Assessment and in vitro experiment of artificial anal sphincter system based on rebuilding the rectal sensation function

Research on biomechanical compatibility for a novel artificial anal sphincter with constant force

BACKGROUND

Existing artificial anal sphincter studies have shown that biomechanical compatibility problem between artificial anal sphincter and rectum caused by long-term morphological changes of the tissue surrounding the implanted prosthesis can lead to device failure or tissue ischemic necrosis. In this article, a mechanical artificial anal sphincter with constant force clamping is designed based on the superelasticity of shape memory alloys, which improved the biomechanical compatibility of implantable artificial anal sphincter.

METHODS

Firstly, the anatomical structure and the biomechanical properties of the rectum are analyzed to obtain the size parameters and material parameters of the rectal model. Secondly, a novel artificial anal sphincter with constant force is designed to improve the biomechanical compatibility between the artificial sphincter and the rectum. Thirdly, the static analysis of artificial anal sphincter is carried out by finite element analysis.

RESULTS

The simulation results show that the artificial anal sphincter can maintain a constant clamping force of 4 N within a certain variation range of intestinal tissue thickness, which verifies the constant force characteristic of the artificial anal sphincter. The constant clamping force of the artificial anal sphincter to the rectum is 4 N that is greater than the clamping force 3.99 N required to close the rectum, which verifies the effectiveness the artificial anal sphincter. The surface contact stress and the minimum principal stress of the rectum in the clamping state are less than the pressure threshold, which verifies the safety of the artificial anal sphincter.

CONCLUSIONS

The novel artificial anal sphincter has better biomechanical compatibility and improves the mechanical match between artificial sphincter and intestinal tissue. This study may provide more reasonable and effective simulation data for in vivo experiments of artificial anal sphincter in future, which may provide theoretical and technical support for further research about clinical application of artificial anal sphincter.

Research on Biomechanical Compatibility for the Artificial Anal Sphincter Based on Improved Actuator

Anal incontinence, also known as fecal incontinence, refers to the loss of the body's ability to accumulate and control the liquid, solid, and gas contents in the rectum, increasing the frequency of bowel movements. It is a symptom of defecation disorders. The artificial anal sphincter provides a new solution for clinical treatment. In this paper, in order to solve the problem of biomechanical compatibility of the actuator of the artificial anal sphincter system, the original actuator was improved. The model of the rectum and the actuator was constructed by ANSYS. The mechanical finite element analysis of the clamping mechanism was carried out by simulating sphincter behavior, and the displacement cloud diagram and stress cloud diagram of the clamping rectum were obtained. in vitro experiments were carried out using pig intestine to simulate the rectum, which verified the effectiveness of the actuator. The results of the experiment show that the successful rate of holding the rectum reached 96% under the condition of ensuring the normal blood supply to the rectum. It fully proves that the actuator has good biomechanical compatibility.

Design and Evaluation of an Intelligent Artificial Anal Sphincter System Powered by an Adaptive Transcutaneous Energy Transfer System

Objectives

The aim of this study was to optimize an intelligent artificial anal sphincter system (AASS) II for patients with severe fecal incontinence.

Methods

Redesigning and integrating a pressure sensor into the sphincter prosthesis allows us to reduce the sensor volume and makes it suitable for a chronic, ambulatory application. Furthermore, a close-loop frequency control method was designed for the transcutaneous energy transfer system. Finally, a longer working time of the implanted device was obtained by the low-power design of the hardware and software. The new model was implanted in 2 dogs and studied for periods of up to 5 weeks.

Results

The output voltage induced on the load of 30 Ω, for a variation range in k of 0.12 ~ 0.42, was maintained at approximately 6.8 V with a frequency control range of the 270 ~ 320 kHz. The minimum and maximum output voltages of the pressure sensor were found to be 1.7 V and 2.34 V, respectively, which corresponded to a pressure range of 90 ~ 120 kPa with maximum change rate of approximately 3.7% caused by the temperature variations. Moreover, compared with AASS I, the low-power design resulting in 94% reduction in power consumption.

Conclusions

The efficacy of the device in achieving continence and sensing the need to defecate was assessed in an animal model. The technical concept and the design of the AASS II turned out to be capable of fulfilling the medical requirements.