Infiltration into inclined fibrous sheets

The flow from line and point sources through an inclined fibrous sheet is studied experimentally and theoretically for wicking from a saturated region and flow from a constant-flux source. Wicking from a saturated line generates a wetted region whose length grows diffusively, linearly or tends to a constant, depending on whether the sheet is horizontal or inclined downwards or upwards. A constant-flux line source generates a wetted region which ultimately grows linearly with time, and is characterized by a capillary fringe whose thickness depends on the relative strength of the source, gravitational and capillary forces. Good quantitative agreement is observed between experiments and similarity solutions.Capillary-driven and constant-flux source flows issuing from a point on a horizontal sheet generate a wetted patch whose radius grows diffusively in time. The flow is characterized by the relative strength of the source and spreading induced by the action of capillary forces, gamma. As gamma increases, the fraction of the wetted region which is saturated increases. Wicking from a saturated point corresponds to gamma = gamma(c), and spreads at a slower rate than from a line source. For gamma < gamma(c), the flow is partially saturated everywhere. Good agreement is observed between measured moisture profiles, rates of spreading, and similarity solutions.Numerical solutions are developed for point sources on inclined sheets. The moisture profile is characterized by a steady region circumscribed by a narrow boundary layer across which the moisture content rapidly changes. An approximate analytical solution describes the increase in the size of the wetted region with time and source strength; these conclusions are confirmed by numerical calculations. Experimental measurements of the downslope length are observed to be slightly in excess of theoretical predictions, though the dependence on time, inclination and flow rate obtained theoretically is confirmed. Experimental measurements of cross-slope width are in agreement with numerical results and solutions for short and long times. The affect of a percolation threshold is observed to ultimately arrest cross-slope transport, placing a limitation on the long-time analysis

Friction between a surrogate skin (Lorica Soft) and nonwoven fabrics used in hygiene products

Incontinence pad wearers often suffer from sore skin, and a better understanding of friction between pads and skin is needed to inform the development of less damaging materials. This work investigated friction between a skin surrogate (Lorica Soft) and 13 nonwoven fabrics representing those currently used against the skin in commercial pads. All fabrics were found to behave consistently with Amontons' law: coefficients of friction did not differ systematically when measured under two different loads. Although the 13 fabrics varied considerably in composition and structure, their coefficients of friction (static and dynamic) against Lorica Soft were remarkably similar, especially for the ten fabrics comprising just polypropylene (PP) fibres. The coefficients of friction for one PP fabric never differed by more than 15.7% from those of any other, suggesting that the ranges of fibre decitex (2.0–6.5), fabric area density (13–30 g m−2) and bonding area (11%–25%) they exhibited had only limited impact on their friction properties. It is likely that differences were largely attributable to variability in properties between multiple samples of a given fabric. Of the remaining fabrics, the one comprising polyester fibres had significantly higher coefficients of friction than the highest friction PP fabric (p < 0.005), while the one comprising PP fibres with a polyethylene sheath had significantly lower coefficients of friction than the lowest friction PP fabric (p < 10−8). However, fabrics differed in too many other ways to confidently attribute these differences in friction properties just to the choice of base polymer

Quantifying the frictional forces between skin and nonwoven fabrics

When a compliant sheet of material is dragged over a curved surface of a body, the frictional forces generated can be many times greater than they would be for a planar interface. This phenomenon is known to contribute to the abrasion damage to skin often suffered by wearers of incontinence pads and bed/chairbound people susceptible to pressure sores. Experiments that attempt to quantify these forces often use a simple capstan-type equation to obtain a characteristic coefficient of friction. In general, the capstan approach assumes the ratio of applied tensions depends only on the arc of contact and the coefficient of friction, and ignores other geometric and physical considerations; this approach makes it straightforward to obtain explicitly a coefficient of friction from the tensions measured. In this paper, two mathematical models are presented that compute the material displacements and surface forces generated by, firstly, a membrane under tension in moving contact with a rigid obstacle and, secondly, a shell-membrane under tension in contact with a deformable substrate. The results show that, while the use of a capstan equation remains fairly robust in some cases, effects such as the curvature and flaccidness of the underlying body, and the mass density of the fabric can lead to significant variations in stresses generated in the contact region. Thus, the coefficient of friction determined by a capstan model may not be an accurate reflection of the true frictional behavior of the contact region

