11.3.2　Surface wettability

Some serious skin wounds（e.g.，scalds，ulcers）can cause excessive exudation of wound tissue fluid，forming highly exudative wounds that are difficult to heal.The amount of exudation in 24 h can exceed 10 mL，and the dressing infiltration rate is more than 75％.It is also easy to cause adhesion of the wound and dressing，and will cause great pain and inconvenience to the patients.Therefore，high-exudation wounds have higher requirements for the surface infiltration performance of dressing materials.Dressings for high-exudation wounds need to absorb and drain exudate，while they must also maintain the moistness of the wound to promote healing.The commonly used gauze cannot keep moist，which would delay wound healing.At present，wet dressings（e.g.，alginate gels，hydrophilic fibers，foams，and silver ion dressings）can absorb wound tissue fluid and keep the wound moist，promote granulation growth and resist bacterial infections，and are the first choice for high-exudation wounds.Excessive wound tissue fluid caused excessive wound hydration is a serious problem.Generally，traditional wet hydrophilic dressings can absorb part of the wound tissue fluid，but due to its inherent hydrophilicity，it is inevitably to produce wound tissue fluid at the interface between the wound and the dressing.Residual wound tissue fluid will continue to hydrate the wound and complicate the healing process.The biological interface plays an important role in the interaction between wound tissue fluid and biological materials.The surface wettability of the wound dressings usually affects the wetting behavior of the tissue fluid around the wound.Like most traditional dressings，hydrophilic materials are easily wetted by wound tissue fluid，which can over-hydrate the wound.On the contrary，as a waterproof outer layer of the dressing，hydrophobic materials can prevent accidental contact of external liquid with the wound，but they cannot promote the removal of wound tissue fluid.Recently，several asymmetrically（Janus type）wetting materials have shown unique ability to transfer fluid，such as polyester fabrics with wettability gradients，polyurethane（PU）/poly（vinyl acetate）composite fiber membranes，and single-sided fluorinated cotton fabric membrane（Figure 11-13）.Therefore，manipulation of surface wettability may provide opportunities for designing wound dressings with effective wound tissue fluid capabilities.

Wang et al.prepared electrospun hydrophobic polyurethane（PU）nanofiber membranes onto a hydrophilic ultrafine fiber network and constructed a self-absorbent dressing as a biological fluid pump（Figure 11-14）.The network provided drainage force to pump excess biological fluid through the hydrophobic nanofiber membrane to discharge the fluid unidirectionally from the hydrophobic side to the hydrophilic side，thereby preventing the biological fluid from wetting the wound.In the infected wound model，they showed that this self-pumping dressing can heal wounds faster than conventional dressings.This study provided new clues to manage excess biological fluid around wounds to promote faster wound healing and the self-pumping dressing has great potential as the next generation dressing for clinical wound healing.(https://www.daowen.com)