## 3 Nanosized-Lipid-Based Drug Delivery Systems in Wound Healing
### Vesicular Systems
#### 3.1.3 Ethosomes in Wound Healing  
Ethosomes are updated versions of conventional liposomes and are composed of phospholipids, cholesterol and a large amount of alcohol (20-45%) [40; 109] (see Figure 2c). Their lipid membranes are less tightly packed than other vesicle membranes, allowing them to be more flexible. Commonly used phospholipids for the preparation of ethosomes are phosphatidylcholine, phosphatidylcholine, phosphatidylserine and phosphatidylethanolamine. Some preferred alcohols are ethanol and isopropyl alcohol [119]. The presence of ethanol determines a negative surface charge that prevents the aggregation of vesicles due to electrostatic repulsion. Ethanol is an efficient penetration enhancer and, due to its properties, ethosomal formulations have shown higher permeation, more prolonged action and long-term stability in storage [40]. Furthermore, increasing the ethanol concentration increases the EE% of the ethosomes [120], which is typically reported as high [121]. Ethosomes also improved the access for both highly hydrophobic [122] and highly hydrophilic drugs to the deep skin layers [123]. This improvement of drug permeability is a result of the ethanol effect. The synergy between ethanol and the polar head of the lipid molecules creates increased fluidity and diminished density in the lipid layers, releasing the drug into the deep layers of the skin [124]. The size range of the ethosomes is 103-200 nm, depending on the amount of ethanol [125]. Therefore, the storage stability of the vesicular systems is a significant concern. However, ethosomes present superior stability compared with conventional liposomes [126]. The lyophilization (freeze-drying) process had different results in terms of drug-containing ethosomes. Although the evidence showed no difference before or after this process in a study [127], other authors expressed that this method is suitable to increase the stability of ethosomes [125]. Ethosomes are easy to scale up through the cold process, which is the most-used technique for preparation, or the hot method [125]. Several studies have investigated the relevance of ethosomes in wound-healing treatment and have shown the superior skin delivery of active substances loaded in ethosomes compared with liposomes or classical formulations. Recent studies found that encapsulated natural substances and antibacterial agents increase their efficacy in the treatment of burn wounds. For instance, curcumin, a natural compound of turmeric, was encapsulated in ethosomes to evaluate its wound-healing effects in rats with second-degree burns [128]. This formulation presented a mean size of the particle of ~120 nm and an optimum EE% for curcumin of approximately 85%. The results suggest that curcumin loaded in ethosomes has a potent antibacterial effect, as well as a strong wound-healing capacity better than that of free curcumin, in burn wound therapy [128]. [PERSON] et al. evaluated the particle sizes and drug release behavior of curcumin loaded in ethosomes and other vesicular systems. Ethosomal curcumin formulation with a mean particle size of 289 nm presented a higher EE% and higher skin deposition of curcumin compared with classical liposomes [129]. In another study, ethosomes loaded with silver sulfadiazine (SSD), a topical antibiotic considered the gold standard in burn wounds, were tested in vivo and in vitro to evaluate their capacity to reduce bacterial infections and healing times in second-degree burns [82]. An increased ethanol concentration in this formulation and lecithin levels of 1% led to a decrease in vesicle size. Moreover, a higher level of lecithin and alcohol enhanced the EE% and drug release stability. The study results revealed that topical application of the SSDethosome along with Carbopol gel 974 could overcome the disadvantages of commercial cream, enhancing the wound contraction rate in Wistar rats by 30% compared with the control group. Furthermore, this formulation presented a significant in vivo antimicrobial activity on the tested bacterial strains [82].