1,720,952 research outputs found
Permeability and mechanical properties of triply periodic minimal surface scaffolds for bone regeneration
No full textScaffolds for bone regeneration have been investigated as bone substitutes in critical sized bone defects. It is known that the architecture of these scaffolds is important for the bone regeneration process, which depends on cell response and vascular ingrowth into the scaffold. With advanced fabrication techniques, such as selective laser melting, it is possible to manufacture complex geometries. In this study, Ti6Al4V scaffolds based on four different minimal surfaces, primitive, I-WP, gyroid and diamond, with different porosities were evaluated. Of these scaffolds, the morphological and mechanical properties, and the permeability were determined with micro-CT, static compression tests and fatigue tests, and permeability experiments and computational fluid dynamic simulations. Porosities of 71.3-49.2%, 65-44.3%, 65.6-52% and 59.7-44.2% were found for the primitive, I-WP, gyroid and diamond scaffolds, respectively. It was observed that the permeability depends on the shape of the unit cell as well as on the apparent density of the scaffold. Permeability values of 5.48 10-11-6.10 10-9m2 and 1.29-6.96 10-9m2 were obtained from the laminar experimental and computational approaches, respectively. The static compression tests showed that the mechanical properties, such as the plateau stress, quasi-elastic gradient, plateau end stress, and the yield strength depend on the type of unit cell and the porosity. The lowest fatigue lives were found for the primitive unit cells, while the I-WP scaffolds and the diamond scaffolds with the lowest and highest apparent density, respectively, were still intact after 106 cycles. The results in this study suggest that some of the scaffolds evaluated would be suitable as scaffolds for bone regeneration.Tissue biomechanics and implantsBiomedical engineeringMechanical, Maritime and Materials Engineerin
To fold or not to fold?: An exploration of deployable porous biomaterials for the treatment of large bone defects
No full textWithout our musculoskeletal system, which consists of bones, joints, and muscles, we would not be able to live. Our bones are responsible for the protection of our organs, the support of our body, and they enable our mobility. Therefore, it is important to keep them healthy. This is done by cells who repair small cracks and fractures caused by our daily activities through continuous remodeling of the skeleton. However, severe bone damage and defects can occur, for example, due to trauma (e.g., car accidents) and bone tumor resection. In this case, the defects are too large for the cells to repair and surgical intervention is required to support the bone regeneration process. Bone substitutes or porous biomaterials are used to fill these defects to help the cells to regenerate the bone. Bone substitutes require implantation via open surgery due to their large dimensions and rigidity. This causes great damage to the body, which results in a long recovery time for the patient and increases the risk of infections. To reduce the invasiveness of the implantation process, minimally invasive surgery (MIS) could be used. MIS techniques make it possible to perform surgical treatments through specific minimally invasive tools that are inserted into the body through small incisions. In order to make minimally invasive implantation possible, the dimensions of porous biomaterials should be reduced to fit through these small incisions. In addition, it has been demonstrated that the bone regeneration process can be optimized and infections could be prevented by applying precisely controlled nanopatterns to the surface of bone substitutes. However, surface patterning techniques can only be applied to flat surfaces. Therefore, it is not possible to apply surface patterns to the inner surfaces of three-dimensional porous structures, such as those fabricated through 3D printing techniques. To resolveBiomaterials & Tissue Biomechanic
Effects of bone substitute architecture and surface properties on cell response, angiogenesis, and structure of new bone
No full textThe success of bone substitutes used to repair bone defects such as critical sized defects depends on the architecture of the porous biomaterial. The architectural parameters and surface properties affect cell seeding efficiency, cell response, angiogenesis, and eventually bone formation. The relevant parameters include pore size and porosity, pore shape and fibre orientation, surface properties, and mechanical properties. For example, small pores are preferable for cell seeding, but limit cell viability, cell proliferation and differentiation. Moreover, the pore size and geometry affect the alignment of cells and the structure of the regenerated bone. This paper presents an overview of the effects of porous biomaterial architecture including pore size and porosity, pore shape and fibre orientation, surface topography and chemistry, and structure stiffness on cell seeding efficiency, cell response, angiogenesis, and bone formation
Towards deployable meta-implants
No full textMeta-biomaterials exhibit unprecedented or rare combinations of properties not usually found in nature. Such unusual mechanical, mass transport, and biological properties could be used to develop novel categories of orthopedic implants with superior performance, otherwise known as meta-implants. Here, we use bi-stable elements working on the basis of snap-through instability to design deployable meta-implants. Deployable meta-implants are compact in their retracted state, allowing them to be brought to the surgical site with minimum invasiveness. Once in place, they are deployed to take their full-size load-bearing shape. We designed five types of meta-implants by arranging bi-stable elements in such a way to obtain a radially-deployable structure, three types of auxetic structures, and an axially-deployable structure. The intermediate stable conditions (i.e. multi-stability features), deployment force, and stiffness of the meta-implants were found to be strongly dependent on the geometrical parameters of the bi-stable elements as well as on their arrangement.Biomaterials & Tissue Biomechanic