Absorbent products for urinary/faecal incontinence: a comparative evaluation of key product designs

Background: The UK health service, nursing homes and public spend around £94 million per year on incontinence pads (absorbent products) to contain urine and/or faeces, but the research base for making informed choices between different product designs is very weak.Objectives: The aim of this trial was to compare the performance and cost-effectiveness of the key absorbent product designs to provide a more solid basis for guiding selection and purchase.A further aim was to carry out the first stage in the development of a quality of life instrument for measuring the impact of absorbent product use on users' lives.Design: The work involved three clinical trials focusing on the three biggest market sectors. Each trial had a similar crossover design in which each participant tested all products within their group in random order.Settings, participants and methods: In Trial 1, 85 women with light urinary incontinence living in the community tested three products from each of the four design categories available (total of 12 test products): disposable inserts (pads); menstrual pads; washable pants with integral pad; and washable inserts. In Trial 2a, 85 moderate/heavily incontinent adults (urinary or urinary/faecal) living in the community (49 men and 36 women) tested three (or two) products from each of the five design categories available (total of 14 test products): disposable inserts (with mesh pants); disposable diapers (nappies); disposable pull-ups (similar to toddlers' trainer pants); disposable T-shaped diapers (nappies with waist-band); and washable diapers. All products were provided in a daytime and a (mostly more absorbent) night-time variant. In these first two trials, the test products were selected on the basis of data from pilot studies. In Trial 2b, 100 moderate/heavily incontinent adults (urinary or urinary/faecal) living in 10 nursing homes (27 men and 73 women) evaluated one product from each of the four disposable design categories from Trial 2a. Products were selected on the basis of product performance in Trial 2a and, again, daytime and night-time variants were provided. The first phase of work to develop a quality of life tool for measuring the impact of using different pad designs was carried out by interviewing participants from Trials 1 and 2a.Outcome measures: Product performance was characterised using validated questionnaires, which asked the participants (in Trials 1 and 2a) or carers (all participants in Trial 2b, except for the few who could report for themselves) to evaluate various aspects of pad performance (leakage, ease of putting on, discreetness, etc.) using a five-point scale (very good–very poor) at the end of the week (or 2 weeks for Trial 2b) of product testing. In addition, participants/carers were asked to save individual used pads in bags for weighing and to indicate the severity of any leakage from them on a three-point scale (none, a little, a lot). These data were used to determine differences in leakage performance. Numbers of laundry items and pads used were recorded to estimate costs, and skin health changes were recorded by the participant or by the researchers (Trial 2b). At the end of testing, participants were interviewed and ranked their preferences (with and without costs), stated the acceptability of each design (highly acceptable–totally unacceptable) and recorded their overall opinion on a visual analogue scale (VAS) of 0–100 points (worst design–best design). This VAS score was used with product costs to estimate cost-effectiveness. In addition, a timed pad changing exercise was conducted with 10 women from Trial 2b to determine any differences between product designs.Results: Results presented are for statistically and clinically significant findings.<br/

The Impact of Microclimate on Skin Health With Absorbent Incontinence Product Use An Integrative Review

This integrative review considers the role of skin occlusion and microclimate in incontinence-associated dermatitis (IAD), with a particular focus on disposable, body-worn, absorbent incontinence products. Although the mechanisms are not fully understood, the primary causes of IAD are well-established: occluded skin, in prolonged contact with urine and/or feces and exposed to abrasive forces, is more likely to be affected, and each of these factors can be influenced by wearing absorbent incontinence products. Studies comparing the effect of various absorbent products on skin health have been hindered by the many differences between compared products, making it difficult to clearly attribute any differences in performance to particular materials or design features. Nevertheless, the large and significant differences that have sometimes been found invite further work. Breathable back sheets can significantly reduce the temperature of occluded skin and the humidity of the adjacent air, and several treatments for nonwoven top sheet materials (used next to the skin) have been shown to impart antimicrobial properties in the laboratory, but an impact on IAD incidence or severity has yet to be demonstrated directly. Recent work to introduce sensing technology into absorbent incontinence products to reduce the exposure of skin to urine and feces, by encouraging prompt product changing, seems likely to yield measurable benefits in terms of reducing incidents of IAD as the technology develops. Published work to date suggests that there is considerable potential for products to be engineered to play a significant role in the reduction of IAD among users

