TISSUE DEVELOPMENT WITH TISSUE ENGINEERING APPROACH

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TISSUE DEVELOPMENT WITH TISSUE ENGINEERING
APPROACH
PRESENTED BY
FELIX CHIBUZO OBI (20144610) MSc.
SUPERVISOR PROFESSOR S. ISMET DELILOGLU GURHAN
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INTRODUCTION

• Tissue Engineering is the development and
  practice of combining scaffolds, cells, and
  suitable biochemical factors (regulatory factors
  or Signals) into functional tissues. The goal of
  tissue engineering is to assemble functional
  constructs that restore, maintain, or improve
  damaged tissues or whole organs.

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Cells are the building blocks of tissue, and
tissues are the basic unit of function in the
body. Generally, groups of cells make and secrete
their own support structures, called
extracellular matrix. This matrix, or scaffold,
does more than just support the cells it also
acts as a relay station for various signaling
molecules. Thus, cells receive messages from many
sources that become available from the local
environment. Each signal can start a chain of
responses that determine what happens to the
cell. By understanding how individual cells
respond to signals, interact with their
environment, and organize into tissues and
organisms, Tissue Engineers are now able to
manipulate these processes to amend damaged
tissues or even create new ones.
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STEM CELLS TECHONOLOGY

• Stem cells are undifferentiated biological cells
  that are capable of differentiating into
  specialized cells and can divide through Mitosis
  to produce more stem cells. Most current
  strategies for tissue engineering depend upon a
  sample of autologous cells from the diseased
  organ of the host.
• However, for many patients with extensive
  end-stage organ failure, a tissue biopsy may not
  yield enough normal cells for expansion and
  transplantation. In other instances, primary
  autologous human cells cannot be expanded from a
  particular organ, such as the pancreas. In these
  situations, pluripotent human embryonic stem
  cells are envisioned as a viable source of cells
  because they can serve as an alternative source
  of cells from which the desired tissue can be
  derived.
• Embryonic stem cells exhibit two remarkable
  properties the ability to proliferate in an
  undifferentiated but pluripotent state
  (self-renew), and the ability to differentiate
  into many specialized cell types. They can be
  isolated by immunosurgery from the inner cell
  mass of the embryo during the blastocyst stage
  (4-5 days after fertilization), and are usually
  grown on feeder layers consisting of mouse
  embryonic fibroblasts or human feeder cells. More
  recent reports have shown that these cells can be
  grown without the use of a feeder layer, and thus
  avoid the exposure of these human cells to mouse
  viruses and proteins. These cells have
  demonstrated longevity in culture by maintaining
  their undifferentiated state for at least 80
  passages when grown using current published
  protocols.

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ORGAN DEVELOPMENT FROM EMBRYONIC STEM CELLS
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Human embryonic stem cells have been shown to
differentiate into cells from all three embryonic
germ layers (Endoderm, Mesoderm and Ectodrem) in
vitro. In addition, as further evidence of their
pluripotency, embryonic stem cells can form
embryoid bodies, which are cell aggregations that
contain all three embryonic germ layers, while in
culture, and can form teratomas in vivo. Due to
the Ethical concern of the Human Embryonic stem
cell, some Tissue Engineers are working with
Mesenchymal Stem cell (MSCs) to develop Tissues,
such Tissue have no risk of rejection by the body.
STEN CELLS TECHNOLOGY CONT.
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NEW DEVELOPMENT IN EMBRYONIC STEM CELL
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SCAFFOLDS IN TISSUE ENGINEERING

• A scaffold is a material that can be formed in
  the shape of tissue that needs to be
  replaced. The scaffold can be biologically
  derived or a synthesized material.  The scaffold
  material must be biologically compatible for
  human implantation. The scaffold is typically
  impregnated (seeded) with a patients cells
  before implantation.
• Typically, Scaffolds are synthesized from
  Biomaterials. These Biomaterials replicate the
  biologic and mechanical function of the native
  Extracellular Matrix (ECM) found in tissues by
  serving as an artificial ECM. As a result,
  biomaterials provide a three-dimensional space
  for the cells to form into new tissues with
  appropriate structure and function, and also can
  allow for the delivery of cells and appropriate
  bioactive factors (e.g., cell adhesion peptides,
  growth factors), to desired sites in the body.
  Because the majority of mammalian cell types are
  anchorage dependent and will die if no
  cell-adhesion substrate is available,
  biomaterials provide a cell-adhesion substrate
  that can deliver cells to specific sites in the
  body with high loading efficiency. Biomaterials
  can also provide mechanical support against in
  vivo forces such that the predefined
  three-dimensional structure is maintained during
  tissue development. Furthermore, bioactive
  signals, such as cell-adhesion peptides and
  growth factors, can be loaded along with cells to
  help regulate cellular function.

