Biomimetic Tribology: Exploiting Natural Lubrication Mechanisms for Mechanical Systems
Researcher: Murali Manoj
Supervisor: Dr Marc Masen, Dr Philippa Cann
The replacement of oil-based lubricants with biodegradable water-based lubricants has been a long-standing unfulfilled ambition. The physical instabilities and poor wear performance associated with water-based lubricants has led to minimal adoption within mechanical systems. However, many water-based lubrication systems exist within nature that are capable of providing extremely low friction and minimal wear.
This project aims to explore these natural lubrication mechanisms with the intention of exploiting their behaviour for application within mechanical systems. This will lead to the development of a biolubricant that is capable of providing suitable friction and wear characteristics for a multitude of applications. The biolubricant will be tuned to be compatible with materials that are likely to be adopted into many of the systems around us in the future. This allows for application of the lubricant within novel systems previously unexplored that may come to the forefront in the near future. Nature exhibits countless complex lubrication mechanisms and biological methods to achieve targeted lubrication. Hence, the focus is towards creating a biolubricant which is capable of local activation at a contact, thereby providing a local high viscosity zone with a bulk low viscosity and reducing energy losses due to churning or fluid shear. Some of the lubricant additive possibilities to be explored are proteins, cationic surfactant micelles and polymer-colloids amongst others.
Brain Mimicking Hydrogels
Researcher: Zhengchu Tan
Supervisor: Professor Daniele Dini
The characterisation of the mechanical response of real soft tissues, such as brain, liver and cartilage, is immensely important as it allows us to understand the way they respond under a variety of different loads. Hence, ways to reduce damage to living tissues during real life scenarios can be identified and developed. However, real tissue is difficult to obtain and test due to accessibility. Therefore, there is a huge advantage in developing an accurate synthetic tissue phantom that is easier to procure and produce. This has led to the popularity of hydrogels, which have been developed into tissue mimicking materials due to their biocompatibility and stiffness tunability.
This project focuses on the development of a composite hydrogel (CH) constituting of poly(vinyl) alcohol (PVA) and phytagel that is able to match the complex viscoelastic behaviour of brain. The CH can be tuned to achieve different stiffness and relaxation responses by varying the concentrations of each hydrogel component, which allows the material to mimic other soft tissues.
Consequently, a mechanically accurate tissue phantom material opens the doors to many applications in the study of mechanobiology and regenerative medicine. This project investigates cell viability of the CH substrate, therefore extending the range of applicability to explore a variety of different mechanical loads affects cells seeded on a CH substrate These experiments include impact tests, needle insertion tests and tribological tests to match the high strain rate behaviour of brain for the study of TBI, fracture behaviour of liver during surgery and tribological behaviour of cartilage, respectively.
Coarse-Grained Simulations of the Tribology of Wet Hair
Researcher: Erik Weiand
Sponsor: EPSRC and Proctor and Gamble (iCASE)
Hair friction behavior is of particular interest for the development of hair care products. Mammal hair is formed by complex structures and requires a multi-scale approach for both experimental and numerical investigations. Despite past research efforts, the nanoscale interactions on the hair surface are not completely understood yet – particularly in the presence of hair care formulations which have been shown to drastically modify the macroscopic quantities such as the friction coefficient of hair in past
The aim of this project is to gain fundamental knowledge on the friction behavior of human hair in the presence of coacervate formulations, as used in hair care products. Coarse-grained molecular dynamics (MD) simulations will be conducted to explore the nanoscale interactions on the hair surface in the presence of such formulations.
