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Pressure ulcers (PUs) and incontinence-associated dermatitis (IAD) are types of skin damage that result from prolonged exposure to external insults including pressure, shear, friction, and moisture. The clinical symptoms, which often lead to chronic wounds, can involve erythema, skin swelling, oedema and skin breakdown. It is imperative to detect early signs of these conditions prior to chronic damage. However, subjective visual and tactile skin assessments typically used by clinicians lack predictive capability. Objective biophysical approaches have been suggested to provide the means of monitoring the early signs of damage, although further evidence is required to establish their performance in a range of clinically relevant situations. The goal of the doctoral research is to utilise an array of non-invasive biophysical sensors to understand the pathophysiological changes in the skin following different insults associated with PUs and IAD. This thesis presents the results from a series of complimentary retrospective and prospective studies. These involved the analysis of established data from the host lab, a survey of skin damage resulting from the application of personal protective equipment (PPE), and two prospective lab-based studies. The former involved the recruitment of able-bodied volunteers and healthcare workers who were exposed to moisture and mechanical loads through incontinence pads and lying postures, and respirator protective equipment (RPE), respectively. These findings were used to inform a cohort study of hospitalised patients with stage I pressure ulcers. Results revealed that prolonged exposure of the skin to mechanical loads and moisture can disrupt its barrier function, as evidenced by enhanced values of trans-epidermal water loss and stratum corneum hydration. Furthermore, among the biophysical skin parameters evaluated, TEWL and hydration were able to distinguish between compromised and healthy adjacent skin sites, but not between different insults. During a COVID-19 study of adverse reactions to PPE, cohorts of healthcare workers revealed that they had indentation marks, pressure damage, itchiness, rashes, and spots. The subsequent study of biophysical changes in skin health identified distinct changes in skin barrier function and hydration over vulnerable bony landmarks on the face (bridge of the nose) associated with RPE application. Findings from this study showed that the outputs of these parameters were influenced by the subject extrinsic and intrinsic factors, namely body mass index and daily working hours. The final clinical study revealed highly localised changes (< 5mm) in skin barrier function over the pressure ulcer site. In contrast to the lab-based studies, skin hydration did not differentiate between healthy and damaged skin. Complementary analyses also revealed the important role of inflammatory cytokines in the early detection of skin compromise, as well as the potential of epidermal corneocytes as novel biomarkers reflective of changes in skin health. The use of biophysical tools to monitor local changes in skin health could represent an important adjunct to clinical practice, which currently relies on subjective skin assessment. However, to support its wider translation in different care settings, future research is required to analyse time-dependent changes in these parameters, in both acute and long-term care facilities, to assess the prognostic value when determining skin status (healing or progressing to wounds). In addition, engagement with healthcare workers to analyse the barriers and facilitators to adoption along with the cost-effectiveness of introducing these tools is needed prior to wider adoption in practice.

There are many clinical situations in which skin and soft tissues are subjected to sustained mechanical loading, particularly in individuals with restricted mobility. This can result in the breakdown of soft tissues in vulnerable areas, leading to the development of pressure ulcers (PUs). For several decades, interface pressure measuring systems have been employed to assess the magnitudes of pressures at the support surface interface of individuals at risk of developing PUs, typically to evaluate the short-term performance of pressure relieving systems (e.g. mattresses) and promote optimal postures. These technologies have recently been adapted to monitor over extended periods, providing the opportunity to estimate clinically-relevant temporal trends in posture and mobility. However, their ability to detect individual postural movements has not been established. Therefore, the present research was designed to assess the combination of pressure monitoring and intelligent data processing for the detection of postural changes during prolonged lying. A series of experimental studies utilised biomechanical parameters derived from pressure distribution and signals representative of body segmental movements using actimetry systems. Continuous measures were taken in cohorts of healthy individuals during evoked lying postures involving a raised head of the bed (HOB) and automated lateral tilt. The sensitivity and specificity of parameters for detecting changes in defined lying postures were examined. Data optimisation with Receiver Operating Characteristics (ROC) and Principal Component Analyses were performed to establish the most robust parameters, thus reducing the large