Intermittent catheters (ICs) are commonly used to alleviate chronic urinary retention in individuals suffering from neurogenic bladder dysfunction, most notably patients with spinal cord injury (SCI) (1). The majority of ICs are coated with hydrophilic polymers, such as polyvinylpyrrolidone (PVP), to reduce friction and discomfort during catheterisation. However, these coatings can delaminate during use, resulting in coating residue remaining within the urethra. Repeated catheterisation coupled with a lack of a natural urethral flushing mechanism in SCI patients may encourage a build-up of PVP within the urinary tract. Interestingly, PVP is exploited clinically for intracytoplasmic sperm injection (ICSI) to reduce spermatozoa motility and under long-term exposure can alter spermatozoa morphology (2). Patients with SCI are predisposed to infertility (3). It is hypothesised that repeated exposure to PVP from hydrophilic-coated ICs may impair spermatozoa function, potentially contributing to a further risk factor for infertility in pateints with SCI. This study will aim to:
1.	Determine the effect of residual PVP from catheter coatings on sperm morphology.
2.	Determine the effect of residual PVP from catheter coatings on sperm motility.

Porcine semen (Deer Park, Gloucester Old Spot, Reg No.R012707GS UKPO5) diluted 1:4 with an antimicrobial extender (53.3 % penicillin, 26.7 % polymyxin E, 13.3 % kanamycin and 20 % neomycin)  was enumerated using a haemocytometer and diluted in phosphate-buffered saline to an average human sperm count of 23.5 million/mL. 1.5 mL of diluted sperm (a volume representative of average human ejaculate) was heated to 34°C and artificially ejaculated (1000 mm min-1) through a previously catheterised ex vivo porcine urethral model, using a texture analyser. The urethral model underwent a single catheterisation or five repeated catheterisations (representative of daily use) with four commercially available hydrophilic PVP ICs (CH 10). Immediately following ejaculation, the percentage of abnormal sperm morphology was evaluated microscopically. Random fields of view were captured and defects in the spermatozoa head, midpiece, and tail identified. Videos of spermatozoa were captured, and spermatozoa motility (µm/sec) was analysed using ImageJ, measuring the distance travelled per second.

Spermatozoa morphology was not significantly altered following artificial ejaculation through the model, indicating that structural integrity remained intact. However, a significant reduction in progressive spermatozoa motility (p<0.001) was observed, with velocities falling below the critical threshold of 25 µm/s required for successful fertilisation. Following a single catheterisation of the model, spermatozoa motility was reduced by 54.35% ± 12.28% with Brand 1 and 57.23% ± 7.11% with Brand 3, relative to the uncatheterised control. Microscopic analysis revealed expelled catheter coating residue alongside the spermatozoa, with spermatozoa trapped within the residual material exhibiting immobilisation.

These findings suggest that while sperm morphology remains unaffected, exposure to coating residue discarded by PVP-coated catheters can significantly impair sperm motility and thus may impact fertility. The immobilisation of spermatozoa entrapped within residual catheter material is indicative of a physical mechanism whereby the viscous or adhesive properties of the expelled PVP coating hinder motility through direct entrapment or restriction of flagellar movement.

Exposure to residual PVP within the urethra was found to negatively affect spermatozoa motility. In SCI patients, who commonly rely on repeated intermittent catheterisation and lack natural urethral flushing mechanisms, PVP accumulation may represent an unrecognized factor contributing to their already compromised fertility. These findings suggest that PVP accumulation could further impair spermatozoa's ability to travel effectively through the reproductive tract, potentially compounding the known fertility challenges in this population.

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Sinha (et al)., Topics in Spinal Cord Injury Rehabilitation 2017; 23 (1), 31- 41.