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Tissue Engineering โโAn interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function.
Stem Cells โโA cell that has the ability to self renew and differentiate into various other specialized cell types.
Cells in Tissue Engineering โโCell Location (based on tissue types):
- Skin cells for skin tissue engineering
- Chondrocytes for cartilage tissue engineering cells sources: autologous, allogenic, xenogenic
- Stem cells for various tissue engineering: embryonic stem cells, induced pluripotent stem cells (IPS), adult stem cells
Scaffold in Tissue Engineering โโ- Natural Scaffolds
- Synthetic Scaffolds
- Polymers
- Ceramics
- Nano/micro tubes and fibers
- Composites
Bioreactors โโ- System where conditions are closely controlled to permit and induce a certain behavior in living cells or tissues
- Provide controlled and steady flow of cell media
- Factors necessary for cell growth: pH, temp., pressure, nutrient supply, waste removal
- Type of Bioreactors: spinner flasks, rotating vessels, hollow fiber, perfusion reactors
Two Key Features of Stem Cells โโ- Self-renewal capacity (can copy themselves)
- Multi-differentiation potency (can differentiate to different cell environments)
Types of Stem Cells โโTotipotent: cells can develop into a new individual cells from early embryos (1-3 days)
Pluripotent: cells can give rise to any fetal or adult cell type (over 220); the inner cell mass of blastocyst from early embryo (5 to 14 days)
Multipotent: cells can give rise to cells from multiple, but a limited number of lineages; cord blood and adult stem cells
- Most embryonic stem cells are from embryos that develop from an invitro fertilization (IVF) clinic - and then donated for research purposes with informed consent of the donors
Potential Solutions (Embryonic Stem Cells) โโ- Teratoma formation -> Pre-differentiate cells in culture then insert
- Animal Pathogens -> Feeder-free culture conditions
- Immune Response -> Somatic cell nuclear transfer
- Ethics -> Scientists have announced the development of 5 human embryonic stem cell lines without the destruction of embryos
- Single cells were removed from embryos
- The embryos continued to develop normally and were then frozen
- The removed cell was cultured in optimal culture environments
Pluripotent Stem Cells: Induced Pluripotent Stem Cells (iPS) โโ- iPS cells are a type of artificial pluripotent stem cells derived from adult cells, which were genetically reprogrammed to add certain genes
- They are similar to natural embryonic stem cells and differentiate into specialized cells. But no need for embryos.
Summary of iPS Cells โโStengths:
- Autologous cell source to potentially avoid immune responses
- Similar to embryonic stem cells without using an embryo
Major Limitations:
- Tumor formation and less safe than hESCs
Multipotent Stem Cells: Human Mesenchymal Stem Cells โโ- MSCs are multipotent stem cells that are of stromal origin can differentiate into a variety of cell types
- Also called multipotent stromal cells
Sources:
- Bone marrow
- Fat tissue (adipose)
- Umbilical cord
Lineages:
- Osteogenic
- Chondrogenic
- Adipose
- Myogenic
Materials Role in Tissue Engineering โโ- Structure Support
- Control Cellular microenvironment
Types of Materials for Biomedical Applications โโAccording to bulk properties:
- Polymer
- Metal
- Ceramic
- Composite
According to Sources:
- Natural materials
- Synthetic materials
Materials for Tissue Engineering โโPolymer: long-chain molecules that consist of a large number of small repeating units - collagen, chitosan, silk, fibrin, GAG; poly(glycolic acid), poly(lactic acid), poly(eta-coprolactone), PLGA
Ceramics: a class of inorganic solids which are prepared by action of heating and subsequent cooling - coral for bone; calcium phosphates
Composite: engineered or naturally occurring materials made from two or more constituent materials - decellularized tissue; nanocomposite
Material Criteria for Tissue Regeneration โโ- Biocompatible
- Biodegradable
- Suitable surface chemistry
- Matching mechanical properties
Nanomaterials โโMaterials with basic structural units, grains, particles, fibers, or other constituent components smaller than 100 nm in at least one dimension ( 1 nm = 10^-9)
Natural Tissue Structure: Cells and Extracellular Matrix (ECM) โโThe ECM promotes a unique microenvironment that fosters cell and tissue organization
Role:
- Support cell growth
- Regulate intercellular communication
- Segregate tissues
CNT is configurationally equivalent to a 2-D graphene sheet rolled into a tube.
Carbon Nanotube Properties โโ- Superior mechanical properties
- Outstanding electric properties
- Special surface chemical properties
- Twice the thermal conductivity of diamonds
- Mimicking tissue dimension
- Excellent biocompatibility
Scaffold Roles โโ- Provide appropriate structures support
- Control cellular microenvironment
- Encourage cell growth and tissue regeneration
- Exchange nutrients and wastes
3-D and porous
Tissue Engineered Scaffold Fabrication Methods โโ- Electrospinning
- Solvent casting, particle leaching, and gas foaming
- Freeze drying
- Phase separation
Introduction to Electrospinning โโ- A versatile technique applicable to a wide range of polymers and solvents
- Uses an electrical charge to draw a very fine polymer nano/micro fibers with various thickness from polymer solutions.
