130,447 research outputs found
Photo-Polymerization Damage Protection by Hydrogen Sulfide Donors for 3D-Cell Culture Systems Optimization
No full textPhoto-polymerized hydrogels are ideally suited for stem-cell based tissue regeneration and three dimensional (3D) bioprinting because they can be highly biocompatible, injectable, easy to use, and their mechanical and physical properties can be controlled. However, photo-polymerization involves the use of potentially toxic photo-initiators, exposure to ultraviolet light radiation, formation of free radicals that trigger the cross-linking reaction, and other events whose effects on cells are not yet fully understood. The purpose of this study was to examine the effects of hydrogen sulfide (H2S) in mitigating cellular toxicity of photo-polymerization caused to resident cells during the process of hydrogel formation. H2S, which is the latest discovered member of the gasotransmitter family of gaseous signalling molecules, has a number of established beneficial properties, including cell protection from oxidative damage both directly (by acting as a scavenger molecule) and indirectly (by inducing the expression of anti-oxidant proteins in the cell). Cells were exposed to slow release H2S treatment using pre-conditioning with glutathione-conjugated-garlic extract in order to mitigate toxicity during the photo-polymerization process of hydrogel formation. The protective effects of the H2S treatment were evaluated in both an enzymatic model and a 3D cell culture system using cell viability as a quantitative indicator. The protective effect of H2S treatment of cells is a promising approach to enhance cell survival in tissue engineering applications requiring photo-polymerized hydrogel scaffolds
Comparison of Four Different Preparation Methods for Making Injectable Microgels for Tissue Engineering and Cell Therapy
No full textPurpose One of the major challenges in cell-laden microgel bioprocessing is to design an effective method of cell encapsulation in the biomaterial carrier while retaining high cell viability and ensuring small enough particles for injectability. In this study we aim to compare four bioprocessing techniques for making hydrogel microcarriers, including by emulsification gelation and dropwise gelation approaches. Methods A Pluronic-Fibrinogen (FF-127) hydrogel biomaterial was used to make the microgels based on a lower critical solubility temperature (LSCT) phase transition. Additional cross-linking of the hydrogels was achieved using light-activated photochemistry (i.e., photopolymerization). The four bioprocessing methodologies include emulsification gelation in oil (with and without dual photo-initiator free-radical polymerization), reverse thermal gelation (in warm cell culture media), dropwise gelation through a vibrating needle device, and dropwise gelation through an atomization device (in warm cell culture media gelation baths). The microgels made with each method were characterized with and without cells; comparisons of microgel size and cell growth were reported. Results The dual photo-initiator emulsification technique produced FF-127 spherical microgels with an average diameter of 222 and 256 mu m, with and without cells, respectively. The reverse thermal encapsulation produced irregularly shaped microgels with an average diameter of 241 and 702 mu m, with and without cells, respectively. The vibrating needle and atomization techniques produced irregularly shaped microgels with an average diameter of 195 and 151 mu m without cells, respectively, and 464 and 332 mu m with cells, respectively. The viability of fibroblasts in the microgels was high after 24 h, except for those treatments that underwent photo-polymerization (i.e., emulsification photo-polymerization and vibrating needle with photo-polymerization). The cells remained viable for up to 3 weeks in culture and spread three-dimensionally in the microgels over this time course. Conclusions The rapid temperature-induced phase transition of the FF-127 enables the formation of microgels either through dropwise gelation or by emulsification, both through physical cross-linking. The use of a free-radical polymerization cross-linking reaction was more cyto-toxic to the cells as compared to the physical cross-linking by reverse thermal gelation alone. The average microgel size in all the techniques was significantly smaller and more uniform when producing the