Micro-manufacturing : research, technology outcomes and development issues

Besides continuing effort in developing MEMS-based manufacturing techniques, latest effort in Micro-manufacturing is also in Non-MEMS-based manufacturing. Research and technological development (RTD) in this field is encouraged by the increased demand on micro-components as well as promised development in the scaling down of the traditional macro-manufacturing processes for micro-length-scale manufacturing. This paper highlights some EU funded research activities in micro/nano-manufacturing, and gives examples of the latest development in micro-manufacturing methods/techniques, process chains, hybrid-processes, manufacturing equipment and supporting technologies/device, etc., which is followed by a summary of the achievements of the EU MASMICRO project. Finally, concluding remarks are given, which raise several issues concerning further development in micro-manufacturing

One-step deposition of nano-to-micron-scalable, high-quality digital image correlation patterns for high-strain in-situ multi-microscopy testing

Digital Image Correlation (DIC) is of vital importance in the field of experimental mechanics, yet, producing suitable DIC patterns for demanding in-situ mechanical tests remains challenging, especially for ultra-fine patterns, despite the large number of patterning techniques in the literature. Therefore, we propose a simple, flexible, one-step technique (only requiring a conventional deposition machine) to obtain scalable, high-quality, robust DIC patterns, suitable for a range of microscopic techniques, by deposition of a low melting temperature solder alloy in so-called 'island growth' mode, without elevating the substrate temperature. Proof of principle is shown by (near-)room-temperature deposition of InSn patterns, yielding highly dense, homogeneous DIC patterns over large areas with a feature size that can be tuned from as small as 10nm to 2um and with control over the feature shape and density by changing the deposition parameters. Pattern optimization, in terms of feature size, density, and contrast, is demonstrated for imaging with atomic force microscopy, scanning electron microscopy (SEM), optical microscopy and profilometry. Moreover, the performance of the InSn DIC patterns and their robustness to large deformations is validated in two challenging case studies of in-situ micro-mechanical testing: (i) self-adaptive isogeometric digital height correlation of optical surface height profiles of a coarse, bimodal InSn pattern providing microscopic 3D deformation fields (illustrated for delamination of aluminum interconnects on a polyimide substrate) and (ii) DIC on SEM images of a much finer InSn pattern allowing quantification of high strains near fracture locations (illustrated for rupture of a Fe foil). As such, the high controllability, performance and scalability of the DIC patterns offers a promising step towards more routine DIC-based in-situ micro-mechanical testing.Comment: Accepted for publication in Strai

Multi-scale data fusion for surface metrology

The major trends in manufacturing are miniaturization, convergence of the traditional research fields and creation of interdisciplinary research areas. These trends have resulted in the development of multi-scale models and multi-scale surfaces to optimize the performance. Multi-scale surfaces that exhibit specific properties at different scales for a specific purpose require multi-scale measurement and characterization. Researchers and instrument developers have developed instruments that are able to perform measurements at multiple scales but lack the much required multi- scale characterization capability. The primary focus of this research was to explore possible multi-scale data fusion strategies and options for surface metrology domain and to develop enabling software tools in order to obtain effective multi-scale surface characterization, maximizing fidelity while minimizing measurement cost and time. This research effort explored the fusion strategies for surface metrology domain and narrowed the focus on Discrete Wavelet Frame (DWF) based multi-scale decomposition. An optimized multi-scale data fusion strategy ‘FWR method’ was developed and was successfully demonstrated on both high aspect ratio surfaces and non-planar surfaces. It was demonstrated that the datum features can be effectively characterized at a lower resolution using one system (Vision CMM) and the actual features of interest could be characterized at a higher resolution using another system (Coherence Scanning Interferometer) with higher capability while minimizing the measurement time

Surface modification of zirconia-based bioceramics for orthopedic and dental applications

