Current review work was conducted using mainly a PubMed electronic database (supported with sporadic use of Google Scholar). The search of the available scientific contributions was limited to the last five years. The following keywords during collecting scientific reports were used: biomaterials, bioactive dressings, wound dressings, skin regeneration, curcumin, essential oils, vitamins, and chronic wounds.