107 results found
Pandelani T, Masouros SD, Calvo-Gallego JL, 2023, Application of quasi-linear viscoelasticity for the characterisation of human buttocks adipose tissue, Pages: 315-319
The mechanical properties of the human buttocks adipose tissue were investigated theoretically. The material properties obtained from the stress relaxation test were fitted to with a new algorithm using Fung’s quasilinear viscoelastic (QLV) model with Prony series in conjunction with a hyperelastic model. The model was applied to fit the stress-time data during both the ramp and relaxation phases. By using the material properties obtained from the stress relaxation test, a numerical model was developed and the data from the model was fitted to Polynomial, Ogden and Exponential hyperelastic strain energy density (SED) function. It was found that, the QVL with the Polynomial SED function could predict the peak stress better than the other SED functions.
Rankin IA, Nguyen TTN, McMenemy L, et al., 2022, Protective Clothing Reduces Lower Limb Injury Severity Against Propelled Sand Debris in a Laboratory Setting, Human Factors and Mechanical Engineering for Defense and Safety, Vol: 6, ISSN: 2509-8004
The contribution of energised environmental debris to injury patterns of the blast casualty is not known. The extent to which personal protective equipment (PPE) limits the injuries sustained by energised environmental debris following an explosive event is also not known. In this study, a cadaveric model exposed to a gas-gun mediated sand blast was utilised which reproduced soft-tissue injuries representative of those seen clinically following blast. Mean sand velocity across experiments was 506 ± 80 ms−1. Cadaveric samples wearing standard-issue PPE were shown to have a reduced injury severity to sand blast compared to control: a statistically significant reduction was seen in the total surface area (143 mm2vs. 658 mm2, p = 0.004) and depth of injuries (0 vs. 23 deep injuries, odds ratio = 0.0074, 95% confidence intervals 0.0004–0.1379). This study is the first to recreate wounds from propelled sand in a human cadaveric model. These findings implicate environmental debris, such as sand ejected from a blast event, as a critical mechanism of injury in the blast casualty. Tier 1 pelvic PPE was shown to reduce markedly the severity of injury. This injury mechanism should be a key focus of future research and mitigation strategies.
Nguyen TTN, Tsukada H, Breeze J, et al., 2022, The Critical Role of a Backing Material in Assessing the Performance of Soft Ballistic Protection, Human Factors and Mechanical Engineering for Defense and Safety, Vol: 6, ISSN: 2509-8004
Penetrating trauma by energised fragments is the most common injury from an explosive event. Fragment penetrations to the truncal region can result in lethal haemorrhage. Personal armour is used to mitigate ballistic threats; it comprises hard armour to protect from high-velocity bullets and soft armour to protect against energised fragments and other ballistic threats (such as from a hand gun) with low impact velocities. Current testing standards for soft armour do not focus on realistic boundary conditions, and a backing material is not always recommended. This study provides a comprehensive set of evidence to support the inclusion of a backing used in testing of soft body armour. Experiments were performed with a gas-gun system using fragment-simulating projectiles (FSPs) of different shapes and sizes to impact on a woven aramid and a knitted high-performance polyethylene ballistic fabric, with and without the ballistic gelatine soft tissue simulant as the backing material. The results showed statistically significant differences in the impact velocities at 50% risk (V50) of fabric perforation across all test configurations when the gelatine backing was used. Furthermore, the backing material enabled the collection of injury-related metrics such as V50 of tissue-simulant penetrations as well as depth of penetration against impact velocity. The normalised energy absorbed by the fabric could also be calculated when the backing material was present. This study confirms that a backing material is essential, particularly when assessing the performance of single layer fabrics against FSPs of low mass. It also demonstrates the additional benefits provided by the backing for predicting injury outcomes.
