Drug-Loaded Elastin-Like Polypeptide-Collagen Hydrogels with High Modulus for Bone Tissue Engineering.

Emphasizing the role of hydrogel stiffness and cellular differentiation, this study develops collagen and elastin-like polypeptide (ELP)-based bone regenerative hydrogels loaded with recombinant human bone morphogenetic protein-2 (rhBMP-2) and doxycycline with mechanical properties suitable for osteogenesis. The drug-incorporated collagen-ELP hydrogels has significantly higher modulus of 35 ± 5 kPa compared to collagen-only hydrogels. Doxycycline shows a bi-phasic release with an initial burst release followed by a gradual release, while rhBMP-2 exhibits a nearly linear release profile for all hydrogels. The released doxycycline shows anti-microbial activity against Pseudomonas aeruginosa, Streptococcus sanguinis, and Escherichia coli. Microscopic observation of the hydrogels reveals their interconnected, macroporous, 3D open architecture with pore diameters between 160 and 400 µm. This architecture supports human adipose-derived stem cell attachment and proliferation from initial days of cell seeding, forming a thick cellular sheath by day 21. Interestingly, in collagen and collagen-ELP hydrogels, cell morphology is elongated with stretched slender lamellipodial formation, while cells assemble as spheroidal aggregates in crosslinked as well as drug-loaded hydrogels. Osteogenic markers, alkaline phosphatase and osteocalcin, are expressed maximally for drug-loaded hydrogels compared to those without drugs. The drug-loaded collagen-ELP hydrogels are thus promising for combating bacterial infection and promoting guided bone regeneration.