Design of Scaffold for Tissue engineering of Aortic valve

Design of Scaffold for Tissue engineering of

Aortic valve

By:Prajakt BadgujarGaurav Molankar

Arun ChavanSanjeev Musakwad

Objectives

• Introduction to Aortic valve• Need for tissue engineered valves• Scaffolds for tissue engineered aortic valve• Extracellular matrix • Scaffold fabrication techniques• Bionanotechnology• Nanofibrous scaffolds

06 October 2009Design of Scaffold

for Tissue engineering of Aortic valve 2

The Aortic valve



The valve opens and closes about 3.7 billion times in a lifetime

Valve replacement• Cases like calcification of valve leaflets, cardiac stenosis and

inherited diseases impairs the valve function • This causes insufficient supply of oxygen to the whole body• A common treatment is replacement of the valve with either a

– Mechanical valve. or– Bioprosthetic valve.

Mechanical valve Bioprosthetic valve



Need for Tissue engineered valves

• Patients with mechanical valve implants require a lifelong anticoagulation therapy which eventually results in increased risks of internal bleeding

• Valve thrombo-embolism

• The bioprosthetic valves are less durable, leading to enhanced calcification and immune reactions of the body

• Main disadvantage is that they are “Non-living structures” therefore cannot grow, repair and remodel in response to changing environments

Limitations of mechanical and bioprosthetic valves:



Tissue engineered valves

• Principle of tissue engineering:

1. Seed and culture cells from the recipient onto a carrier material (scaffold)

2. The carrier material then degrades while the tissue is developing outside the body (in vitro)

3. Once the tissue properties are sufficient enough to withstand in-vivo conditions, the tissue can be implanted into the recipient



Importance of Scaffold

• Scaffold is a three dimensional template for valve formation

• An initial supportive structure for the cells

• The desired architecture and biomaterial required for building the scaffold is obtained using nanotechnology



Characteristics of Scaffolds

• Rate of degradation should be proportional to rate of tissue formation

• Degradation products should not be cytotoxic nor inflammatory

• Compatible and pliable with cells• Should promote the acceleration of extracellular matrix

(ECM) formation• It must be chemically inert, to avoid damage to blood cells• Resemblance with the natural valve architecture is also

important



Biomaterials for Scaffold

• Polylactic acid (PLA)• Polyglycolic acid (PGA)• Polycaprolactone (PCL)

• Collagen or Fibrin• Chitosan or

glycosaminoglycans(GAGs)• Hyaluronic acid

• Biomaterials used are of two types:

Synthetic biomaterials:

Natural biomaterials:



Electrospun P4HB:PCL scaffold

• 80:20 mixture of poly(4-hydroxybutyrate) (P4HB) and poly(ε-caprolactone)

• Deposited on a collector plate in the form of a highly interconnected porous non-woven mesh

• Having diameter between 500nm-3µm, pore size ~18µm

P4HB:PCL scaffold 6 weeks in cell culture Gradual degradation

(M.I. van Lieshout, C.M. Vaz, M.C.M. Rutten, G.W.M. Peters, F.P.T. Baaijens)



The P4HB:PCL scaffold

Bottom view Top view

(Anita Mol “Functional tissue engineering of human heart valve leaflets.” Technische University Eindhoven, 2005)



Extracellular Matrix

(Anita Mol “Functional tissue engineering of human heart valve leaflets.” Technische University Eindhoven, 2005)



Functions of ECM

• Gives strength, resistance and shape to the tissue

• Serves as a biologically active scaffolding on which cells migrate and adhere

• An anchor for many proteins and enzymes

• Provides aqueous environment for the diffusion of nutrients, ions and hormones



Scaffold fabricationTechniques

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• Isolation of cells from a blood vessel of the patient and separation myofibroblasts & endothelial cells.

• Seeding of myofibroblasts onto a scaffold material in the shape of a trileaflet heart valve and subsequent seeding of endothelial cells onto the surfaces.