Rankin IA, Nguyen TT, Webster C, et al., 2022, The Injury Mechanism of Explosive Blast Trauma, with Protective Strategies for the Pelvis and Lower Limbs, Pages: 652-653
Tsukada H, Nguyen TTN, Breeze J, et al., 2022, Fragment penetration into the heart: initial findings, Pages: 789-790
Breeze J, Fryer RN, Nguyen T-TN, et al., 2022, Injury modelling for strategic planning in protecting the national infrastructure from terrorist explosive events, BMJ MILITARY HEALTH, ISSN: 2633-3767
Nguyen TT, Breeze J, Masouros S, 2022, Penetration of Energised Metal Fragments to Porcine Thoracic Tissues, Journal of Biomechanical Engineering, ISSN: 0148-0731
Energised fragments from explosive devices have been the most common mechanism of injury to both military personnel and civilians in recent conflicts and terrorist attacks. Fragments that penetrate into the thoracic cavity are strongly associated with death due to the inherent vulnerability of the underlying structures. The aim of this study was to investigate the impact of fragment-simulating projectiles (FSPs) to tissues of the thorax in order to identify the thresholds of impact velocity for perforation through these tissues and the resultant residual velocity of the FSPs. A gas-gun system was used to launch 0.78-g cylindrical and 1.13-g spherical FSPs at intact porcine thoracic tissues from different impact locations. The sternum and rib bones were the most resistant to perforation, followed by the scapula and intercostal muscle. For both FSPs, residual velocity following perforation was linearly proportional to impact velocity. These findings can be used in the development of numerical tools for predicting the medical outcome of explosive events, which in turn can inform the design of public infrastructure, of personal protection, and of medical emergency response.
Rebelo EA, Grigoriadis G, Carpanen D, et al., 2021, An experimentally validated finite element model of the lower limb to investigate the efficacy of blast mitigation systems, Frontiers in Bioengineering and Biotechnology, Vol: 9, ISSN: 2296-4185
Improvised explosive devices (IEDs) used in the battlefield cause damage to vehicles and their occupants. The injury burden to the casualties is significant. The biofidelity and practicality of current methods for assessing current protection to reduce the injury severity is limited. In this study, a finite-element (FE) model of the leg was developed and validated in relevant blast-loading conditions, and then used to quantify the level of protection offered by a combat boot. An FE model of the leg of a 35 years old male cadaver was developed. The cadaveric leg was tested physically in a seated posture using a traumatic injury simulator and the results used to calibrate the FE model. The calibrated model predicted hindfoot forces that were in good correlation (using the CORrelation and Analysis or CORA tool) with data from force sensors; the average correlation and analysis rating (according to ISO18571) was 0.842. The boundary conditions of the FE model were then changed to replicate pendulum tests conducted in previous studies which impacted the leg at velocities between 4 and 6.7 m/s. The FE model results of foot compression and peak force at the proximal tibia were within the experimental corridors reported in the studies. A combat boot was then incorporated into the validated computational model. Simulations were run across a range of blast-related loading conditions. The predicted proximal tibia forces and associated risk of injury indicated that the combat boot reduced the injury severity for low severity loading cases with higher times to peak velocity. The reduction in injury risk varied between 6 and 37% for calcaneal minor injuries, and 1 and 54% for calcaneal major injuries. No injury-risk reduction was found for high severity loading cases. The validated FE model of the leg developed here was able to quantify the protection offered by a combat boot to vehicle occupants across a range of blast-related loading conditions. It can now be used as a design an
Rankin I, Nguyen T, McMenemy L, et al., 2021, The injury mechanism of traumatic amputation, Frontiers in Bioengineering and Biotechnology, Vol: 9, ISSN: 2296-4185
Traumatic amputation has been one of the most defining injuries associated with explosive devices. An understanding of the mechanism of injury is essential in order to reduce its incidence and devastating consequences to the individual and their support network. In this study, traumatic amputation is reproduced using high-velocity environmental debris in an animal cadaveric model. The study findings are combined with previous work to describe fully the mechanism of injury as follows. The shock wave impacts with the casualty, followed by energised projectiles (environmental debris or fragmentation) carried by the blast. These cause skin and soft tissue injury, followed by skeletal trauma which compounds to produce segmental and multifragmental fractures. A critical injury point is reached, whereby the underlying integrity of both skeletal and soft tissues of the limb has been compromised. The blast wind that follows these energised projectiles completes the amputation at the level of the disruption, and traumatic amputation occurs. These findings produce a shift in the understanding of traumatic amputation due to blast from a mechanism predominately thought mediated by primary and tertiary blast, to now include secondary blast mechanisms, and inform change for mitigative strategies.
