Avidin adsorption on silicone elastomer: Effects of stretching and polyelectrolyte coatings

Zeta potential and avidin adsorption of silicone elastomer (SE) and SE coated with polyethyleneimine (PEI) and heparin is studied under controlled hydrodynamic conditions. Zeta potential (ζ) of SE depends on the duration of contact with buffer (0.02 M MOPS–KCl, pH 7.2): ζ descends from 12 mV to a plateau value of −32 mV during 5 h and decreases further if SE is stretched (30% elongation). The time variation of ζ is attributed to surface charging of the core polymer PDMS. Coating the negatively charged SE with PEI results in ζ = 42 mV; a layer of heparin on top of PEI yields ζ = −46 mV. On the negatively charged surfaces, avidin adsorption levels off at 5 mV. Desorption of avidin from SE is negligible even when SE with adsorbed avidin is stretched, or when the stretching force is removed after adsorption of avidin. The results can be employed for designing biomaterials with properties such as surface charge and protein adsorption adjustable by stretching; the strong attachment of avidin can allow for further surface modification.