Additive manufacturing of non-assembly deployable mechanisms for the treatment of large bony defects
No full textPorous biomaterials are often used to treat large bony defects or fractured vertebras. Most of such biomaterials are made of metals and their alloys and have a pre-defined, fixed shape. Due to their predefined fixed shape, however, they are not suitable for implantation through minimally invasive surgical procedures. To overcome this problem, we designed three different deployable non-assembly mechanisms, which were manufactured using selective laser melting. These deployable geometries, including a bicapped cube, a bicapped trigonal antiprism, and a bicapped square antiprism, possess a large aspect ratio in their retracted state. Upon the application of an external force, they expand radially into their deployed load-bearing configuration. Using non-assembly manufacturing, revolute joints, wavelike elements, rigid rods and restrictions could be integrated into the design. The designs were manufactured in such a way that the least amount of support structures was required during the fabrication process. Additionally, the deployable structures were functional immediately after printing. Mechanical tests were performed to determine the forces required to deploy the designed structures and to determine their failure load. A maximum change of 322 ± 7% in the circumdiameter was found for the bicapped trigonal antiprism while the bicapped square antiprism showed the largest reduction in the height (61 ± 1%). A maximum force of 10.3 ± 1.6 N was required during the deployment process of the bicapped square antiprism 3. The bicapped antiprisms could support up to 1212 ± 45.5 N before they failed, while the bicapped cubes failed under a force of 232 ± 5.5 N. The elongated geometry of our designs makes them ideal for implantation using minimally invasive surgical procedures. Given the fact that these are the first non-assembly deployable bone substitutes manufactured using selective laser melting, further studies are required to make them suitable as orthopedic implants.</p
Ultra-programmable buckling-driven soft cellular mechanisms
No full textBuckling, which was once considered the epitome of design failure, has been harnessed during the last few years to develop mechanical metamaterials with advanced functionalities. Soft robotics in general and soft actuators in particular could greatly benefit from such designer materials. Unlocking the great potential of buckling-driven materials is, however, contingent on resolving the main limitation of the designs presented to date, namely the limited range of their programmability. Here, we present multi-material buckling-driven metamaterials with high levels of programmability. We combined rational design approaches based on predictive computational models with advanced multi-material additive manufacturing techniques to 3D print cellular materials with arbitrary distributions of flexible and stiff materials in the central and corner parts of their unit cells. Using the geometry and spatial distribution of material properties as the main design parameters, we developed soft mechanical metamaterials behaving as mechanisms whose actuation force and actuation amplitude could be adjusted both independently and concomitantly within wide ranges. Our designs also resulted in the emergence of a new lowest instability mode, i.e. double-side buckling, in addition to the already known modes of side-buckling and symmetric compaction. Finally, we proposed a general approach to pre-dispose our soft mechanical metamaterials such that they can reliably actuate their higher instability modes without any need for additional boundary conditions or fixtures. To demonstrate this approach, we created a cellular mechanism with a rotational buckling pattern that clones the functionality of mechanical machines. The potential of the presented designs in robotics is then demonstrated by applying them as a force switch, kinematic controllers, and a pick and place end-effector.Biomaterials & Tissue Biomechanic
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Russian doll deployable meta-implants: Fusion of kirigami, origami, and multi-stability
No full textDeployable meta-implants aim to minimize the invasiveness of orthopaedic surgeries by allowing for changes in their shape and size that are triggered by an external stimulus. Multi-stability enables deployable implants to transform their shape from some compact retracted state to the deployed state where they take their full sizes and are load-bearing. We combined multiple design features to develop a new generation of deployable orthopaedic implants. Kirigami cut patterns were used to create bi-stability in flat sheets which can be folded into deployable implants using origami techniques. Inspired by Russian dolls, we designed multi-layered specimens that allow for adjusting the mechanical properties and the geometrical features of the implants through the number of the layers. Because all layers are folded from a flat state, surface-related functionalities could be applied to our deployable implants. We fabricated specimens from polylactic acid, titanium sheets, and aluminum sheets, and demonstrated that a deployment ratio of up to ≈2 is possible. We performed experiments to characterize the deployment and load-bearing behavior of the specimens and found that the above-mentioned design variables allow for adjustments in the deployment force and the maximum force before failure. Finally, we demonstrate the possibility of decorating the specimens with micropatterns.Biomaterials & Tissue Biomechanic
Variations on the Author
Full text link“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
- …
