One of the main goals of contemporary systems neuroscience is to understand how sensory inputs are processed, networks are formed and the resulting functional outputs. To achieve this, a recording technique is required that can detect action potentials with single-cell resolution for a long period of time across a large network. Current imaging techniques available are limited in at least one of the four elements needed to fulfill this aim (a) the technique needs to be able to detect every action potential (b) from every neuron (c) for a long period of time (d) from an entire network. Neural activity has been shown to produce fast intrinsic optical signals that are the result of refractive index changes causing light scattering and birefringence associated with membrane depolarisation. To date no one has successfully managed to exploit these intrinsic optical signals in a practical robust recording system. Surface plasmon resonance (SPR) is a technique that can detect extremely small changes in refractive index and is capable of detecting this membrane localised refractive index change with a high spatio-temporal resolution. This thesis describes the design and development of an imaging system based on surface plasmon resonance to detect the refractive index change of a cell membrane during neural activity. This thesis, first theoretically examines the different processes that occur during neural activity that could affect the resulting SPR response. The change in refractive index and therefore, light intensity was calculated considering the reorientation of dipoles and ion flux during an action potential. The planar gold surfaces required to produce surface plasmon resonances were characterised and the imaging system was shown to be sensitive enough to detect these small refractive index changes. There were no visible light intensity changes after recording the optical response from one action potential. This led to the development of the experimental protocol and a data analysis tool was developed to align and average over a number of action potentials to reduce the noise floor as much as possible and increase the signal-to-noise ratio. Unfortunately, it was determined to a high degree of certainty that no action potentials were detected by the planar gold SPR sensors. It was hypothesised the SPR signal from these cell membrane localised refractive index changes was averaged across the relatively large surface area of the planar gold sensor which was why no response was detected. A novel sensor design was investigated by reducing the gold sensor size to that of one cell to improve coupling or isolation of the plasmons to a single cell. SPR at planar metal/dielectric interfaces and localised SPR for metal nanoparticles have both been extensively studied, but it is less clear what happens to the optical properties at the micrometer scale. Gold patterns of different sizes in the micrometer range were therefore, produced using photolithography. Typical SPR responses were observed for all gold microstructures, however, as expected they were not as sensitive and were wider than that of the planar gold controls. This phenomenon became more pronounced as the length of the gold structure decreases, as expected because of the spatial constriction of the propagating surface plasmon. Although the sensitivity of the micron-sized gold surfaces was less than that of the planar gold surface, with the latter unable to detect these refractive index changes. The process still suggested that the SPR technique could be successfully implemented to detect individual action potentials. Reducing the sensor size to that of one cell could improve coupling and stop the signal being averaged across the sensor. Unfortunately, it was determined to a high degree of certainty that no action potentials were detected by the gold microstructure SPR sensors.

Controlled by extracellular signals, tumour-induced angiogenesis is a crucial step in the development of tumours. Among the many cell signals already identified, the VEGF and Notch signalling pathways play a critical role in controlling endothelial cells (ECs) during angiogenesis. Although this regulatory mechanism has become a current research focus in biology, its computational modelling is still rare. We focus on developing a computational model to simulate the VEGF and Notch signalling regulatory mechanism to perceive the micro procedure of angiogenesis in silico and fill the gap between biology and computer engineering. We first developed a mathematical model with nonlinear partial differential equations (PDEs) to describe the migration of endothelial tip cells during tumour-induced angiogenesis. The simulation results show that both chemotaxis and haptotaxis have impacts on the migration of ECs in velocity and density, and the impacts depend on the gradient and direction of tumour angiogenenic factor (TAF), and fibronectin, implying a possible malignant mechanism for some subgroups of tumour. We then developed the model further to simulate the regression, recurrence or clearance of tumours due to tumour cytotoxic factors, including the immune system and drugs delivered through the vessels formed during angiogenesis, providing a broader understanding of tumours. Based on the PDE model which provided parameters of continuum mathematical model, we finally developed an enzymatic catalysed regulating model in the form of ordinary differential equations (ODEs) with agent-based modelling (ABM) using Java and MATLAB languages, to visually realise the sprouting regulated by VEGF and Notch signalling during angiogenesis. The simulation describes the process of how an endothelial stalk cell becomes an endothelial tip cell, and sprouts under the influence of VEGF and Notch signalling, revealing the relationship between sprouting and branching. As the simulation results are consistent with reported in vitro and in vivo assays, the study bridges angiogenesis research and computer modelling from the dynamic regulatory mechanism perspective, offering a huge leap over previous studies in computationally simulating tumour-induced angiogenesis. It is hoped that the results will assist researchers in both the experimental and theoretical angiogenesis communities to improve understanding of the complexity and identify the fundamental principles of angiogenesis, whilst also using modelling approaches that will enrich knowledge for computational scientists in this field.

