Peter S Theobald

Cardiff University | CU · Bioengineering & High Value Manufacturing research groups

Soft tissue growth is crucial across various physiological applications, with mathematical modelling playing a pivotal role in understanding the underlying processes. The volumetric growth theory serves as a commonly used mathematical framework in this context. Our previous research on volumetric growth theory primarily concentrated on defining the...

Association football, also known as soccer in some regions, is unique in encouraging its participants to intentionally use their head to gain a competitive advantage, including scoring a goal. Repetitive head impacts are now being increasingly linked to an inflated risk of developing long-term neurodegenerative disease. This study investigated the...

Advances in computational modelling now offer an efficient route to developing novel helmet liners that could exceed contemporary materials' performance. Furthermore, the rise of accessible additive manufacturing presents a viable route to achieving otherwise unobtainable material structures. This study leverages an established finite element-based...

The design freedom afforded by additive manufacturing (AM) is now being leveraged across multiple applications, including many in the fields of imaging for personalised medicine. This study utilises a pellet-fed, multi-material AM machine as a route to fabricating new imaging phantoms, used for developing and refining algorithms for the detection o...

Anterior cruciate ligament (ACL) injury is one of the most common knee injuries among athletes and during sports activities for which ligament reconstruction is the optimal therapeutic procedure. Functional instability of the knee because of ACL injury is prone to relapse. Relapse is commonly reported following surgery due to various reasons. Knowi...

This paper reports on a comprehensive investigation of gyroid lattice structures subject to impact loading. AlSi10Mg samples were manufactured using selective laser melting (SLM) and mechanically characterized using Digital Image Correlation (DIC). Universal testing machines, drop weight rig, and a split pressure Hopkinson bar were used to mechanic...

Selective laser sintering has been used to manufacture different structural variations of a pre-buckled circular honeycomb. The mechanical behaviour of these structures has been examined under both quasi-static and dynamic impact loading. Pre-buckled circular honeycombs with aspect ratios e = 0.8 and e = 0.6 were compared to a traditional, straight...

Finite element simulation was used to analyse the response of an elastomeric pre-buckled honeycomb structure under impact loading, to establish its suitability for use in helmet liners. A finite element-based optimisation was performed using a search algorithm based on a radial basis function. This approach identified optimisation configurations of...

Background Falls are a common and costly problem, with poor balance a significant contributor. Wobble boards are commonly used for balance enhancement. However, the efficacy of wobble board training is not well understood, particularly in the older adult. Objectives To appraise and synthesise literature pertaining to the effect of wobble board tra...

This review describes the principles of skin friction and wear for the benefit of sports scientists, engineers and clinicians. Skin exhibits complex behaviour, defying tribological laws for dry contact; hence, its friction and wear characteristics are affected by sliding speed, normal load, and contact area. Some sports seek to increase skin fricti...

American football has a comparatively high rate of sports-related concussions, despite mitigating strategies including the use of protective helmets. The traditional energy absorbing component, elastomeric foam pads, have limited scope for leveraging any further protection. Alternative structures and materials that exhibit novel deformation mechani...

The field of biomechanics serves to link the seemingly disparate specialisms of biology and mechanical engineering. Application of biomechanics to the musculoskeletal system is documented from the early twentieth century, as innovators and pioneers began investigating synovial joint behavior with a view to understanding the link between its structu...

This study evaluates a fluid-filled, closed-cell lattice as a novel route to reducing peak acceleration Cellular lattice structures provide effective energy absorption in repeat impact environments. This study evaluates a fluid-filled, closed-cell lattice as a novel route to further enhance energy absorption. A conical structure was designed and bu...

In the original version of the book, the author name has been updated from “Khaled Gaisin” to “Khaled Giasin” in the Chapter “Using FFF and topology optimisation to increase crushing strength in equestrian helmets”. The chapter and book have been updated with the changes.

International standards ensure that equestrian helmets achieve high performance. Recently, one such standard (PAS 015) was revised to include a lateral deformation requirement, ensuring helmets can withstand the potential crushing forces associated with equestrian. This increased performance needs to be achieved against a minimal mass penalty, whic...

Honeycomb structures display extraordinary stiffness-to-weight ratio when loaded in the out-of-plane direction. When realized using thermoplastic polyurethane (TPU), the structures offer the potential for repeatable and high specific energy absorption. Varying the cell size and wall thickness of TPU honeycombs facilitates changes in stiffness magni...

