1. Wound Healing

2. The Wound Definition
Interruption of continuity of tissue
resulting from a certain injury
especially external physical trauma
Wound: a disruption of normal anatomic
relations as a result of injury intentional or
unintentional.

3. Types of traumatic wounds
ACCORDING TO SKIN LOSS
 Closed wound: skin surface intact Without loss of skin
◦ Abrasions: partial division of superficial layer
◦ Contusion: Diffuse extravasation of blood and exudate
 ecchymotic.
◦ Hematoma: Localized collection in fascial planes – ve
signs of inflammation.
 Opened wound: skin surface interrupted or loss of skin.
◦ Incised
◦ Stab and punctured wound
◦ Lacerated
◦ Crushed and gun shots.

4.  According to contamination
◦ Clean
◦ Contaminated
 According to the age of the wound
◦ Early (within 6 hours).
◦ Late ( 6-24h).
◦ delayed (after 24 h).

6. WOUND HEALING
 Natural spontaneous response for
restoration of tissue continuity after injury
 Healing is the interaction of a complex
cascade of cellular events that generates
◦ Reconstitution and Resurfacing,
◦ Restoration of the tensile strength of injured skin.
 Sometimes, tissue has been disrupted so
severely that it cannot heal naturally.

7. Wound Healing
 Regardless of causation or
tissue type, wound healing
presents with identical
biochemical and physiologic
processes, though wound
healing may vary in timing and
intensity.
 Repair Vs Regeneration
(speed Vs accuracy)
 Acute (orderly and timely) Vs
Chronic (stalled in
inflammatory phase)

8. Phases of wound healing:
[I]
Inflammation
(biochemical activation)
[II]
Proliferation
(granulation&
cellular activation)
[III]
Remodeling
(maturation &differentiation

9. Phases: Inflammatory, Proliferative, &
Maturational

10. Inflammatory
Biochemical -cellular activation
 Aim:
◦ translation of mechanical injury into biochemical
signals.
 This starts by:
◦ Changes the charge on the surface of collagen
molecule.
◦ Platelets aggregation and extravasated plasma
 contact with the extravascular tissue proteins
 leads to activation of Hageman's factors
(factor XII) and platelets.

11. Inflammatory
Biochemical -cellular activation
Substrate or reactive phase, immediate
typically days 1-10
Response to limit and prevent further injury,
inflammation, hemostasis, sealing surface,
removing necrotic tissue and debris, migration of
cells into wound by chemotaxis, cytokines, and
growth factors
Initial intense local vasoconstriction of arterioles and
capillaries followed by vasodilation and vascular
permeability

12. (signs of inflammation)
◦ Vasodilatation (more persistent) Increase capillary
engorgement ,Increase the capillary
permeability, and blood flow under effect of
histamine and bradykinin, serotonin, prostaglandins
from platelets and mast cells  flow of the
necessary inflammatory cells and factors that fight
infection and deriding the wound.
◦ This period is the event responsible for the
erythema, edema, and heat observed after tissue
injury
◦ Alterations in pH (secondary to tissue and bacterial
degradation), The increase fluid tension in the area
 swelling  press of the nerve endings, and
tissue hypoxemia at the injury site contribute to the
sensation of wound pain

13. Defending [migration of inflammatory cells &
Chemoattraction to WBCs]
◦ PNL & Lymphocytes invade
the wound and fibrin
network within 3 hours
 defending and lysis with
their lysosomes.
 release inflammatory
mediators and bactericidal
oxygen-free radicals.
 Lymphocytes also play a
role in cellular immunity
and antibody production.
◦ O2 is essential for the
optimistic results of this
defending process.

16. 1ry vascular reaction:
 Activation of clotting factors cascade.
 Platelet aggregation
 Clot formation (The scab) which temporarily closes
the wound consists mainly of fibrin mesh trapped
other blood cells hemostasis.
 Temporary constricting of small blood vessels (few
minutes) temporary blanching.

17.  Activation of complement system  chemotaxis
 degranulation of mast cells and cytolysis.
 Platelets: accumulate  release alpha
granules containing:
 vasoactive agents
 chemotactic factors
 growth factors.
 Alpha granules (growth factors) initiator 
proliferative phase by activating the local
mesenchymal and epidermal cells.

18. Inflammatory
Tissue injury & blood vessel damage
exposure of subendothelial collagen
to platelets and vWF activates
the coagulation pathway
Plugging: Platelet and fibrin
Provisional matrix:
platelets, fibrin, and fibronectin
Platelet aggregation:
Thromboxane (vasoconstrict),
thrombin, platelet factor 4

19. Platelet
s
 Alpha granules contain:
-platelet factor 4: aggregation
-Beta-thrombomodulin: binds
thrombin
-PDGF: chemoattractant
-TGF-beta: key component tissue repair
 Dense granules contain vasoactive substances:
adenosine, serotonin, and calcium
 Other factors released: TXA, Platelet activate
factor, Transform. growth factor alpha, Fibroblast
growth factor, Beta lysin (antimicrobial), PGE2
and PGI2 (vasodilate) and PGF2 (vasoconstrict).

20. Types of growth factors

21. Extra Cellular Matrix
 Mast cell Histamine and platelet
serotonin increases capillary vascular
permeability
 Complement factors C5a and
leukotreine B4 promote neutrophil
chemoattraction
 As do IL1 and TNF alpha (from
endothelial cells & macrophages)
Increase chemotactic factors and
spillage of intravascular plasma into
interstitial fluid aid diapedesis of
neutrophils
 Neutrophils release elastase and
proteases,
further vasc. dilation and permeability
causes inflammation:

22. Polymorphonuclear Cells
 Chemotaxins attract after extravasation
 Migrate through the ECM by transient
interaction with integrins
 PMNs scavenge, present antigens,
provide cytotoxicity-free radicals
(H2O2)
 Migration PMNs stops with wound
contamination control usually a few
days
 Persistant contaminant: continuous
influx PMN’s and tissue
destruction, necrosis, abscess, &

23. DEBRIDMENT
 Macrophages
 are essential for wound healing.
 Macrophages (monocytes) enter the wound from the
2nd after wounding and present until the reparative
process is complete.
 Along time macrophages continue
◦ phagocytose & cleaning the wound site of
bacteria, debris, F.B and necrotic matter.
◦ producing the activation growth and chemotactic
factors similar to those of platelets (complete the
function of platelets)…...

