Hydrogels

Question 1

Hydrogels

Answer 1

mimics the physical properties of biological tissues, excellent candidate for various medical and biological applications

Question 2

Crosslinks may be physical or chemical:

Answer 2

• by reaction of one or more monomers with pendant functional groups
• hydrogen or ionic bonding
• van der waals

Question 3

Classification of Hydrogels

Answer 3

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

Question 4

Key properties of hydrogels for biomedical applications

Answer 4

• 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

Question 5

Degree of swelling

Answer 5

degree of swelling quantified by: (put in weight compare vol or weight to the dry state)
- volume
- weight

Question 6

why is the degree of swelling important?

Answer 6

• 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

Question 7

polymer-based hydrogel has to have at least

Answer 7

10% of total weight for a material to be a hydrogel.

Question 8

when content of water over 95% of total weight or vol, hydrogel is

Answer 8

superabsorbent

Question 9

Chemically linked hydrogel

Answer 9

can maintain shape before and after hydrolyzation, covalent bonds

Question 10

Gel transitions through in situ crosslinking physical gels

Answer 10

• add ionic crosslinker
• change temp
• change pH

Question 11

Gel transitions through in situ crosslinking covalent gels

Answer 11

polymerization initiation (light, temp,… )

Question 12

Formation of crosslinked hydrogels

Answer 12

1. by polymerization
2. with cross-linkers (functional group that can join polymer or monomers together)

Question 13

Hydrogel formation: physical cross-linking

Answer 13

1. heating/cool of a polymer solution
2. ionic crosslinking
3. hydrogen bonding

Question 14

Hydrogel formation: chemical cross-linking

Answer 14

1. chemical cross-linkers
2. grafting

Question 15

Synthetic polymers advantages

Answer 15

• 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

Question 16

Synthetic polymers disadvantages

Answer 16

• low biodegradability
• can include toxic substances

Question 17

Natural polymers advantages

Answer 17

• generally high biocompatibility
• intrinsic cellular interactions
• biodegradable
• cell controlled degradability
• low toxicity byproducts

Question 18

Natural polymers disadvantages

Answer 18

• mechanical strength
• batch variation
• animal-derived materials may contain pathogens

Question 19

Smart hydrogels

Answer 19

respond to environmental stimuli like temp, pH, light, or electric fields

Question 20

thermoresponsive hydrogels

Answer 20

swell or shrink in response to change in temp

Question 21

pH-responsive hydrogels

Answer 21

swell or shrink in respond to change in pH, used in drug delivery system

Question 22

Polyelectrolytes

Answer 22

polymer with charge

Question 23

polycations (polyelectrolyte)

Answer 23

used in gene delivery

Question 24

ampoteric polyelectrolytes

Answer 24

charged groups, act as either a polyanion or polycation depending on the pH.

Question 25

polyanions (polyelectrolyte)

Answer 25

used in drug delivery, thickeners in foods and cosmetics, superabsorbents

Question 26

Polyelectrolytes

Answer 26

expand after dissolved in solution, reverse process by adding salt

Question 27

Ionic Strength Sensitivity

Answer 27

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.

Question 27

Superabsorbent Polymers

Answer 27

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.

Question 28

Which of the following best describes a hydrogel?

Answer 28

A 3D polymer network capable of absorbing and retaining water

Question 29

What makes hydrogels particularly useful in biomedical applications?

Answer 29

Their ability to mimic the physical properties of biological tissues

Question 30

Which of the following factors primarily governs the mechanical properties of chemically cross-linked hydrogels?

Answer 30

The degree of cross-linking between the polymer chains

Question 31

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

Answer 31

Respond to physiological ions

Question 32

True or false: The mechanical strength of a hydrogel decreases as the degree of cross-linking between polymer chains increases.

Answer 32

False

Question 33

True or false: pH-responsive hydrogels can change their swelling behavior depending on the pH of the surrounding environment

Answer 33

True

Question 34

True or false: Physically cross-linked hydrogels use covalent bonds, making them stronger and more durable than chemically cross-linked

Answer 34

False