A Novel Technology for Needle-Free Injections of Liquids, Particles and Viable Cells into the Submucosa of the Urethra by a Pressure-Controlled Waterjet Technology

<b>Objectives:</b> The injection of bioactive compounds into the delicate urethral sphincter muscle to facilitate sphincter regeneration in incontinent patients poses a surgical challenge. In previous preclinical animal studies, approximately half of the 96 pigs treated by transurethral needle injection exhibited misplaced cells or cell loss. We, therefore, investigated whether pressure-controlled waterjet injections delivered nano- and microparticles or liquids more precisely in the urethra and without a risk of full penetration. <b>Methods:</b> Fresh cadaveric urethrae were prepared from 12 female pigs. Nano- and microparticles or liquids were injected by waterjet in a proximal (i.e., H5) and distal (i.e., H10) position of the urethral tissue samples employing waterjet pressures of effect 40 (E40), E60, and E80. The injection depths and widths were investigated by histochemistry. <b>Results:</b> E40 injections were not sufficient to inject particles into the tissue, while E60 and E80 injections delivered the components into the urethral mucosa, submucosa and close to the urethral muscle. However, employing E80 increased the risk of full penetration of the urethrae. Significant differences in injection depth were not observed between nano- and microparticles. Liquids, however, penetrated the tissue somewhat deeper. Using the optimised pressure protocols facilitated the injection of cells by a novel waterjet prototype with excellent viability into capture fluid. <b>Conclusions:</b> Target-specific and pressure-controlled waterjet injections deliver liquids and particles with high precision in the urethra. For future injections of bioactive components, including cells, waterjet injections into the urethrae of incontinent pigs with a pressure of E60 are most promising to investigate the efficacy of regenerative therapies in animal models of urinary incontinence and other diseases or malfunctions.