Cardiovascular Tissue Cardiovascular Tissue EngineeringEngineering

Devin NelsonDevin NelsonJuly 2010July 2010

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 (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

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.

What do these have in common?What do these have in common?All BiomaterialsAll Biomaterials

BiomaterialsBiomaterials Synthetic 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

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 3-D tissue into which the cells will be implanted

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

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 to open and close > 31 million times a year

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.

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

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-Work well in large-

diameter replacements (6-diameter replacements (6-10 mm)10 mm)

Fail in small-diameter Fail in small-diameter replacements (3-5 mm)replacements (3-5 mm)

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 (burst pressure) and hemodynamic function, mature ECM, durability, nervous system response

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, PU)

• Natural (collagen)

• Decellularized biological matrices

Mechanical Stimulation• Pulsatile Flow Systems

• Cyclic & longitudinal strain

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

•Cytokines

Cell-Seeded CollagenCell-Seeded Collagen

Cells can remodel and reorganize in collagenCells can remodel and reorganize in collagen Collagen may be weak but is strengthened through Collagen may be weak but is strengthened through

various techniques (magnetic pre-alignment, glycation, various techniques (magnetic pre-alignment, glycation, mechanical training)mechanical training)

Mechanical TrainingMechanical Training

Seliktar et al. Ann Biomed Eng 2000

Self-Assembled SheetsSelf-Assembled Sheets

Good 3D architectureGood 3D architecture Good mechanical strengthGood mechanical strength Disadvantages: need cell Disadvantages: need cell

source, requires > 2 months in source, requires > 2 months in vitro to makevitro to make

Seeding and CultureSeeding and Culture

ElectrospinningElectrospinning

Stankus et al. Biomaterials 2007

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 demands High cell density Complex cell architecture High vascularity Mechanical 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

• Injectables

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

Signalling Factors• Growth Factors

•(Insulin-like, bFGF, PDGF, hGH)

• Cytokines

• Conditioned media

• Co-culture

Cardiac PatchCardiac Patch

Cell Sheet EngineeringCell Sheet Engineering

Artificial Muscle – Be CreativeArtificial Muscle – Be Creative

NATIVE

TISSUE ENGINEERED

Extracellular MatrixExtracellular Matrix

Injectable MaterialInjectable Material

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