Preparation of artificial kidney stones of reproducible size, shape, and mass by precision injection molding

Purpose: To prepare artificial kidney stones of defined shape, size, mass, and material composition via precision injection molding of Ultracal 30 cement slurries into an inexpensive biodegradable mold. Materials and Methods: A calcium alginate and silica-based mold was used to prepare casts of varying shapes in a reproducible manner. Ultracal 30 cement slurries mixed 1:1 with water were injected into these casts and allowed to harden. The artificial stones were recovered and their physical properties determined. Ex-vivo and in-vivo responses to holmium laser lithotripsy were examined. Results: Spheres, half spheres, cylinders, cubes, tapered conical structures, and flat angulated structures were prepared with high precision without post-molding manipulations. Large spheres of average mass 0.661 g (± 0.037), small spheres of average mass 0.046 g (± 0.0026), and hexagons of average mass 0.752 g (± 0.0180) were found to have densities (1610-1687 kg/m³) within the expected range for Ultracal 30 cement stones. Ex-vivo holmium laser lithotripsy of small spheres in saline showed uniformly reproducible efficiencies of comminution. Implantation of a tapered conical stone into the ureter of a porcine model demonstrated stone comminution in vivo consistent with that seen in the ex-vivo models. Conclusions: We present an environmentally safe, technically simple procedure for the formation of artificial kidney stones of predetermined size and shape. The technique does not require the use of hazardous solvents or postprocedural processing of the stones. These stones are intended for use in standardized experiments of lithotripsy efficiency in which the shape of the stone as well as the mass can be predetermined and precisely controlled.