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.

The porcine islet-derived organoid showed the characteristics as pancreatic duct.

Organoid is a tissue-engineered organ-like structure that resemble as an organ. Porcine islet-derived organoid might be used as an alternative donor of porcine islet xenotransplantation, a promising therapy for severe diabetes. In this study, we elucidated the characteristics of porcine islet organoids derived from porcine islets as a cell source for transplantation. Isolated porcine islets were 3D-cultured using growth factor-reduced matrigel in organoid culture medium consist of advanced DMEM/F12 with Wnt-3A, R-spondin, EGF, Noggin, IGF-1, bFGF, nicotinamide, B27, and some small molecules. Morphological and functional characteristics of islet organoids were evaluated in comparison with 2D-cultured islets in advanced DMEM/F12 medium. Relatively short-term (approximately 14 days)-cultured porcine islet organoids were enlarged and proliferated, but had an attenuated insulin-releasing function. Long-term (over a month)-cultured islet organoids could be passaged and cryopreserved. However, they showed pancreatic duct characteristics, including cystic induction, strong expression of Sox9, loss of PDX1 expression, and no insulin-releasing function. These findings were seen in long-term-cultured porcine islets. In conclusion, our porcine islet organoids showed the characteristics of pancreatic ducts. Further study is necessary for producing porcine islet-derived organoids having characteristics as islets.