Debido a sus excelentes propiedades mecánicas y una excelente biocompatibilidad, el uso de las cerámicas de base de circona en aplicaciones dentales y ortopédicas ha crecido rápidamente durante las últimas décadas. Sin embargo, tanto la alúmina como la circona son bioinertes, lo cual dificulta su implantación en contacto directo con el hueso. Además, las infecciones siguen siendo una de las principales causas de fallo de implantes. Para resolver ambos problemas, se requiere un mejor diseño de la superficie: en particular, una topografía adecuada puede promover la osteointegración y limitar la adhesión bacteriana. Por otro lado, la fiabilidad a largo plazo es un asunto crítico para los implantes estructurales, y las cerámicas que contienen circona requieren una atención especial. Como para otras cerámicas, las alteraciones superficiales pueden comprometer sus propiedades mecánicas. Además, la transformación de fase de tetragonal a monoclínica, que les proporciona una tenacidad excepcional, puede ocurrir espontáneamente en presencia de agua, lo cual puede afectar las propiedades del material. La cinética de este fenómeno, conocido como envejecimiento hidrotérmico, es muy sensible a los cambios de procesamiento. Por lo tanto, cualquier modificación de la superficie debe ir acompañada de una evaluación de su impacto en la fiabilidad de los implantes. Basado en estas observaciones, el objetivo de esta tesis fue desarrollar procesos para modificar la superficie de los implantes a base de circona, en particular la topografía, sin comprometer sus propiedades mecánicas y estabilidad hidrotérmica. El esfuerzo de investigación se centró en dos materiales: la circona estabilizada con itria (3Y-TZP), que se utiliza cada vez más para aplicaciones dentales (por ejemplo: coronas, implantes), y la alúmina reforzada con circona (ZTA), que es el estándar actual en ortopedia para la fabricación de componentes cerámicos estructurales. Por lo tanto, este trabajo se puede dividir en dos partes principales. En la primera parte, se llevó a cabo un amplio estudio del ataque de la circona con ácido fluorhídrico (HF). Se demostró que ajustando el tiempo de decapado es posible controlar la rugosidad y la dimensión fractal de la superficie. Además, los resultados indican condiciones adecuadas para incrementar la rugosidad de forma rápida y uniforme, sin comprometer su resistencia mecánica ni tampoco su resistencia al envejecimiento. Basándose en estos hallazgos, se obtuvieron muestras con gradientes de rugosidad mediante inmersión con una velocidad controlada en una solución de ataque. Gracias a este método, que reduce drásticamente los esfuerzos y recursos necesarios para estudiar las interacciones célula-superficie, se realizó un análisis rápido de la influencia de la micro- y nano-topografía inducida por HF en las células madre mesenquimales. Se determinaron correlaciones entre parámetros de rugosidad y morfología celular, destacando la importancia de la optimización de la topografía a múltiples escalas para inducir la respuesta celular deseada. En la segunda parte, una estrategia integrada fue desarrollada para proporcionar propiedades antibacterianas y osteointegrativas a las superficies de ZTA La micro-topografía se controló mediante moldeo por inyección. Mientras tanto, un nuevo procedimiento que implica la disolución selectiva de la circona por HF (ataque selectivo) se utilizó para producir nano-rugosidad y una nanoporosidad superficial interconectada. La utilización potencial de la porosidad para la liberación de antibióticos fue demostrada, y se evidenció que la encapsulación liposomal puede aumentar la cantidad de fármaco cargada. Además, se demostró que el impacto del ataque selectivo sobre las propiedades mecánicas y la estabilidad hidrotermal era limitado. Por lo tanto, la combinación del moldeo por inyección y del ataque selectivo parece prometedora para la fabricación de componentes de ZTA implantables en contacto directo con el huesoDue to their outstanding mechanical properties and excellent biocompatibility, the use of zirconia-based ceramics in dental and orthopedic applications has grown rapidly over the last decades. However, both alumina and zirconia are bioinert, which hampers their implantation in direct contact with bone. Furthermore, infections remain one of the leading causes of implant failure. To address both issues, an improved surface design is required: in particular, an adequate topography can promote osseointegration and limit bacterial adhesion. On the other hand, long-term reliability is a major concern for load-bearing implants, and zirconia-containing ceramics require special attention. As for other ceramics, surface alterations can impair their mechanical properties. Besides, the tetragonal to monoclinic phase transformation, which accounts for their exceptional toughness, can occur spontaneously in the presence of water, potentially deteriorating the material properties. The kinetics of this phenomenon, known as hydrothermal ageing, are highly sensitive to processing changes. Any surface modification of zirconia-containing ceramics should thus be accompanied by a careful assessment of its impact on implant reliability. Based on these observations, the objective of this thesis was to develop processes to modify the surface of zirconia-based implants, in particular the topography, without compromising their mechanical properties and hydrothermal stability. The research effort focused on two materials of particular interest: yttria-stabilized zirconia (3Y-TZP), which is increasingly used for prosthodontic applications (e.g., crowns, implants), and zirconia toughened alumina (ZTA), which is the current gold Standard in orthopedics for the fabrication of load-bearing ceramic components. Accordingly, this work can be divided into two main parts. In the first part, an extensive study of the hydrofluoric acid (HF) etching of zirconia was carried out. It was shown that monitoring etching time allows controlling the roughness and fractal dimension of the surface. Furthermore, the results indicated suitable processing conditions for a fast and uniform roughening of zirconia components, without compromising substantially their strength and ageing resistance. Based on these findings, zirconia samples with roughness gradients were obtained by immersing specimens into an etching solution with a controlled speed. Thanks to this method, which drastically reduces the efforts and resources necessary to study cell-surface interactions, a rapid screening of the influence of HF-induced micro- and nano-topography on mesenchymal stem cell morphology was conducted. Correlations between roughness parameters and cell morphology were evidenced, highlighting the importance of multiscale optimization of topography to induce the desired cell response. In the second part, an integrated strategy was developed to provide both osseointegrative and antibacterial properties to ZTA surfaces. The micro-topography was controlled by injection molding. Meanwhile a novel process involving the selective dissolution of zirconia by HF (selective etching) was used to produce nano-roughness and interconnected Surface nanoporosity. Potential utilization of the porosity for delivery of antibiotic molecules was demonstrated, and it was shown that liposomal encapsulation could improve drug loading. Furthermore, the impact of selective etching on mechanical properties and hydrothermal stability was shown to be limited. The combination of injection molding and selective etching thus appears promising for fabricating a new generation of ZTA components implantable in direct contact with bone