24. Macrophages
Necessary
 Monocytes migrate &
activate: Macrophages
 Appear when PMN’s
disappear 24-48 hr
 Do the same activities as PMN’s
 Plus orchestrate release of
enzymes (collagenase,
elastase), PGE’s, cytokines (IL-
1, TNF alpha, IFN ), growth
factors (TGF & PDGF), and
fibronectin (scaffold/anchor for
fibroblasts)
 Activate Fibroblasts,
endothelial and epithelial cells to
form Gran.

26. Proliferative
 Regenerative or Reparative
(granulation & cellular activation)
starts after 3-5 days takes 5-20 days
INCLUDES:
 Granulation tissue formation
 Epithelization
 Contraction
 Angiogenesis: endothelial cells activate & degrade
Basement membrane, migrate, and divide to form more
tubules
 Granulation Tissue: capillary
ingrowth, collagen, Macrophages, Fibroblasts, Hyaluroni
c acid (GAG)

27. Granulation tissue
 Granulation tissue formation occurs 3-
5 days following injury
 Includes: Inflammatory
cells, Fibroblasts and collagen, ground
substance and Vascular and lymphatic
proliferation

28. Fibroblast
 The fibroblast is a critical
component of granulation tissue.
 Fibroplasia begins from
surrounding mesenchymal cells
3-5 days after injury and may last
as long as 14 days.
 Fibroblasts migrate and
proliferate in response to platelets
growth factors.
 Fibroblasts are responsible for
the production of
collagen, elastin, ground

29. Collagen synthesis
 The collagen fibers which is essential for:
◦ bridging the wound gap
◦ supporting the growing vessels and
◦ wound strength.
 Fibroblasts Collagen III  held together by weak
electrostatic forces and is soluble in weak salt solution. It
is laid down irregularly and haphazardly
 then polymerization occurs by cross linked to the
collagen molecules  Thick strong less soluble collagen
[I] become more regular and perpendicular on the plane
of wound.
 The process of collagen synthesis :
◦ Starts on the 3rd day
◦ The peak reaches by the 5-7 days

30.  This active metabolic process depends
mainly on:
◦ Vitamins: B, ascorbic acid
◦ O2
◦ amino acids
◦ Elements: zinc, iron, copper
 Collagen formation decreased by:
◦ decrease of vit C.
◦ steroids (high dose).
◦ Protein starvation.

31. Proline every 3rd amino-
acid and abundant lysine
hydroxylation required for
x-link
Vit C required for normal
hydroxylation

32. Collagen
Type III predominant
collagen synthesis days
1-2
Type I days 3-4
Type III replaced by
Type I in 3 weeks

33.  Ground substance
◦ Produced by fibroblasts (water – electrolytes –
mucopolysaccharides (proteoglycans) –
fibronectins – glycoproteins).
 Angiogenesis (Vascular and lymphatic
proliferation):
◦ The macrophage growth factors stimulates
angiogenesis
◦ New capillaries bud from endothelial cells in
capillary near the wound edges appear
proliferation  a new network of capillaries
is formed inside the granulation tissues red
granulations.

34. Epithelization
 Stats within hours by mitosis of the basal cell
layer.
 The epidermal cells advanced from the edges
and creep across the wound surface in a
favorable plane dissecting the wound
between the living and dead tissue. Migration
stops when it meets the opposite advanced
epithelium.
 The new epithelium is thin non-pigmented.
 Incisional wounds are epithelized within 24-48
hours after injury (distance of less than 1
mm). This epithelial layer provides a seal

35.  In open wounds: if the wound is
moist well oxygenated with viable
moist surface and 
epithelization rapid (few days)
and cell migrate over the surface
of the wound.
 However, The process is more
slower if the wound dry. The cells
burring under the eschar and
slowly separating the mobile from
the immobile tissue.
 This explain why the epithelial is
more rapid in intact blister than
after the blister has been debride
and the base of the blister

36.  In sutured wounds: epithelium may invade
the lining of the suture tracks. It usually
degenerate with early removal of sutures.
However, prolonged sutures  ugly
punctuate scars. This may be avoided by
adhesions taps  better cosmoses.

37. Epithelialization: Physical Barrier
 Begins within hours of injury
 Growth Factors (PDGF, TGF, and EGF) stimulate
Mitosis of epithelial cells
 Migration: dom. factor = epithelial bottleneck (relies
on gran. tissue)
 Epiboly leapfrog like
motion until contact
inhibition reestablished
 Early Tensile Strength: blood vessel
growth, epithelialization, protein (fibrin)
aggregation, later collagen formation

38. Wound contraction
 fibroblasts in the peripheral granulations  maturation 
myofibroblasts  centripetal movement of wound edges
 contraction decrease wound size  facilitates
closure of a defect.
 Lag period 2-3 days (with collagen synthesis) with
Maximum rapid contraction 3-14 days (The maximal rate
of contraction is 0.75 mm/d)
 It specially occurs at the back of the neck, trunk and face
where the skin is loose
 Contraction must be distinguished from contracture.
 Contraction is decreased by :
 x-ray
 steroids
 grafting with dermis
 Burns
If prevented
 slow healing – large fibrous tissue - ugly scar
 cicatrisation & complications.

39. Contraction Vs Contracture
 Contraction: centripetal movement of the whole
thickness of surrounding skin reducing scar
 Myofibroblasts: special Fibroblasts express smooth
muscle and bundles of actin connected through cellular
fibronexus to ECM fibronectin, communicate via gap
junctions to pull edges of the wound
 Contracture: the physical constriction or limitation of
function as the result of Contraction (scars across
joints, mouth, eyelid)
Burn/Keloid causing
contracture

40. Phase of remodeling
(maturation &differentiation of
scare tissue)
◦ It occurs after 20 days and continue for
many months and years or indefinitely.
Devascularization
Collagen remodeling
Cicatrisation

41. Maturational
 Remodeling of wound 3 week-1+year
 Type I replaces Type III Collagen: net amount
doesn’t change after 6 weeks, organization &
crosslinking
 Decreased vascularity, less fibroblasts &
hyaluronic acid
 Peripheral nerves regenerate @ 1mm/day
 Accelerated Wound Healing: reopening
results in quicker healing 2nd time around

43. Devascularization:
The granulation tissue is gradually
replaced by a scare tissue which is
relatively acellular and avascular
tissue.
◦  pale scare tissue.
◦ The extracellular tissue change its
contents. Water is resorbed from the scar.