microgels without cells as compared to with cells. The reverse thermal gelation technique produced cell-laden microgels with the least amount of specialized equipment and bioprocessing steps of all the methods reported. Lay Summary This study provides the framework for producing cell-laden microgels that are of a sufficiently small diameter to be used for injectable cell therapy. The challenge in this regard is to design a simple, scalable, and efficient methods of cell encapsulation in the biomaterials, retaining high cell viability and ensuring small enough particles for injectability. For this purpose, we evaluated four methods that are commonly applied in microgel bioprocessing, and tested these with two types of cells using hydrogels that exhibit lower critical solubility temperature (LCST) properties. This investigation has enabled us to identify advantages and disadvantages for each system of bioprocessing of cell-laden microgels
Injectable silk fibroin hydrogels functionalized with microspheres as adult stem cells-carrier systems
No full textHydrogels are good candidate materials for cell delivery scaffolds because they can mimic the physical, chemical, electrical and biological properties of most of the native tissues. In this study, composite biosynthetic hydrogels were produced by combining the bio-functionality of silk fibroin (SF) with the structural versatility of polyethylene-glycol-diacrylated (PEGDa). The formation of a photopolymerizable PEGDa-SF hydrogel (PSFHy) was optimized for 3D-cell culture. Functionalization of the 3D-PSFHy with protein microspheres (MS) was required to increase the porosity and cell-adhesive properties of the material. Cardiac mesenchymal stem cells, which were cultured within the MS-embedding PSFHy, exhibited good viability and expression of proteins that are characteristic of the initial phases of the cardiac muscle differentiation process. Further, the addition of chondroitin sulfate into the scaffolds improved the cell viability. A cell-preconditioning of the scaffold was also performed, suggesting a potential application of these sponge-like scaffolds for analysing the effects of several extracellular microenvironments, produced by different kinds of cells, on the stem cells fate. The results presented herein highlight on the possibility to use the PSFHys functionalized with MS as stem cell-carrier systems with sponge-like properties, potential ultrasound-imaging contrast agents and controlled biochemical factor delivery
Modelling the disease: H2S-sensitivity and drug-resistance of triple negative breast cancer cells can be modulated by embedding in isotropic micro-environment
No full textThree-dimensional (3D) cell culture systems provide more physiologically relevant information, representing more accurately the actual microenvironment where cells reside in tissues. However, the differences between the tissue culture plate (TCP) and 3D culture systems in terms of tumour cell growth, proliferation, migration, dif- ferentiation and response to the treatment have not been fully elucidated. Tumoroid microspheres containing the MDA-MB 231 breast cancer cell line were prepared using either tunable PEG-fibrinogen (PFs) or tunable PEG-silk fibroin (PSFs) hydrogels, respectively named MDAPFs and MDAPSFs. The cancer cells in the tumoroids showed changes both in globular morphology and at the protein expression level. A decrease of both Histone H3 acet- ylation and cyclin D1 expression in all 3D systems, compared to the 2D cell culture, was detected in parallel to changes of the matrix stiffness. The effects of a glutathionylated garlic extract (GSGa), a slow H2S-releasing donor, were investigated on both tumoroid systems. A pro-apoptotic effect of GSGa on tumour cell growth in 2D culture was observed as opposed to a pro-proliferative effect apparent in both MDAPFs and MDAPSFs. A dedi- cated ad hoc 3D cell migration chip was designed and optimized for studying tumour cell invasion in a gel-in-gel configuration. An anti-cell-invasion effect of the GSGa was observed in the 2D cell culture, whereas a pro- migratory effect in both MDAPFs and MDAPSFs was observed in the 3D cell migration chip assay. An increase of cyclin D1 expression after GSGa treatment was observed in agreement with an increase of the cell invasion index. Our results suggest that the “dimensionality” and the stiffness of the 3D cell culture milieu can change the response to both the gasotransmitter H2S and doxorubicin due to differences in both H2S diffusion and changes in protein expression. Moreover, we uncovered a direct relation between the cyclin D1 expression and the stiffness of the 3D cell culture milieu, suggesting the potential causal involvement of the cyclin D1 as a bio-marker for sensitivity of the tumour cells to their matrix stiffness. Therefore, our hydrogel-based tumoroids represent a valid tunable model for studying the physically induced transdifferentiation (PiT) of cancer cells and as a more reliable and predictive in vitro screening platform to investigate the effects of anti-tumour drugs