A multiscale analysis of frictional interaction between human skin and nonwoven fabrics

Various hygiene products, notably incontinence pads, bring nonwoven “topsheet” fabrics into contact with individuals’ skin. This contact can damage the skin in various ways, including abrading it by friction, a mechanism enhanced by the presence of moisture. In recent years skin-nonwoven friction has been the subject of significant experimental study in the Continence and Skin Technology Group, UCL, in the course of which methods have been developed which can detect differences in friction between a chosen nonwoven and equivalent skin sites on different individuals under fixed conditions. The reasons for these differences are unknown; their elucidation is one focus of this work. The other is to establish the influence of coarse geometry on the dynamics of a tense nonwoven sheet sliding over a substrate and interacting with it by friction. The first part of this work (“microfriction”) is primarily experimental in nature, and involves two separate experiments. The first involves using a microscope with a shallow depth of field to determine the length of nonwoven fibre in contact with a facing surface as a function of pressure; the second consists of measuring friction between chosen nonwovens and a skin surrogate at a variety of pressures and speeds whilst simultaneously observing the behaviour of the interface down a microscope. Both techniques were extensively validated, and the data from the two experiments were then compared. It had originally been intended to conduct the friction experiment on skin (the other experiment does not require it), and though all equipment was developed with this in mind and all relevant permission was sought and obtained, it was not eventually possible. Instead, a skin friction surrogate (Lorica Soft) established in the literature was used. Data from this show that Amontons’ law (with respect to load) is obeyed to high precision (R2 > 0.999 in all cases), though there is the suggestion of sublinearity at low loads. Detailed consideration of the friction traces suggests that two different friction mechanisms are important, and comparison with the contact data suggests tentatively that they may correspond to adhesion between two different populations of contacts, one “rough” and one “smooth”. Further work applying these techniques to skin is necessary. The second aspect of the work is “geometric friction”; that is, the relationship between the geometry of a surface (on the centimetre scale and upwards) and the friction experienced by a compliant sheet (such as nonwoven topsheet) laid over it in tension. A general equation of motion for slippage between sheet and surface has been derived which in principle allows for both objects to deform and interact according to any plausible friction law. This has then been solved in integral form for Amontons’ law and a low density strip exhibiting no Poisson contraction sliding over any surface with zero Gaussian curvature; closed form solutions for the specific cases of a prism and a circular cone have then been derived and compared. Experimental verification has been provided by a colleague, which shows very good agreement between theory and experiment. It has also been shown that, taking a naïve approach, the classic model for a rigid cylinder can be applied even to a quite extreme cone with experimentally negligible error. NB All prior copyrighted material (diagrams in all cases) has been removed from this edition to facilitate electronic distribution. They have been replaced with boxes of the same size, so pagination is identical with the complete version

Making research-based education more successful: Improving critical thinking and engagement through well-directed peer assessment