Applications:
- Scaffolds for tissue engineering
- Scaffolds for wound healing
- Matrices for the controlled release of therapeutic molecules
- Medical device coatings
Electrospinning vs. Electrospraying โโSpinning: molecular cohesion of the liquid must be sufficiently high so stream won't break up
Spraying: streams break up into droplets
- To produce scaffolds of desired spatially distributed morphogenetics
- To create novel core-shell fiber structure
- To deposit nanomaterials creating desirable surface features
Wet Electrospinning โโA standard electrospinning setup alligned with the collector plate and submerged in a water or organic bath.
3-D Printing โโ- 3-D printing is a process of creating 3-D objects from digital files using a materials printer
- It was used a lot for rapid prototyping
- Various objects such as auto parts, toys, and statues can be constructed out of a given material
- It was used to make prototypes of new products or even the final product
3-D Printing for Tissue and Organ Regeneration โโ- A normal inkjet printer
- Instead of paper, petri dishes are used
- Instead of ink cells, hydrogels, or cross-linking chemical agents are used
- The cells are autologous from the patient
The Steps for a 3-D Printed Organ โโ- The petri dish is filled with water or uncrosslinked hydrogel
- When the printer "prints" the crosslink transforms the solution into a jell-o like substance which allows the cells to be put in
- This method is repeated until the organ that you want is created
CT scan -> CAD image -> Bone scaffold fabricated from 3-D printer -> Surgeons implant customized scaffold into patient
Advantages of 3-D Printing for Tissue Engineering โโ- Biomimetric 3-D
- Rapid prototyping
- Quick customization using CT scan of patient
- Complexity of scaffold
Bioactive Factors - Growth Factors โโ- Growth factor is a naturally occurring substance and helps facilitate cellular growth, proliferation, and differentiation
- They typically act as signaling molecules between cells. Examples are cytokines and hormones that bind to specific receptors on their target cell surface
- There are numerous growth factors for each tissue that can be engineered
Bone-Morphogenic Protein (BMPs) โโ- BMPs are multi-functional growth factors that belong to the transforming growth factor-b superfamily
- To date, around 20 BMP family members have been identified and characterized
- Osteoprogenitors, mesenchymal cells, osteoblasts, and chondrocytes within the extracellular matrix produce BMPs
- BMP-2, BMP-3, BMP-4, BMP-5, BMP-6, BMP-
Research in Growth Factors for Tissue Engineering โโ- The effects of growth factors on cells
- Techniques to incorporate growth factors into biomatierals based scaffolds
Growth Factors for Bone and Cartilage Cells โโ- Transforming growth factor-b superfamily
- Platelet-derived growth factor enhances chondrocyte migration and bone healing
- Basic fibroblast growth factor
- Insulin-like growth factor: increase collagen and proteoglycan deposition: mitigate the injurious response of impacted cartilage by limiting the loss of matrix components
Typical Mechanical Stimulations for Cartilage Regeneration โโ- Dynamic shear
What are Bioreactors โโ- System where conditions are closely controlled to permit and induce a certain behavior in living cells or tissues
- Provide controlled and steady flow of cell media
- Factors necessary for cell growth: pH, temperature, pressure, nutrient supply, waste removal
Main Objective of Bioreactors in Tissue Engineering โโ- To establish spatially uniform cell distributions on 3-D scaffolds
- To maintain desired concentration of gases and nutrients in the culture medium
- To expose developing tissue to appropriate physical stimuli
Bioreactor Types โโ- Spinner flask bioreactors
- Rotating-wall vessels
- Hollow fiber bioreactors
- Perfusion bioreactors
- Bioreactors that apply controlled mechanical forces (ex. hydrostatic chamber)
DNA Based Helical Rosette Nanotubes โโHRNs or RNTS are a new class of nanotubes obtained through the self-assembly of the DNA base pair building blocks (Guanine^Cytosine) in aqueous solutions.
Advantages of Self-Assembly Nanotubes/Nanofibers for Tissue Engineering โโ- Biomimetic nano structural features
- Ease of chemical functionalization
- Ability to gel
- Rapid preparation through self-assembly
Medical Application of Electrospinning โโ- Scaffolds for tissue engineering
- Scaffolds for wound healing
- Matrices for the controlled release of therapeutic molecules
- Medical device coatings
Electrospinning Materials โโSynthetic Polymers
- Polyglycolic acid (PGA) -> highly crystalline, hydrophilic
- Ploylactic acid (PLA) -> hydrophobic, lower melting temperature
- Polycaprolactone (PCL) -> semi-crystalline properties, easily co-polymerized, mixed frequently with other materials
- Polyvinyl alcohol (PVA) -> water soluble
- Nylon
- Copolymers (PLGA, PGA-PCL, PLA-PCL)
Natural Polymers
- Elastin
- Collagen
- Collagen blends
- Fibrinogen
Nanocomposites
- Carbon Nanotubes
- Nanocrystalline hydroxyapatites
- Self-assembly nanotubes/nanofibers
- Bioglasses
- Various growth factors
3-D Printed Hard Tissue โโ- Predesigned CAD patterns
