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During the COVID-19 pandemic healthcare workers (HCWs) have used respiratory protective equipment for prolonged periods, which has been associated with detrimental effects on the underlying skin. The present study aims to evaluate changes in the main cells (corneocytes) of the stratum corneum (SC) following prolonged and consecutive use of respirators. 17 HCWs who wore respirators daily during routine hospital practice were recruited to a longitudinal cohort study. Corneocytes were collected via tape stripping from a negative control site (area outside the respirator) and from the cheek which was in contact with the device. Corneocytes were sampled on three occasions and analysed for the level of positive-involucrin cornified envelopes (CEs) and the amount of desmoglein-1 (Dsg1), as indirect measurements of immature CEs and corneodesmosomes (CDs), respectively. These were compared to biophysical measurements (Transepidermal water loss, TEWL, and SC hydration) at the same investigation sites. A large degree of inter-subject variability was observed, with maximum coefficients of variation of 43% and 30% for the level of immature CEs and Dsg1, respectively. Although it was observed that there was not an effect of prolonged respirator usage on the properties of corneocytes, the level of CDs was greater at the cheek than the negative control site (p < 0.05). Furthermore, low levels of immature CEs correlated with greater TEWL values after prolonged respirator application (p < 0.01). It was also noted that a smaller proportion of immature CEs and CDs was associated with a reduced incidence of self-reported skin adverse reactions (p < 0.001). This is the first study that investigated changes in corneocyte properties in the context of prolonged mechanical loading following respirator application. Although differences were not recorded over time, the levels of CDs and immature CEs were consistently higher in the loaded cheek compared to the negative control site and were positively correlated with a greater number of self-reported skin adverse reactions. Further studies are required to evaluate the role of corneocyte characteristics in the evaluation of both healthy and damaged skin sites. [ABSTRACT FROM AUTHOR]

Incontinence-associated dermatitis (IAD) is a painful complication in elderly patients, leading to reduced quality of life. Despite recent attention, its underlying inflammatory mechanisms remain poorly understood. This study was designed to quantify the release of inflammatory cytokines in a human model of IAD. The left volar forearm of ten healthy volunteers was exposed to synthetic urine and synthetic faeces for 2 h, simulating the effects of urinary and faecal incontinence, respectively, and the subsequent cytokine response compared to that of an untreated control site. Inflammatory cytokines were collected using both the Sebutape® absorption method and dermal microdialysis and quantified using immunoassays. Results from the former demonstrated an upregulation in IL-1α, IL-1RA and TNF-α. Synthetic urine caused a higher median increase in IL-1α from baseline compared to synthetic faeces, whereas synthetic faeces were associated with significantly higher median TNF-α levels compared to synthetic urine (p = 0.01). An increase in IL-1α/IL-1RA ratio was also observed with significant differences evident following exposure to synthetic urine (p = 0.047). Additionally, microdialysis revealed a time-dependent increase in IL-1β and IL-8 following exposure of up to 120 min to synthetic urine and synthetic faeces, respectively. This study demonstrated the suitability of both sampling approaches to recover quantifiable cytokine levels in biofluids for the assessment of skin status following exposure to synthetic fluids associated with incontinence. Findings suggest some differences in the inflammatory mechanisms of IAD, depending on moisture source, and the potential of the cytokines, IL-1α and TNF-α, as responsive markers of early skin damage caused by incontinence. • Inflammatory cytokines recovered in a human model of incontinence-associated dermatitis (IAD) using appropriate techniques. • Increased cytokine levels were evident following exposure to synthetic urine and synthetic faeces. • IL-1α and TNF-α could serve as responsive markers for early identification of skin damage caused by incontinence. • Longitudinal studies need to characterize the temporal relationship between cytokine release and IAD development. [ABSTRACT FROM AUTHOR]

Technologies have been developed to monitor changes in dermal oedema, indicative of the early signs of pressure ulcers. However, there is limited information on the effects of regional differences in tissue morphology on these sub-epidermal moisture (SEM) parameters. This study was designed to investigate the absolute SEM readings across different anatomical sites using a commercial device. Twenty-four healthy participants were recruited to evaluate basal SEM values at different bony prominences, sampled by an experienced operator. Distinct differences were observed in unloaded SEM values across different anatomical sites, notably between the upper and lower extremities. A high degree of variability was observed in particular sites, such as the heels. Moreover, SEM values at certain locations revealed significant relationships with age, BMI and gender (p < 0.05). The study revealed a high level of variability between and within anatomical sites in a healthy cohort of participants. Determining the changes in local skin and sub-dermal tissue status using SEM may require consideration of both site specific and individual demographic factors, with further research needed in cohorts at risk of pressure ulcers. • Influence of anatomical locations and demographics on baseline SEM values were examined. • Significant associations between basal SEM readings at selected locations and participant demographics were revealed. • The study suggests the use of site-specific thresholds to expand the utility of the technology. • The study will form the basis for further clinical studies to assess the effects of anatomical variability on SEM thresholds. [ABSTRACT FROM AUTHOR]

To examine the inter-practitioner variability of repositioning for pressure ulcer prevention, the effectiveness of the intervention, and whether the provision of written guidance influenced the repositioning technique. A pre-test post-test study design was utilised. Descriptive data regarding the work history of participants was collected. Participants were invited to reposition a healthy volunteer before and after reviewing guidance detailing the 30° side-lying technique. The researchers measured the resulting turn angles and assessed offloading of bony prominences. The repositioning technique varied considerably in the sample of nurse participants. Turn angles decreased following the guidance, but offloading of body sites vulnerable to pressure damage remained sporadic. Pressure ulcer prevention training should include practical demonstrations of repositioning. Clear guidance regarding the optimal repositioning technique for pressure ulcer prevention is needed. [ABSTRACT FROM AUTHOR]