Recent increases in life expectancy, combined with the rise of chronic diseases, have led to a rise in the use of medical devices to monitor and treat illnesses in people’s homes. To date, however, little attention has been paid to understanding the impact that these devices have on the home environment, the users of these devices and their partners. This thesis presents three studies investigating the physical, personal and social issues faced by people using home medical devices. The first study consisted of qualitative interviews with 12 device users and seven partners and investigated their experiences of home use medical devices. Analysed thematically, this study described how medical devices can foster or threaten people’s experience of the physical, personal and social aspects of the home environment when medical devices are integrated into their homes. In study two, a questionnaire was developed to investigate the attitudes of healthcare professionals and patients about the relative importance of different medical device characteristics. Different groups of healthcare professionals involved with the provision of medical devices were included (doctors, nurses, pharmacists) as well as medical device users and non-users. The results showed that practical factors (user testing, clear instructions, clinical trials, reducing appointments, training and cost effectiveness) are viewed as more important by professional groups than factors that relate to the home environment (choice and appearance). This indicates a lack of a whole person approach to patient care and the selection of home medical devices. In the third study longitudinal interviews were carried out with four couples, where one of the couple had been diagnosed with Chronic Obstructive Pulmonary Disease (COPD) and prescribed an oxygen concentrator to use at home. The aim of this study was to discover how couples experience the process of being given a medical device to use at home over time. The interviews identified that being given an oxygen concentrator can be the source of an acute episode of uncertainty for some couples and the process of coping was mediated by the expectations that they had prior to being given the device. This research has provided a valuable insight into the poorly understood impact that medical devices have on people’s experience of the home environment.

A common approach in tissue engineering strategies is to deliver living cells together with supporting scaffolds to damaged or injured body parts and then induce cell proliferation and differentiation for the purpose of regenerating functional tissues. Porous polymeric microparticles (Por-MPs), as scaffolds have recently received extensive interest for their pores, facilitating exchange of nutrients throughout the scaffolds and, sizes ( micrometre scale) and shapes (spherical), offering delivery of the cell-scaffold system via narrow bore needle with minimally invasive surgical intervention to repair irregularly shaped tissue defect. For fabrication of MPs, conventional emulsion-solvent evaporation (CE) methods are most commonly used; however the size distributions of the prepared MPs are broad, which could bring negative impacts on the efficiency of the scaffolds as cell-delivering vehicles. On the other hand, cross-flow membrane emulsification (X-ME) is a promising technique for preparation of uniform-sized MPs. One of the aims of this study was to develop a robust protocol for preparing uniform-sized, large and porous poly (lactide-co-glycolide) (PLGA) MPs using the X-ME method. The method development process started with fabrication of solid polycaprolactone (PCL) MPs (Sol-MPs). Different process and formulation parameters, such as working pressure (Pw), membrane pore diameter (D0), viscosity of disperse phase (DP) and emulsifier concentration (Conc.CP) were optimised for preparing Sol-MPs with mean diameter of approximately 100 µm. Span factor was used as a criteria of degree of monodispersity of the MPs; in general the lower the span factor, the narrower the size distribution. The same emulsion conditions were taken into account for preparation of monodisperse porous PLGA MPs (Por-ME MPs) with mean dimeter of approximately 100 µm. The further aim of this study was to assess the performance of the novel porous MPs (Por-ME MPs) as scaffolds for delivery of stem cells in bone tissue regeneration. Immortalised human mesenchymal stem cells (ihMSCs) were seeded with Por-ME MPs and the attachment, viability, proliferation and osteogenic differentiation of the cells were assessed. Under the optimal emulsification conditions, such as at certain Pw, D0, DP, Conc.CP, Sol-MPs with mean diameter of 109 µm (± 20.75) and span factor of 0.52 (± 0.04) were prepared via the ME method. On the other hand, the mean diameter and span factor of Por-ME MPs prepared via X-ME were 114 µm (± 19) and 0.43 (± 0.02), respectively. The size distributions of the Por-ME MPs, prepared via X-ME were substantially narrower than those of the Por-CE MPs, prepared via conventional high shear homogenizer. The mean diameter and span factor of Por-CE MPs were 78 µm (± 25) and 0.70 (± 0.07), respectively. On the other hand, the novel porous MPs were biocompatible with ihMSCs in terms of viability, proliferation and osteogenic differentiation of the cells. Via this study, a new platform for fabrication of porous PLGA MPs was introduction. The strategy used to prepare these MPs, could be applied for preparing MPs with other biodegradable polymers. The newly developed scaffold system (Por-ME MPs) has the potential to regenerate bone tissues; however, further research is necessary in order to establish the scaffold system as a reliable stem cell delivering vehicle.