• The cell/scaffold structure is placed into a bioreactor to simulate tissue development


for Tissue engineering of Aortic valve

Scaffold fabrication

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Conventional methods • The formation of a porous structure constitutes a

central goal of scaffold fabrication and a number of techniques were developed to achieve this aim including -phase separation-gas foaming-freeze drying

• The limitation of these technologies is lack of precise control over scaffold specification such as pore size, shape , distribution etc



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• The other scaffold fabrication technologies can be categorized as follows depending on their modes of assembly

1. Heat based fabrication

e g. Fused deposition modeling, Selective laser

sintering

Other scaffold fabrication techniques



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2. Light based fabrication e.g. Stereolithography

• It relies on light-mediated chemical reactions.• Light energy can also be used to build three dimensional

structure.• Photopolymerization involves the application of light to

initiate a chain reaction, resulting in the solidification of a liquid polymer solution.




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• Here surface is lowered into a vat of photocurable polymer & resultant layer on top of surface is exposed to a laser to harden the polymer




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3. Adhesive based Fabrication e.g. 3D-printing, wax printing.

• In 3D-printing an ink jet printer is used to deposit a binder solution onto a biomaterial powder bed to create structures (200 to 500 µm) one layer at a time

• The process is repeated after spreading a new layer of powder on the top of previous layer resulting in creation of 3D structure




22 3D Bioprinting Technology

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Bionanotechnology



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Bionanotechnology• Nanotechnology that uses

biology as a guidance .

• Human body -complex system of interacting molecules

• Technology required to understand & repair the body is molecular machine technology -- nanotechnology.

• Design of tissue engineered scaffold with properties & function of native tissue



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• Since nanofibres are 1000 times smaller than synthetic polymer fibers, they surround cells as ECM surrounds

• Thus biomolecules diffuse slowly, creating local molecular gradients which play vital & fundamental role in cell differentation signal transduction organ development and other biological processes

Bionanotechnology



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Nanofibrous scaffold

• Electrospinning is used for constructing nano-to microfiber-based scaffolds

• Produces nanofibrous scaffold in a continuous fashion that are interconnected

• The fiber diameter can range from 5nm to more than 1µm• Our goal is their application in tissue engineered (TE) aortic

valves

• For e.g.poly(4-hydroxybutyrate) (P4HB) and poly(ε-caprolactone) (PCL) was developed electrospun and studied in terms of pliability, degradability, & ability to accelerate ECM formation for mechanical stability



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(M.I. van Lieshout, C.M. Vaz, M.C.M. Rutten, G.W.M. Peters, F.P.T. Baaijens)



Electrospinning

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(Adv. Mater. 16 (14) 2004In: Principles of tissue engineering. LanzaRP, Langer R, Chick)

Example of an electrospun stented aortic valve.



Summary



• The clinical performance of the tissue engineered valves are superior to those of prosthetic valves

• The development of scaffolds play a vital role in tissue engineering

• Bionanotechnology helps in achieving the desired architecture with appropriate biomaterial of tissue engineered scaffolds

• This approach would provide the ultimate solution for treating valvular heart diseases

References• Patricia M. Taylor: “Biological matrices and bionanotechnology,

phil,” Trans. R.Soc.B(2007) 362, pp.1313-1320 • Adrian H Chester, Najma Latif, Magdi H Yacoub, Patricia M

Taylor, Aortic valve from functions to tissue engineering “Vascular complications in Human diseases,” pp.229-239

• Cato T Laurencin, Lakshmi S Nair: “Nanotechnology and tissue engineering,” pp-9-13 & 87

• Peter X Ma, Jennifer Elisseeff: “Scaffolding In tissue engineering,” pp. 3-5

• Ivan Vesely, “Heart valve tissue engineering,” Circ. Res. 2005: 97: pp.743- 755

• Thubrikar M, Pipgrass WC, Shaner TW, Nolan SP, “The design of a normal aortic valve”. Am J Physiol 1981: 241: H pp. 795-801

• B. Chevallay and D. Herbage “Collagen-based biomaterials as 3D scaffold for cell cultures: applications for tissue engineering and gene therapy,” Med. Biol. Eng. Comput., 2000, 38, pp.211-218

• James H Thrall, “Nanotechnology and medicine” Radiology 2004;230, pp.315–318.



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Design of Scaffold for Tissue engineering of Aortic valve