Additive manufacturing: studio delle non conformità geometriche e dimensionali in componenti realizzati mediante tecnica fused deposition modelling

La fabbricazione additiva è una classe di metodi di fabbricazione in cui il componente viene costruito aggiungendo strati di materiale l’uno sull’altro, sino alla completa realizzazione dello stesso. Si tratta di un principio di fabbricazione sostanzialmente differente da quelli tradizionali attualmente utilizzati, che si avvalgono di utensili per sottrarre materiale da un semilavorato, sino a conferire all’oggetto la forma desiderata, mentre i processi additivi non richiedono l’utilizzo di utensili. Il termine più comunemente utilizzato per la fabbricazione additiva è prototipazione rapida. Il termine “prototipazione”’ viene utilizzato in quanto i processi additivi sono stati utilizzati inizialmente solo per la produzione di prototipi, tuttavia con l’evoluzione delle tecnologie additive questi processi sono sempre più in grado di realizzare componenti di elevata complessità risultando competitivi anche per volumi di produzione medio-alti. Il termine “rapida” viene invece utilizzato in quanto i processi additivi vengono eseguiti molto più velocemente rispetto ai processi di produzione convenzionali. La fabbricazione additiva offre diversi vantaggi dal punto di vista di: • velocità: questi processi “rapidi” hanno brevi tempi di fabbricazione. • realizzazione di parti complesse: con i processi additivi, la complessità del componente ha uno scarso effetto sui tempi di costruzione, contrariamente a quanto avviene nei processi tradizionali dove la realizzazione di parti complesse può richiedere anche settimane. • materiali: la fabbricazione additiva è caratterizzata dalla vasta gamma di materiali che può utilizzare per la costruzione di pezzi. Inoltre, in alcuni processi si possono costruire pezzi le cui parti sono di materiali diversi. • produzioni a basso volume: molti processi tradizionali non sono convenienti per le produzioni a basso volume a causa degli alti costi iniziali dovuti alla lavorazione con utensili e tempi di setup lunghi.

Anisotropic Mechanical Properties of ABS Parts Fabricated by Fused Deposition Modelling

In recent years, layered manufacturing (LM) processes have begun to progress from rapid prototyping techniques towards rapid manufacturing methods, where the objective is now to produce finished components for potential end use in a product (Caulfield et al., 2007). LM is especially promising for the fabrication of specific need, low volume products such as replacement parts for larger systems. This trend accentuates the need for a thorough understanding of the associated mechanical properties and the resulting behavior of parts produced by layered methods. Not only must the base material be durable, but the mechanical properties of the layered components must be sufficient to meet in-service loading and operational requirements, and be reasonably comparable to parts produced by more traditional manufacturing techniques. This chapter presents the details of a study completed to quantitatively analyze the potential of fused deposition modelling to fully evolve into a rapid manufacturing tool. The project objective is to develop an understanding of the dependence of the mechanical properties of FDM parts on raster orientation and to assess whether these parts are capable of maintaining their integrity while under service loading. The study examines the effect of fiber orientation, i.e. the direction of the polymer beads relative to the loading direction of the part, on a variety of important mechanical properties of ABS components fabricated by fused deposition modeling. Tensile, compressive, flexural, impact, and fatigue strength properties of FDM specimens are examined, evaluated, and placed in context in comparison with the properties of injection molded ABS parts.

Analisi della correlazione tra i parametri di processo e le prestazioni dei materiali polimerici ottenuti tramite fused deposition modeling

Questa tesi si propone di realizzare una caratterizzazione del polimero ABS ottenuto con tecnica Fused Deposition Modeling in modo da ottenere dati utili alla realizzazione di parti strutturali tramite rapid prototyping.

