Hydrogel network engineering Flashcards
Explain the concept interpenetrating polymer networks (IPN) and the difference between semi-IPN and full-IPN.
IPN means that a second polymer is entrapped into the already existing hydrogel.
For a semi-IPN are only linear polymers entrapped in the network. For a full-IPN is an entire second network added in the already existing network and the two networks are connected.
What are the advantages of IPNs?
They are tougher and mechanically stiffer due to more crosslinked polymers inside the network. More efficient drug loading.
Explain how drug released is realised with a hydrogel grafted to the surface of another hydrogel.
The drug is contained within the first hydrogel and another hydrogel is grafted on its surface, which first is collapsed. When the grafted hydrogel swells can the drug be released.
Explain what a composite hydrogel is and how it works.
Micelle hydrogels are incorporated into another hydrogel network. This gives two barriers to pass through and more control of the release. First the drug need to escape the micelle hydrogel and then diffuse out of the second network.
Assuming 1st order kinetics of the swelling of hydrogel, derive a relation between the current weight and the maximum weight.
Starting for the derivative of the weight, which is related to the maximum weight. dw/dt=k(w_inf-w).
Integrate! Giving ln(w_inf/(w_inf-w))=kt
This gives that at some point the weight stops increasing because at some point the water diffuse slower than the relaxation of the polymer and no more water diffuse into the network.
Approximate the kinetics of the hydrogel swelling to 2nd order and derive the relation.
2nd order: dw/dt=-k(w_ing-w)^2
Integrate! In the end obtain w=(ktw_inf^2)/(1+ktw_inf)
–> t/w=1/(kw_inf^2)+1/w_inf*t.
Giving a linear relation between t/w and t.
The kinetics of acrylamide hydrogels are normally 2nd order.
Explain how a self-regulated glucose sensing system can work.
3 examples:
Using a hydrogel with nitrogen sidegroup when the pH decrease, the nitrogen will bind to H-ions and the hydrogel will swell up allowing insulin to escape.
There are glucose enzymes, glucose oxidase in the hydrogel that binds to glucose and become gluconic acids –> pH goes down and hydrogel swells.
Hydrogel with glucose bound to chains, to these glucose molecules is insulin bound. When more glucose comes in from outside it competes with that already bound to the insulin and the insulin is released.
Hydrogel network with glucose oxidase and nanoparticles, glucose comes in and lower pH, same principle as in first example, the hydrogel swells and the distance between the particles increase and the wavelength of the light scatter increases. Can use this as lense in eye which turns red when need insulin.
Explain how antigen-responsive hydrogel works.
Between the chains of the hydrogel network are antibodies bound to antigens that are connected to the hydrogel polymer chains. When antigen comes in from the outside the antibodies are released and number of crosslinking sites decrease –> swollen state
Explain magnetic-sensitive hydrogel.
Inside the hydrogel network there are magnetic beads, when applying an alternating magnetic field the beads starts to move and squeeze the network to push out drug.
Explain light (UV) sensitive hydrogel.
A hydrogel with either COOH, NH2 or CO-H2 and by illuminating create ions.
At the appropriate temp. one can make the hydrogel swell by illuminating and then when removing the UV it will deswell. The swelling is not due to charges, because the net-charge is still 0 but rather because the conc. of ions increase and create osmotic pressure. The water wants to dilute the ion conc. and diffuse into the network.
–> increasing the LCST, because there is more water in the system, which means that the system is favoured by more water and need more energy to collapse.
If stay just under the higher LCST, can change between swollen and collapsed state with UV.
Disadvantage of hydrogel as drug delivery system.
The response is slow.
It can be toxic, one needs to find a biocompatible hydrogel-
Don’t have necessary mechanical strength.
Explain how hydrogels can be used as optical transducers and give examples.
When the hydrogel collapses it changes from see-through to milky and will thus scatter more light, can measure scattering spectrum.
When it collapses the refractive index goes up since there is less water in the system, and water has lower refractive index than the polymer.
Ex. 1: Thin film resonance: Au particles on hydrogel and when hydrogel swells will change the wavelength of the reflected light making other wavelengths interfere.
Ex. 2: Optical fibre with hydrogel drop at end, when swollen no scattering since have almost same n as water, when collapsed scatter more light.
Ex. 3: based on mechanical work, have a hydrogel drop on some membrane, and reflect light on this membrane from one optical fibre and measure with another, when the hydrogel swells the amount of light reflected back to the fibre is decreased.
Give one example of mechanical transducers using hydrogels.
Can have hydrogel on Si cantilever and when hydrogel absorbs more water it will be heavier and make the cantilever bend.
Explain how an artificial muscle works using hydrogel.
Have electrolyte with positively charged surfactants molecules and negatively charged hydrogel. When applying an electric field between two electrodes the surfactants molecules will start moving towards the negative electrode and aggregate on one side of the hydrogel. The water on this side of the hydrogel will because of osmotic pressure diffuse out of the hydrogel to lower the concentration of surfactant molecules and the hydrogel will bend because one side collapses and the other not.
Explain how hydrogels can be used for humidity control through nanocoating.
On the surface there is first a layer of hydrogel removing water from the surface into the polystyrene structure. Inside the PS is small volumes of hydrogel encapsulated, these are allowed to swell when water is absorbed into the structure. Can be used in smart-phones etc.
