Cardiovascular Tissue Engineering

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Cardiovascular Tissue Engineering

• Priya Ramaswami
• July 26, 2006
• Department of Bioengineering, University of
  Pittsburgh
• McGowan Institute for Regenerative Medicine

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Overview

• Tissue Engineering
• Biomaterials
• Cells
• Tissue Engineered Heart Valves
• Tissue Engineered Blood Vessels
• Tissue Engineered Myocardium
• Discussion

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Tissue Engineering

• In recent years, the field of tissue engineering
  has emerged as an alternative to conventional
  methods for tissue repair and regeneration
• Health care costs in the U.S. for patients
  suffering from tissue loss and/or subsequent
  organ failure are estimated to be on the order of
  hundreds of billions of dollars a year
• As such, the field of tissue engineering has
  grown to encompass a number of scientific
  disciplines with the ever-increasing demand for
  clinical methods to replace and regenerate tissue

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Biomaterials

• Provide cells/tissue with a scaffold on which to
  grow and/or deliver drugs, cytokines, growth
  factors, and other signals for cell
  differentiation, growth, and organization
• Synthetic biomaterials provide a number of
  parameters that can be adjusted for optimal
  mechanical, chemical, and biological properties
  for a given application
• Design criteria proper mechanical and physical
  properties, adequate degradation rate without the
  production of toxic degradation products,
  suitable cell adhesion, integration into
  surrounding tissue without extensive inflammatory
  response or support of infection, proper mass
  transfer

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Embryonic Stem Cells (ESCs)

• Collected at the blastocyst stage (day 6) of
  embryogenesis
• Give rise to cells from all three germ layers of
  the body (ectoderm, endoderm, and mesoderm)
• Capable of self-renewal and undifferentiated
  proliferation in culture for extended periods of
  time

Adapted from Gepstein,L. Circ. Res, 91866 2002
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Mesenchymal Stem Cells (MSCs)

• Have been found in many tissues and organs of the
  body
• Are multipotent and possess extensive
  proliferation potential
• Bone marrow-derived adult stem cells have been
  differentiated to a number of cell types
  including bone, cartilage, and fat
• Use of adult stem cells allows for autologous
  cell transplantation

Adapted from www.nih.gov
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Cells

• There has recently been much excitement
  surrounding the use of stem cells for tissue
  repair and regeneration
• In vitro differentiation of stem cells via
  humoral factors and direct in vivo utilization of
  these cells have been proposed as a method for
  tissue regeneration
• The use of a biomaterial to guide stem cell
  commitment provides cells a scaffold on which to
  grow and permits cell differentiation in vivo
  while minimizing in vitro manipulation
• The ideal cell source for various TE applications
  is still elusive

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3-Dimensional Environment

• The context in which a cell is grown is critical
  to its development and subsequent function
• Cells cultured ex vivo on TCPS are in a 2-D
  environment which is far-removed from the 3-D
  tissue from which the cells originated as well as
  the 3-D tissue into which the cells will be
  implanted for tissue engineering applications
• Culture of cells in a 3-D vs. 2-D environment has
  been shown to alter cell behavior, gene
  expression, proliferation, and differentiation

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Autogeneic Allogeneic Xenogeneic Primary Stem
Cells
Tissue Engineered Construct
Signals
Scaffolds
Natural Synthetic
Growth Factors Cytokines Mechanical
Stimulation Differentiation Factors
From An Introduction to Biomaterials. Ch 24.
Fig. 1. Ramaswami, P and Wagner, WR. 2005.
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Tissue Engineered Heart Valves (TEHV)
An estimated 87,000 heart valve replacements were
performed in 2000 in the United States
alone Approximately 275,000 procedures are
performed worldwide each year Heart valve
disease occurs when one or more of the four heart
valves cease to adequately perform their
function, thereby failing to maintain
unidirectional blood flow through the
heart Surgical procedures or total valve
replacement are necessary
Adapted from http//z.about.com/d/p/440/e/f/19011.
jpg
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TEHV Replacements
Mechanical prostheses Bioprostheses Homografts
Each of these valve replacements has limitations
for clinical use Can you think of any
limitations? Infection Thromboembolism Tissue
deterioration Cannot remodel, repair, or grow
From http//www.rjmatthewsmd.com/Definitions/img/1
07figure.jpg
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Requirements for a TEHV

• Biocompatible
• Should not elicit immune or inflammatory
  response
• Functional
• Adequate mechanical and hemodynamic function,
  mature ECM, durability
• Living
• Growth and remodeling capabilities of the
  construct should mimic the native heart valve
  structure

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Whats being done?