Resorbable composite scaffolds for craniofacial bone tissue engineering

Aim: Bone loss associated with trauma, osteo-degenerative diseases and tumors has tremendous socioeconomic impact related to personal and occupation disability and health care costs. In the present climate of increasing life expectancy with an ensuing increase in bone-related injuries, orthopaedic surgery is undergoing a paradigm shift from bone-grafting to bone engineering, where a scaffold is implanted to provide adequate load bearing and enhance tissue regeneration. We aim to develop composite scaffolds for bone tissue engineering applications to replace the current gold standard of autografting. ---------- Methods: Medical grade polycaprolactone-tricalcium phosphate (mPCL/TCP) scaffolds (80/20 wt%) were custom made using fused deposition modelling to produce 1x1.5x2 cm sized implants for critical-sized pig cranial implantations, empty defects were used as a control. Autologous bone marrow stromal cells (BMSCs) were extracted and precultured for 2 weeks, dispersed within fibrin glue and injected during scaffold implantation. After 2 years, microcomputed tomography and histology were used to assess bone regenerative capabilities of cell versus cell-free scaffolds. ---------- Results: Extensive bone regeneration was evident throughout the entire scaffold. Clear osteocytes embedded within mineralised matrix and active osteoblasts present around scaffold struts were observed. Cell groups performed better than cell-free scaffolds. ---------- Conclusions: Bone regeneration within defects which cannot heal unassisted can be achieved using mPCL/TCP scaffolds. This is improved by the inclusion of autogenous BMSCs. Further work will include the inclusion of growth factors including BMP-2, VEGF and PDGF to provide multifunctional scaffolds, where the three-dimensional (3D) template itself acts as a biomimetic, programmable and multi-drug delivery device.

Evolutionary design of bone scaffolds with reference to material selection

The favourable scaffold for bone tissue engineering should have desired characteristic features, such as adequate mechanical strength and three-dimensional open porosity, which guarantee a suitable environment for tissue regeneration. In fact, the design of such complex structures like bone scaffolds is a challenge for investigators. One of the aims is to achieve the best possible mechanical strength-degradation rate ratio. In this paper we attempt to use numerical modelling to evaluate material properties for designing bone tissue engineering scaffold fabricated via the fused deposition modelling technique. For our studies the standard genetic algorithm was used, which is an efficient method of discrete optimization. For the fused deposition modelling scaffold, each individual strut is scrutinized for its role in the architecture and structural support it provides for the scaffold, and its contribution to the overall scaffold was studied. The goal of the study was to create a numerical tool that could help to acquire the desired behaviour of tissue engineered scaffolds and our results showed that this could be achieved efficiently by using different materials for individual struts. To represent a great number of ways in which scaffold mechanical function loss could proceed, the exemplary set of different desirable scaffold stiffness loss function was chosen. © 2012 John Wiley & Sons, Ltd.

Application of a human bone engineering platform to an in vitro and in vivo breast cancer metastasis model

Breast cancer in its advanced stage has a high predilection to the skeleton. Currently, treatment options of breast cancer-related bone metastasis are restricted to only palliative therapeutic modalities. This is due to the fact that mechanisms regarding the breast cancer celI-bone colonisation as well as the interactions of breast cancer cells with the bone microenvironment are not fully understood, yet. This might be explained through a lack of appropriate in vitro and in vivo models that are currently addressing the above mentioned issue. Hence the hypothesis that the translation of a bone tissue engineering platform could lead to improved and more physiological in vitro and in vivo model systems in order to investigate breast cancer related bone colonisation was embraced in this PhD thesis. Therefore the first objective was to develop an in vitro model system that mimics human mineralised bone matrix to the highest possible extent to examine the specific biological question, how the human bone matrix influences breast cancer cell behaviour. Thus, primary human osteoblasts were isolated from human bone and cultured under osteogenic conditions. Upon ammonium hydroxide treatment, a cell-free intact mineralised human bone matrix was left behind. Analyses revealed a similar protein and mineral composition of the decellularised osteoblast matrix to human bone. Seeding of a panel of breast cancer cells onto the bone mimicking matrix as well as reference substrates like standard tissue culture plastic and collagen coated tissue culture plastic revealed substrate specific differences of cellular behaviour. Analyses of attachment, alignment, migration, proliferation, invasion, as well as downstream signalling pathways showed that these cellular properties were influenced through the osteoblast matrix. The second objective of this PhD project was the development of a human ectopic bone model in NOD/SCID mice using medical grade polycaprolactone tricalcium phosphate (mPCL-TCP) scaffold. Human osteoblasts and mesenchymal stem cells were seeded onto an mPCL-TCP scaffold, fabricated using a fused deposition modelling technique. After subcutaneous implantation in conjunction with the bone morphogenetic protein 7, limited bone formation was observed due to the mechanical properties of the applied scaffold and restricted integration into the soft tissue of flank of NOD/SCID mice. Thus, a different scaffold fabrication technique was chosen using the same polymer. Electrospun tubular scaffolds were seeded with human osteoblasts, as they showed previously the highest amount of bone formation and implanted into the flanks of NOD/SCID mice. Ectopic bone formation with sufficient vascularisation could be observed. After implantation of breast cancer cells using a polyethylene glycol hydrogel in close proximity to the newly formed bone, macroscopic communication between the newly formed bone and the tumour could be observed. Taken together, this PhD project showed that bone tissue engineering platforms could be used to develop an in vitro and in vivo model system to study cancer cell colonisation in the bone microenvironment.