Health monitoring devices are changing the way we treat, manage and understand chronic health conditions by continuously collecting data about medication use, symptoms, vital signs and a patient’s surrounding environment. Asthma is the most common chronic condition worldwide and has symptoms that include wheezing, coughing and shortness of breath - all typically treated with inhaled medication. By taking a daily ‘preventer’ inhaler a patient should be able to control their asthma and remain relatively symptom free. However, adherence to preventer medication is often poor, making patients prone to severe symptoms and asthma attacks. This leads to avoidable healthcare costs, mainly through preventable hospitalisations and wasted medication. Electronic monitoring devices (EMDs) are the most accurate method currently available for recording inhaler use. Through rigorous testing they have been shown to be sufficiently accurate and reliable for use in clinical practise. Early signs also suggest that they may improve inhaler use when a ringtone is used to remind the patient when a new dose is due. However, no research to date has considered the attitudes of patients with asthma as well as healthcare providers towards these devices. Human factors in healthcare is a now established area of research, with an international standard (ISO 62366) meaning that medical device developers are required to design for a usable and error-free experience. This creates clear scope for assessing the perceptions of patients and healthcare providers towards EMDs for use in the management of asthma. This was investigated in this thesis using three separate but related research studies. Two studies assessed the attitudes of patients and healthy volunteers, whilst the other analysed the opinions of healthcare providers and stakeholders in asthma care. The first study assessed the attitudes of a sample of adolescents with asthma towards an exemplar EMD – the SmartTrack. Asthma is most prevalent in adolescents, adherence is notoriously poor, and they are often overlooked in medical device design - making assessing their views a priority. The participants used a SmartTrack device for one month and completed questionnaires and interviews on their opinions towards important issues including being monitored and the device’s appearance, social acceptability and practicality. For the second study, a Delphi survey method was used to collect the opinions of stakeholders in asthma care including respiratory consultants, nurses and GPs towards EMDs. They were asked to state the key benefits they thought these devices could have, as well as the key potential costs and barriers for their introduction. Additional rounds of surveys were then used to assess which points they felt were most important and should be prioritised in the future development of these devices. EMDs developed new capabilities over the course of this thesis, meaning that the third study was used to investigate attitudes towards location and activity data, as both were beginning to be integrated with data on inhaler use. Two workshops and a technology trial were conducted with a sample of healthy adolescents from a local sixth form. Participants had their location and activity tracked and then had this data presented back to them. They were asked for their opinions on the usefulness of this data, as well as any potential risks associated with recording it. The findings from all three studies were then brought together to determine the requirements of EMDs going forward. A systems model of asthma care was developed to firstly consider the routes through which EMDs could be purchased, as well as the impacts EMDs could have on various points of the asthma care process, both for the patient and the healthcare provider. The requirements for EMDs were then also related back to this model, to help outline their importance and relevance to the asthma care pathway. From the research it was determined that developers need to reduce the size of EMDs, as well as integrate the ability to monitor inhalation and technique. Commissioners need to work with clinical researchers to identify the types of patients who would benefit most from an EMD, in order to reduce risks of over- purchasing. Furthermore, researchers need to work with healthcare standards bodies to establish how the vast quantities of data produced by EMDs can be successfully integrated into the clinical care process. This thesis has three key contributions. Firstly, it introduces human factors research methods to the domain of EMDs for asthma care. Secondly, it provides a set of requirements for EMDs to help ensure that these devices can be successfully introduced and used in clinical care. Lastly, it supplements the literature on human factors methods being applied to healthcare and provides a new example of where user-focused research has been used to elicit requirements for a medical device.

