Urinary tract stones represent a prevalent condition in urology, holding the top position among patients admitted to urology departments. At present, the main treatment methods for renal stones include extracorporeal shock wave lithotripsy, ureteroscopy, and PCNL [10]. For multiple and stag-horn renal stones, PCNL remains the preferred treatment [11, 12]. However, because of the extensive stone burden and involvement of multiple renal calyces, addressing all the stones with a single-tract PCNL proves challenging. A large swing angle of the nephroscope increases the risk of calyx neck injury and significant bleeding, making it challenging to clear stones in parallel calyces and reducing the one-stage clearance rate. Prior research indicated that among patients with staghorn renal stones undergoing PCNL, the initial stone clearance rate was only 56.9% [13], and 60% of residual stones after PCNL required secondary surgery [14].

In order to improve surgical outcomes, current options include: (1) multi-tracts lithotripsy, which, although it increases stone clearance rates, also markedly elevates the risk of bleeding [15]. It has been demonstrated that each additional tract increases the risk of puncture-related bleeding increases by 2.77 times [16, 17]. (2) The dual-scope approach was employed, and intraoperative positioning was adjusted to either the horse-riding stance or lateral decubitus with split legs, promoting stone treatment [18]. This method is highly suggested to female patients. While combining the stone clearance efficiency of PNL with the extensive exploration range of flexible ureteroscopy has its merits [19], However, this method requires the patient to be in a special position, such as the horse-riding stance or lateral decubitus with split legs position, requires two sets of surgeons and surgical equipment, and places high demands on the skills and coordination of both sets of surgeons. This makes the surgical steps more complex, increasing operation time, costs, and the incidence of related surgical complications.

The use of a percutaneous renal single tract in combination with flexible cystoscope was previously suggested for managing complex renal stones. Although this approach can improve the one-stage stone clearance rate, the diameter of the flexible cystoscope is extremely large. Its limited flexibility in the renal collecting system and inability to enter the ureter for inspection pose a risk of residual fragments from ureteral stones [20].

Considering the shortcomings of the current nephroscope, a novel digital flexible nephroscope was fabricated in the present study by modifying and reconfiguring the parameters of the existing ureteroscopes. When used alone or in conjunction with a single-tract percutaneous nephroscope, this novel digital flexible nephroscope can give access to most target calyces. It also avoids the limitations of the bulky flexible cystoscope in bending in the renal collecting system. Furthermore, it does not require the patient to be in a special position and only needs one set of surgeons to freely switch nephroscopes during the procedure, enabling the detection and treatment of most stones. The novel digital flexible nephroscope may reduce personnel and equipment requirements, save operation time, lower surgical risks, reduce clinical costs, and decrease the occurrence of complications.

The advent of 3D printing technology has remarkably influenced clinical urology, as it promotes the development of visual and intuitive models that simulate surgical procedures [21]. Specifically, 3D-printed kidneys provide a comprehensive and simplified approach for evaluating the renal collecting system and stones. This allows for more precise selection of PCNL puncture points and tracts and facilitates better preoperative communication with patients [22]. Additionally, this technology avoids formation of large renal vessels, ensures precise needle puncture depths, and provides preoperative tract planning for PCNL [23].

To confirm the efficacy of the novel digital flexible nephroscope, 3D printing technology was employed to successfully develop a human urinary model. The novel digital flexible nephroscope could smoothly access the upper, middle, and lower calyces of the renal collecting system and freely navigate to most target calyces and the upper segment of the ureter in the renal collecting system. To further confirm the efficacy of the proposed digital flexible nephroscope, isolated porcine kidneys were utilized. Moreover, the digital flexible nephroscope could enter the renal collecting system from the upper, middle, and lower posterior renal calyces of the porcine kidney. The proposed digital flexible nephroscope could bend its tip to reach the upper, middle, and lower calyces in the kidney and most minor calyx. It was also able to navigate into the ureter. This eliminates the need of traditional rigid nephroscope for swinging the nephroscope or creating new tracts to reach the target renal calyces, thereby enhancing surgical efficiency while reducing the occurrence of surgical complications. It was hypothesized that its clinical application could substantially enhance the stone clearance rate in a single procedure.

To observe and verify the effectiveness of the novel digital flexible nephroscope, 10 intact porcine kidneys were utilized. Notably, PCNL procedures were simultaneously carried out using both the traditional rigid nephroscope and the novel digital flexible nephroscope in kidney models. Using the traditional rigid nephroscope, after entering the renal pelvis, all renal calyx openings of upper and lower calyces were visible, while only one upper calyx and two lower calyces were accessible. In contrast, the novel digital flexible nephroscope could not only visualize all renal calyx openings, but also access all calyces except for one in each of the upper and lower groups. It could visualize and access most minor calyces, highlighting its notable advantages. This confirms the efficacy and clinical relevance of the novel digital flexible nephroscope.

The present study elucidated that the novel digital flexible nephroscope provided distinct advantages that were not found in the traditional rigid nephroscope. It could effectively detect renal stones and other lesions in the kidney and allow the use of holmium laser to treat corresponding lesions. It makes PCNL procedures safer, more efficient, significantly increases the stone clearance rate, and reduces the risks of bleeding and related complications. This further confirms the clinical value of the percutaneous digital flexible nephroscope and provides theoretical and practical support for the development of new surgical equipment and techniques in clinical practice. With further advancements in manufacturing technology, this digital flexible nephroscope maybe thinner with a smaller bending radius, allowing better access to the target renal calyces, thus enhancing its safety and effectiveness.

Nevertheless, the limitations of the present study should be pointed out, as the data obtained were based on initial experience with porcine kidney models from a single center, and human kidney validation is pending. The study primarily concentrated on the technical feasibility of the novel digital flexible nephroscope using 3D printing technology and porcine kidney models, and future clinical validation is needed. In the future research, the efficacy of this digital flexible nephroscope will be assessed in stone fragmentation and compared with clinically used traditional rigid nephroscopes regarding stone clearance rate and the occurrence of complications. Further large-scale multicenter prospective clinical trials are required to verify the cost-efficacy and safety of the proposed digital flexible nephroscope.