Development of a Biomaterial Scaffold Integrated with Osteoinductive Oxysterol Liposomes to Enhance Hedgehog Signaling and Bone Repair

Abstract

Bone repair requires the tightly regulated control of multiple intrinsic and extrinsic cell types and signaling pathways. One of the positive regulatory signaling pathways in membranous and endochondral bone healing is the Hedgehog (Hh) signaling family. Here, a novel therapeutic liposomal delivery vector was developed by self-assembly of an Hh-activating cholesterol analog with an emulsifier, along with the addition of Smoothened agonist (SAG) as a drug cargo, for the enhancement of Hh signaling in bone regeneration. The drug-loaded nanoparticulate agonists of Hh signaling were immobilized onto trabecular bone-mimetic apatite-coated 3D scaffolds using bioinspired polydopamine adhesives to ensure favorable microenvironments for cell growth and local therapeutic delivery. Results showed that SAG-loaded liposomes induced a significant and dose-dependent increase in Hh-mediated osteogenic differentiation, as evidenced by in vitro analysis of bone marrow stromal cells, and in vivo calvarial bone healing, as evidenced using all radiographic parameters and histomorphometric analyses. Moreover, favorable outcomes were achieved in comparison to standards of care, including collagen sponge-delivered rBMP2 or allograft bone. In summary, this study demonstrates using a nanoparticle packaged Hh small molecule as a widely applicable bone graft substitute for robust bone repair.

NGF-p75 signaling coordinates skeletal cell migration during bone repair

“…Calvarial defects were performed based on our prior methods ( 3, 35, 36 ). In Pdgfrα mT/mG or p75 PDGFRα mice, TM administration was performed 14 d prior to defect creation as previously validated ( 12, 35 ).…”

Bioactive Scaffolds Integrated with Liposomal or Extracellular Vesicles for Bone Regeneration

“…The incorporation of 20S-hydroxycholesterol into SA-liposomes successfully induced in vitro osteogenesis and in vivo calvarial defect healing when localized to the methacrylated glycol chitosan (MeGC) hydrogel scaffold [27]. Recently, the potential of those osteoinductive liposomes as a drug carrier was further examined by delivering osteogenic molecules such as purmorphamine, smoothened agonist (SAG), and signaling molecule Shh [22,29,30]. The combined delivery of several osteogenic molecules achieved the enhancement of osteogenesis and in vivo bone repair.…”

“…The integrated hydrogel scaffold with osteoinductive sterosomes showed excellent osteogenic activity with biocompatibility in vitro and effective bone healing in vivo in non-healing calvarial defect model. The loading of osteogenic hydrophobic small molecules (purmorphamine, SAG) in the osteogenic sterosomes and further hybrid designs of sterosome-coated PLGA scaffolds showed combinatory and synergistic pro-osteogenic events in vitro and in vivo re-ossification [29,30].…”

“…Various drug-encapsulated liposomes can be incorporated into biomaterial scaffolds via physical, covalent, and non-covalent interactions for further applications in bone tissue engineering. The liposomes were generally incorporated by non-specific encapsulation in the pores of hydrogels [27,29,30,37,41,42]. Various dried state biomaterial scaffolds commonly incorporated the liposomes via electrostatic interactions [21,22,25,34,43].…”

“…To overcome such shortcomings, covalent cross-linking methods, such as a thioether linkage, were introduced [18,33,40,44]. Particularly, polydopamine-mediated layer-by-layer coating via Schiff base formation and Michael-type addition has been proposed to establish the stable binding of liposomes to the biomaterial scaffold [29,30,35,36]. The polydopamine-mediated coating approaches are highly biocompatible, chemical catalyst-free, and byproduct-free in comparison to conventional covalent cross-linking methods [45], demonstrating their potentials in building advanced liposome-integrated scaffolds for local bone regenerative therapy.…”