This document discusses the past, present, and future of tissue engineering and biomedicine. It covers the basics of tissue engineering, including the use of cells, scaffolds, and signals. It also discusses different cell sources for tissue engineering like embryonic stem cells, adult stem cells, and directed differentiation. Applications of stem cells in tissue engineering are also reviewed, such as engineering skin, bone, and cardiovascular tissues. The future of the field is seen to involve further understanding stem cell biology and differentiation, as well as moving from small lab experiments to large-scale production of cells and tissues.

1. PAST, PRESENT AND FUTURE
BIOMEDEEKS

2. Tissue engineering
• Interdisciplinary field that combines principles of
biology and medicine with engineering;
• Design and construction of functional
components that can be used for maintenance,
replacement or regeneration of damaged
biological tissues.

3. Past
• First Report in 1933: Implantation of tumor
cells wrapped in a polymer membrane into a
pig to protect them from immune attack;
• Modern Era of Tissue Engineering in the
1980s: Development and clinical use of skin
replacements.

4. Past
• Basic components of tissue engineering: Cells,
scaffolds and biological signs.
Cells
Signals
Scaffolds
Tissue Engineering
• Over the last decades,
engineers have turned
to all cells to try and
determine the best cell
source for each type of
tissue that needs to be
constructed.

5. Stem Cells
• Undifferentiated cells capable of self-renew
and to differentiate into different cell types
or tissues during embryonic development
and throughout adulthood;
• They can be classified into two groups
according to their origin:
- Embryonic Stem Cells – pluripotent;
- Adult Stem Cells.

6. Viability of Stem Cells
Sometimes arise changes in populations of these
cells, leading to its decrease such as:
• Defects in the bone marrow due to
malignancies of hematopoietic stem cells
(leading to leukemias and lymphomas);
• Genetic defects of the hematopoietic stem
cells (Fanconi anemia);
• Diabetes type I, which is due to autoimmune
destruction of pancreatic beta cells.

7. Viability of Stem Cells
In order to overcome this problem these
cells may be treated by:
• Organ transplantation in bankruptcy - for
heart failure, liver or pancreas;
• Substitution of the population of stem
cells - for bone marrow transplantation.

8. Associate problems
• Limitations in organ transplantation - a lack of
donors and difficulties in blood compatibility
between donor and recipient.
• In the past decade: Large interest in using
stem cells to generate clinically cells to rebuild
these populations of cells to repair organs or
tissues.
Immune Barrier
Solution: Autologous cells - Stem cells derived
from the patient, which were isolated and
transplanted.

9. Universidade de Aveiro
Cell Sources
Embryonic stem cells (ESC)
•Found temporarily in embryos
before mitotic division.
•Capable of producing all the 220
types of cells which form an adult
human body.
•In 1981, ESC from the inner mass of
the blastocyst of mice were isolated
before implantation into the uterus.
Process of isolation of ESC

10. Cell Sources
Embryonic stem cells (ESC)
•The first human ESC were
derivate in 1998.
•Differences between ESC of
mice and ESC of humans
were noticed.
•The culture medium used to
study the ESC of mice was
not adequate for the
derivation of ESC of humans.
Culture medium for ESC of mice

11. Cell Sources
Directed differentiation of stem cells
• Stem cells can be encouraged to differentiate to the
required phenotype by manipulating the culture conditions
under which they are maintained.

12. Cell Sources
Directed differentiation of stem cells
• Such manipulations include stimulation of cells with
particular cytokines, growth factors, amino acids, other
proteins and active ions and co-culture with a relevant
cell/tissue type.
By using Directed differentiation of
stem cells it was possible to correct
in vitro defects in hematopoietic
stem cells from patients with
Fanconi Syndrome.

13. Cell Sources
Adult stem cells
• Fetal stem cells;
• Hematopoietic stem cells;
• Mesenchymal stem cells;
• Neural stem cells;
• Cancer stem cells.

14. Cell Sources
Adult stem cells
• There is an extensive repository of
these stem cells located in various
tissue niches throughout the body,
including bone marrow, brain, liver,
and skin as well as in the circulation.
• Undifferentiated cells found among
differentiated cells in a tissue or
organ that can renew itself.
• To maintain and repair the tissue in
which they are found.

15. Universidade de Aveiro
Cell Sources
Identification and Isolation of adult stem cells
• Fluorescent molecules adhere very
specifically to the receptors of the
stem cells acting as cell markers.
• The fluorescent markers emit
visible light providing the
visualization of the targeted stem
cells ( FACS and fluorescence
microscopy).

16. Cell Sources
Fetal stem cells
• Have the ability to differentiate into hematopoietic and
mesenchymal stem cells lineages.

17. Cell Sources
Hematopoietic stem cells
• Origin all blood cell types:
Red blood cells, white blood
cells, lymphocytes and
platelets.
• Intervain in the regeneration
and repair of periferic tissues
in a case of damage or wound,
promoting immune response
by acquiring the properties of
the cells in which they are
combined.

18. Cell Sources
Mesenchymal stem cells
• Multipotent adult cells,
capable of raising various
types of cells by differentiation,
including chondrocytes,
myocytes, adipocytes,
fibroblasts and osteoblasts.
•Possess anti-inflammatory and
immunomodulating properties
(supress the toxicity from certain
cells).