Background Individuals with limited mobility can spend prolonged periods in leisure chairs, increasing their risk of developing a seated acquired pressure ulcer. The present study aims to use objective measures of posture and tissue viability to identify the associated risks of leisure chair related pressure ulcers. Methods Healthy participants (n = 13) were recruited to sit on a leisure chair with either a viscoelastic foam or air cushion. Participants were asked to adopt four different postures for a period of 10 min followed by a 10 min refractory period. Measurements at the leisure chair-participant interface included interface pressure, transcutaneous tissue gas tensions at the ischial tuberosities, accelerometer data collected from the sternum and subjective comfort levels. Results Results indicated that interface pressures remained consistent, with peak pressure index values of less than 60 mmHg across all conditions. A proportion of participants exhibited decreased oxygen tensions associated with increased carbon dioxide tensions during one or more test condition. This was particularly prevalent during the right lean posture on the air cushion (46%). In all cases, normal tissue viability was restored during standing. The accelerometer was able to detect significant changes (p < 0.05) in relative trunk angles during slump and right lean when compared to optimal sitting posture. Conclusion Commercially available leisure chairs have little evidence to support their pressure relieving properties. This study revealed that a proportion of healthy individuals demonstrated a compromised tissue viability in specific postures. Further research is required to assess the impact of these sitting conditions in vulnerable individuals. [ABSTRACT FROM AUTHOR]

Background Spinal immobilisation using a rigid long spineboard is a well-established procedure in trauma care. During immobilisation, the body is exposed to high tissue-interface pressures. This may lead to a localised inflammatory response of the skin, which may be used to monitor the body's response to different types of immobilisation device. Aim In this study we compared the standard rigid spineboard with a new soft-layered spineboard regarding tissue-interface pressures, skin redness as an indicator of reactive hyperaemia and cutaneous IL1α and lactate release. Methods Twelve healthy male participants were asked to lie supine on both a rigid and a soft-layered spineboard, loading the sacrum for one hour, followed by one hour in unloaded position. Tissue-interface pressures on the buttocks during loading were measured continuously using a pressure mapping mat. Cutaneous IL1α and lactate concentrations were assessed using Sebutapes, during 20-min periods. After each 20-min period, a photo of the buttocks was taken, which was later assessed for redness by two observers. Results Significant differences in tissue-interface pressure and reactive hyperaemia were found between the two types of spineboard. Release of IL1α and lactate were found to increase with prolonged exposure to pressure, and to decrease in the unloaded prone position. A significant relationship was found between tissue-interface pressure and reactive hyperaemia, but not with IL1α nor lactate release. Time course of IL1α and lactate release was similar for both types of spineboard. Conclusions IL1α and lactate both have a strong relationship with pressure exposure time, but not with pressure magnitude. Furthermore, IL1α was measured even in the absence of visible redness of the skin. The study offers the potention of biomarkers, reflecting inflammation and/or tissue metabolism, for use in assessing the effects of prolonged spineboard support. [ABSTRACT FROM AUTHOR]

Introduction Although measuring vasti muscle onset may reveal whether pain relief is associated with altering this parameter during activities in subjects with patellofemoral pain syndrome (PFPS), it may be necessary to determine whether the inherent properties of the dominant leg influences the reliability of measuring VMO-VL muscle onset. The aim of the present study was to examine the effect of leg predomination on reliability testing of the VMO-VL muscle onset measurement during single leg squatting in healthy subjects. Methods The onset of VMO and VL muscles of ten healthy subjects with a right dominant leg was assessed during single leg squatting. Data was collected from the muscle bellies of the VMO and VL. This procedure was performed on the both legs, during three separate single leg squats from a neutral position to a depth of approximately 30° of knee flexion. Subjects were then asked to repeat the test procedure after a minimum of a week's interval. The full wave rectified onsets of VMO and VL were then calculated. Results There was no significant difference between the VMO-VL onset mean values of paired test of right and left knees. The ICC (intra class correlation coefficient) values during within and between sessions tests showed the poor reliability of these measurements on both knees. Conclusion The low intratester reliability of within and between sessions measurement of VMO-VL onset on the both dominant and non-dominant legs revealed that repeatability of these measurements have little accepted reliability, however similar values of these measurements indicated that leg predomination does not affect the measurements during single leg squatting. [ABSTRACT FROM AUTHOR]