Contact Mechanics of Soft and Complex Biological Tissues (BIOCONTACT)
In the last decade, a number of medical and bio-engineering challenges, requiring a deep understanding of the phenomena occurring at biological interfaces, have boosted scientific interest in the field of biological contact mechanics. The MSCA-awarded BIOCONTACT project will develop an innovative methodology to tackle bio-lubricated contacts involving soft tissues in the presence of complex fluids, enhancing the understanding of these interactions, by pursuing new models and numerical methodologies, specifically suited for this class of problem. This approach is key to provide long-term societal benefits by solving long-standing issues including the prevention of hospital bedsores, the mechanical compatibility of prosthetic implants or contact lens, and the optimization of surgical procedures and tools.
In particular, our vision is to first build a mechanical model for biological soft tissues that specifically relies on constitutive laws for multi-layered linear viscoelastic materials. This model will be then implemented in a newly developed contact mechanics solver, based on improved Boundary Element Method schemes that we have recently proposed, able to capture specific chemo-mechanical local responses. Interfacial interactions will adopt an atomistic and molecular description, thus relying on interfacial mean potentials modelling. In the framework of inverse analysis, the material properties of individual layers will be tuned to best replicate the experimental behavior captured using an innovative procedure which, probing the materials at different dimensional scales, is able to extract mechanical properties of the different layers composing the tissue.
Finally, in order to provide a complete and widely applicable tool, solid-liquid interaction will be addressed by coupling the contact solver with a lubrication model, based on non-Newtonian Reynolds theory. The development of this ready-to-use numerical tool will foster the uptake of my proposed methodologies for use in the above mentioned complex cases of industrial and medical relevance.
Coupled Fluid-Mechanical Modelling of the Brain
Researcher: Andrea Bernardini
Supervisor: Professor Daniele Dini
The brain is composed of two main types of tissues, namely grey and white matter. In this project, we focus on the latter, which is where glioblastoma is localised (i.e. where the EDEN system will infuse medication). The white matter is comprised of several types of cells and components which make it possible to theorise it as an anisotropic mechanical entity. Segmentation of the components from SEM images enables the 3-D reconstruction of the representative units to be modelled and then analysed via FEA.
A coupled fluid-mechanical model of the brain will be developed by modelling the mechanical behaviour of such tissue and its interaction with the fluidic environment in which it is submerged. This will enable the prediction of diffusive phenomena and patterns in the enhanced drug delivery in order to optimise the surgical procedure and the point of cancer-drug dosing.
Design Principles for Low-Friction Polymer Brushes as a Synthetic Analogue of Cartilage
Researcher: Mohamed Abdelbar
The articular cartilage found covering the ends of bones in the synovial joints of mammals exhibit exceptional tribological properties, giving a low friction response (μ = 0.001) even when subjected to normal loads exceeding 100 atm. The goal of this project is to use coarse-grained molecular dynamics in order to study the system focusing on the architecture of the polymers on the surface and thus provide rational design principles for cartilage analogues.
EDEN2020 (An Enhanced Delivery Ecosystem for Neurosurgery)
Due to an aging population and the spiralling cost of brain disease in Europe and beyond, EDEN2020 aims to develop the gold standard for one-stop diagnosis and minimally invasive treatment in neurosurgery. Supported by a clear business case, it will exploit the unique track record of leading research institutions and key industrial players in the field of surgical robotics to overcome the current technological barriers that stand in the way of real clinical impact.
Finite Element Modelling of Prosthetics and Orthotics
Researcher: Jack Hayes
Supervisor: Dr Marc Masen, Claire Higgins (Bioengineering) and Peter Worsley (Southampton)
Sponsor: EPSRC Centre of Doctoral Training (CDT) in Prosthetics and Orthotics (P&O)
This project will study the effect of contact pressures on residuum-socket interactions. Finite Element Modelling (FEM) will be used to inform redesign with regards to socket geometry and material parameters.
