Equilibrium water and solute uptake in silicone hydrogels.
Equilibrium water content of and solute partitioning in silicone hydrogels (SiHys) are investigated using gravimetric analysis, fluorescence confocal laser-scanning microscopy (FCLSM), and back extraction with UV/Vis-absorption spectrophotometry. Synthesized silicone hydrogels consist of silicone monomer, hydrophilic monomer, cross-linking agent, and triblock-copolymer macromer used as an amphiphilic compatibilizer to prevent macrophase separation. In all cases, immiscibility of the silicone and hydrophilic polymers results in microphase-separated morphologies. To investigate solute uptake in each of the SiHy microphases, equilibrium partition coefficients are obtained for two hydrophilic solutes (i.e., theophylline and caffeine dissolved in aqueous phosphate-buffered saline) and two oleophilic solutes (i.e., Nile Red and Bodipy Green dissolved in silicone oil), respectively. Measured water contents and aqueous-solute partition coefficients increase linearly with increasing solvent-free hydrophilic-polymer volume fraction. Conversely, oleophilic-solute partition coefficients decrease linearly with rising solvent-free hydrophilic-polymer volume fraction (i.e., decreasing hydrophobic silicone-polymer fraction). We quantitatively predict equilibrium SiHy water and solute uptake assuming that water and aqueous solutes reside only in hydrophilic microdomains, whereas oleophilic solutes partition predominately into silicone microdomains. Predicted water contents and solute partition coefficients are in excellent agreement with experiment. Our new procedure permits a priori estimation of SiHy water contents and solute partition coefficients based solely on properties of silicone and hydrophilic homopolymer hydrogels, eliminating the need for further mixed-polymer-hydrogel experiments.
Chemical and Biomolecular Engineering Department, University of California, Berkeley, CA 94720, United States.
D E
DE
Liu
Chemical and Biomolecular Engineering Department, University of California, Berkeley, CA 94720, United States.
T J
TJ
Dursch
Chemical and Biomolecular Engineering Department, University of California, Berkeley, CA 94720, United States.
Y
Y
Oh
Chemical and Biomolecular Engineering Department, University of California, Berkeley, CA 94720, United States.
D T
DT
Bregante
Chemical and Biomolecular Engineering Department, University of California, Berkeley, CA 94720, United States.
S Y
SY
Chan
Chemical and Biomolecular Engineering Department, University of California, Berkeley, CA 94720, United States; Vision Science Group, University of California, Berkeley, CA 94720, United States. Electronic address: radke@berkeley.edu.
C J
CJ
Radke
D002110:Caffeine / Q000737:chemistry; D020100:Hydrogels / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D012828:Silicones / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013806:Theophylline / Q000737:chemistry; D014867:Water / Q000737:chemistry*
D020100:Hydrogels; D012828:Silicones; D012997:Solvents; D014867:Water; D002110:Caffeine; D013806:Theophylline
Drug; Fluorescence confocal microscopy; Partition coefficient; Silicone hydrogel; Water content