A robotic venous leg ulcer system reveals the benefits of negative pressure wound therapy in effective fluid handling

Abstract

We applied a market-leading, single-use negative pressure wound therapy device to a robotic venous leg ulcer system and compared its fluid handling performance with that of standard of care, superabsorbent and foam dressings and compression therapy. For each tested product, we determined a metrics of retained, residual, evaporated and (potential) leaked fluid shares, for three exudate flow regimes representing different possible clinically relevant scenarios. The single-use negative pressure wound therapy system under investigation emerged as the leading treatment option in the aspects of adequate fluid handling and consistent delivery of therapeutic-level wound-bed pressures. The superabsorbent dressing performed reasonably in fluid handling (resulting in some pooling but no leakage), however, it quickly caused excessive wound-bed pressures due to swelling, after less than a day of simulated use. The foam dressing exhibited the poorest fluid handling performance, that is, pooling in the wound-bed as well as occasional leakage, indicating potential inflammation and peri-wound skin maceration risks under real-world clinical use conditions. These laboratory findings highlight the importance of advanced robotic technology as contemporary means to simulate patient and wound behaviours and inform selection of wound care technologies and products, in ways that are impossible to achieve if relying solely on clinical trials and experience.

Keywords: bioengineering laboratory testing; chronic wounds; compression therapy; exudate management; superabsorbent and foam dressings.

FIGURE 1

The robotic venous leg ulcer (VLU) system: (A) Experiments were conducted in three identical leg units (upper frame). The experimental setup consisted of the following elements: (1) Computer‐controlled syringe pump (the control panel of the LabView code developed for these robotic legs, showing the pressure sensor readings in real‐time, is magnified at the bottom left frame). (2) Robotic VLU systems (three leg units), each containing a VLU simulator (magnified at the bottom right frame). (3) PICO™7 negative pressure wound therapy systems (×3, each applied to one leg unit). (4) Infrared heating lamp for temperature control.

FIGURE 2

The fluid handling performance metrics of the tested wound care products applied to the robotic venous leg ulcer (VLU) systems. The flow regimes of the simulant wound fluid (SWF) delivered into the VLU simulators were as follows. (i) Discontinuous flow (DF): 4 exudation events × 6 mL/h of flow rate per event × 2 h duration of each bolus event resulting in delivery of a total of 48 mL of the SWF. (ii) Continuous flow (CF) at a flow rate of 0.96 mL/h (termed ‘CF‐bsl’), consistent with the design and instructions for use of the PICO™7 single‐use negative pressure wound therapy system, for 50 h, resulting in delivery of a total of 48 mL of the SWF. (iii) CF at a flow rate of 2 mL/h (termed ‘CF‐high’), for 24 h, resulting in the delivery of a total of 48 mL of the SWF. The error bars are the standard deviations from the mean values of three test repetitions per each wound care product and flow regime. Asterisks indicate a statistically significant difference in the relevant outcome measure (p < 0.01). SAD = Superabsorbent dressing; CompT, compression therapy; FMD, foam dressing.

FIGURE 3

The pressures measured at the simulated ‘wound‐bed’ region of the robotic venous leg ulcer (VLU) systems (the location of the pressure sensor is shown at the bottom right frame of Figure 1) for the tested wound care products applied to the VLU robots. The pressure data are plotted over time for the three flow regimes used to evaluate the fluid handling metrics of the wound care products under investigation (Figure 2), as follows. (A) Discontinuous flow (DF) whereas each grey shading indicates a bolus event. (B) Continuous flow (CF) at a flow rate of 0.96 mL/h (referred to in the text as ‘CF‐bsl’). (C) CF at a flow rate of 2 mL/h (referred to as ‘CF‐high’). The colour shades under the pressure curves indicate the standard deviations from the mean values at each time point. CompT, compression therapy; FMD, foam dressing.

FIGURE 4

Wound size changes over time for the two venous leg ulcers (VLUs) on the same right leg of a patient whose characteristics are described in case #1, with the larger wound (A) treated by means of single‐use negative pressure wound therapy (sNPWT) PICO™7 and the smaller VLU (B) using a superabsorbent dressing (SAD), both combined with compression thrapy (CompT) as per the standard of care. The healing rate achieved using the sNPWT+CompT is 7.3‐fold greater than for the SAD+CompT. The mean (linearized) healing rates are provided for both VLUs (grey dashed lines) as a guide to the eye. Note the fluctuations in the healing rate observed for the smaller VLU treated with the SAD, which may have been caused by backflow and pooling of exudate and/or swelling‐induced compression of the dressing onto the wound, as opposed to the consistent healing process with the currently studied sNPWT system. The wound images shown in the left and centre panels were taken on admission to the clinic.

FIGURE 5

Wound size changes over time for the venous leg ulcers (VLUs) of the patients whose characteristics are reported in case #2 (A) and case #3 (B). In case #2 (panel ‘a’), the VLU was treated with superabsorbent dressings (SADs) combined with compression therapy (CompT) and this SADs+CompT treatment delivered over 60 days yielded a wound healing rate of 0.11 cm²/day, similar to the healing rate associated with the SADs+CompT treatment (for the smaller VLU) in Case #1. In case #3 (panel ‘b’), the VLU was treated with foam dressings (FMDs) combined with CompT and this FMD + CompT combination applied for 66 days resulted in a healing rate of ~0.05 cm²/day that was considerably slower than the rates calculated for cases #1 and #2 (Figures 4 and 5B, respectively), supporting the findings obtained using the robotic VLU system which identified FMDs as having the poorest performance in VLU management compared to the tested alternatives (see case #1). The mean (linearized) healing rates (grey dashed lines) are shown as a guide to the eye. The wound images shown in the left panels were captured when the patients were admitted to the wound clinic.