There is a wide range of applications for 3D printing technology with an additive manufacturing such as aerospace, automotive, marine and oil/gas, medical, consumer, electronics, building construction, and many others. There have been many pros and cons for 3D additive manufacturing. Even though 3D printing technology has many advantages: freedom to design and innovate without penalties, rapid iteration through design permutations, excellence mass customization, elimination of tolling, green manufacturing, minimal material wastes, energy efficiency, an enablement of personalized manufacturing. 3D additive manufacturing still has many disadvantages: unexpected pre- and post-processing requirement, high-end manufacturing, low speed for mass production, high thermal residual stress, and poor surface finish and dimensional accuracy, and many others. Especially, the issues for 3D additive manufacturing are on high cost for process and equipment for high-end manufacturing, low speed for mass production, high thermal residual stress, and poor surface finish and dimensional accuracy. In particular, it is relatively challenging to produce casting products with lattice or honeycomb shapes having sophisticated geometries. In spite of the scalable potential of periodic cellular metals to structural applications, the manufacturing methods of I∙AM Casting have been not actively explored nor fully understood. A few qualitative studies of I∙AM Casting has been reported. Recently, a sand casting of cellular structures was attempted, resulting in casting porosity and the sharp corners in the lattice structure of the cellular structural molds, a sharpness which prevent fluid-flow and causes undesired solidification, resulting in misrun casting defects. Research on the indirect AM methods has not been aggressively conducted due to the highly complex and multidisciplinary problems across the process – continuum modeling (thermal stress, flow, heat transfer, and water diffusion) with multiple materials (polymer, metals, and ceramic) for multiphase simulations – solid, liquid, and gas. As an initial step to fully understand the processing of I∙AM Casting, a quantitative study on I∙AM Casting is conducted in this work.

Orientador: Antonio Riul Júnior / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-02T23:09:29Z (GMT). No. of bitstreams: 1 Gaal_Gabriel_M.pdf: 44712274 bytes, checksum: 82729c0ddf725ae1aecd4acf867ce13e (MD5) Previous issue date: 2017 / Resumo: Hoje em dia um dos maiores desafios na área de fabricação de eletrodos é o desenvolvimento de novos materiais e métodos alternativos às técnicas tradicionais. Neste cenário, a eletrônica impressa aparece como alternativa interessante devido à simplicidade e robustez para deposição de trilhas condutoras em designs diversos. Aliado a tal fato, o desenvolvimento de novos materiais e novas tecnologias de impressão 3D facilita a aplicação dessa técnica no desenvolvimento de dispositivos, diminuindo custos, etapas de fabricação e tempo de prototipagem. Nesse projeto apresentamos o desenvolvimento de eletrodos interdigitados (IDEs, do inglês interdigitated electrodes) impressos utilizando uma impressora 3D Mendel90, totalmente montada pelo nosso grupo de pesquisa em colaboração com o Prof. Varlei Rodrigues. Utilizamos um filamento comercial a base de ácido polilático (PLA) dopado com fibras de grafeno para a impressão das trilhas condutoras, além de PLA transparente, também comercial, para impressão do suporte sobre o qual os IDEs foram impressos. Conseguimos imprimir IDEs em ~ 10 minutos, algo impraticável com técnicas fotolitográficas. Alternativamente, realizamos a funcionalização química das trilhas condutoras utilizando um banho de 2 h em solução de KMnO4 diluído em H2SO4, seguido por uma limpeza em água ultrapura e nova lavagem em HCl. Finalmente, para remoção do permanganato residual da superfície dos eletrodos, banhamos rapidamente as trilhas em solução de H2SO4 com H2O2 em proporção de 25% para 75% respectivamente. Realizamos caracterizações morfológicas, composição química, medidas elétricas e eletroquímicas das trilhas impressas e dos eletrodos funcionalizados quimicamente, comparando com resultados de IDEs de ouro de geometria idêntica. Em particular, verificamos diferenças significativas na impedância dos eletrodos impressos em relação aos de ouro, devido a baixa capacidade de formação de dupla-camada elétrica nos IDEs impressos. Foi observado também que o tratamento químico proposto modifica a resposta elétrica, aproximando o espectro de impedância dos eletrodos impressos ao obtido com os IDEs de ouro. Verificamos que a funcionalização química aumenta o desbalanceamento de cargas na superfície dos eletrodos impressos, favorecendo a formação de dupla-camada elétrica na interface eletrodo/eletrólito. Aproveitando esse desbalanceamento, realizamos a deposição de filmes poliméricos nanoestruturados visando o desenvolvimento de uma língua eletrônica totalmente impressa. Como etapa final, utilizamos esse sensor na distinção de amostras