(526a) 3D Tissue Model for Studying Adhesion of Microparticles Using MRI

In every development of functional particles, there is an important part consisting of the study of their behaviour in conditions simulating their end use. In the case of colloidal drug delivery carriers, this involves the study of biodistribution and deposition in biological tissues. For both ethical and economic reasons, there is a drive to reduce the use of laboratory animals for in vivo studies, and instead use in vitro systems that would still be bio-relevant. Three-dimensional (3D) tissue engineering constructs can act as such models. They can contain human cell lines cultured on porous supports with a defined structure that can mimic the target tissue (e.g. a solid tumour). Under perfusion conditions, the hydrodynamic shear forces can be adjusted to values characteristic of the physiological flows. Additionally, magnetic Resonance Imaging (MRI) can be used as non-destructive, non-invasive method that provides an opportunity to observe the adhesion of drug delivery particles within the 3D cell culture in a “real-time” arrangement.

This work is focused on the design and development of a measuring protocol for the study of adhesive and bio-adhesive properties of particle systems capable of bio-specific targeting. For such purposes, composite Alginate/SiO₂/Fe₃O₄ microparticles and silica nanoparticles modified by IgG-M75 antibody, which is specific for carbonic anhydrase IX antigen on HT-29 cancer cells, were used. The measuring cell itself was designed especially for such purposes and was assembled from a cylindrical body, two sealing caps and a slide-in module where 3D scaffolds overgrown by cells can be placed. The slide-in modules were fabricated using a 3D printer and their pore structure was designed using the AutoCAD software. The chosen cell line was cultured on the porous supports in an incubator prior to the measurement. The perfusion cell itself was connected to a peristaltic pump, enabling controled flow through the system. Thus, such setting allowed for both stationary and flow measurements in the MRI scanner (Bruker ICON). The resulting scans were evaluated and processed using graphic software ImageJ.

The adhesion study was performed using different polymer-based media (Polydimethylsiloxane PDMS, Poly-L-Lactic acid PLA and Acrylonitrile butadiene styrene ABS) and in all of the cases, the adhesion of microparticles was observed with results confirmed by the concentration loss of Fe³⁺ ions in inlet and outlet streams during the experiments. 3D scaffolds for the bio-specific adhesion in the form of lattices were printed by a 3D printer using biocompatible polymer PLA. The growth of two cell lines, HT-29 colon cancer cells and NIH-3T3 mouse fibroblasts, was studied on these 3D structures. Both cell lines were able to grow on the 3D structures, overgrowing their whole surface. Such 3D tissue model was used for studying the adhesion of antibody-modified nanoparticles under the conditions simulating interstitial fluid flow velocities in normal and tumor tissues. Character of flow in the cell (at flow rates ranging from 1 ml/min to 22 ml/min) was studied using MRI (Magnetic Resonance Imaging) and CFD (Computational Fluid Dynamics) techniques. For the evaluation of the bio-specific adhesion experiments, the combination of methods including fluorescent microscopy, fluorescent spectroscopy, flow cytometry and MRI will be used.