44. Collagen remodeling
 Collagen remodeling during the maturation phase
depends on continued collagen synthesis in the
presence of collagen destruction under effect of
collagenase.
 The ratio of the collagen type [I] increase. New
collagen is formed in more orderly fashion along the
lines of tension in the scare.
 Facilitating collagen fibers cross-linking and ultimately
decreasing scar thickness and increasing wound
bursting strength.

45. Finally
 4-12 w  a pale red thick strong scare tend
to contract is formed.
◦ Excessive contracture of the scare tissue 
cicatrisation.
[contracture] a pathologic process of excessive fibrosis that
limits motion of the underlying tissues and is typically
caused by the application of excessive stress to the wound.
 12-40 w soft white scare tend to relax.
 Hyalinization, calcification and even
ossification may sometimes occur.

46. Closure of Wounds
 Primary: 1st intention immediately
sealed with suturing, skin graft,
flap closure (tensile strength)
 Secondary: Spontaneous
involves no active intent to seal
wound, gen. For highly
contaminated wound, closes by
reepithelialization and contraction
of the wound (epithelial integrity)
 Tertiary: delayed primary closure
of contaminated wound initially
treated to control infection
(repeated debridement, abx, wnd
vac) then closed by suturing, skin
graft, flap design, steri-strip etc.

47. Wound Closure

48. Summary
 Inflammatory phase:
◦ A clot forms stop bleeding
◦ Vasodilatation  of WBCs
◦ cells of inflammation  defending and debridment
of injured tissue.
 Proliferative phase
◦ Epithelization,
◦ Fibroplasia (fibroblasts and collagen), and
◦ Angiogenesis occur during the; additionally,
◦ Granulation tissue forms and
◦ The wound begins to contract.
 Remodeling (maturation) phase
◦ Collagen forms tight cross-links to other collagen
and with protein molecules,
◦ Increasing the tensile strength of the scar.

49. The phases of cutaneous wound healing
Injury leads to accumulation of platelets and coagulation
factors.
Coagulation results in fibrin formation and release of PDGF
and TGF-band other inflammatory mediators by activated
platelets. This leads to more Neutrophil recruitment which
signals the beginning of inflammation (24 h).
After 48 h macrophages replace neutrophils. Neutrophils and
macrophages are responsible for removal of cellular debris
and release growth factors to reorganize the cellular matrix.
At 72 hours the proliferation phase begins as recruited
fibroblasts stimulated by FGF and TFG-b begin to
synthesize collagen.
Previously formed fibrin forms initial matrix for fibroblasts
Collagen cross-linking and reorganization occurs following
months after injury in the remodeling phase of repair.
Wound contraction follows in large surface wounds and is
facilitated by actin-containing fibroblasts (myofibroblasts)

51. Wound strength
 6 Week = 60% original, 80% final strength
 8 Week-1 year ≈ 80% original (Max)
 Net Collagen = 6 weeks amount stays the
same but cont. crosslink increase strength
= maturation

52. Tensile strength:
 The work done (force) in breaking a wound per unit
area.
 The bursting strength of a wound is the force required to
break a wound regardless of its dimension.
 Peak tensile strength of a wound occurs approximately
60 days after injury.
 A healed wound only reaches approximately 80% of the
tensile strength of unwounded skin

53.  the increase of cross linkage between the fibers
increase its quality which is reflected in
continuing increase in tensile strength.
 Factors affecting tensile strength:
◦ Factors affecting collagen synthesis specially vit C 
decrease.
◦ Direction of the w
  Parallel to the lines of Langer  faster the healing
and increase the tensile strength
 In the direction of the pull of the underlying muscle
 line of creases  line scare least visible.
◦ no diff detectable between the wound that are taped
and those that are sutured .

54. Complications of wound healing
1. Bleeding - shock - anemia.
2. Injury of Imp. structures.
3. Infection:
4. Dehiscence (bursting wound).
5. Implantation or epidermoid cyst
6. Keloid formation
7. Pigmentation  tattooing
8. Painful scare local or reformed
neuroma.
9. Cicatrization : burns 
deformity stricture and stenosis in
tubes.
10.Neoplasia: sq cell ca. on scare
tissue.
11.F.b. retained

55. Impediments to Wound Healing
 Bacteria>105/cm2 : Decreased
O2 content, collagen lysis,
prolonged inflammation
 Devitalized Tissue & Foreign
Body: Retards Granulation
Tissue formation and healing
 Cytotoxic drugs: 5FU, MTX,
Cyclosporine, FK-506 can
impair wound healing. D-
Penicillamine- inhibit collagen
x-linking
 Chemotherapy: no effect after
14 days
 Radiation: Collagen synthesis
abnormal, fibrosis of vessel

56. More Impediments
 Diabetes: impedes the early phase response
 Malnurishment: Albumin<3.0, Vit-C
 Smoking:
vasoconstriction, atherosclerosis, carboxyhemo
globin, decreased O2 delivery
 Steroids: inhibit macrophages, PMNs, Fibroblast
collagen synthesis, cytokines, and decreased wound
tensile strength
-Vit A (25,000 IU QD) counteracts effect of steroids
DENERVATION has NO EFFECT on Wound Healing

57. Dehiscence (bursting wound)
 PF:
◦ Infection.
◦ Weak scare due to continuous strain
(coughing vomiting) or stretch Decrease the
bursting strength.
◦ Rapid absorbed catgut.
◦ Poor surgical technique.
◦ General conditions  poor wound healing
◦ Decrease nutrition (Proteins) and vitamins (vit
c)

58. Keloid formation & hypertrophic scars
 Unknown etiology
 P.F.
◦ Sex: females
◦ Race: black
◦ Repeated trauma
◦ TB patients – burns
◦ Irritation of FB, hair, keratin
◦ Age: In young, thin skin 1st year of life. And very old
◦ Common Site: Neck over the sternum. Wounds that
cross skin tension lines or wounds that are located on
the ear lobes or presternal and deltoid areas.

