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Keywords:

  • artificial urinary sphincter (AUS);
  • urinary incontinence;
  • sphincter device;
  • mechanism of action;
  • innovative design

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Dynamic continence device with circumferential urethral cuff occlusion
  5. Urinary continence device with partial urethral occlusion
  6. Novel and experimental urinary continence devices
  7. Conclusions
  8. Conflict of interest
  9. References

Introduction

  • The current artificial urinary sphincter (AUS), AMS 800™ (American Medical Systems, Minnesota, MN, USA) is considered the standard of care for the treatment of urinary incontinence (UI).
  • While the long-term effectiveness, safety, and durability of the current model of the AMS 800 are well documented, it is not without its limitations and complications. Over the last few years, improvements in design and innovative research into AUS devices have increased the treatment arsenal in male UI.

Methods

  • Articles from peer-reviewed journals, abstracts from scientific meetings and electronic literature searches formed the basis of this review.

Results

  • Newer AUS models, e.g. FlowSecure™, Zephyr™, Pro-ACT™ and other novel experimental AUS devices, are designed to simulate a healthy human sphincter and address the limitation of the existing AMS 800 device.

Conclusions

  • Newer and novel AUS models are innovative and showed promising outcomes in short- to intermediate-term follow-up.
  • However, there exists the need for prospective randomised clinical trials and complete reporting of adverse and long-term results before these AUS models can replace the existing AMS 800 device.

Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Dynamic continence device with circumferential urethral cuff occlusion
  5. Urinary continence device with partial urethral occlusion
  6. Novel and experimental urinary continence devices
  7. Conclusions
  8. Conflict of interest
  9. References

The urinary sphincter is composed of an internal sphincter and an external sphincter. The internal sphincter is not a true sphincter and rather viewed as a continuation of the bladder. By contrast, the external sphincter is a true urinary sphincter and consists of striated muscles, the rhabdosphincter [1]. In addition, the prostate in men assists in maintaining the shape of the bladder neck with the pre-prostatic sphincter assuming some role in the maintenance of urinary continence. The peri-urethral striated sphincter forms part of the levator ani muscle complex and together constitutes the pelvic floor or urogenital diaphragm [2-5]. The urinary sphincter muscle ensures continence during the filling phase of the bladder, while the relaxation of the sphincteric system during bladder contraction allows natural voiding to occur. The anatomy of the urinary sphincters and the interplay between the contraction of bladder muscle and relaxation of bladder outlet and urinary sphincteric complex during voiding, however, is rather complex.

Presently, the artificial urinary sphincter (AUS) is the only mechanical device that closely simulates the function of a biological urinary sphincter. Novel and ingenious in technical design, the hydraulically controlled AMS 800TM (American Medical Systems, Minnetonka, MN, USA) device has been used for nearly 40 years, since it was first introduced in 1973 and continues to restore the quality of life for many men and women plagued by severe stress urinary incontinence (UI) [6]. It consists of three components; a pressure-regulating balloon (PRB), an inflatable cuff, and a control pump (Figure 1a). The PRB serves dual functions, as a pressure regulator and also acts as fluid reservoir. When the AUS is in its active (closed) state, the ‘resistor’ in the pump allows the fluid from the PRB to travel down the pressure gradient to the urinary cuff and gradually closes the urethral lumen. The inflated cuff maintains urine in the bladder and prevents urine loss. Manual compression of the control pump transfers fluid from the control pump into the PRB. The control pump then automatically re-expands, drawing fluid out of the sphincter cuff, so that the urinary cuff deflates and the patient is therefore able to void. The addition of the locking mechanism on the side of the control pump allows for the AUS device to remain open (deactivated) for delayed AUS activation postoperatively and opportunity for nocturnal deactivation of the AUS device.

figure

Figure 1. AMS 800 device (a); FlowSecure device (b); Zephyr ZSI 375 device (c); Periurethral constrictor (d); Adjustable Continence Therapy (Pro-ACT) (e); Tape mechanical occlusive device (TMOD) (f) and German artificial sphincter system (GASS) (g).

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Published data has supported the AMS 800 device as a highly durable, effective and safe treatment option for stress UI. In fact, the AMS 800 remains the standard of care for the treatment of severe UI [7]. Published data [6] showed that Kaplan–Meier projections for freedom from mechanical failure were 79% at 5 years and 72% at 10 years, and Kaplan–Meier 5-year projections for freedom from any operation were 50% in a small series and 79.4% for a larger series. While there was no significant differences in overall satisfactory continence and device failure rates between men and women treated with AMS 800 devices [8], women appeared to have a higher complete continence rate and longer duration of functioning device than their male counterparts, perhaps related to the more physiological location of the AUS cuff around the bladder neck in women than the bulbous urethral cuff location in men. The AUS device is equally effective in children too [9]. Amongst patients with neurogenic and poorly compliant bladder, concomitant augmentation cystoplasty did not result in higher complication rates, although an AUS device implanted before puberty appeared to be associated with better clinical outcomes [10].

