Hydrogels Flashcards
Hydrogels
mimics the physical properties of biological tissues, excellent candidate for various medical and biological applications
Crosslinks may be physical or chemical:
- by reaction of one or more monomers with pendant functional groups
- hydrogen or ionic bonding
- van der waals
Classification of Hydrogels
based on origin
- natural hydrogels: derived from natural sources such as polysaccharides and proteins (alginate: algae, chitosan: shrimp)
- synthetic hydrogels: created from synthetic polymers such as polyvinyl alcohol (PVA) and polyethyleneglycol (PEG) (should know the structures of these)
- chemically crosslinked hydrogels: exhibit permanent linkages formed by covalent bonds
- physically crosslinked hydrogels: formed through temporary interactions like hydrogen bonding, hydrophobic interactions
Key properties of hydrogels for biomedical applications
- ease of chemical modification
- in situ formability
- control over 3D structure/morphology
- mild conditions for cell/protein encapsulation
- degradability
- responsive swelling “smart” hydrogels (contain certain functional group that can respond to change)
- soft tissue-like structure/properties
Degree of swelling
degree of swelling quantified by: (put in weight compare vol or weight to the dry state)
- volume
- weight
why is the degree of swelling important?
- solute diffusion coefficient through the hydrogel, drug delivery system
- higher degree of swelling faster drug release- surface properties and surface mobility
- optical properties
- mechanical properties
- high swelling enhances flexibility, permeability, and drug release but may reduce mechanical strength and stability
polymer-based hydrogel has to have at least
10% of total weight for a material to be a hydrogel.
when content of water over 95% of total weight or vol, hydrogel is
superabsorbent
Chemically linked hydrogel
can maintain shape before and after hydrolyzation, covalent bonds
Gel transitions through in situ crosslinking physical gels
- add ionic crosslinker
- change temp
- change pH
Gel transitions through in situ crosslinking covalent gels
polymerization initiation (light, temp,… )
Formation of crosslinked hydrogels
- by polymerization
- with cross-linkers (functional group that can join polymer or monomers together)
Hydrogel formation: physical cross-linking
- heating/cool of a polymer solution
- ionic crosslinking
- hydrogen bonding
Hydrogel formation: chemical cross-linking
- chemical cross-linkers
- grafting
Synthetic polymers advantages
- precise control over composition
- can be tailored to give a wide range of properties to meet specific needs
- large scale production
- low immunogenicity
- no biological pathogens or contaminants
Synthetic polymers disadvantages
- low biodegradability
- can include toxic substances
Natural polymers advantages
- generally high biocompatibility
- intrinsic cellular interactions
- biodegradable
- cell controlled degradability
- low toxicity byproducts
Natural polymers disadvantages
- mechanical strength
- batch variation
- animal-derived materials may contain pathogens
Smart hydrogels
respond to environmental stimuli like temp, pH, light, or electric fields
thermoresponsive hydrogels
swell or shrink in response to change in temp
pH-responsive hydrogels
swell or shrink in respond to change in pH, used in drug delivery system
Polyelectrolytes
polymer with charge
polycations (polyelectrolyte)
used in gene delivery
ampoteric polyelectrolytes
charged groups, act as either a polyanion or polycation depending on the pH.
polyanions (polyelectrolyte)
used in drug delivery, thickeners in foods and cosmetics, superabsorbents
Polyelectrolytes
expand after dissolved in solution, reverse process by adding salt
Ionic Strength Sensitivity
polyelectrolytes are highly sensitive to the ionic strength of a solution; At low ionic strength, the chains tend to extend due to electrostatic repulsion between the charged groups on the polymer; At higher ionic strength, the charges are screened by counterions, leading to a more coiled or collapsed state.
Superabsorbent Polymers
Polyelectrolytes like sodium polyacrylate are used in products such as diapers and agricultural soil conditioners, where they can absorb and retain large amounts of water.
Which of the following best describes a hydrogel?
A 3D polymer network capable of absorbing and retaining water
What makes hydrogels particularly useful in biomedical applications?
Their ability to mimic the physical properties of biological tissues
Which of the following factors primarily governs the mechanical properties of
chemically cross-linked hydrogels?
The degree of cross-linking between the polymer chains
Why are ionic strength-responsive hydrogels useful in wound healing?
Respond to physiological ions
Strengthen at higher ionic strength
Release drugs in response to pH
Temperature-sensitive drug release
Respond to physiological ions
True or false: The mechanical strength of a hydrogel decreases as the degree of cross-linking between polymer chains increases.
False
True or false: pH-responsive hydrogels can change their swelling behavior depending on
the pH of the surrounding environment
True
True or false: Physically cross-linked hydrogels use covalent bonds, making them stronger
and more durable than chemically cross-linked
False