59. Keloids: Beyond the Borders
 Excess Deposition
of Collagen Causes
Scar Growth
Beyond the Border
of the Original
wound
Tx: XRT, steroids, silicone
sheeting, pressure, excise. often Autosomal Dominant,
Refractory to Darker Pigment, Often
Tx & not preventable
above clavicle but not
always

60. Difference:
 Keloid grow beyond the wound
borders
 It does not tend to resolve
spontaneously.
◦ Hypertrophic scars stay within the
limit of the original wound and do
tend to regress spontaneously.
 It can form as late as a year
after injury
◦ whereas Hypertrophic scars are
generally seen soon after tissue
injury,
 if the active scare continue
more than 6 month it is
considered true keloid which

61. Hypertrophic Scar: confined within
 Excess collagen deposit
causing raised scar remains
within the original wound
confines
 Darker pigmented skin &
flexor surfaces of upper torso
 Often occurs in burns or
wounds that take a long time
to heal, sometimes
preventable
 Can regress spontaneously
 Tx:
steroids, silicone, pressure
garments

62. Histologically:
 Keloid also contain a greater
amount of type III collagen than a
mature scar, which suggests a
failure in scar maturation.
 The collagen is loose disorganized
wavy pattern of irregularly shaped
fibers with a lower content of
collagen cross-links compared to
normal skin.
 keloid and hypertrophic scars have
rich blood supply, high

63. TTT:
 The recurrence rate of these abnormal
scars is high.
 Conservative management includes:
 Intralesional injection of triamcinolone.
 pressure,
 Laser, and
 radiotherapy.
 Excision & grafting :only if no response
to conservative management.

64. Maggots

65. Langer’s Lines
Lines lie perpendicular to underlying muscle
fibers, as fibers contract wound edges are
reapproximated as apposed to gapping caused
parallel wound edges (plus camouflage)

66. Cachexia, anorexia
Cancer 
 Altered host
metabolism.
 Protein catabolism
 Abnormal
inflammatory cell
response
 Impaired healing
(decreased
chemotaxis and
phagocyte function)
 Risk of infection

68. Factors affecting repair

69. Intraoperative surgical factors
 Length & Direction
 The best cosmetic results may be achieved when
incisions are made parallel to the direction of the tissue
fibers.
 Tissue
handling, Hemostasis, Maintain
ing moisture
 Materials of closure.

70. Diseases Assoc With Abnormal
Wound Healing
 Osteogenesis Imperfecta: Type I Collagen
defect
 Ehler-Danlos syndrome: Collagen
disorder, 10 types
 Marfan Syndrome: fibrillin defect (collagen)
 Epidermolysis Bullosa: Excess fibroblasts
Tx: phenytoin
 Scurvy: Vit C req. for proline hydroxylation
 Pyoderma gangrenosum: proud flesh

71. Mechanisms of regeneration,
wound healing and repair

72. Repair of tissue damage can be broadly separated
into two processes
 Regeneration
◦ Restitution of lost tissue
 Tissue with high proliferative capacity = labile
tissue (e.g hematopoietic cells, epithelial cells of
skin and gastrointestinal tract regenerate from stem
cells)
 Quiescent tissues = stable tissue
which normally have low levels of
replication, however can undergo rapid cell division
when stimulate (e.g pancreas, kidney, parenchymal
cells of liver, ; mesenchymal cells as
lymphocytes, fibroblasts, smooth muscle , endothelial
cells)
 Healing
◦ may restore original structures but results in
collagen deposition and scar formation
 in tissue where scaffold is disrupted

73. Regeneration requires
 Presence of stem cells
for renewal
 or tissue cells that are
capable to divide in
response to growth
factors
 Intact tissue scaffold
Most of the processes that are
referred to as “regeneration “ in
mammalian organs
are actually compensatory growth
processes
that involve cell hypertrophy and
hyperplasia (e.g liver regeneration)

74. Stem cells
 They are undifferentiated cells that do not
yet have a specific function.
 They can replicate for a long period of time
and give rise to differentiated cells.
 In every cell division one cell retains its self
renewing capacity while the other cell can
undergo differentiation (“asymmetric
replication”)

75. Two types of stem cells
 embryonic stem cells
◦ derived from the inner cell mass of a blastocyst
from in vitro fertilized eggs
◦ are pluripotent and can generate all tissues

76.  adult (somatic) stem cells
◦ they are present in small numbers in various
tissues of the adult body
◦ are typically programmed to form different cell
types of their own tissue and are therefore
multipotent
◦ in tissues with high turn over (hematopoietc
system, epithelial lining of the gut and skin) they
are instrumental in renewal
◦ although present in a variety of permanent non-
dividing tissues they are not very active

77. Bone marrow contains two different types of
adult stem cells:
the hematopoietic stem cell and the bone
marrow stromal cell

78. Potential plasticity of hematopoietic stem cells

79. Hematopoietic stem cell transplantation:
an established treatment option for hematological
disorders and cancers
 Hematopoietic stem cells can be retrieved from the
peripheral blood or the bone marrow and identified by
the expression of the CD34 marker
 2X106 HSC/KG body weight of recipient are needed for
a successful autologous HSC transplantation
 Under steady state conditions the number of CD34+
cells in peripheral blood is 1-5/mm3
 Mobilization procedures of CD34+ stem cells into the
peripheral blood can be accomplished by administration
of G-CSF or GM-CSF to the donor and can increase the
HSC count in the peripheral blood 50 fold

80. Repair by Healing
(Scarring)
 Healing is a fibro-proliferative
responses that “patches”
rather than restores tissue
and involves the following
processes
◦ Induction of an inflammatory
response to remove dead and
damaged tissue
◦ Proliferation of parenchymal and
connective tissue cells
◦ Angiogenesis (blood vessel
formation) and formation of
granulation tissue
◦ Synthesis of ECM proteins and
collagen deposition
◦ Tissue remodeling
◦ Wound contraction
◦ Acquisition of wound strength
 It usually leads to scar formation
and does not lead to complete

81. Angiogenesis = growth of new blood vessels
 Angiogenesis occurs in the healthy body for
healing wounds and for restoring blood flow
after tissue injury
 Healthy angiogenesis is tightly controlled by
a serious of “on” and “off switches
(Angiogenic growth factors versus
angiogenesis inhibitors)
 In many serious diseases the body loses
control over angiogenesis and
angiogenesis-related diseases occur when
new blood vessels grow excessively or

83. Angiogenesis / Neovascularization
is critical to chronic inflammation and fibrosis,tumor growth
and vascularization of ischemic tissue
Sprouting

84. VEGF and Angiopoietins
are the most important angiogenic factors

85. Role of extracellular matrix in wound healing
and scar formation
 Extracellular matrix (ECM) is formed by specific
secreted macromolecules that form a network on which
cells grow and migrate along
 ECM is secreted locally and forms a significant
proportion of the tissue volume
 ECM sequesters
◦ water that provides turgor to soft tissues
◦ and minerals that provides rigidity to skeletal muscles
◦ Forms a reservoir for growth factors
 ECM proteins assemble into two general organizations
◦ Interstitial matrix (present between cells)
◦ Basement membrane [BM] (produced by epithelial
and mesenchymal cells and is closely associated with
the cell surface)

