Tissue engineering components of tissue engineering Stem cell applications

1. TISSUE ENGINEERING
Dr. P. SAMUEL
Assistant Professor of Biotechnology

2. Introduction
• Tissue Engineering is an interdisciplinary discipline addressed to create
functional three-dimensional (3D) tissues combining scaffolds, cells and/or
bioactive molecules.
• The term Tissue Engineering (TE) was first presented to the broad
scientific community in 1993 by Langer and Vacanti .
• TE is the development of biological substitutes that maintain, improve or
restore tissue function.
• TE could sidestep the problems associated with tissue damage, in the
present treated with transplants, mechanical devices or surgical
reconstruction.

3. • These three medical therapies have saved and improved countless patients’
lives, but they present associated problems.
• For example, organ transplants show important limitations such as
transplant rejection and lack of donor to cover all the worldwide demand.
• Mechanical devices are not capable of accomplishing all the functions
associated with the tissue and cannot prevent progressive patient
deterioration.
• Finally, surgical reconstruction can result in long-term problems.
• Therefore, TE arises from the need to provide more definitive solutions to
tissue repair in clinics and aims to achieve this goal by the development
of in vitro devices that would repair in vivo the damaged tissue.

4. • TE also leads to engineered tissues, which could allow us to
study human physiology in vitro.
• Cells in the body grow within an organized 3D Extra-Cellular
Matrix (ECM), surrounded by other cells.
• Indeed, the interactions between cell-cell and cell-ECM can
determine whether a given cell undergoes proliferation,
differentiation, apoptosis or invasion.
• However, studies on cellular biology have commonly been
performed on 2D cultures, where cells grown under non-
physiological conditions.
• Specifically, they are unnaturally polarized having one side
attached to a rigid and flat substrate and the other one exposed
to culture media, which reduces cell-cell and cell-ECM
interactions.

5. Scaffold
A major goal in TE is the design of scaffolds capable of recreating the in
vivo microenvironment, which is mainly provided by the ECM.
Regarding biophysical signaling, an essential function of the ECM is to give
anchorage to cells.
Indeed, the ECM highly porous nanostructure provides them a proper 3D
microenvironment and imparts biochemical signaling through two mechanisms:
(i) the binding of a wide variety of soluble Growth Factors (GF), enzymes and
other effector molecules, controlling their diffusion and local concentrations and
(ii) the exposure of specific motifs that are recognized by cellular adhesion
receptors.

6. Properties of Biomaterials
•An ideal biomaterial designed for clinical applications should fulfill a serial of
requirements.
•First of all, biocompatibility and biodegradability are required; allowing
scaffold replacement by proteins synthesized and secreted by native or implanted
cells.
•Besides, the material must be clinically compliant (Good Manufacturing
Practice) to minimize inflammatory and immunological response avoiding
further tissue damage.
•Moreover, as cell degradation products are toxic to other cells, it would be
important that the material allow host macrophages to infiltrate and remove
cellular debris.
•Finally, material production, purification and processing should be easy and
scalable.

7. •Scaffolds for TE can be divided in natural and synthetic, depending on its origin.
• Natural scaffolds are readily accessible and provide a broad range of cues that in
vivo participate in the process of morphogenesis and function acquisition of
different cell types.
•However, its composition strongly depends on the specific animal origin and the
isolation and purification procedures, compromising assay reproducibility.
•On the other hand, synthetic scaffolds can be custom tailored to mimic specific
ECM properties, providing controllable cellular environments.
Polymeric
Scaffolds for Tissue
Engineering

8. What are biomaterials?
Biomaterials play an integral role in medicine today—restoring function and
facilitating healing for people after injury or disease.
The first historical use of biomaterials dates to antiquity, when ancient
Egyptians used sutures made from animal sinew.
The modern field of biomaterials combines medicine, biology, physics, and
chemistry, and more recent influences from tissue engineering and materials
science.
Metals, ceramics, plastic, glass, and even living cells and tissue all can be used
in creating a biomaterial.
They can be reengineered into molded or machined parts, coatings, fibers, films,
foams, and fabrics for use in biomedical products and devices.
These may include heart valves, hip joint replacements, dental implants, or
contact lenses.
They often are biodegradable, and some are bio-absorbable, meaning they are
eliminated gradually from the body after fulfilling a function.

