Injectable cryogel microcarriers for cell transplantation and growth factor delivery.

Biohybrid cryogel microcarriers comprised of heparin and four-arm poly(ethylene glycol) (starPEG) were synthesized by combining an emulsion technique with cryogelation processing. Freezing the gelling reaction mixture whilst dispersed in an organic solvent at −20 °C or −40 °C followed by lyophilisation gave rise to micron scale hydrogel particles with interconnected macropores, which could be loaded with various cell types. Due to their spongy structure and their dense pore walls the microcarriers could be injected through a 27 gauge needle without a negative effect on the cell viability. The artificial 3D cell microenvironment provided by the macropores could be further enhanced by covalent attachment of adhesion ligands. The highly negative charge of heparin allowed for strong binding of growth factors and their sustained release. Consequently, this microcarrier platform creates exiting new options for combination therapies, e.g. for the treatment of neurodegenerative diseases or for therapeutic vascularization.