Im Seung Hyuk, Kim Chang Yong, Jung Youngmee, Jang Yangsoo, Kim Soo Hyun
KU-KIST Graduate School of Converging Science and Technology, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul, 02841, Korea.
Center for Biomaterials, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea and Korea University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Korea.
Biomater Sci. 2017 Feb 28;5(3):422-431. doi: 10.1039/c7bm00011a.
Monofilaments such as those consisting of polyamide (PA), polydioxanone (PDS), and poly(vinylidene fluoride) (PVDF), have been commonly used in various industries. However, most are non-biodegradable, which is unfavorable for many biomedical applications. Although biodegradable polymers offer significant benefits, they are still limited by their weak mechanical properties, which is an obstacle for use as a biomaterial that requires high strength. To overcome the current limitations of biodegradable monofilaments, a novel solid-state drawing (SSD) process was designed to significantly improve the mechanical properties of both PA and poly(l-lactic acid) (PLLA) monofilaments in this study. Both PA and PLLA monofilaments exhibited more than two-fold increased tensile strength and a highly reduced thickness using SSD. In X-ray diffraction and scanning electron microscopy analyses, it was determined that SSD could not only promote the α-crystal phase, but also smoothen the surface of PLLA monofilaments. To apply SSD-monofilaments with superior properties to cardiovascular stents, a shaped-annealing (SA) process was designed as the follow-up process after SSD. Using this process, three types of vascular stents could be fabricated, composed of SSD-monofilaments: double-helix, single-spring and double-spring shaped stents. The annealing temperature was optimized at 80 °C to minimize the loss of mechanical and physical properties of SSD-monofilaments for secondary processing. All three types of vascular stents were tested according to ISO 25539-2. Consequently, it was confirmed that spring-shaped stents had good recovery rate values and a high compressive modulus. In conclusion, this study showed significantly improved mechanical properties of both tensile and compressive strength simultaneously and extended the potential for biomedical applications of monofilaments.
单丝，例如由聚酰胺（PA）、聚二氧六环酮（PDS）和聚偏二氟乙烯（PVDF）制成的单丝，已广泛应用于各个行业。然而，大多数单丝是不可生物降解的，这对许多生物医学应用不利。尽管可生物降解聚合物具有显著优势，但它们仍然受到机械性能较弱的限制，这成为其作为需要高强度的生物材料的障碍。为了克服可生物降解单丝目前的局限性，本研究设计了一种新型的固态拉伸（SSD）工艺，以显著提高PA和聚（L-乳酸）（PLLA）单丝的机械性能。使用SSD工艺，PA和PLLA单丝的拉伸强度均提高了两倍以上，厚度大幅减小。在X射线衍射和扫描电子显微镜分析中，确定SSD不仅可以促进α晶相，还可以使PLLA单丝表面光滑。为了将具有优异性能的SSD单丝应用于心血管支架，设计了一种成型退火（SA）工艺作为SSD后的后续工艺。使用该工艺，可以制造出由SSD单丝组成的三种类型的血管支架：双螺旋、单弹簧和双弹簧形状的支架。退火温度优化为80°C，以尽量减少SSD单丝在二次加工时机械和物理性能的损失。所有三种类型的血管支架均按照ISO 25539-2进行测试。结果证实，弹簧形支架具有良好的回收率值和高压缩模量。总之，本研究表明单丝的拉伸强度和压缩强度同时得到显著提高，并扩展了其在生物医学应用中的潜力。