de solos com diferentes tipos de macro nutrientes, obtendo resultados semelhantes aos obtidos por sensores tradicionais. Com esta prova de conceito esperamos contribuir para uma metodologia mais simples, barata e rápida na fabricação de eletrodos e dispositivos explorando as facilidades da técnica de impressão 3D, permitindo sua prototipagem em geometrias complexas e tridimensionais que possam ser futuramente aplicados em sensoriamento e biossensoriamento / Abstract: Nowadays, one of the biggest issues addressed to sensor fabrication is build up efficient electrodes as an alternative way to the complex and expensive processes required by traditional techniques. Within this context, printed electronics arises as an interesting alternative due its simplicity and robustness to put electrodes on various surfaces. Furthermore, the development of new materials and technologies to 3D printing techniques eneables its exploration as a cheap and accessible technology to fabricate electrodes and potentiates several fields with more creative ideas, cost-effective and alternative materials for a rapid prototyping of complex devices. We show here the fabrication of fully 3D printed interdigitate electrodes (IDE) using a standard home-made Mendel90 Fused Deposition Modeling 3D printer, assembled in our research group in collaboration with Prof. Varlei Rodrigues. We used a commercial polylactic acid (PLA) filament doped with graphene fibers to print the conductive tracks and transparent PLA filament to print the electrodes substrate. As a result, we were able to develop fully 3D printed IDEs within 10 minutes, something impossible to achive with photolitographic techniques. We also applied a chemical functionalization to the electrodes with a 2 hours bath of KMnO4 dissolved in a H2SO4 solution, followed by a cleaning process with ultra-pure water and HCl. The IDEs were then immersed in a 25% H$2SO4 and 75% H2O2 solution in order to remove the potassium permanganate thin film adhered to the IDE surface. Finally, we carried out morphological, chemical composition, electrical and electrochemistry characterizations of the 3D printed IDEs, besides the functionalized electrodes and the results were compared with identical gold IDEs. In particular, we noticed a great difference between the electrical impedance response of the gold IDE compared with the 3D printed due to its low capacity to form electrical double layer. Moreover, we verified that the chemically treated IDEs show a similiar impedance behavior compared with the gold electrodes due a higher unbalance of superficial charges. Therefore, we explored this higher surface charge distribution to deposit polimeric nanostructured films aiming the development of a fully 3D printed electronic tongue. Lastly, we used this sensor to distinguish different soil samples fertilized with different macro nutrients. We obtained a distinguish equivalent to a tradicional e-tongue system built with microfabrication techniques. With this proof of concept, we expect to contribute with a simpler, cheaper and faster thecnique of electrode and device fabrication that explore the facilities and strengths of 3D printing technologies, eneabling their development in complex and 3D geometries for its appication in sensing and biosensing devices / Mestrado / Física / Mestre em Física / 156050/2015-3 / CNPQ

In recent years, additive manufacturing (AM) has become an increasingly promising method used for the production of structural metallic components. There are a number of reasons why AM methods are attractive, including the ability to produce complex geometries into a near-net shape and the rapid transition from design to production. Ti-6Al-4V is a titanium alloy frequently used in the aerospace industry which is receiving considerable attention as a good candidate for processing via electron beam additive manufacturing (EBAM). The Sciaky EBAM method combines a high-powered electron beam, weld-wire feedstock, and a large build chamber, enabling the production of large structural components. In order to gain wide acceptance of EBAM of Ti-6Al-4V as a viable manufacturing method, it is important to understand broadly the microstructural features that are present in large-scale depositions, including specifically: the morphology, distribution and texture of the phases present. To achieve such an understanding, stereological methods were used to populate a database quantifying key microstructural features in Ti-6Al-4V including volume fraction of phases, a lath width, colony scale factor, and volume fraction of basket weave type microstructure. Microstructural features unique to AM, such as elongated grains and banded structures, were also characterized. Hardness and tensile testing were conducted and the results were related to the microstructural morphology and sample orientation. Lastly, fractured surfaces and defects were investigated. The results of these activities provide insight into the process-structure-properties relationships found in EBAM processed Ti-6Al-4V.

