Browsing by Author "Vicatos, George"

Now showing 1 - 17 of 17
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    An Attempt to Improve Stance Mechanics of Trans-Tibial Amputee Gait by the Design of a Modular Ankle Joint Prosthetic
    (2018) During, Alastair B; Vicatos, George; Sivarasu, Sudesh
    Background: A-priori research shows that trans-tibial (TT) amputees display poor gait parameters when walking with low-cost ankle-foot prosthetics (here referred to as baseline AFP’s). This has drastic implications for the amputee populations in the developing world specifically, as they have limited access to advanced prosthetic technologies. Low-cost AFP’s are unable to adequately replicate natural stance mechanics, and reliance on these devices results in increased energy expenditure, osteoarthritis and lower-limb joint deterioration. Methodology: This project details the design of a novel ankle joint prosthetic (AJP) that serves as an attachment to baseline AFP’s, with the aim of facilitating better stance mechanics via the restoration of ankle joint mechanisms. The work is presented in three core sections: Part 1 explains the rationale as to why adequately replicating natural stance mechanics is an appropriate need; Part 2 presents the design of the modular low-cost AJP that utilises only simple mechanical elements; and Part 3 presents the experimental quantification of the impact the AJP has on stance mechanics of a baseline AFP (Otto Bock 1D10) in a simulation of the TT amputee walking gait cycle, via the use of three able-bodied participants and a pseudo-prosthesis. Results: The results indicate that the AJP significantly improves the stance mechanics of the baseline AFP. During forefoot rollover a stable joint moment and an increase in joint range of motion (RoM) was observed, yielding a decrease in ankle stiffness. During initial weight acceptance of early stance, an increase in joint RoM displays the restoration of controlled plantarflexion, which indicates an improved transition from heelstrike to footflat. This is a critical mechanism that facilitates stability control during weight acceptance, and the results suggest that the designed AJP is performing better in this regard than its closest functional competitor. However, equipment errors limited the ability to accurately report on ankle stiffness of this phase. Conclusions: Overall the final conclusions are that the designed AJP improves rollover shapes of the baseline AFP, eases phase transitions, and facilitates stability control and forward tibial progression. In combination with the low cost price (±50 USD), its ease of assembly and modular design, the AJP is thus a preferable option for low-income amputees in developing countries. Finally, there is significant evidence of functional and mechanical reliability, and therefore testing of the device can progress to a clinical study involving amputee participants.
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    The design and testing of a vapour pump in the absorption refrigeration cycle
    (1995) Krafft, Eike; Vicatos, George
    This thesis presents a new pumping method in absorption refrigeration. A vapour pump, powered by a fraction of the high pressure refrigerant, is proposed to replace the conventionally used electric pump. The only energy required to power the cycle is the heat supplied to the generator. The system thus becomes completely independent of the availability of electricity and can be driven by low grade energy such as waste heat.
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    Design of a knee simulator for the testing of total knee prostheses
    (2008) Campbell, Neil; Vicatos, George
    Includes abstract. Inlcudes bibliographical references (leaves 75-77).
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    Design of an affordable anthropomorphic mechanical prosthetic hand
    (2014) Tenim, Severin; Vicatos, George
    This dissertation outlines the conceptualisation, design, manufacture, assembly and experimental testing of an affordable anthropomorphic mechanical hand prosthesis. In many countries, upper-limb amputees lack access to prosthetic hand devices. Furthermore, currently available mechanical devices require a large amount of effort to actuate; fatiguing and frustrating patients who have no other alternative but to use them. Consequently, a need has arisen to provide a mechanical device that is affordable enough to be accessible to low and middle-income patients, is functional enough to allow users to easily perform their Activities of Daily Living (ADLs), and is aesthetically appealing enough to ensure that patients feel comfortable and confident when wearing it. Concept solutions of several mechanisms were identified and evaluated from which the final design was selected. Analytical force analysis was used to generate a mathematical model to analyse the response of each dynamic member in the hand. A linear relationship between the input-force and applied grasp-forces of the hand was identified. Finite Element Analysis (FEA) used to investigate the lateral and hyperextensive loading limits of the phalanges, generated results that corresponded well to the experimental outcomes. Amongst the utilised actuation mechanisms (levers, pulleys, tendon-wires, bearings and springs), the tendon-wires were of concern due to their repetitive tensile loading and relative movement with the phalanges. Tensile testing of various tendon-wires and endurance testing of the phalangeal tendon-channels, yielded a combination which surpassed the infinite life requirement of 1,200,000 loading cycles; with carbon-nylon contact wearing at the lowest rate as confirmed by gravimetric tests in accordance with ASTM F2025 (2000). Manufacture of the hand used rapid prototyping in combination with traditional machining methods and standard components, enabling a fully-assembled cost of R 11,628.37; below the required R 18,000 limit. Various power and precision grasping configurations were achieved and the contact forces satisfactorily maintained, using the hand’s built-in locking mechanism. Feedback gathered from the prosthetist and patients suggested making slight alterations to the hand’s aesthetics and to address minor functional challenges, such as the control of the closing trajectory for precision grasps.
