Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Laboratory of Biological Structure Mechanics (LaBS) - Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milano, Italy.
Institute of Materials Physics and Engineering, Department of Applied Science and Technology - Politecnico di Torino, 10129 Torino, Italy.
J Mech Behav Biomed Mater. 2023 May;141:105760. doi: 10.1016/j.jmbbm.2023.105760. Epub 2023 Mar 6.
Hydroxyapatite is one of the materials of choice for tissue engineering bone scaffolds manufacturing. Vat photopolymerization (VPP) is a promising Additive Manufacturing (AM) technology capable of producing scaffolds with high resolution micro-architecture and complex shapes. However, mechanical reliability of ceramic scaffolds can be achieved if a high fidelity printing process is obtained and if knowledge of the intrinsic mechanical properties of the constituent material is available. As the hydroxyapatite (HAP) obtained from VPP is subjected to a sintering process, the mechanical properties of the material should be assessed with specific reference to the process parameters (e.g. sintering temperature) and to the specific characteristic size of the microscopic features in the scaffolds. In order to tackle this challenge the HAP solid matrix of the scaffold was mimicked in the form of miniaturized samples suitable for ad hoc mechanical characterization, which is an unprecedented approach. To this purpose small scale HAP samples, having a simple geometry and size similar to that of the scaffolds, were produced through VPP. The samples were subjected to geometric characterization and to mechanical laboratory tests. Confocal laser scanning and Computed micro-Tomography (micro-CT) were used for geometric characterization; while, micro-bending and nanoindentation were used for mechanical testing. Micro-CT analyses have shown a highly dense material with negligible intrinsic micro-porosity. The imaging process allowed quantifying the variation of geometry with respect to the nominal size showing high accuracy of the printing process and identifying printing defects on one specific sample type, depending on the printing direction. The mechanical tests have shown that the VPP produces HAP with an elastic modulus as high as approximately 100GPa and flexural strength of approximately 100MPa. The results of this study have shown that vat photopolymerization is a promising technology capable of producing high quality HAP with reliable geometric fidelity.
羟基磷灰石是组织工程骨支架制造的首选材料之一。光固化立体造型（VPP）是一种很有前途的增材制造（AM）技术，能够制造具有高分辨率微观结构和复杂形状的支架。然而，如果获得高保真打印工艺并且了解组成材料的固有机械性能，则可以实现陶瓷支架的机械可靠性。由于通过 VPP 获得的羟基磷灰石（HAP）要经过烧结过程，因此应根据工艺参数（例如烧结温度）和支架中微观特征的特定特征尺寸来评估材料的机械性能。为了应对这一挑战，支架的 HAP 固体基质被模拟成适合特定机械特性的小型化样品，这是一种前所未有的方法。为此，通过 VPP 生产了具有类似于支架的简单几何形状和尺寸的小型 HAP 样品。对这些样品进行了几何特性和机械实验室测试。共聚焦激光扫描和计算机微断层扫描（micro-CT）用于几何特性分析；而微弯曲和纳米压痕用于机械测试。微 CT 分析表明，该材料具有高度致密且几乎不存在内在微孔的特性。成像过程能够定量地比较几何形状与标称尺寸之间的变化，显示出打印工艺的高精度，并在一个特定的样品类型上识别出打印缺陷，这取决于打印方向。机械测试表明，VPP 生产的 HAP 弹性模量高达约 100GPa，弯曲强度约为 100MPa。这项研究的结果表明，光固化立体造型是一种很有前途的技术，能够生产出具有可靠几何保真度的高质量 HAP。
