1,720,952 research outputs found
The curious case of curvature: Geometric perspectives on biomaterial design
No full textThe rapidly expanding field of tissue engineering presents enticing, yet demanding challenges for scientists and engineers across many different disciplines. The ultimate goal of tissue engineering is ambitious: to regenerate damaged or missing tissue in its full complexity, either in vitro or in situ, and restore organ function. In addition to cells and biochemical factors, biomaterial scaffolds form the other essential ingredient within the tissue engineering paradigm. These scaffolds support, guide, and stimulate neotissue formation and are rationally designed to meet the desired balance between mechanical, mass transport and biological properties necessary for regeneration and implantation.Biomaterials & Tissue Biomechanic
Meta-biomaterials with minimal surface morphology
No full textTriply Periodic Minimal Surfaces (TPMS) have earned great popularity in porous meta- biomaterials by cause of unique mass transfer properties, tunable mechanical properties, large pore space and high surface to volume ratio. Numerical and experimental studies suggest a great potential for TPMS-based architectures in the treatment of segmental bone defects, where supporting scaffolds are crucial in bridging the gap unable to heal naturally. However, current studies are limited to investigating the properties of classic TPMS archi- tectures. In this thesis, I present the design, fabrication and characterisation of a novel type of meta-biomaterials inspired by TPMS morphology. I show a practical application of Weierstrass equations to define Schwarz P, Schwarz D and Gyroid surfaces, which pro- vides an opportunity to remove fundamental patches from the original surface and design unique structures. Moreover, one of the developed designs applied basics of graph theory to construct the material which mimics the randomness of the trabecular bone structure, while preserving the benefits of regular TPMS morphology. The results demonstrate the improved performance of the modified TPMS scaffolds compared to classic structures in terms of permeability and compliance properties, crucial for the materials applied in or- thopaedic implants. The porosity and permeability values of the developed metamaterial were found to be in the range of trabecular bone. Additionally, the possibilities to simulate the mass transfer properties of the novel material were examined in COMSOL and valu- able qualitative results, like fluid velocity distribution and flow-induced wall shear stress, retrieved. Overall my thesis introduces an innovative idea for biomaterial design and adds a strong argument in favour of TPMS morphology application in the orthopaedic material research field.Biomedical Engineerin
Shape-shifting of hyperbolic surfaces: Design and analysis of a shape-shifting method for complex hyperbolic surfaces, based on a passive frame in combination with an active shape-memory polymer
No full textAlmost every tissue in the human body is curved in a certain way. Examples are the extracellular matrix of different tissues such as trabecular bone, different acini and blood vessels. As such, the ability to create complex curved structures is crucial in the development of biomimetic biomaterials that could be used, for example, for tissue regeneration purposes. Currently, most of these different curved substrates and porous materials are fabricated with 3D-printing techniques. These techniques, however, have limitations. The 3D-printed structures, for example, have limited resolution and the production process is not compatible with planar functionality-inducing processes. A solution for these problems could be the concept of shape-shifting. Shape-shifting is the process through which an object transforms itself into a different shape under the influence of an external stimulus, such as temperature or light. A special interest goes to shape-shifting of initially flat materials (2D) into different complex 3D structures. This method has as main advantage that planar printing, patterning or other 2D processing techniques can be used on the planar (non-shape-shifted) state. In this research, the most important principles of shape-shifting of curved hyperbolic surfaces are explored. With this technique, the benefits of both hyperbolic surfaces and shape-shifting can be combined and exploited. A new way of hyperbolic shape-shifting is introduced. This is done by using a passive rigid frame and an active shape memory polymer (SMP). The passive material determines how and where the structure will fold, while the active SMP generates the force in order to fold and forms a curved (hyperbolic) surface spanned between the frame. A simple square patch design consisting of four rigid beams and an SMP was used as the basis of this research. When activated, this patch forms a saddle shaped (hyperbolic) surface. The design, activation and materials of the patch were changed and manipulated in different ways in order to perform a parametric study and to analyse different important aspects of the process. In order to quantify and assess the quality of the different patches and the effects of the manipulations, different test set-ups were made and the most valuable output parameters were chosen. Lastly, a finite element model of the principle was developed in order to further analyse the concept.Biomedical Engineerin
