Hydrogels and Natural Polymers

Hydrogels

Polymeric networks that absorb large amounts of water while remaining insouluble in aqueous hydrogel

Crosslink density (elastic Modulus)

low E = more flexibility

Higher E = Stiffer material

Hydrogel Molecular Weight

High crosslink density → Low Mc → Larger G or E → stiffer Hydrogel.

• Basically Mw for Mc

Predicting diffusion through a network

Mesh size >1

Fast diffusion

Mesh size ~1

Slow diffusion

Mesh size < 1

Immobilization → Deformation/Degradation/swelling

Chemistry influences hydrophilicity

Changing the chemistry of the hydrogel can change the swelling ratio

Hydrophilic functional groups: •

Chemistry influences hydrophilicity Alternative

• Monomer sol. weight

• Monomer functionality

• [Monomer]

• Monomer : crosslinker ratio

Swelling ratio

Q = Vswollen/ Vdry

V = volume

pH-responsive hydrogels

• Crosslinked polymer networks containing ionizable functional groups

Temperature-responsive hydrogels

Crosslinked polymer networks that undergo a phase transition at a specific temperature (i.e., lower critical solution temperature (LCST))

Natural polymers

Natural polymers (e.g., cotton, silk, natural rubber) harvested, processed and used by humans since at least several millennia BCE