Fluid Flow and Mass Transfer in Brain Tissue
Researcher: Tian Yuan
Supervisor: Prof. Daniele Dini, Dr Marc Masen
This project is to investigate how drug fluid flows inside the brain and how the drug particles diffuse
within the fluid domain in order to improve the therapy name Convection-Enhanced Delivery (CED)
for the treatment of brain diseases. The research works are mainly focused on numerical modelling
but also involve experimental validations. Arbitrary Lagrangian Euler (ALE) method is used to
describe the Fluid-Solid Interaction (FSI) between drug fluid and neuron cells and Finite Element
Method (FEM) is used to solve the deformation of the neuron cells and the fluid flow in the brain.
The interaction between drug particles and neuron cells will be calculated based on molecular
modelling. Experiments at different scales will be done as well to validate the simulations. With this
establishment of this modelling framework, the influence of factors that affect the efficiency of CED
will be clear and this therapy could be improved. This numerical model could also serve as a
consultant for the surgical preparation.
Lubrication and Fluid Load-Support in Hydrogels for Cartilage Substitutes
Researcher: Elze Porte
Sponsor: Imperial College London
This research focuses on gaining a better understanding of the lubrication mechanisms in articular cartilage. Currently, there is no thorough understanding of the relationship between the lubrication of the material, its fluid load support, and its mechanical properties.
Hydrogels have been suggested as promising substitute materials for cartilage because of their specific mechanical and tribological properties. This makes them suitable substitutes for use in lubrication experiments and, ultimately, as a potential cartilage replacement material in the surgical treatment of osteoarthritis
Fluid exudation from the bulk material into the loaded region is believed to provide the fluid load support and lubrication. To study the lubricating mechanisms of hydrogels as cartilage substitutes, contact and lubrication experiments are done on the newly developed Biotribometer (PCS Instruments, London UK). The obtained knowledge can be used to improve the existing hydrogel structures.
Micro-Mechanical Model Development for Predicting the Effect of Microstructure on Bulk Behaviour of Aerated Soft Solids
Researcher: Georgios Samaras
Soft food systems are often used in confectionery products, such as emulsion or foam fillings, to provide consumers with a unique experience. Traditionally, the mechanical and rheological properties of these systems are studied in combination with sensory evaluation to describe their in-mouth flow properties. However, oral processing of food is very complex and several multi-scale mechanisms take place at the same time in the mouth. This is especially noticeable when dealing with more complex systems, e.g. when hard particles (inclusions) are included within a semi solid system, or products with different micro- and macroscopic structure, e.g. aerated systems. This hinders predictions of the in-mouth behaviour of the food. Knowledge of this behaviour is crucial as it is directly linked to sensory perception.
The aim of the project is to develop a multi-scale thermo-mechanical computational model for simulating the interaction between aerated fluid and solid structures. This includes first bite model for fracture and progressive damage of product into particles and subsequent shearing of particles in tongue/palate contact whilst they heat up, flow, mix with saliva and form cohesive bolus. Necessary rheological experiments, in compression and shear of boluses, will be developed to provide data for validating simulations.
Numerical Modelling of Tactile Perception
Supervisor: Dr Marc Masen, Professor Daniele Dini
We are numerically modelling skin-surface interaction in order to better understand the sensations of touch and perception. The project involves developing finite element models and utilising data science methods to evaluate the stress, strain and energy fields within multi-layered hyper/viscoelastic soft tissue in the vicinity of mechanoreceptors. A better understanding of the processes of tactile perception and mechanotransduction have applications in a variety of fields, from the development of new skincare products, to the tailoring of product/surface engineering methods.
