Biomedical Engineering Reference
In-Depth Information
namely,hairfolliclesandsweatglands,traversebothlevels.Beneath
the dermis is the hypodermis, a loose connective layer comprising
primarilyadiposetissue.Theselayersplayanimportantroleinpro-
tecting the body from any mechanical damage such as wounds and
infection. 2
Normal wound healing involves a complex and dynamic process
involvingsolublemediators, bloodcells,ECMcomponents,andresi-
dent cells that eventually result in the restoration of tissue integrity,
but a superbly orchestrated series of overlapping processes result
in a varying degree of functional and structural restoration. When
successful, wound healing restores normal function with a well-
organized minimal scar. But when the control mechanisms are
abnormal, chronic wound or hypertrophic scar formation can occur.
Wound healing occurs in interrelated and interdependent phases:
inflammation, cell proliferation, and remodeling. During the initial
stages of wound healing, a temporary repair is usually achieved in
the form of a blood clot. Inflammatory cells, fibroblasts, and capil-
laries later invade the clot to form a contractile granulation tissue
that draws the wound margins together; meanwhile, the cut epider-
mal edges migrate to cover the degenerated wound surface. 3 For
improvement of wound-healing cases, a number of biomaterials are
usedasdressingsorscaffoldsthatmayusenaturalorartificialmate-
rials.Polymers,suchassemipermeablepolyurethanedressings,algi-
natedressing,andsoon,areusedaswounddressingsforsuperficial
wounds. 4 - 6 More complicated dressings vary from dermal replace-
ments made from collagen and/or other proteins backed by a poly-
mer layer to the biological dressing, which contains ECMs such as
collagen, hyaluronic acid (HA), and fibrin with seeded cells. 7 , 8 Bio-
materials for promoting wound healing have already been applied
successfully in various clinicalfields. 8
Artificial skin research using tissue-engineered skin replace-
ments such as cultured autologous and allogenic keratinocytes
grafts, autologous or allogenic composites, acellular biological
matrices,andcellularmatrices,includingbiologicalsubstancessuch
as fibrin sealant and various types of collagen and HA is an active
field in regenerative medicine and has opened new options for clin-
icians to restore various skin defects. 9 In tissue-engineered skin
 
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