Cardiovascular Tissue Cardiovascular Tissue EngineeringEngineering

Priya RamaswamiPriya RamaswamiJuly 26, 2006July 26, 2006

Department of Bioengineering, University of PittsburghDepartment of Bioengineering, University of PittsburghMcGowan Institute for Regenerative MedicineMcGowan Institute for Regenerative Medicine

OverviewOverview

Tissue EngineeringBiomaterialsCellsTissue Engineered Heart ValvesTissue Engineered Blood VesselsTissue Engineered MyocardiumDiscussion

Tissue EngineeringTissue 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

BiomaterialsBiomaterials 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

Embryonic Stem Cells (ESCs)Embryonic Stem Cells (ESCs)

Adapted from Gepstein,L. Circ. Res, 91:866; 2002

Collected at the Collected at the blastocyst stage (day blastocyst stage (day 6) of embryogenesis 6) of embryogenesis

Give rise to cells from Give rise to cells from all three germ layers all three germ layers of the body (ectoderm, of the body (ectoderm, endoderm, and endoderm, and mesoderm) mesoderm)

Capable of self-Capable of self-renewal and renewal and undifferentiated undifferentiated proliferation in culture proliferation in culture for extended periods for extended periods of timeof time

Mesenchymal Stem Cells (MSCs)Mesenchymal Stem Cells (MSCs)

Adapted from www.nih.gov

Have been found in Have been found in many tissues and many tissues and organs of the bodyorgans of the body

Are multipotent and Are multipotent and possess extensive possess extensive proliferation potentialproliferation potential

Bone marrow-derived Bone marrow-derived adult stem cells have adult stem cells have been differentiated to a been differentiated to a number of cell types number of cell types including bone, including bone, cartilage, and fat cartilage, and fat

Use of adult stem cells Use of adult stem cells allows for autologous allows for autologous cell transplantationcell transplantation

CellsCells 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

3-Dimensional Environment3-Dimensional Environment The context in which a cell is grown is critical to its The context in which a cell is grown is critical to its

development and subsequent functiondevelopment and subsequent function

Cells cultured Cells cultured ex vivoex vivo on TCPS are in a 2-D on TCPS are in a 2-D environment which is far-removed from the 3-D environment which is far-removed from the 3-D tissue from which the cells originated as well as the tissue from which the cells originated as well as the 3-D tissue into which the cells will be implanted for 3-D tissue into which the cells will be implanted for tissue engineering applications tissue engineering applications

Culture of cells in a 3-D vs. 2-D environment has Culture of cells in a 3-D vs. 2-D environment has been shown to alter cell behavior, gene expression, been shown to alter cell behavior, gene expression, proliferation, and differentiationproliferation, and differentiation

SignalsScaffolds

Tissue Engineered Construct

CellsAutogeneicAllogeneic

XenogeneicPrimary

Stem

NaturalSynthetic

Growth FactorsCytokines

Mechanical StimulationDifferentiation Factors

From An Introduction to Biomaterials. Ch 24. Fig. 1. Ramaswami, P and Wagner, WR. 2005.

Tissue Engineered Heart Valves Tissue Engineered Heart Valves (TEHV)(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

TEHV ReplacementsTEHV ReplacementsMechanical prostheses

Bioprostheses

Homografts

Each of these valve replacements has limitations for clinical use

Can you think of any limitations?

InfectionThromboembolismTissue deteriorationCannot remodel, repair, or grow

From http://www.rjmatthewsmd.com/Definitions/img/107figure.jpg

Requirements for a TEHVRequirements for a TEHV

BiocompatibleShould not elicit immune or inflammatory response

FunctionalAdequate mechanical and hemodynamic function,

mature ECM, durability

LivingGrowth and remodeling capabilities of the construct should mimic the native heart valve structure

What’s being done?What’s being done?

Cells Vascular cells Valvular cells Stem cells (MSCs)

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

Mechanical Stimulation• Pulsatile Flow Systems• Cyclic flexure bioreactors

From An Introduction to Biomaterials. Ch 24. Fig.3 Ramaswami, P and Wagner, WR. 2005.

Tissue Engineered Blood Tissue Engineered Blood Vessels (TEBV)Vessels (TEBV)

From An Introduction to Biomaterials. Ch 24. Fig.4 Ramaswami, P and Wagner, WR. 2005.

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

TEBV ReplacementsTEBV Replacements

Synthetic GraftsSynthetic GraftsWork well in large-diameter replacementsWork well in large-diameter replacementsFail in small-diameter replacementsFail in small-diameter replacements

WHY???WHY???Intimal hyperplasiaIntimal hyperplasiaThrombosisThrombosis

Requirements for a TEBVRequirements for a TEBV

BiocompatibleBiocompatibleShould not elicit immune/inflammatory responseShould not elicit immune/inflammatory response

FunctionalFunctionalAdequate mechanical and hemodynamic function, mature ECM, durability

LivingLivingGrowth and remodeling capabilities of the construct should

mimic the native blood vessel structure

LOOK FAMILIAR???LOOK FAMILIAR???

What’s being done?What’s being done?Cells Endothelial cells Smooth muscle cells Fibroblasts &

myofibroblasts Genetically modified cells Stem cells (MSCs & ESCs)

Scaffolds• Synthetic (PET, ePTFE, PGA, PLA, PUs)

• Natural (collagen)

• Decellularized biological matrices

Mechanical Stimulation• Pulsatile Flow Systems

• Cyclic & longitudinal strain

From An Introduction to Biomaterials. Ch 24. Fig.5 Ramaswami, P and Wagner, WR. 2005.

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

•Cytokines

Tissue Engineered MyocardiumTissue Engineered Myocardium

From www.aic.cuhk.edu.hk/web8/Hi%20res/Heart.jpg

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

Requirements for a Myocardial PatchRequirements for a Myocardial Patch

Biological, Functional, and Living (same as TEHV and TEBV)

High metabolic demandsHigh vascularityMechanical and Electrical anisotropy

VERY DIFFICULT!!!VERY DIFFICULT!!!

What’s being done?What’s being done?

Cells Cardiocytes Cardiac progenitor cells Skeletal muscle cells Smooth muscle cells Stem cells (MSCs &

ESCs)

Scaffolds• Synthetic (PET, ePTFE, PEUU)

• Natural (collagen, ECM proteins, alginate)

• Cell sheets

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

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

Signalling Factors• Growth Factors (Insulin, transferrin, PDGF, 5-azacytidine)

• Cytokines

• Conditioned media

• Co-culture`

In Conclusion…In Conclusion…

We have a lot of work to doWe have a lot of work to do

Taking these tissue engineered Taking these tissue engineered constructs from benchtop to bedsideconstructs from benchtop to bedside

Better understanding the human body Better understanding the human body and how to manipulate cellsand how to manipulate cells