Sudarmadji Novella, Chua Chee Kai, Leong Kah Fai
Division of Systems and Engineering Management, Rapid Prototyping Research Laboratory, School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore, Singapore.
Methods Mol Biol. 2012;868:111-23. doi: 10.1007/978-1-61779-764-4_7.
Computer-aided system for tissue scaffolds (CASTS) is an in-house parametric library of polyhedral units that can be assembled into customized tissue scaffolds. Thirteen polyhedral configurations are available to select, depending on the biological and mechanical requirements of the target tissue/organ. Input parameters include the individual polyhedral units and overall scaffold block as well as the scaffold strut diameter. Taking advantage of its repeatability and reproducibility, the scaffold file is then converted into .STL file and fabricated using selective laser sintering, a rapid prototyping system. CASTS seeks to fulfill anatomical, biological, and mechanical requirements of the target tissue/organ. Customized anatomical scaffold shape is achieved through a Boolean operation between the scaffold block and the tissue defect image. Biological requirements, such as scaffold pore size and porosity, are unique for different type of cells. Matching mechanical properties, such as stiffness and strength, between the scaffold and target organ is very important, particularly in the regeneration of load-bearing organ, i.e., bone. This includes mimicking the compressive stiffness variation across the bone to prevent stress shielding and ensuring that the scaffold can withstand the load normally borne by the bone. The stiffness variation is tailored by adjusting the scaffold porosity based on the porosity-stiffness relationship of the CASTS scaffolds. Two types of functional gradients based on the gradient direction include radial and axial/linear gradient. Radial gradient is useful in the case of regenerating a section of long bones while the gradient in linear direction can be used in short or irregular bones. Stiffness gradient in the radial direction is achieved by using cylindrical unit cells arranged in a concentric manner, in which the porosity decreases from the center of the structure toward the outside radius, making the scaffold stiffer at the outer radius and more porous at the center of the scaffold. On the other hand, the linear gradient is accomplished by varying the strut diameter along the gradient direction. The parameters to vary in both gradient types are the strut diameter, the unit cell dimension, and the boundaries between two scaffold regions with different stiffness.
组织支架计算机辅助系统（CASTS）是一个内部的多面体单元参数库，这些多面体单元可以组装成定制的组织支架。根据目标组织/器官的生物学和力学要求，可以从13种多面体构型中进行选择。输入参数包括各个多面体单元、整体支架块以及支架支柱直径。利用其可重复性和再现性，然后将支架文件转换为.STL文件，并使用快速成型系统选择性激光烧结进行制造。CASTS旨在满足目标组织/器官的解剖学、生物学和力学要求。通过支架块与组织缺损图像之间的布尔运算来实现定制的解剖支架形状。不同类型的细胞对支架孔径和孔隙率等生物学要求各不相同。使支架与目标器官之间的力学性能（如刚度和强度）相匹配非常重要，特别是在承重器官（即骨骼）的再生中。这包括模拟整个骨骼的压缩刚度变化以防止应力屏蔽，并确保支架能够承受骨骼通常承受的负荷。根据CASTS支架的孔隙率-刚度关系，通过调整支架孔隙率来定制刚度变化。基于梯度方向的两种功能梯度类型包括径向梯度和轴向/线性梯度。在再生长骨的一段时，径向梯度很有用，而线性方向的梯度可用于短骨或不规则骨。径向刚度梯度是通过使用同心排列的圆柱形单元细胞来实现的，其中孔隙率从结构中心向外半径减小，使支架在外半径处更硬，在支架中心处孔隙更多。另一方面，线性梯度是通过沿梯度方向改变支柱直径来实现的。两种梯度类型中变化的参数是支柱直径、单元细胞尺寸以及两个具有不同刚度的支架区域之间的边界。
