Introduction: Kidney stones affect nearly 1 in 9 individuals in the USA. The most common surgical stone treatments include laser lithotripsy by ureteroscopy and extracorporeal shock wave lithotripsy. Photonic lithotripsy (PL) is based on a new paradigm of minimally-invasive kidney stone treatment that has the potential to target and fragment stones non-invasively. PL utilizes photonic nanoparticles that can produce a photothermal and/or photoacoustic energy for the fragmentation of kidney stones when exposed to a near-infrared (NIR) laser. Herein we investigate the failure mechanism of stones during PL.
Methods: Human kidney stones, ranging from 2–4 mm with a composition of 70% calcium oxalate monohydrate, 20% uric acid and 10% calcium oxalate dihydrate were used in this study. Stones were obtained from the Cleveland Clinic Pathology Labs and were treated with photonic nanoparticles and exposed to a NIR laser (1320 nm; QPC Lasers, CA) for three, 3-minute intervals. The treatments were successful if two or more fragments were produced. The failure mechanism was investigated using Fourier Transform Infrared (FTIR) spectroscopy and Micro Computed Tomography (µCT) pre and post PL treatment.
Results: The 1320 nm laser (wavelength of least absorption by kidney tissue in the NIR region) was successful at fragmenting stones (Fig 1A). There was significant degradation of the stones as shown by the pre and post irradiation µ-CT images (Fig. 1B). Figure 1C shows that stone degradation creates more surface area for a similar volume and the reduction in the mean Hounsfield unit suggests that the stone matrix has been degraded to a less radio dense material. The FTIR spectra (Fig 1D) shows the presence of calcium carbonate (CaCO3) in post-treatment stones, which results from thermal degradation of the calcium oxalate phase. This suggests that the mode of failure includes a component of photothermal degradation.
Conclusions: We have shown that photonic nanoparticles can fragment stones using a laser wavelength that is minimally absorbed by kidney tissue. Importantly, the FTIR results suggest that photothermal degradation is a component of the failure mechanism, as observed with the formation of CaCO3. Mechanistic studies will help in optimizing parameters for photonic lithotripsy.
Source of Funding: LRI Accelerator Grant, Cleveland Clinic Caregiver Catalyst Award and U2Csupport 1U2CDK129440.
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