Summary Introduction Although measuring vasti muscle activity may reveal whether pain relief is associated with altering this parameter during functional activities in subjects with patellofemoral pain syndrome (PFPS), it may be necessary to determine whether the inherent properties of the dominant leg influences the reliability of measuring VMO/VL amplitude. The aim of the present study was to examine the effect of leg predomination on reliability testing of the VMO/VL amplitude measurement during single leg squatting in healthy subjects. Methods Using an electromyography (EMG) unit, the ratio amplitudes of VMO and VL muscles of ten healthy subjects with a right dominant leg was assessed during single leg squatting. Data was collected from two silver–silver surface electrodes placed over the muscle bellies of the VMO and VL. This procedure was performed on the both right and left legs, during three separate single leg squats from a neutral position to a depth of approximately 30° of knee flexion. Subjects were then asked to repeat the test procedure after a minimum of a week's interval. The amplitude of VMO and VL were then calculated using root mean square (RMS). Results There was no significant difference between the VMO/VL amplitude mean values of paired test of right (mean, SD of 0.85, 0.10) and left knees (mean, SD of 0.82, 0.10) (p > 0.05). The CV (coefficient of variation) values during within and between session tests, revealed the high repeatability and reproducibility of VMO/VL amplitude measurements on both knees. The ICC (intra class correlation coefficient) values during within and between sessions tests showed the high reliability of these measurements on both knees. Conclusion The high reliability of VMO/VL amplitude measurements on both dominant and non-dominant legs of healthy subjects suggests that the VMO/VL amplitude measurement would not be influenced by the leg predomination during single leg squatting. [ABSTRACT FROM AUTHOR]

Objective Impaired lymph formation and clearance has previously been proposed as a contributory factor in the development of pressure ulcers. The present study has been designed to trial fluorescence lymphangiography for establishing how lymphatic function is altered under a clinically relevant form of mechanical loading. Methods Lymph formation and clearance was traced in both forearms by an intradermal injection of indocyanine green (ICG) (50 μl, 0.05%w/v), imaged using a commercial near-infrared fluorescence imaging unit (Fluobeam ® 800). External uniaxial loading equivalent to a pressure of 60 mmHg was applied for 45 min in one arm using a custom-built indenter. Results Loading was associated with a decreased frequency of normal directional drainage (DD) of ICG within delineated vessels, both immediately after loading and 45 min thereafter. Loading was also associated with non-directional drainage (NDD) of ICG within the interstitium. Signal intensity within NDD was often greatest at areas of stress concentration, producing a ‘halo pattern’, corresponding to the rounded edges of the indenter. Conclusions These results suggest that loading skin with a clinically relevant magnitude of pressure alters both lymph formation and clearance. Further work to quantify impaired clearance under mechanical loading could provide valuable insight into their involvement in the development of pressure ulcers. [ABSTRACT FROM AUTHOR]

Delivering a drug into and through the skin is of interest as the skin can act as an alternative drug administration route for oral delivery. The development of new delivery methods, such as microneedles, makes it possible to not only deliver small molecules into the skin, which are able to pass the outer layer of the skin in therapeutic amounts, but also macromolecules. To provide insight into the administration of these molecules into the skin, the aim of this study was to assess the transport of macromolecules within and between its various layers. The diffusion coefficients in the epidermis and several locations in the papillary and reticular dermis were determined for fluorescein dextran of 40 and 500 kDa using a combination of fluorescent recovery after photobleaching experiments and finite element analysis. The diffusion coefficient was significantly higher for 40 kDa than 500 kDa dextran, with median values of 23 and 9 µm 2 /s in the dermis, respectively. The values only marginally varied within and between papillary and reticular dermis. For the 40 kDa dextran, the diffusion coefficient in the epidermis was twice as low as in the dermis layers. The adopted method may be used for other macromolecules, which are of interest for dermal and transdermal drug delivery. The knowledge about diffusion in the skin is useful to optimize (trans)dermal drug delivery systems to target specific layers or cells in the human skin. [ABSTRACT FROM AUTHOR]

Abstract: Physiological loading is essential for the maintenance of articular cartilage by regulating tissue remodelling, in the form of both catabolic and anabolic processes. To promote the development of tissue engineered cartilage which closely matches the long term functionality of native tissue, bioreactors have been developed to provide a combination of loading modalities, which reflect the nature of normal physiological loads. This study describes the design and validation of an in vitro mechanical system for the controlled application of bi-axial loading regimes to chondrocyte-seeded agarose constructs. The computer-controlled system incorporates a robust gripping system, which ensures the delivery of precise values of cyclic compressive and shear strain to 3D cell-seeded constructs. Sample prototypes were designed, optimised using finite element analysis and validated performing compressive and shear fatigue mechanical tests. The horizontal and vertical displacements within the bioreactor are precisely controlled by a dedicated programme that can be easily implemented. The synchronisation of the orthogonal displacements was shown to be accurate and reproducible. Constructs were successfully loaded with a combined compressive and shear loading regimen at 1Hz for up to 48h with no appreciable loss of cell viability or mechanical integrity. These features along with the demonstrated high consistency make the system ideally suitable for a systematic investigation of the response of chondrocytes to a complex physiologically relevant deformation profile. [Copyright &y& Elsevier]

Summary: Introduction: Measuring vasti muscles activity may provide reliable evidence for patellar taping to correct probable malalignment in subjects with patellofemoral pain syndrome (PFPS). The aim of present study was to examine the reliability of vasti activity measurements in different patellofemoral conditions during squatting in healthy subjects. Methods: Using an electromyography (EMG) unit, the ratio amplitudes and onsets of VMO and VL muscles of twelve healthy subjects were assessed during single leg squatting. Data was collected from surface electrodes placed over the muscle bellies of the VMO and VL. This procedure was performed on the right knees, before (BT), during (WT) and shortly after patellar taping (SAT). Results: While the CV (coefficient of variation), ICC (intra class correlation coefficient), LSD (least significant difference) and SEM (standard error of measurement) values revealed the high reliability of the VMO/VL amplitude measurements during single leg squatting (p < 0.05), the related values demonstrated poor to moderate reliability of VMO-VL onset measurements during the similar activity (p > 0.05). Conclusion: Reliability tests conducted during the current study showed that, while the relative amplitude of vasti could be used as highly reliable parameter, the muscle onsets of vasti had poor to moderate reliability. [Copyright &y& Elsevier]

