Heparin-decorated, hyaluronic acid-based hydrogel particles for the controlled release of bone morphogenetic protein 2.

We are interested in developing hydrophilic particulate systems that are capable of sequestering growth factors, regulating their release and potentiating their biological functions. To this end heparin (HP)-decorated, hyaluronic acid (HA)-based hydrogel particles (HGPs) were synthesized using an inverse emulsion polymerization technique employing divinyl sulfone as the crosslinker. By varying the feed composition of the aqueous phase the amount of HP integrated in the particles can be systematically tuned. The resulting microscopic particles are spherical in shape and contain nanosized pores suitable for growth factor encapsulation. The covalently immobilized HP retained its ability to bind bone morphogenetic protein-2 (BMP-2) specifically, and its release kinetics can be adjusted by tuning the particle composition. Compared with pure HA particles the hybrid HA/HP HGPs show a higher BMP-2 loading capacity. While BMP-2 was released from HA HGPs with a significant initial burst, a near zero order release kinetics was observed from HA/HP hybrid particles with an optimized heparin content of 0.55 μg per mg HGPs. The ability of HA/HP hybrid particles to present BMP-2 in a controlled manner, combined with the innate bioactivity of HA, induced robust and consistent chondrogenic differentiation of murine mesenchymal stem cells, as shown by up-regulation of the mRNA levels of chondrogenic markers and the production of cartilage-specific extracellular matrix components. The simplicity of the particle synthesis, combined with the defined biological activities of the constituent building blocks, renders the HP-decorated, HA-based hydrogel particle system an attractive candidate for the sustained release of BMP-2, possibly for cartilage repair and regeneration.