Constitutive laws that describe the mechanical responses of cardiac tissue under loading hold the key to accurately model the biomechanical behaviour of the heart. There have been ample choices of phenomenological constitutive laws derived from experiments, some of which are quite sophisticated and include effects of microscopic fibre structures of...

Thermoplastic elastomers (TPE) are commonly used to fabricate structures for application in repeatable, energy absorption environments. The emergence of additive manufacturing (AM) means scope now exists to design and build complex TPE components that can mechanically outperform traditionally manufactured equivalents. The ability to efficiently cha...

Background Performing high-quality chest compressions during cardiopulmonary resuscitation (CPR) requires achieving of a target depth, release force, rate and duty cycle. Objective This study evaluates whether ‘real time’ feedback could improve infant CPR performance in basic life support-trained (BLS) and lay rescuers. It also investigates whethe...

Additive manufacturing (AM) enables production of geometrically-complex elastomeric structures. The elastic recovery and strain-rate dependence of these materials means they are ideal for use in dynamic, repetitive mechanical loading. Their process-dependence, and the frequent emergence of new AM elastomers, commonly necessitates full material char...

Background: Flexor tendon injuries are extremely common and they are usually the result of incised traumatic glass or knife injury. The process of tendon healing is a complicated and exceptionally-regimented mechanism that is originated and monitored by a vast number of diverse molecules. One of the most pivotal groups of mediators that are crucia...

Abstract Introduction The risk of fracture from a non-accidental injury is highest in the infant age group. A spiral fracture of the long bone can occur equally from accidental and non-accidental causes, meaning the clinical judgement of non-accidental injury in an infant is particularly challenging. This study aimed to assist in differentiating a...

The neonate transitions from placenta-derived oxygen, to supply from the pulmonary system, moments after birth. This requires a series of structural developments to divert more blood through the right heart and onto the lungs, with the tissue quickly remodelling to the changing ventricular workload. In some cases, however, the heart structure does...

Aim Surface tribological properties of a tendon in terms of coefficient of friction and lubrication mechanism are expected to change with the progression of surface tears which can affect the optimal function of the tendon. This study investigated whether coefficient of friction proportionally increases with the progression of a surface tear in a b...

This paper aims to build a theoretical foundation for parametric design thinking by exploring its cognitive roots, unfolding its basic tenets, expanding its definition through new concepts, and exemplifying its potential through a use-case scenario. The paper focuses on a specific type of topological parameter, called non-manifold topology as a nov...

Head injury in childhood is the single most common cause of death or permanent disability from injury. However, despite its frequency and significance, there is little understanding of the response of a child’s head to injurious loading. This is a significant limitation when making early diagnoses, informing clinical and/or forensic management or i...

Head injury in childhood is a common cause of death or permanent disability from injury. However, despite its frequency and significance, there is little understanding of how a child's head responds during injurious loading. Whilst Infant Post Mortem Human Subject (PMHS) experimentation is a logical approach to understand injury biomechanics, it is...

Simulations of blood flow have gained a great relevance in the understanding of the human cardiovascular system. Cardiac pathologies, such as atherosclerosis or aneurysms, are closely related to blood flow characteristics, such as areas of flow reversal or low and oscillatory shear stress. Therefore, a detailed understanding of the local haemodynam...

Head injury severity is dependent on the loading and accelerations experienced during, and immediately after, impact. In England and Wales alone, for example, 700,000 head injury cases are reported annually within Emergency Departments; however, there remains a lack of data that quantifies the fundamental interaction of the head with an impacting s...

This paper focusses on demonstrating the effectiveness of our new code at producing curved, formerly planar structures that comprise complex internal architecture. This development is particularly significant as it will, ultimately, allow further exploitation of the design freedom offered by additive manufacturing (AM). This particular application...

Presented is the development of a simulation that allows for preliminary investigation of impact to a 10 day old infant head. A computer-aided drafting (CAD) model is reconstructed from high resolution computerised tomography (CT) scan images and meshed for finite element analysis (FEA); soft tissue responses were defined using recently derived mat...

Background Scrummaging is unique to rugby union and involves 2 ‘packs’ of 8 players competing to regain ball possession. Intending to serve as a quick and safe method to restart the game, injury prevalence during scrummaging necessitates further evaluation of this environment. Aims The aim of this study was to determine the effect of scrummage enga...

