169 research outputs found
Characterization of Colloidal Drug Carriers
No full textHydrophobic interaction chromatography (HIC) is presented as a suitable method to determine the surface hydrophobicity of colloidal drug carriers. The experimental design is described in great detail. Results obtained with surface-modified polystyrene particles as model carriers and parenteral fat emulsions are discussed as examples. HIC was able to distinguish between particles chemically modified by the introduction of functional groups. Polystyrene particles of various size were surface-modified by adsorption of the block-polymer Poloxamine 908. HIC distinguished between the hydrophobicities of these adsorption layers. The measured surface hydrophobicities of particles and fat emulsions were well in agreement with the in vivo organ distribution data obtained after i. v. injection of the carriers
Shaping Synthetic Multicellular and Complex Multimaterial Tissues via Embedded Extrusion‐Volumetric Printing of Microgels
No full textIn living tissues, cells express their functions following complex signals from their surrounding microenvironment. Capturing both hierarchical architectures at the micro- and macroscale, and anisotropic cell patterning remains a major challenge in bioprinting, and a bottleneck towards creating physiologically-relevant models. Addressing this limitation, we introduced a novel technique, termed Embedded Extrusion-Volumetric Printing (EmVP), converging extrusion-bioprinting and layer-less, ultra-fast volumetric bioprinting, allowing to spatially pattern multiple inks/cell types. Light-responsive microgels were developed for the first time as bioresins (μResins) for light-based volumetric bioprinting, providing a microporous environment permissive for cell homing and self-organization. Tuning the mechanical and optical properties of gelatin-based microparticles enables their use as support bath for suspended extrusion printing, in which features containing high cell densities can be easily introduced. μResins can be sculpted within seconds with tomographic light projections into centimetre-scale, granular hydrogel-based, convoluted constructs. Interstitial microvoids enhanced differentiation of multiple stem/progenitor cells (vascular, mesenchymal, neural), otherwise not possible with conventional bulk hydrogels. As proof-of-concept, EmVP was applied to create complex synthetic biology-inspired intercellular communication models, where adipocyte differentiation is regulated by optogenetic-engineered pancreatic cells. Overall, EmVP offers new avenues for producing regenerative grafts with biological functionality, and for developing engineered living systems and (metabolic) disease models
Plasmaproteinadsorption auf kolloidalen Arzneistoffträgern. Analytik, Korrelation mit Oberflächeneigenschaften, Implikationen für das Drug Targeting
No full textHyalocytes in tissue engineering - First steps towards a cell-based vitreous substitute
No full textThe vitreous body represents the main compartment of the eye. This unique tissue is free of cells in its centre, however, in the cortex of the vitreous body and in the vitreous base, there are a sparse number of cells, designated as hyalocytes. In an increasing number of clinical situations, removal of the vitreous body becomes necessary to prevent blindness. Subsequent to this surgical procedure, the removed tissue has to be replaced by an artificial substitute. At the moment, however, all materials in clinical use are associated with a plethora of side effects, especially in the long-term use. To overcome these limitations, a novel concept for vitreous replacement based on tissue engineering strategies was developed. By incorporation of the native cells of the vitreous body, namely hyalocytes, into a suitable and biocompatible material, a cellular vitreous substitute can eventually be developed. This proposed system may be reorganized by the embedded cells and, therefore, could yield a biocompatible vitreous substitute with long-term stability. To pursue this development, it seemed mandatory to gain extensive knowledge about hyalocytes to allow for their precise control within a vitreous substitute. However, information about hyalocytes was almost completely missing. To overcome these limitations, the presented work addressed some basic aspects of hyalocytes that were of importance for tissue engineering applications.
