Tissue engineering involves using cells, biomaterials, and growth factors to regenerate damaged tissues and organs. There are several strategies for tissue engineering, including injecting stem cells, using scaffolds to guide cell growth, and inducing cell differentiation. Ideal scaffolds are biocompatible, porous, and gradually degrade as new tissue forms. Common scaffold materials include natural polymers, ceramics, and synthetic polymers. Tissue-engineered dental tissues are being developed by harvesting patient cells and growing them on scaffolds or as cell sheets to regenerate the periodontal ligament.

1. Tissue Engineering

2. Tissue engineering
• Can be defined as the use of a combination of cells, engineering materials (living
cells), and suitable biochemical factors to improve or replace biological functions
in an effort to improve clinical procedures for the repair of damaged tissues and
organs (i.e., bone, cartilage, blood vessels, bladder, etc).
• This field is concerned with the transplantation of cells that perform a specific
biochemical function (e.g. an artificial pancreas, or an artificial liver).
• And could be artificial skin that includes living fibroblasts, cartilage repaired with
living chondrocytes, or other types of cells used in other ways.

3. Goals of Tissue Engineering:
• Save lives
• Replace a structure with a completely living structure
• Improve or replace tissues such as:
(Tissue, Skin, Muscle, Bone).
• Improve or replace organs such as:
(Heart, Kidney, Liver).
• Diagnostic applications in which the tissue have been
fabricated in vitro and used for biocompatibility testing
of compound (i.e. application in metabolism and up
taking of drugs, pathogenicity or toxicity).

4. Sources of tissue grafting:
There are four primary classes of tissue organ
transplants: autograft, allograft, xenograft,
and alloplast.

5. AUTOGRAFT
• An autograft is a tissue or organ that is transferred from one location to
another within a single individual. It is common to transplant tissues such as
hair, blood, and even limited amounts of skin and bone. These tissues
regenerate to some extent, repairing the void left after their removal. This
method of transplantation avoids immunologic complications and is
considered the “gold standard” for success.
• Autograft: The patient’s own tissue
A
B
Autograft bone (B) is harvested (A) from the patient into whom it will be
reimplanted.

6. ALLOGRAFT
Allografts are tissues or organs that are transplanted from one
individual to another within the same species. Routinely, tissues
and organs are removed from deceased individuals (as well as
living donors) and transferred to a different individual. Blood,
bone, skin, corneas, ligaments, and tendons are collected in banks
and frozen, to be used in future surgical procedures.
Allograft: Human source other than the patient
BA
Freeze-dried bone allograft is harvested from
humans and sold in sterilized vials in both a
demineralized form (A) as well as a fully mineralized
form (B).

7. XENOGRAFT
They define xenotransplants as “transplantation, implantation, or infusion into
a human recipient of either (a) live cells, tissues, or organs from a nonhuman
animal source or (b) human body fluids, cells, tissues, or organs that have had
ex vivo contact with live nonhuman animal cells, tissues, or organs.” This
therapeutic regimen has been used experimentally to treat neurodegenerative
disorders, liver failure, and diabetes, when compatible human materials are
not widely available.
Xenografts are now common in dentistry. Two examples are BioOss (a product
derived from cow bone) and BioCoral (a corraline product) that are used to
augment defects in the maxilla and mandible.
Xenograft: Tissue from a different species.
B
A
Bone matrices. BioOss, A, is a porous bone mineral
matrix xenograft prepared from bovine sources;
Pepgen P-15, B, combines an organic component—
a synthetically manufactured amino acid sequence
(P-15) designed to
elicit cell bonding, with an inorganic calcium-
phosphate matrix that acts as a carrier for the
amino acid sequence and a scaffold for bone
growth.

8. ALLOPLAST
Alloplasts are the newest type of grafting procedure materials and its quite
different from the previous three types. These grafts are fabricated completely
from synthetic materials, making them quite different from the other three types of
grafts, because no living component is used. Alloplasts, such as dental implants, are
becoming increasingly common in dentistry. Dental implants fabricated from metals
and ceramics are considered routine restorative treatment in many countries.
These materials integrate with bone and help restore function for the patient, with
excellent long-term success. Bone grafting alloplasts are also common Autograft
bone placed in the reconstruction of craniofacial structures can be augmented with
ceramic and bioactive glasses. These alloplasts are available in nearly unlimited
quantity with no adverse immunological reaction. An important benefit is that they
do not pose the risk of transmitting disease from one individual to another.
Alloplast: Synthetic origin.

9. B
A
Bioactive glasses have received increased attention as a result of their surface
bioactivity. Shown here are PerioGlas, A, and Biogran, B.

