Material Design of Porous Hydroxyapatite Ceramics via Inverse Analysis of an Estimation Model for Bone-Forming Ability Based on Machine Learning and Experimental Validation of Biological Hard Tissue Responses.

Hydroxyapatite and ß-tricalcium phosphate have been clinically applied as artificial bone materials due to their high biocompatibility. The development of artificial bones requires the verification of safety and efficacy through animal experiments; however, from the viewpoint of animal welfare, it is necessary to reduce the number of animal experiments. In this study, we utilized machine learning to construct a model that estimates the bone-forming ability of bioceramics from material fabrication conditions, material properties, and in vivo experimental conditions. We succeeded in constructing two models: 'Model 1', which predicts material properties from their fabrication conditions, and 'Model 2', which predicts the bone-formation rate from material properties and in vivo experimental conditions. The inclusion of full width at half maximum (FWHM) in the feature of Model 2 showed an improvement in accuracy. Furthermore, the results of the feature importance showed that the FWHMs were the most important. By an inverse analysis of the two models, we proposed candidates for material fabrication conditions to achieve target values of the bone-formation rate. Under the proposed conditions, the material properties of the fabricated material were consistent with the estimated material properties. Furthermore, a comparison between bone-formation rates after 12 weeks of implantation in the porcine tibia and the estimated bone-formation rate. This result showed that the actual bone-formation rates existed within the error range of the estimated bone-formation rates, indicating that machine learning consistently predicts the results of animal experiments using material fabrication conditions. We believe that these findings will lead to the establishment of alternative animal experiments to replace animal experiments in the development of artificial bones.

Growth of submillimeter SrTaO2N single crystals by an NH3-assisted SrCl2 flux method.

Perovskite-type oxynitrides have recently been highlighted due to their dielectric and photocatalytic properties. Numerous studies have addressed the synthesis and characterization of their nanocrystals and ceramics. However, few research works have considered single-crystal formation in such systems due to difficulties in melt growth. In this study, we explore the crystal growth of perovskite-type oxynitride SrTaO2N by an NH3-assisted SrCl2 flux method. Submillimeter-sized single crystals with lengths of approximately 300 µm were grown at a temperature of 1200 °C for 10 h with a solute concentration of 1.5 mol%. Subsequently, the crystal growth mechanism of SrTaO2N in an SrCl2 flux was studied systematically through experiments with variable holding temperature, holding time, cooling rate, and solute concentration. Our results suggest that SrTaO2N crystal growth is induced by the evaporation of SrCl2 flux.

Preparation of antimicrobial calcium phosphate/protamine composite powders with fluoride ions using octacalcium phosphate.

Calcium phosphates are key biomaterials in dental treatment and bone regeneration. Biomaterials must exhibit antibacterial properties to prevent microbial infection in implantation frameworks. Previously, we developed various types of calcium phosphate powders (amorphous calcium phosphate, octacalcium phosphate (OCP), dicalcium phosphate anhydrate, and hydroxyapatite) with adsorbed protamine (which is a protein with antibacterial property) and confirmed their antibacterial property. In this study, as foundational research for the development of novel oral care materials, we synthesized calcium phosphate composite powders from three starting materials: i) OCP, which intercalates organic compounds, ii) protamine, which has antibacterial properties, and iii) F- ion, which promotes the formation of apatite crystals. Through investigating the preparation concentration of the F- ions and their loading into OCP, it was found that more F- ion could be loaded at higher concentrations regardless of the loading method. It was also observed that the higher the preparation concentration, the more the OCP converted to fluorapatite. The synthesized calcium phosphate composite powders were evaluated for biocompatibility through proliferation of MG-63 cells, with none of the powders exhibiting any growth inhibition. Antimicrobial tests showed that the calcium phosphate composite powders synthesized with protamine and F- ion by precipitation had enhanced antimicrobial properties than those synthesized by protamine adsorption. Thus, the calcium phosphate composite powder prepared from OCP, protamine, and F- ion forms the basis for promising antimicrobial biomaterials. Graphical abstract.

Influence of Culture Period on Osteoblast Differentiation of Tissue-Engineered Bone Constructed by Apatite-Fiber Scaffolds Using Radial-Flow Bioreactor.

With the limitation of autografts, the development of alternative treatments for bone diseases to alleviate autograft-related complications is highly demanded. In this study, a tissue-engineered bone was formed by culturing rat bone marrow cells (RBMCs) onto porous apatite-fiber scaffolds (AFSs) with three-dimensional (3D) interconnected pores using a radial-flow bioreactor (RFB). Using the optimized flow rate, the effect of different culturing periods on the development of tissue-engineered bone was investigated. The 3D cell culture using RFB was performed for 0, 1 or 2 weeks in a standard medium followed by 0, 1 or 2 weeks in a differentiation medium. Osteoblast differentiation in the tissue-engineered bone was examined by alkaline phosphatase (ALP) and osteocalcin (OC) assays. Furthermore, the tissue-engineered bone was histologically examined by hematoxylin and eosin and alizarin red S stains. We found that the ALP activity and OC content of calcified cells tended to increase with the culture period, and the differentiation of tissue-engineered bone could be controlled by varying the culture period. In addition, the employment of RFB and AFSs provided a favorable 3D environment for cell growth and differentiation. Overall, these results provide valuable insights into the design of tissue-engineered bone for clinical applications.

Histological evaluations of apatite-fiber scaffold cultured with mesenchymal stem cells by implantation at rat subcutaneous tissue.

BACKGROUND: There is a strong impetus for the development of alternative treatments for bone disease that avoid the complications associated with autografts and allografts. To address this, we previously developed porous apatite-fiber scaffolds (AFSs) which have three-dimensional interconnected pores, and constructed tissue-engineered bone by culturing rat bone marrow cells (RBMCs) using AFSs in a radial-flow bioreactor (RFB). OBJECTIVE: To generate additional baseline data for the development of tissue-engineered bone constructed for clinical application using a RFB, we cultured RBMCs using AFSs under static conditions (hereafter, RBMC AFS culture), and monitored RBMC growth and differentiation characteristics in vitro, and two weeks after subcutaneous inoculation into recipient rats. METHODS: RBMCs were seeded to AFSs and growth, differentiation and calcification were monitored in vitro and in vivo by histological evaluation using hematoxylin eosin, alkaline phosphatase and alizarin red S stains. RESULTS: RBMCs in/on AFSs proliferated and differentiated normally in vitro and in vivo, and calcification was evident two weeks after subcutaneous AFS culture implantation. Histological assays revealed that AFSs and RBMC AFS cultures were biocompatible, and did not induce inflammation or immunological rejection in vivo. CONCLUSIONS: These findings suggest that AFSs are a conducive microenvironment for bone regeneration and are well tolerated in vivo. The results provide valuable baseline data for the design of implant studies using tissue-engineered bone constructed by RFB.