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    Evaluation of the clinical outcome of curvilinear transport distraction osteogenesis and revascularised fibula free flaps in the reconstruction of large post-maxillectomy defects
    (2017) Hendricks, Mogamat Rushdi; Vicatos, George; Hudson, Donald
    Background: Maxillary defects caused by trauma or tumour resection in the head and neck region can be devastating to the patient from a cosmetic and functional perspective. Patients who undergo maxillectomy procedures experience a substantial deterioration in their primary oral functions such as breathing, mastication, salivation, deglutition and phonation, which has a collective adverse influence on their quality of life (QOL). The revascularised free fibula flap (RFFF) has been demonstrated to be most reliable for the reconstruction of maxillary defects, and has been regarded as the 'gold standard.' A novel method of regenerating bone and soft tissue through the process of curvilinear transport distraction oseteogenesis (CTDO) has been developed and compared with the RFFF technique. Method: A prospective cohort study of 6 post-maxillectomy patients was compared regarding the clinical outcome of function and aesthetics with a group of 6 patients who had undergone RFFF reconstruction. The new bone (regenerate) was compared with the parent bone from which it had been generated. Objective measuring tools were employed to assess pre and post quality of life (QOL) aspects. The RFFF patients were not subjected to any invasive procedures save to undergo a clinical evaluation and undergo a CT scan of their maxillae. A cohort of 6 participants was treated prospectively using CTDO and the results were analysed within that cohort. These results were compared with a retrospective group of 6 participants of similar age and gender distribution who had undergone RFFF reconstruction as an external control. The patented Hendricks-Vicatos (H-V) maxillary transport distractor was applied to all selected participants by the primary investigator under general anaesthesia at Groote Schuur Hospital or a private clinic. The H-V maxillary transport distractor (5 prototypes) was pre-shaped and pre-fitted onto a 3-D model of the participant's maxilla, in a laboratory. This method reduced clinical installation time. If teeth were present in the area to be distracted, then at least 2 teeth were removed from the maxilla, preferably three months before the date of distraction. In the first few cases, this was the protocol for developing bone stock. This protocol was revised in the last 2 patients of the study, where no teeth were extracted at all. A linear fracture (bi-cortical) was created in the maxilla in a vertical direction (segmentally) to develop a mobile, well-vascularised transport disc. This carrier disc was attached to the metal plate of the 'crawler' via small titanium screws. The crawler was then moved on the reconstruction plate (BiometTM Zimmer Biomet,
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    Exploring the range of motion between the acetabular component and the femoral component in hip resurfacing
    (2012) Mudd, Richard William; Vicatos, George
    Accurate placement of the femoral and acetabular components is crucial to retain the natural hip Range of Motion (RoM) in hip resurfacing, as well as prevent accelerated wear and subsequent premature component failure. Currently, magnetic resonance images and anterior-posterior radiographs are commonly used to diagnose and assess pathological conditions of the hip that may require a hip resurfacing arthroplasty...The main objective of this study was to investigate the use of an existing computer-aided design (CAD) software package to generate a three-dimensional (3D) computer model of the pelvis and upper femur, for use by a surgeon in pre-surgical planning.