Structure Breakdown During Oral Processing of Aerated Chocolates
Researcher: Dimitrios Bikos
Aerated chocolate products are popular consumer items associated with positive textural and sensory attributes. Among other microstructural features such as cocoa solids, sugar particles, etc. aerated chocolate consists of bubbles as well. Interaction between bubbles and particles occur during the structure build-up and structure breakdown process and therefore it needs to be investigated. Therefore, a multidisciplinary approach is taken to predict how microbubbles impact on the rheological, thermal and lubrication processes through progressive structure breakdown in the mouth. However, the effect of the aerated microstructure on the chocolate’s behavior during both industrial and oral processes is a very complex research field. During oral processing, food first fractures into particles, which interact with saliva to form a bolus, which is then swallowed. During this process, mechanical and thermal loads are applied whilst the effect of the contact with the oral cavity is also crucial in determining the consumer’s taste experience. Chocolate changes phase as it melts further complicating the behavior. However, the effect of aeration on industrial processing or manufacturing of chocolate cannot be neglected. Specifically, the effect of bubbles on the thermal properties of the chocolate is to be determined such that manufacturing can be controlled to ensure that chocolate will have the desirable textural and sensorial attributes.
Synovial Fluid Lubrication and Wear of Artificial Joints
Researcher: Harriet Stevenson
In 2015 there were over 180,000 primary hip and knee joint replacement procedures recorded in the United Kingdom. These devices are used to relive pain and restore function in degenerated joints caused by disease, trauma or genetic condition. Artificial joints are essentially tribological devices as the bearing surfaces articulate under load. As such they are susceptible to the usual tribology issues of high friction, wear, corrosion and fatigue and these problems can contribute to failure and revision.
Implant procedures are currently carried out for hips, knees, shoulder, elbows, ankles and spinal disks; the most common of which are hips and knees totalling 48 % and 49 % of all replacements recorded in the United Kingdom respectively. Whilst most implants remain fully functional nearly 10 % of hips required revision surgery in 2015. Prostheses are increasingly being implanted into younger patients and therefore the life expectancy and performance requirements are on the rise.
The aims of this study are to understand the fundamental lubrication mechanisms of synovial fluid (SF) and to characterise how friction and implant wear are related to SF chemistry. There is a limited amount of published work on the effects of SF chemistry on implant wear and most of this is limited to UHMWPE rather than CoCrMo with model or Bovine Calf Serum (BCS) fluids. One important aspect of this work is to include human SF in the research programme. There are very few studies on lubrication and wear with human SF, which is a significant omission to our understanding of the problem. At the start of the PhD project an opportunity arose to obtain human SF through collaboration with Dr Mathew Jaggard (Muscleoskeletal Research Laboratory). Bench testing of human SF and comparing the results to model formulations will contribute to our fundamental knowledge of the effect of chemistry on wear and the validity of using 25 % BCS as a reference fluid. The image shows metallic and organic deposits around a ball wear scar.
Articular Cartilage – Biomechanics, Osteoarthritis and Tissue Engineering
Researcher: Mario Alberto Accardi
The project involves research on early diagnosis of Osteoarthritis and on state of the art treatments for this pathology. The project focuses on characterising stress-induced damage to cartilage and the effect on tribological mechanisms. Cartilage damage often leads to osteoarthritis and a key objective of research in this area is to identify the physical signs at an early stage and correlate these with biochemical changes. The project characterises physical degradation in cartilage subject to repeated stresses and use this information to develop analytical and numerical models to describe mechanical function of cartilage. The model will be used to explore the effects of mechanical degradation on the tribological function and to design artificial tissues. Additionally biochemical analysis will be carried out on the cartilage test samples. The overall objective is to link cartilage damage and biochemical changes and to understand the effect on mechanical function. The project is in collaboration with Professor Justin Cobb (Faculty of Medicine, Biosurgery & Surgical Technology) and Professor Hideaki Nagase (Kennedy Institute).
There are several parts to the project, both experimental and the development of an analytical/numerical model to describe cartilage mechanical function and the effect of damage. Parts of the investigation include:
- In vitro tests - samples of articular cartilage will be subject to repeated loading and shearing at physiological levels in bench top tests.
- Characterisation of mechanical properties of cartilage. The physical condition (surface roughness, wear loss, mechanical properties) of the cartilage will then be measured and the results compared to ‘in vivo' degraded specimens and osteoarthritic cartilage.
