Glycerol solutions of highly concentrated biomineral counter-ions towards water-responsive mineralization: Demonstration on bacterial cellulose and its application in hard tissue repair

Mineralization has found widespread use in the fabrication of composite biomaterials for hard tissue regeneration. The current mineralization processes are mainly carried out in neutral aqueous solutions of biomineral counter-ions (a pair of cation and anion that form the corresponding minerals at certain conditions), which are stable only at very low concentrations. This typically results in inefficient mineralization and weak control over biomineral formation. Here, we find that, in the organic solvent glycerol, a variety of biomineral counter-ions (e.g., Ca/PO₄, Ca/CO₃, Ca/SO₄, Mg/PO₄, or Fe/OH) corresponding to distinct biominerals at significantly high concentrations (up to hundreds-fold greater than those of simulated body fluid (SBF)) are able to form translucent and stable solutions (mineralizing solution of highly concentrated counter-ions (MSCIs)), and mineralization can be triggered upon them with external solvents (e.g., water or ethanol). Furthermore, with pristine bacterial cellulose (BC) membrane as a model, we demonstrate an effective and controllable mineralization performance of MSCIs on organic substrates. This approach not only forms the homogeneous biominerals on the BC fibers and in the interspaces, but also provides regulations over mineralization rate, mineral content, phase, and dopants. The resulting mineralized BC membranes (MBCs) exhibit high cytocompatibility and favor the proliferation of rat bone marrow mesenchymal stem cells (rBMSC). Following this, we prepare a mineralized bone suture (MBS) from MBC for non-weight bearing bone fixation, which then is tested on a rabbit median sternotomy model. It shows firm fixation of the rabbit sternum without causing discernible toxicity or inflammatory response. This study, by extending the mineralization to the organic solution system of highly concentrated counter-ions, develops a promising strategy to design and build targeted mineral-based composites.