86. Three groups of macromolecules
constitute the ECM
 Fibrous structural proteins
◦ Collagen
◦ Fibrillins
 Adhesive glycoproteins
◦ Cadherin
◦ Integrins
◦ Immunoglobulin family
◦ Selectins
 Proteoglycans and Hyaluronic Acid

87.  Fibrous structural proteins
◦ Collagens
 Collagens are the most abundant proteins
 27 different types
 Type I,II, III, V and XI are the most abundant (interstitial or
fibrillar collagens)
 Provide tensile strength of tissue
 Fibrillar collagen requires hydroxylation of proline and lysine
in procollagen which is dependent on Vitamin C
 Type IV is the main component of Basemant membrane and
forms sheets)
◦ Elastins and Fibrillins
 Provide tissue with the ability to recoil
 Elastins are found in large vessels, uterus, skin and
ligaments
 Fibrillins form a scaffolding for the deposition of elastins
 Marfan syndrome is an inherited autosomal dominant defect in
fibrillin synthesis. Without the structural support provided by
fibrillin, many tissues are weakened, which can have severe
consequences, for example, ruptures in the walls of major

89.  Proteoglycans and hyaluronic acid
◦ Proteoglycans (mucoproteins) are formed of
glucosaminoglycans (GAGs) covalently attached to
core proteins and are highly negatively charged
 Biophysical functions due to ability to fill space, bind and
organize water molecules and repel negatively charges
molecules
 They are ideal lubricating fluids in the joint due to high
viscosity and low compressibility
 Biochemical functions are mediated by specific binding of
GAGs to other macromolecules
 e.g Antithrombin III (AT III) binds tightly to heparin and
heparan sulfates and inactivates factor II, IXa and XIa thus
controlling blood coagulation
 Proteoglycans (such as Syndecan) act as reservoirs for
growth factors secreted into the ECM by binding the latter.

90. TGF- functions as a central regulator of tissue repair
and negatively regulates both acquired and adaptive
immunity
Lack of the TGF gene in mice results in excessive tissue inflammation
and autoimmunity resulting in death of the animals, however increased
activity leads to excessive scar formation and loss of organ function

91. Mechanisms of fibrosis
TH-2 cytokines IL-4 and IL-13 lead to
“alternative” activation of macrophages
Nicole Meissner-Pearson

92. Mechanisms of Fibrosis:
a result of chronic inflammation and repair
 Fibrosis:
excessive accumulation of extracellular-matrix
components such as collagen that is produced by local
fibroblasts leading to a permanent fibrotic scar
 Macrophages and fibroblasts are the main effector
cells involved in the pathogenesis of fibrosis
 Pro-fibrotic mediators such as TGF-b and IL-13 amplify
this process
 The degradation of collagen is controlled by Matrix-
Metallo-proteinases (MMPs) and are activated by IFN-g
 Therefore the net increase of collagen within a wound is
controlled by the balance of these opposing
mechanisms
 Although severe acute injuries can cause marked tissue
remodeling. Fibrosis that is associated with chronic injury
(repetitive) is unique in that the adaptive immune
response is thought to have an important role

94. TH-2 cytokines IL-4 and IL-13 lead to “alternative”
activation of macrophages
 Macrophages differentiate into at least two functionally
distinct populations depending on whether they are
exposed to TH-1 or TH-2 cytokines
 TH-1 cytokine activate NOS2 in classically activated
macrophages whereas TH-2 cytokines IL-4 and IL-13
preferentially stimulate Arginase-1 (ARG1) leading to an
alternative activation pathway
 ARG1 promotes the generation of polyamines and L-
proline via metabolism of L-arginine to L-ornithine and
activation of ODC and OAT
 Polyamines are crucial for cell growth and L-proline is a
substrate for collagen synthesis

96. A balance between TH-2 and TH-1 cytokines is
necessary to promote healing but inhibit excessive
fibrotic tissue remodeling
Therapeutics that modulate this balance may be beneficial in patients
suffering from fibrotic diseases. Drugs that directly inhibit TGF-b1 and
IL-13 might prove the safest and most effective approach

97. Fibrotic tissue remodeling can result in
loss of organ function
 Fibrotic changes can occur in various
vascular diseases including
◦ Cardiac diseases
◦ Peripheral vascular diseases
 They affect as well main organ systems like
◦ Skin
◦ Lung
◦ Liver
◦ Kidney

98. Artificial Skin
 The term “artificial skin” has been used to
describe a cell-free membrane comprising a
highly porous graft copolymer of type I
collagen and chondroitin 6-sulfate which
degrades at a specific rate in the wound and
regenerates the dermis in dermis-free
wounds in animal models and patients

99. History of Skin Replacement
 Thirty years ago, burn surgeons determined that badly
burned skin should be removed as quickly as
possible, followed by immediate and permanent
replacement of the lost skin.
 Doctors are able to take a postage stamp-sized piece of
skin from the patient and grow the skin under special
tissue culture conditions.
• From this small piece of skin, technicians can grow enough
skin to cover nearly the entire body in just 3 weeks
• Although attempts to cover wounds and treat severe burns
is cited as far back as 1500 B.C., it has only been in the
past few centuries that a significant number of solutions
have emerged.
• The bulk of these solutions involve using skin grafts from
humans (allografts) or animals (xenografts), or using
membranes fabricated from natural or synthetic polymers.

100. History of Artificial Skin
 The first synthetic skin was invented by John
F. Burke, V. Yannas, at the Massachusetts
Institute of Technology (MIT)
 In 1979 Burke and Yannas used their artificial
skin on their first patient, a woman whose
burns covered over half her body
 Integra is the first FDA approved tissue
engineered product for burn and
reconstructive surgery. It was Patented on
August 14, 1990

101. Why is it Needed?
 When skin is damaged or lost due to severe
injury or burns, bacteria and other
microorganisms have easy access to
warm, nutrient-rich body fluids.
 To treat a severe burn, surgeons first remove
the burned skin and then quickly cover the
underlying tissue, usually with a combination
of laboratory-grown skin cells and artificial
skin.