Historically, the surgical treatment of flexor tendon injuries has always been associated with controversy. It was not until 1967, when the paper entitled Primary repair of flexor tendons in no man’s land was presented at the American Society of Hand Surgery, which reported excellent results and catalyzed the implementation of this technique into w...

Background: It is commonplace for clinicians to measure range of motion (ROM) in the assessment of the lumbar spine. Traditional single 'joint' models afford measuring only a limited number of regions along the spine and may, therefore, over-simplify the description of movement. It remains to be determined if additional, useful information can be...

Background Motocross is a form of motorcycle racing held on established off-road circuits and has been a recreational and competitive sport across the world for over 100 years. In the UK alone, motocross has grown into a phenomenally ambitious and popular franchise. There are over 200 motocross clubs across the country, permitting over 900 events a...

Background: The relationship between muscular force and electromyography (EMG) has been investigated by numerous researchers. EMG has not previously been used as a means of estimating force in the cervical erector spinae (CES). Objective: Use EMG of the CES musculature to indirectly predict neck extension force. Methods: Isometric contractions...

Background: A fall-height threshold is important when evaluating the likelihood of structural head injury or abusive head trauma. This study investigates witnessed falls to correlate the fall characteristics with the extent of injury. Method: Case-control study of children aged ≤48 months who attended one hospital following a fall from <3 m (10...

Artificial surfaces are now an established alternative to grass (natural) surfaces in rugby union. Little is known, however, about their potential to reduce injury. This study characterises the spinal kinematics of rugby union hookers during scrummaging on third-generation synthetic (3G) and natural pitches. The spine was sectioned into five segmen...

OsteoArthritis is a debilitating disease throughout the developed world, causing significant loss of quality of life to individuals and damaging economies, the imaging system described in this paper has the potential to provide an objective means of measuring and reporting lesion dimensions and providing a machine readable data archive for future s...

The purpose of this study was to explore the relationship between the kinematic profiles of flexion of the upper lumbar and lower lumbar (LL) spine and hip and 3 sagittally dominant functional tasks (lifting, stand-to-sit, and sit-to-stand). Fifty-three participants were recruited for this study. Four sensors were attached to the skin over the S1,...

The purpose of this study was to investigate the reliability of a novel motion analysis device for measuring the regional breakdown of spinal motion and describing the relative motion of different segments of the thoracolumbar (TL) spine. Two protocols were applied to 18 healthy participants. In protocol 1, 2 sensors were placed on the forehead and...

Bicycle helmets are designed to attenuate forces and accelerations experienced by the head during cycling accidents. An essential element of bicycle helmet design is, therefore, the appropriate manufacturing of energy-dissipating components. The focus of this study was to evaluate the feasibility of using thermoplastic elastomer (TPE) cellular stru...

The wearing process of an ultrahigh molecular weight polyethylene (UHMWPE) bearing surface in orthopaedic surgical implants cannot be tracked at present; hence, implant failure only becomes apparent when the patient experiences some discomfort. In exploring the integration of wireless stress sensors into UHMWPE, this paper describes the first step...

The inertial loading thresholds for infant head injury are of profound medico-legal and safety-engineering significance. Injurious experimentation with infants is impossible, and physical and computational biomechanical modelling has been frustrated by a paucity of paediatric biomechanical data. This study describes the development of a computation...

The ultimate tensile repair strength and gap formation of the pig extensor tendons repaired with a standard 4-strand Savage with epitendinous suture repair, was compared with a new technique of adding a vein sleeve. Force and displacement data were recorded, and video images during linear cyclic loading up to failure. At 35 N, video-graphic observa...

Ankle fracture is one of the most common lower limb fractures for they account for 9% of all frac-tures representing a significant portion of the trauma workload. Ankle fractures usually affect young men and older women, however, below the age of 50; ankle fractures are the commonest in men. Two commonly used classification systems for ankle fractu...

Purpose: The surgical treatment of paediatric fractures is increasing. Open reduction and internal fixation (ORIF) with plates and screws is long established, whilst the use of elastic stable intramedullary nailing (ESIN) has become increasingly popular. This study quantifies, in terms of the energy required to produce a fracture, the biomechanica...