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    Heat and mass transfer characteristics: design and optimisation of absorption refrigeration machines
    (1995) Vicatos, George; Gryzagoridis, Jasson
    An extensive literature study on the subject of absorption refrigeration has revealed that there is no proven methodology that can be used to design, optimise and size a plant. On the contrary there are numerous methods which analyse the performance of an existing plant from collected data. These methods however, do not provide any means of predicting how the analysed plant would perform if one or more of its working conditions should change. This work provides a complete design for an ammonia-water absorption refrigeration plant. The ranges of the working conditions in the evaporator and condenser are from -5°C to -55°C and from 5°C to 45°C respectively. For any combination of temperatures within these ranges, the temperature of the generator is optimised for maximum performance of the plant. Depending on the refrigeration capacity, the components are sized and designed. The proper design of the various components takes into account both heat and mass transfer correlations, something which has not been considered in the past as a necessary step for absorption refrigeration machines. Literature indicates that there is a vast amount of research into the absorption of gases into liquids and two-phase flows through tubes of various sections. The correlations cited in these studies have been used in designing the absorption column, evaporator and generator. The proposed optimisation method is a novel approach in designing a plant and stems from the fact that the performance of the absorption refrigerator reaches a maximum at a specific generator temperature. For this, optimisation curves have been developed, which for a particular combination of evaporator and cooling environment temperatures, both the optimum generator temperature and the maximum performance of the plant are predicted. The equations used in the computerised simulation procedure are based on the well-established enthalpy-concentration chart for the ammonia-water mixtures. Thus the properties of the mixture at various points in the plant are accurately predicted. Published computerised procedures in the past have been proven inaccurate in predicting the properties of the mixtures at near pure-ammonia concentrations. The validity of the simulation model is verified by tests performed on a laboratory size absorption plant. The plant was built from design parameters predicted by the simulation model for a refrigeration capacity of 1 kW at -l5°C evaporator coil and 25°C condensate temperatures. Thereafter the unit was operated for a range of evaporator conditions while the generator temperature was varied.
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    Multiple lift tube bubble pumps to increase the capacity of diffusion absorption refrigerators
    (2004) Bennett, A J; Gryzagoridis, Jasson; Vicatos, George
    Includes bibliographical references.
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    'No-touch' breast-implant insertion device
    (2016) Ameen, Shaa'ista; Vicatos, George
    Capsular Contracture (CC) has been identified as the major cause of breast-implant failures and subsequent discomfort, pain and shape deformation following cosmetic breast implantation procedures. It has been documented that CC is primarily due to bacteria which are transmitted in the breast-cavity through conventional implantation. A 'no-touch' implant insertion technique has therefore been identified as the optimal method in potentially reducing CC rates. This describes an implant delivery without the implant ever touching: gloves (even during post-insertion implant orientation assessments), retractors or the patient's skin and breast-tissue; which is inherently unachievable with the traditional finger-manipulation method. To date, the most significant improvement in the insertion process has been a 'minimal-touch' technique, i.e. with the Keller-Funnel. This study was therefore in the design and development of a safe 'no-touch' insertion device for the delivery of silicone breast-implants. Parameters included a horizontal 45 mm incision, which can stretch up to a maximum vertical central distance of 35 mm. The proposed design featured a positive-displacement method with: (a) pressurized air as the insertion 'force', (b) an inverting-bag (partially inserted with the implant) to eliminate direct glove/implant contact, and (c) a built-in retractor with a breast-cavity air-removal path to reduce implant insertion resistance due to trapped air. The implant, in the device, remains closed to the environment and separated from the wound margin thus, eliminating skin/implant contact and further providing wound protection. Finally, the design employed an eccentric funnel shape for device use at the inframammary incision site with a suggested subpectoral or submuscular pocket placement, i.e. to eliminate breast-tissue/implant contact. Through experimentation with various implant sizes, device dimensions were suitable for implant-volumes up to 428.57 cm3. A 1 bar air supply was used to test the prototype and prove the concept on a silicone cast breast-model. Leverage of the built-in retractor efficiently opened the incision for device placement multiple times and, the successful insertions of the implants and inverting-bag into the breast-model indicated that a 'no-touch' technique was achievable. This was at a maximum insertion time of 4.2 seconds, amongst eight implants ranging from 242 to 428.57 cm3. However, the continued post-insertion air supply resulted in inflation of the inverted bag in the breast. This is at a high risk of developing a thoracic wall deformity and/or embolism. Suggestions were made to improve the design and eliminate this fault.
