lec 14 Flashcards
Why are organs on chips important?
The process of drug development includes animal trials before human trials
94% of drugs fail during the clinical trials due to toxicity or efficacy.
If drugs are being passed from animal to clinical and then failing the animal model must not be that good.
Also the failed drugs might actually be good in the clinical trials but we would never know.
Therefore there is a use for more accurate organs on chips. As we can measure a human like response to unknown drugs.
What were the 2 challenges to promote organs on chips
DARPA came up with a challenge in 2012:
Create 10 organs to study complex human physiology outside the body.
32 mill to MIT
37 mill to Harvard
NIH challenge
Smaller scale
30 challenges and to produce 2 organs per year.
But incorporated more institutions
What criteria need to be met when making a lung chip
Tissue: air/cell interface and lung/blood interface
Chip: translucent. Autoclavable, biocompatible and material does not absorb drugs.
How do we make the chip?
- They used 2 PDMS layers and a porous membrane to form a structure that had 3 chambers running through it.
What happens in the 3 chambers of the chip
- They grew epithelial cells (lung) on the top layer of the middle chamber
- Endothelium cells (capillaries) on the bottom
- Fibronectin coat to act as the extracellular matrix.
- Air would flow in the top compartment and media flows in the bottom compartment to replicate lung and blood vessel.
- Epithelial cells produced surfactant just like lung epithelium and formation of tight junctions.
The side chambers act as a vacuum to replicate the inspiration and expiration of lungs. This is done by stretching the membrane that the cells are seeded on.
How do we test the immune system in the lung chip
If we have neutrophils normally flowing in the blood there will be no reaction.
When we introduce TNF a or E.coli to promote inflammation of the lung epithelium we also get iCAM expression on the endothelium. This signals the neutrophils and therefore neutrophils can migrate through pore in the membrane into the lung epithelium to respond to the inflammation. Neutrophils engulf and destroy E.coli. Neutrophil presence in lung epithelium is a hallmark for lung inflammation.
Immune system and vacuum importance in lung chip
Response can also be seen with silica nanoparticles from aerosols.
They usually cause an inflammatory response with neutrophils. Without the stretch and relaxation of the vacuum the infiltration of the neutrophils is low but once the vacuum is set up the response increasing significantly, proving that the vacuum in the side chambers contribute heavily to proper physiological responses of the chip.
IL-2 increases oedema, by breakdown of tight junctions, when there is no stretch the response to IL-2 is minimal and when there is stretch/strain the response increases significantly.
What are the criteria for a heart chip
Tissue:
Contractility
Electrophysiological properties
Tissue structures
Chip: Autoclavable and material does not absorb drugs.
Heart chip making process?
- Take cover glass
- Place tape on glass edges leaving a gap
- Spin coat in PIPAAm
- Remove the tape so we are left with a stripe of PIPAAm in the middle
- Coat with PDMS
Make fibronectin stamps in PMDS, since the fibronectin is aligned nicely the CM will align anisotropically.
We can then seed the CM onto the chip, in order to get more films per chip we can score it with a scapel to give individual films in one chip. The individual film can have the same thickness or different thickness.
The electrodes are placed on each side of the chip to provide an electrical stimulus.
The CMs can be seen contracting.
What is the importance of making individual films on one chip?
So each film on the chip will represent an independent experimental sample with its own stress profile.
Stress profiles can be recorded to give the frequency contractility and regularity of each film.
When comparing a chip with anisotropic and isotropic alignment we can see that the isotropic chip does not have a regular contractility or stress profile that follows the normal CM.
What is the future goal and current problem?
The goal is to integrate several chips together.
The problem is that when making the chips they use different culture and media, so we need to standardize the media used as it is effectively the blood.
