Cell Seeding Process Experiment and Simulation on Three-Dimensional Polyhedron and Cross-Link Design Scaffolds

Abstract

Cell attachment to a scaffold is a significant step toward successful tissue engineering. Cell seeding is the first stage of cell attachment, and its efficiency and distribution can affect the final biological performance of the scaffold. One of the contributing factors to maximize cell seeding efficiency and consequently cell attachment is the design of the scaffold. In this study, we investigated the optimum scaffold structure using two designs - truncated octahedron (TO) structure and cubic structure - for cell attachment. A simulation approach, by ANSYS Fluent coupling the volume of fluid (VOF) model, discrete phase model (DPM), and cell impingement model (CIM), was developed for cell seeding process in scaffold, and the results were validated with in vitro cell culture assays. Our observations suggest that both designs showed a gradual lateral variation of attached cells, and live cell movements are extremely slow by diffusion only while dead cells cannot move without external force. The simulation approaches supply a more accurate model to simulate cell adhesion for three-dimensional structures. As the initial stages of cell attachment in vivo are hard to observe, this novel method provides an opportunity to predict cell distribution, thereby helping to optimize scaffold structures. As tissue formation is highly related to cell distribution, this model may help researchers predict the effect of applied scaffold and reduce the number of animal testing.

Keywords: DPM model; cell distribution; cell seeding; scaffold; simulation.

FIGURE 1

Cubic and truncated octahedron structures were used for titanium scaffold structure [(A) Unit cell; (B) scaffold].

FIGURE 2

Illustration of test and simulation framework.

FIGURE 3

CIM model and impinge regimes definition.

FIGURE 4

Cells growth on porous titanium matrix was examined by confocal microscopy, and the confocal image was further processed to determine the cells distribution.

FIGURE 5

Attached cell numbers at the top surface of scaffolds [(A) 6 h on cubic scaffold; (B) 12 h on cubic scaffold; (C) 6 h on TO scaffold; (D) 12 h on TO scaffold; (E) cell distribution analysis at 6 h on cubic scaffold; (F) cell distribution analysis at 6 h on TO scaffold; (G) alive and dead cells on cubic scaffold all timeline; (H) alive and dead cells on TO scaffold all timeline]; n = 3 for each scaffold; error bars show standard deviation.

FIGURE 6

Predicted cell distribution during cell seeding process. From left to right represent the cells distribution at second one, two, three, four, five and six, respectively.

FIGURE 7

Predicted attached cell mass at second 3, 4 and 5 during cell seeding process. Top row: cubic design; Bottom row for truncated octahedron design.

FIGURE 8

Variation of calculated attached cell mass during sell seeding process.

FIGURE 9

The predicted cell distributions in the scaffold are in line with the experimental results as confirmed by confocal examinations (6 and 12 hours time points).