Towards Cellular Sieving: Exploring the Limits of Scaffold Accessibility for Cell Type Specific Invasion

Abstract

of directing the regeneration of such complex tissues, a detailed understanding of the cell type dependent link between scaffold structure and cell motility is therefore required. In this work, we describe how this cell type dependence may be exploited toward cellular sieving: scaffold structures that permit differing degrees of invasion according to cell type. By comparing the invasion behavior of cells from three different sources, in scaffolds of systematically increasing accessibility, we probe the structural requirements for cell movement. In this way, we demonstrate that highly occlusive structures may be used to allow differential invasion according to cell type, therefore physically separating cells according to their invasive capacity.Freeze-dried collagen scaffolds are promising materials in the tissue engineering field, since their highly tunable structure and properties provide potential for the regeneration of a wide range of tissues. [5][6][7][8][9] In recent work, we have shown that measurement of pore size in these scaffolds is insufficient for predicting accessibility to cell invasion, and that characterizing the transport pathways through the pore space is also necessary. [10,11] These transport pathways can be characterized by measurement of percolation diameter, which describes the maximum object diameter that can move through a structure unimpeded. Percolation diameters below 40 µm have been shown to inhibit the invasion of primary fibroblasts, even in structures of constant pore size and collagen wall orientation. [11] In this study, we present simultaneous analysis of pore size and percolation diameter, meaning that, for the first time, we are able to compare their relative influences on the invasion potential of each cell type. The cells chosen for investigation reflect three distinct tissue engineering applications: human primary fibroblasts, for soft tissue regeneration; [12] the MC3T3 mouse osteoprogenitor cell line, for bone regeneration; [13] and the HT1080 cell line from human fibrosarcoma, reflecting the use of 3D models for studying tumor cell invasion. [14] As well as providing a tool for assaying the invasive capability of different cells in response to defined structures, this approach demonstrates how the informed design of tissue engineering scaffolds could be used to control the directed invasion of multiple cell types. The differing species, phenotype and origin of these cells is also relevant for demonstrating how the application of interest may determine the structural design criteria required for tissue engineering scaffolds, as well as the choice of cell line needed to provide an accurate biological assessment of such materials.Coordinating the behavior of multiple cell types provides a challenge for the tissue engineer, since response to structure is highly cell type dependent. Here, human primary fibroblast invasion is compared with that of the MC3T3 and HT1080 cell lines to demonstrate proof-of-concept that controlled changes in 3D collagen scaffold architecture can m...

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