9. • Hydrogel sealants may allow
pain-free dressing changes for
patients with burns.
• Grinstaff lab, Boston University

10. How are biomaterials used in current medical practice?
Doctors, researchers, and bioengineers use biomaterials for the following broad
range of applications:
Medical implants, including heart valves, stents, and grafts; artificial joints,
ligaments, and tendons; hearing loss implants; dental implants; and devices that
stimulate nerves.
Methods to promote healing of human tissues, including sutures, clips, and
staples for wound closure, and dissolvable dressings.
Regenerated human tissues, using a combination of biomaterial supports
or scaffolds, cells, and bioactive molecules. Examples include a bone
regenerating hydrogel and a lab-grown human bladder.
Molecular probes and nanoparticles that break through biological barriers and
aid in cancer imaging and therapy at the molecular level.
Biosensors to detect the presence and amount of specific substances and to
transmit that data. Examples are blood glucose monitoring devices and brain activity
sensors.
Drug-delivery systems that carry and/or apply drugs to a disease target. Examples
include drug-coated vascular stents and implantable chemotherapy wafers for cancer
patients.

11. Cells
An important decision to make when designing strategies for TE is the cell
source selection.
This step becomes a critical issue especially when these strategies are
designed to be clinically applied.
Importantly, cells should fulfill a basic requirement: integrate themselves in
the specific tissue and secret various GF and cytokines that activate the
endogenous tissue regeneration program.
The first approach in cell based techniques is the use of native progenitor
cells.
The main problem is the inherent difficulty of growing some specific cell
types to obtain large quantities.
As a consequence, stem cells either Embryonic (ESCs) or Adult (ASCs) have
emerged as promising alternative cell sources.
An alternative cell type under study for their application in TE are induced
Pluripotent Stem Cells (iPSCs), which were first generated by Yamanaka and
collaborators.

12. Biomolecules
Besides an appropriate scaffold and cell source, signaling molecules
represent an interesting tool in TE to modulate several aspects of cell biology,
from proliferation capacity to specific phenotypic features of fully
differentiated cells.
 In the cellular environment, the presence and gradient of soluble factors
such as GF, chemokines, and cytokines play an important role in biological
phenomena such as chemotaxis, morphogenesis and wound healing. In
particular, these signals are tightly controlled and unique to each organ.
Signaling molecules used in TE can be added to the culture media as
soluble factors or attached to the scaffold by covalent and non-covalent
interactions.
Consequently, the controlled release of different factors from scaffolds
allows their constant renewal, having a great potential to direct tissue
regeneration and formation.
Several matrix systems, micro particles and encapsulated cells have been
reported to locally deliver bioactive factors and to maintain effective
concentrations for their use in the application areas, such as musculoskeletal,
neural and hepatic tissue.

13. Applications of stem cell
Stem cells from the umbilical cord are special.
They are young, potent, and viable.
Numerous clinical studies are being conducted worldwide researching the
suitability of stem cells for the regeneration of damaged tissues after accidents,
degenerative diseases like e.g. slipped intervertebral discs, or cancer treatment.
 Many health professionals and scientists believe in the potential of stem cells:
Umbilical cord blood and tissue that is rich in stem cells will be an important
therapeutic option in future medicine.

15. Stem cell in cancer therapy
• Stem cells have been applied in
the treatment of serious diseases
for more than 55 years.
• They are applied especially to
treat cancers, which require high-
dose chemotherapy within the
scope of medical care.
• The patient’s own stem cells are
extracted from bone marrow or
peripheral blood prior to high-
dose chemotherapy, stored
temporarily and transplanted after
the treatment in order to minimize
the side effects of the aggressive
chemotherapy and to support the
regeneration of destroyed cells.

