Photonic Lithotripsy: Near-Infrared Laser Activated Nanomaterials for Kidney Stone Comminution

Abstract

Near-infrared activated nanomaterials have been reported for biomedical applications ranging from photothermal tumor destruction to biofilm eradication and energy-gated drug delivery. However, the focus so far has been on soft tissues, and little is known about energy delivery to hard tissues, which have thousand-fold higher mechanical strength. We present photonic lithotripsy with carbon and gold nanomaterials for fragmenting human kidney stones. The efficacy of stone comminution is dependent on the size and photonic properties of the nanomaterials. Surface restructuring and decomposition of calcium oxalate to calcium carbonate support the contribution of photothermal energy to stone failure. Photonic lithotripsy has several advantages over current laser lithotripsy, including low operating power, noncontact laser operation (distances of at least 10 mm), and ability to break all common stones. Our observations can inspire the development of rapid, minimally invasive techniques for kidney stone treatment and extrapolate to other hard tissues such as enamel and bone.

Proof-of-concept for a novel nanotechnology-based treatment for urolithiasis

“…There was also a decrease in the Hounsfield units, for which we propose two different mechanisms. One is the breakdown and ultimate reduction in density as the stone fragments, and the other is a change in the mineral composition of the stone due to the thermal energy generated by the nanoparticles (this thermal degradation has been shown previously using FTIR [ 22 ]). Use of micro-CT in identifying mineral composition of stones has been reported in the literature, although it has not been used to determine mineral compositional changes pre and post stone treatment [ 23 , 24 ].…”

“…7 Comparison of the time period in which fragmentation of the COM stones occurred using a 785 nm (left) or 1320 nm (right) energy source with different photonic nanoparticles. Exposure times were broken into three periods over a total of 9 min, where n = 10 stones was used for each nanoparticle tested, this data has been reported previously [ 22 ] …”

“…Both compositional change and stone fragmentation can have a significant effect on HU and therefore, it is challenging to differentiate between the two mechanisms in a quantitative manner. The proposed mechanism of stone failure and the contribution of these effects has been outlined in more detail previously using scanning electron microscopy and thermal imaging during photonic lithotripsy [ 22 ]. Based on these studies, current byproducts of this technology appear to be predominantly thermal in nature, although these nanoparticles can be further engineered to enhance the acoustic or mechanical effect for fragmentation (and potentially decrease the thermal effect) as well as modified with ligands to directly target stones [ 11 , 12 ].…”