Summary: Introduction: Although measuring patellofemoral joint reaction forces (PFJRF) may provide reliable evidence for conservative treatments to correct probable malalignment in subjects with patellofemoral pain syndrome (PFPS), it may be necessary to determine whether the inherent properties of the dominant leg influences the reliability of measuring PFJRF. The aim of the present study was to examine the effect of leg predomination on reliability testing of the PFJRF measurement during single leg squatting in healthy subjects. Methods: Using a motion analysis system and one force plate, PFJRF of 10 healthy subjects with a right dominant leg was assessed during single leg squatting. Data was collected from superficial markers taped to selected landmarks. This procedure was performed on the both right and left legs, during three separate single leg squats from a neutral position to a depth of approximately 30° of knee flexion. Subjects were then asked to repeat the test procedure after a minimum of a week’s interval. The PFJRF was calculated using a biomechanical model of the patellofemoral joint. Results: There was significant difference between the PFJRF mean values of paired test of right (mean, SD of 1887.7, 325.1 N) and left knees (mean, SD of 2022.6, 270.5 N) (p < 0.05). The CV (coefficient of variation) values during within and between session tests, revealed the high repeatability and reproducibility of PFJRF measurements on both knees. The ICC (intra class correlation coefficient) values during within and between sessions tests showed the high reliability of these measurements on both knees. Conclusion: The high reliability of PFJRF measurements on both dominant and non-dominant legs of healthy subjects suggests that the PFJRF measurement would not be influenced by the leg predomination during single leg squatting. [Copyright &y& Elsevier]

Summary: Introduction: Anterior knee pain or patellofemoral pain syndrome (PFPS) is supposed to be related to patellofemoral joint reaction forces (PFJRF). Measuring these forces may therefore provide reliable evidence for conservative treatments to correct probable malalignment in subjects with PFPS. The aim of the present study was to examine the reliability of PFJRF measurements during double-legged squatting in healthy subjects. Methods: Using a motion analysis system and one forceplate, PFJRF of 10 healthy subjects were assessed during double-legged squatting. Data were collected from superficial markers taped to selected landmarks. This procedure was performed on the right knees, at three different knee flexion angles of 30, 45 and 60° during three separate double-legged squats. Subjects were then requested to repeat this test procedure on two separate test sessions at different occasions. The PFJRF was calculated using a biomechanical model of the patellofemoral joint. Results: The data reveal an increase in PFJRF values (from mean, SD of 425.2, 35.5N to 1075.4, 70.1N)with an increase in the tibiofemoral joint angle during double-legged squatting. The CV (coefficient of variation) values during within and between session tests, revealed the high repeatability and reproducibility of PFJRF measurements, while the ICC (intra class correlation coefficient) values showed the low reliability of these measurements. Conclusion: The low reliability of PFJRF measurements suggests that the PFJRF measurement during double-legged squatting should be performed with caution with improving the method of kinetic measurement of the patellofemoral joint in healthy subjects. [Copyright &y& Elsevier]

Abstract: The complex tri-layered structure of the aortic valve (AV) results in anisotropic quasi–static mechanical behaviour. However, its influence on AV viscoelasticity remains poorly understood. Viscoelasticity may strongly influence AV dynamic mechanical behaviour, making it essential to characterise the time-dependent response for designing successful substitutes. This study attempts to characterise the time-dependent behaviour of the AV at different strain and load increments, and to gain insight into the contribution of the microstructure to this behaviour. Uniaxial incremental stress-relaxation and creep experiments were undertaken, and the experimental data analysed with a generalised Maxwell model, to determine the characteristic time-dependent parameters. Results showed that the time dependent response of the tissue differed with the loading direction, and also with the level of applied load or strain, in both stress-relaxation and creep phenomena. Both phenomena were consistently more pronounced in the radial loading direction. Fitting of the Maxwell model highlighted that the time dependent modes required to model the data also varied in different increments, and additionally with the loading direction. These results suggest that different micro-structural mechanisms may be activated in stress-relaxation and creep, determined by the microstructural organisation of the valve matrix in each loading direction, at each strain or load increment. [Copyright &y& Elsevier]

Summary: Introduction: Measuring patellofemoral joint reaction forces (PFJRF) may provide reliable evidence for patellar taping to correct probable malalignment in subjects with anterior knee pain, or patellofemoral pain syndrome (PFPS). The aim of the present study was to examine the reliability of PFJRF measurements in different patellofemoral conditions during squatting in healthy subjects. Methods: Using a motion analysis system and one forceplate, PFJRF of eight healthy subjects was assessed during single leg squatting. Data was collected from superficial markers taped to selected landmarks. This procedure was performed on the right knees, before (BT), during (WT) and shortly after patellar taping (SAT). The PFJRF was calculated using a biomechanical model of the patellofemoral joint. Results: The results revealed that, there were no significant differences between the PFJRF mean values for three conditions of BT (2100.55 ± 455.25), WT (2026.20 ± 516.45) and SAT (2055.35 ± 669.30) (p > 0.05). The CV (coefficient of variation), ICC (intra class correlation coefficient), LSD (least significant difference) and SEM (standard error of measurement) values revealed the high reliability of PFJRF measurements during single leg squatting (p < 0.05). Conclusion: The high reliability of PFJRF measurements reveals that the future studies could rely on these measurements during single leg squatting. [Copyright &y& Elsevier]

