What are some examples of tissues that could be replaced by tissue engineering?
skin, cartilage, bone, muscle, blood vessels etc
What is the difference between tissue engineering anf regenerative medicine?
tissue engineering is producing tissue in vitro and implanting it
regenerative medicine is implanting stem cells to facilitate tissue regenerative in vivo
What are some advantages of tissue engineering over regenerative medicine?
- can evaluate tissue prior to implantation and look for markers and asses its function
what are some disadvantages of tissue engineering over regenerative medicine?
- 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
What are some advantages of regenerative medicine over tissue engineering?
- incorporation and formation can occur under the influence of endogenous regulators and mechanical strains
- receieves all the biological cues that it would normally
What are some disadvantages of regenerative medicine over tissue engineering?
dislodgement and degradation by mechanical stressors in vivo is common
Where are we currently at with tissue engineering in the clinic?
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
How do we go about engineering a tissue?
need to provide all the cues and signals that a tissue needs to perform its natrual function
What is a functional subunit?
- 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
What is the microenvironment? What is it characterised by?
- 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
How does cellularity characterise the microenvironment?
- 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?
How do cellular communications characterise the microenvironment? How does cellularity affect these?
- 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
How does the local chemical environment charactierse the microenvironment in tissue enginerring?
- oxygen
- too low = hypoxia
- too high = ocidative stress
- metabolsim
- uptake of glucose and amino acids etc
- rate depends on the local concentrations
How does local geometry characterise the microenvironment in tissue engineering?
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
What is the role of tissue engineering scaffolds?
act as an artificial microenvironment
mimic the ECM and facilitate secretions, integrin expression and cell migration
Name 3 types of scaffolds with examples
- 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
What properties are important to consider when designing a scaffold? (5)
- porosity to allow vascularisation
- biocompatibility
- some may be biodegradable
- matching mechanical strength of tissue
- correct surface chemistry and topography
accesibility/affordability
What is bioprinting?
printing complex 3D tissues using a mixture of biocompatible materials (natrual or synthetic), cells (stem or differentiated) and growth factors
What is the ideal overall process for tissue enginerring?
- 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
What are some sources of cells for tissue enginerring?
- 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
Name 3 formats in which cells might be cultured for tissue enginerring
- monolayer (adherent cells)
- suspension (non-adherent cells)
- 3D scaffolds
How might cells be sterilised in culture for tissue enginerring?
- UV light
70% ethanol
steam autoclave
gamma radiation
What kind of growth conditions and media might be used to culture cells for tissue enginerring?
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
What is the Hayflick limit?
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