102. A Literary Review
Wayne R. Fischer
ME 597 Introduction to Solid Biomechanics Boise State
University
May 8th, 2003

103. The best material for wound closure is the
patient’s own skin; however autografting
has several disadvantages (Schulz, 2000):
1. The donor site is a new wound.
2. Scarring and pigmentation changes
occur.
3. Dermis is not replaced.
4. Donor site is a potential site for
infection.
5. Donor site is not unlimited.
6. Extensive burns makes it impossible.

104. Cadaver Skin: Allograft as a
Temporary Skin Substitute
 The annual
national
requirement for
cadaver skin is
estimated to be
only 3000 m2.
 Yet only 14% to
19% of human
skin needed is
being recovered.

105. Xenografts
• Xenografts, particularly porcine skin grafts, are
commercially available and are an effective
means of short-term wound closure
(Yannas, 1980).
• A Xenograft is normally removed on the third or
fourth day of use before extensive adhesion
onto the wound bed sets in, thereby
necessitating its traumatic excision prior to
drying and sloughing off (Yannas, 1980).

106. Observations from designing dermal
replacements (Schulz, 2000)
 The thicker the dermal layer of a split-thickness skin
graft, the less the graft contracts.
 Partial-thickness wounds with superficial dermal
loss heal with less hypertrophic scarring.
 Full-thickness skin grafts contract minimally.
 The length of illness in burn cases is essentially
restricted to the length of time the burn wound is
open.
 Full-thickness dermal injuries heal by contraction
and hypertonic scarring, producing subepithelial
scar tissue that is nothing like the original dermis.

107. Research topics of Dr. Yannas
at Dept. of Engineering, MIT
1. Study the mechanical behavior of artificial skin as
a function of processing variables.
2. Study the surface tension of artificial skin.
3. Study the stress relaxation rate of artificial skin in
standardized solutions of tissue enzymes.
4. Study the design of novel processes for the
inexpensive and reproducible fabrication of
artificial skin.
5. Study the pore structure of artificial skin by
scanning electron microscopy.
6. Study the moisture permeability of artificial skin.

108. Synthetic Polymers
(Yannas, 1980)
 The use of synthetic polymers has not so far
led to the solution of the problem of a skin
substitute.
 A high incidence of infection and a relatively
low capacity for inducing vascularisation and
epithelialisation are frequently reported.
 However, useful insights into the
requirements for a satisfactory skin
replacement have been discovered through
the use of synthetic polymers.

109. Schematic Representation of Specific
Mechanical Problems that Should Not
Arise (Yannas, 1985).

110. Specific Physiochemical and
Mechanical Problems to Overcome
(Yannas, 1985).
a) Skin graft does not displace
air pockets efficiently from
graft-woundbed interface.
c) Shear stress causes
buckling of graft, rupture of
graft woundbed bond and
formation of air pockets.
e) Excessively high moisture
flux rate through graft
causes dehydration and
development of shrinkage
stresses at edges and
peeling.

111. Specific Physiochemical and
Mechanical Problems to Overcome
(Yannas, 1985).
b) Flexural rigidity of graft is
excessive; graft does not deform
sufficiently under its own weight
to make contact with depressions
in woundbed surface, thus air
pockets form.
d) Peeling force lifts graft away from
woundbed.
f) Very low moisture flux causes
fluid accumulation at graft-
woundbed interface and peeling.

112. Literary Review Up to 1990’s (Beele, 2002)
Antiquity: Indian description of using autologous soft tissue flaps.
Greeks used dressings for skin wounds.
Renaissance: Amboise-Pare provide wound healing foundation.
1850’s: Reverdin and Thiersch use autologous skin grafts.
1914: Kreibich was the first person to cultivate keratinocytes in vitro.
1948: Medawar autotransplanted keratinocytes.
1960’s: Yannas and Burke begin their work using materials science
mechanics.
1975: Rheinwald & Green describe a technique to cultivate human
keratinocytes.
1980’s: Yannas and Burke describe a bilaminate collagen-glycosaminoglycan
matrix with a silicon surface. After take of the matix. The silicon surface is
removed and can be replaced with autologous cultured epidermal cells.
1981: Bell constructs the first living skin equivalent with collagen fibroblast gel
with keratinocytes cultured on top of contracted gel.
1983: Helton used cultured allografts in burn patients
1985: Boyce and Ham introduce an alternative culturing method.

113. Further Research (Buras, 1989)
 The actual biological elements and events being critically
tested in mechanical studies are only guessed at, and
analysis can rarely go beyond the science of mechanics.
 There are promising possibilities:
Pulsed ultrasound techniques may soon provide
accurate imaging of skin structures as well as
measurements of blood flow in the skin.
The multifrequency shear wave method may be able to
resolve mechanical properties of the epidermal tissues
discretely.

114. Some References
And we’re up and walking
again! Beele, H. Artificial skin: Past, present
and future. The International
Journal of Artificial Organs. 25(3):
163-173, 2002.
Jones, I., Currie, L., Martin, R. A guide
to biological skin substitutes. British
Journal of Plastic Surgery. 55: 185-
193, 2002.
Schulz
III, J.T., Tompkins, R.G., Burke, J.F.
Artificial Skin. Annu. Rev. Med. 51:
231-244, 2000.
Yannas, I.V. Artificial Skin and Dermal
Equivalents. In The Biomedical
Engineering Handbook, ed. J. D.
Bronzino, pp. 2025-2038. Boca
Raton: CRC Press, 1995.

115. Literary Review: 1990’s to Present (Chart in British 2002 Journal of Plastic Surgery)

116. Types of Skin
Replacements
 Epicel skin replacement technology
◦ Introduced by Genzyme Biosurgery in
1987.
◦ Physicians isolate individual cells from a
postage-stamp-sized biopsy of skin.
◦ Grow the cells for about 2 to 3 weeks and
allow them to form individual sheets of
tissue.
◦ Then surgeons transplant these sheets of
tissue to the burnt area where these
sheets fuse over time with the burnt area.

117. Types of Skin Replacements
 Integra Dermal Regeneration Template®
◦ Semi -synthetic approach to skin regeneration
◦ Researchers develop a bi-layer membrane
system called the Dermal Regeneration
Template
◦ The first and only FDA approved tissue
engineered product for burn and reconstructive
surgery
◦ Dermal replacement layer is constructed of a
porous, biodegradable matrix of cross-linked
bovine tendon collagen and the glycos-
aminoglycan chondroitin 6-sulfate.