Background: Current spinal range of motion (ROM) measurement methods have limitations ranging from the amount of detail obtained to environmental costs and complexity. In particular, limited regional spinal motion is obtained using the current methods. However, a new portable ‘string’ of accelerometers is proposed to overcome these limitations. Ob...

Background: Data pertaining to infant sagittal cervical range of motion (CROM) is lacking. Previous studies have either quantified motions other than sagittal or quantified sagittal range of motion in children >3 years old. Data capture in infants is complex and novel methods are required to overcome previous limitations. Such data is invaluable to...

Background: It is common for patients with spinal pain to report evoked pain, associated with a variety of everyday tasks. Despite this, the assessment of an individual with spinal pain usually involves the completion of movements in the cardinal planes, for example flexion and extension. The relationship between these cardinal motions and more fun...

Human bite-mark analyses can play a prominent role in forensic case investigations, including those involving sexual assault. High-quality photographs routinely secure a link between a bite-mark and an individual's dentition. Access to around the clock forensic photography, however, is often limited, resulting in delay and/or missed opportunities t...

Lifting presents a significant risk for the development of low back pain. It is not known what effect lifting from a supermarket shopping trolley has on sagittal spinal curvature. The aim of this study is to determine the effect of lifting from a shopping trolley on sagittal spinal curvature. Fifteen female subjects (height 1.67 ± 0.04 m, weight 64...

Aims: Current International Liaison Committee on Resuscitation (ILCOR) guidelines emphasise the provision of high quality chest compressions during infant cardiopulmonary resuscitation (CPR). Recent research, however, reports that <1% of all chest compressions achieve all four internationally recommended quality targets during simulated infant CPR....

Setting: European and Advanced Paediatric Life Support training courses. Participants: Sixty-nine certified CPR providers. Interventions: CPR providers were randomly allocated to a 'no-feedback' or 'feedback' group, performing two-thumb and two-finger chest compressions on a "physiological", instrumented resuscitation manikin. Baseline data wa...

Background Morbidity and mortality remain high following infant cardiac arrest. Optimal cardiopulmonary resuscitation (CPR) is therefore imperative. Objective Comparison of two-thumb (TT) and two-finger (TF) infant chest compression technique compliance with international recommendations. Design Randomised cross-over experimental study. Methods Twe...

Articular cartilage maturation is the postnatal development process that adapts joint surfaces to their site-specific biomechanical demands. Maturation involves gross morphological changes that occur through a process of synchronised growth and resorption of cartilage and generally ends at sexual maturity. The inability to induce maturation in biom...

Poor survivability following infant cardiac arrest has been attributed to poor quality chest compressions. Current infant CPR manikins, used to teach and revise chest compression technique, appear to limit maximum compression depths (CDmax) to 40mm. This study evaluates the effect of a more "physiological" CDmax on chest compression quality and ass...

Long bone fractures in children can be due to accidental or non-accidental injury. Fractures, along with soft tissue injuries, are the main physical signs of child abuse. The identification of non-accidental nature of fractures in children remains a major diagnostic challenge for clinicians [1]. The clinical situation is sensitive due to child prot...

Approximately 50% of infant and toddler long bone fractures are attributed to non-accidental trauma; however, differentiating from benign mechanisms is subjective, due to an absence of evidence-based diagnostic tools. Previous studies investigated small ranges of rotational velocities in animal long bone models, although did not report the variatio...

Frictional resistance to tendon gliding is minimized by surrounding loose areolar tissue. During periods of prolonged immobilization, for example, post-tendon-repair, adhesions can form between these two adjacent tissues, thereby limiting tendon function. Anti-adhesive agents can be applied during surgery to prevent adhesion formation, whilst repor...

ObjectiveA recent increase in the number of infants presenting at autopsy with rib fractures associated with cardio-pulmonary resuscitation (CPR) precipitated a study to determine whether such a phenomenon was related to recent revision of paediatric resuscitation guidelines.

When considering cases of infant head injury as a result of a short fall, investigators often have to base their opinions on the potential severity of a head injury on a scene description and/or photographic evidence of the potential impact surfaces. While variation in the attenuation properties of typical domestic surfaces and underlying support s...

A rise in neck pain cases has initiated an exponential interest in the assessment and treatment of cervical spine range of motion (CROM). Experimental limitations, however, have been reported as therapists strive to collect continuous, dynamic data to aid prognosis. This technical report seeks to explore the viability of using inertial sensors to r...