A indústria de pedras preciosas de Soledade/RS e região gera em seus processos de beneficiamento grande quantidade de rejeitos gemológicos, que acabam sendo depositados nos pátios das empresas, podendo causar danos ao meio ambiente. A gema de maior volume de beneficiamento na região é a ágata. Este trabalho propõe uma técnica para efetuar a reutilização de rejeitos oriundos do beneficiamento da ágata e transformá-los em matériaprima para a fabricação de objetos via impressão tridimensional a jato de tinta (3DP). Através da utilização de metodologia adequada para moagem e classificação dos rejeitos, foi possível obter pó com granulometria adequada ao processo. Foram efetuadas duas formulações de matéria-prima, utilizando o método de aglutinação orgânico, com material de ligação misturado ao pó e líquido de deposição reologicamente simples. Foram efetuados testes de bancada para interação entre o pó e o aglutinante, testes em equipamento de prototipagem rápida e confecção de corpos de prova, que mais tarde foram submetidos a medição e ensaios de resistência mecânica à flexão a 4 pontos. Das análises efetuadas, a primeira formulação não foi considerada satisfatória, pois teve grandes deformações durante a construção e manipulação e pós-tratamento. Já a segunda formulação alcançou a mesma resistência mecânica do material disponibilizado pelo fabricante, com coerência nas formas geométricas e desvios dimensionais reduzidos. Com a utilização desta nova matéria-prima, estima-se que o custo final de fabricação das peças seja reduzido em até 70%, viabilizando a utilização do processo por empresas de micro e pequeno porte. / The gem processing industries of Soledade/RS and region generate a large amount of waste which is eventually deposited in the companies’ grounds and may damage the environment. The gem with largest volume of processing in the region is the agate. This work is a review of the reuse of wastes of agate as raw materials for inkjet three-dimensional printing (3DP). Through the use of appropriate methodology for grinding and classification of waste it was possible to obtain powder with a particle size indicated to the process. Two formulations of raw material were made, using the organic binding method with the binder material mixed into the powder and using the deposition simple rheological liquid. Bench tests were performed for powder binder interaction, and equipment was used for produce of test specimens which were later subjected to measurement and testing of mechanical strength. Based on the analysis the first formulation was not considered acceptable as it had large deformations during construction, manipulation and post-treatment. The second formulation reached the same mechanical strength of the manufacturer material with consistency in geometric shapes and dimensional deviation. Using this new raw material the estimated final cost of parts manufacturing is reduced by 70% making the use of the process available to micro and small businesses.

The purpose of the present study is to develop techniques for manufacturing anatomically-shaped substrates of implants made from calcium polyphosphate (CPP) ceramic. These substrates have tissue-engineered cartilage growing on their top surfaces and can be used as implants for osteochondral focal defect repair. While many research groups have been fabricating such substrates using standard material shapes, e.g., rectangles and circular discs, it is considered beneficial to develop methods that can be integrated in the substrate fabrication process to produce an implant that is specific to a patient’s own anatomy (as obtained from computer tomography data) to avoid uneven and/or elevated stress distribution that can affect the survival of cartilage. The custom-made, porous CPP substrates were fabricated with three-dimensional printing (3DP) and computer numerically controlled (CNC) machining for the first time to the best of the author’s knowledge. The 3DP technique was employed in two routines: indirect- and direct-3DP. In the former, 3DP was used to fabricate molds for pre-shaping of the CPP substrates from two different powder size ranges (<75 μm and 106-150 μm). In the latter, CPP substrates were produced directly from the retrofitted 3DP apparatus in a layer-by-layer fashion from 45-75 μm CPP powder with a polymeric binder. The prototyped samples were then sintered to obtain the required porosity and mechanical properties. These substrates were characterized in terms of their dimensional shrinkage and density. Also, SEM images were used to assess the particle distribution and neck and bond formations. The substrates produced using the indirect-3DP method yielded densities (<75 μm: 66.28 ± 11.62% and 106-150 μm: 65.87 ± 6.12%), which were comparable to the substrates used currently and with some success in animal studies. Geometric adjustment factors were devised to compensate for the slight expansion inherent in the 3DP mold fabricating process. These equations were used to bring the plaster molds into true dimension. The direct-3DP method has proven to be the ultimate choice due to its ability to produce complex anatomically-shaped substrates without the use of a chemical solvent. In addition, it allows for precise control of both pore size and internal architectures of the substrates. Thus, the direct-3DP was considered to