Landaeta Felix J, Shiozawa Jose Nauaki, Erdman Arthur, Piazza Cara
Earl E. Bakken Medical Devices Center University of Minnesota-Twin Cities, 420 Delaware Street SE, MMC 95, G217 Mayo Building, Minneapolis, MN, 55455, USA.
Centro de Salud B La Troncal, Instituto Ecuatoriano de Seguridad Social, Quito, Ecuador.
3D Print Med. 2020 Oct 23;6(1):31. doi: 10.1186/s41205-020-00084-3.
External fixation is a mainstream limb reconstruction technique, most often used after a traumatic injury. Due to the high rates of trauma in developing countries, external fixation devices are often utilized for immediate fracture stabilization and soft tissue repair. Proper external fixation treatment too often still fails to be adopted in these regions due to the high cost and trauma complexity. A novel, inexpensive, unilateral fixator was constructed using 3D printed clamps and other readily available supporting components. ASTM standard F1541 tests were used to assess the biomechanical properties of this novel external fixator.
Applicable sections of ASTM standard F1541 were used to determine the biomechanical properties of the novel external fixator. 3D printed clamps modeled using SolidWorks and printed with chopped carbon fibers using a fuse deposition modeling (FDM) based 3D printer by Markforged (Boston, MA) were used. This study included 3 different testing configurations: axial compression, anterior-posterior (AP) bending, and medial-lateral (ML) bending. Using the novel unilateral fixator with 3D printed clamps previously sterilized by autoclave, an input load was applied at a rate of 20 N/s, starting at 0 N via a hydraulic MTS tester Model 359. Force and deformation data were collected at a sampling rate of 30 Hz. There was a load limit of 750 N, or until there was a maximum vertical deformation of 6 mm. Also, 4 key dimensions of the 3D printed clamps were measured pre and post autoclave: diameter, width, height and length.
The novel external fixator had axial compression, AP and ML bending rigidities of 246.12 N/mm (σ = 8.87 N/mm), 35.98 N/mm (σ = 2.11 N/mm) and 39.60 N/mm (σ =2.60 N/mm), respectively. The 3D printed clamps shrunk unproportionally due to the autoclaving process, with the diameter, width, height and length dimensions shrinking by 2.6%, 0.2%, 1.7% and 0.3%, respectively.
Overall, the biomechanical properties of the novel fixator with 3D printed clamps assessed in this study were comparable to external fixators that are currently being used in clinical settings. While the biomechanics were comparable, the low cost and readily available components of this design meets the need for low cost external fixators in developing countries that current clinical options could not satisfy. However, further verification and validation routines to determine efficacy and safety must be conducted before this novel fixator can be clinically deployed. Also, the material composition allowed for the clamps to maintain the appropriate shape with minimal dimensional shrinkage that can be accounted for in clamp design.
外固定是肢体重建的主流技术，最常用于创伤后。由于发展中国家创伤发生率高，外固定装置常被用于骨折的即时固定和软组织修复。由于成本高和创伤复杂，这些地区往往仍未采用适当的外固定治疗方法。一种新型、廉价的单侧固定器由3D打印夹具和其他易于获得的支撑部件制成。采用美国材料与试验协会（ASTM）标准F1541测试来评估这种新型外固定器的生物力学性能。
采用ASTM标准F1541的适用部分来确定新型外固定器的生物力学性能。使用通过SolidWorks建模并由Markforged（马萨诸塞州波士顿）的基于熔丝沉积成型（FDM）的3D打印机用短切碳纤维打印的3D打印夹具。本研究包括3种不同的测试配置：轴向压缩、前后（AP）弯曲和内外侧（ML）弯曲。使用先前经高压灭菌的带有3D打印夹具的新型单侧固定器，通过液压MTS 359型测试仪以20 N/s的速率施加输入载荷，从0 N开始。以30 Hz的采样率收集力和变形数据。载荷极限为750 N，或直到最大垂直变形达到6 mm。此外，在高压灭菌前后测量3D打印夹具的4个关键尺寸：直径、宽度、高度和长度。
新型外固定器的轴向压缩、AP和ML弯曲刚度分别为246.12 N/mm（σ = 8.87 N/mm）、35.98 N/mm（σ = 2.11 N/mm）和39.60 N/mm（σ = 2.60 N/mm）。由于高压灭菌过程，3D打印夹具不成比例地收缩，直径、宽度、高度和长度尺寸分别收缩2.6%、0.2%、1.7%和0.3%。
总体而言，本研究中评估的带有3D打印夹具的新型固定器的生物力学性能与目前临床使用的外固定器相当。虽然生物力学性能相当，但这种设计的低成本和易于获得的部件满足了发展中国家对低成本外固定器的需求，而目前的临床选择无法满足这一需求。然而，在这种新型固定器能够临床应用之前，必须进行进一步的验证和确认程序以确定其有效性和安全性。此外，材料成分使夹具能够以最小的尺寸收缩保持适当的形状，这在夹具设计中可以考虑到。