Grundlagen des Rapid Prototyping

Generative Verfahren sind seit etwa 1987 in den USA und seit etwa 1990 in Europa und Deutschland in Form von Rapid Prototyping Verfahren bekannt und haben sich in dieser Zeit von eher als exotisch anzusehenden Modellbauverfahren zu effizienten Werkzeugen für die Beschleunigung der Produktentstehung gewandelt. Mit der Weiterentwicklung der Verfahren und insbesondere der Materialien wird mehr und mehr das Feld der direkten Anwendung der Rapid Technologie zur Fertigung erschlossen. Rapid Technologien werden daher zum Schlüssel für neue Konstruktionssystematiken und Fertigungsstrategien. Die Anwendertagung Rapid.Tech befasst sich mit den neuen Verfahren zur direkten Produktion und den daraus erwachsenden Chancen für Entwickler und Produzenten. Die Kenntnis der Rapid Prototyping Verfahren wird bei den meisten Fachvorträgen auf der Rapid.Tech vorausgesetzt. Für diejenigen, die sich bisher mit generativen Verfahren noch nicht beschäftigt haben, oder die ihre Grundkenntnisse schnell auffrischen wollen, haben wir die folgenden Zusammenfassung der Grundlagen der generativen Fertigungstechnik, der heutigen Rapid Prototyping Verfahren, zusammengestellt.

Comparison of different stomatal conductance algorithms for ozone flux modelling

A multiplicative and a semi-mechanistic, BWB-type [Ball, J.T., Woodrow, I.E., Berry, J.A., 1987. A model predicting stomatalconductance and its contribution to the control of photosynthesis under different environmental conditions. In: Biggens, J. (Ed.), Progress in Photosynthesis Research, vol. IV. Martinus Nijhoff, Dordrecht, pp. 221–224.] algorithm for calculating stomatalconductance (gs) at the leaf level have been parameterised for two crop and two tree species to test their use in regional scale ozone deposition modelling. The algorithms were tested against measured, site-specific data for durum wheat, grapevine, beech and birch of different European provenances. A direct comparison of both algorithms showed a similar performance in predicting hourly means and daily time-courses of gs, whereas the multiplicative algorithm outperformed the BWB-type algorithm in modelling seasonal time-courses due to the inclusion of a phenology function. The re-parameterisation of the algorithms for local conditions in order to validate ozone deposition modelling on a European scale reveals the higher input requirements of the BWB-type algorithm as compared to the multiplicative algorithm because of the need of the former to model net photosynthesis (An)

Repair and regeneration of osteochondral defects in the articular joints

People suffering from pain due to osteoarthritic or rheumatoidal changes in the joints are still waiting for a better treatment. Although some studies have achieved success in repairing small cartilage defects, there is no widely accepted method for complete repair of osteochondral defects. Also joint replacements have not yet succeeded in replacing of natural cartilage without complications. Therefore, there is room for a new medical approach, which outperforms currently used methods. The aim of this study is to show potential of using a tissue engineering approach for regeneration of osteochondral defects. The critical review of currently used methods for treatment of osteochondral defects is also provided. In this study, two kinds of hybrid scaffolds developed in Hutmacher's group have been analysed. The first biphasic scaffold consists of fibrin and PCL. The fibrin serves as a cartilage phase while the porous PCL scaffold acts as the subchondral phase. The second system comprises of PCL and PCL-TCP. The scaffolds were fabricated via fused deposition modeling which is a rapid prototyping system. Bone marrow-derived mesenchymal cells were isolated from New Zealand White rabbits, cultured in vitro and seeded into the scaffolds. Bone regenerations of the subchondral phases were quantified via micro CT analysis and the results demonstrated the potential of the porous PCL and PCL-TCP scaffolds in promoting bone healing. Fibrin was found to be lacking in this aspect as it degrades rapidly. On the other hand, the porous PCL scaffold degrades slowly hence it provides an effective mechanical support. This study shows that in the field of cartilage repair or replacement, tissue engineering may have big impact in the future. In vivo bone and cartilage engineering via combining a novel composite, biphasic scaffold technology with a MSC has been shown a high potential in the knee defect regeneration in the animal models. However, the clinical application of tissue engineering requires the future research work due to several problems, such as scaffold design, cellular delivery and implantation strategies.