PEGylation is a popular approach for the surface functionalization of nanoparticles to achieve improved properties and better performance. Herein, we developed a facile method for surface PEGylation of hydrophobic fluoridated hydroxyapatite (FAp):Ln³⁺ (Ln = Eu or Tb) nanorods via hydrophobic interactions between oleic acid and amphiphilic synthetic copolymers, which were synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization using stearyl methacrylate (SMA) and poly(ethylene glycol) methacrylate (PEGMA) as monomers. Our results demonstrated that the morphology and fluorescent properties of the FAp nanorods are not significantly changed by the PEGylation procedure, and the resulting FAp nanorods were found to be stable in aqueous solution. More importantly, these PEGylated FAp nanorods are biocompatible with cells and could be utilized for cell imaging applications. Therefore, we believe that the method described in this work is a simple, efficient and general strategy for the surface PEGylation of hydrophobic nanoparticles.

Designing the “ideal” hydrogel/matrix which can load bone morphogenetic protein-2 (BMP-2) in a low dose and with a sustained release is the key for its successful therapeutic application to enhance osteogenesis. The current use of natural collagen sponges as hydrogel/matrix is limited due to the collagen matrix showing weak mechanical strength and unmanageable biodegradability. Furthermore, the efficiency and safe dose usage of the BMP-2 has never been seriously considered other than purely chasing the lowest dose usage and extended-release time. In this paper, we customized a novel enzymatically cross-linked recombinant human-like collagen (HLC) sponge with low immunogenicity, little risk from hidden viruses, and easy production. We obtained a unique vertical pore structure and the porosity of the HLC, which are beneficial for Mesenchymal stem cells (MSCs) migration into the HLC sponge and angiopoiesis. This HLC sponge loading with low dose BMP-2 (1 µg) possessed high mechanical strength along with a burst and a sustained release profile. These merits overcome previous limitations of HLC in bone repair and are safer and more sensitive than commercial collagens. For the first time, we identified that a 5 µg dose of BMP-2 can bring about the side effect of bone overgrowth through this sensitive delivery system. Osteoinduction of the HLC-BMP sponges was proved by an in vivo mouse ectopic bone model and a rat cranial defect repair model. The method and the HLC-BMP sponge have the potential to release other growth factors and aid other tissue regeneration. Additionally, the ability to mass-produce HLC in our study overcomes the current supply shortage, which limits bone repair in the clinic.