The composition of the top-most molecular layers of solid materials is of great importance in the understanding of many technologically important processes. This is especially so, for example for devices exposed to the in vivo environment of our bodies especially if long term functionality is required. Cardiovascular stents or scaffolds are a biomedical implant that must maintain structural and functional integrity for periods of months to achieve their therapeutic goal. In this work, the fully polymeric drug-eluting bioresorbable scaffold, ArterioSorbTM is characterised, paying particular attention to surface and near surface properties. The introduction of cardiovascular stents has considerably enhanced the potential of surgical intervention via angioplasty. Biomaterials used for implants may be metallic, ceramic, polymeric or composite. A new generation of drug eluting stent are now emerging, such as the Poly(L-lactide) (PLLA) based fully biodegradable stents studied here, that have the potential to increase the therapeutic potential of this approach even further. PLLA is a bioabsorbable semi-crystalline polymer that possesses a low elongation and high tensile strength, which makes it appropriate for this medical application. Using a spray-coating method a sirolimus/PDLLA layer was coated onto the surface of a bioresorbable PLLA scaffold by Arterius Ltd. The aim of this thesis is the study of the drug distribution and physiochemical properties of the biomedical device and to relate this information to likely drug release mechanisms under physiological conditions. Complementary surface and near-surface analysis techniques including scanning electron microscopy (SEM), atomic force microscopy (AFM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS) and confocal Raman imaging (CRM) have been used to assess structure, composition and their relation to drug release. Primarily, this work was carried out on a series of extruded and orientated (die-drawn) PLLA tubing before considering the actual bioresorbable medical device (uncoated, coated expanded and crimped scaffolds). ToF-SIMS has been used to confirm the chemical homogeneity of the PLLA coating and provide evidence of some minor surface elemental contamination likely due to transfer of fluorine from packaging/sample handling. The drug (sirolimus) was clearly observed and mapped at the microscale at the surface and in the bulk of the scaffold coating. In addition, the physical properties of these materials were investigated using nano and micro thermal analysis. The percentage of crystallinity of the PLLA materials was studied using Differential Scanning Calorimetry (DSC). Attenuated total reflection infrared (ATR-IR) helped in assessing the structure of PLLA. Factors including the manufacturing process used have been shown to have an effect on the materials. The degradation in vitro has been shown to be influenced by the molecular weight of the polymer and the concentration of the drug. This thesis is organised into six chapters. Chapter 1 provides an introduction to the technical requirements needed for bioresorbable stent and outlines the literature review and research context for the development of the scaffold, including materials used for the manufacturing of the scaffold, spray coating method and laser cutting techniques. Chapter 2 describes the instrumentation and methodology used for characterising such medical device as well as a description of laser cutting used in manufacture. Chapter 3 presents a feasibility study on the extruded and oriented tubing. Chapter 4 describes the characterisation of the drug distribution in the drug/polymer matrix. Chapter 5 provides a detailed characterisation of the in vitro degradation of sirolimus/PDLLA coating layer revealing the release kinetics of the device. Finally, Chapter 6 gathers information learnt throughout this thesis and explored future directions to improve release and performance of such a device.

