- 學位論文
水膠式人工髓核功能性試驗裝置之開發
Developing an Instrument for Measuring Functional Test of Hydrogel Prosthetic Nucleus
摘要
人工髓核置換術為治療退化性椎間盤疾病較新的手術技術，但因受限於手術操作空間與植體的力學特性，人工髓核以水膠式最為廣泛使用。人工髓核置換術能有效舒緩病患疼痛，並恢復術處椎間盤之生物力學表現。但長期的臨床追蹤指出，該手術後的併發症仍具有高發生率，顯示目前人工髓核的設計仍有改良空間。瞭解人工髓核的功能性有助於評估其臨床適用性。在ASTM F2789-10中，已針對水膠式人工髓核功能性進行測試規範的草擬，包含提升力與潛變試驗。故本研究之主要目的，即為參考該規範草案，開發出一套能夠有效測試人工髓核功能性之實驗裝置。本研究將利用自製的水膠試片評估該實驗裝置之功能與實驗流程的適當性。此外，本研究使用雙相線性數學模型進行水膠材料參數之擬合，進而獲得試片的材料參數，包含聚合模數與液體滲透度。 本研究結果中測得水膠試片含水量為79%，膨脹倍率為4.8倍。在無拘束性的提升力測試中，水膠產生之最大提升力為5.68±0.65N。在拘束性的潛變測試中，當水膠承受0.16 MPa負載96小時後，其高度減少量為4.8±0.17 mm；而其聚合模數為0.18±0.01 MPa，以及液體滲透度為3.03±0.27×10-15 m4/Ns。 本研究裝置成功測試水膠試片之提升力和潛變下的材料參數。人工髓核提升力數值即代表植體於椎間盤中抵抗外力的能力，但過大的提升力可能使得植體與軟骨終板間有著不當的接觸行為與負載，經長期植入後則可能提高植體下沉之風險。人工髓核在潛變下的高度減少量能用於評估植體長時間承受固定負載時的高度改變，而聚合模數與液體滲透度則可用於評估植體的強度與材料內液體流動的情形。本研究已成功開發水膠式人工髓核功能性之試驗裝置，並建立其完整試驗流程，希冀未來能提供水膠式人工髓核功能性之量測，作為該植體設計與開發的有效工具與參考指標。
並列摘要
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.