Tissue engineering
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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.
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.