PHOTOCHEMICAL CONJUGATION OF MAMMALIAN-CELLS TO POLYMERIC SUPPORTS AND MEMBRANES - A KINETIC-STUDY

A commercial polyester acrylate prepolymer, to which a 2:3 wt/wt ratio of tripropyleneglycol diacrylate was added to increase photopolymeriz ation rate, was employed as photochemical conjugating agent, through p hotografting. 1,2-Diphenyl,2,2-dimethoxyethanone was added as standard photoinitiator (7.0 wt/wt%), together with varying amounts (0.003-4.0 wt/wt%) of some proprietary photocatalytic systems, based on the foll owing photocatalysts: [N,N'-ethylene-bis(salicylideneiminato)cobalt(II I) (I), vanadium(V) triethoxide (II), and a synergic mixture of vanadi um(V) tri-t-butoxide and tri-i-propoxide (III). A homogeneous suspensi on containing (10 +/- 2) x 10(5) human thyroid follicular cells per mi lliliter of photochemically reacting medium was photografted, at a sur face density of 6.5 +/- 0.7 mg . cm(-2) of diacrylate prepolymer mixtu re, onto polystyrene plates or onto commercial microfiltration and ult rafiltration membranes consisting of nonwoven cellulose tissues with k nown porosities varying between 5 and 30 mu m and in photografted poly ester acrylate-based membranes with a cutoff of 50 +/- 5 KD. Bioconjug ation yields, as a function of photografting time, were measured gravi metrically and by multiple internal reflection IR spectroscopy. Three series of experiments were performed: 1) measurements of graft yields of the prepolymer, and of the parallel disappearance of double bonds, in the absence of mammalian cells; 2) the same as 1), in the presence of thyroid follicular cells; 3) the same as 2), but with the photoinit iating system formed by the standard photoinitiator alone, with no pho tocatalyst. Results show that if a suitable photocatalyst is not added , no practical conjugation is possible. An appropriate choice of the p hotocatalytic system and of its concentration allows reduction of irra diation times (e.g., by a factor of about 2 x 10(4) calculated as the mean lifetime ratio, between the uncatalyzed system and that with 0.1 wt% of [III]), thus minimizing cell inactivation and/or improving resp onsiveness to the bioassay. From this point of view, photoactivity of (III) is outstanding. The very small, but clearly perceptible, influen ce of polymeric support on bioconjugation is also commented upon. (C) 1994 John Wiley & Sons, Inc.