The invention relates to a block copolymer containing: a) hydrophobic biodegradable polymer; b) a hydrophilic polymer and c) at least one reactive group for covalent binding of a surface-modifying substance d) to the hydrophilic polymer b). The invention relates to shaped bodies consisting of the block copolymer and to their utilization, particularly as carriers for tissue culture and active substances and for controlled release and targeted administration of active substances.