Draper D, Newell N, Masouros S, et al., 2021, Multiscale validation of multiple human body model functional spinal units, Journal of Biomechanical Engineering, Vol: 143, ISSN: 0148-0731
A validation comparing five human body model (HBM) lumbar spines is carried out across two load cases, with the objective to use and apply HBMs in high strain rate applications such as car occupant simulation. The first load case consists of an individual intervertebral disc (IVD) loaded in compression at a strain rate of 1/s by a material testing machine. The second load case is a lumbar functional spine unit (FSU) loaded in compression using a drop tower setup, producing strain rates of up to 48/s. The IVD simulations were found to have a better agreement with the experiments than the FSU simulations, and the ranking of which HBMs matched best to the experiment differed by load case. These observations suggest the need for more hierarchical validations of the lumbar spine for increasing the utility of HBMs in high strain rate loading scenarios.
Carpanen D, Masouros SD, Stinner DJ, 2021, Biomechanical evaluation of a tool-less external fixator, BMJ MILITARY HEALTH, ISSN: 2633-3767
Rankin IA, Thuy-Tien N, Carpanen D, et al., 2021, Pelvic Protection Limiting Lower Limb Flail Reduces Mortality, JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME, Vol: 143, ISSN: 0148-0731
Tavana S, Masouros S, Baxan N, et al., 2021, The Effect of Degeneration on Internal Strains and the Mechanism of Failure in Human Intervertebral Discs Analyzed Using Digital Volume Correlation (DVC) and Ultra-High Field MRI, Frontiers in Bioengineering and Biotechnology, Vol: 8, ISSN: 2296-4185
The intervertebral disc (IVD) plays a main role in absorbing and transmitting loads within the spinal column. Degeneration alters the structural integrity of the IVDs and causes pain, especially in the lumbar region. The objective of this study was to investigate non-invasively the effect of degeneration on human 3D lumbar IVD strains (n = 8) and the mechanism of spinal failure (n = 10) under pure axial compression using digital volume correlation (DVC) and 9.4 Tesla magnetic resonance imaging (MRI). Degenerate IVDs had higher (p < 0.05) axial strains (58% higher), maximum 3D compressive strains (43% higher), and maximum 3D shear strains (41% higher), in comparison to the non-degenerate IVDs, particularly in the lateral and posterior annulus. In both degenerate and non-degenerate IVDs, peak tensile and shear strains were observed close to the endplates. Inward bulging of the inner annulus was observed in all degenerate IVDs causing an increase in the AF compressive, tensile, and shear strains at the site of inward bulge, which may predispose it to circumferential tears (delamination). The endplate is the spine's “weak link” in pure axial compression, and the mechanism of human vertebral fracture is associated with disc degeneration. In non-degenerate IVDs the locations of failure were close to the endplate centroid, whereas in degenerate IVDs they were in peripheral regions. These findings advance the state of knowledge on mechanical changes during degeneration of the IVD, which help reduce the risk of injury, optimize treatments, and improve spinal implant designs. Additionally, these new data can be used to validate computational models.
Rankin IA, Nguyen TT, Webster C, et al., 2021, The Injury Mechanism of Explosive Blast Trauma, with Protective Strategies for the Pelvis and Lower Limbs, Pages: 652-653, ISSN: 2235-3151
Tsukada H, Nguyen TTN, Breeze J, et al., 2021, Fragment penetration into the heart: initial findings, Pages: 789-790, ISSN: 2235-3151
- Citations: 1
Nguyen TT, Carpanen D, Rankin I, et al., 2020, Mapping the risk of fracture of the tibia from penetrating fragments, Frontiers in Bioengineering and Biotechnology, Vol: 8, Pages: 1-11, ISSN: 2296-4185
Penetrating injuries are commonly inflicted in attacks with explosive devices. The extremities, and especially the leg, are the most commonly affected body areas, presenting high risk of infection, slow recovery, and threat of amputation. The aim of this study was to quantify the risk of fracture to the anteromedial, posterior, and lateral aspects of the tibia from a metal fragment-simulating projectile (FSP). A gas gun system and a 0.78-g cylindrical FSP were employed to perform tests on an ovine tibia model. The results from the animal study were subsequently scaled to obtain fracture-risk curves for the human tibia using the cortical thickness ratio. The thickness of the surrounding soft tissue was also taken into account when assessing fracture risk. The lateral cortex of the tibia was found to be most susceptible tofracture,whose impact velocity at 50% risk of EF1+, EF2+, EF3+, and EF4+ fracture types –according to the modified Winquist-Hansen classification –were 174, 190, 212,and 282 m/s respectively. The findings of this study will be used to increase the fidelity of predictive models of projectile penetration.