- Development of advanced analytical and numerical models to predict fluid flow and stresses within the cartilage matrix using the physical parameters measured in this study. To do this it is necessary to obtain measurements for the physical properties of cartilage. Cartilage will be modelled as a visco-elastic porous structure with the inclusion of collagen fibrils. The swelling behaviour of the tissue will also be included. The model can be used to explore the effect of cartilage degeneration and property changes on tribological and mechanical function.
- Investigation and assessment of potential early stage treatments for osteoarthritis.
Biomechanics of the Human Brain
Researcher: Dr Antonio Elia Forte
Supervisor: Professor Daniele Dini
The main objective of this project is to develop phantoms capable of providing detailed anatomical structures along with an accurate tactile response when performing surgical tasks such as cutting, indention and suturing. This can be achieved by replacing conventional materials with custom-designed multicomponent polymer blends that can mimic the mechanical behaviour of complex organic tissues. The project is aimed at designing, making and testing synthetic tissues tailored to reproduce the mechanical response of different human organs and tissues (lung, brain, liver, skin, cartilage, etc.). Direct comparisons with data acquired from real tissues using either in-vitro data or imaging during surgical procedures, and feedback from a number of experienced surgeons, will be used to validate the effectiveness of the proposed solutions, with an initial focus on brain tissue.
The first stage of the project will involve experimental testing protocols based on methodologies developed to assess the response of materials for engineering applications, such as rheometric and oedometric analyses, friction and fracture tests, porosity measurements, strain-hardening and hysteresis studies. In the second stage, the mechanical characterisation of the tissue will be used to design new synthetic materials using engineering principles (integrity and functional response of the tissue). This will be coupled to the chemical and tissue engineering components of the project, whereby the focus will shift on understanding the relations between aggregation methods of polymeric chains and variation in the elastic and viscous properties, dynamic moduli, and porosity of the synthetic materials. The match with the mechanical behaviour of specific organic tissues will be obtained by balancing the concentrations of the components to fine tune the final behaviour of the synthetic material. Full 3D models of the human brain for different surgical procedures will also be introduced. The results obtained from the simulations will be evaluated against the experimental result presented in the first part of the work. The resultant human models will be the outcomes of a multidisciplinary approach that involves chemistry, materials science, mechanical engineering and mathematical modelling. The models could become a useful tool in the preoperative planning stage, supporting surgeons in increasing the success rate in the operating theatre.
In-contact imaging of synovial lubricant films
Total hip replacement is a well-established and highly successful treatment for end stage hip arthritis and in recent years there have been significant improvements in prosthetic components. However there are still concerns about performance and component life as implants are increasingly being used in younger and more active patients. Wear of the articular surfaces remains a problem and is known to be a major cause of failure in metal-polymer joints through osteolysis. Although wear is reduced significantly with the new generation of metal-on-metal joints there are concerns about the formation of nano-wear particles which lead to increased levels of chromium and cobalt in the body. Recently this problem has been accentuated by reports of 'pseudo-tumours' which are associated with high metal ion levels. Thus prosthesis wear remains an important area of research and most experimental studies have concentrated on this aspect. Relatively little attention has been paid to analysing the properties of the synovial lubricating film and the mechanisms of film formation, although such knowledge is key to the development of strategies to reduce wear. Wear of prosthetic joints is controlled by the properties of the synovial lubricating film and the nature of the articulating surface. The current proposal will focus on understanding lubrication mechanisms and the role of synovial fluid constituents in artificial hip joints.
The proposed study will analyse the chemical and physical properties of synovial fluid lubricating films formed during rubbing. This project will use In-contact Fluorescence Imaging whilst a partner project will use Atomic Force Microscopy to analyse the chemical composition, molecular structure and local physical properties (rheology, friction) of SF lubricating films. The analysis will be carried out 'in contact' so the film properties are measured during the lubrication process rather than post-test. The proposed work will provide information on the fundamental lubrication mechanisms occurring in artificial hip joints. The research has important implications for the development of low-wear strategies and new prosthesis designs.