Biomaterials used for implants may be metallic, ceramic, polymeric or composite. Currently, metals that are gradually broken down in the body have been attracting much attention, as a new generation of biodegradable implants. Magnesium (Mg) and related alloys are promising candidates for degradable biomaterials, comprising temporary mechanical properties with biological acceptance to the human body. However, the target periods set clinically, with respect to the practical uses of Mg for biodegradable stents, have yet to be achieved. Hence, improved understanding of the corrosion behaviour of Mg in the biological environment is needed. Novel Mg narrow walled minitubes, for degradable stent applications, have been produced using radio frequency magnetron sputtering (RF-MS) physical vapour deposition (PVD). The microstructural development of the as-deposited minitubes have been investigated, as a function of annealing temperature, using the combined complementary analytical techniques of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffractometry (XRD) and microhardness indentation. The as-deposited minitubes exhibited columnar grain structures with high levels of porosity, but were very brittle. Slight alteration to the crystal structure, from columnar to more isotropic grain growth, was demonstrated at elevated temperature, along with increasing material densification, hardness and corrosion resistance. It is suggested that stabilisation of the columnar grains and the formation of oxide layers during the sequential Mg-layer deposition process, acted as a barrier, preventing the development of a fully dense, equiaxed structures. The onset and development of Mg corrosion may be addressed by the use of coatings or near surface modification processes. Accordingly, the corrosion resistance of ~ 1-2 µm thick Al coatings, deposited by RF-MS on polished Mg surfaces, within Ar and Ar/H2 environments, were appraised. The coatings were heat-treated at 300°C and 450°C, with the aim of inducing the formation of bioinert Al2O3, and samples were corroded within phosphate buffered saline (PBS) solution at 37°C to mimic the biological environment. Both as-deposited and heat-treated coatings were found to delay the onset of corrosion, but showed higher initial corrosion rates, once established, as compared to the polished Mg surfaces. Slight improvement in coating performance was achieved through the addition of H2 to the system, which acted to inhibit Al-Mg alloying and enhance Al2O3 formation. However, localized accelerated corrosion associated with substrate polishing damage emphasised the need for improved process control and coating uniformity. Si-H coatings deposited on Mg surfaces within Ar/H2 ambient using a PVD technique was also investigated. The as-deposited coatings comprised dense, crack-free amorphous a-Si-H layers with thickness of ~ 1 µm. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses provided evidence for the presence of SiH2 as well as SiOx. The corrosion resistance of a-Si-H coated Mg increased significantly in contact with PBS, in both electrical and immersion tests, due to improved coverage of the substrate. The effect of rapid thermal processing techniques on the corrosion resistance of Mg surfaces was also investigated. Mg surfaces treated by large area electron beam (LAEB) irradiation showed refinement of the surface grain structure, with increased grain boundary delineation, although localised ablation, roughness and crater formation increased with increasing cathode voltage and number of pulses. The corrosion potential and corrosion rate of LAEB modified surfaces generally increased with increase the energy imparted to the surface. The extended corrosion performance of low energy EB processed surfaces, under immersion testing was consistent with the trend of improved corrosion resistance during the early stages of immersion in PBS. However, surfaces over-processed at high energies experienced higher corrosion rates in both potentiodynamic and immersion testing, due to the development of inclusions, craters and cracks on the modified surface. Further, Mg surfaces, modified by laser surface melting (LSM) under conditions of low energy laser irradiation, experienced rapid melting, causing surface smoothening and grain refinement centred along the laser beam tracks, whilst coarser grains decorated the overlapping regions, due to the Gaussian shape of the laser beam profile. More uniform surface processing was achieved by increasing the laser beam spot size, which acted to improve the corrosion resistance of Mg. Under high energy LSM processing conditions, Mg surfaces showed conventional laser melting rippled patterns, along with craters and cracks, and the redeposition of MgO particles, causing an increase in surface roughness and corrosion rate. The corrosion performance under immersion testing showed the corrosion rate similar to that of the original polished Mg samples, due to non-uniform surface modification and the mixed development of fine and coarser grains. However, observation revealed that refined grain regions along the centre of the laser tracks were able to resist corrosion for longer times. Generally, annealed Mg-minitubes produced by PVD, and the near surface modification of Mg by EB and LSM, showed that fine grained Mg can affect the electrochemical response of Mg within the physiological environment, due to the rapid, enhanced development of the passivation layer, promoted by improvements in surface homogeneity and an increase in grain boundary density.

This thesis describes the development and utilisation of a self-reporting scaffold to improve current monitoring methods of the cellular microenvironment. In vitro tissue models hold a lot of promise for regenerative medicine and tissue engineering. However, many models lack the ability to non-invasively monitor in situ cellular responses in a physiologically relevant environment. By development of electrospun self-reporting scaffolds and incorporation of flow culture conditions, this limitation can be overcome. Electrospun matrices have been shown to mimic the structural architecture of the native extracellular matrix, whilst flow conditions have been shown to regulate cellular processes, and enhance mass transport and nutrient exchange throughout polymeric scaffolds. Here we show the development of optically transparent self-reporting electrospun scaffolds that incorporate ratiometric pH-sensitive nanosensors and respond to biological and mechanical cues of the native extracellular matrix through exposure to shear stress. Optically transparent self-reporting scaffolds were fabricated by directly electrospinning pH responsive, ratiometric nanosensors within a gelatin biopolymer matrix. The sensors consist of a porous polyacrylamide matrix which encapsulates pH-sensitive fluorophores that exhibit an additive fluorescent response across the full physiological range between pH 3-8, and a pH-insensitive reference fluorophore. The self-reporting scaffold was able to support cell growth whilst being able to simultaneously monitor local pH changes in real time. A Quasi-Vivo® bioreactor system was also used to generate a flow of cell culture medium and expose cell-seeded scaffolds to a continual shear stress. This novel diagnostic scaffold and the use of flow conditions can help simulate enhance the understanding of in vitro conditions, and generate advanced simulations in vivo to facilitate tissue engineering and regenerative medicine applications.

