Soft Matter Composites Interfacing with Biomolecules, Cells, and Tissues - Bioinspired Approaches for Human-Centric Technologies - page 39

Over the past decades, the concept of scaffolds has been strongly redefined: from
the original definition of a space-filling material to the most modern vision of
programmable bioactive material, able to guide and control complex cellular
processes. Thanks to a sapient integration of cellular and molecular biology com-
bined with the advancement in material science and nanotechnology, future scaf-
folds can be envisaged as a simplified, yet effective, replica of the natural ECM—
with the potentiality to make tissue engineering a real clinical success.

2.4 Introduction to Skin Wound Active Dressing Materials

The skin is the largest organ in the human body and the one interfacing with the
external environment, keeping protected the rest of the body but also receiving
sensory stimuli. It consists of three layers. The outermost layer is the bloodless
epidermis and is bonded to the underlying dermis layer. In the dermis are included
blood vessels, collagen and elastin fibers, glands, hair follicles, and nerves' endings.
The innermost layer is the subcutis, an energy reservoir and impact protective layer,
composed of mainly fat tissue. When the skin layers are damaged, an acute wound
is formed. The treatment of acute wounds should involve first the cleaning, to
reduce the risk of infection, and then the closure, where appropriate dressings are
involved. The wound closure helps in the reduction of the infections risks, brings
the separated tissues close together, and promotes the healing process. Such healing
process goes through four phases: (1) hemostasis, (2) inflammation, (3) prolifera-
tion, and (4) maturation remodeling. As the healing progresses, the different phases
often overlap, as schematically demonstrated in Fig. 2.3 . When the healing of an
acute wound does not go through the usual phases, failing to close in the expected
time due to intrinsic or extrinsic causes, then a chronic wound can develop. In such
wound, the septic infections are common, but resolving their origin can help in
restarting the healing process.
The dressing of a skin wound has a crucial role in the healing process since it
provides the right conditions that assure its optimized progress till the final closure.
There are already numerous wound dressings in the market, each one tackling
diverse types of wounds, acute or chronic. These dressings can be categorized
according to their interactions with the wound: (1) passive dressings that just cover
the wound (i.e., gauzes), (2) interactive dressings that promote the healing by being
oxygen and water vapor permeable but not permeable to bacteria (i.e., transparent
films, foams, gels), and (3) active dressings that deliver substances that contribute
to the healing process (alginates, chitosan, hydrocolloids). Usually, the skin wound
dressing types that are available in the market are traditional gauzes and tulles,
transparent films, and foams that cannot absorb the exudates but are moisture
permeable and dressings that upon contact with the wound exudates form a gel
creating a moist environment (hydrocolloids, alginates, hydrofibers). Lately, the
availability of active dressings containing silver or other antimicrobial agents or
antibiotics is progressively increasing.