Significance of the type and the size of biomaterial particles on phagocytosis and tissue distribution.

Particulates generated by dissolution or wear of injected or implanted biomaterials may migrate into various tissues and lead to activation of the host's inflammatory and immune responses. The purpose of this study was to evaluate the relevance of size and chemical composition of biomaterial particles on the pattern of particle distribution in host tissues. Adult female B6C3F1 mice were injected intraperitoneally with polymethylmethacrylate (PMMA) particles (size 1.4 and 6.4 micro in diameter) and polystyrene (PS) particles (size 1.2, 5.2, and 12.5 micro in diameter), and euthanized 1, 7, and 28 days later. Peritoneal exudate cells (PECs) were collected and the number of cells and percentage of actively phagocytic cells was determined. Macroscopic examination of the tissues in the peritoneal cavity peritoneum revealed visible accumulations of the colored PS particles in the adipose tissues adjacent to the spleen and pancreas, and caudal to the stomach. Distribution of the PS particles appeared similar regardless of the particle size. The location of PMMA particles, which were not colored, could not be distinguished from host tissue and could not be observed in this manner. Intensive phagocytosis of the small and medium sized particles by peritoneal macrophages was observed on day 1, and was diminishing by day 7 after injection. The largest PS particles (12.5 micro) were not engulfed by the peritoneal macrophages. Histological examination of the spleen, lymph nodes, and the adjacent adipose tissues revealed a marked difference in the deposition patterns of the two polymers used. PS particles, regardless of size, were accumulated primarily in the white adipose tissues adjacent to the spleen and pancreas gland, but very few particles were observed in the splenic tissue. On the other hand, mice injected with PMMA particles of either size had enlarged and activated spleens with marked deposits of particles in the red pulp. These results indicate that these PS and PMMA particles induce different patterns and intensities of the host response. The chemical makeup of the particle is more important in the distribution pattern than is the size of the particle. Copyright 2001 John Wiley & Sons, Inc. J Biomed Mater Res 55: 523-529, 2001