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The ideal biomaterial should be
biocompatible in that it is biodegradable and
bioresorbable to support the replacement of
normal tissue without inflammation. Furthermore,
the biomaterial should provide an environment in
which appropriate regulation of cell behavior
(e.g., adhesion, proliferation, migration, and
differentiation) can occur such that functional
tissue can form. Cell behavior in the newly
formed tissue has been shown to be regulated by
multiple interactions of the cells with their
microenvironment, including interactions with
cell-adhesion ligands and with soluble growth
factors.Generally, three classes of
biomaterials have been used for engineering
tissues naturally derived materials (e.g.,
collagen and alginate), Acellular tissue matrices
(e.g., bladder submucosa and small intestinal
submucosa), and synthetic polymers (e.g.,
polyglycolic acid (PGA), polylactic acid (PLA),
and poly(lactic-co-glycolic acid) (PLGA). These
classes of biomaterials have been tested in
respect to their biocompatibility. Naturally
derived materials and acellular tissue matrices
have the potential advantage of biologic
recognition. However, synthetic polymers can be
produced reproducibly on a large scale with
controlled properties of their strength,
degradation rate, and microstructure.
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Figure a b Synthetic Scaffolds Figure c d
Acellular Scaffolds
Synthetic Breast Scaffolds
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SCAFFOLDING APPROCHES IN TISSUES ENGINEERING

• There are basically four major scaffolding
  approaches for tissue engineering.(Fig. 1). Table
  1 (on next slide) highlights some of the working
  principles and the characteristics of these
  approaches.

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Table 1 Characteristics of different scaffolding
approaches in tissue engineering
Scaffolding approach (1) Pre-made porous scaffolds for cell seeding (2)Decellularized extracellular matrix for cell seeding (3) Confluent cells with secreted extracellular matrix (4) Cell encapsulated in self-assembled hydrogel
Raw materials Processing or fabricating technology Strategy to combine with cells Strategy to transfer to host tissues Synthetic or natural Biomaterials Incorporation of porogens in solid materials solid free-form fabrication technologies techniques using woven or non-woven fibers Seeding Implantation Allogenic or Xenogenic Tissue Decellularization technologies Seeding Implantation Cells Secretion of extracellular matrix by confluent cells Cells present before extracellular matrix secretion Implantation Synthetic or natural biomaterials able to self-assemble into hydrogels Initiation of self-assembly process by parameters such as pH and temperature Cells present before self-assembly Injection
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Table 1 Characteristics of different scaffolding
approaches in tissue engineering (Cont)
Scaffolding approach (1) Pre-made porous scaffolds for cell seeding (2)Decellularized extracellular matrix for cell seeding (3) Confluent cells with secreted extracellular matrix (4) Cell encapsulated in self-assembled hydrogel
Advantages Disadvantages Preferred applications Most diversified choices for materials precise design for microstructure and architecture Time consuming cell seeding procedure inhomogeneous distribution of cells Both soft and hard tissues load-bearing tissues Most nature-simulating scaffolds in terms of composition and mechanical properties Inhomogeneous distribution of cells, difficulty in retaining all extracellular matrix, immunogenicity upon incomplete decellularization Tissues with high ECM content load-bearing tissues Cell-secreted extracellular matrix is biocompatible Need multiple laminations Tissues with high cellularity, epithelial tissues, endothelial tissues, thin layer tissues Injectable, fast and simple one-step procedure intimate cell and material interactions Soft structures
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Pre-made porous scaffolds for cell
seeding Scaffolds are made of degradable
biomaterials and these has become the most
commonly used and well-established scaffolding
approach. This approach represents the bulk of
biomaterial research in tissue engineering,
leading to enormous efforts in development of
different types of biomaterials and fabrication
technologies. Many types of biomaterials can be
used to make porous scaffolds for tissue
engineering provided that a fabrication
technology compatible with the biomaterial
properties is available
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Decellularized ECM from Allogenic or Xenogenic
Tissues for cell seeding Acellular ECM processed
from allogenic or xenogenic tissues are the most
nature-simulating scaffolds, which have been used
in tissue engineering of many tissues including
heart valves, vessels, nerves, tendon and
ligament. This scaffolding approach removes the
allogenic or xenogenic cellular antigens from the
tissues as they are the sources for
immunogenicity upon implantation but preserves
the ECM components, which are conserved among
species and therefore well tolerated
immunologically. Specialized decellularization
techniques are developed to remove cellular
components and this is usually achieved by a
combination of physical, chemical and enzymatic
methods. In brief, cell membranes are lysed by
physical treatments such as freeze-thaw cycles or
ionic solutions such as hypo or hypertonic
solutions before separating the cellular
components from the ECM by enzymatic methods.
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Cell sheets with self-secreted ECM Cell sheet
engineering represents an approach where cells
secrete their own ECM upon confluence and are
harvested without the use of enzymatic methods.
This is achieved by culturing cells on
thermo-responsive polymer, such as
poly(N-isopropylacrylamide) coated culture dish
until confluence. The confluent cell sheet is
then detached by thermally regulating the
hydrophobicity of the polymer coatings without
enzymatic treatment. Such approach can be
repeated to laminate multiple single cell layers
to form thicker matrix.
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Cell encapsulation in self-assembled hydrogel
matrix Encapsulation is a process of entrapping
living cells within the confines of a
semi-permeable membrane or within a homogenous
solid mass. The biomaterials used for
encapsulation are usually hydrogels, which are
formed by covalent or ionic crosslinking of
water-soluble polymers. Many types of
biomaterials including natural and synthetic
hydrogels can be used for encapsulation provided
that the conditions inducing the hydrogel
formation or the polymerization are compatible
with living cells. Encapsulation has been
developed over several decades and the
predominating use is for immunoisolation during
allogenic or xenogenic cell transplantation.
A Synthetic Hydrogel
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GROWTH FACTORS IN TISSUE DEVELOPMENT