16. Besides cancer, several 100,000 people come down with common
diseases like dementia, which belongs to the neurodegenerative diseases,
cardiac infarction, stroke, arthritis, or diabetes every year.
The lifelong therapy causes enormous costs in the health care system.
Stem cell therapy offers great potential for the treatment of such diseases.
Experts expect that every seventh person up to the age of 70 will need a
therapy based on stem cells in the future to regenerate sick or aged cells and
tissues.

17. The possible applications of stem cells
increase

18. Stem cells have already been applied successfully for:
Hematopoietic disorders
Acute and chronic leukemia (AML/ALL or CML/CLL)
Myelodysplastic syndrome
Lymphomas (Hodgkin lymphoma, non-Hodgkin lymphoma)
Aplastic anemia
Sickle cell anemia
Beta thalassemia
Immunodeficiency
SCID
Whiskott Aldrich syndrome
Metabolic disorders
Mucopolysaccharidosis
Cancer
Multiple myeloma
Neuroblastoma

20. Stem cell therapy is a promising option for
repairing heart tissue damaged by heart attack.
However, the main obstacle to cardiac stem
cell therapy also happens to be pretty difficult
to get around – and that's the fact that the heart
is constantly in motion.
"Cell retention is always problematic when
you do cell transplantation, but in the heart it is
particularly difficult," says Ke Cheng, associate
professor of regenerative medicine at NC State.
"The heart's pumping can wash cells out of
the organ and they'll either disappear or end up
in other organs – where they are essentially
wasted.
“Cheng specializes in regenerative medicine,
and he wanted to address the problem of
keeping cardiac stem cells where they belong
long enough for them to settle in and start
working.
In 2010, he showed that it was possible to
attach an iron nanoparticle to cardiac stem cells
and use a magnetic field to keep the cells where
they needed to be.

21. Now, Cheng has taken his process one step further.
In a recently published paper in Biomaterials, Cheng used nanoparticles
from an FDA-approved anemia drug called Feraheme to label the cardiac
stem cells, then used magnets to direct the cells to the hearts of rats
with cardiac disease.
"The magnetic field dramatically improved cell retention and the
therapeutic effects," Cheng says. "We're talking about a three-fold increase in
cell retention.
And the fact that the label we used is an already FDA-approved drug means
that we are one step closer to bringing the therapy to clinical trials in
humans."

22. Stem cell self renewal mechanism
• Self-renewal is the process by which stem cells divide to make more stem cells,
perpetuating the stem cell number throughout life.
• Self-renewal is division with maintenance of the undifferentiated state.
• This requires cell cycle control and often maintenance of multipotency or
pluripotency, depending on the stem cell.
• Self-renewal programs involve networks that balance proto-oncogenes (promoting
self-renewal), gate-keeping tumor suppressors (limiting self-renewal), and care-
taking tumor suppressors (maintaining genomic integrity).
• These cell-intrinsic mechanisms are regulated by cell-extrinsic signals from the
niche, the microenvironment that maintains stem cells and regulates their function
in tissues.
• In response to changing tissue demands, stem cells undergo changes in cell cycle
status and developmental potential over time, requiring different self-renewal
programs at different stages of life. Reduced stem cell function and tissue
regenerative capacity during aging are caused by changes in self-renewal programs
that augment tumor suppression. Cancer arises from mutations that inappropriately
activate self-renewal programs.

23. THE REGULATION OF PLURIPOTENT
STEM CELL SELF-RENEWAL
• Embryonic stem (ES) cells are derived from the inner cell mass of the
blastocyst prior to implantation.
• They possess indefinite self-renewal potential as well as the ability to
generate all cell types within the body (pluripotency).
• These characteristics distinguish ES cells from tissue stem cells, which
have more limited self renewal and developmental potentials.
• The unlimited self-renewal potential and pluripotency of ES cells are
conferred by unique transcriptional and cell cycle regulation (Jaenisch &
Young 2008).