Tissue Engineering Flashcards
Explain what tissue engineering is?
Tissue Engineering is the in vitro development (growth) of tissues or organs to replace or support the function of defective or injured body parts
Name the three ways cells can communicate?
- Soluble signals
- Cell to Cell contact
- Cell - ECM interactions
What are soluble signals? How does this process work
small proteins (15-20 kDa) which are chemically stable with long half-lives (unless specifically degraded) growth factors, steroids, hormones, cytokines, chemokines
Bind to membrane receptors usually with high affinity (low binding constants: 10-100 pM)
Diffusion driven process
How does cell - to - cell contact work?
Some membrane receptors are adhesive molecules
adherent junctions and desmosomes
Other serve to create junctions between adjacent cells allowing for direct cytoplasmic communication
gap junctions
1.5-2 nm diameter and only allow transport of small molecules ~1 kDa
How does ECM interactions work?
ECM is multifunctional and also provides a substrate that cells can communicate
Since cells synthesize the ECM, they can modify the ECM to elicit specific cellular responses
Several specialized receptors that allow for cell-ECM interactions
integrins, CD44, etc.
also a mechanism by with cells respond to external stimuli (“mechanical transducers”)
What is the role of a scaffold?
substrate material must be inserted to aid in organization of the cells in three dimensions
What are the three types of scaffold material? and give examples
- Polymeric e.g. Chitosan, Alginate, Foams, Hydrogels
- Natural e.g.Collagen, Elastin, Fibrin a.k.a Factor Ia
- Ceramic e.g. calcium phosphate based for bone tissue engineering
Calcium phosphate ceramics (CPCs)
How is Fibrin formed?
Fibrin is a fibrous, non-globular protein involved in the clotting of blood.
It is formed by the action of the protease thrombin on fibrinogen which causes it to polymerize. The polymerized fibrin together with platelets forms a hemostatic plug or clot over a wound site.
What is Elastin and what is it composed of?
Major protein component of tissues that requires elasticity like arteries, lungs, bladder, skin and elastic ligaments.
It is composed of soluble tropoelastin protein containing primarily, glycine, valine and modified alanine and proline residues
How can elastin/tropoelastin work as a scaffold?
Tropoelastin is a ~65kDa protein that is highly cross-linked to form an insoluble complex.
What are CPCs and what do they do?
CPC = Calcium phosphate ceramics are a class of tunable bioactive materials that have been widely used for bone tissue repair and augmentation
They have surface properties that support osteoblast adhesion/proliferation (i.e. osteoconduction) and stimulate new bone formation (i.e. osteoinduction)
More significantly, CPCs have been shown to promote bone growth in vivo, and recruit bone marrow stromal cells (BMSCs) to ectopic sites to induce bone formation
What are the features of an ideal extracellular matrix?
3-dimensional Cross-linked Porous Biodegradable Proper surface chemistry Matching mechanical strength Biocompatible Promotes natural healing Accessibility Commercial Feasibility
What are some important scaffold variables?
Surface chemistry
Matrix topography
- Cell organization, alignment
- Fiber alignment -> tissue development
Rigidity
5-23 kPa
Porosity
- Large interconnected
- small disconnected
Define Mechanotransduction
Conversion of a mechanical stimulus into a biochemical response
What are the mechanical forces that may be involved?
Flow-induced shear stress
- Laminar blood flow
- Rhythmic pulses
Uniaxial, Equiaxial stretch
- Magnitude
- Frequency
What are the different types of cell culture?
Monolayer (adherent cells)
Suspension (non-adherent cells)
Three-dimensional (scaffolds or templates)
What sterilization methods can be used for culturing of cells?
ultra-violet light, 70% ethanol, steam autoclave, gamma irradiation, ethylene oxide gas
What are the growth conditions for culturing of cells?
simulate physiological environment
pH 7.4, 37°C, 5% CO2, 95% relative humidity
culture (growth) media replenished periodically
The use of which type of cell would avoid any potential immunological complications?
Autologous cells
Describe the various classifications of cells used for tissue engineering
- Primary cells
differentiated cells harvested from the patient (tissue biopsy)
low cellular yield (can only harvest so much)
potential age-related problems - Passaged cells
serial expansion of primary cells (can increase population by 100-1000X)
tendency to either lose potency or de-differentiate with too many passages
3. Stem cells undifferentiated cells self-renewal capability (unlimited?) can differentiate into functional cell types very rare
What are the two lineages of stem cells?
- mesenchymal
give rise to connective tissues (bone, cartilage, etc.)
although found in some tissues, typically isolated from bone marrow - Hematopoietic
give rise to blood cells and lymphocytes
isolated from bone marrow, blood (umbilical cord)
What does CFU stand for?
Colony-Forming Units
Describe the different bioreactors?
a) Spinner Flask:
semi-controlled fluid shear
can produce turbulent eddies which could be detrimental
b) Rotating Wall
low shear stresses, high mass transfer rate
can balance forces to stimulate “zero gravity”
c) Hollow Fibre
used to enhance mass transfer during the culture of highly metabolic cells
d) Perfusion
media flows directly through construct
e) Controlled Mechanics
to apply physiological forces during culture
Define a skin graft
A skin graft is a tissue of epidermis and varying amounts of dermis that is detached from its own blood supply and placed in a new area with a new blood supply.
Define a skin flap
Any tissue used for reconstruction or wound closure that retains all or part of its original blood supply after the tissue has been moved to the recipient location.
What’s the difference between a graft and a flap?
Graft - does NOT maintain original blood supply
Flap - Maintains original blood supply
What are the classifications of grafts? (3)
Autografts – A tissue transferred from one part of the body to another.
Homografts/Allograft – tissue transferred from a genetically different individual of the same species.
Xenografts – a graft transferred from an individual of one species to an individual of another species.
What are the two types of grafts?
Split Thickness(Partial): Contains 100% of the epidermis and a portion of the dermis. Split thickness grafts are further classified as thin or thick.
Full Thickness: Contains 100% of the epidermis and dermis.
