Sulfated alginate based complex for sustained calcitonin delivery and enhanced osteogenesis.

Direct administration of salmon calcitonin (sCT) by subcutaneous or intramuscular injection is limited by its low efficiency. Drug delivery systems with sustained delivery properties and high bioactivity are urgently needed. For clinical applications an economical and effective carrier is required, which has been a challenge until now. In this study, a simple alginate/alginate sulfate-sCT (Alg/AlgS-sCT) complex was successfully constructed for sustained release of sCT. The negatively charged sulfate groups facilitate bonding with sCT, which avoids the burst release of sCT and extends the release time up to 15 d (it is only 2 d for pure sCT). More importantly, the bioactivity of the released sCT is not affected during such a long release time, suggesting a conformation similar to that of native sCT.In vitroanalysis implies that the complex is biocompatible. Moreover, the combination of AlgS and sCT synergistically improves the osteogenic ability of MC3T3 cells, which show higher alkaline phosphatase levels and intracellular and extracellular calcium ion concentrations. The concentration of intracellular calcium ions is 5.26-fold higher than in the control group after 10 d of incubation. This simple yet effective system has potential applications in clinical trials and may inspire the design of other protein delivery systems.

Bioinspired enamel-like oriented minerals on general surfaces: towards improved mechanical properties.

As the hardest tissue in human body, enamel has attracted significant research interest in recent years. It has been acknowledged that the highly oriented arrangement of hydroxyapatite (HAp) crystallites of the enamel plays a crucial role owing to its excellent mechanical properties. So far, the preparation of enamel-like HAp crystallites on general substrates using mild conditions remains a challenge. Here, inspired by natural enamel, we developed a biomimetic, anodic alumina oxide (AAO)-assisted, double-layered gel system to fabricate well-oriented HAp crystals on universal surfaces. The one-directional ion flow was elaborately modulated for mineralization based on the synergistic effect of the double-layered gel and the AAO membrane, leading to highly oriented HAp crystallites. In addition, the introduction of polydopamine as a nucleating agent makes this method applicable for a wide range of substrates. The as-prepared minerals show a well-aligned enamel-like structure, exhibiting an elastic modulus of 52 GPa and nanohardness of 0.73 GPa, which are close to those of natural enamel. We envision that the strategy has potential applications for tooth repair and will provide guidelines for the mineralization of other inorganic minerals.