Scholarly Works, School of Biomedical Engineering and Sciences

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https://hdl.handle.net/10919/23275
Research articles, presentations, and other scholarship

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Browsing Scholarly Works, School of Biomedical Engineering and Sciences by Department "Chemical Engineering"

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    The assembly of integrated rat intestinal-hepatocyte cultures
    Kothari, Anjaney; Rajagopalan, Padmavathy (2019-11)
    The jejunum is the segment of the small intestine responsible for several metabolism and biotransformation functions. In this report, we have cultured rat jejunum explants in vitro and integrated them with hepatocyte cultures. We have also investigated the changes in jejunum function at different locations since spatial variations in intestinal functions have been reported previously. We divided the length of the rat jejunum into three distinct regions of approximately 9 cm each. We defined the regions as proximal (adjacent to the duodenum), medial, and distal (adjacent to the ileum). Spatiotemporal variations in functions were observed between these regions within the jejunum. Alkaline phosphatase activity (a marker of enterocyte function), decreased twofold between the proximal and distal regions at 4 hr. Lysozyme activity (a marker of Paneth cell function) increased from the proximal to the distal jejunum by 40% at 24 hr. Mucin-covered areas, a marker of goblet cell function, increased by twofold between the proximal and distal segments of the jejunum at 24 hr. When hepatocytes were integrated with proximal jejunum explants, statistically higher urea (similar to 2.4-fold) and mucin (57%) production were observed in the jejunum explants. The integrated intestine-liver cultures can be used as a platform for future investigations.
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    Effects of receptor clustering on ligand dissociation kinetics: Theory and simulations
    Gopalakrishnan, Mahima; Forsten-Williams, Kimberly; Nugent, Matthew A.; Täuber, Uwe C. (Cell Press, 2005-12-01)
    Receptor-ligand binding is a critical first step in signal transduction and the duration of the interaction can impact signal generation. In mammalian cells, clustering of receptors may be facilitated by heterogeneous zones of lipids, known as lipid rafts. In vitro experiments show that disruption of rafts significantly alters the dissociation of fibrbroblast growth factor-2 (FGF2) from heparan sulfate proteoglycans (HSPGs), co-receptors for FGF-2. In this article, we develop a continuum stochastic formalism to address how receptor clustering might influence ligand rebinding. We find that clusters reduce the effective dissociation rate dramatically when the clusters are dense and the overall surface density of receptors is low. The effect is much less pronounced in the case of high receptor density and shows nonmonotonic behavior with time. These predictions are verified via lattice Monte Carlo simulations. Comparison with FGF-2-HSPG experimental results is made and suggests that the theory could be used to analyze similar biological systems. We further present an analysis of an additional cooperative internal-diffusion model that might be used by other systems to increase ligand retention when simple rebinding is insufficient.
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    Fabrication and Characterization of Three Dimensional Electrospun Cortical Bone Scaffolds
    Andric, Tea; Taylor, Brittany L.; Degen, Katherine E.; Whittington, Abby R.; Freeman, Joseph W. (De Gruyter Open, 2014)
    Bone is a composite tissue composed of an organic matrix, inorganic mineral matrix and water. Structurally, bone is organized into two distinct types: trabecular (or cancellous) and cortical (or compact) bone. Cortical bone is highly organized, dense and composed of tightly packed units or osteons whereas trabecular bone is highly porous and usually found within the confines of cortical bone. Osteons, the subunits of cortical bone, consist of concentric layers of mineralized collagen fibers. While many scaffold fabrication techniques have sought to replicate the structure and organization of trabecular bone, very little research focuses on mimicking the organization of native cortical bone. In this study we fabricated three-dimensional electrospun cortical scaffolds by heat sintering individual osteon-like scaffolds. The scaffolds contained a system of channels running parallel to the length of the scaffolds, as found naturally in the haversian systems of bone tissue. The purpose of the studies discussed in this paper was to develop a mechanically enhanced biomimetic electrospun cortical scaffold. To that end we investigated the appropriate mineralization and cross-linking methods for these structures and to evaluate the mechanical properties of scaffolds with varying fiber angles. Cross-linking the gelatin in the scaffolds prior to the mineralization of the scaffolds proved to help prevent channels of the osteons from collapsing during fabrication. Premineralization, before larger scaffold formation and mineralization, increased mineral deposition between the electrospun layers of the scaffolds. A combination of cross-linking and premineralization significantly increased the compressive moduli of the individual scaffolds. Furthermore, scaffolds with fibers orientation ranging between 15° and 45° yielded the highest compressive moduli and yield strength.
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    Transcriptomic Analysis of Hepatic Cells in Multicellular Organotypic Liver Models
    Tegge, Allison N.; Rodrigues, Richard R.; Larkin, Adam L.; Vu, Lucas T.; Murali, T. M.; Rajagopalan, Padmavathy (Springer Nature, 2018-07-27)
    Liver homeostasis requires the presence of both parenchymal and non-parenchymal cells (NPCs). However, systems biology studies of the liver have primarily focused on hepatocytes. Using an organotypic three-dimensional (3D) hepatic culture, we report the first transcriptomic study of liver sinusoidal endothelial cells (LSECs) and Kupffer cells (KCs) cultured with hepatocytes. Through computational pathway and interaction network analyses, we demonstrate that hepatocytes, LSECs and KCs have distinct expression profiles and functional characteristics. Our results show that LSECs in the presence of KCs exhibit decreased expression of focal adhesion kinase (FAK) signaling, a pathway linked to LSEC dedifferentiation. We report the novel result that peroxisome proliferator-activated receptor alpha (PPAR alpha) is transcribed in LSECs. The expression of downstream processes corroborates active PPAR alpha signaling in LSECs. We uncover transcriptional evidence in LSECs for a feedback mechanism between PPAR alpha and farnesoid X-activated receptor (FXR) that maintains bile acid homeostasis; previously, this feedback was known occur only in HepG2 cells. We demonstrate that KCs in 3D liver models display expression patterns consistent with an anti-inflammatory phenotype when compared to monocultures. These results highlight the distinct roles of LSECs and KCs in maintaining liver function and emphasize the need for additional mechanistic studies of NPCs in addition to hepatocytes in liver-mimetic microenvironments.