Rankin I, Nguyen TT, Carpanen D, et al., 2020, A new understanding of the mechanism of injury to the pelvis and lower limbs in blast, Frontiers in Bioengineering and Biotechnology, Vol: 8, ISSN: 2296-4185
Dismounted complex blast injury (DCBI) has been one of the most severe forms of trauma sustained in recent conflicts. This injury has been partially attributed to limb flail; however, the full causative mechanism has not yet been fully determined. Soil ejecta has been hypothesized as a significant contributor to the injury but remains untested. In this study, a small-animal model of gas-gun mediated high velocity sand blast was used to investigate this mechanism. The results demonstrated a correlation between increasing sand blast velocity and injury patterns of worsening severity across the trauma range. This study is the first to replicate high velocity sand blast and the first model to reproduce the pattern of injury seen in DCBI. These findings are consistent with clinical and battlefield data. They represent a significant change in the understanding of blast injury, producing a new mechanistic theory of traumatic amputation. This mechanism of traumatic amputation is shown to be high velocity sand blast causing the initial tissue disruption, with the following blast wind and resultant limb flail completing the amputation. These findings implicate high velocity sand blast, in addition to limb flail, as a critical mechanism of injury in the dismounted blast casualty.
Stewart S, Tenenbaum O, Masouros S, et al., 2020, Fracture non-union rates across a century of war: a systematic review of the literature, BMJ Military Health, Vol: 166, Pages: 271-276, ISSN: 2633-3767
IntroductionFractures have been a common denominator of the injury patterns observed over the past century of warfare. The fractures typified by the blast and ballistic injuries of war lead to high rates of bone loss, soft tissue injury and infection, greatly increasing the likelihood of non-union. Despite this, no reliable treatment strategy for non-union exists. This literature review aims to explore the rates of non-union across a century of conflict and war, in order to determine whether our ability to heal the fractures of war has improved.MethodsA systematic review of the literature was conducted, evaluating the rates of union in fractures sustained in a combat environment over a one hundred year period. Only those fractures sustained through a ballistic or blast mechanism were included. The review was in accordance with the Preferred Items for Systematic Reviews and Meta-Analyses (PRISMA). Quality and bias assessment was also undertaken. ResultsThirty studies met the inclusion criteria, with a total of 3232 fractures described across fifteen different conflicts from the period 1919-2019. Male subjects made up 96% of cases, and tibial fractures predominated (39%). The lowest fracture union rate observed in a series was 50%. Linear regression analysis demonstrated that increasing years had no statistically significant impact on union rate.ConclusionFailure to improve fracture union rates is likely a result of numerous factors, including greater use of blast weaponry and better survivability of casualties. Finding novel strategies to promote fracture healing is a key defence research priority, in order to improve the rates of fractures sustained in a combat environment.
Nguyen TT, Meek G, Breeze J, et al., 2020, Gelatine backing affects the performance of single-layer ballistic-resistant materials against blast fragments, Frontiers in Bioengineering and Biotechnology, Vol: 8, Pages: 1-10, ISSN: 2296-4185
Penetrating trauma by energized fragments is the most common injury from explosive devices, the main threat in the contemporary battlefield. Such devices produce projectiles dependent upon their design, including preformed fragments, casings, glass, or stones; these are subsequently energized to high velocities and cause serious injuries to the body. Current body armor focuses on the essential coverage, which is mainly the thoracic and abdominal area, and can be heavy and cumbersome. In addition, there may be coverage gaps that can benefit from the additional protection provided by one or more layers of lightweight ballistic fabrics. This study assessed the performance of single layers of commercially available ballistic protective fabrics such as Kevlar®, Twaron®, and Dyneema®, in both woven and knitted configurations. Experiments were carried out using a custom-built gas-gun system, with a 0.78-g cylindrical steel fragment simulating projectile (FSP) as the impactor, and ballistic gelatine as the backing material. FSP velocity at 50% risk of material perforation, gelatine penetration, and high-risk wounding to soft tissue, as well as the depth of penetration (DoP) against impact velocity and the normalized energy absorption were used as metrics to rank the performance of the materials tested. Additional tests were performed to investigate the effect of not including a soft-tissue simulant backing material on the performance of the fabrics. The results show that a thin layer of ballistic material may offer meaningful protection against the penetration of this FSP. Additionally, it is essential to ensure a biofidelic boundary condition as the protective efficacy of fabrics was markedly altered by a gelatine backing.
