Research On Key Technology And Experiments Of Artificial Anal Sphincter With Sensor Feedback Powered By Transcutaneous Energy Transmission

Severe fecal incontinence(FI) — defined as recurring episodes of involuntary loss of solid or liquid feces or mucus — is a major unresolved clinical condition of multifactorial etiology. The social stigma and embarrassment of being incontinent of feces can lead people to severely limit their activity. However, the existing artificial anal sphincter system(AASS) can’t perceive the quantity of faces. Patients can’t control defecation time autonomously, they need to pump the liquids with hands, and surgical procedure of this system is complex. With the development of science and technology and the improvement of patients requirements on life quality, against the more and more common fecal incontinence disorder, the research of intelligent artificial anal sphincter system associated with transcutaneous energy transfer(TET) and RF control which is suitable for bowel control and defecation sensation has already become an important direction in the medical field.Under the supports of the National Natural Science Fund of China(NO.31170968), and the Medical Cross Fund of Shanghai Jiao Tong University(YG2011MS05), this paper conducts the intensive study on the key technologies of artificial anal sphincter system with sensor feedback powered by transcutaneous energy transfer. Designs of TET, RF control system and sphincter prosthesis are accomplished by adopting the combination of theory, engineering, and experiment methods. Moreover, the efficacy of the AASS in achieving continence and sensing the need to defecate is assessed in animal model. The main content and achievements of this paper are summarized as follows:1. According to the research target and technical solutions, the basic functions of intelligent control system are accomplished by hardware and software design. The hardware design mainly include wireless communication module, bio-feedback module, charging manager module and microcontroller module. The software program degisn mainly include duplex communication program based on Rf data transceiver and low-power design of the internal control module. On this basis, the internal system is integrated package with biocompatible materials. The final purpose of hardware and software design is to simulate the normal neurological perception and control mechanism of defecation, also make the system has perfect synergy and control ability.2. The critical importance of the link transfer efficiency ηL on performance enhancement of the TET system is analyzed by circuit modeling. Around the parametric design of coil structure, planar solenoidal coil with ferrite disk is EMF modeled by using of free space differential field law and boundary conditions. In this way, the lumped parameter models(L、M、RS) of the coil with respect to the number of turns Nt, wire diameter Фc, external diameter ro, internal diameter ri, ferrite disk thickness t and ferrite disk relative permeability μr are constructed, thus providing important theoretical basis for link efficiency optimization. In order to improve the ηL, the Nt、Фc、ro、ri、t、μr and Nl of primary and secondary coil were parametric designed based on Matlab graphical design method and FEA analysis. Within 5 ~ 25 mm transmission distance, the ηL of the optimized coil pair is 84.91%~98.78%, the average ηL increased by 36.1% comparing with the original solid copper wire coil which was designed according to the experience. During the design process, combined with multiple sets of sample coil, the accuracy and validity of analytical models and optimization method were verified by FEA simulation and experimental measurement.3. In order to guarantee the stability of energy supply, the transfer function of TETS with respect to the coupling factor, secondary load and operation frequency was constructed. According to different conditions, a closed-loop frequency and phase feedback control regulation were designed respectively in order to transmit the power adaptively. The frequency control regulation was designed for the working condition of varying coupling factor. In this control, the relationship between frequency and coupling factor was obtained by deducing of frequency control function. According to this function, the influence of coupling factor change on receiving voltage can be compensated by adjusting the transmission frequency. The performance of this method was validated in vitro experiment with the coupling variation between 0.12 and 0.42. The results show that the receive power of the secondary side can be maintained at a constant 700 m W across the whole coupling coefficient range with a maximal end-to-end power efficiency of 67.5%. The phase control regulation was designed for the working condition of varying coupling factor and secondary load. In this control, the relationship between phase difference of MOSFETs driving signals and primary effective input voltage was obtained by deducing of phase control function. According to this function, the influence of coupling factor and secondary load change on receiving voltage can be compensated by adjusting the phase difference. The performance of this method was validated in vitro experiment across the whole coupling coefficient range(0.09~0.29) as well as load resistance(50~120 Ω). The results show that the output voltage of the secondary side can be maintained at a constant 7 V with a receiving power range of 410 to 950 m W, and the proposed controller has reached a maximal end-to-end power efficiency of 74.2%.4. In actual application of TETS, on concerning that the human abdominal subcutaneous tissue will expose to the electromagnetic field. Modeling and simulation of multilayer structure with respect to coil pair and transplant environment were conducted in Maxwell FEA software by applying the theory of dosimetry methods, thus, the distribution of current density and specific absorption rate(SAR) in the tissue can be analyzed. The simulation parameters(model structure, tissue electrical characteristics and sending current) are set to the actual application value. Experimental results showed that the influence of electromagnetic radiation on subcutaneous tissue was within the scope of security.5. In this paper, there were three artificial anal sphincter prosthesises including traditional water pump prosthesis, elastic spring prosthesis and puborectalis muscle prosthesis having been developed. The traditional water pump prosthesis can transport fluid bidirectional with a maximum flow rate of 8.5 m L/min and can build up backpressure up to 70 k Pa. The design of this prosthesis reduces the occlusion pressure and allows low inflation volumes(9~10.5 m L), operating pressures between 3.34 and 7.26 k Pa indicate a minor risk of ischemic injury to the bowel. The elastic spring prosthesis and puborectalis muscle prosthesis are mechanical bionic prosthesis. The former makes use of elastic spring characteristics of natural stretch and controllable isometric contraction to realize the occlusion and release of the intestinal wall. Design inspiration of the latter originates from the understanding and abstract of puborectalis muscle’s anatomical structure and function. The puborectalis muscle prosthesis simulates the U-shaped muscle to pull the anorectal junction forwardly, thus forming the angle of rectum. The angle of rectum can be released and shrinked to realize the control function of defecation. Compared with the traditional water pump prosthesis, the implanted module of the mechanical bionic prosthesis is more simplified. In vitro experimental results showed that the three artificial anal sphincter prosthesises described above can control simulated fecal behavior effectively.6. In vivo experiment was conducted for the first generation traditional water pump AASS(WP-AASS Ι). The functionality of bowel control and the feasibility of defecation sensation rebuild were verified for the first time, and gathered experiences of surgical procedure, transplant placement, postoperative management and system testing. At the same time, the deficiencies were also found in the WP-AASS Ι. Based on this, beagle experiments were conducted for the optimized WP-AASS(WP-AASS ΙΙ). The effectiveness of fecal continence and detecting of defecation sensation were futher studied in this experiment, and the X-ray imaging, anorectal manometry analysis, serum chemistry and histopathological analysis were also conducted. Two animal experiments, which provided valuable experience and data for prosthetic design, system optimization and further clinical trials, have verified the system function and application value.In this paper, the prosthesis structure, detecting of defecation sensation, TETS and communication cotrol technology were researched deeply for the AASS and practical application, providing a theoretical basis and design experience for futher development of intelligent AASS. At last, the work and experiments in the dissertation are summarized. And combined with the data of animal experiments and experience, putting forward research direction in future.