be superior than the indirect-3DP as a fabrication method. In the alternative CNC machining approach to fabrication, the ability to machine the CPP ceramic was feasible and by careful selection of the machining conditions, anatomically-shaped CPP substrates were produced. To develop strategies for optimizing the machining process, a mechanistic model was developed based on curve fitting the average cutting forces to determine the cutting coefficients for CPP. These cutting coefficients were functions of workpiece material, axial depth of cut, chip width, and cutter geometry. To explore the utility of this modelling approach, cutting forces were predicted for a helical ball-end mill and compared with experimental results. The cutting force simulation exhibits good agreement in predicting the fundamental force magnitude and general shape of the actual forces. However, there were some discrepancies between the predicted and measured forces. These differences were attributed to internal microstructure defects, density gradients, and the use of a shear plane model in force prediction that was not entirely appropriate for brittle materials such as CPP. The present study successfully developed 3DP and CNC fabrication methods for manufacturing anatomically-shaped CPP substrates. Future studies were recommended to explore further optimization of these fabrication methods and to demonstrate the utility of accurate substrates shapes to the clinical application of focal defect repair implants.

The purpose of the present study is to develop techniques for manufacturing anatomically-shaped substrates of implants made from calcium polyphosphate (CPP) ceramic. These substrates have tissue-engineered cartilage growing on their top surfaces and can be used as implants for osteochondral focal defect repair. While many research groups have been fabricating such substrates using standard material shapes, e.g., rectangles and circular discs, it is considered beneficial to develop methods that can be integrated in the substrate fabrication process to produce an implant that is specific to a patient’s own anatomy (as obtained from computer tomography data) to avoid uneven and/or elevated stress distribution that can affect the survival of cartilage. The custom-made, porous CPP substrates were fabricated with three-dimensional printing (3DP) and computer numerically controlled (CNC) machining for the first time to the best of the author’s knowledge. The 3DP technique was employed in two routines: indirect- and direct-3DP. In the former, 3DP was used to fabricate molds for pre-shaping of the CPP substrates from two different powder size ranges (<75 μm and 106-150 μm). In the latter, CPP substrates were produced directly from the retrofitted 3DP apparatus in a layer-by-layer fashion from 45-75 μm CPP powder with a polymeric binder. The prototyped samples were then sintered to obtain the required porosity and mechanical properties. These substrates were characterized in terms of their dimensional shrinkage and density. Also, SEM images were used to assess the particle distribution and neck and bond formations. The substrates produced using the indirect-3DP method yielded densities (<75 μm: 66.28 ± 11.62% and 106-150 μm: 65.87 ± 6.12%), which were comparable to the substrates used currently and with some success in animal studies. Geometric adjustment factors were devised to compensate for the slight expansion inherent in the 3DP mold fabricating process. These equations were used to bring the plaster molds into true dimension. The direct-3DP method has proven to be the ultimate choice due to its ability to produce complex anatomically-shaped substrates without the use of a chemical solvent. In addition, it allows for precise control of both pore size and internal architectures of the substrates. Thus, the direct-3DP was considered to be superior than the indirect-3DP as a fabrication method. In the alternative CNC machining approach to fabrication, the ability to machine the CPP ceramic was feasible and by careful selection of the machining conditions, anatomically-shaped CPP substrates were produced. To develop strategies for optimizing the machining process, a mechanistic model was developed based on curve fitting the average cutting forces to determine the cutting coefficients for CPP. These cutting coefficients were functions of workpiece material, axial depth of cut, chip width, and cutter geometry. To explore the utility of this modelling approach, cutting forces were predicted for a helical ball-end mill and compared with experimental results. The cutting force simulation exhibits good agreement in predicting the fundamental force magnitude and general shape of the actual forces. However, there were some discrepancies between the predicted and measured forces. These differences were attributed to internal microstructure defects, density gradients, and the use of a shear plane model in force prediction that was not entirely appropriate for brittle materials such as CPP. The present study successfully developed 3DP and CNC fabrication methods for manufacturing anatomically-shaped CPP substrates. Future studies were recommended to explore further optimization of these fabrication methods and to demonstrate the utility of accurate substrates shapes to the clinical application of focal defect repair implants.