Rankin IA, Webster CE, Gibb I, et al., 2020, Pelvic injury patterns in blast: Morbidity and mortality, JOURNAL OF TRAUMA AND ACUTE CARE SURGERY, Vol: 88, Pages: 832-838, ISSN: 2163-0755
- Author Web Link
- Citations: 3
Tavana S, Clark JN, Prior J, et al., 2020, Quantifying deformations and strains in human intervertebral discs using Digital Volume Correlation combined with MRI (DVC-MRI), Journal of Biomechanics, Vol: 102, Pages: 1-7, ISSN: 0021-9290
Physical disruptions to intervertebral discs (IVDs) can cause mechanical changes that lead to degeneration and to low back pain which affects 75% of us in our lifetimes. Quantifying the effects of these changes on internal IVD strains may lead to better preventative strategies and treatments. Digital Volume Correlation (DVC) is a non-invasive technique that divides volumetric images into subsets, and measures strains by tracking the internal patterns within them under load. Applying DVC to MRIs may allow non-invasive strain measurements. However, DVC-MRI for strain measurements in IVDs has not been used previously. The purpose of this study was to quantify the strain and deformation errors associated with DVC-MRI for measurements in human IVDs.Eight human lumbar IVDs were MRI scanned (9.4T) for a ‘zero-strain study’ (multiple unloaded scans to quantify noise within the system), and a loaded study (2mm axial compression). Three DVC methodologies: Fast-Fourier transform (FFT), direct correlation (DC), and a combination of both FFT and DC approaches were compared with subset sizes ranging from 8 to 88 voxels to establish the optimal DVC methodology and settings which were then used in the loaded study.FFT+DC was the optimal method and a subset size of 56 voxels (2520 micrometers) was found to be a good compromise between errors and spatial resolution. Displacement and strain errors did not exceed 28 µm and 3000 microstrain, respectively.These findings demonstrate that DVC-MRI can quantify internal strains within IVDs non-invasively and accurately. The method has unique potential for assessing IVD strains within patients.
Nguyen TT, Carpanen D, Stinner D, et al., 2020, The risk of fracture to the tibia from a fragment simulating projectile, Journal of The Mechanical Behavior of Biomedical Materials, Vol: 102, ISSN: 1751-6161
Penetrating injuries due to fragments energised by an explosive event are life threatening and are associated with poor clinical and functional outcomes. The tibia is the long bone most affected in survivors of explosive events, yet the risk of penetrating injury to it has not been quantified. In this study, an injury-risk assessment of penetrating injury to the tibia was conducted using a gas-gun system with a 0.78-g cylindrical fragment simulating projectile. An ovine tibia model was used to generate the injury-risk curves and human cadaveric tests were conducted to validate and scale the results of the ovine model. The impact velocity at 50% risk (±95% confidence intervals) for EF1+, EF2+, EF3+, and EF4+ fractures to the human tibia – using the modified Winquist-Hansen classification – was 271 ± 30, 363 ± 46, 459 ± 102, and 936 ± 182 m/s, respectively. The scaling factor for the impact velocity from cadaveric ovine to human was 2.5. These findings define the protection thresholds to improve the injury outcomes for fragment penetrating injury to the tibia.