118. ◦ Second layer
 acts as a temporary replacement
(Epidermal ) – made from silicone polymer
 Following completion of the dermal layer
physicians replace the temporary epidermal
with an epidermal auto-graft.
 Skin Graft
◦ taking cells from
a non-burned epidermal
layer of skin,
growing them into
large sheets of cells
in a laboratory

119. How does it work?
 The burn surgeon drapes a
sheet of Integra ® over the
wounded area for 2 to 4
weeks.
 Allows the victim’s cells to
grow a new dermis on top of
matrix of the Integra ®.
 Then the surgeon removes
the top layer of the Integra®
and applies a very thin sheet
of the victim’s own epithelial
cells.
 Over time, a normal
epidermis (except for the Skin replacement. scientists at Integra
Using a bilayer
membrane system,
absence of hair follicles) is
LifeSciences help repair skin lesions and
burns.

120. General Design Properties
 Essential Design Properties
◦ "The dermal replacement should provide both the
information necessary to control the inflammatory and
contractile processes and also the information necessary to
evoke ordered recreation of autologous tissue in the form
of a neodermis" (Schulz, 2000).
◦ "The initial replacement material should provide immediate
physiologic wound closure and be eliminated once it has
provided sufficient information for neodermis reconstitution
of " (Schulz).
◦ It should protect the wound by providing a barrier to the
outside (Beele, 2002)
◦ It should control water evaporation and protein and
electrolyte loss and It should limit excessive heat loss
(Beele)
◦ It should decrease pain and allow early mobilization and It
should provide an environment for accelerated wound

121. More General Design Properties
 Physical Characteristics
◦ It should be easy to manipulate the product, i.e.
easy to place and dress the skin substitute
effectively (Beele)
◦ It should improve the cosmetic appearance of the
scar (Beele)
 Availability
◦ It should be readily available off the shelf and
custom made.
 Cost
◦ Cost should not preclude the use of the device.

122. Advantages -Disadvantages of Temporary Skin
Substitutes

123. Advantages and Disadvantages of Permanent Skin
Substitutes

124. Preparing Artificial Skin

125.  Cultured skin cells , polyglycolic fabric ,
collage gels and glycosaminoglycans are
incorporated
 Rapid Keratinocyte cultures are obtained by
growing the same on a feeder layer of
irradiated fibroblasts.
 Also , neonatal fibroblasts are being used
(Paed Medical Center , Munster –

126.  The graft is a bilayer membrane.
 In this approach, the top layer , a Silicone Layer
incorporates the features of moisture control.
 While the bottom layer delivers the performance of
sealing the skin breach and preventing scarring.
 The top layer is removed after a period of about 10–15
days.
 Following removal of the top layer, the epidermal cover is
provided by covering with a thin epidermal graft.

127. Design Parameters
 The ratio of the time constant of biodegradation
to the time constant for normal healing of a skin
incision ideally must be unity
 Adequate Moisture Flux
 Dermis Regeneration Template - porous
matrix seeded with cells, induces synthesis of a
new dermis, simultaneously synthesis of a new
epidermis occurs by migration of epithelial cell.
 The depth of tissue loss must be known as
epithelial cells cannot migrate if loss of tissue is
high.

128. Limitation
 3-4 weeks are required for the cell
expansion in the graft
 Certain limitations while implanting the graft
 Air pocketing between graft and underlying skin
 Shear stresses can cause buckling of the skin while
grafting
 Excess or low Moisture flux may cause lifting of the
skin or edema underneath
 No appendages of skin
 Take rates are less.

129. Advantages
 Less Scarring
 Reduction in the
nutritional
requirements may
be observed while
using skin
substitutes
 Can be used even
in extensive burns
 Does not initiate an
inflammatory or
foreign body
response

131. Biological skin substitutes
 The epidermis injuries are healed by
regeneration of the epidermis
 The migration of keratinocytes from the
periphery of the wound and the proliferation
would lead to the total healing without scars
 However if dermis is injured recovery is harder
since the dermis cannot regenerate
 In order to shorten the healing process or
abolish the side effects, skin substitutes
should be used temporarily or permanently.

132. Desired properties for skin substitutes
 Adhere to the substrate
 Be durable and sufficiently elastic to tolerate
some deformation
 Allow evaporative water loss at the rate
typical of the external layer
 Have optimal water permeability to prevent
either desiccation of the wound or fluid
accumulation under the covering

133. Categories of skin substitutes
 Skin substitutes for wound closure
 Skin substitutes for wound cover
 Wound closure requires a material to restore
the epidermal barrier function and become
incorporated into the healing wound
 Wound cover necessitates a material which
relies in the in growth of granulation for
adhesion.
 They are used in superficial burns

134. Skin substitutes for wound
cover
 Biobrane
 Transcyte
 Cultured allogenic keratinocytes
 Apligraf ( graft skin )
 Dermagraft

135. Biobrane
 It is a bilaminate
membrane of nylon
mesh bonded to a
thin layer of slicone
which is
semipermeable
 The nylon mesh is
coated with peptides
to aid adherence
 Used temporarily for
freshly excised full
thickness wounds

136. Transcyte
 The difference between trancyte and biobrane is the
seeding the neonatal fibroblast on to the collagen coated
nylon membrane
 Since nylon is not
biodegradable,
it cannot be used as
a dermal substitute
 The removal process
is more successful
because of less
bleeding

138. Cultured allogenic keratinocytes
 The survival period of allogenic cells is one
week
 The healing with allogenic cells can be
enhanced with cytokines and growth factors
by the cells
 They are used as dressing for chronic
wounds

139. Apligraf ( graft skin )
 Composed of two layers.
 Inner layer- gel type 1 bovine collagen with
living neonatal fibroblast
 Outer layer – neonatal allogenic
keratinocytes
 Used to treat chronic ulcers

140. Dermagraft
 Cyropreserved human fibroblast derived dermal
substitute on polyglactin-910 mesh scaffold
 Enhances healing by stimulating the ingrowth of
firbovascular tissue from the wound bed
 Used in chronic lesions

141. Skin substitutes for wound closure
 Alloderm
 Integra
 Cultured autologous keratinocytes
 Composite epidermal skin substitutes

142. Alloderm
 Derived from human cadaveric skin in which the
epidermis is removed and cellular components of
the dermis are extracted and preserved to avoid
specific immune response
 After application, the wound bed is
repopulated, revascularised and incorporated
into the tissue