The primary beneficiaries will be the NHS, orthopaedic surgeons and their patients as the outcome will be improved joint life and reduced incidence of prosthesis revision. In 2007, the UK performed 10,500 THR revision operations, each of which may cost up to 25K, totalling 255 million per year. Thus a reduction in revision rate, particularly for MoM joints, is an important goal as it is a costly and demanding procedure, which already consumes 10% of the NHS joint replacement budget.
The research will also deliver fundamental information of the effect of SF chemistry on joint wear. Such knowledge will enable surgeons to make an informed choice of the most appropriate type of prosthesis for each patient depending on their SF chemistry. The study could also contribute to the development of a SF 'tribo' health check and remedial strategies to improve joint lubrication. Prosthesis manufacturers will also benefit from the proposed research as a detailed understanding of the lubrication process will aid improved design of joints to reduce wear and increase implant life.
Oral Tribology of Regular and Diet Cola Drinks
Researcher: Dr Sophie Bozorgi
Sponsor: Pepsi Co.
This project is a collaboration between PepsiCo, Kings College and Imperial College London, and is investigating the links between the tribological/rheological characteristics of saliva and mouthfeel. The goal is to understand how beverages interact with saliva and how this interaction affects the lubricating conditions within the mouth. This will providing a greater understanding of how beverage formulation affects mouth feel and taste perception.
Origins of Ostheoarthritis
Researcher: Maryam Imani Masouleh
Supervisor: Professor Daniele Dini
Osteoarthritis (OA) is a common form of arthritis that causes joint degradation and affects up to 15% of the adult population. It is characterized by chronic and irreversible degeneration of articular cartilage (AC). Hemiarthoplasty is a surgical procedure, where the diseased (OA) cartilage on one side of the joint is replaced with an implant, while the other side remains intact. A key factor in determining the longevity of the implant is the friction properties of the material used as a counter-surface in contact with AC and their effect on the mechanical characteristics of the tissue.
The main aim of this study is to analyse the mechanical and frictional response of different shoulder humeral component materials against the natural glenoid. This has been developed as a two stage process. Initially, friction and wear properties of four different grades of human osteoarthritic AC were measured using pin-on-disc technique against three major types of implant materials used in hemiarthoplasty including Cobalt-Chromium alloy (Co-Cr), Ceramic (Al2O3) and Polycarbonate-urethane (PCU) polymer. The second stage of this study focuses on creating a model more anatomically realistic of the hemi-replaced shoulder joint and assesses the cartilage mechanical behaviour. A custom made joint simulator has been built and will be used to investigate the response of shoulder joints under representative loads. The glenoid will be tested against different humeral component materials to understand the friction/wear response of the cartilage. The correlation between mechanically/enzymatically damaged and healthy cartilage will be investigated. Histological analysis will be performed on the tissue to observe any structural changes due to wear. The results from this study can aid the surgeons to choose the best possible material for hemiarthoplasty according to the disease state of the patient.
The Fundamentals of the Tribology of Shaving
Researcher: Suzannah Whitehouse
This project looks to gain a fundamental understanding of shaving tribology and the lubrication within the skin-razor cartridge interface. Tribology is the study of friction, wear and lubrication; the science of interacting surfaces in relative motion. As such, shaving is a complex tribological system and is affected by the skin, hair, shaving cartridge and lubricant.
The aim is to understand the fundamental mechanisms of the skin-cartridge interface, the impact of cartridge design on fluid flow through the skin-cartridge contact and the effect of lubricant chemistry and film thickness on friction. These aspects of shaving will be explored through skin-cartridge model experiments conducted under controlled conditions. The model experiments fall into three main categories: friction measurements (MTM – effect of lubricant on friction), film thickness measurements (laser induced fluorescence) and lubricant chemistry.