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    Optimum time to refurbish a boiler feed pump at Eskom's power stations
    (2014) Mortlock, Steven Peter; Vicatos, George
    A key focus area in power generation today is to improve equipment and plant efficiency, with this study specifically aimed to determine the optimum time to refurbish a boiler feed pump by analysing the internal wear of the annular seals. The boiler feed pump (BFP) installed in a power station is either driven by a steam turbine or an electric motor and the BFP is the highest auxiliary power consumer within the power station. In the 13 Eskom generating fossil fired power stations the installed BFPs consume approximately 1000 MWs of auxiliary power continuously. The focus of the study is to understand how the BFPs efficiency changes with time as a result of increased internal clearances and the effect this has on the auxiliary power consumption. An in-depth analysis of the efficiency degradation has been studied to understand the contributing factors to these changes and specifically the change in leakage rate and friction in the annular seals of the impellers and axial thrust balancing devices.
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    Osseointegration potential for heat treated 3D Ti6Al4V scaffolds seeded with mysenchymal stem cells in vitro
    (2014) Van Heerden, Esther; Vicatos, George; Kidson, Susan
    Aseptic loosening of artificial joints occurs due to the loss of implant fixation. By implementing a 3D porous structure at the bone-implant interface, the ingrowth of bone will permit better and stronger interlocking of the implant to prevent loosening. In this study, it is hypothesized that the seeding of 3D scaffolding structures with mesenchymal stem cells (MSCs) will improve the potential for osseointegration of the implants, as the existing bone may be more inclined to unite with developing bone than with the implant substrate. Titanium-6 Aluminium-4 Vanadium (Ti64) is one of the most commonly used implant materials. Heat treatment of Ti64 was seen in tests done at the University of Cape Town to further improve against implant failure by vastly improving the materials strength and reducing debris formation. Thus the aim of this study was to investigate the effects the heat treatment of Ti64 would have on the capabilities of seeded MSCs in vitro.
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    Simulation of a power station's condensate pumping system in view of improving its efficiency
    (2014) Meyburgh, Pieter Leonardo Du Toit; Vicatos, George
    With increasing environmental awareness, higher electricity production costs, and a shortage in electricity supply to the South African grid, increased focus has been placed on the efficiency of power plants, and the improvement thereof. On the majority of the Condensate Extraction Pumps (CEPs) installed in power stations, the flow control is implemented by conventional valve throttling of the discharge valve of these pumps. This type of flow control is uneconomical, as more than 30 of the flow – and the pressure – that can be supplied by the CEPs, is throttled under normal operating conditions. As an energy-efficiency improvement measure, many sources recommend retrofitting of this flow control mechanism with variable speed flow control; but as different applications have different requirements, a need was identified to develop a systematic approach that would assist in determining the feasibility of a variable speed drive (VSD) retrofit. In order to develop this approach, a case study was conducted on an Eskom coal-fired power station – comparing different flow-control techniques with the aid of efficiency calculations, a simulated model, and an economic evaluation. In this case study, an electrical VSD was identified as a feasible retrofit, with an energy saving of 34.6 achievable in pump power consumption at full load conditions.
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    Surgical restoration of maxillofacial defects by transport disc distraction osteogenesis : engineering aspects
    (2013) Boonzaaier, James Angus; Vicatos, George
    Transport disc distraction osteogenesis (TDDO) harnesses the natural healing mechanisms of bone to regenerate, and thus repairs, bone defects. Presently, no system is available for applying TDDO to the maxillary anatomy; specifically anterior-to-posterior distraction on a three-dimensional curvilinear vector. The objective of this study was to devise a system to enable repair of the defective maxilla. The mechanical and ergonomic requirements of treatment by TDDO were investigated in the literature and through consultation with experts in the medical and bio-medical engineering fields. These requirements were distilled into a definitive Product Requirement Specification. Three iterative versions of the device were manufactured and tested. After satisfying the functional requirements in bench-tests, each version of the device was evaluated clinically. The operational performance of each device directed refinement of subsequent versions, directing major improvements to ease-of-use and comfort. The project culminated in a fully-functional maxillary TDDO device that addresses the requirements of both surgeon and patient. Proven in practice, the prototype can be easily and accurately customised by the surgeon to suit a wide range of defective maxillofacial geometries. The current version of the device performed successfully in bench-testing, confirming the strength of critical features and demonstrating the presence of adequate safety factors. The current version of the device has been implemented in two clinical cases where it successfully facilitated the repair of substantialdefects of the maxillary alveolus and hard palate. In total, four patients with large maxillary defects were treated with successful outcomes using devices developed in this project. One case has reached completion, with structural restoration of the maxillary alveolus and hard palate, and supporting permanent implanted dentition. Three ongoing cases are awaiting consolidation of the bone regenerate before final dental rehabilitation can commence.