• Cells
• Vascular cells
• Valvular cells
• Stem cells (MSCs)

• Mechanical Stimulation
• Pulsatile Flow Systems
• Cyclic flexure bioreactors

• Scaffolds
• Synthetic (PLA, PGA)
• Natural
• (collagen, HA, fibrin)
• Decellularized biological
• matrices

From An Introduction to Biomaterials. Ch 24.
Fig.3 Ramaswami, P and Wagner, WR. 2005.
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Tissue Engineered Blood Vessels (TEBV)
Atherosclerosis, in the form of coronary artery
disease results in over 515,000 coronary artery
bypass graft procedures a year in the United
States alone Many patients do not have suitable
vessels due to age, disease, or previous
use Synthetic coronary bypass vessels have not
performed adequately to be employed to any
significant degree
From An Introduction to Biomaterials. Ch 24.
Fig.4 Ramaswami, P and Wagner, WR. 2005.
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TEBV Replacements

• Synthetic Grafts
• Work well in large-diameter replacements
• Fail in small-diameter replacements
• WHY???
• Intimal hyperplasia
• Thrombosis

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Requirements for a TEBV

• Biocompatible
• Should not elicit immune/inflammatory response
• Functional
• Adequate mechanical and hemodynamic function,
  mature ECM, durability
• Living
• Growth and remodeling capabilities of the
  construct should mimic the native blood vessel
  structure

LOOK FAMILIAR???
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Whats being done?

• Mechanical Stimulation
• Pulsatile Flow Systems
• Cyclic longitudinal strain

• Cells
• Endothelial cells
• Smooth muscle cells
• Fibroblasts myofibroblasts
• Genetically modified cells
• Stem cells (MSCs ESCs)

• Signalling Factors
• Growth Factors
• (bFGF, PDGF, VEGF)
• Cytokines

• Scaffolds
• Synthetic
• (PET, ePTFE, PGA, PLA, PUs)
• Natural (collagen)
• Decellularized biological
• matrices

From An Introduction to Biomaterials. Ch 24.
Fig.5 Ramaswami, P and Wagner, WR. 2005.
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Tissue Engineered Myocardium
Ischemic heart disease is one of the leading
causes of morbidity and mortality in Western
societies with 7,100,000 cases of myocardial
infarction (MI) reported in 2002 in the United
States alone Within 6 years of MI, 22 of men
and 46 of women develop CHF MI and CHF will
account for 29 billion of medical care costs
this year in the US alone Cardiac
transplantation remains the best solution, but
there is an inadequate supply of donor organs
coupled with the need for life-long
immunosuppression following transplantation
From www.aic.cuhk.edu.hk/web8/Hi20res/Heart.jpg
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Requirements for a Myocardial Patch

• Biological, Functional, and Living (same as TEHV
  and TEBV)
• High metabolic demands
• High vascularity
• Mechanical and Electrical anisotropy

VERY DIFFICULT!!!
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Whats being done?

• Mechanical Stimulation
• Pulsatile Flow Systems
• Rotational seeding
• Cyclic mechanical strain

• Cells
• Cardiocytes
• Cardiac progenitor cells
• Skeletal muscle cells
• Smooth muscle cells
• Stem cells (MSCs ESCs)

• Signalling Factors
• Growth Factors
• (Insulin, transferrin, PDGF,
• 5-azacytidine)
• Cytokines
• Conditioned media
• Co-culture

• Scaffolds
• Synthetic (PET, ePTFE, PEUU)
• Natural
• (collagen, ECM proteins,
• alginate)
• Cell sheets

From An Introduction to Biomaterials. Ch 24.
Fig.6 Ramaswami, P and Wagner, WR. 2005.
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In Conclusion

• We have a lot of work to do
• Taking these tissue engineered constructs from
  benchtop to bedside
• Better understanding the human body and how to
  manipulate cells

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THANK YOU!
Any Questions???