Influence of polyelectrolyte mixtures on the nanomechanical properties of calcium oxalate monohydrate crystals

Calcium oxalate monohydrate (COM) kidney stones remain an incurable disease, affecting approximately 10% of individuals in developed countries. Despite decades of research, the mechanisms underlying stone formation remain poorly understood.

COM stones form as hard, dense aggregates of inorganic calcium oxalate crystals and proteins. Notably, many proteins appear in COM stones as layers between and on the surfaces of COM crystals, comprising 1–2% of the stone mass. Both strongly charged anionic and cationic proteins are found within stones and exhibit preferential association with the stone rather than urine. Therefore, we hypothesize that a complex mixture of oppositely charged proteins interacts with COM crystals to produce the dense aggregates characteristic of kidney stones.

Nanoindentation was used to compare the mechanical properties of pure COM crystals with those grown in the presence of polyelectrolyte mixtures and peptides known to influence crystal morphology. Preliminary results show that both the elastic modulus and hardness of the crystals increase with polymer concentration for an anionic polyelectrolyte compared to pure COM, likely due to polymer incorporation within the crystals and coating their surfaces.

Altogether, this work explores how mixtures of oppositely charged polymers alter the mechanical properties of COM crystal composites, providing insight into inorganic–polymer interactions that may underlie kidney stone formation.