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Regenerative medicine > Tissue Engineering > Flashcards

Tissue Engineering Flashcards

1
Q

What are some examples of tissues that could be replaced by tissue engineering?

A

skin, cartilage, bone, muscle, blood vessels etc

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2
Q

What is the difference between tissue engineering anf regenerative medicine?

A

tissue engineering is producing tissue in vitro and implanting it
regenerative medicine is implanting stem cells to facilitate tissue regenerative in vivo

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3
Q

What are some advantages of tissue engineering over regenerative medicine?

A
  • can evaluate tissue prior to implantation and look for markers and asses its function
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4
Q

what are some disadvantages of tissue engineering over regenerative medicine?

A
  • stress induced architechure is hard to reproduce in virtro - e.g. caritalge is formed due to high pressure
  • remodelling is required for incorporation and integration
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5
Q

What are some advantages of regenerative medicine over tissue engineering?

A
  • incorporation and formation can occur under the influence of endogenous regulators and mechanical strains
  • receieves all the biological cues that it would normally
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6
Q

What are some disadvantages of regenerative medicine over tissue engineering?

A

dislodgement and degradation by mechanical stressors in vivo is common

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7
Q

Where are we currently at with tissue engineering in the clinic?

A

cannot yet fully regenerate tissue that does not have the capacity for spontaneous regeneration
full regeneration may not be needed for significant clinical results
- pain relief
- aesthetics
- recovery of functions

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8
Q

How do we go about engineering a tissue?

A

need to provide all the cues and signals that a tissue needs to perform its natrual function

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9
Q

What is a functional subunit?

A
  • the smallest level at which the basic function of a tissue/organ is provided
  • organs are made up of many functional subunits
  • contains many different cell types and ECM molcules
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10
Q

What is the microenvironment? What is it characterised by?

A
  • the local environment of a cell
  • influences cell phenotype, tissue type
  • provides physical and mechanical signals
  • important to replicate in tissue engineering
  • characterised by cellularity, local chemical environment, local geometry and cellular communications
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11
Q

How does cellularity characterise the microenvironment?

A
  • cell packing = spatial organisation of cells within a tissue
  • packing density = the density of cells within a given volume
  • do we need to have similar cell density in engineered tissues?
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12
Q

How do cellular communications characterise the microenvironment? How does cellularity affect these?

A
  • secretion of soluble signals such as growth factors, cytokines, hormones and steroids
  • signal may not diffuse evenly if cells are packed too tightly
  • cell-cell interactions via adherens/gap junctions and desmosomes
  • cells at low density may not communicate properly
  • also need cell-ECM interactions so ECM needs to be produced correctly
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13
Q

How does the local chemical environment charactierse the microenvironment in tissue enginerring?

A
  • oxygen
  • too low = hypoxia
  • too high = ocidative stress
  • metabolsim
  • uptake of glucose and amino acids etc
  • rate depends on the local concentrations
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14
Q

How does local geometry characterise the microenvironment in tissue engineering?

A

local geometry depends on tissue type
- physical space around the cells in vivo will help to determine cell fate and tissue development
- need to recreate this environment in vitro - can use scaffolds

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15
Q

What is the role of tissue engineering scaffolds?

A

act as an artificial microenvironment
mimic the ECM and facilitate secretions, integrin expression and cell migration

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16
Q

Name 3 types of scaffolds with examples

A
  • natrual polymers such as collagen can form decellularised tissues
  • synthetic polymers such as poly-lactide
  • ceramics such as calcium phosphate can be used for bone
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17
Q

What properties are important to consider when designing a scaffold? (5)

A
  • porosity to allow vascularisation
  • biocompatibility
  • some may be biodegradable
  • matching mechanical strength of tissue
  • correct surface chemistry and topography
    accesibility/affordability
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18
Q

What is bioprinting?

A

printing complex 3D tissues using a mixture of biocompatible materials (natrual or synthetic), cells (stem or differentiated) and growth factors

19
Q

What is the ideal overall process for tissue enginerring?

A
  • start with ECM and shape as needed
  • seed with living cells and bathe with growth factors
  • once cells grow, implant into the body
  • cells recreate their intested functions, blood vessels form and the scaffold dissolves if applicable
20
Q

What are some sources of cells for tissue enginerring?

A
  • autologous or non-atologous from cell banks
  • can be primary undifferentiated cells from tissue biopsy but yield is low and cells are old
  • can passage primary cells for serial expansion but they can losepotency ober time in culture
  • stem cells have much better self renewal capacity but are few and harder to collect
21
Q

Name 3 formats in which cells might be cultured for tissue enginerring

A
  • monolayer (adherent cells)
  • suspension (non-adherent cells)
  • 3D scaffolds
22
Q

How might cells be sterilised in culture for tissue enginerring?

