Browsing by Subject "Cells--Permeability"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Effect of scaffold architecture on diffusion of oxygen in tissue engineering constructs(2007) Karande, Tejas Shyam; Agrawal, C. Mauli (Chandra Mauli)Viable tissue formation is often observed in peripheral regions of tissue engineering scaffolds whereas the interior fails to support viable tissue. This could be attributed to the fact that as cells within the pores of the scaffold begin to proliferate and secrete extracellular matrix, they simultaneously begin to occlude the pores and decrease supply of nutrients to the interior. Since transport within the scaffold is mainly a function of diffusion, careful design of the diffusion characteristics of the scaffold is critical. These transport issues relate to oxygen and nutrient delivery, waste removal, protein transport and cell migration, which in turn are governed by scaffold porosity and permeability. The current study addresses these issues by evaluating the effect of these architectural parameters on oxygen concentration and cell behavior in the interior of scaffolds with different architectures. Cylindrical polycaprolactone (PCL) scaffolds fabricated using precision extrusion deposition and having the same pore size but different porosities and tortuosities, and hence different permeabilities, were statically seeded with MG63 cells. The bases of the scaffolds were sealed with an impermeable layer of PCL and the scaffolds were surrounded with a tubing of low air permeability to allow diffusion of air into the constructs mainly from the top. These constructs were evaluated at days 1 and 7 for cell viability and proliferation as well as oxygen concentration as a function of depth within the construct. A simple mathematical model was used to describe the process of diffusion of oxygen in these cell-seeded scaffolds of varying permeability. It was hypothesized that there would be better diffusion and cell function with increasing permeability. This was found to be true in case of cell viability. However, cell proliferation data revealed no significant differences as a function of depth, day or architecture. Oxygen concentration data revealed trends showing decreasing concentrations of oxygen as a function of depth across all architectures. Tortuosity had a greater influence on oxygen concentration profiles on day 1 compared to porosity, whose effect seemed to dominate on day 7. Overall, porosity seemed to play a greater role than tortuosity in supporting viability, proliferation and oxygen diffusion.Item Measurement of transient transport of hyperosmotic agents across cell membranes and resulting optical clearing using differential phase contrast optical coherence microscopy(2005) Rylander, Christopher Grady; Diller, K. R. (Kenneth R.)The response of tissue to hyper-osmotic agents is a reduction in light scattering and corresponding increase in optical clarity. “Tissue optical clearing” permits delivery of near-collimated light deeper into tissue potentially improving the capabilities of optical diagnostic and therapeutic applications. The overall objective of the proposed research is to characterize the mass transport of hyper-osmotic agents across cell membranes and the resulting optical clearing. To accomplish this task, a differential phase contrast optical coherence microscope (DPC-OCM) is configured to permit quantitative spaciotemporal optical path length (OPL) imaging of biological cell specimens. The first application of DPC-OCM is analyzing the intracellular dry mass of individual biological cells. Differences between normal and cancerous cell dry mass are investigated. Populations of normal and cancerous human dermal fibroblast cells and human prostate cells demonstrate a statistically significant difference in mean dry mass and mean en face area. Linear discriminant analysis yields a maximum of 79% accurate classification. The second application of DPC-OCM is use as a novel technique for determining cell membrane permeability parameters due to an osmotic chemical stimulus. Glycerol, a hyperosmotic agent, is perfused across an adherent layer of human keratinocytes, and the dynamic osmotic response of individual cells is imaged with DPC-OCM. A novel optical path length (OPL) mass transport model is devised relating chemical concentration to intrinsic refractive index and OPL. Hydraulic conductivity and solute permeability are determined by fitting the OPL mass transport model to transient OPL data collected with DPC-OCM. The final study investigates the mechanisms of optical clearing of cellular and collagenous tissue using hyperosmotic agents and evaporation. OCT and photographic images quantify optical scattering reduction between native and dehydrated tissue states. Air-drying optically clears tissue as effectively as the most successful hyperosmotic agent, glycerol. Tissue ultrastructural alterations due to dehydration are investigated using transmission electron microscopy. The Rayleigh-Gans model is used to simulate light scattering effects due to tissue ultrastructural alterations and measured refractive index excursion using DPC-OCM.