Post on 14-Apr-2018
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2.79J/3.96J/20.441J/HST522J
Biomaterials-Tissue Interactions
ECM does not regeneratespontaneously
ORInjury to ECM is Irreversible
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Reversible and Irreversibleinjury
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Reversible injury
Spontaneous regeneration of amputated limb in thenewt occurs independently of severity of injury
Goss, 1992
Figure removed due to copyright restrictions.See Figure 1.1 in [TORA].
[TORA] = Yannas, I. V. Tissue and Organ Regeneration in Adults.
New York, NY: Springer-Verlag, 2001. ISBN: 9780387952147.[Preview in Google Books]
http://books.google.com/books?id=L7GFObDs2FkC&lpg=PP1&pg=PP1#v=onepage&q&f=falsehttp://books.google.com/books?id=L7GFObDs2FkC&lpg=PP1&pg=PP1#v=onepage&q&f=false7/29/2019 bio materials course study for medicine
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Irreversible injury
Burn victim suffering
from severe contraction
and scar formation Tomasek et al., 2000
Photo removed due tocopyright restrictions.
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Injury to adult ECM is irreversible
Summary:1. After severe injury, and in contrast to the fetus, the
adult heals most organs irreversibly (no regeneration).
2. Most organs are made up of three basic tissues( tissue triad ): epithelia, basement membrane, andstroma.
3. Epithelia and basement membrane are spontaneouslyregenerative; the stroma is not.
4. Therefore, the central problem in biomaterials selectionfor organ replacement by regeneration is synthesis of
the stroma.
Text: Chaps. 1 and 2 ofTissue and Organ Regeneration in
Adults, by I.V.Yannas, New York, Springer, 2001 (onreserve in MIT Libraries).
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The healed liver has the
same mass, but a different
shape (resected lobes are
not regenerated), than theintact organ
Figure removed due to copyright restrictions.See Figure 1.2 in [TORA].
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scarred heart muscle(heart attack)
scarred liver
(cirrhosis)
scarred cornea
(infection)
scarred kidneyImage removed due to copyright restrictions.
See Figure 1.3 in [TORA].(infection)
scarred heart valve
(rheumatic fever)
Pathology resulting from irreversibility of injury in various organs
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The tissue triad in organs
epithelial tissue: 100% cellular, no
ECM
basement membrane: 100% ECM , no
cells
stroma: cells, ECM, blood vessels
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Organs are made of tissues which heal
differently from each other. The tissue
triad in skin and nerves
100 m
1 m
Figure by MIT OpenCourseWare.
Figure by MIT OpenCourseWare.
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Skin. Reversible Injury
Figure by MIT OpenCourseWare.
Left: a controlled injury (e.g. stripping or blistering) which leaves the dermis intact.
Right: the epidermis recovers completely at the defect site. Hair follicles are lined
with epidermal tissue and also regenerate.
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Left: Excision of the epidermis and dermis to its full thickness.
Right: Wound edges contract and close, while scar tissue forms
simultaneously in place of a physiological dermis. The epidermisthat forms over the scar is thinner and lacks undulations (rete ridge).
Figure by MIT OpenCourseWare.
Skin. Irreversible Injury
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Mildly crushed
nerve healsspontaneously
by
regeneration
Peripheral nerve. Reversible injury
Within the nerve fiber, axons and their myelin sheath are regenerative.
Top: Following mild crushing injury, the axoplasm separates and the
myelin sheath degenerates at the point of injury. However, the basement
membrane stays intact.
Bottom: The nerve fiber regenerates after a few weeks.
Figure by MIT OpenCourseWare.
P i h l I ibl i j
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Peripheral nerve. Irreversible injury
Transected
nerve heals
spontaneouslyby contraction
and neuroma
(neural scar)
formation. Noreconnection of
stumps.
Most supporting tissues (stroma) that surround nerve fibers are not regenerative.
Thus, while nerve fibers can regenerate following a transection, the other tissues
in the nerve trunk cannot regenerate. After transection, the nerve trunk stumps
become neuromas -- clumps of scarred tissue that close largely by contraction.
Figure by MIT OpenCourseWare.
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intact nerve with
myelinated (M)
axon (A) and
Schwann cell (S)
spontaneously
healed nerve
(following
transection) is fil led
with collagen fibers
(scar) but has no
myelinated axon
or Schwann cell
Peripheral Nerve. Irreversible Injury
Figure removed due tocopyright restrictions.
See Figure 2.5 in [TORA].
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injury mode
basic blisterconfiguration
through dermis:
irreversible healing
through epidermis:
reversible healing
between epidermis
and dermis:
reversible healing
Is the basement
membraneregenerative?
Yes!
Figure removed due tocopyright restrictions.See Figure 2.6 in [TORA].
Use of tissue triad model with other organs
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tissue triad in skin
Cartoon of organism
shows that basement
membrane(thick solid line)
appears
In almost all organsanatomy
Use of tissue triad model with other organstissue triad in nerve
Figures by MIT OpenCourseWare.
Figure by MIT OpenCourseWare.
Figure by MIT OpenCourseWare.
SUMMARY SO FAR
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Regenerative
tissues.Reversible injury.
No contraction.
Nonregenerative
tissues. Irrever-sible injury.
Contraction
+scar.
SKIN epidermis dermis
BM
NERVE myelin endoneurial
stroma
BM
SUMMARY SO FAR
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Conclusion
The central problem in organ
regeneration is regeneration of the
stroma. Once the stroma has been
regenerated, epithelial tissues
regenerate spontaneously andsynthesize the basement membrane
as well
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MIT OpenCourseWarehttp://ocw.mit.edu
20.441J / 2.79J / 3.96J / HST.522J Biomaterials-Tissue Interactions
Fall 2009
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