Ink-jet deposition is an emerging technology that provides a more efficient, economic, scalable method of manufacturing than other traditional additive techniques by laying down droplets layer by layer to build up 3-D objects. The focus of this thesis is to investigate the material interface evolution during the droplet deposition process, which holds the key to understanding the material joining process. Droplet deposition is a complicated process and can be broken down into droplet impingement dynamics and droplet hardening. This research focuses on the study of the interface dynamics of droplet impingement. In order to study the interface dynamics, a novel metric is developed to quantify the evolving geometry of the droplet interface in both 2-D and 3-D for single and multiple droplets respectively, by measuring the similarity between the evolving droplet geometry and a desired shape. With the developed shape metric, the underlying physics of the interface evolution for single droplet impingement are examined with simulations using an experimentally validated numerical model. Results show that the Weber number determines the best achievable shape and its timing during the droplet impingement when Ohnesorge number is smaller than 1, while the Reynolds number is the determining factor when Ohnesorge number is larger than 1. A regime map is constructed with the results and an empirical splash criterion to guide the choice of process parameters for given fluid properties in order to achieve the best shape without splash for single droplet impingement. In order to study the interface dynamics for multiple droplet interaction, which is computationally prohibitive for commercial software packages, an efficient numerical model is developed based on the Lattice Boltzmann (LB) method. A new LB formulation equivalent to the phase-field model is developed with consistent boundary conditions through a multiscale analysis. The numerical model is validated by comparing its simulation results with that of commercial software COMSOL and experimental data. Results show our LB model not only has significant improvement of computational speed over COMSOL but is also more accurate. Finally, the developed numerical solver is used to study the interface evolution of multiple droplet interaction with the aid of the 3-D shape metric proposed before. Simulations are performed on a wide range of impingement conditions for two-droplet, a-line-of-droplet, and an-array-of-droplet interactions. The underlying physics of the interface coalescence and breakup coupling with the impingement dynamics are examined. For line-droplet interaction, the strategy for achieving the equilibrium shape in the shortest time is studied. An important issue is discovered for array-droplet interaction, which is the air bubble formation during the droplet interaction. The mechanism for the air bubble formation is investigated and the strategy to avoid this undesirable effect is also suggested. This thesis has largely reduced the gap between basic science of studying droplet impingement dynamics and engineering application in inkjet deposition and provided preliminary insights on the material joining process for additive manufacturing.

Orientador: Ruis Camargo Tokimatsu / Resumo: Na medicina atual, uma técnica destaca-se cada vez mais, a biomodelagem. Esta técnica consiste na construção de um biomodelo físico a partir de imagens bidimensionais (de tomografias, ressonâncias, ultrassom), que são tratadas e através de softwares transformadas em um biomodelo virtual que por fim torna-se um biomodelo físico, impresso por uma impressora tridimensional, possibilitando a equipe médica, a percepção de detalhes dificilmente observados apenas através de imagens bidimensionais. Porém o material importado utilizado na biomodelagem é de custo elevado. Neste trabalho o objetivo foi através de uma formulação tida como ideal, publicada no artigo de (Meira), variar as porcentagens de sua composição, o ligante utilizado, o método de mistura, as granulometrias dos pós e adicionar um novo constituinte (sulfato de magnésio), e assim, adquirir um material mais barato e observar qual a influência da composição e granulometria em propriedades fundamentais para a qualidade de um pó para manufatura aditiva, tais como fluidez para distribuição homogênea, alto empacotamento das partículas para maximizar a densidade das peças, espessura da camada maior que as dimensões dos aglomerados e bom acabamento superficial após a camada ser depositada. Posteriormente, foram produzidos corpos de prova com diferentes composições, granulometrias e submetidos a ensaios de compressão e flexão três pontos. Após estes ensaios, médias e desvios padrões foram calculados para cada composição e granul... (Resumo completo, clicar acesso eletrônico abaixo) / Mestre

3D printers are a type of digital fabrication tool being used by communities committed to shared software, hardware, and digital designs. This shared digital knowledge can be understood as an emerging common resource for the fabrication of physical goods and services. Yet the knowledge associated with physical resources used in 3D printing is less understood. This thesis explores what factors enable or prevent knowledge about physical materials entering the commons. 3D printing, with its particular configuration of digital and physical goods, offers a unique angle to advance the field of commons scholarship. This thesis elaborates the use of commons theory for traversing the boundary between knowledge associated with physical materials and digital content from the perspective of 3D printer users. Particular contributions are made to the branch of knowledge commons theory: notably, how design rules in technological systems can be used to theorise boundaries; how differentiating between the nature of underlying resources can help explain the inclusion of knowledge in the commons; and, how patterns of user engagement with types of knowledge in the commons can be studied over time. To develop these contributions I employ theory on the design rules of technological architecture, and use insights from the study of peer production in online communities. Empirical data comes from a qualitative study of users of Fab Labs, community workshops for digital fabrication, as well as from a quantitative study of the online user forum for the Ultimaker 3D printer.