Universities increasingly recognize the need to train students using research-based education, using their discipline knowledge within group practical activities and to develop their critical thinking and teamwork skills to prepare them for their careers after graduation. With that in mind, students carry out substantial research-based projects many of which are in groups. These research-based projects may take the form of short labs, longer projects within a module during term time, or intensive one or two-week long full-time projects. In these cases, students may work together in disciplinary or multidisciplinary teams. In addition, some MEng students have a group project in the 3rd or 4th year of their degree that traditionally accounts for an equivalent of 2 taught modules. Despite the well-accepted educational benefits of getting students to work in research-based activities and in teams, some issues can detract from the student experience, i.e. (i) critical thinking skills are needed but difficult to obtain; and (ii) dissatisfaction with the assessment of group work. This paper presents work aimed at overcoming these two issues. Acquiring critical thinking is challenging and requires practice. Academic staff should implement long-term approaches to facilitate it. Introducing students to the critical analysis of someone else’s work early on in their degree programme is an excellent way of developing critical skills. We have incorporated this via peer assessment activities (e.g. of a report, a set of calculations, etc.) that initiates students in reviewing and constructively criticizing peers’ work. This stretches them because assessing a piece of work can be harder than completing the work itself, requiring a deeper understanding of the material and of alternative approaches. However, there are problems with traditional peer assessment which include (i) student disengagement leading to provide poor feedback to their peers, and (ii) students lacking confidence in their peers’ marking skills, and therefore the mark obtained. We have developed and successfully run for the past 3 years a new method of peer assessment (360 degree peer assessment) that addresses these main two issues, providing a better experience for students, and a successful tool for academics to foster and support the students’ critical thinking development. In the simplest way of assessing group work, the project deliverable (e.g. a report, a prototype, a video) is assessed and all members of the team would receive the same mark regardless of their individual effort. This leads to various problems: (i) dysfunctional behaviour and uneven participation, with some students not contributing their share; and (ii) frustration of high-performing students who do not see their work as being recompensed. Often, the mark will include an individual component, but it is either based on a separate piece of work (not practical to mark neither encouraging students into the group spirit), or they are set by the tutor based on some criteria considering the attitude of the individual in the group with just partial information. Alternatively, various practitioners have started to include an element of individual peer assessed contribution (IPAC) to team work. With this approach, each student in the group receives a mark based both on the overall “group mark” but also on the individual’s personal contribution towards the final product. This contribution is assessed directly by their peers, who are more aware of each team member’s contribution, and encourages self-reflection. However, the IPAC factor needs to be carefully assessed and applied. Following some initial work on the field, Pilar Garcia-Souto set up the IPAC Consortium whose ultimate goal is to “Identify a method for peer assessment of individual contribution in group work, develop or obtain an appropriate tool to implement it, and disseminate these across UCL and beyond; showing how to make the practice successful and efficient.” This consortium is currently formed by 40 members of staff from over 20 departments across UCL, and includes teaching staff in a range of fields (biomedical engineering, mechanical engineering, electrical engineering, physics, management, archaeology, architecture, culture, etc.), educational researchers (e.g. the Centre for Advanced Teaching and Learning, and the Institute of Education), and support staff (e.g. from the Digital Education and e-learning environment department). In this paper we will talk of our achievements so far and make recommendations for practitioners. In summary, this paper explores how a well-thought peer assessment method can aid students to develop critical thinking skills and allow academics to address group work assessment concerns, such that Research-based Education is more successful. Our approach is scalable and should appeal to anyone interested on incorporating or updating research-based education activities, regardless if you are designing a small activity within a module or a full programme of studies

An investigation of laboratory test methods for predicting the in-use leakage performance of urine-absorbing aids in nursing homes

The absorption before leakage method for measuring the absorption capacity of urine-absorbing aids was investigated. Along with the existing international standard (ISO 11948-1:1996, the Rothwell method), it was run on 12 experimental products whose in-use leakage performance was established by 55 incontinent nursing home residents. Methods were evaluated by considering their simplicity, their repeatability within - and their reproducibility between - six laboratories, and their correlation with in-use product performance. ISO 11948-1:1996 - which measures the absorption capacity of products under simple conditions - showed good repeatability and reproducibility, and reasonable correlation with in-use data. However, it proved blind to the effects of leg cuffs that conferred measurable benefits in real use. It should, therefore, be used with caution. The absorption before leakage method - which measures how much a product will hold before leakage when it is mounted on a manikin and standard aliquots of liquid are applied - is more complex and had poorer repeatability and reproducibility. However, it had stronger correlations with in-use data and successfully detected the benefits of leg cuffs on insert products. It is concluded that it holds potential as a new international standard to replace or complement ISO 11948-1:1996, and the necessary refinement work has been ongoing since the 2007 project described here. Two other laboratory methods were run opportunistically. A rewet method (Spanish national standard UNE 153601-2:2008) - for measuring the escape of fluid from a product under pressure - showed poor repeatability and reproducibility. Finally, an acquisition method was used to measure how quickly products absorbed two successive standard aliquots of liquid. It proved robust, showing good repeatability and reproducibility. Although measurements generally correlated well with in-use leakage performance, a direct causal link is unlikely. Products with high absorption capacity tend also to absorb quickly