A
  • UV light
    70% ethanol
    steam autoclave
    gamma radiation
23
Q

What kind of growth conditions and media might be used to culture cells for tissue enginerring?

A

want to stimulate physiological environment
- ph7, 37 degrees, 95% humidity
- media replenishment
- correct chemical environment i.ee osmolality, ions, buffers
- correct nutrional environment i.e. nutrients, amino acids, vitamins growth factors

24
Q

What is the Hayflick limit?

A

30-50 doublings occur per cell before it dies
depends on age and cell type
want cells to be in the exponential growth phase when in culture

25
Q

How can we move from tissue enginerring experiments to mass production? What are some important design challenges?

A
  • bioreactors
  • must maintain balance down to the microenvironment
  • mass transfer of nutrients and waste
  • fluis flow
26
Q

What aspects of mass transfer are important to consider and control in bioreactors?

A
  • o2 supply througought whole tissue
  • nutrient delivery mimics phyisiological and is provided at the rate its consumed
  • O2, CO2, nutrients etc too high or low can be inhibitory or even toxic
27
Q

Why is fluid flow important in bioreactors?

A

in vivo the circulatory system provides fluid flow and is difficult to mimic in vitro
- static cells can have oxygen at the top waste at the bottom
fluid forces also provide mechanical signals
- bioreactors can rock, spin, pump to produce flow while also keeping tissues warm and provided with growth factors etc

28
Q

What successes in tissue engineering have been made? What is the problem for thicker more complex tissues?

A
  • avascualar or thin tissues such as skin,cartilage and cornea
  • need multiple cell types
  • tissue needs to become vascularised and vascularisation of 3D constructs is an unsolved problem
29
Q

Describe the basic structure of trabecular bone

A
  • porous and vascularised
  • well structured and strong
  • gaps are filled with stroma/bone marrow
30
Q

Describe the basic structure of compact bone

A
  • outer edge is compact cortical bone that is very densly packed
  • towards the centyre is vascularised sponget trabecular bone lined with osteoblasts that lay down a matrix and form mature bone
31
Q

What are oestoblasts?

A

bone forming cells

32
Q

What are oesteocytes?

A

mature bone cells

33
Q

What are osteroclasts?

A

large cells that resorb or break down bone matrix

34
Q

What are osteoids?

A

unmineralised bone matrix composed of collagen, proteoglycans and glycoproteins

35
Q

Autologous chondrocytes taken for treatment of oestroarthritis may not be appropriate. Why?

A
  • cells will be old and potentially defective / less useful
  • could differentiate adult MSCs or iPSCs
  • both have had sucess especially iPSCs which provide good results with increase hyaline and decreased type 1 cartilage
36
Q

How is bone regenerated?

A

in stageswith many cytokines, morphagens and growth signals
- MSCs can differentiate into oesteoblasts
- can be isolatde and culture and used for tissue enginerring or to augment host cells in regenererative medicine

37
Q

What are some current bone graft materials?
What are the issues with each?

A
  • autographts of bone from the patient can have chronic pain at the harvest site and the supply is limited
  • allografts from donors can induce immune rejection and has the risk of disease transmission
  • metallic implants have been the most sucessful but can still cause immune rejection, have different mechanical properties and a risk of poor positioning
38
Q

What would be some ideal properties of a bone scaffold?

A
  • biodegradeable and biocompatibly
  • porosity
  • handleability
  • oestoconductive or osteoinducive
39
Q

What is osteoconduction?

A

the ability of materials to serve as a scaffold to which bone cells can attach, grow and divide

40
Q

What is oestoinduction?

A

capacity of normal chemicals in the body to stimulate primitive stem cells or immature bone cells to grow and mature into healthy bone tissue

41
Q

Describe bone scaffold synthetic matrices?

A

scaffolds of synthetic material that provide support for osteoblast proliferation
- dissolve when osteogenesis is induced
- can present oesteoinductive growth factors but lack the osteoconductivity of conventional graft matierals

42
Q

What is a possible bone tissue engineering scenario?

A

biodegradable bone screws and nails that can deliver drugs
biodegradable nail that holds fractured bone in place while stimulating new bone growth around it by slowly releasing factors as it degrades

43
Q

What is the traditional pathway for new biologicals, devices and medicines from research to market approval?

A
  • discovery and development
  • pre-clinical trials
  • phase human clinical trials
  • market application and approval
    takes 6-10 years
44
Q

Why does the traditional pathway from research to market approval not always suit regenerative medicine?

A

saftey studies in healthy individuals may not apply - cant replace a healthy organ with experimental ones
placebos?
regenerative products may have characteristics of mor than one traditional type of product

Regenerative medicine (13 decks)

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