Does UV irradiation affect polymer properties relevant to tissue engineering?

For most tissue engineering approaches aiming at the repair or generation o f living tissues the interaction of cells and polymeric biomaterials is of paramount importance. Prior to contact with cells or tissues, biomaterials have to be sterilized. However, many sterilization procedures such as steam autoclave or heat sterilization are known to strongly affect polymer prope rties. UV irradiation is used as an alternative sterilization method in man y tissue engineering laboratories on a routine basis, however, potential al terations of polymer properties have not been extensively considered, In this study we investigated the effects of UV irradiation on spin-cast fi lms made from biodegradable poly(D,L-lactic acid)-poly(ethylene glycol)-mon omethyl ether diblock copolymers (Me.PEG-PLA) which have recently been deve loped for controlled cell-biomaterial interaction. After 2 h of UV irradiat ion, which is sufficient for sterilization, no alterations in cell adhesion to polymer films were detected, as demonstrated with 3T3-L1 preadipocytes. This correlated with unchanged film topography and molecular weight distri bution. However, extended UV irradiation for 5-24 h elicited drastic respon ses regarding Me.PEG-PLA polymer properties and interactions with biologica l elements: Large increases in unspecific protein adsorption and subsequent cell adhesion were observed, Changes in polymer surface properties could b e correlated with the observed alterations in cell/protein-polymer interact ions. Atomic force microscopy analysis of polymer films revealed a marked " smoothing" of the polymer surface after UV irradiation. Investigations usin g GPC, H-1-NMR, mass spectrometry, and a PEG-specific colorimetric assay de monstrated that polymer film composition was time-dependently affected by e xposure to UV irradiation, i.e., that large amounts of PEG were lost from t he copolymer surface. The data indicate that sterilization using UV irradiation for 2 h is an app ropriate technique for the recently synthesized Me.PEG-PLA diblock copolyme rs. However, the study also serves as an example that it is indispensable t o control the duration of exposure to UV irradiation for a given biomateria l in order not to compromise polymer properties relevant to tissue engineer ing purposes. (C) 2001 Elsevier Science B.V. All rights reserved.