Fluid Handling Dynamics and Durability of Silver-Containing Gelling Fiber Dressings Tested in a Robotic Wound System.

OBJECTIVE: To develop a robotic phantom system containing multiple simulated wound replicates to determine the synergy in fluid absorbency and retention (sorptivity) performances and the post-simulated-use mechanical durability of silver-containing gelling fiber primary dressings when used with a secondary dressing, as per clinical practice. METHODS: Using a robotic system containing six identical wound simulators, the authors tested the sorptivity performances of the Exufiber Ag + (Mölnlycke Health Care, Gothenburg, Sweden) primary dressing (ExAg-polyvinyl alcohol [PVA]) against a market-leading comparator product, when used with a secondary foam dressing. The durability of the primary dressings after simulated use was further investigated through tensile mechanical testing. RESULTS: The ExAg-PVA primary dressing delivered greater fluid amounts for absorbency and retention by the secondary foam dressing, approximately 2- and 1.5-fold more than the comparator dressing pair after 10 and 15 hours, respectively. The ExAg-PVA dressing was also substantially less sensitive to the direction of pulling forces and, accordingly, exhibited post-use mechanical strength that was approximately four and six times greater than that of the other primary dressing (when the latter dressing was tested out-of-alignment with its visible seams) after 10 and 15 hours, respectively. CONCLUSIONS: The dynamics of the sorptivity and fluid sharing between primary and secondary dressings and the effect of directional preference of strength of the primary dressings for adequate durability, resulting in safe post-use removals, have been described. The comparative quantification of these capabilities should help clinical and nonclinical decision-makers select dressings that best meet their patient needs.

The performance of gelling fibre wound dressings under clinically relevant robotic laboratory tests.

The effectiveness of wound dressing performance in exudate management is commonly gauged in simple, non-realistic laboratory setups, typically, where dressing specimens are submersed in vessels containing aqueous solutions, rather than by means of clinically relevant test configurations. Specifically, two key fluid-structure interaction concepts: sorptivity-the ability of wound dressings to transfer exudate, including viscous fluids, away from the wound bed by capillary action and durability-the capacity of dressings to maintain their structural integrity over time and particularly, at removal events, have not been properly addressed in existing test protocols. The present article reviews our recent published research concerning the development of clinically relevant testing methods for wound dressings, focussing on the clinical relevance of the tests as well as on the standardisation and automation of laboratory measurements of dressing performance. A second objective of this work was to compile the experimental results characterising the performance of gelling fibre dressings, which were acquired using advanced testing methods, to demonstrate differences across products that apparently belong to the same "gelling fibre" family but differ remarkably in materials, structure and composition and, thereby, in performance.

Fluid management and strength postsimulated use of primary and secondary dressings for treating diabetic foot ulcers: Robotic phantom studies.

Non-offloaded diabetic heel ulcers and the wound dressings used to treat them may be subjected to considerable bodyweight forces. A novel robotic foot phantom with a diabetic heel ulcer was designed and constructed to test the combined performances of applied primary and secondary dressings, in simulated non-offloaded (standing) and offloaded (supine) postures. We specifically compared the performances of the primary Exufiber dressing (Mölnlycke Health Care) combined with the secondary Mepilex Border Flex dressing (Mölnlycke) against a corresponding pair from an alternative manufacturer. Fluid retention and distribution between the primary and secondary dressings of each pair were determined using weight tests, and mechanical strength of the primary dressings was further measured postsimulated use through tensile testing. The Exufiber and Mepilex Border Flex pair performed similarly in the two simulated postures (retention = ~97%), whereas the comparator pair exhibited a 13%-decrease in retention for a supine to standing transition. Furthermore, the Exufiber dressing delivered up to 2-times more fluid to its paired secondary dressing and endured 1.7-times greater strain energy than the corresponding primary dressing before failure occurred. The present robotic foot phantom and associated methods are versatile and suitable for testing any dressing, in consideration of the relevant clinical factors and practice.

Three-dimensional shape-conformation performances of wound dressings tested in a robotic sacral pressure ulcer phantom.