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    The Design, Development, and Validation of a Residual Limb Evaluation System for the Real-Time Data Mapping of the Trans-Tibial Amputee Socket-Limb Interface for Prosthetic Fitment
    (2018) Bruton, Scott; Vicatos, George; Sivarasu, Sudesh
    Introduction: Skin problems are known to occur on the residual limb (RL) of trans-tibial amputees (TTAs). These are induced by an improper prosthetic socket fitment, alignment or component selection. It was identified that there is a lack of RL evaluation systems (RLESs) that are tailored for the prosthetic fitting procedure that analyse the pressures and temperatures on the RL, as well as the gait phases of stance. This observation established the hypothesis that a tactile RL evaluation device and recording software system can provide reliable socket-limb interface (SLI) information which can be used to identify vulnerable areas on the RL induced by the socket during the gait movements of TTAs. Methods: A prototype RLES was designed and developed. It was comprised of tactile pressure and temperature transducers, gait ground reaction force (GRF) transducers and device-specific software tailored for the evaluation of the RL within the SLI. A pilot study was designed to evaluate the capabilities of the RLES which entailed the evaluation of its skin temperature tracking ability, pressure measurement repeatability within the SLI, and ability to interpret the pressures during (natural) walking movements. Study participants were recruited through the private practice of prosthetist Eugene Russouw, as well as Vincent Palloti Hospital (South Africa, Cape Town) and consisted of two bilateral and three unilateral TTAs, who were enrolled in the pilot study. Each participant performed three experimental procedures: a static stand (SS); a straight-line walk (SLW); and a figure-of-8 walk (F8W). Skin temperature change due to loading and unloading was monitored during the SS procedure. Peak pressure results from the SLW and F8W procedures were gathered to evaluate the coefficient of variance (COV) between strides. This was used to evaluate the repeatability of the pressure measurements and allowed for a comparison between the SLW and F8W methods. GRF data collected from the SLW dataset was used to evaluate the RLES's ability to track gait phases. Results: The developed RLES software provided a tailored prosthetic fitting analysis platform (in the form of a graphical user interface) which allowed the user to perform a real-time, in-depth analysis of different RL areas, as well as provided an overview of all areas simultaneously. It provided functions for the recording, playback, and export of testing data which was used to evaluate the RLES capabilities. The RLES produced an average COV of 7.16%, which fell within the 6.94% ± 1.7% range in literature. The SS procedure produced an average temperature increase of 0.45 °C, found over all RL areas, which corresponds to similar studies in literature. This validated its ability to track RL skin temperature by producing the expected skin temperature change trend. Additionally, the RLES produced an expected TTA gait GRF curve (similar to literature) in which different gait phases could be identified. The comparison between the SLW and F8W methods found that pressure sore areas endured large pressures without relief from other movements (when compared to healthier areas), and suggests that the SLW and F8W comparison may be an important additional evaluation method during the prosthetic fitting procedure. The RLES identified all of the pressure sores presented within the 24 RL areas over all the TTA participants and suggested that a safe pressure threshold of 100 kPa is an appropriate guideline to be used during the prosthetic fitting procedure. Conclusions: The RLES proved to work efficiently and successfully within the study, and was capable of identifying vulnerable areas of pressure sores. With the high prevalence of skin problems on the RLs of TTAs, the implementation of a RLES during the fitting procedure, which can tailor the prosthesis design and fitment to the amputee, may potentially identify vulnerable areas of future skin problems and allow preventative actions to be performed.