• A growth factor is a naturally occurring
  substance capable of stimulating cellular growth,
  cellular growth, proliferation, healing, and
  cellular differentiation. Usually it is a protein
  or a steroid hormone. Growth factors are
  important for regulating a variety of cellular
  processes.
• Growth factors typically act as signaling
  molecules between cells. Examples are cytokines
  and hormones that bind to specific receptors on
  the surface of their target cells.
• They often promote cell differentiation and
  maturation, which varies between growth factors.
  For example, bone morphogenetic proteins
  stimulate bone cell differentiation, while
  fibroblast growth factors and vascular
  endothelial growth factors stimulate blood vessel
  differentiation (angiogenesis).

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TISSUE DEVELOPMENT

• Basically Tissue development begins with building
  a scaffold from a wide set of possible sources,
  from proteins to plastics. Once scaffolds are
  created, cells with or without a cocktail of
  growth factors can be introduced. If the
  environment is right, a tissue develops.  In some
  cases, the cells, scaffolds, and growth factors
  are all mixed together at once, allowing the
  tissue to self-assemble. 
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Another method to create new tissue uses an
existing scaffold. The cells of a donor organ are
stripped and the remaining collagen scaffold is
used to grow new tissue. This process has been
used to bioengineer heart, liver, lung, and
kidney tissue. This approach holds great promise
for using scaffolding from human tissue discarded
during surgery and combining it with a patients
own cells to make customized organs that would
not be rejected by the immune system.
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CONCLUSION

• Tissue engineering efforts are currently
  underway for virtually every type of tissue and
  organ within the human body. Because tissue
  engineering incorporates the fields of cell
  transplantation, materials science, and
  engineering, personnel who have mastered the
  techniques of cell harvest, culture, expansion,
  transplantation, and polymer design are essential
  for the Successful application of this
  technology. Various engineered tissues are at
  different stages of development, with some
  already being used clinically, a few in
  preclinical trials, and some in the discovery
  stage. Recent progress suggests that engineered
  tissues may have an expanded clinical
  applicability in the future because they
  represent a viable therapeutic option for those
  who require tissue replacement. More recently,
  major advances in the areas of stem cell biology,
  tissue engineering, and nuclear transfer
  techniques have made it possible to combine these
  technologies to create the comprehensive
  scientific field of regenerative medicine.

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REFERENCES

• http//www.nibib.nih.gov/science-education/science
  -topics/tissue-engineering-and-regenerative-medici
  ne
• http//www.regenerativemedicine.net/Tissue.html
• http//rsif.royalsocietypublishing.org/content/8/5
  5/153
• http//jasn.asnjournals.org/content/15/5/1113.full
  .pdfhtml
• http//www.ncbi.nlm.nih.gov/pmc/articles/PMC258765
  8/
• http//en.wikipedia.org/wiki/Growth_factor
• John P, Fisher A, Mikos J, Tissue Engineering.
  CRC Press, Taylor Francis Group
• Professor S. Ismet Deliloglu Gurhan Tissue
  Engineering Lecture Note, Department of
  Biomedical Engineering, Near East University.

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