1,720,962 research outputs found
Polylactide-based materials science strategies to improve tissue-material interface without the use of growth factors or other biological molecules
No full textIn a large number of medical devices, a key feature of a biomaterial is the ability to successfully bond to living tissues by means of engineered mechanisms such as the enhancement of biomineralization on a bone tissue engineering scaffold or the mimicking of the natural structure of the extracellular matrix (ECM). This ability is commonly referred to as “bioactivity”. Materials sciences started to grow interest in it since the development of bioactive glasses by Larry Hench five decades ago. As the main goal in applications of biomedical devices and tissue scaffolds is to obtain a seamless tissue-material interface, achieving optimal bioactivity is essential for the success of most biomaterial-based tissue replacement and regenerative approaches. Polymers derived from lactic acid are largely adopted in the biomedical field, they are versatile, FDA approved and relatively cost-effective. However, as for many other widespread biomedical polymers, they are hydrophobic and lack the intrinsic ability of positively interacting with surrounding tissues. In the last decades scientists have studied many solutions to exploit the positive characteristics of polylactide-based materials overcoming this bottleneck at the same time. The efforts of this research fruitfully produced many effective tissue engineering technologies based on PLA and related biopolymers. This review aims to give an overview on the latest and most promising strategies to improve the bioactivity of lactic acid-based materials, especially focusing on biomolecule-free bulk approaches such as blending, copolymerization or composite fabrication. Avenues for future research to tackle current needs in the field are identified and discussed
Multilayered Scaffolds for Osteochondral Tissue Engineering Based on Bioactive Glass and Biodegradable Polymers
Full text linkInjuries of the articular cartilage may penetrate to the underlying subchondral bone, forming osteochondral defects which have a limited capacity of self-regeneration. Accompanied with limited surgical treatments and the fact that the causes are not understood well, an approach based in tissue engineering becomes a promising strategy for osteochondral repair. Such tissue engineering approaches are based on the combination of synthetic scaffolds, suitable cell sources and active molecules or growth factors. The suitable osteochondral scaffold should be developed considering appropriate biomaterials and processing techniques in order to fabricate engineered scaffolds as suitable 3D microenvironment with sufficient mechanical integrity for cells growth and tissue regeneration. The combination of biodegradable polymers and bioactive glasses in the form of bi- or multilayered composite scaffolds is a promising approach in osteochondral regeneration, whereby the development of robust fabrication methods is crucial for the success of this strategy. In this investigation, two different structural architectures of scaffolds are comparatively studied for the cartilage phase, including (I) porous foams and (II) electrospun fibers fabricated by using freeze drying and electrospinning techniques, respectively. A biocompatible polysaccharide, namely sodium alginate, processed on the upper surface of 3D highly porous interconnected Bioglass®-based foams by freeze-drying followed by ionically crosslinking to produce a cartilage-engineered substrate. Sodium alginate coated Bioglass®-based scaffolds (fabricated by foam replication technique followed by polymer coating), were manufactured as scaffold for subchondral bone. Both phases were integrated by different methods; including using a sodium alginate adhesive layer to from Alg/Na-Alg coated Bioglass® bilayered scaffolds and formation of a monolithic biphasic scaffold. In the second approach, sodium alginate is fabricated into submicron fibers by electrospinning, and deposited on the alginate coated Bioglass®-based scaffold, forming electrospun Alg/Alg-coated Bioglass® bilayered scaffold. In addition, synthetic biodegradable polymer (PDLLA) was used to fabricate the same structural architectures (by using the same techniques) in order to compare between different scaffold materials. The scaffold architecture, constitutive microstructural features, and mechanical properties were investigated with respect to their requirements for regeneration of both cartilage and subchondral bone.
Alginate freeze-dried foams provide pore sizes in the range of 125 to 225 µm, whereas alginate coated Bioglass®-based scaffolds for bone regeneration show larger pore sizes (100-600 µm), required for bone regeneration. Both scaffolds exhibit high porosity and pore interconnectivity and they were confirmed to be suitable pore sizes for chondrocyte seeding, for synthesis of cartilaginous ECM, and for bone in-growth and vascularization, respectively. The mechanical properties of Alg-foams and Alg-c-BG scaffolds were confirmed to be closer to those of native tissues. In addition, antibiotic drug, i.e. tetracycline, was incorporated into polymer coated Bioglass-based scaffolds in order to enhance functionality of the scaffolds for use as a drug or biomolecule carrier in bone regeneration.
