Alginate hydrogels crosslinked with different strontium-calcium ratios as injectable scaffolds for bone tissue engineering.

The easy loss of crosslinking ions in alginate can result in a structural collapse of the physiological environment, thereby losing its characteristics as a bone scaffold. Meanwhile, alginate lacks osteoconductive properties, which are necessary for ideal bone scaffolds. In this study, strontium (Sr) in combination with calcium (Ca) at different ratios were used as a crosslinking agent for the alginate to investigate the effect of Ca–Sr ratio on the physicochemical properties and biological preformation of alginate hydrogel. Here, Ca and Sr in different weight ratios (4:0, 3:1, 2:2, 1:3, and 0:4) were employed as crosslinking agents. The physicochemical properties of hydrogels, including pore size, elastic modulus, degradation rate and swelling ratio, could be effectively tuned by controlling the amount of Sr. The ion release experiment revealed a burst release of Sr²⁺ in the first day after crosslinking. However, after 3 days, the amount of Sr²⁺ release had significantly declined and was proportional to the total strontium initially introduced into the alginate. Meanwhile, the live/dead results exhibited higher cell viability for alginate with 2:2 Ca–Sr weight ratio. The alginate with 2:2 Ca–Sr ratio not only improved osteoblastic attachment, but also up-regulated the alkaline phosphatase activity, the expression of osteogenic marker genes, and relative growth factors. These findings indicate that alginate with 2:2 Ca–Sr ratio might be a promising scaffold for bone tissue engineering. [ABSTRACT FROM AUTHOR]