Developing an Instrument for Measuring Functional Test of Hydrogel Prosthetic Nucleus

• Main Authors: Yi-Quan Wen 溫翊荃, 溫翊荃
• Other Authors: Weng-Pin Chen 陳文斌
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/3m5ugz

碩士 === 國立臺北科技大學 === 機電整合研究所 === 102 === Nucleus pulposus (NP) replacement is a newer surgical technique for the degenerative disc disease (DDD). The hydrogel is a widely used material for an artificial nucleus pulposus because of the space limitation in surgical procedure and insufficient mechanical properties of the implant. NP replacement could effectively relieve pain in patient with chronic low-back pain and restore the biomechanical behavior of the operated disc. However, long-term clinical follow-up rsults suggested that the rate of complication is still high post operation, which shows requirement to improve the current designs of artificial nucleus pulposus. Better understanding of the functional properties of an artificial nucleus pulposus can help to evaluate the clinical applicability of the implant. The guideline for measuring the functional properties of an artificial nucleus pulposus has been drafted in ASTM F2789-10. The draft includes testing methods for lifting force test and creep test. The objective of the current study was to develop an instrument for evaluating the functional properties of a hydrogel prosthetic nucleus according to ASTM F2789-10. In addition, custom-made hydrogel specimens were used to examine the function of the instrument and the appropriateness of the testing procedures. Furthermore, the biphasic material properties of the specimen, including aggregate modulus and permeability, were analyzed by curve fitting of the creep data based on a linear biphasic model. The water content and expansion ratio of the hydrogel specimen tested were 79% and 4.8, respectively. In the unconfined lifting force test, the maximum lifting force produced by the specimen was 5.68±0.65 N. In the confined creep test (0.16 MPa, 96 hours compression load), the reduction of specimen height was 4.8±0.17 mm. Aggregate modulus and permeability analyzed based on a linear biphasic model were 0.18±0.01 MPa and 3.03±0.27×10-15 m4/Ns, respectively. This study successfully measured the lifting force and mechanical properties in creep test for the hydrogel specimen by the custom-made instrument. The lifting force represents the ability of an artificial nucleus pulposus to resist external forces. However, excessive lifting force produced by the implant may lead to improper contact loading to the endplate, which may raise the risk of subsidence in long-term result. The height reduction of an artificial nucleus pulposus in creep test can be used to assess the long-tern change in implant height under a constant loading. Aggregate and permeability of the artificial nucleus pulposus can represent the stiffness of the implant and the interaction of fluid to the material matrix. This study has successfully developed the instrument which could be used for evaluating the functional properties of the hydrogel specimen, and we build up the experimental procedure for the related tests. We expect the instrument which could provide the measurement for functional properties of a hydrogel prosthetic nucleus, as well as the functional parameters of a hydrogel prosthetic nucleus measured by the instrument could be usd as reference for design and development of the implant in the future.