A macrophage-activating, injectable hydrogel to sequester endogenous growth factors for in situ angiogenesis

Abstract Biomaterials scaffolds designed for many regenerative applications are expected to support neo-vascularisation, which is now being hampered by two limitations – the instability of exogenous growth factors (GFs) that are delivered to promote angiogenesis; and the loss of extracellular matrix components that bind and stabilise GFs. Here, we report the design and evaluation of an injectable hydrogel system aimed at restoring a GF-binding microenvironment to enhance the pro-angiogenic functions of endogenous GFs. This gel comprises two polysaccharides with their unique bioactivities: Konjac glucomannan (KGM) as the building block of the gel scaffold, for its demonstrated capacity to activate macrophages/monocytes to secrete pro-angiogenic/-mitogenic GFs; and heparin (Hep), a representative glycosaminoglycan molecule that binds numerous pro-angiogenic GFs, as functional moieties to sequester the macrophage-produced GFs. Modified with tyramine (TA) groups, the two polysaccharides can be co-polymerised and rapidly form into hydrogel upon enzyme catalysis. The designed KGM-TA/Hep-TA hydrogel successfully preserves the macrophage-activating function and GF-binding affinity of the two components, respectively, and, once subcutaneously implanted, effectively sequestered the locally-produced GFs in situ and promote the formation and maturation of blood vessels in mice. In summary, the designed hydrogel system demonstrates a feasible approach to stimulate the production and harness the function of endogenous GFs for inducing blood vessel formation in vivo , without the addition of any exogenous proteins. This design may provide an innovative, open platform to promote vascularisation for various regenerative purposes.