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Octacalcium phosphate (OCP) is an attractive base material to combine into components developed for medical purposes, especially those used in bone replacement procedures, not only because of its excellent biocompatibility but also because of its ability to intercalate with multiple types of molecular layers such as silica, dicarboxylic acid, and various cations. On the other hand, there are no examples of simultaneous substituting for several different compounds on OCPs. Therefore, in this study, the physical and mechanical strength (DTS: diametral tensile strength) of OCPs substituted with both silica and dicarboxylic acids (thiomalate: SH-malate) were evaluated. By optimizing the amount of SH-malate, we were able to prepare a block consisting of OCPs with both silica and SH-malate supported in the interlayer. The composition of the OCP-based compound comprising this block was Ca8Na1.07H6.33(PO4)4.44(SiO4)1.32(SH-malate)2.40·nH2O. Interestingly, the low mechanical strength, a drawback of silica-substituted OCP blocks, could be improved by dicarboxylic acid substituting. The dicarboxylic acid addition increased the mechanical strength of silica-substituted OCP blocks, and the acid successfully incorporated into the interlayer, even with the presence of silica. These results are expected to advance the creation of better silica-substituted OCPs and improved bone replacement materials.

Abstract Quinacridone, a π-conjugated planar molecule, and common red pigment in industrial and painting applications, easily aggregates to form large clusters of pigment particles, resulting in a reduction in color strength. Cotton-derived cellulose nanofiber (NF), which almost consists of cellulose without hemicellulose and lignin, has been found to adsorb quinacridone on the surface, which inhibits pigment aggregation. The aggregation inhibition property of cellulose NF was induced by the strong intermolecular interactions between cellulose and quinacridone. In this study, the properties of lignocellulosic fibers for suppressing the aggregation of quinacridone pigments were investigated to reveal the influence of hemicellulose and lignin on the intermolecular interactions between quinacridone and fibers. Two lignocellulosic fibers with different degrees of fibrillation were used as dispersants of the pigment. In the scanning electron microscopy (SEM) images of the quinacridone–lignocellulose mixture, quinacridone particles were observed along the lignocellulose fiber, indicating that the quinacridone particles were well-adsorbed on the fiber surface. Consequently, the color of the aqueous suspension of quinacridone–lignocellulose mixture became increasingly vivid as the weight ratio of the lignocellulose fibers increased and as the fiber was fibrillated. The nuclear Overhauser effect spectroscopy (NOESY)–nuclear magnetic resonance (NMR) spectrum for quinacridone–lignocellulose suspension in d-dimethyl sulfoxide showed several NOE cross-peaks between quinacridone and cellulose/hemicellulose, whereas no cross-peaks between quinacridone and lignin were observed. It can be concluded that cellulose and hemicellulose promote the adsorption of quinacridone on the fiber surface, whereas lignin does not interact with quinacridone, even though both are aromatic molecules. This suggests that the intermolecular interactions based on hydrogen bonding and CH–π attraction are more dominant than the π–π attraction between quinacridone and lignocellulosic fibers.