Due to the great
similarity to the natural extracellular matrix
and minimally invasive surgeries, injectable hydrogels are appealing
biomaterials in cartilage and bone tissue engineering. Nevertheless,
undesirable mechanical properties and bioactivity greatly hamper their
availability in clinic applications. Here, we developed an injectable
nanocomposite hydrogel by in situ growth of CaP nanoparticles (ICPNs)
during the free-radical polymerization of dimethylaminoethyl methacrylate
(DMAEMA) and 2-hydroxyethyl methacrylate (HEMA) matrix (PDH) for bone
regeneration. The ICPNs are self-assembled by incorporation of poly-l-glutamic acid (PGA) with abundant carboxyl functional groups
during the formation of carboxyl–Ca2+ coordination
and further CaP precipitation. Furthermore, the carboxyl groups of
PGA could interact with the tertiary amines of DMAEMA fragments and
thus improve the mechanical strength of hydrogels. Upon mixing solutions
of DMAEMA and HEMA bearing PGA, Ca2+, and PO4
3–, this effective and dynamic coordination led
to the rapid self-assembly of CaP NPs and PDH nanocomposite hydrogels
(PDH/mICPN). The obtained optimal nanocomposite hydrogels exhibited
suitable injectable time, an enhanced tensile strength of 321.1 kPa,
and a fracture energy of 29.0 kJ/m2 and dramatically facilitated
cell adhesion and upregulated osteodifferentiation compared to hydrogels
prepared by blending ex situ prefabricated CaP NPs. In vivo experiments
confirmed the promoted osteogenesis, which shows a striking contrast
to pure PDH hydrogels. Additionally, the methacrylate groups on the
monomers could easily be functionalized with aptamers and thereby
facilitate recognition and capturing of bone marrow stromal cells
both in vitro and in vivo and strengthen the bone regeneration. We
believe that our conducted research about in situ self-assembled CaP
nanoparticle-coordinated hydrogels will open a new avenue for bone
regeneration in the future endeavors.