144. Integra
 Produced by Burke and Yannas, producer of
GAG(gylcosamine) sponges.
 Widely accepted skin substitute
 Integration of the GAG sponge with a silicone layer
 Pore size-70-200micrometer,to allow the migration of
patient’s own endothelial cells and fibroblasts
 Pore size small- delay or the prevention of
biointegration is observed
 Pore size large- insufficient
attachment are for invading
host cells
 Advantage-improved elasticity
 Disadvantage- cost

145. Cultured autologous keratinocytes
 Grown in vitro conditions as confluent
sheets
 Since they are fragile, they require
separation from tissue culture substrate by
using proteolytic enzyme before they are
applied to the wound bed
Cultured autologous delivery
systems
 Fibrin-glue suspension
 Fibrin glue sheets
 Upside down membrane delivery systems
 Sprayed cell suspension

146. Composite epidermal-dermal
skin substitute
 Healing quality can be enhanced by
combining the cultured keratinocytes
with a dermal matrix
 Keratinocytes should be maintained on a
biomaterial
 Epidermis binds-to the biomaterial and
receives adequate nutrition, the
epidermal barrier is replaced.
COS
 Approximately €700 for 125 cm 2
T
(Journal of Pediatric Orthopaedics 14(5):381-384, September 2005)

147. Recent
Advances

148. Artificial Skin From Hair Roots
 Fraunhofer - Gesellschaft (2008, January 4).
Growing Artificial Skin From Hair Roots
 Euroderm and the Fraunhofer Institute for Cell
Therapy and Immunology in Leipzig have been
granted approval to produce artificial skin from
patients’ own cells.
 Few hairs off the back of the patient’s head are
pulled
 Adult stem cells from the roots are extracted,

149. ICX-SKN - Mimicking nature
 Paul Kemp and colleagues at British
biotech company Intercytex
 Fully and consistently integrates into
the human body
 No need for further grafting

151. FILM Skin – For robots, Artificial
Limbs
 Flexible, Integrated, Lightweight, Multifunctiona
l skin
 Oak Ridge National Laboratory's
Nanomaterials Synthesis and Properties Group
 Carbon Nanotubes are being used
 The material can be designed to behave as
both a temperature and pressure sensor, as a
flexible electrical conductor, or as part of a
polymer material with mechanical and thermal
properties similar to those of human skin.

152. Skin cells genetically engineered to
be resistant to bacteria
 Scientists at the Cincinnati Shriners Hospital
for Children have engineered bacteria resistant
skin cells.
 Due to delay in angiogenesis, the skin is
vulnerable to bacteria as there are no circulating
macrophages.
 Hence incorporating anti-bacterial factors like
Human Beta Defensin 4, will help void bacteria at
an initial stage

154. HOW IT WORK

163. In the Near Future

164. Self Healing Artificial Skin
 http://www.mvac.uiuc.edu
 Microvascular Autonomic Composites
Initiative (µVAC) is creating materials
with a microvascular network, capable of
pumping self-healing polymers to repair
sites of skin breech
 Skin capable of healing, even though
only to a certain degree, could prove
incredibly useful for the robotics industry.

165. The surface layer acts as a
catalyst
for the healing agent, causing it
to
Microvascular network
polymerize upon contact
embedded in the substrate layer
carrying the healing agent
Residue healing agent
repairing cracks on the
surface of the µVAC
material.

166.  Microvascular Autonomic Composites
Initiative (µVAC) is for Robotic Skin…..
 Imagine the same with our Artificial
Skin
 Skin that regenerates when breeched
accidentally or intentionally

167. Questions for Future Research
How does the skin transform and grow naturally on a biochemical and
physiologic level?
How can these natural transformations be combined with concepts
from materials science and biomechanics in order to develop and
design a cost effective and viable skin substitute?
Which designs already incorporate natural growth components with
concepts from materials science and biomechanics?
How can these designs be enhanced or re-deigned using the concepts
within the domain of materials science and biomechanics?

168. Overview- Integumentary Development
 Development of Skin
 Skin
◦ largest organ
◦ protective layer
◦ 2 embryonic origins
◦ epidermis
 surface ectoderm
◦ dermis
 mesoderm

169.  A totally new epidermis is present every 25
to 45 days.
 Melanocytes create melanin, the substance
that gives our skin color. These cells are
found deep in the epidermis layer.
 Accumulations of melanin are packaged in
melanosomes (membrane-bound granules).
 These granules form a pigment shield
against UV radiation for the keratinocyte
nuclei.

170. Embryology of skin
Ectoderm
forms the surface
epidermis and the
associated glands.
Mesoderm
forms the underlying
connective tissue of
dermis and hypodermis

172. Skin tissue culture.
Kultur jaringan kulit .
 Keratinocyte cells is the most upper
part of skin, epidermis.

173. For burns grafting
 The keratinocyte cell is the building block of
the top layer of skin, the epidermis. Burns
are traditionally treated by taking a thin
layer of skin from an undamaged area
(donor site) and placing it onto the burn
wound. In severely burnt patients, the donor
sites are few and the potential to re-harvest
the area is limited. Skin allografts
(harvested from one person and grafted
onto another) can be used as temporary
dressings, but are rejected by the body
within a short time.

174. The Tissue Culture
laboratory
 grows keratinocyte cells into epithelial grafts
for burn patients in hospitals. From a small
piece (2 x 2cm) of the patient’s own skin, it
can be can grew enough epithelial grafts to
cover a whole person in 3 weeks. The
individual grafts are typically 10 x 7cm in
size and are multi-layered, very much like
normal epidermis. At the base of the graft is
the basal cell layer. As the cells move
through each layer of the skin, they become
increasingly differentiated. Once the
epithelial graft is placed on the patient and
exposed to air, the top layer takes on the
protective role of the skin by becoming

175. Normal epidermis

176. Cultured epithelium
(H&E stain, magnification approx. x350)

177. Detached cultured epithelial graft

178. For chronic skin ulcer treatment
 It has been established a keratinocyte cell
line from neonatal foreskin. These cells are
free of contamination by HIV, Hepatitis B &
C and CMV and have been used to
produce cultured epithelial allografts for the
successful treatment of chronic leg ulcers.
 Cryo-preserved allografts are available as
biological dressings for immediate use on
request.

179. One of medium culture for skin
growing in the lab.
 medium culture consist of
 insulin,
 epidermal growth factor (EGF),
 hydrocortisone,
 Penicillin /streptomycin and
 fungizone.