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    Theoretical aspects of sorption refrigeration using organic compounds
    (2016) Jin, Meihua; Vicatos, George
    Refrigeration devices for essential food storage and preservation of medicine are among the most significant techniques developed in the past few decades. In many regions of Africa, the shortage of sustainable power sources and the abundance of solar energy make solar refrigerators a promising solution for basic refrigeration needs. Among all the solar cooling techniques, the solar sorption refrigerator is considered to be a promising alternative to the dominant vapour-compression refrigerator, which encompasses both absorption and adsorption refrigerators. It has advantages of being silent, having no compressor, lasting a long life cycle, and utilising waste heat or solar energy. In this work, the development of sorption refrigerators is outlined, and as a part of it, a theoretical diffusion absorption chiller using organic compounds is designed. The alternative working fluids used is R134a as the refrigerant, tetraethylene glycol dimethyl ether (TEG.DME) as the absorbent, and helium as the auxiliary gas. The corresponding modelling is carried out as a potential cooling system based on calculations. Furthermore, as a second part of this work, a laboratory prototype of a solid adsorption system being developed by the "Institute of Chemical Process Engineering (ICVT)" in Stuttgart University, is studied and compared. The study focuses on adsorption properties of methanol on activated carbon in adsorption process. Adsorption equilibrium data has been measured, and a good agreement between the measured equilibrium data and theoretical Dubinin-Astakhov model has been obtained. This prediction model can now be used to provide accurate data-sets, and consequently help to optimise the adsorption performance of the cooling unit. [Please note: this thesis file has been deferred until December 2016]
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    Thermodynamic analysis of a three-fluid absorption refrigeration machine
    (2000) Zulu, Andrew; Vicatos, George
    This thesis investigates the three-fluid absorption refrigeration system operating on lowgrade (heat) energy. In particular the temperature-time response of the various components of a domestic size absorption unit were investigated with respect to the pressure of hydrogen in the system under varying power input. Design modifications of the boiler, lift tube, vapour-liquid separator and heat exchanger were made while maintaining the same principle of operation.
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    Ultrasonic capsulotomy in cataract surgery
    (1998) Giesecke, Tonia; Vicatos, George
    The human lens has two functions to fulfil. It has to transmit light and it has to change its shape according to the requirements of the accommodative process. These functions are determined respectively by the optical and mechanical properties of the lens. It is well documented that cataracts contribute to the gradual changes of the lens matrix properties. The fact is that loss of transparency due to cataract is a universal phenomenon occurring in 70% of the population over 70 years of age and that the only effective treatment for cataracts is its operative removal. In cataract surgery, anterior capsulotomy is a highly defined and crucial procedure. It involves creating a circular opening in the lens by incising the anterior surface of the lens capsule. This gives access to the lens cortex which is then extracted and replaced with a permanent plastic lens. The most popular capsulotomy technique involves tearing the capsule in a circular fashion using forceps. However, there are many potential problems to this technique such as: it is difficult to master, it takes a long time to perform and above all, it runs the risk of creating tears on the periphery of the opening. Since the capsule is retained post-operatively and acts as a support and centralisation of the artificial lens, it is necessary that the integrity of the capsule remain intact. Since anterior capsulotomy is an unpredictable procedure in cataract surgery, there is a definite need for a surgical device that can perform a reliable incision on the capsule. Using ultrasound to perform a capsulotomy is an innovative technique and its application has to be thoroughly investigated. The investigation includes a numerical and experimental analysis of the lens capsule. The numerical analysis shows that the lens capsule reaches states of resonance at frequencies above 80 kHz. It is at resonance that the capsule oscillations are increased and the cellular bonds are strained and broken. Attempts were made to perforate the human lens capsule using experimental piezoelectric transducer systems operating at resonance frequencies of 81.6, 106 and 187 kHz. Although each ultrasonic system was able to denature the lens cortex, a perforation of the lens capsule was only achieved at a frequency of 81.6 kHz. However, the perforation was irregular and exhibited several tears. This result is not acceptable as one of the main design requirements is to produce a capsulotomy that has a smooth and continuous margin. The amplitudes for the higher frequencies were inadequate to strain and break the capsule, even when the crystals were driven at their maximum voltage of 400 Volts. The present investigation proves that it is highly unlikely that an ultrasonic tool can be designed within a safe margin of frequencies and voltages. As long as no other alternative method is devised, surgeons will have to contend with the occasional complication of radial tears that occur during anterior capsulotomy using current anterior capsulotomy techniques.