Bioengineering

Question 1

Role of Scaffolds

Answer 1

• 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

Question 2

Bone regeneration scaffold

Answer 2

• 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

Question 3

Screw extruded scaffold considerations

Answer 3

• fibre diameter
• slice thickness
• filament distance

Question 4

Screw extruded scaffold manufacture parameters

Answer 4

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

Question 5

Screw extruded procedure

Answer 5

• 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

Question 6

Bioreactor definition

Answer 6

• 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

Question 7

Bioreactor system examples

Answer 7

• spinner flask bioreactors
• rotation wall bioreactors
• compression bioreactor
• strain bioreactor
• hydrostatic pressure bioreactor
• flow perfusion bioreactor
• pulsatile pressure bioreactor

Question 8

Flow perfusion bioreactor

Answer 8

• 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

Question 9

Biomanufacturing definition

Answer 9

• combines additive manufacturing. biocompatible and biodegradable materials, cells and biomolecular signals to produce tissue constructs for tissue engineering

Question 10

Main therapies for tissue engineering & regenerative medicine

Answer 10

• cell based therapy
• scaffold based therapy
• implantation of cell-laden 3D constructs

Question 11

Tissue engineering definition

Answer 11

• 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

Question 12

Autografting

Answer 12

• 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

Question 13

Allografting

Answer 13

• 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

Question 14

Xenografting

Answer 14

• 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

Question 15

Medical device definition

Answer 15

• 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

Question 16

Degradation process variables

Answer 16

material structure: chemical composition, molecular weight, crystallinity, morphology

macroscopic features: implant shape, size, porosity

environmental conditions: temperature, pH of medium, presence of enzymes

Question 17

Sterilisation methods

Answer 17

• UV
• Gamma radiation
• Ethylene oxide

Question 18

Hydrogel definition

Answer 18

• 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)

Question 19

Drug delivery: polymer matrix

Answer 19

• 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

Question 20

Drug delivery: reservoir system

Answer 20

• more constant release over time

- rate is determined by the thickness of the polymer/hydrogel and remains constant over time

Question 21

Conventional scaffold techniques

Answer 21

• solvent-casting particulate leaching
• gas foaming
• liquid-liquid phase separation

Question 22

Electrospinning diameter

Answer 22

• increase in viscosity increases fibre diameter
• increase in voltage decreases fibre diameter
• increase in solution conductivity decreases fibre diameter

Question 23

Stem cell characterstics

Answer 23

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

Question 24

Stem cell properties

Answer 24

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

Question 25

Stem cell origins

Answer 25

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

Question 26

Adult stem cells

Answer 26

• 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

Question 27

Influence factors on stem cells

Answer 27

Chemical - presence of certain proteins and other macromolecules

Physiological - temperature, pH, oxgen levels

Mechanical - extracellular matrix stiffness

Question 28

Causes of anisotropy in scaffold

Answer 28

• consequence of the printing strategy during the layer-by layer fabrication
• the orientation of the crystalline structures and polymeric chains during printing process

Question 29

Effect of printing parameters on anisotropy

Answer 29

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

Question 30

Compression bioreactor

Answer 30

• 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

Question 31

Shear thinning

Answer 31

• 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

Question 32

Physical properties of bone scaffold

Answer 32

• 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

Question 33

Melt moulding scaffold process

Answer 33

• 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