Hyperbolic origami-inspired folding of triply periodic minimal surface structures
No full textOrigami-inspired folding methods present novel pathways to fabricate three-dimensional (3D) structures from 2D sheets. A key advantage of this approach is that planar printing and patterning processes could be used prior to folding, affording enhanced surface functionality to the folded structures. This is particularly useful for 3D lattices, possessing very large internal surface areas. While folding polyhedral strut-based lattices has already been demonstrated, more complex, curved sheet-based lattices have not yet been folded due to inherent developability constraints of conventional origami. Here, a novel folding strategy is presented to fold flat sheets into topologically complex cellular materials based on triply periodic minimal surfaces (TPMS), which are attractive geometries for many applications. The approach differs from traditional origami by employing material stretching to accommodate non-developability. Our method leverages the inherent hyperbolic symmetries of TPMS to assemble complex 3D structures from a net of self-foldable patches. We also demonstrate that attaching 3D-printed foldable frames to pre-strained elastomer sheets enables self-folding and self-guided minimal surface shape adaption upon release of the pre-strain. This approach effectively bridges the Euclidean nature of origami with the hyperbolic nature of TPMS, offering novel avenues in the 2D-to-3D fabrication paradigm and the design of architected materials with enhanced functionality.Biomaterials & Tissue Biomechanic
From flat sheets to curved geometries: Origami and kirigami approaches
No full textTransforming flat sheets into three-dimensional structures has emerged as an exciting manufacturing paradigm on a broad range of length scales. Among other advantages, this technique permits the use of functionality-inducing planar processes on flat starting materials, which after shape-shifting, result in a unique combination of macro-scale geometry and surface topography. Fabricating arbitrarily complex three-dimensional geometries requires the ability to change the intrinsic curvature of initially flat structures, while simultaneously limiting material distortion to not disturb the surface features. The centuries-old art forms of origami and kirigami could offer elegant solutions, involving only folding and cutting to transform flat papers into complex geometries. Although such techniques are limited by an inherent developability constraint, the rational design of the crease and cut patterns enables the shape-shifting of (nearly) inextensible sheets into geometries with apparent intrinsic curvature. Here, we review recent origami and kirigami techniques that can be used for this purpose, discuss their underlying mechanisms, and create physical models to demonstrate and compare their feasibility. Moreover, we highlight practical aspects that are relevant in the development of advanced materials with these techniques. Finally, we provide an outlook on future applications that could benefit from origami and kirigami to create intrinsically curved surfaces.Biomaterials & Tissue Biomechanic
Two-matrix composites: Carbon fiber micropultrusions embedded in flexible epoxy matrices
No full textTwo-matrix composites combine fibers with two distinct matrices. This is achieved by impregnating fiber bundles with a high-stiffness matrix and embedding the cured bundles in a flexible matrix. Two-matrix composites have been shown to offer unprecedented combinations of transverse flexibility and longitudinal tensile strength, and could offer improved fiber alignment and manufacturability. Here, we explore this concept further by embedding carbon fiber micropultrusions in flexibilized epoxy matrices and examining the longitudinal compression behavior. Our results on thin-walled rings reveal that the failure mode depends on micropultrusion diameter, with small diameters resulting in micropultrusion kinking and larger diameters in splitting and crushing. Additionally, we find that two-matrix composites can offer higher compression strength than conventional composites with the same flexible matrix, despite a lower fiber volume fraction. The inherent manufacturing advantages and high anisotropy could make two-matrix composites interesting candidates for specific applications, such as morphing wings or additively manufactured composites.Biomaterials & Tissue BiomechanicsAerospace EngineeringStructural Integrity & Composite
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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