Summary: Introduction: The mechanisms of pain reduction have not completely been established following patellar taping in subjects with patellofemoral pain syndrome (PFPS); although it might be related to alteration in the kinetics of the patellofemoral joint. Methods: Patellofemoral Joint Reaction Force (PFJRF) of eighteen subjects with PFPS and eighteen healthy subjects as controls were assessed by a motion-analysis system and one force plate. This procedure was performed on the affected knee of subjects with PFPS, before, during and finally after patellar taping during unilateral squatting. A similar procedure was also performed on the unaffected knees of both groups. Results: The mean values of PFJRF prior to taping (2025N, SD 347N) were decreased significantly following a period of taping (1720N, SD 303N) (P <0.05). There were no significant differences between the mean values of PFJRF among controls (1922N, SD 398N) and subjects with PFPS prior to taping (P >0.05) which might be due to small sample size in both groups and large variability observed in the study. Interpretation: Decreased values of PFJRF may explain the mechanism of pain reduction following patellar taping in subjects with PFPS. [Copyright &y& Elsevier]

Abstract: Stekelenburg A, Gawlitta D, Bader DL, Oomens CW. Deep tissue injury: how deep is our understanding? Deep pressure ulcers, necessarily involving deep tissue injury (DTI), arise in the muscle layers adjacent to bony prominences because of sustained loading. They represent a serious type of pressure ulcer because they start in underlying tissues and are often not visible until they reach an advanced stage, at which time treatment becomes problematic. Underlying mechanisms of DTI require further investigation if appropriate preventive measures are to be determined. The present commentary illustrates a hierarchic research approach selected to study these mechanisms. To differentiate between the individual roles of deformation and ischemia in the onset of skeletal muscle damage, 2 complementary approaches have been selected. In an in vivo animal model, the effects of ischemia combined with deformation and ischemia per se were studied. An in vitro muscle model was used to study the separate effects of deformation and several aspects of ischemia, including hypoxia, glucose depletion, and tissue acidification, in more detail. Based on the results of both models a sequence of events leading to cell necrosis is proposed. Deformation levels exceeding a threshold value can result in rapid tissue damage that may persist, whereas ischemia has a more gradual effect as a result of glucose depletion and tissue acidification. [Copyright &y& Elsevier]

Abstract: Tendon is multi-level fibre composite material, responsible for the transmission of forces from muscles to the skeleton. It is composed of a hierarchical arrangement of collagenous units surrounded by a proteoglycan-rich matrix, arranged to support strain transfer, and thus contribute to the mechanical behaviour of tendon. This study examines the effect of swelling and enzymatic degradation on structural integrity at different levels of the tendon hierarchy. Biochemical and microstructural analysis are used to examine the effects of incubation on the composition and swelling of the matrix, prior to a mechanical characterisation of sample integrity. Results indicated significant swelling of tendon fibrils and interfibrillar matrix after incubation in phosphate buffered saline, leading to a reduction in ultimate tensile load, with failure initiated between fibrils and sub-fibrils. In contrast, incubation with the enzyme chondroitinase ABC resulted in a total removal of glycosaminoglycan from the samples, and a subsequent reduction in the extent of swelling. These fascicles also demonstrated an increase in failure loads, with failure predominating between fibres. The findings from this work confirm the importance of the non-collagenous matrix components in controlling strain transfer within tendon structures. It also highlights the necessity to maintain samples within a suitable and controlled environment prior to testing. [Copyright &y& Elsevier]

Mechanical conditioning has been widely used to attempt to enhance chondrocyte metabolism for the evolution of functionally competent cartilage. However, although upregulation of proteoglycans have been reported through the application of uniaxial compression, minimal collagen has been produced. The study is designed to examine whether alternative loading regimens, equivalent to physiological conditions, involving shear in addition to compression can enhance collagen production. Finite element models were developed to determine how the local chondrocyte environments within agarose constructs were influenced by a range of static and dynamic loading regimens. 3-D poro-viscoelastic models were validated against experimental data. In particular, these models were used to characterise chondrocyte deformation in compression with and without shear superimposed, with special reference to the formation of pericellular matrix around the cells. The models of the hydrogel constructs under stress relaxation and dynamic cyclic compression conditions were highly correlated with the experimental data. The cell deformation (y / z) in the constructs was greatest in the centre of the constructs, increasing with magnitude of compression up to 25%. The superposition of shear however did not produce significant additional changes in deformation, with the presence of PCM reducing the chondrocyte deformation. The use of FE models can prove important in the definition of appropriate, optimised mechanical conditioning regimens for the synthesis and organisation of mature extra cellular matrix by chondrocyte-seeded constructs. They will also provide insight into the mechanisms relating cell deformation to mechanotransduction pathways, thereby progressing the development of functionally competent tissue engineered cartilage. • FE models can predict chondrocyte deformation in constructs under static and dynamic loading. • Superposition of shear on compression does not produce significant changes in cell deformation. • Pericellular matrix resulting from cell activity reduces chondrocyte deformation. • Modelling highlights the importance of cell deformation in mechanotransduction pathways. • Modelling offers the potential of optimising the development of functional cartilage. [ABSTRACT FROM AUTHOR]

