1,720,994 research outputs found
Preclinical biological and physicochemical evaluation of two-photon engineered 3D biomimetic copolymer scaffolds for bone healing
Get PDFA major challenge in orthopedics is the repair of large non-union bone fractures. A promising therapy for this indication is the use of biodegradable bioinspired biomaterials that stabilize the fracture site, relieve pain and initiate bone formation and healing. This study uses a multidisciplinary evaluation strategy to assess immunogenicity, allergenicity, bone responses and physicochemical properties of a novel biomaterial scaffold. Two-photon stereolithography generated personalized custom-built scaffolds with a repeating 3D structure of Schwarz Primitive minimal surface unit cell with a specific pore size of ∼400 μm from three different methacrylated poly(D,L-lactide-co-ε-caprolactone) copolymers with lactide to caprolactone monomer ratios of 16 : 4, 18 : 2 and 9 : 1. Using in vitro and in vivo assays for bone responses, immunological reactions and degradation dynamics, we found that copolymer composition influenced the scaffold physicochemical and biological properties. The scaffolds with the fastest degradation rate correlated with adverse cellular effects and mechanical stiffness correlated with in vitro osteoblast mineralization. The physicochemical properties also correlated with in vivo bone healing and immune responses. Overall these observations provide compelling support for these scaffolds for bone repair and illustrate the effectiveness of a promising multidisciplinary strategy with great potential for the preclinical evaluation of biomaterials
In vitro degradation of a chitosan-based osteochondral construct points to a transient effect on cellular viability
Get PDFBioresorbable chitosan scaffolds have shown potential for osteochondral repair applications. The in vivo degradation of chitosan, mediated by lysozyme and releasing glucosamine, enables progressive replacement by ingrowing tissue. Here the degradation process of a chitosan-nHA based bioresorbable scaffold was investigated for mass loss, mechanical properties and degradation products released from the scaffold when subjected to clinically relevant enzyme concentrations. The scaffold showed accelerated mass loss during the early stages of degradation but without substantial reduction in mechanical strength or structure deterioration. Although not cytotoxic, the medium in which the scaffold was degraded for over 2 weeks showed a transient decrease in mesenchymal stem cell viability, and the main degradation product (glucosamine) demonstrated a possible adverse effect on viability when added at its peak concentration. This study has implications for the design and biomedical application of chitosan scaffolds, underlining the importance of modelling degradation products to determine suitability for clinical translation
Manufacture and characterisation of bioresorbable fibre reinforced composite rods and screws for bone fracture fixation applications
No full textBioresorbable implants are an attractive alternative to metallic bone fixation devices and offer potential to eliminate some of the clinical challenges with the latter. This work explores the manufacturing of fully bioresorbable fibre-reinforced composite rods and screws for such applications. Poly lactic acid (PLA) and phosphate glass fibres (PGF) were combined to provide mechanical reinforcement and biocompatibility characteristics. Aligned and randomly reinforced PLA/PGF composites were prepared by compression moulding prior to thermomechanical deformation into rod and screw forms. In vitro degradation and mechanical properties retention were investigated in phosphate buffered saline (PBS) at 37°C. The composite rods and screws exceeded published data for bioresorbable implants in their virgin state and were towards the upper range of cortical bone properties. The properties reduced rapidly in an aqueous medium and this was attributed to matrix plasticisation and fibre/matrix disbonding. The degraded samples maintained strength and stiffness close to the lower limits of the cortical bone. Water uptake and mass loss for composites exceeded equivalent values for PLA alone due to water wicking at the fibre/matrix interface. Ion release tests correlated linearly with mass loss profiles confirming that the dominant degradation mechanism was fibre dissolution. The PLA/PGF composites also exhibited good biocompatibility to human osteosarcoma and human mesenchymal stem cells
Manufacture and characterisation of bioresorbable fibre reinforced composite rods and screws for bone fracture fixation applications
Get PDFBioresorbable implants are an attractive alternative to metallic bone fixation devices and offer potential to eliminate some of the clinical challenges with the latter. This work explores the manufacturing of fully bioresorbable fibre-reinforced composite rods and screws for such applications. Poly lactic acid (PLA) and phosphate glass fibres (PGF) were combined to provide mechanical reinforcement and biocompatibility characteristics. Aligned and randomly reinforced PLA/PGF composites were prepared by compression moulding prior to thermomechanical deformation into rod and screw forms. In vitro degradation and mechanical properties retention were investigated in phosphate buffered saline (PBS) at 37°C. The composite rods and screws exceeded published data for bioresorbable implants in their virgin state and were towards the upper range of cortical bone properties. The properties reduced rapidly in an aqueous medium and this was attributed to matrix plasticisation and fibre/matrix disbonding. The degraded samples maintained strength and stiffness close to the lower limits of the cortical bone. Water uptake and mass loss for composites exceeded equivalent values for PLA alone due to water wicking at the fibre/matrix interface. Ion release tests correlated linearly with mass loss profiles confirming that the dominant degradation mechanism was fibre dissolution. The PLA/PGF composites also exhibited good biocompatibility to human osteosarcoma and human mesenchymal stem cells.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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