Hydroxyapatite-collagen nanoparticles reinforced polyanhydride based injectable paste for bone substitution: effect of dopant addition in vitro

Abstract

The present study focuses on the synthesis and characterization of hydroxyapatite-collagen nanoparticles incorporated polyanhydride paste and investigating its bone regeneration capacity in vitro. Photocrosslinkable polyanhydride paste was prepared after synthesizing methacrylate derivatives of 1,6-bis(p-carboxyphenoxy)hexane (MCPH) and sebacic acid dimethacrylate (MSA). These multifunctional monomers, namely 45 wt% MSA, 45 wt% MCPH in addition to 10 wt% poly(ethylene glycol)diacrylate (PEGDA) were photopolymerized under ultraviolet light (365 nm) to produce highly crosslinked polyanhydride networks using camphroquinone (CQ)/ethyl 4-(dimethylamino)benzoate [4-EDMAB] for light initiated crosslinking and benzoyl peroxide (BPO)/dimethyl toludine (DMT) for chemically initiated crosslinking. Separately, using the co-precipitation process, (1 wt%) Si, (1 wt%) Sr, and (0.5 + 0.5) wt% Si/Sr was doped into hydroxyapatite-collagen nanoparticles in size range between 50 and 70 nm. Si, Sr, and both Si/Sr doped hydroxyapatite-collagen nanoparticles to the extent 10 wt% were added to polyanhydride monomer mixture containing 40 wt% MSA, 40 wt% MCPH and 10 wt% PEGDA and subsequently photopolymerized as previously mentioned. Incorporation of hydroxyapatite-collagen nanoparticles to the extent of 10 wt% into polyanhydride matrix enhanced compressive strength of the hardened paste from 30 to 49 MPa. Mesenchymal stem cells obtained from the human umbilical cord were cultured onto pure polyanhydride and hydroxyapatite-collagen added scaffold to assess their cellular proliferation and differentiation capacity to bone cell. MTT assay showed that mesenchymal stem cell proliferation was significantly higher in Si/Sr binary doped hydroxyapatite-collagen-polyanhydride sample as compared to other samples. Again from immunocytochemistry study using confocal images suggested that expression of osteocalcin, a marker indicating differentiation into osteoblast, was the highest in Si/Sr binary doped hydroxyapatite-collagen-polyanhydride sample against the other samples studied in this case. This study thus summarizes the development of photocurable biocomposites containing polyanhydride and Si, Sr doped hydroxyapatite-collagen nanoparticles that exhibited tremendous promise to regenerate bone tissues in complex-shaped musculoskeletal defect sites.