Hypothesis / aims of study
Hydrophilic-coated intermittent catheters (ICs) offer an enhanced user experience when compared to traditional uncoated urinary ICs. These hydrophilic coatings absorb water, creating a lubricious surface that reduces friction between the IC and urethral tissue. However, many hydrophilic coatings contain polyvinylpyrrolidone (PVP) which can lead to the IC surface becoming mucoadhesive (1). As a result, increased force and friction during IC withdrawal may result in complications including urethral microtrauma and discomfort. Moreover, the hydrophilic coatings have be shown to delaminate from the catheter surface (1).
To address these concerns, IC devices with novel coating-free hydrophilic technology incorporating integrated amphiphilic surfactants (IAS) have been developed (1). IAS technology has hydrophilic surface properties comparable to existing hydrophilic coated ICs, without the mucoadhesive complications associated with PVP coated catheters when their surface dries out.
Current methods used to assess IC performance, such as the ISO 8295:1995 friction test, remain focused on mechanical assessments, with a lack of physiological relevance. To address this, we previously described a novel in vitro biomimetic model for comparison of ICs in terms of surface lubricity and effect on urethral microtrauma (2). To complement this in vitro biomimetic model, we developed an ex vivo model using porcine urethral tissue. Unlike the previous model, which comprised a cell monolayer, the inclusion of the multilayer porcine tissue allows for greater representation of in vivo conditions.
The aim of this study is firstly, to close the gap in physiologically relevant IC performance testing by developing a novel ex vivo porcine urethral model. Secondly, we aim to compare the performance of the IAS catheter surfaces and hydrophilic coated catheters using an ex vivo porcine urethral model.
It was hypothesised that the IAS catheters will require less force to remove them from the porcine urethra than the hydrophilic coated catheters.
Study design, materials and methods
To investigate catheter performance, an ex vivo porcine urethral model was designed using a Mecmesin Multitest 2.5-dv texture analyser (TA) apparatus (Figure 1) (1). A commercial uncoated PVC IC and four hydrophilic PVP-coated ICs were compared with the IAS IC. No ethical approval was required. Male porcine urethra was cut into 9 cm segments, placed into a centrifuge tube and a 2% tryptone soya broth and 0.8% bacteriological agar solution was poured into the bottom, surrounding the end of the urethral tissue. A hole was cut in a finger cot and the top of the urethral tissue fed through. The agar solution was also poured into the cot, surrounding the top of the urethral tissue. ICs were attached to the upper grips of the TA, leaving 9 cm exposed, and lowered vertically (5 mms-1) into the urethra to a depth of 55 mm. After 120 s (to represent the typical average time to self-catheterise), the IC was elevated vertically (5 mms-1). The force (N) required for IC withdrawal from the urethra was determined.
To examine for tissue trauma, 1 cm segments of porcine urethra were fixed using 4% w/v paraformaldehyde. After fixation and wax embedding, 4 µm sections were cut and stained with haematoxylin and eosin. Stained sections were observed for damage to the urethral transitional epithelium (3). The attachment of urethral cells to the catheter surfaces was also examined by fluorescent staining. 4% w/v paraformaldehyde was added to the catheter surface to fix potentially adhered urethral cells. Fluorescent microscopy was used to visually examine and quantify cell attachment.
Based on a one-way ANOVA, performing the ex vivo porcine model with 12 replicate samples allowed for a 10% difference between force required to remove the IAS catheters and the hydrophilic coated catheters from porcine urethra to be determined.
Results
An ex vivo model was successfully developed that allowed 360° contact with the IC surface, thus allowing better representation of the intermittent catheterisation process. The force required to remove the uncoated PVC, PVP-coated brand 2, PVP-coated brand 4 and the IAS ICs from the porcine urethra was 0.29 N ± 0.05, 0.38 N ± 0.06, 0.38 N ± 0.06 and 0.24 N + 0.06 respectively, n=5, (Figure 2). Furthermore, the hydrophilic PVP-coatings were observed to delaminate from the catheter surface and remain within the urethra after catheterisation.
Interpretation of results
Following a 120 s indwelling time in the ex vivo porcine urethral model, the novel IAS hydrophilic catheter required significantly less force to withdraw than two of the hydrophilic PVP-coated ICs. As the PVP-coated catheters dry out, the potentially adhesive surfaces may stick, increasing the force required to remove the catheters from the urethra. These preliminary findings from the ex vivo porcine urethral model suggest that IAS hydrophilic ICs could have the potential to cause less frictional force on withdrawal from the urethra, resulting in less pain and damage to urethral tissue than uncoated and hydrophilic PVP-coated ICs.