3D列印支架結構設計與應力分析

Abstract

結構對於骨支架的性質有著至關重要的影響，骨支架需要具有開放式的孔洞讓 養分進入供給細胞和血管的增生，越高的比表面積則有越多的面積提供細胞附著， 同時又要具備足夠的結構強度與穩定性承受手術操作與日常動作時的應力，因此 透過結構設計來解決兩性質矛盾之處，本實驗透過 3D 列印出設計的三大組（共 12 個結購）體積佔比都是 50 %的骨支架結構，包含第一組為支柱型(Z 結構), 第二組 為原子晶格型(BCC 和 FCC 結構) 和第三組為前兩組依照不同質量配比組合而成的 混合結構 (BCC-Z 和 FCC-Z)，Z 軸與 XY 軸的抗壓強度都會被量測（12 個結構, 每 個方向 6 個試片, 總共 144 個 PLA 試片），並搭配有限元素分析法來解釋結構應 力分布與結構強度的關係，這使我們更了解各結構的優缺點。 在混合組中，透過調整支柱型與晶格型結構的質量配比，可以成功在一個結構(FCC Z/U1）達到高比表面積與高抗壓強度兩個優異的性質，在質量由支柱結構轉 移到內部晶格結構時，應力分布的結果顯示沒有明顯的應力遮蔽，是此結構特殊之 處。在 FCC-Z 組的應力分析中發現，結構中應力由高到低的位置可以預測抗壓強 度測試時破裂的先後順序，越高的應力集中處越早破裂。在 Square 結構中加入 Joint 結構而不改變孔隙率的前提下，強度不變且可以大大增加結構外觀與強度維持性。 此外，透過三組結構由 3D 列印製作的硫酸鈣試片來印證在 PLA 試片發現的結構 性質，並在測試XY方向抗壓強度時，觀察破裂行為以研究 3D 列印層與層之間的 介面是否是此結構中強度較弱之處。

The structure is crucial to the property of scaffold. Porous structure is needed for the transportation of nutrients and cells, which is important for the cell proliferation and vascularization. The cell proliferation can be accelerated with higher specific surface area. Besides, the mechanical property of the structure must be high enough to withstand the stress during surgery and subsequent motion after implant. Therefore, structure design is important to solve the contradiction between the porous structure and the mechanical property of scaffold. Twelve structures were designed and prepared with 3D printing using PLA material. Every structure has 50 % volume ratio and printed with 100 % infill density. The first group is pillar-structure (Z group), the second group is unit cell structure (BCC and FCC, U group) and the third group is the mixed structure of the former two groups with different mass ratio. The third group were named as BCC-Z and FCC-Z (U+Z group). The Z-axis and XY-axis compressive strength are measured for all structures (each structure has five samples for each direction, total for 120 samples). The result shows that porous structure with good compressive strength and high specific surface area can be achieved on mixed structure, FCC-Z. With the assistance of Finite Element Analysis (FEA), the relation between the stress distribution and the compressive strength of the structure can be explained. It allows us to realize the benefit and drawback of each design. The location and priority of fractures estimated by FEA stress analysis can correspond to the results in compressive testing. The Joint Square structure has much better structure sustainability and can bear more energy than Square in terms of the same strain. In addition, 3 structures made by calcium sulfate (CS) are used to prove the behavior found on PLA samples. The XY compressive testing is used to evaluate the weakness between 3D printing layers.