Boyle C, Carpanen D, Pandelani T, et al., 2020, Lateral pressure equalisation as a principle for designing support surfaces to prevent deep tissue pressure ulcers, PLoS One, Vol: 15, ISSN: 1932-6203
When immobile or neuropathic patients are supported by beds or chairs, their soft tissues undergo deformations that can cause pressure ulcers. Current support surfaces that redistribute under-body pressures at vulnerable body sites have not succeeded in reducing pressure ulcer prevalence. Here we show that adding a supporting lateral pressure can counter-act the deformations induced by under-body pressure, and that this ‘pressure equalisation’ approach is a more effective way to reduce ulcer-inducing deformations than current approaches based on redistributing under-body pressure.A finite element model of the seated pelvis predicts that applying a lateral pressure to the soft tissue reduces peak von Mises stress in the deep tissue by a factor of 2.4 relative to a standard cushion (from 113 kPa to 47 kPA) — a greater effect than that achieved by using a more conformable cushion, which reduced von Mises stress to 75 kPa. Combining both a conformable cushion and lateral pressure reduced peak von Mises stresses to 25 kPa. The ratio of peak lateral pressure to peak under-body pressure was shown to regulate deep tissue stress better than under-body pressure alone. By optimising the magnitude and position of lateral pressure, tissue deformations can be reduced to that induced when suspended in a fluid.Our results explain the lack of efficacy in current support surfaces and suggest a new approach to designing and evaluating support surfaces: ensuring sufficient lateral pressure is applied to counter-act under-body pressure.
Stewart S, Darwood A, Masouros S, et al., 2020, Mechanotransduction in osteogenesis, Bone and Joint Research, Vol: 9, Pages: 1-14, ISSN: 2046-3758
Bone is one of the most highly adaptive tissues in the body, possessing the capability to alter its morphology and function in response to stimuli in its surrounding environment. The ability of bone to sense and convert external mechanical stimuli into a biochemical response, which ultimately alters the phenotype and function of the cell, is described as mechanotransduction. This review aims to describe the fundamental physiology and biomechanisms that occur to induce osteogenic adaptation of a cell following application of a physical stimulus. Considerable developments have been made in recent years in our understanding of how cells orchestrate this complex interplay of processes, and have become the focus of research in osteogenesis. We will discuss current areas of preclinical and clinical research exploring the harnessing of mechanotransductive properties of cells and applying them therapeutically, both in the context of fracture healing and de novo bone formation in situations such as nonunion.
Newell N, Carpanen D, Grigoriadis G, et al., 2019, Material properties of human lumbar intervertebral discs across strain rates, Spine Journal, Vol: 19, Pages: 2013-2024, ISSN: 1529-9430
Background context:The use of finite-element (FE) methods to study the biomechanics of the intervertebral disc (IVD) has increased over recent decades due to their ability to quantify internal stresses and strains throughout the tissue. Their accuracy is dependent upon realistic, strain-rate dependent material properties, which are challenging to acquire. Purpose:The aim of this study was to use the inverse FE technique to characterize the material properties of human lumbar IVDs across strain rates.Study Design:A human cadaveric experimental study coupled with an inverse finite element study.Methods:To predict the structural response of the IVD accurately, the material response of the constituent structures was required. Therefore, compressive experiments were conducted on 16 lumbar IVDs (39 ± 19 years) to obtain the structural response. An FE model of each of these experiments was developed and then run through an inverse FE algorithm to obtain subject-specific constituent material properties, such that the structural response was accurate.Results:Experimentally, a log-linear relationship between IVD stiffness and strain rate was observed. The material properties obtained through the subject-specific inverse FE optimization of the anulus fibrosus (AF) fiber and AF fiber ground matrix allowed a good match between the experimental and FE response. This resulted in a Young’s Modulus of AF fibers (YMAF - MPa) to strain rate (ε ̇ - /s) relationship of YMAF=31.5ln(ε ̇ )+435.5, and the C10 parameter of the Neo-Hookean material model of the AF ground matrix was found to be strain-rate independent with an average value of 0.68 MPa.Conclusions:These material properties can be used to improve the accuracy, and therefore predictive ability of FE models of the spine that are used in a wide range of research areas and clinical applications.Clinical SignificanceFinite element models can be used for many applications including investigating low-back p
Rankin IA, Thuy-Tien N, Carpanen D, et al., 2019, Restricting Lower Limb Flail is Key to Preventing Fatal Pelvic Blast Injury, ANNALS OF BIOMEDICAL ENGINEERING, Vol: 47, Pages: 2232-2240, ISSN: 0090-6964
- Author Web Link
- Citations: 4
Boyle C, Plotczyk M, Fayos Villalta S, et al., 2019, Morphology and composition play distinct and complementary roles in the tolerance of plantar skin to mechanical load, Science Advances, Vol: 5, Pages: 1-13, ISSN: 2375-2548
Plantar skin on the soles of the feet has a distinct morphology and composition that is thought to enhance its tolerance to mechanical loads, although the individual contributions of morphology and composition have never been quantified. Here, we combine multiscale mechanical testing and computational models of load bearing to quantify the mechanical environment of both plantar and nonplantar skin under load. We find that morphology and composition play distinct and complementary roles in plantar skin’s load tolerance. More specifically, the thick stratum corneum provides protection from stress-based injuries such as skin tears and blisters, while epidermal and dermal compositions provide protection from deformation-based injuries such as pressure ulcers. This work provides insights into the roles of skin morphology and composition more generally and will inform the design of engineered skin substitutes as well as the etiology of skin injury.
