THEORETICAL-ANALYSIS OF IN-VIVO MACROPHAGE ADHESION AND FOREIGN-BODY GIANT-CELL FORMATION ON STRAINED POLY(ETHERURETHANE UREA) ELASTOMERS

Quantitative description of foreign body giant cell (FBGC) formation o n poly(etherurethane urea) (PEUU) surfaces as a function of time can c onceivably predict the effects of polymer characteristics on cellular responses in vivo. In the present study, the formation of FBGCs on str ained and unstrained PEUUs was quantified with two parameters: the den sity of adherent macrophages present initially that participate in FBG C formation (d(o)) and the rate constant for cell fusion (k); both kin etic parameters were used to calculate the time-dependent F;BGC densit y (d(fc)). Relationships were sought between results of the cellular a nalysis and the extent of environmental stress cracking (ESC), as char acterized by scanning electron microscopy. Surface degradation was sem iquantified with percent light transmittance. The materials used were: base PEUU, base PEUU with 1% Santowhite(R) antioxidant powder, base P EUU with 5% Methacrol 2138F(R) antifume agent, and base PEUU with both 1% Santowhite(R) and 5% Methacrol 2138F(R). A comparison of unstraine d base PEUU with base PEUU strained to 400% elongation indicated that the rate of cell fusion, but not d(o) and d(fc), increased in the pres ence of strain. In all strained samples, additives that strongly affec ted the ESC also influenced FBGC kinetic parameters. Strained PEUU con taining Santowhite(R) had the lowest d(o), the slowest rate of cell fu sion, and lowest d(fc), and the least incidence of ESC. The results su ggest that the incidence of ESC in PEUU was decreased in the presence of Santowhite(R), which also lowered the number of adherent macrophage s participating in FBGC formation, the rate of FBGC formation and the subsequent FBGC density. These studies also indicate that strain in PE UUs does not directly modulate the adherent macrophage and FBGC densit y. Further studies are necessary to delineate the relationship between PEUU strain and adherent macrophage and FBGC activation, which leads to the exocytosis of degrading agents and the observed incidence of bi odegradation. (C) 1994 John Wiley and Sons, Inc.