The first part of this thesis aimed at the development of suitable culture conditions for hyalocytes. The outlined isolation and culture system is based on enzymatic digestion of the vitreous bodies and guarantees a suitable yield of porcine hyalocytes after second passage. Since differentiation markers for hyalocytes were still unknown, it was critical to identify markers that allow for the assessment of cell function. The quantitative accumulation of extracellular matrix components (ECM), of which the vitreous is made, was hypothesized to be a suitable surrogate. To that end, analytical tools that allowed quantification of glycosaminoglycan (GAG) and collagen accumulation by the cells were developed. Using the established methods, ascorbic acid was demonstrated to clearly enhance hyalocyte proliferation and collagen accumulation in a 2-dimensional (2D) and a 3-dimensional (3D) culture system. Further investigations into the mechanism of the ascorbic acid effect indicated that the enhanced collagen production was at least partly due to an enhanced expression of mRNA coding for collagen type V/XI. In a follow up study, the observed effect of ascorbic acid was found to be dependent upon the presence of pyruvate within the medium. Although the exact mechanism of this interaction remained to be elucidated, these two factors were identified as important supplements for in vitro hyalocyte culture. Further improvements in control of hyalocyte behavior were achieved by supplementation of basic fibroblast growth factor (bFGF) or transforming growth factor beta-1 (TGF-beta1) to the culture medium. Both factors were demonstrated to clearly affect the cell morphology as well as the actin organization. Furthermore, bFGF was demonstrated to enhance cell proliferation, thereby decreasing the ECM production, whereas TGF-beta1 increased the accumulation of ECM while inhibiting cell proliferation. Moreover, accelerated cells expansion due to the use of bFGF was found to increase collagen production in the propagated cells, while the GAG accumulation remained unaffected. To enable investigations into cell-biomaterial interactions, in vitro culture systems that mimic the native environment of the cells were designed and tested with collagen type I as model material. The established systems proved suitable, although their relevance to in vivo situations remained to be elucidated. As there were two reports on morphologically different types of hyalocytes in literature, it seemed reasonable to separate these populations prior to cultivation and/or characterization. Using fluorescence activated cell sorting, separation of clearly defined hyalocyte populations became possible without any additional staining. Further studies of the two populations indicated that only one population of cells adheres to and proliferates on tissue culture plastics.
To conclude, the present thesis provided fundamental methods and techniques that allow for in vitro investigations into hyalocyte characteristics and functions in 2D, as well as 3D culture systems. Using these techniques, ascorbic acid and pyruvate were demonstrated to be key factors for in vitro cultivation. Furthermore, bFGF and TGF-beta1 were identified as tools that may allow for the control of hyalocyte proliferation as well as accumulation of ECM. Finally, an isolation method for distinct hyalocyte populations instead of a mixture of populations was developed. This enabled for the first time characterization of distinct hyalocyte populations in their native state
Impact of fruit orientation and pelleting material on water uptake and germination performance in artificial substrate for sugar beet
No full text© 2020 Blunk et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Water uptake into seeds is a fundamental prerequisite of germination and commonly influenced by commercial seed enhancement technologies. The effect of fruit orientation and contrasting pelleting materials on germination and biological performance of sugar beet was assessed. The results indicated there was orientation dependent fruit shrinkage of 37% for the operculum side supplied by moisture compared to 4% for the basal pore side. The expansion rate of 5% compared to the original size, which was also observed for non-shrinking seeds, indicated this was a temporary effect. This behaviour has importance for the application pelleting materials to seeds. Pellets composed of materials exhibiting low levels of swelling act as a water distribution layer which increased germination rates. Careful selection of pelleting material is crucial as it has direct implications on germination speed and subsequent establishment rates
Cell-delivery therapeutics for adipose tissue regeneration
No full textIn reconstructive surgery, there is a tremendous clinical need for adequate implants to repair soft tissue defects resulting from traumatic injury, tumor resection, or congenital anomalies. Adipose tissue engineering holds the promise to provide answers to this still increasing demand. The current approaches to adipose tissue engineering are comprehensively reviewed detailing the different cell carriers under investigation. A special focus is put on the applied cells. The delivered mesenchymal stem cells act in a dual role as building block of the new tissue and modulators of the host response. The conditioning of the cells in vitro prior to implantation decisively influences the tissue development and long-term survival in vivo. The special role of vascularization in adipose engineering is discussed. In all parts, key messages are defined providing the base for future advances in the generation of fat substitutes. (C) 2010 Elsevier B.V. All rights reserved
Quantification of Cell Subpopulations, Fractions of Dead Cells and Debris in Cell Suspensions by Laser Diffractometry
No full textLaser diffractometry was employed for size analysis in liver cell and blood cell suspensions to assess its suitability for characterizing cell populations. The method proved sensitive to detect subpopulations in liver cells (bimodal or trimodal distributions) and to quantify their volume fractions. Cell debris and aggregates of cells could also be quantified, dead cell populations recognized by their shift in the mean cell diameter. Laser diffractometry is therefore suitable for determining the quality of cell isolations (e.g. by liver perfusion) or for following alterations in cell populations during culture of cells in suspension. Analysis of human blood allowed differenciations to be made between thrombocytes and other blood cells. No peak separation was obtained for the populations of erythrocytes and granulocytes due to their similarity in size. Monocytes could not be detected due to their extremely low number in the blood indicating the limit of the metho
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