Visualizing cell-laden fibrin-based hydrogels using cryogenic scanning electron microscopy and confocal microscopy
No full textThe present investigation explores the microscopic aspects of cell-laden hydrogels at high resolutions, using three-dimensional cell cultures in semi-synthetic constructs that are of very high water content (>98% water). The study aims to provide an imaging strategy for these constructs, while minimizing artefacts. Constructs of poly(ethylene glycol)-fibrinogen and fibrin hydrogels containing embedded mesenchymal cells (human dermal fibroblasts) were first imaged by confocal microscopy. Next, high-resolution scanning electron microscopy (HR-SEM) was used to provide images of the cells within the hydrogels, at submicron resolutions. Because it was not possible to obtain artefact-free images of the hydrogels using room-temperature HR-SEM, a cryogenic HR-SEM imaging methodology was employed to visualize the sample while preserving the natural hydrated state of the hydrogel. The ultrastructural details of the constructs were observed at subcellular resolutions, revealing numerous cellular components, the biomaterial in its native configuration, and the uninterrupted cell membrane as it relates with the biomaterial in the hydrated state of the construct. Constructs containing microscopic albumin microbubbles were also imaged using these methodologies to reveal fine details of the interaction between the cells, the microbubbles, and the hydrogel. Taken together with the confocal microscopy, this imaging strategy provides a more complete picture of the hydrated state of the hydrogel network with cells inside. As such, this methodology addresses some of the challenges of obtaining this information in amorphous hydrogel systems containing a very high water content (>98%) with embedded cells. Such insight may lead to better hydrogel-based strategies for tissue engineering and regeneration
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Trichormus variabilis (Cyanobacteria) Biomass: From the Nutraceutical Products to Novel EPS-Cell/Protein Carrier Systems
No full textA native strain of the heterocytous cyanobacterium Trichormus variabilis VRUC 168 was mass cultivated in a low-cost photobioreactor for a combined production of Polyunsaturated Fatty Acids (PUFA) and Exopolymeric Substances (EPS) from the same cyanobacterial biomass. A sequential extraction protocol was optimized leading to high yields of Released EPS (REPS) and PUFA, useful for nutraceutical products and biomaterials. REPS were extracted and characterized by chemical staining, Reversed Phase-High-Performance Liquid Chromatography (RP-HPLC), Fourier Transform Infrared Spectroscopy (FT-IR) and other spectroscopic techniques. Due to their gelation property, REPS were used to produce a photo-polymerizable hybrid hydrogel (REPS-Hy) with addition of polyethylene glycol diacrylated (PEGDa). REPS-Hy was stable over time and resistant to dehydration and spontaneous hydrolysis. The rheological and functional properties of REPS-Hy were studied. The enzyme carrier ability of REPS-Hy was assessed using the detoxification enzyme thiosulfate:cyanide sulfur transferase (TST), suggesting the possibility to use REPS-Hy as an enzymatic hydrogel system. Finally, REPS-Hy was used as a scaffold for culturing human mesenchymal stem cells (hMSCs). The cell seeding onto the REPS-Hy and the cell embedding into 3D-REPS-Hy demonstrated a scaffolding property of REPS-Hy with non-cytotoxic effect, suggesting potential applications of cyanobacteria REPS for producing enzyme- and cell-carrier systems
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
TRICHORMUS VARIABILIS (NOSTOCALES, CYANOBACTERIA) EXOPOLYMERS FOR HYDROGEL APPLICATIONS IN ENZYME ENCAPSULATION AND TISSUE ENGINEERING
No full text- …