In this work differential scanning calorimetry, dynamic mechanical analysis, Fourier-Transformed Infrared Spectroscopy [FT-IR] and polarized light microscopy will be employed to characterize polymeric systems. The first chapter broadly covers polymer synthesis and important characterization methods. In the second chapter, a polyamide (PA12) will be sintered via a novel additive manufacturing (AM) technology developed here at USF termed LAPS (Large Area Projection Sintering). LAPS uses extended sintering timespans to ensure complete melting and densification of the polymer powder over the entire two-dimensional area of the part’s footprint. Further, it allows for the printed layer to crystallize and shrink in its entirety as the temperature falls below the crystallization temperature prior to the next layer being added. The printed parts (termed coupons) will be assayed by DSC and polarized light microscopy to determine sintering efficacy. Additionally, the parts will be compared to coupons printed with conventional methods to show that the USF AM technology shows superior elongation at break (EaB), with comparable ultimate tensile strength (UTS) and Young’s Modulus to laser sintered coupons. This is notable as conventional AM methods produce parts which usually compromise between EaB and modulus. The EaB of LAPS-printed parts is comparable to injection molding (IM) grade PA12, which is remarkable as IM grade PA12 powder normally has higher molecular weight and limited crystallinity. The reduced crystallinity of IM grade PA12 parts is thought to be due to the high shear rates during injection and fast cooling rates post-fabrication. Further, the USF LAPS parts show minimal or no detectable porosity. Porosity is an artifact of the sintering process which conventional techniques like laser sintering (LS) have little ability to mitigate, as higher energy wattages simply burn and degrade the polymer surface with insufficient time available for heat transfer and bulk melt flow. Porosity is documented as one of the leading causes of part failure and decreased mechanical properties in the literature, and as such the USF AM technology is in the process of being patented as of March, 2018. Chapters three through six will explore a phenomenon first noticed by clinicians at the James A. Haley Veterans Hospital. They observed that starch-thickened drinks for patients suffering from dysphagia became dangerously thinned down upon addition of the osmotic drug polyethylene glycol (PEG) 3350, marketed as Miralax®. Starch-based hydrocolloids are common thickeners used for patients with dysphagia, and so any incompatibility with such a ubiquitous drug as PEG 3350 poses an immediate danger. Patients with the disorder can suffer increased rates of aspiration-related pneumonia, incurring up to nearly a 60% fatality rate within a year. Chances for aspiration greatly increase for food items which are too inviscid to safely swallow. Rheology and FT-IR spectroscopy will be used to show that the breakdown of the starch network in aqueous solution is dependent upon the molecular weight of PEG. As the molecular weight of PEG is reduced to that of a small molecule (~300MW) from its large drug form (3350MW), the structure stabilizes and can resist shearing forces in a steady shear rheological experiment. Spectroscopy will show that PEG molecular weight also influences syneresis and the crystallinity of the starch hydrocolloid solutions. It is postulated that the molecular weight of PEG influences its miscibility in starch solutions, and its ability to interrupt the hydrogen bonding and entanglements which maintain the elastic framework which allow starch thickeners to impart viscosity and resist shearing forces. When this framework collapses, absorbed water is expelled as evidenced as a biphasic separation where water collects on top of the starch suspension. This was the phenomenon observed by the clinicians at the Veterans’ Hospital.