volume of data associated with long-term monitoring. In particular, contact area and centre of pressure signals at specific body regions i.e. whole body and buttock, proved the most accurate of the interface pressure parameters, with ROC curve values (AUC) exceeding 0.5 for the majority of evoked postures. Signals derived from actimetry at the sternum also proved accurate in detecting postural movements, with the majority of postures revealing high AUC values. These parameters were combined with an automated detection method and machine learning algorithms to develop a robust methodology capable of predicting the frequency and magnitude of postural changes. The methodology was refined to accommodate a random sequence of postures on different support surfaces. The final automated methodology was then tested on pressure monitoring data from a small cohort of spinal cord injured subjects, who are vulnerable to PU development. Prediction of lying postural changes was achieved with a derivative threshold - based method, which yielded an accuracy of 100% when pressure signals were combined with body angles, and >85% for pressure signals in isolation. Prediction of lying postures was achieved by applying machine learning classifiers to either a combination of actimetry and pressure data or the pressure parameters in isolation. The most accurate combination of clinically relevant parameters involved pressure signals and body angles, achieving an average accuracy of ≥88%.The series of experiments and analytical approaches undertaken in this project contributed to the development of a semi-automated methodology based on robust biomechanical parameters for prediction of posture and mobility during prolonged lying. This was translated to a clinical data set, where long-term pressure monitoring was employed to evaluate previously unknown postures and provide the objective means to evaluate whether repositioning for pressure ulcer prevention adhered to international guidelines. Although further improvements are required for the analysis and visualisation of pressure data in clinical settings, this novel methodology has the potential to provide objective indication of posture and mobility which will inform effective personalised PU prevention.

It is well established that hospitalised neonates are at risk of iatrogenic skin damage. However, published prevalence and incidence rates vary, with the proportion of different types of damage unknown. It is unclear which factors act as barriers to and facilitators of skin care in this population. This motivated the aims of the thesis, which was to identify potential determinants of change related to the prevention of skin damage in neonatal units. In order to achieve this aim a multiphase mixed methods approach was adopted. This included an analysis of nursing staff practice and beliefs using a 19-part survey, a focus group with neonatal nurses, and interviews with lead Tissue Viability Nurses (TVNs). In addition, a prevalence and incidence study of all forms of skin damage on two neonatal intensive care units was conducted. The free text comments from the survey, the focus group, and the interviews were analysed using a thematic analysis approach informed by the determinants of change outlined in the Implementation of Change Model. This revealed concerns about damage from medical devices and diaper dermatitis. Participants reported that peer-to-peer learning represented their main source of skin education, and that balancing skin care with other clinical needs was challenging. It was also apparent that the unique nature of the neonatal unit acts as a barrier to reporting damage, involving outside specialists, and accurately classifying wounds. Prevalence data were collected from 54 neonates, 21 of whom presented with some form of skin damage (38.9%). Incidence data were collected from 51 neonates, 36 of whom developed some form of skin damage (70.6%). Of these, 23 neonates developed diaper dermatitis (45.1%), 23 developed damage associated with a medical device (45.1%), and four developed immobilityrelated pressure ulcers (7.8%). No single device was identified as the primary cause of devicerelated damage, with 12 of the 21 devices observed during the study noted to be associated with damage. Logistic regression analysis found that lower gestational age at birth was associated with an increased risk of developing both general skin damage and device-related damage. It was not, however, associated with an increased risk of developing diaper dermatitis. In summary, this thesis has improved our understanding of the issues and complications currently facing hospitalised neonates in relation to skin care. There are a number of clinical implications for these findings. Proposed practice changes include the introduction of skin rounds and 'skin champions', standardised guidelines for when damage should be escalated to TVNs, and training for neonatal nurses on wound assessment and classification. Proposed areas for future research include the development of medical devices that take into consideration the unique requirements of preterm skin. Further qualitative research is needed with healthcare professionals and parents focussing on the role and experiences of the wider care team. In conjunction with the findings of this thesis, these next steps will allow nurses and other professionals to better protect and promote skin health in these most vulnerable of patients.