Photoplethysmography (PPG) is a technique that uses light to measure the local changes in blood-volume in subjects (predominantly humans). Multiple useful statistics can be gained from such a measurement; heart-rate and it's variability, blood-oxygen saturation and even an estimation of blood pressure, to name but a few. Compared to other measurement techniques, photoplethysmography is favourable as it is both non-invasive, since nothing physical penetrates the subjects skin, and safe, as the subject is galvanically isolated from the test equipment (additional benefits also exist). Motion artefacts (errors in the measured signal caused by physical movement) are the largest source of error when photoplethysmographic measurements are made, and with the majority of applications involving some form of movement, a motion-tolerant PPG extraction technique would allow for more precise recordings/research/diagnosis etc. This thesis presents the development of an improved photoplethysmography technique that has increased resilience to motion. The developed technique uses multiple PPG measurements at different locations to reconstruct a single PPG signal. It is shown that despite the signals being taken in close proximity to each other (less than 3 cm separation between the farthest elements), the variation in the signals gives sufficient redundancy to extract the uncorrupted PPG to a much higher accuracy using Independent Component Analysis, achieving in the worst case, a 78% reduction in the calculated artefact presence (using quality calculating functions, also presented). As the vast majority of existing PPG systems use a single sensing element, it is hypothesised that such systems cannot be used to accurately and continuously detect the PPG for most motion types and severities. A working prototype of the developed system is demonstrated and directly compared to a single-channel system, showing its effectiveness.

Thesis (MTech(Medical Technology))--Cape Technikon, 1997 / Cryoprecipitates are used as the raw material for the preparation of Factor VIII (FVIIIl) for replacement therapy for haemophiliacs. Routinely, cryoprecipitate only recovers 50% of the Factor VIII in the plasma. The purpose of this study, production of cryoprecipitate, was to investigate those variables which play a key role in determining the yield of Factor VIII present in cryoprecipitate. Cryoprecipitate production involves a wide range of variables which could effect the final outcome of the product. These vary from the donor blood group, time of donation, exercise levels of the donor, to a time delay prior to processing, temperature storage conditions, to the method utilised for plasma freezing and thawing. The objective was to explore which combination of variables in the procedure would lead to a process which would optimize the preparation of cryoprecipitate in a routine environment, to yield the highest levels of Factor VIII. Frequently in scientific investigations, particularly when a practical approach has to be adopted, questions arise in which the effects of a number of different variables in a process, require evaluation. Such questions can usually be most economically investigated, by arranging the analysis according to an ordered plan in which all the factors are viewed in a regular way. Provided the plan has been correctly chosen, it is possible to determine not only the effect of each individual variable, but also the way in which each effect depends on the other factor, by means of an interaction. This makes it possible to obtain a more complete picture of what is happening, than would have been obtained by varying each of the variables one at a time while keeping the others constant. Designs of this sort lend themselves well to statistical analysis, and provide their own estimates of experimental error. This type of statistical analysis called, 2K Fractional Factorial Experimental Design, forms the basis of this study in which 14 key variables in the production process of cryoprecipitate were defined as possible areas in which Factor VIII levels in the cryoprecipitate are effected. Key variables have been identified on an individual basis in previous studies (Burka et al., 1975), however this blended approach to optimise the key variables within the production environment, and define further combinations which could be incorporated into the production, has never been attempted. The statistical design used in the study was compiled by the Institute for Biostatistics of the Medical Research Council (MRC). Units of blood were collected and processed, from blood donors under the stipulated criteria, corresponding to the study design.