Carpanen D, Kedgley A, Shah D, et al., 2019, Injury risk of interphalangeal and metacarpophalangeal joints under impact loading, Journal of the Mechanical Behavior of Biomedical Materials, Vol: 97, Pages: 306-311, ISSN: 1751-6161
Injuries to the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints of the hand are particularly disabling. However, current standards for hand protection from blunt impact are not based on quantitative measures of the likelihood of damage to the tissues. The aim of this study was to evaluate the probability of injury of the MCP and PIP joints of the human hand due to blunt impact.Impact testing was conducted on 21 fresh-frozen cadaveric hands. Unconstrained motion at every joint was allowed. All hands were imaged with computed tomography and dissected post-impact to quantify injury. An injury-risk curve was developed for each joint using a Weibull distribution with dorsal impact force as the predictive variable.The injury risks for PIP joints were similar, as were those for MCP joints. The risk of injury of the MCP joints from a given applied force was significantly greater than that of the PIP joints (p = 0.0006). The axial forces with a 50% injury risk for the MCP and PIP joints were 3.0 and 4.2 kN, respectively.This is the first study to have investigated the injury tolerance of the MCP and PIP joints. The proposed injury curves can be used for assessing the likelihood of tissue damage, for designing targeted protective solutions such as gloves, and for developing more biofidelic standards for assessing these solutions.
Newell N, Carpanen D, Evans JH, et al., 2019, Mechanical function of the nucleus pulposus of the intervertebral disc under high rates of loading, Spine, Vol: 44, Pages: 1035-1041, ISSN: 0362-2436
Study Design. Bovine motion segments were used to investigate the high-rate compression response of intervertebral discs (IVD) before and after depressurising the nucleus pulposus (NP) by drilling a hole through the cranial endplate into it.Objective. To investigate the effect of depressurising the NP on the force-displacement response, and the energy absorption in IVDs when compressed at high strain rates.Summary of Background Data. The mechanical function of the gelatinous NP located in the centre of the IVDs of the spine is unclear. Removal of the NP has been shown to affect the direction of bulge of the inner anulus fibrosus (AF), but at low loading rates removal of the NP pressure does not affect the IVD's stiffness. During sports or injurious events, IVDs are commonly exposed to high loading rates, however, no studies have investigated the mechanical function of the NP at these rates.Methods. Eight bovine motion segments were used to quantify the change in pressure caused by a hole drilled through the cranial endplate into the NP, and eight segments were used to investigate the high-rate response before and after a hole was drilled into the NP.Results. The hole caused a 28.5% drop in the NP pressure. No statistically significant difference was seen in peak force, peak displacement, or energy-absorption of the intact and depressurised NP groups under impact loading. The IVDs absorbed 72% of the input energy, and there was no rate dependency in the percentage energy absorbed.Conclusions. These results demonstrate that the NP pressure does not affect the transfer of load through, or energy absorbed by, the IVD at high loading rates and the AF, rather than the NP, may play the most important role in transferring load, and absorbing energy at these rates. This should be considered when attempting surgically to restore IVD function.Level of Evidence: N/A
Nguyen TT, Masouros S, 2019, Penetration of Blast Fragments to the Thorax, International Research Council On Biomechanics Of Injury
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