What is the time like of protien surface interaction
- proteins arrive at the surface in less than a second
- within seconds/minutes, a protein monolayer is absorbed
- Cells arrive next and see the protein layer and not the biomaterial and the cells interact with the protein layer
Why do transplants and biomaterials invoke different responses from the body
transplants have MHC markers which will be slightly different from the hosts MHC which means that the body registers them as foreign and an immune response is invoked. Due to the protein monolayer, cells recognise the biomaterial (with integrins) and won’t attack it
What are the 4 principles of protein absorption?
Diffusion, the forces that drive protein absorption, Langmuir model and beyond Langmuir
Explain Diffusion as a mechanism for protein absorption?
Proteins are in solution, diffusion means that things will move from low concentration to high concentration. Ficks Law explains how fast proteins will move to the surface. Flux is proportional to the negative of diffusion constant multiplied by the concentration gradient.
How does Ficks Law explain that smaller proteins will arrive at the surface faster than larger proteins?
Smaller proteins have a larger diffusion constant than larger proteins. As we are going from high concentration to low the concentration gradient would be negative, so, therefore, the negatives cancel out and would mean that smaller proteins have a larger flux
What does the cottrels law state?
the concentration of something with time depends on the diffusion constant and correlates with the surface area of the protein (small ones would arrive faster?
What is the strongest surface-protein binding?
Electrostatic forces
What are electrostatic forces?
positive and negative poles like magnets
What is the middle surface-protein binding?
Hydrogen bonding - if you have enough they can be pretty strong
What is the least strong surface-protein binding?
Vanderwaals
What is the basic theory of Langmuir?
its a simple model for reversible adsorption, basically stating that once a surface is full no more proteins will bind
What is stated in the beyond Langmuir section?
- Restructuring can happen, so there can be a stepped isotherm
- It’s possible to have multilayer formation where protiens adhere to each other
What does it mean when a protein denatures? What factor influences denaturing?
The protein spreads on the surface and loses its structure.
There is more protein denaturing when a surface is hydrophobic
Why might problems arise from absorption of your own proteins?
- The concentration is different in bulk vs surface
- There might be a change in reactivity e.g. active site of enzymes might be blocked
- Denaturing of the protein might make it unrecognisable to cells
What factors might affect the surface spreading of proteins?
- time
2. concentration - less means more spreading, more means less
What are the rules of thumb?
- smaller proteins arrive first
- larger proteins have a greater affinity to attach
- charge and distribution of charge on a protein affect absorption
- less stable proteins denature
How do charge and distribution of charge on a protein affect absorption?
proteins have greater surface activity near pH neutral and they don’t just react with the surface but each other
- THIS IS WHAT CAUSES THE EXTRINSIC COMPLEMENT!!
What surface properties affect absorption?
- Geometrical (pores)
- Chemical
- Microscopic Scale (alpha and beta phases and grain boundaries)
- Electrical
Why is it hard to predict how a material will react?
- the complex protein mixture
- Multiple protein absorption
- Blood material interaction is complex
What is the Vroman effect?
The highest mobility proteins generally arrive first and are later replaced by less mobile proteins that have a higher affinity for the surface.
Which protein denominates the initial absorption?
Albumin
Which proteins are the most problematic if a lot adhere to a surface?
fibrinogen, Factor XII