High optical contrast nanoimprinted speckle patterns for digital image correlation analysis

For the characterization of the mechanical deformation of materials at microscopic length scales, image processing of a high-quality surface pattern was used. We imprinted speckle patterns onto a thin polymer film attached to the surface of flat and curved metal substrates using flexible molds and soft-thermal nanoimprint lithography. High optical contrast was achieved by mixing black dye into the film generating high absorption in the elevated structures, and by adding titania nanoparticles as fillers to the recessed areas to induce diffuse scattering. For accessing resolution suitable to detect deformation at an individual grain level, the structure sizes were scaled down from 20 μm to 2 μm. For both structure sizes imaging was tested using a digital image correlation setup, that enables 3D imaging of samples with angles of up to 10° of inclination

Bioinspired Design of Wetting and Anti-Wetting Surfaces via Thiol-ene Photopolymerization

Surface wettability is known to have a profound influence in both academic study and industrial application of materials. Superhydrophobic surfaces, with a static contact angle higher than 150° and a contact angle hysteresis lower than 10°, have received continued attention for their broad applications, such as self-cleaning, antifogging and frosting, and drag reduction. The continuous development of materials and approaches that used to create superhydrophobic surfaces has led to further exploration of coatings with other desirable properties such as superamphiphobicity, mechanical robustness and thermal stability. In this work, coatings with super wetting and super anti-wetting properties were designed and fabricated by tailoring the chemical composition and the morphology of the surface in an effort to expand the application and to improve the mechanical property of the coatings. In the first study, a superamphiphobic coating was prepared by spray deposition and followed up UV-polymerization of a hybrid organic-inorganic thiol-ene precursor. The combination of dual-scale roughness and low surface energy materials led to surfaces with strong water/ oil repellency and self-cleaning properties. In the second study, a superhydrophilic and superoleophobic membrane for oil/water separation applications was developed. The textured membrane morphology enhanced the hydrophilic and oleophobic properties of the surface. The efficiency of the superhydrophilic/superoleophobic membrane on oil/water separation was demonstrated by emulsion and dye contained emulsion separation studies. In the third study, a superhydrophobic surface was prepared with porogen leaching approach in an effort to reduce the loading level of NPs. The microphase separation and porogen leaching process resulted in microscale roughness. NPs migration from bulk to interphase led to the formation of nanoscale roughness. The combination of micro- and nano-scale feature provides the surface with superhydrophobicity with 50 wt.% reduced NPs loading level

