Nano-needle strontium-substituted apatite coating enhances osteoporotic osseointegration through promoting osteogenesis and inhibiting osteoclastogenesis

Implant loosening remains a major clinical challenge for osteoporotic patients. This is because osteoclastic bone resorption rate is higher than osteoblastic bone formation rate in the case of osteoporosis, which results in poor bone repair. Strontium (Sr) has been widely accepted as an anti-osteoporosis element. In this study, we fabricated a series of apatite and Sr-substituted apatite coatings via electrochemical deposition under different acidic conditions. The results showed that Ca and Sr exhibited different mineralization behaviors. The main mineralization products for Ca were CaHPO4·2H2O and Ca3(PO4)2 with the structure changed from porous to spherical as the pH values increased. The main mineralization products for Sr were SrHPO4 and Sr5(PO4)3OH with the structure changed from flake to needle as the pH values increased. The in vitro experiment demonstrated that coatings fabricated at high pH condition with the presence of Sr were favorable to MSCs adhesion, spreading, proliferation, and osteogenic differentiation. In addition, Sr-substituted apatite coatings could evidently inhibit osteoclast differentiation and fusion. Moreover, the in vivo study indicated that nano-needle like Sr-substituted apatite coating could suppress osteoclastic activity, improve new bone formation, and enhance bone-implant integration. This study provided a new theoretical guidance for implant coating design and the fabricated Sr-substituted coating might have potential applications for osteoporotic patients

The Incorporation of Strontium in a Sodium Alginate Coating on Titanium Surfaces for Improved Biological Properties

Orthopedic implant failure is mainly attributed to the poor bonding of the implant to bone tissue. An effective approach to minimize the implant failure would be modifying the surface of the implant. Strontium (Sr) can stimulate the proliferation and differentiation of osteoblasts and reduce the activity of osteoclasts. In this study, a titanium (Ti) surface was successively functionalized by covalently grafting dopamine, sodium alginate (SA), and Sr2+ via the electrostatic immobilization method. The as-prepared coatings on the Ti surface were characterized by using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and contact angle. The results indicated that the Sr-incorporated coatings were successfully prepared and that Sr distributed uniformly on the surface. A long-lasting and sustained Sr release had been observed in Sr2+ release studies. The Ti/DOPA/SA/Sr exhibited little cytotoxicity and a robust effect of Sr incorporation on the adhesion and spreading of MG63 cells. The proliferation and alkaline phosphatase (ALP) activity of MG63 cells were enhanced by immobilizing Sr2+ on the SA-grafted Ti. The Sr-containing coatings, which displayed excellent biocompatibility and osteogenic activity, may provide a promising solution for promoting the tissue integration of implants

Synthesis, Characterization, and Biological Evaluation of Nanostructured Hydroxyapatite with Different Dimensions

Nanosized hydroxyapatite (HA) is a promising candidate for a substitute for apatite in bone in biomedical applications. Furthermore, due to its excellent bone bioactivity, nanosized strontium-substituted HA (SrHA) has aroused intensive interest. However, the size effects of these nanoparticles on cellular bioactivity should be considered. In this study, nanosized HA and SrHA with different dimensions and crystallization were synthesized by hydrothermal methods. The phase, crystallization and chemical composition were analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), respectively. The morphology was observed under field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The degradation behaviors of the samples were monitored by determining the ions release profile with inductively coupled plasma mass spectrometry (ICP-MS). The releasing behavior of Ca2+ and Sr2+ showed that the degradation rate was proportional to the specific surface area and inversely proportional to crystallization. The in vitro experiment evaluated by MG63 cells showed that SrHA nanorods with a length greater than 100 nm had the best biological performance both in cell proliferation and differentiation (* p < 0.05 compared with HA-1 and SrHA-1; * p < 0.01 compared with HA-2). In addition, HA nanoparticles with a lower aspect ratio had better bioactivity than higher ones (* p < 0.05). This study demonstrated that nanosized HA and SrHA with subtle differences (including dimensions, crystallization, specific surface area, and degradation rate) could affect the cellular growth and thus might have an impact on bone growth in vivo. This work provides a view of the role of nano-HAs as ideal biocompatible materials in future clinical applications