Bioengineering Flashcards
Role of Scaffolds
- 3D porous, biodegradable structures
- Provide necessary support for cell attachment, proliferation and differentiation
- Deliver and retain cells and growth factors
- Enable diffusion and cell nutrients and oxygen
- Enable an appropriate mechanical and biological environment for tissue regeneration in an organised way
Bone regeneration scaffold
- bio compatible: non-toxic, allow cell attachment, proliferation and differentiation
- biodegradable: must degrade into non-toxic products
- controlled degradation rate: rate must be adjustable to match tissue regeneration, release of acidic degradation products can cause tissue necrosis or inflammation
- appropriate porosity: macro/microstructure of pores and shape, highly interconnected pore structure, large surface area to allow high seeded cells and promote neovascularisation
- typically ~90% porosity with pore size of 200-400 nano m
Screw extruded scaffold considerations
- fibre diameter
- slice thickness
- filament distance
Screw extruded scaffold manufacture parameters
Heating temp: increase in temp reduces viscosity, more material will be supplied, increasing fibre diameter, reducing porosity and improving mechanical properties
Deposition Velocity: an increase causes a narrowing of filaments, creating wider pores and higher porosity, reducing mechanical perpormance
Screw rotation velocity: increase results in thicker filaments, structures with lower void spaces, lower porosity, improving mechanical properties
Screw extruded procedure
- polymer polymer/ceramic pellets are melted by heating, guided by robotic device controlled by computer to form the scaffold
- material leaves the extruder as a viscous melt and hardens immediately
- previously formed layer acts as substrate for the next layer
- substrate must be kept at temperature just below solidification point of polymeric material to assure good inter-layer adhesion
Bioreactor definition
- device that uses mechanical means to influence biological processes
- assist the in vitro development of new tissues by offering physical and biochemical regulatory signal to cells
- stimulate and encourage cells to differentiate and/or produce extra-cellular matrix prior to in vivo implantation
- biochemical or biological processes developed under a tightly controlled and closely monitored environment
Bioreactor system examples
- spinner flask bioreactors
- rotation wall bioreactors
- compression bioreactor
- strain bioreactor
- hydrostatic pressure bioreactor
- flow perfusion bioreactor
- pulsatile pressure bioreactor
Flow perfusion bioreactor
- uses pump system to pirectly perfuse media through a scaffold
- design includes a media resevoir, tubing circuit, a pump and a perfusion cartridge
- scaffold is housed in a sealed perfusion cartridge and media cant move around it, media perfuse directly through the pores of the scaffold
Biomanufacturing definition
- combines additive manufacturing. biocompatible and biodegradable materials, cells and biomolecular signals to produce tissue constructs for tissue engineering
Main therapies for tissue engineering & regenerative medicine
- cell based therapy
- scaffold based therapy
- implantation of cell-laden 3D constructs
Tissue engineering definition
- emerging field that applies principles of engineering and life sciences toward development of biological substitutes that restore, maintain or improve tissue or whole organ function
Autografting
- transplanted from one part of the body to another of the same individual
- does not induce rejection, best clinical results can be obtained
- pain and morbidity of donor site, limited quantity and avilability
- prolonged hospitalisation time, risk of deep infection or haematoma
Allografting
- transplanted from one individual and implanted in another, cadavers or living
- risk of rejection, transmission of disease and infection,
- limited supply, loss of mechanical properties due to processing
Xenografting
- transplanted from one individual and implanted into another of a different species
- low cost and highly available
- risk of transmission of disease and infection, poor clinical outcome
- present ethical problems
Medical device definition
- an instrument/apparatus/implant intended for diagnosis/cure/prevention of diseases for human or animal
- medical implants are placed either inside or on the surface of the body to accomplish some function ie replace, assist or enhance functionality of a biological structure
Degradation process variables
material structure: chemical composition, molecular weight, crystallinity, morphology
macroscopic features: implant shape, size, porosity
environmental conditions: temperature, pH of medium, presence of enzymes
Sterilisation methods
- UV
- Gamma radiation
- Ethylene oxide
Hydrogel definition
- 3D networks o hydrophilic polymer chains that dont dissolve but can swell in water
- highly biocompatible materials, environmental stimuli respondent, both solid and liquid like properties
- formed through chemical cross-linking (covalent, permanent) and physical (non-covalent, reversible)
Drug delivery: polymer matrix
- matrix progressively releases the pharmaceutical and the drug is homogeneously distributed in the matrix
- release rate decreases over time as drug has longer path from internal core
Drug delivery: reservoir system
- more constant release over time
- rate is determined by the thickness of the polymer/hydrogel and remains constant over time
Conventional scaffold techniques
- solvent-casting particulate leaching
- gas foaming
- liquid-liquid phase separation
Electrospinning diameter
- increase in viscosity increases fibre diameter
- increase in voltage decreases fibre diameter
- increase in solution conductivity decreases fibre diameter
Stem cell characterstics
Totipotent - can differentiate into an entire organism
Pluripotent - can differentiate into any tissue type except for placenta tissue
Multipotent - can differentiate into multiple cells in a closely related family of cells
Oligopotent - can differentiate into only a few cell types
Unipotent - cab differentiate into only one cell but still possess self-renewal
Stem cell properties
Self-renewal - must be able to go through multiple cell division cycles while remaining undifferentiated
Potency - must have ability to differentiate into specialized cell types
Stem cell origins
Embryonic - derived from the inner cell mass of a blastocyst
Adult - found in developed organisms that can divide to form more differentiated cells
Amniotic - multipotent stem cells found in amniotic fluid
Induced pluirpotent - cells reprogrammed through genetic engineering to become stem cells
Adult stem cells
- found in certain tissues that have the ability to divide into specific cell types
- found in children and umbilical cord blood
- typically multipotent and restricted to certain cell lineages
Influence factors on stem cells
Chemical - presence of certain proteins and other macromolecules
Physiological - temperature, pH, oxgen levels
Mechanical - extracellular matrix stiffness
Causes of anisotropy in scaffold
- consequence of the printing strategy during the layer-by layer fabrication
- the orientation of the crystalline structures and polymeric chains during printing process
Effect of printing parameters on anisotropy
screw rotational velocity: increases orientation of polymer chains along the flow direction
increasing processing temp: facilitates increased orientation by increasing the mobility of the polymeric chains, increasing directionality
- final orientation of polymer chains is determined by the cooling conditions
- this controls the available time for the polymeric chains to reorient, the crystallinity level and the proportion of amorphous regions
Compression bioreactor
- normally used to cultivate cartilage
- designed to allow for both static and dynamic loading
- comprise a motor, a controlling mechanism sand a system providing linear motion
- flat patens distribute load evenly, allows loads to be transferred to the constructs via them
- mass transfer is considerably improved since compression leads to the fluid flowing through the scaffolds
Shear thinning
- characterised by a reduction of viscosity with the increase in shear rate
- moving from a large reservoir to a small needle creates large increase in shear rate
- makes a material suitable to use for printing as it is not necessary to use large pressures or high power from the machine
Physical properties of bone scaffold
- sufficient strength and stiffness to withstand stresses in the host tissue environment
- adequate surface finish to ensure that good biochemical coupling is achieved
- easily sterilised either by high temperature or by immersion in a sterilisation agent, remaining unchanged by both
Melt moulding scaffold process
- fills a teflon mould with polymer in powder form with gelatin microspheres of specific diameter
- mould heated above glass-transition temperature of polymer while pressure is applied
- gelatin component is leached out by immersing in water, scaffold is dried
