The durability and effectiveness of hydrogel retrieval method for urinary stone fragments: an in-vitro study

To evaluate the effectiveness of MediNik hydrogel for retrieval of stone fragments of varying sizes and to assess how application technique influences its performance.

An in vitro experimental study was conducted using blood sample containers, natural stone fragments ranging from 0.2 to 2 mm, a 7.5 Fr single-use flexible ureteroscope, and a 2.2 Fr endoscopic basket. The MediNik system consists of a blue alginate component (K1) and a yellow calcium-based activator (K2) that interact to form a hydrogel. The evaluated parameters included K1:K2 ratios (2:1, 1:1, 1:2, and 1:3), stone fragment size (0.2-0.45 mm, 0.45-0.6 mm, 0.6-1.0 mm, 1-2 mm, and mixed fragments), application method (surface application versus delivery of K1 into the fragment mixture), and waiting time (3, 5, and 10 s).

Hydrogel performance was strongly influenced by the application technique. Effective integration of the two components occurred when K1 was delivered directly into the stone fragments and K2 was subsequently applied, particularly at K1:K2 ratios of 1:1, 1:2, and 1:3. Successful retrieval was achieved across all fragment sizes, including mixed fragments. Surface application of the components alone did not consistently produce a stable hydrogel clot.

Stable MediNik hydrogel clot formation was achieved at K1:K2 ratios of 1:1, 1:2, and 1:3 when K1 was applied first and followed by K2, with effective clot formation observed at waiting times of 3, 5, and 10 s. Stone fragment size did not affect clot formation. The most reliable clot suitable for basket extraction was obtained using intrafragment application of the alginate component followed by calcium binder delivery.