• Interface pressures can be monitored over prolonged periods to establish spatial trends in the biomechanical interactions between individuals and their support surface. • Signals from pressure monitoring systems can be used as a surrogate for movements. • The relative position of the individual influences the sensitivity and specificity of these pressure signals to detect movement. • The combination of actimetry and pressure monitoring could provide a robust methodology to inform clinical practice regarding pressure ulcer prevention regimens. Pressure mapping systems have been traditionally used to assess load distributions in individuals at risk of pressure ulcers. Recently, the technology has been adapted to monitor pressures over prolonged periods. The present study aims to investigate the predictive ability of selected biomechanical parameters estimated from pressure distributions for detecting postural changes in lying. Healthy participants (n = 11) were recruited and positioned in different lying postures, by utilizing the head of bed (HOB) angle and an automated tilting system to achieve evoked movements in the sagittal and transverse planes, respectively. Measurements included continuous monitoring of interface pressures and accelerations from the trunk and waist. Selected interface pressure parameters included; centre of pressure, contact area and pressure gradient. A threshold range for all parameters was established and Receiver Operating Characteristic (ROC) curves presented to determine the sensitivity and specificity for detecting postural changes. Temporal trends in the data revealed significant variance in the signal perturbations during each evoked postural change. Indeed, sensitivity and specificity were influenced by the specific threshold values and the relative position of the individual. As an example, sensitivity of some parameters exhibited a compromised trend at higher HOB angles, with low corresponding area under the ROC curve. By contrast, contact area provided the highest values, with 7/12 signals achieve AUC >0.5. This corresponded with actimetry signals, which provided high discrimination between postures. Parameters estimated from a commercial pressure monitoring can have the potential to detect postural changes. Further research is required to convert the data into meaningful clinical information, to inform patient repositioning strategies. [ABSTRACT FROM AUTHOR]

Discrete element models have often been the primary tool in investigating and characterising the viscoelastic behaviour of soft tissues. However, studies have employed varied configurations of these models, based on the choice of the number of elements and the utilised formation, for different subject tissues. This approach has yielded a diverse array of viscoelastic models in the literature, each seemingly resulting in different descriptions of viscoelastic constitutive behaviour and/or stress-relaxation and creep functions. Moreover, most studies do not apply a single discrete element model to characterise both stress-relaxation and creep behaviours of tissues. The underlying assumption for this disparity is the implicit perception that the viscoelasticity of soft tissues cannot be described by a universal behaviour or law, resulting in the lack of a unified approach in the literature based on discrete element representations. This paper derives the constitutive equation for different viscoelastic models applicable to soft tissues with two characteristic times. It demonstrates that all possible configurations exhibit a unified and universal behaviour, captured by a single constitutive relationship between stress, strain and time as: σ + A σ ̇ + B σ ¨ = P ε ̇ + Q ε ¨ . The ensuing stress-relaxation G ( t ) and creep J ( t ) functions are also unified and universal, derived as G ( t ) = c 1 e − A + A 2 − 4 B 2 B t + ( σ 0 − c 1 ) e − A − A 2 − 4 B 2 B t and J ( t ) = c 2 + ( ε 0 − c 2 ) e - P Q t + σ 0 P t , respectively. Application of these relationships to experimental data is illustrated for various tissues including the aortic valve, ligament and cerebral artery. The unified model presented in this paper may be applied to all tissues with two characteristic times, obviating the need for employing varied configurations of discrete element models in preliminary investigation of the viscoelastic behaviour of soft tissues. [ABSTRACT FROM AUTHOR]

Abstract: Deep tissue injury (DTI) is a severe pressure ulcer that results from sustained deformation of muscle tissue overlying bony prominences. In order to understand the etiology of DTI, it is essential to determine the tolerance of muscle cells to large mechanical strains. In this study, a new experimental method of determining the time-dependent critical compressive strains for necrotic cell death in a planar tissue-engineered construct under static loading was developed. A half-spherical indentor is used to induce a non-uniform, concentric distribution of strains in the construct, and is calculated from the radius of the damage region in the construct versus time. The method was employed to obtain for bio-artificial muscles (BAMs) cultured from C2C12 murine cells, as a model system for DTI. Specifically, propidium iodine was used to fluorescently stain the development of necrosis in BAMs subjected to strains up to 80%. Two groups of BAMs were tested at an extracellular pH of 7.4 (n=10) and pH 6.5 (n=5). The lowest strain levels causing cell death in the BAMs were determined every 15min, during 285-min-long trials, from confocal microscopy fluorescent images of the size of the damage regions. The experimental data fitted a decreasing single-step sigmoid of the Boltzmann type. Analysis of the parameters of this sigmoid function indicated a 95% likelihood that cells could tolerate engineering strains below 65% for 1h, whereas the cells could endure strains below 40% over a 285min trial period. The decrease in endurance of the cells to compressive strains occurred between 1–3h post-loading. The method developed in this paper is generic and suitable for studying E zz c(t) in virtually any planar tissue-engineered construct. The specific curve obtained herein is necessary for extrapolating biological damage from muscle-strain data in biomechanical studies of pressure ulcers and DTI. [Copyright &y& Elsevier]

