BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Kinetcs for ph change from 3 to 6: Kinetics for pH change from 6 to 3 pe ad AIn 2002 o Kinetics: deswelling faster(-10X) than swelling Swelling in -166 mi De-swelling in-16 min (300 Hm thick gels) Theory based on diffusion of ions into and out of gel semi-quantitatively predicts observed swelling behavior Swelling rate inversely proportional to square of gel size the size of the gel o Implies that response time of gels will scale inversely with th o Swelling rate can also be increased by creating greater porosity in gel-increase surface/volume ratio allows solute to diffuse into gel more rapidly Rapid swelling/deswelling of superporous gels Low pH and shrinking kinetics of I )in a ph=11.77 NaOH solution and a 1. 92 buffer with ionic strength of 0. 2 M. Three cycles of swelling inking were shown for gel 1; two cycles were shown fo o hydrogels containing basic groups show opposite pH sensitivity o swelling in acidic solutions o e.g. Peppas papers Lecture 9-polyelectrolyte hydrogels 3of17BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 o Kinetics: deswelling faster (~10X) than swelling • Swelling in ~166 min. • De-swelling in ~16 min. • (300 µm thick gels) • Theory based on diffusion of ions into and out of gel semi-quantitatively predicts observed swelling behavior o Implies that response time of gels will scale inversely with the size of the gel o Swelling rate inversely proportional to square of gel size3 o Swelling rate can also be increased by creating greater porosity in gel- increase surface/volume ratio allows solute to diffuse into gel more rapidly Rapid swelling/deswelling of superporous gels: Low pH High pH (Zhao and Moore, 2001) o hydrogels containing basic groups show opposite pH sensitivity o swelling in acidic solutions o e.g. Peppas papers Lecture 9 – polyelectrolyte hydrogels 3 of 17