Laboratory for Biomedical Microtechnology, Department of Microsystems Engineering - IMTEK, University of Freiburg, Georges-Koehler-Allee 102, 79110 Freiburg, Germany.
Biomaterials. 2010 May;31(13):3449-58. doi: 10.1016/j.biomaterials.2010.01.053. Epub 2010 Feb 9.
In order to be used as a material for neural prostheses, polyimide has to withstand the body environment over years. To obtain more information about the long-term stability of this material, we tested three commercially available polyimides (PI2611 - HD-Microsystems (type: BPDA-PPD), U-Varnish-S - UBE (type: BPDA-PPD), Durimide 7510 - Fujifilm (type: information not provided)). Specimens were stored in phosphate buffered saline (PBS) at 37 degrees C to simulate body temperature and at elevated temperatures of 60 degrees C and 85 degrees C to accelerate aging. During the course of 20 months, stress-strain curves were measured monthly by tensile testing. From these curves the Young's modulus, the stress and strain at break, the stress at 10% strain as well as the fracture energy were extracted and used to characterize and to statistically evaluate the mechanical material properties. Mass loss was determined by weighing polyimide foils (Upilex25S - UBE) and optical measurements were conducted to examine changes in chemical structure and crystallinity. At 37 degrees C and 60 degrees C no change in material behavior could be observed, except for an increase of the Young's modulus of the BPDA-PPD type stored at 60 degrees C. This demonstrates the long-term stability of all tested polyimides with respect to PBS. All extracted quantities mentioned above, as well as the mass, decreased in specimens stored in PBS at 85 degrees C. As a comparison, BPDA-PPD type specimens stored at 85 degrees C in deionized water showed no change in any property but behaved similarly to the reference material.
为了将聚酰亚胺用作神经假体材料，它必须能够在数年内耐受人体环境。为了获得有关这种材料长期稳定性的更多信息，我们测试了三种市售的聚酰亚胺（PI2611-HD-Microsystems（BPDA-PPD 型）、U-Varnish-S-UBE（BPDA-PPD 型）、Durimide 7510-Fujifilm（信息未提供））。将样品储存在磷酸盐缓冲盐水（PBS）中，温度为 37°C 以模拟体温，温度为 60°C 和 85°C 以加速老化。在 20 个月的过程中，每月通过拉伸测试测量应力-应变曲线。从这些曲线上提取杨氏模量、断裂时的应力和应变、10%应变时的应力以及断裂能，用于表征和统计评估力学材料性能。通过称重聚酰亚胺薄膜（Upilex25S-UBE）来确定质量损失，并进行光学测量以检查化学结构和结晶度的变化。在 37°C 和 60°C 下，除了在 60°C 下储存的 BPDA-PPD 型聚酰亚胺的杨氏模量增加外，未观察到材料行为的变化。这表明所有测试的聚酰亚胺在 PBS 中具有长期稳定性。在 PBS 中储存的样品中，除了质量外，上述所有提取的量以及质量都减少了。作为比较，在去离子水中储存的 85°C 的 BPDA-PPD 型样品在任何性质上都没有变化，但与参考材料的行为相似。