• Continuous pressure monitoring provides a robust means for detection of postural movements. • Movements detection was achieved by combining pressure parameters and intelligent processing. • Posture and mobility were successfully detected in a cohort of Spinal Cord Injured patients. • The novel algorithm could offer the potential for targeted interventions for pressure ulcer prevention. Pressure mapping technologies provide the opportunity to estimate trends in posture and mobility over extended periods in individuals at risk of developing pressure ulcers. The aim of the study was to combine pressure monitoring with an automated algorithm to detect posture and mobility in a vulnerable population of Spinal Cord Injured (SCI) patients. Pressure data from able-bodied cohort studies involving prescribed lying and sitting postures were used to train the algorithm. This was tested with data from two SCI patients. Variations in the trends of the centre of pressure (COP) and contact area were assessed for detection of small- and large-scale postural movements. Intelligent data processing involving a deep learning algorithm, namely a convolutional neural network (CNN), was utilised for posture classification. COP signals revealed perturbations indicative of postural movements, which were automatically detected using individual- and movement-specific thresholds. CNN provided classification of static postures, with an accuracy ranging between 70-84% in the training cohort of able-bodied subjects. A clinical evaluation highlighted the potential of the novel algorithm to detect postural movements and classify postures in SCI patients. Combination of continuous pressure monitoring and intelligent algorithms offers the potential to objectively detect posture and mobility in vulnerable patients and inform clinical-decision making to provide personalized care. [ABSTRACT FROM AUTHOR]

Abstract Background Deep tissue injury is a type of pressure ulcer which originates subcutaneously due to sustained mechanical loading. The relationship between mechanical compression and damage development has been extensively studied in 2D. However, recent studies have suggested that damage develops beyond the site of indentation. The objective of this study was to compare mechanical loading conditions to the associated damage in 3D. Methods An indentation test was performed on the tibialis anterior muscle of rats (n = 39). Changes in the form of oedema and structural damage were monitored with MRI in an extensive region. The internal deformations were evaluated using MRI based 3D finite element models. Findings Damage propagates away from the loaded region. The 3D analysis indicates that there is a subject specific tolerance to compression induced deep tissue injury. Interpretation Individual tolerance is an important factor when considering the mechanical loading conditions which induce damage. Highlights • Damage propagates away from the loaded regions in compression induced deep tissue injury. • There is an individual tolerance to mechanically induced damage. • Factors other than mechanical loading can influence damage development in deep tissue injury. [ABSTRACT FROM AUTHOR]

The bespoke interface between a lower limb residuum and a prosthetic socket is critical for an amputee's comfort and overall rehabilitation outcomes. Analysis of interface kinematics and kinetics is important to gain full understanding of the interface biomechanics, which could aid clinical socket fit, rehabilitation and amputee care. This pilot study aims to investigate the dynamic correlation between kinematic movement and kinetic stresses at the interface during walking tests on different terrains. One male, knee disarticulation amputee participated in the study. He was asked to walk on both a level surface and a 5° ramped surface. The movement between the residuum and the socket was evaluated by the angular and axial couplings, based on the outputs from a 3D motion capture system. The corresponding kinetic stresses at anterior-proximal (AP), posterior-proximal (PP) and anterior-distal (AD) locations of the residuum were measured, using individual stress sensors. Approximately 8° of angular coupling and up to 32 mm of axial coupling were measured when walking on different terrains. The direction of the angular coupling shows strong correlation with the pressure difference between the PP and AP sensors. Higher pressure was obtained at the PP location than the AP location during stance phase, associated with the direction of the angular coupling. A strong correlation between axial coupling length, L , and longitudinal shear was also evident at the PP and AD locations i.e. the shortening of L corresponds to the increase of shear in the proximal direction. Although different terrains did not affect these correlations in principle, interface kinematic and kinetic values suggested that gait changes can induce modifications to the interface biomechanics. It is envisaged that the reported techniques could be potentially used to provide combined kinematics and kinetics for the understanding of biomechanics at the residuum/socket interface, which may play an important role in the clinical assessment of prosthetic component settings, including socket fit quality. [ABSTRACT FROM AUTHOR]

Design and fitting of artificial limbs to lower limb amputees are largely based on the subjective judgement of the prosthetist. Understanding the science of three-dimensional (3D) dynamic coupling at the residuum/socket interface could potentially aid the design and fitting of the socket. A new method has been developed to characterise the 3D dynamic coupling at the residuum/socket interface using 3D motion capture based on a single case study of a trans-femoral amputee. The new model incorporated a Virtual Residuum Segment (VRS) and a Socket Segment (SS) which combined to form the residuum/socket interface. Angular and axial couplings between the two segments were subsequently determined. Results indicated a non-rigid angular coupling in excess of 10° in the quasi-sagittal plane and an axial coupling of between 21 and 35 mm. The corresponding angular couplings of less than 4° and 2° were estimated in the quasi-coronal and quasi-transverse plane, respectively. We propose that the combined experimental and analytical approach adopted in this case study could aid the iterative socket fitting process and could potentially lead to a new socket design. [ABSTRACT FROM AUTHOR]

