Macrophage phagocytosis of biodegradable microspheres composed of L‐lactic acid/glycolic acid homo‐ and copolymers

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Abstract
A variety of biodegradable microspheres were prepared from L‐lactic acid, DL‐lactic acid, or glycolic acid homopolymers and copolymers of different molecular weights and monomer compositions. Phagocytosis of the microspheres by mouse peritoneal macrophages was studied in cell culture system using scanning electron microscopy as well as light microscopy. The diameter of microspheres prepared was less than 2 μm, regardless of the starting polymers. No dependence of the chemical nature of starting polymers was observed on the extent of phagocytosis of the microspheres by macrophages. Precoating the microspheres with water‐soluble macromolecules such as proteins had great influence on phagocytosis by macrophages. It was demonstrated that precoating with bovine serum albumin and non‐proteinaceous macromolecules reduced the phagocytosis of microspheres, while bovine γ‐globulin, human fibronectin, bovine tuftsin, and gelatin precoating enhanced the phagocytosis. This trend was not influenced by the presence of serum. Only in the case of gelatin precoating, the phagocytosis was greatly enhanced by the presence of serum as compared to precoating with other proteins. Microscopic observation clearly indicated that the phagocytosed microspheres were gradually degraded in the macrophage interior with the incubation time, leading to release of a fluorescent dye encapsulated in the microspheres. The rate of microsphere degradation in cells could be controlled by changing the molecular weight and the monomer composition of the copolymers comprising the microspheres.