Effective exudate retention by dressings requires close and intimate dressing-wound contact, immediately and continuously after the dressing application. Any dressing-wound spaces may allow for build-up of non-retained fluids, causing exudate pooling which forms a favourable environment for pathogen growth. Maceration may follow if the pooled exudates spread to peri-wound skin. Dressings with a claimed 3D-shape-conformation technology are commercially available; however, their effectiveness in minimising dressing-wound gaps has never been scientifically investigated. We present a novel bioengineering methodology for testing the effectiveness of such 3D-shape-conformation dressings, using our recently reported robotic phantom system of a sacral pressure ulcer. By means of 3D laser scanning and bespoke software, we reconstructed dressing shapes after simulated use and calculated the goodness-of-fit between each dressing (swelled to near-saturation) and the corresponding wound geometry. Two dressing sizes (10 × 10 cm and 12.5 × 12.5 cm) and two wound depths (2.5 or 2 cm) were considered. All the tested dressings were far from reaching good contact with the (simulated) wounds: Approximately one-third of the wound volume and nearly half of the wound surface were not in contact with the swelled dressings. Our present findings question whether 3D-shape-conformation dressings are effective, by revealing their swelling behaviour which was previously unknown.

The sorptivity and durability of gelling fibre dressings tested in a simulated sacral pressure ulcer system.

Wound-dressing performances are affected by exudate viscosity, resistance to flow because of gravity, and bodyweight loads, the level of which is related to the body position. Here, we focussed on two dressing properties: (a) Sorptivity-the ability of dressings to transfer exudate away from the wound bed by capillary action-and (b) Durability-the capacity of dressings to maintain their integrity over time and during their removal. Both properties are critically important for avoiding further tissue damage but require the development of new laboratory tests for their measurement. A computer-controlled phantom of an exuding sacral pressure ulcer has therefore been developed and used to compare the performances of Exufiber (Mölnlycke Health Care) vs an alternative market-leading dressing. Sorptivity was determined using weight tests, and durability was measured through tensile tests of the used dressings. For a supine configuration, the Exufiber dressing demonstrated ~three times higher sorptivity and better durability, withstanding ~five times greater strain energy than the other product before failure occurred. This work paves the way for quantitative, standardised testing of dressings in all aspects of exudate management. The reported tests are further suitable for testing dressing combinations or how dressings interact with negative pressure wound therapy.

Higher cognitive load interferes with head-hand coordination: virtual reality-based study.

Daily life activities often involve decision-based reaching movements in different contexts and circumstances. These activities span a wide array of cognitive load types we face while executing motor functions. Here we use a virtual reality-based neurocognitive testing platform to assess cognitive-induced changes in motor behavior as reflected by modulations in head-hand coordination. Our paradigm is based on the Color Trails Test (CTT), which is designed to assess two types of cognitive functions: Trails A-sustained visual attention (SVA), and Trails B-divided attention (DA). The virtual reality CTT adaptation (VR-CTT) requires execution of large multi-directional hand movements and head rotations. We employed a cross-correlation analysis on hand and head kinematics data collected from 122 healthy participants (ages: 20-90 years; divided as follows: young, middle-aged, and older adults) who completed the VR-CTT. The level of spatial coherence of head-hand movements was found to be high (R ≥ 0.76) in both Trails A and B, in all age groups. However, assessing head-hand phase shifts revealed longer time lags (i.e., in which head leads hand) in Trails B versus Trails A, in all age groups. We conclude that allocating cognitive resources to DA task reduces head-hand synchrony as compared to SVA conditions.

The mechanobiology theory of the development of medical device-related pressure ulcers revealed through a cell-scale computational modeling framework.

Pressure ulcers are localized sites of tissue damage which form due to the continuous exposure of skin and underlying soft tissues to sustained mechanical loading, by bodyweight forces or because a body site is in prolonged contact with an interfacing object. The latter is the common cause for the specific sub-class of pressure ulcers termed 'medical device-related pressure ulcers', where the injury is known to have been caused by a medical device applied for a diagnostic or therapeutic purpose. Etiological research has established three key contributors to pressure ulcer formation, namely direct cell and tissue deformation, inflammatory edema and ischemic damage which are typically activated sequentially to fuel the injury spiral. Here, we visualize and analyze the above etiological mechanism using a new cell-scale modeling framework. Specifically, we consider here the deformation-inflicted and inflammatory contributors to the damage progression in a medical device-related pressure ulcer scenario, forming under a continuous positive airway pressure ventilation mask at the microarchitecture of the nasal bridge. We demonstrate the detrimental effects of exposure to high-level continuous external strains, which causes deformation-inflicted cell damage almost immediately. This in turn induces localized edema, which exacerbates the cell-scale mechanical loading state and thereby progresses cell damage further in a nonlinear, escalating pattern. The cell-scale quantitative description of the damage cascade provided here is important not only from a basic science perspective, but also for creating awareness among clinicians as well as industry and regulators with regards to the need for improving the design of skin-contacting medical devices.