Influence of the main parameters of a parallel-plate dialyser under laminar flow conditions
A mathematical model describing the mass transfer in a parallel-plate dialyser with co-current laminar flow in both channels based on the Navier-Stokes equations and Fick's second law was developed. Numerical solutions are presented for pulse- and stepwise concentration changes of the solute in one of the channels using the Laplace transform technique. By simulation the influence of the main design and operational parameters of the dialyser and the most important physical constants for the mass transfer process were investigated. Conclusions with regard to optimum design and operation were drawn and some possibilities for simplifying the model were established
Mass transfer between capillary blood and tissues
The Krogh cylinder type of model for capillary-tissue mass transfer is solved analytically as a conjugated boundary value problem. The analysis avoids recourse to the use of arbitrary interphase mass transfer coefficients. For O2, CO2 and glucose, the model was solved to obtain axial, interfacial, and radial concentration profiles in both the blood and tissue phases, for various conditions, e.g. zero and first order metabolic consumption rates. Both plug and parabolic blood velocity profiles were considered. Blood phase flow rates and diffusivities were varied, as were the magnitudes of the zero order metabolic rate constants and the relative degree of solute binding to hemoglobin. Little computation is required to obtain numerical results from the solutions presented. The results indicate which factors are most important in determining the shapes and magnitudes of concentration profiles in such systems.
In Vivo Comparison of Synthetic Macroporous Filamentous and Sponge-like Skin Substitute Matrices Reveals Morphometric Features of the Foreign Body Reaction According to 3D Biomaterial Designs
Synthetic macroporous biomaterials are widely used in the field of skin tissue engineering to mimic membrane functions of the native dermis. Biomaterial designs can be subclassified with respect to their shape in fibrous designs, namely fibers, meshes or fleeces, respectively, and porous designs, such as sponges and foams. However, synthetic matrices often have limitations regarding unfavorable foreign body responses (FBRs). Severe FBRs can result in unfavorable disintegration and rejection of an implant, whereas mild FBRs can lead to an acceptable integration of a biomaterial. In this context, comparative in vivo studies of different three-dimensional (3D) matrix designs are rare. Especially, the differences regarding FBRs between synthetically derived filamentous fleeces and sponge-like constructs are unknown. In the present study, the FBRs on two 3D matrix designs were explored after 25 days of subcutaneous implantation in a porcine model. Cellular reactions were quantified histopathologically to investigate in which way the FBR is influenced by the biomaterial architecture. Our results show that FBR metrics (polymorph-nucleated cells and fibrotic reactions) were significantly affected according to the matrix designs. Our findings contribute to a better understanding of the 3D matrix tissue interactions and can be useful for future developments of synthetically derived skin substitute biomaterials.