Three-Dimensional (3D) Printed Microneedles for Microencapsulated Cell Extrusion

Cell-hydrogel based therapies offer great promise for wound healing. The specific aim of this study was to assess the viability of human hepatocellular carcinoma (HepG2) cells immobilized in atomized alginate capsules (3.5% (w/v) alginate, d = 225 µm ± 24.5 µm) post-extrusion through a three-dimensional (3D) printed methacrylate-based custom hollow microneedle assembly (circular array of 13 conical frusta) fabricated using stereolithography. With a jetting reliability of 80%, the solvent-sterilized device with a root mean square roughness of 158 nm at the extrusion nozzle tip (d = 325 μm) was operated at a flowrate of 12 mL/min. There was no significant difference between the viability of the sheared and control samples for extrusion times of 2 h (p = 0.14, α = 0.05) and 24 h (p = 0.5, α = 0.05) post-atomization. Factoring the increase in extrusion yield from 21.2% to 56.4% attributed to hydrogel bioerosion quantifiable by a loss in resilience from 5470 (J/m3) to 3250 (J/m3), there was no significant difference in percentage relative payload (p = 0.2628, α = 0.05) when extrusion occurred 24 h (12.2 ± 4.9%) when compared to 2 h (9.9 ± 2.8%) post-atomization. Results from this paper highlight the feasibility of encapsulated cell extrusion, specifically protection from shear, through a hollow microneedle assembly reported for the first time in literature

Наноструктурне и микроархитектонске карактеристике врата бутне кости: утицај на повећану коштану фрагилност са старењем код жена

Background: Hip fractures are among the most important health problems in elderly population worldwide, particularly in elderly women. However, despite extensive research on age-related bone fragility, the factors leading to decreased bone strength in advanced age are not yet clear enough. Indeed, in clinical settings bone mineral density (BMD) assessed by dual energy X-ray absorptiometry has been used as an indicator of hip fracture risk. However, as it has been already pointed out that age-related decrease in BMD fails to fully explain the high increase in hip fracture risk with aging, other bone features also account for age-related deterioration in bone strength. Since bone is a hierarchically organized structure, it can be hypothesized that its strength depends on various features from nano-scale to macro-scale. Although numerous studies addressed macro- and microstructural basis of bone fragility, so far the direct data at microarchitectural level have been scarce. Moreover, nanostructure of the bone mineralized matrix has received insufficient attention with regard to effects of aging and its relation to bone fragility. Hypotheses: Our hypotheses were that region-dependant worsening of bone microarchitecture in elderly women leads to increased femoral neck fragility, and that - besides the microarchitectural deterioration - the age-related nanostructural changes at the bone matrix level contribute to increased bone fragility in elderly women. Material and methods: To test these hypotheses, we analyzed bone specimens from the femoral neck region obtained at autopsy in young and elderly women without hip fracture as well as in a group of postmenopausal women who sustained a hip fracture. Following sectioning process, micro-computed tomography was performed to assess bone microarchitectural properties. Bone nanostructure was analyzed via Topography and Phase modes of Atomic Force Microscopy (AFM), while chemical evaluation of bone material composition encompassed energy dispersive X-ray spectroscopy, quantitative backscatter electron imaging, inductively coupled plasma optical emission spectroscopy and direct current argon arc plasma optical emission spectrometry...Увод: Преломи кука су један од најзначајнијих здравствених проблема код старих особа широм света, а посебно код старијих жена. Међутим, упркос многобројним истраживањима узрока фрагилности скелета код старијих особа, још увек се врло мало зна о чиниоцима који доводе до смањене чврстоће кости у старости. Минерална густина кости (bone mineral density, BMD) утврђена применом дензитометријске методе (dual energy X-ray absorptiometry, DXA) је дуго сматрана главним показатељем коштане чврстоће и до данас коришћена у клиничкој процени коштане фрагилности и ризика за прелом кука. Међутим, будући да је више аутора указало на податак да старосни пад BMD не може потпуно објаснити значајни пораст ризика oд преломa кука код старијих особа, неопходно је испитати и допринос других коштаних карактеристика смањењу коштане чврстоће са старењем. Како је кост хијерархијски организована структура, може се претпоставити да њена чврстоћа зависи од различитих елемената коштане грађе од нанометарске до макро-скале. Премда су се многобројне студије усредсредиле на испитивање макроструктурне и микроструктурне основе коштане фрагилности, још увек недостају директни подаци о микроархитектури костију код особа са преломом кука. Поред тога, старосним променама наноструктурних параметара самог материјала од кога је кост изграђена није посвећена одговарајућа пажња, као ни њиховом значају за коштану фрагилност. Хипотеза: Нашe хипотезе су биле да регион-зависно погоршање коштане микроархитектуре код старијих жена повећава њихов ризик за прелом кука, као и да се, осим микроструктурних промена, са старењем јављају и наноструктурне промене на нивоу коштаног матрикса које такође доприносе повећаној коштаној фрагилности код старијих жена..