10. The main advantages of ALLOPLAST :
1- There is no adverse immunological reaction.
2- No risk of transmitting disease from one person to other.

11. Strategies for tissue engineering
Tissue engineering began with the concept of using biomaterials and cells to
assist the body in healing itself. The goal shifted to developing logical
strategies for optimizing new tissue formation through the good selection of
conditions that will enhance the performance of tissue progenitors in a graft
site, ultimately encouraging the production of a desired tissue or organ.

12. Stem cells
All tissues originate from stem cells. A stem cell is defined as a cell
(undifferentiated) which has the ability to continuously divide and
replicate itself to produce specialized cells that can differentiate into
various other types of cells or tissues.

13. Types of stem cells
1- Embryonic stem cells
These types of cells are derived from embryos that are typically 4–5 days
old called Blastocysts. These cells are able to develop into various different
cell types i.e., they have the capacity to form all tissues.

14. 2- Adult stem cells
They are isolated from various tissues such as dental pulp, periodontal
ligament, bone marrow, and neural tissues.

15. Several strategies are now available for
developing new organs and tissues:
1- Injection of cells: Undifferentiated cells (usually not from the patient) are
injected directly into the vicinity of injury. (the cells commonly referred as the
stem cells) These cells are capable of forming new tissue with one or more
phenotypes. The cells are injected into the vicinity of the site in which they are
intended to propagate, and they migrate to the area of injury and begin to
replicate and replace the lost tissue, or produce a desired compound such as
insulin.

16. 2- Guided tissue regeneration (GTR): Undesired cells are excluded from
repopulating a defect or injury site by placing a physical barrier to prevent their
migration. Desirable cells are able to enter the site from the surrounding tissue.
GTR is commonly used in periodontal treatment to regenerate lost periodontal
tissues such as the bone, periodontal ligament, and connective tissue
attachment that support the teeth. The procedure involves placement of a
membrane under the mucosa and over the residual bone

17. The regeneration are classified into guided bone regenerating (GBR) or
guided tissue regenerating (GTR)
GBR refer to an edentulous area.

19. GTR refer to the generation of bone, periodontal and cementum.

20. 3- Cell induction: Growth and differentiation factors are injected (or
implanted with a time-release substrate) within the injury or defect site.
Circulating cells are induced to differentiate and populate the site with a
desirable phenotype. This technique targets local connective tissue
progenitors already present in the region where new tissues are desired and
induces those cells to generate the desired tissue by developmental
proteins and growth factors. Some of the injected proteins may serve as
mutagens in recruiting cells to migrate into the area, where other growth
factors cause them to differentiate.

21. 4- Cells in a scaffold matrix: Preformed scaffolds are seeded with cells from
a patient. This construct is grown in vitro to expand the number of cells and
to allow the cells to begin to produce a matrix. After a suitable growth
interval, the construct is implanted back into the patient. As the cells grow
and develop into tissues, the scaffold slowly resorbs, leaving no trace of its
former presence.
What is the scaffold?
A scaffold is an artificial three dimensional frame structure the serves as a
mimic of extracellular matrix for cellular adhesion, migration, proliferation
and tissue regeneration in three dimensions.

22. Ideal properties of scaffold
1- The scaffold should be porous enough to allow placement of cells and
growth factors
2- It should be biocompatible with the host tissue.
3- It should degrade gradually so that it is replaced by regenerative tissue.
4- It should be effective in transport of nutrients and waste
5- It should be of correct shape and form to allow replacement of the lost
tissues
6- It should has a three dimensional surface and capable of regenerating tissue
and organs in their normal physiology shape.
7- It should has bioactive surface to encourage faster regeneration

23. Scaffolding procedures:
1- The scaffold is seeded with progenitor cells that are allowed to attach
and proliferate.
2- The cells are often grown in a nutrient media supplemented with
growth factors necessary for cell and tissue development.
3- During the growth phase, a static or dynamic mechanical load may be
applied to the construct in order to align the cells in response to the load.
The aligned cells tend to produce a highly organized extracellular matrix
that results in improved tissue structure and function.
4- After a suitable time in vitro, the entire construct is then implanted in
vivo, where the tissue must continue to develop and forming a
connection with the existing vascular system.

24. 5- The scaffold gradually degrades until it's completely replaced by new tissue.
As the scaffold degrades, the developing tissues gradually experience higher
fractions of the loads on the tissue and begin to function as native tissues.
6- The scaffold can therefore serve a dual function, as both a rigid substrate for
cell growth as well as a delivery vehicle for the release of therapeutic
regulatory compounds in vivo.

