Hydroxyapatite (HAP) is a natural bioceramic which is currently used in scaffolds and coatings for the regrowth of osseous tissue but offers poor load-bearing capacity compared to other biomaterials. The deformation mechanisms responsible for the mechanical behavior of HAP are not well understood, although the advent of multiscale modeling offers the promise of improvements in many materials through computational materials science. This work utilizes molecular dynamics to study the nanoscale deformation mechanisms of HAP in uniaxial tension and compression. It was found that deformation mechanisms vary with loading direction in tension and compression leading to significant compression/tension asymmetry and crystal anisotropy. Bond orientation and geometry relative to the loading direction was found to be an indicator of whether a specific bond was involved in the deformation of HAP in each loading case. Tensile failure mechanisms were attributed to stretching and failure in loading case-specific ionic bond groups. The compressive failure mechanisms were attributed to coulombic repulsion in each case, although loading case-specific bond group rotation and displacement were found to affect specific failure modes. The elastic modulus was the highest for both tension and compression along the Z direction (i.e. normal to the basal plane), followed by Y and X.

羟基磷灰石（HAP）是一种天然生物陶瓷，目前用于骨组织再生的支架和涂层中，但与其他生物材料相比，其承重能力较差。尽管多尺度建模的出现提供了通过计算材料科学改进许多材料的希望，但对导致HAP力学行为的变形机制还没有很好的理解。这项工作利用分子动力学研究HAP在单轴拉伸和压缩过程中的纳米尺度变形机理。发现变形机制随拉伸和压缩中的加载方向而变化，从而导致明显的压缩/拉伸不对称性和晶体各向异性。发现结合方向和相对于加载方向的几何形状是每种加载情况下HAP变形中是否涉及特定结合的指标。拉伸破坏机制归因于加载情况下特定离子键基团的拉伸和破坏。在每种情况下，压缩破坏机制都归因于库仑排斥，尽管发现加载情况下特定的键组旋转和位移会影响特定的破坏模式。沿Z方向（即垂直于基面）的拉伸和压缩弹性模量最高，其次是Y和X。在每种情况下，压缩破坏机制都归因于库仑排斥，尽管发现加载情况下特定的键组旋转和位移会影响特定的破坏模式。沿Z方向（即垂直于基面）的拉伸和压缩弹性模量最高，其次是Y和X。在每种情况下，压缩破坏机制都归因于库仑排斥，尽管发现加载情况下特定的键组旋转和位移会影响特定的破坏模式。沿Z方向（即垂直于基面）的拉伸和压缩弹性模量最高，其次是Y和X。