The in vitro studies of Alg-foams and Alg-c-BG scaffolds are carried out separately by seeding chondrocytes and MSCs, and osteoblasts-like cells, respectively. MG-63 osteoblast-like cells were seeded on RGD-Alg-c-BG and Alg-c-BG scaffolds to evaluate the biocompatibility, cell viability, proliferation and differentiation in comparison with BG scaffolds. It was found that BG scaffolds promote high cell proliferation and bone mineralization upon 21 days culture, followed by RGD-Alg-c-BG and Alg-c-BG scaffolds, respectively. Therefore, alginate coated Bioglass-based composite scaffolds represent promising candidates for the regeneration of subchondral bone in osteochondral tissue engineering.
Simutaneously, in vitro cell culture studies of alginate and alginate/chondroitin sulfate-foams for cartilage regeneration were evaluated by seeding with porcine chondrocytes and mesenchymal stem cells. All tests proved the biocompatibility of the materials to cells and chondrocytes maintained their phenotype over the investigated culture times (14 days). In addition, MSCs promoted the differentiation into chondrocyte-like cells and also provided the expression of collagen type II and proteoglycan after 7 days in culture, which are the specific markers of cartilage regeneration. The results thus confirmed that alginate based scaffolds have a great potential for use as cartilaginous scaffolds
Development of bioactive glass based scaffolds for controlled antibiotic release in bone tissue engineering via biodegradable polymer layered coating
Full text linkHighly porous 45S5 Bioglass®-based scaffolds coated with two polymer layers were fabricated to serve as a multifunctional device with controlled drug release capability for bone regeneration applications. An interior poly(d,l-lactide)/poly(ethylene glycol)-(polypropylene glycol)-poly(ethylene glycol) triblock copolymer (Pluronic P123) coating improved the mechanical stability of Bioglass-based scaffolds, while an exterior natural polymer (alginate or gelatin) coating served as an antibiotic drug carrier. The results showed improved mechanical properties of Bioglass-based scaffolds by the bilayer polymer coating. In addition, hydrochloride tetracycline loaded in either alginate or gelatin coatings was released rapidly at the initial stage (∼1 h), while the released rate subsequently decreased and was sustained for 14 days in phosphate buffered saline. Therefore, these layered polymer coated scaffolds exhibit attractive characteristics in terms of improved mechanical properties and controlled drug release, simultaneously with the added advantage that the drug release rate is decoupled from the intrinsic scaffold Bioglass degradation mechanism. The layered polymer coated scaffolds are of interest for drug-delivery enhanced bone regeneration applications.Fil: Nooeaid, Patcharakamon. Universitat Erlangen-Nuremberg; AlemaniaFil: Li, Wei. Universitat Erlangen-Nuremberg; AlemaniaFil: Roether, Judith A.. Universitat Erlangen-Nuremberg; AlemaniaFil: Mouriño, Viviana Silvia Lourdes. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Tecnología Farmacéutica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Goudouri, Ourania Menti. Universitat Erlangen-Nuremberg; AlemaniaFil: Schubert, Dirk W.. Universitat Erlangen-Nuremberg; AlemaniaFil: Boccaccini, Aldo R.. Universitat Erlangen-Nuremberg; Alemani
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Full text linkWe 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
Osteochondral tissue engineering: scaffolds, stem cells and applications.
Full text linkOsteochondral tissue engineering has shown an increasing development to provide suitable strategies for the regeneration of damaged cartilage and underlying subchondral bone tissue. For reasons of the limitation in the capacity of articular cartilage to self-repair, it is essential to develop approaches based on suitable scaffolds made of appropriate engineered biomaterials. The combination of biodegradable polymers and bioactive ceramics in a variety of composite structures is promising in this area, whereby the fabrication methods, associated cells and signalling factors determine the success of the strategies. The objective of this review is to present and discuss approaches being proposed in osteochondral tissue engineering, which are focused on the application of various materials forming bilayered composite scaffolds, including polymers and ceramics, discussing the variety of scaffold designs and fabrication methods being developed. Additionally, cell sources and biological protein incorporation methods are discussed, addressing their interaction with scaffolds and highlighting the potential for creating a new generation of bilayered composite scaffolds that can mimic the native interfacial tissue properties, and are able to adapt to the biological environment
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