1. Cardiovascular Tissue Engineering
Devin Nelson
July 2010
Department of Bioengineering, University of Pittsburgh
McGowan Institute for Regenerative Medicine

2. Overview Tissue Engineering Biomaterials Cells
Tissue Engineered Heart Valves
Tissue Engineered Blood Vessels
Tissue Engineered Myocardium
Discussion

3. Tissue Engineering
In recent years, the field of tissue engineering (TE) 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 $100,000,000,000’s of dollars a year
TE has grown to encompass many scientific disciplines
Bioengineers
Clinicians
Pathologists
Material Scientists
Molecular Biologists
Mechanical Engineers
etc

4. Mechanical Stimulation Differentiation Factors
Autogeneic
Allogeneic
Xenogeneic
Primary
Stem
Cells
Tissue Engineered
Construct
Scaffolds
Signals
Natural
Synthetic
Growth Factors
Cytokines
Mechanical Stimulation
Differentiation Factors
From An Introduction to Biomaterials. Ch 24. Fig. 1. Ramaswami, P and Wagner, WR

5. What do these have in common?
All Biomaterials

6. Biomaterials Synthetic biomaterials Natural biomaterials
Engineer can control the properties such as mechanical strength, biological activity, degradation rates etc
Natural biomaterials
Built-in structure, environment and cues similar to native body (extracellular matrix ECM, collagen, etc)
Deliver drugs, cytokines, growth factors, and other signals for cell differentiation, growth, and organization
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

7. 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

8. 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
Culture of cells in a 3-D vs. 2-D environment AND WITH APPROPRIATE MECHANICAL STIMULATION has been shown to alter cell behavior, gene expression, proliferation, and differentiation
Especially for cardiovascular applications

9. 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

10. 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

11. Requirements for a TEHV
Biocompatible
Should not elicit immune or inflammatory response
Functional
Adequate mechanical and hemodynamic function, mature ECM, durability to open and close > 31 million times a year
Living
Growth and remodeling capabilities of the construct should mimic the native heart valve structure

12. What’s being done? Cells Mechanical Stimulation Scaffolds
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

13. R.T. Tranquillo Biomaterials 30 (2009) 4078–4084.

14. 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

15. TEBV Replacements Synthetic Grafts WHY???
Work well in large-diameter replacements (6-10 mm)
Fail in small-diameter replacements (3-5 mm)
WHY???
Intimal hyperplasia
Thrombosis

16. Requirements for a TEBV
Biocompatible
Should not elicit immune/inflammatory response
Functional
Adequate mechanical (burst pressure) and hemodynamic function, mature ECM, durability, nervous system response
Living
Growth and remodeling capabilities of the construct should mimic the native blood vessel structure
LOOK FAMILIAR???

17. What’s being done? Mechanical Stimulation Cells 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, PU)
Natural (collagen)
Decellularized biological
matrices

18. Cell-Seeded Collagen Cells can remodel and reorganize in collagen
Collagen may be weak but is strengthened through various techniques (magnetic pre-alignment, glycation, mechanical training)

19. Mechanical Training
Seliktar et al. Ann Biomed Eng 2000

20. Self-Assembled Sheets
Good 3D architecture
Good mechanical strength
Disadvantages: need cell source, requires > 2 months in vitro to make

21. Seeding and Culture

22. Electrospinning
Stankus et al. Biomaterials 2007

23. 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

24. Requirements for a Myocardial Patch
Biological, Functional, and Living (same as TEHV and TEBV)
High metabolic demands
High cell density
Complex cell architecture
High vascularity
Mechanical and Electrical anisotropy
VERY DIFFICULT!!!

25. What’s being done? Mechanical Stimulation Cells 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-like, bFGF, PDGF, hGH)
Cytokines
Conditioned media
Co-culture
Scaffolds
Synthetic (PET, ePTFE, PEUU)
Natural
(collagen, ECM proteins,
alginate)
Cell sheets
Injectables

26. Cardiac Patch

27. Cell Sheet Engineering

28. Artificial Muscle – Be Creative
TISSUE
ENGINEERED
NATIVE

29. Extracellular Matrix

30. Injectable Material

32. 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

33. THANK YOU!
Any Questions???