Biocompatibility of subsieve-size capsules versus conventional-size microcapsules

Biocompatibility of cell‐enclosing capsules, defined as suppression of pericapsular cellular reactions, is one of the factors governing the success of enclosed cell transplantation in in vivo cell therapy. Agarose capsules of subsieve size, less than 100 μm in diameter, and conventional size, ∼300–1000 μm in diameter, were implanted into the peritoneal cavity and epididymal fat pads of mice and rats, respectively, to determine the effect of a reduction in diameter to subsieve size. The degree of cellular reaction to the subsieve‐size capsules was much lower than that of the conventional‐size microcapsules, independent of implantation site. The frequency of overgrown subsieve‐size capsules retrieved from the peritoneal cavities was less than 5% in contrast to ∼20% for capsules 387 μm in diameter. In addition, no increase in floating cells, which are generated through capsule stimulation, was observed in the peritoneal cavity only with subsieve‐size capsules. From these results, we concluded that subsieve‐size capsules are more biocompatible than microcapsules of conventional size. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006