Provided herein are bioactivated polymer/extracellular matrix (ECM) composites and methods of preparation and use thereof. In particular, heparinized cysteine-polymer/ECM composites, and methods of preparation and use thereof, are provided. In some embodiments, provided herein are compositions comprising a composite of: (a) extracellular matrix (ECM), and (b) a polyester covalently linked to a bioactive agent. In some embodiments, the composite is a homogeneous composite. In some embodiments, the ECM is decellularized ECM. In some embodiments, the ECM is not substantially crosslinked.