Attachment of Calcium Oxalate Monohydrate Crystals on Patterned Surfaces of Proteins and Lipid Bilayers

Abstract

The attachment of calcium oxalate monohydrate (COM) crystals to renal tubules is thought to be one of the critical steps of kidney stone formation. Patterns of phosphatidylserine (DPPS) bilayers and osteopontin (OPN) were fabricated on silica substrates through the combination of a microcontact printing technique and fusion of lipid vesicles to create spatially organized surfaces of lipids and proteins that may mimic renal tubule surfaces while allowing direct visualization of the competition for COM attachment to compositionally different regions. In the case of DPPS-OPN patterns, micrometer-sized COM crystals dispersed in saturated aqueous calcium oxalate solutions attached preferentially to the OPN regions, in agreement with other in vitro studies that have suggested a binding affinity of OPN to COM crystal surfaces. COM crystals attached with nearly equal coverage to OPN and DPPS surfaces alone, suggesting that the preferential segregation of COM crystals to the OPN regions on the patterned surfaces reflects reversible attachment of micrometer-sized COM crystals capable of Brownian motion. These attached microcrystals then grow larger over time during immersion in the supersaturated calcium oxalate solutions. Free OPN, a major constituent in urine, adsorbs on COM crystals and suppresses attachment to DPPS, suggesting a link between OPN and reduced attachment of COM crystals to renal epithelium. This patterning protocol can be expanded to other urinary molecules, providing a convenient approach for understanding the effects of biomolecules on COM crystal attachment and the pathogenesis of kidney stones.