CONTROLLED ANTIBODY RELEASE FROM A MATRIX OF POLY(ETHYLENE-CO-VINYL ACETATE) FRACTIONATED WITH A SUPERCRITICAL FLUID

A new method is presented for controlling the rate of antibody (Ab) re lease from an inert matrix composed of poly(ethylene-co-vinyl acetate) (EVAc), a biocompatible polymer that is frequently used to achieve co ntrolled release. Using supercritical propane, a parent EVAc sample (M (n) = 70 kDa, M(w)/M(n) = 2.4) was separated into narrow fractions wit h a range of molecular weights (8.7 < M(n) < 165 kDa, 1.4 < M(w)/M(n) < 1.7). Solid particles of Ab were dispersed in matrices composed of d ifferent polymer fractions and the rate of Ab release into buffered sa line was measured. The rate of Ab release from the EVAc matrix depende d on molecular weight: > 90% of the incorporated Ab was released from low molecular weight fractions (M(n) < 40 kDa) during the first 5 days of release, while < 10% was released from the high molecular weight f raction (M(n) > 160 kDa) during 14 days of release. No significant dif ferences in polymer composition, glass-transition temperature, or crys tallinity were identified in the different molecular weight fractions of EVAc. Mechanical properties of the polymer did depend on the molecu lar weight distribution, and correlated directly with Ab release rates . Because it permits rapid and reproducible fractionation of polymers, supercritical fluid extraction can be used to modify the performance of polymeric biomaterials.