植入式雙極神經電刺激電極用於下背痛治療之發展研究

Development of Implantable Bipolar Neural Stimulation Electrode for Low Back Pain Treatment

吳承暾(Chen-Tun Wu)

指導教授 ： 施文彬

國立臺灣大學/工學院/機械工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.00831

摘要

根據衛生署統計，約70%至80%的民眾都曾有過下背痛的經驗，除了發生在成人身上，青少年也很常發生。現代人工作與生活經常久坐，更容易造成下背痛。美國 1998年統計一年需要花費907億美金於下背痛治療，可見民眾對減輕下背痛症狀之龐大需求。
根據研究指出，對神經通電進行刺激可治療多種慢性病，如帕金森氏症、癲癇、疼痛抑制等。一般下背痛的臨床治療中，對神經進行一次性電刺激，其療效並非永久性，病人約每隔三到六個月就需再進行電刺激。本研究配合跨領域計畫，發展治療下背痛之植入式脈衝射頻電刺激系統，針對需求設計電刺激電極並進行系統封裝。利用此電刺激系統，病患可自行實施神經電刺激緩和下背痛，而不必重複進行手術。系統利用外部射頻無線供電方式供應植入於皮下之系統能量，並非將電池一併埋於皮下來供電，使植入系統可達長期運作之目的。
脈衝射頻電刺激之療效先由大鼠實驗確認。因植入手術難度較低，電極設計以盡可能靠近目標為主，利用聚二甲基矽氧烷(PDMS)為主要包裝材料，並以聚對二甲苯(parylene C)作為防水層，製作出大鼠實驗之植入式電極。 為求更接近實際人體植入，系統各元件設計完成後進行米格魯犬之實驗驗證。因手術切口力求微小，手術難度大幅提高，電極須配合手術執行進行設計。材料部分改以同軸電纜為基底，利用醫療級矽膠為包裝材料製作。
系統之晶片與電路控制包含外部能量傳遞以及產生電刺激訊號，須進行封裝保護，防止生物體內水分滲入而造成短路失效。為減小植入手術傷口，未來植入之微創手術設計是利用一導引針刺入體內，直到開口位置到達目標區域後將電極沿針管內導入，固定後抽出導引針再將電極與埋於皮下之系統電路連接。電極連接系統電路需靠一防水接頭達成。此接頭除須方便執刀醫師操作，更須確保其能有效防止水分進入，並盡可能減小所佔體積。此系統之完整封裝由一整合防水接頭的封裝盒完成。此盒以具生物相容性之聚醚醚酮(PEEK)為材料加工而成，除具備足夠機械強度外，此材料不會屏蔽由外部能量源打入之電磁訊號。
滿足微創植入手術需求之電極除須外型符合和體積微小外，最困難的是到達目標位置後須具備固定能力，且此固定力量須能夠抵抗日後病患身體活動而施加於電極上的拉力，以防電極位移遠離目標神經而失去療效。本研究發展出以軟性電路板為基材，內部儲存生物膠之植入式電極。當電極伸出導引針到達目標後，生物體內水分溶解掉封口，電極即可藉由流出之生物膠而被固定。
本研究因應初期大鼠實驗到米格魯犬實驗，設計各種形態之電極，並利用高分子材料翻模包裝製成。由低頻脈衝訊號刺激觀察到植入生物腳部跳動，可證實各電極成功運作。生物實驗結果並證實此植入式脈衝射頻電刺激系統對疼痛抑制之療效。未來可利用相關製程技術研發出更適合微創手術之電極。

關鍵字

神經電刺激 ； 生醫電極 ； 電極固定 ； 防水接頭 ； 植入式生醫裝置

並列摘要

According to statistics from Department of Health, about 70% to 80% of the population in Taiwan has once suffered from low back pain. Not only adults but also teenagers can experience such a pain. Modern people often engage in sedentary activities in daily life, which makes it more likely to cause low back pain. In 1998, statistics show that the annual cost on low back pain treatment is about 90.7 billion dollars in America. This shows the huge needs for low back treatment.
According to international research, a lot of chronic diseases can be treated by electrical stimulation on nerves, such as Parkinson’s disease, epilepsy, and pain management. For clinical low back pain treatment, the target nerve is treated with one-time stimulation, whose therapeutic effect is not permanent. Patients will need the stimulation surgery every 3 to 6 months to suppress the pain. In this study, the electrode and the system packaging of an implantable pulsed radiofrequency (PRF) stimulation system for low back pain treatment interdisciplinary project is developed. Using this implantable system, the patient can perform neural stimulation by self without the surgery. Furthermore, the power of this system is wireless supplied by outer radiofrequency (RF) power source. Without a battery being stored inside, the implantable system can achieve long-term operation.
The therapeutic effect of PRF stimulation is first verified by lab rat model. Because the implantation for rat is relatively easier, the electrode design can only focus on approaching the target as much as possible. For the electrode fabrication for rat model, polydimethylsiloxane (PDMS) is used as the main packaging material, and parylene C is deposited as waterproof layer. In order to simulate more realistic human implantation process, all the system components are designed and verified on beagle model. Because the surgical incision on beagle should be as small as possible, the surgery is much more difficult than the rat model. Therefore, the electrode is designed according to the requirements of the surgery process. Coaxial cable is used as the new electrode, and medical grade silicone rubber is used as the new packaging material.
The system chip and circuit control the outer power transmission and stimulation signal generation. They need to be encapsulated to avoid system breakdown due to permeating water in animal body. In order to reduce implantation incision, a minimal invasive surgery utilizing a guide needle is designed. When the guide needle reaches the target site, the electrode is inserted through the guide needle. After the guide needle is withdrawn with the electrode being left at the target site, the electrode is connected to the system circuit embedded under skin. The connection is achieved by a waterproof rapid connector. Other than ease of use, the connector should effectively avoid water permeation, and its size should be reduced as much as possible. The whole system is packaged in a system cage with the waterproof rapid connector. The cage is manufactured from a biocompatible polymer - polyetheretherketone (PEEK), which has adequate mechanical strength. The material will not shield the RF power from the outer power source.
The electrode suitable for minimal invasive surgery has to be small enough in size. Furthermore, it should possess the ability to fix itself in place after reaching the target site. The fixing strength should be large enough to resist the pulling force subjected by patient movements so that it will not migrate and invalidate the therapeutic effect. In this thesis, an FPC-based implantable electrode with tissue adhesive stored inside is developed. When the electrode comes out of the guide needle and reaches the target site, water in animal body will dissolve the biodegradable seals. The tissue adhesive flowing out from the chamber inside the electrode will then fix the electrode in place.
In this thesis, electrodes of different types are developed for rat and beagle models, respectively. The electrodes are fabricated by biocompatible polymer packaging utilizing molding technique. From the leg twitches induced by low frequency neural stimulation, the feasibility of the stimulation electrode is verified. In the future, implantable electrodes adequate for minimal invasive surgery can be developed using associated technology reported in this thesis.

並列關鍵字

Neural electrical stimulation ； biomedical electrode ； electrode anchoring ； waterproof connector ； implantable biomedical devices

參考文獻

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