25. 7- Release of bioactive molecules that are attached to the scaffold surface or
encapsulated within the scaffold matrix can change the function of
connective tissue progenitor cells (activation, proliferation, migration,
differentiation or survival) to create new or enhanced tissues.
►All cells require access to metabolic molecules (oxygen, glucose, amino
acids) and removal of cellular waste products (carbon dioxide, nitrogen
compounds and salts).
►There also must be a balance between consumption and delivery of these
molecules if cells are survive, the design of the scaffold must accommodate
these issues.
►Eventually a rich blood supply will perform these tasks, but such a
circulatory takes time to mature.

26. BIOMATERIALS AND SCAFFOLDS
Three types of biomaterials have been studied as scaffolds and carrier
systems:
(1) Natural (or biological) materials.
(2) Ceramic or glass materials.
(3) Polymeric materials.

27. 1- Natural materials such as collagen, lyophilized bone (both allogenous and
xenogenous), and coral have been used as tissue engineering substrates.
Collagen has been extensively tested as a scaffold for bone regeneration.
One of the first materials used for bone tissue engineering was the insoluble
collagenous matrix obtained after extraction of the bone matrix with various
chemical agents. This collagenous matrix, with freeze-dried bone, formed
new endochondral bone when used with growth factors in vivo. Coral, based
on calcium carbonate, is strikingly similar to the structure of alveolar bone.
When coral is treated with phosphoric acids, the resulting calcium phosphate
is very strong and biocompatible. Many patients prefer nonbiological
implantable substrates because of the high potential for viral, prion, and
disease transmission from these biological materials.

28. 2- Ceramic and glass materials certain types of glasses, glass-ceramic
and pure ceramic can bond tightly with the bone living tissues. Hydroxyl
apatite (HA) is the major inorganic (ceramic) constituent of the bone. It
has been know that ceramic is a biocompatible material and perform
adequately when biomechanical applied. Their used is limited with
scaffold because in the long time degradation in vivo and lack of native
porosity. These bioactive glasses chemically bond to the hard and soft
tissues, and this strong bond called "bio reactivity" or "bioactivity". The
active apatite surface layer must form at the interface between the
material and the bone to create a material bond with bone.

29. 3- Polymeric material Polymers are by far the most common materials
used for tissue-engineering scaffolds. Polylactic acid and polyglycolic acid
(and co-polymers of these two) as well as polycaprolactone are common
examples. These polymers are metabolized in vivo, and their acidic
degradation products are easily removed from the body. They can easily be
cast into a mesh or other desired shape or can simply be extruded as
fibers, which are used to loosely pack an anatomically designed mold. The
same material from which the scaffold is designed can be used to
encapsulate growth factors to provide a timed release of the protein as the
capsule degrades. Polymers release acidic and toxic products when they
degrade; that creates inflammation around the implantation site. Their
survival time in the body is difficult to control, and they become stiff as
they degrade (disadvantages).

30. CAD-CAM technique for scaffolding design .
Auricular computer-aided design and manufacturing (CAD/CAM)
3-dimensional (3D)-printed polycaprolactone scaffold. Patient
computed to mography scan (upper left), CAD rendering (upper
middle), pore incorporation (upper right), 3D-printed ear (lower
left), use with hydrogel (lower middle), and in vivo implantation
(lower right).

31. Nasal computer-aided design and manufacturing (CAD/CAM)
3-dimensional-printed polycaprolactone scaffolds (left),
spherical pore design (right), random pore design (left), and
after immediate porcine postauricular subcutaneous
implantation (right).

32. CELL CULTURE METHODS
Cells can be grown as a monolayer (or sheet) on a polystyrene growth plate
treated to optimize cell attachment and proliferation. Culturing cells on
three-dimensional scaffolds for later implantation is more difficult. Scaffolds
thicker than 1 mm often produce a shell of viable cells and new extracellular
matrix surrounding a necrotic core. Some type of perfusion bioreactor
system must be used to more closely mimic the mass transport in vivo
environment. Alternatively, the tissues can be fabricated in a well-
vascularized region, in vivo. This allows a circulatory system to develop along
with the cells.

33. TISSUE-ENGINEERED DENTAL TISSUES
A great amount of research has been done to develop methods for regenerating
tooth structure and
its supporting tissues. Two approaches are being used to fabricate periodontal
ligament (PDL).
The first
1- harvests existing PDL cells from the patient.
2- The cells are grown and expanded in.
3- The cells are then cultured as a monolayer.
4- Once the layer is continuous, with tight intercellular junctions, the sheet of
cells is released from the culture plate and placed in situ on the tooth surface
to repair the periodontal defect.

34. The second (scaffold method)
1- The PDL cells are again harvested from the patient.
2- The cells are then seeded onto a three dimensional polymer matrix.
3- The cells are grown in vitro.
4- And eventually implanted back into the patient’s periodontal defect.