## 3 Nanotechnology in Wound Dressings
### Synergistic Actions between Nanoparticles and Wound Dressing Matrix  
The combination of nanoparticles with a specific matrix allows synergistic actions. Polymeric hydrogels are widespread in wound dressings. Their porous structure can absorb large amounts of exudate, maintain moisture in the wound site, and permit oxygen permeation [88]. Gas exchange is an essential feature since it influences the wound site's acidity conditions, allowing bacteria colonization [89]. Moreover, hydrogels show physical properties similar to those of living tissue. A 3D hydrogel structure protects nanoparticles and their cargo from premature degradation to sustain a controlled response into the wound site. The properties responsible for nanohydrogels success are swelling, stimuli responsiveness, softness, and high biocompatibility. However, studies highlight their deficiency in pharmacodynamic and pharmacokinetic aspects [88].  
For the bioadhesiveness and resistance necessary for dressings, polymeric films and membranes are synthesized to guarantee mechanical flexibility. They are composed of natural polymers, such as alginate, hyaluron, or vegetable oil, or synthetic ones, like polyvinyl alcohol, as well as mixtures of these. Biopolymers, such as collagen, allow for biomimetic and bioactivity features. To improve wound-healing effects, nanoparticles that are able to release bioactive molecules can be added to films during their synthesis [80]. Casting is the most commonly used technique to produce films. It consists of pouring a polymeric solution into a mold and then waiting for the evaporation of the organic solvent until the polymer dries [90]. However, this method has the disadvantage of obtaining dense structures with low permeability, leading to exudate accumulation and infection [80].  
Several studies have focused on using nanofiber scaffolds for wound management due to their structural features and wound-healing potential. Biodegradable scaffolds similar to ECM are considered ideal dressings, and electrospinning is the best technique to produce them since it can create scaffolds made of uniform polymeric nanofibers with desired dimensions. Scaffolds show several properties such as biocompatibility, controlled porosity, and permeability. Furthermore, they allow cell attachment because of their microporous structure similar to ECM. The polymers most used to create scaffolds are collagen, chitosan, and non-degradable fibers, such as polylactic acid, poly (vinyl alcohol) (PVA), polyethylene, and polyurethane. These scaffolds can allocate bioactive molecules that release nanoparticles to enhance the wound-healing process, influence cell behavior, and inhibit infection [91]. Recently, to obtain better-performing dressings, multicomposite scaffolds have been designed. They consist of a mixture of different types of scaffolds and nanoparticles. This combination leads to the synthesis of multifunctional dressings. Composite dressings can be used as one or two layers that are adaptable for several wound types. They show good permeability, compliance, control of infection, and absorptive capacity, but they also have high costs and must be replaced once a day [92].