19. Support Materials
Scaffolds Requirements for Tissue Engineering
• Biocompatibility;
• The capacity to sustain and/or promote the growth of the
relevant cells/tissue;
• Provision of a template for tissue growth in three dimensions.
There are obvious limitations associated with biological materials:
Lack of consistency and structure malleability.
New biomaterials offer many advantages: They can be designed
to meet specific spatial and strength requirements and their rate of
degradation can be precisely controlled.

20. Support Materials
Biocompatibility
Bioinert Resorbable Bioactive
- No material can be totally inert when implanted but the group
known as bioinert only provoke formation of scar tissue (e.g.,
stainless steel in artificial hips);
- Resorbable materials dissolve when implanted with the
generation of harmless dissolution products (e.g., polymers like
PLLA used for suturing);
- Bioactive materials stimulate a biological response from the body
(e.g., synthetic hydroxyapatite ceramics and bioactive glasses).

21. Microenvironment
• Attempting to replicate the natural
microenvironment in which the cell/tissue
would normally grow and function within the
body.
Physical
Insoluble
Macro-molecules
(collagen)
Chemical
Soluble
Macro-molecules
(cytokines)
Cell–Cell
interactions
Proteins on
adjacent
cells

22. Microenvironment
• Basic requirements for the maintenance of
cells in culture:
Oxygen, pH, humidity, temperature, nutrients and
osmotic pressure maintenance.
• Factors or stimuli to induce functionality:
Growth factors, hormones, specific metabolites or
nutrients, chemical and physical stimuli.
A bioreactor is a device that attempts to simulate
a physiological environment in order to promote
cell or tissue growth in vivo.

23. Microenvironment

24. Microenvironment
• For stem cells:
- Co-culture with mature cells or tissues to drive
their differentiation toward required lineages.
- Use of synthetic biomaterials to create
microenvironments that mimic natural
extracellular matrix.
Stem-cell populations are established in
'niches‘:
Specific anatomic locations that regulate how
they participate in tissue generation,
maintenance and repair.

25. Stem Cell Applications in Tissue
Engineering
• There is a variety of considerations to
identifying appropriate cell sources:
Complex tissues
• The final construct needs to replicate the
architecture and complex cellular
interdependence found in the normal tissue
Vascularization
• To maintenance of the nutrient supply to the
tissue as it integrates in situ
Interface stability
• To promote the integration of the construct with
the native tissue

26. Stem Cell Applications in Tissue
Engineering
Function
• The constructs must have the required level of normal
activity in vivo
Storage
• The viability of cell-based products needs to be
maintained during storage and transport
Sterility
• Must be maintained during the production of each
construct
Cost
• Need to develop cost-efficient, scalable processes, and
rapid quality control tools

27. Stem Cell Applications in Tissue
Engineering
Stem cells are being used in the clinic, but most
applications are based on the application of adult
or fetal stem cells and involve cell delivery.
However, broader tissue engineering strategies,
including those using ESC are being developed
and tested:
• Engineering skin,
• Engineering the skeleton,
• Cardiovascular system.

28. Stem Cell Applications in Tissue
Engineering
Engineering skin:
- Skin autografts are produced by culturing
keratinocytes to generate an epidermal sheet and to
maintain the stem cell population- holoclones.
- The epidermal sheet
is placed on top of a
dermal substitute
comprising:
• Devitalized dermis;
• Bioengineered
dermal substitutes
seeded with dermal
fibroblasts.

29. Stem Cell Applications in Tissue
Engineering
Engineering the skeleton
Skeletal stem cells (SSCs) are found in the subset
of clonogenic adherent marrow-derived cells, and are
able to undergo extensive replication in culture.
• Bone regeneration requires ex vivo expansion
of marrow-derived skeletal stem cells and their
attachment to 3-D scaffolds;
• The composite can be transplanted into
segmental defects and will subsequently
regenerate an appropriate 3-D structure in
vivo.

30. Stem Cell Applications in Tissue
Engineering
Engineering the skeleton

31. Stem Cell Applications in Tissue
Engineering
Cardiovascular system
• There has been success in the treatment of
myocardial infarct by stem cell delivery using
autologous bone marrow;
• Tissue constructs, except for cartilage, need a
microvascular network and attempts have
been made to encourage vasculogenesis on
scaffolds
(by seeding with endothelial progenitor cells
(EPC) isolated from human cord blood)

32. Conclusion and Future
• Whereas fighting infectious disease has long been a
preoccupation of medicine, in the future, dealing with
the consequences of a predominantly aging population
is likely to take priority.

33. Conclusion and Future
• Our understanding of stem cell biology continues to increase
but we must be able to not only control but also optimize the
differentiation of stem cells.
• Ethical Problems: The use of ESC remains contentious for
some governments and religious groups.
• The move from small-scale laboratory experiments to large-scale
production of cells: Need innovative bioreactor
technology and level of process quality controls.

34. Conclusion and Future
• A differentiated cell, one derived from a stem cell, will
exhibit the normal immunogenic characteristics of that
particular type of differentiated cell.
• Finding the most effective ways of using stem cells, and
triggering their differentiation in a controlled manner will
provide cell banks for the in vitro growth of tissue and
for cell replacement therapy.

35. Thanks for your attention!