By injecting the microspheres (MS) coated with polymers to be examined, the new method to analyze histologically the tissue or cellular reaction to materials was developed.
MS of about 30 microns in diameter were made from such polymers as poly (p-hydroxy-methyl styrene), poly (2-hydroxyethyl methacrylate) and poly (methyl methacrylate). These MS's suspensions in saline were injected with syringe into any target tissues of rats. The bioreactions were histologically investigated with the course of time. The tissue reactions against the three polymers were mild, but the degree of reaction varied from site to site. The bioreaction occurred most strongly in the subcutaneous tissue and most slightly in the spleen. Then MS were coated with such polyion complexes (PIC) as poly (vinyl phenethyl triethyl ammonium) cationpoly (styrene sulfonate) anion and coated with copolymers of 2-hydroxyethyl methacrylate and styrene which have a hydrophilichydrophobic microphase separated structure, and then MS were injected into rats. The bioreaction was mild against most samples but was strong against the degenerated ones with boiled water and cationic PIC. Effect of charge was remarkable. For the purpose of analyzing the interaction, MS injection method is advantageous compared with the conventional in vivo test of biomaterials because of the following reasons: 1) simply injectable with the least surgical invasion, 2) implantabte into any site, 3) maximum contact area with minimum space occupation, 4) minimum mechanical stress, 5) minimum amount of materials required and 6) usable to select diameter.
