Background: As the major inorganic component of natural bone, nano-hydroxyapatite (n-HA) on its own is limited in its use in bone repair, due to its brittleness. Chitosan (CS) and sodium alginate (SAL) are used to reduce its brittleness and tendency to degradation. However, the compressive strength of the composite is still low, and its biological performance needs further study. Methods: Nano-hydroxyapatite/sodium alginate/chitosan (n-HA/SAL/CS) composite was prepared via an in situ synthesis method. Further, we prepared the n-HA/SAL/CS self-setting bone repair material by mixing n-HA/SAL/CS powder with a curing liquid (20 wt.% citric acid). In addition, the in vitro bioactivity and cell cytotoxicity were also explored. Results: Transmission electron microscopy photos revealed that the n-HA crystals were uniformly distributed throughout the polymer matrix. Infrared IR spectroscopy indicated that the HA interacted with the COO⁻ of SAL and NH₂⁻ of CS. The compressive strength of the n-HA/SAL/CS bone cement was 34.3 MPa and matched the demands of weight-bearing bones. Soaking in vitro in simulated body fluid demonstrated that the composite material had reasonably good bioactivity, while cytotoxicity tests indicated that the n-HA/SAL/CS cement could promote cell proliferation and was biocompatible. Conclusions: Compressive strength of n-HA/SAL/CS can satisfy the needs of cancellous bone, and in vitro bioactivity and cytotoxicity tests results indicated that the n-HA/SAL/CS composite could act as an optimal bone repair material.

Tetracalcium phosphate (TTCP, Ca₄(PO₄)₂O) was prepared by the calcination of coprecipitated mixture of nanoscale hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) and calcium carbonate crystal (CaCO₃), followed by cooling in the air or furnace. The effect of calcination temperature on crystal structure and phase composition of the coprecipitation mixture was characterized by transmission electron microscope (TEM), thermal analysis‐thermogravimetry (DTA‐TG), X‐ray diffraction (XRD), Fourier transform‐infrared spectroscopy (FT‐IR), and Raman spectroscopy (RS). The obtained results indicated that the synthesized mixture consisted of nanoscale HA and CaCO₃ with uniform distribution throughout the composite. TTCP was observed in the air quenching samples when the calcination temperature was above 1185°C. With the increase of the calcination temperature, the amount of the intermediate products in the air quenching samples decreased and cannot be detected when calcination temperature reached 1450°C. Unexpectedly, the mixture of HA and calcium oxide was observed in the furnace cooling samples. Clearly, the calcination temperature and cooling methods are critical for the synthesis of high‐purity TTCP. The results indicate that the nanosize of precursors can decrease the calcination temperature, and TTCP can be calcinated by low temperature.

Background: Magnesium oxychloride cement has good mechanical properties, but poor water resistance. Methods: Phytic acid, which can form chelate with Mg ²⁺ , was used to modify magnesium oxychloride cement, and the effects of phytic acid on the strength, in vitro degradation and biological activity of magnesium oxychloride cement were studied. Based on the preparation of phytic acid modified magnesium oxychloride cement with good water resistance and biological activity, osteoporosis treatment strontium ranelate was loaded on phytic acid- magnesium oxychloride cement, strontium ranelate/phytic acid-magnesium oxychloride cement was prepared. Results: It was found that the compressive strength of 1.25 wt% phytic acid-magnesium oxychloride cement after soaking in SBF for 28 d could reach 40.5 ± 2.0 MPa, 13.33% higher than that of the control group (when phytic acid was 0 wt%), and the mass loss rate of all ages was lower than that of the control group. The water resistance of magnesium oxychloride cement was effectively improved by phytic acid. After loading with strontium ranelate, the water resistance of 1.25 wt% phytic acid-magnesium oxychloride cement was improved. Cell experiments showed that strontium ranelate could effectively promote cell proliferation and improve the expression of osteoblast-related proteins. When strontium ranelate/phytic acid-magnesium oxychloride cement samples were implanted subcutaneously in rats for 4 w, no obvious inflammatory response was observed, and the material was tightly bound to the surrounding tissues. When bone cement was implanted into rat femur for 4 w, the bone cement was gradually wrapped and absorbed by new bone tissue, which grew from the outside to the inside, indicating that the bone cement containing strontium ranelate/phytic acid-magnesium oxychloride cement had excellent bone-forming ability. Conclusions: In conclusion, the results indicated that strontium ranelate/phytic acid-magnesium oxychloride cement composite bone cement had a potential application prospect in clinical bone repair. Graphical

In order to acquire a tetracalcium phosphate/magnesium phosphate (TTCP/MPC) composite bone cement that combines the excellent bioactivity of TTCP and high mechanical strength of MPC, the cement was made and the compressive strength, phase composition of hardened cement, degradation in vitro, and tissue responses in vivo by implantation of TTCP/MPC in bone defect of rabbits were investigated. The results showed that TTCP/MPC was with a markedly better mechanical property than MPC. Moreover, compared with MPC, TTCP/MPC showed significantly delayed degradability in simulated body fluid. To investigate the in vivo biocompatibility and osteogenesis, the TTCP/MPC samples were implanted into bone defects in rabbits. Histological evaluation displayed that the introduction of TTCP into MPC enhanced the efficiency of new bone formation. TTCP/MPC also showed good biocompatibility, biodegradability and osteoconductivity with host bone in vivo. The results suggested that TTCP/MPC meets the basic requirements of bone tissue engineering, has an obvious clinical advantage over MPC and is promising to be applied in orthopedic, reconstructive and maxillofacial surgery.