Background Individuals who have reduced mobility are at risk of developing pressure ulcers if they are subjected to sustained static postures. To reduce this risk, clinical guidelines advocate healthcare professionals reposition patients regularly. Automated tilting mechanisms have recently been introduced to provide periodic repositioning. This study compared the performance of such a prototype mattress to conventional manual repositioning. Methods Ten healthy participants (7 male and 3 female, aged 23–66 years) were recruited to compare the effects of an automated tilting mattress to standard manual repositioning, using the 30° tilt. Measures during the tilting protocols (supine, right and left tilt) included comfort and safety scores, interface pressures, inclinometer angles and transcutaneous gas tensions (sacrum and shoulder). Data from these outcomes were compared between each protocol. Findings Results indicated no significant differences for either interface pressures or transcutaneous gas responses between the two protocols ( P > 0.05 in both cases). Indeed a small proportion of participants (~ 30%) exhibited changes in transcutaneous oxygen and carbon dioxide values in the shoulder during a right tilt for both protocols. The tilt angles at the sternum and the pelvis were significantly less in the automated tilt compared to the manual tilt (mean difference = 9.4–11.5°, P < 0.001). Participants reported similar comfort scores for both protocols, although perceived safety was reduced on the prototype mattress. Interpretation Although further studies are required to assess its performance in maintaining tissue viability, an automated tilting mattress offers the ability to periodically reposition vulnerable individuals, with potential economic savings to health services. [ABSTRACT FROM AUTHOR]

Abstract: Sustained mechanical loading of skeletal muscle may result in the development of a severe type of pressure ulcer, referred to as deep tissue injury. Recently it was shown that the diffusion of large molecules (10–150kDa) is impaired during deformation of tissue-engineered skeletal muscle, suggesting a role for impaired diffusion in the aetiology of deep tissue injury. However, the influence of deformation on diffusion of smaller molecules on its aetiology is less clear. This motivated the present study designed to investigate the influence of deformation of skeletal muscle on the diffusion of water, which can be measured with diffusion tensor magnetic resonance imaging (MRI). It could be predicted that this approach will provide valuable information on the diffusion of small molecules. Additionally the relationship between muscle temperature and diffusion was investigated. During deformation of the tibialis anterior a decrease of the apparent diffusion coefficient (ADC) was observed (7.2±3.9%). The use of a finite element model showed that no correlation existed between the maximum shear strain and the decrease of the ADC. The ADC in the uncompressed gastrocnemius muscle decreased with 5.9±3.7%. In an additional experiment a clear correlation was obtained between the decrease of the ADC and the relative temperature change of skeletal muscle tissue as measured by MRI. Taken together, it was concluded that (1) the decreased diffusion of water was not a direct effect of tissue deformation and (2) that it is likely that the observed decreased ADC during deformation was a result of a decreased muscle temperature. The present study therefore provides evidence that diffusion of small molecules, particularly oxygen and carbon dioxide, is not impaired during deformation of skeletal muscle tissue. [Copyright &y& Elsevier]

Abstract: Pressure-related deep tissue injury (DTI) represents a severe pressure ulcer, which initiates in compressed muscle tissue overlying a bony prominence and progresses to more superficial tissues until penetrating the skin. Individual subjects with impaired motor and/or sensory capacities are at high risk of developing DTI. Impaired diffusion of critical metabolites in compressed muscle tissue may contribute to DTI, and impaired diffusion of tissue damage biomarkers may further impose a problem in developing early detection blood tests. We hypothesize that compression of muscle tissue between a bony prominence and a supporting surface locally influences the diffusion capacity of muscle. The objective of this study was therefore, to determine the effects of large compression strains on free diffusion in a tissue-engineered skeletal muscle model. Diffusion was measured with a range of fluorescently labeled dextran molecules (10, 20, 150kDa) whose sizes were representative of both hormones and damage biomarkers. We used fluorescence recovery after photobleaching (FRAP) to compare diffusion coefficients (D) of the different dextrans between the uncompressed and compressed (48–60% strain) states. In a separate experiment, we simulated the effects of local partial muscle ischemia in vivo, by reducing the temperature of compressed specimens from 37 to 34°C. Compared to the D in the uncompressed model system, values in the compressed state were significantly reduced by 47±22% (p<0.02). A 3°C temperature decrease further reduced D in the compressed specimens by 10±6% (p<0.05). In vivo, the effects of large strains and ischemia are likely to be summative, and hence, the present findings suggest an important role of impaired diffusion in the etiology of DTI, and should also be considered when developing biochemical screening methods for early detection of DTI. [Copyright &y& Elsevier]

Pressure mapping technology has been adapted to monitor over prolonged periods to evaluate pressure ulcer risk in individuals during extended lying postures. However, temporal pressure distribution signals are not currently used to identify posture or mobility. The present study was designed to examine the potential of an automated approach for the detection of a range of static lying postures and corresponding transitions between postures. Healthy subjects (n = 19) adopted a range of sagittal and lateral lying postures. Parameters reflecting both the interactions at the support surface and body movements were continuously monitored. Subsequently, the derivative of each signal was examined to identify transitions between postures. Three machine learning algorithms, namely Naïve-Bayes, k-Nearest Neighbors and Support Vector Machine classifiers, were assessed to predict a range of static postures, established with a training model (n = 9) and validated with new input from test data (n = 10). Results showed that the derivative signals provided a means to detect transitions between postures, with actimetry providing the most distinct signal perturbations. The accuracy in predicting the range of postures from new test data ranged between 82%–100%, 70%–98% and 69%–100% for Naïve-Bayes, k-Nearest Neighbors and Support Vector Machine classifiers, respectively. The present study demonstrated that detection of both static postures and their corresponding transitions was achieved by combining machine learning algorithms with robust parameters from two monitoring systems. This approach has the potential to provide reliable indicators of posture and mobility, to support personalised pressure ulcer prevention strategies. • Actimetry and pressure monitoring signals accurately detected postural movements • Classification of lying postures was achieved using machine learning algorithms • This approach has the potential to provide indicators of posture and mobility. [ABSTRACT FROM AUTHOR]