While the long-term effectiveness, safety, and durability of the current model of the AMS 800 are well documented, it is not without its limitations and complications. The AMS 800 device is a costly device and patients need to have the manual dexterity to manipulate the pump to void. The geometry of the AMS 800 device, i.e. the length and cuff diameter, is given by the manufacturer and cannot be adapted. Furthermore, the PRB and cuff pressures have to be determined at the time of device implantation and are, therefore fixed. Therefore, any increases in intra-abdominal and bladder pressures can exceed the cuff pressure resulting in UI. Furthermore, it appears that the effectiveness of the AUS device would also be significantly diminished if the PRB was not located next to the bladder in the retropubic space for equal transmission of the abdominal pressures. Like any device, it is associated with both mechanical and non-mechanical failures. The mechanical failure of the AUS is mostly secondary to fluid loss from the system, e.g. a tear in tubing, cuff and/or connector site leak. In addition, defective control pump and obstruction of flow from debris, airlock, blood or crystallised material could also result in mechanical failure [7, 8]. Non-mechanical failure of the AMS 800 device includes prosthesis infection, cuff erosion and tissue atrophy. The introduction of kink-resistant tubing, quick connectors, InhibiZoneTM antibiotic coating, narrow-backed cuff and delayed activation button on the control pump appear to address some of these issues [7-12].

Dynamic continence device with circumferential urethral cuff occlusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Dynamic continence device with circumferential urethral cuff occlusion
  5. Urinary continence device with partial urethral occlusion
  6. Novel and experimental urinary continence devices
  7. Conclusions
  8. Conflict of interest
  9. References

FlowSecureTM (Craggs Sphincter) (Figure 1b)

The FlowSecure AUS device (Barloworld Scientific Limited, Stone, UK) was designed by Dr Craggs and associates [13, 14] with the preliminary clinical results first reported in 2006. This new AUS device attempts to address two major weaknesses of the AMS 800, namely the inability of the PRB to adapt to changes in intra-abdominal and bladder pressures; and the need for revision surgery after cuff atrophy (Table 1) [7-21]. The FlowSecure device is implanted as a single unit, thus eliminating the need for tubing connections. This one-piece silicone device comes prefilled with 30 mL of 0.9% saline and is comprised of four parts connected together by silicone connecting tubes: a PRB, a stress-release balloon, a circular occluding urethral cuff and a control pump [14]. The stress-relief balloon is placed extra-peritoneally and transmits transient intra-abdominal pressure changes to the urethral cuff to increase occlusion pressure during periods of stress (conditional occlusion). The PRB establishes a basal occlusive pressure and is identical to the stress-relief balloon. The regulating pressure is adjusted in the range of zero to 80 cmH2O and can be altered by the injection or removal of fluid (based on continence status) from the device in situ. Device pressure can therefore be titrated against continence for each individual patient, removing the need to select a specific pressure range before the operation. The cuff features a pre-moulded and rounded adjustable internal surface to minimise potential cuff creasing and for homogenous pressure transmission. Although it was designed for placement on the male urethra, the cuff sizes go up to 7 cm and therefore large enough to accommodate the female bladder neck [15]. The new control pump features a resistance valve, a fast-filing supplementary mechanism that allows for quicker manual inflation of the cuff and overrides the usual slow automatic process, and a self-sealing port in the pump assembly allows for in situ pressure adjustment [16].

Table 1. Current AUS and AUS-like continence devices in the market
NameMakerDescriptionSpecial featuresReferences
AMS 800AMS

3 pieces; 3 parts

  • Occluding cuff
  • PRB
  • Pump
  1. Considered ‘gold standard’ treatment
  2. Kink resistant tubing, quick connectors, delayed activation button, InhibiZone antibiotic coating and narrow-backed cuff
[7-13]
FlowSecureBarloworld Scientific Limited

1 piece; 4 parts

  • Occluding cuff
  • PRB
  • Stress-release balloon
  • Pump
  1. Single unit system
  2. In situ pressure adjustment via stress-release balloon and self-sealing pump
[13-17]
Zephyr ZSI 375Mayor Group

1 piece; 2 parts

  • Pressure regulating tank
  • Occluding cuff
  1. Single-unit system
  2. No PRB or reservoir
  3. In situ pressure adjustment via pressure-regulating tank
[18]
Peri-constrictor deviceSilimed

2 pieces; 2 parts

  • Occluding cuff
  • Self-sealing port
  1. No PRB or reservoir
  2. Additional pressure adjustment via port
[19-21]
ProACTUromedia

2 pieces; 2 parts

  • Silicone balloon with titanium ports X2
  1. No PRB or reservoir
  2. Additional pressure adjustment via ports
[22-27]

There are several proposed advantages of the FlowSecure device over AMS 800 device, e.g. a single-unit system with no connecting tubing for implantation; the ability to implant at a lower cuff pressure with further in situ pressure adjustment through a self-sealing port in the pump assembly; and a stress-relief mechanism that provides a low resting occlusion pressure and conditional occlusion of the urethra depending on changes in intra-abdominal pressure; thus making this device theoretically an attractive alternative to the AMS 800 device. However, at present there are limited numbers of FlowSecure devices implanted and lack of published long-term follow-up data. While the early report on the outcomes of the FlowSecure device was encouraging for the decrease in mean daily leakage volume (770.6–55.1 mL) and an overall improvement in the Continence Index (54% to 97%) [14], recent publication of larger series showed high mechanical failure (6%) and infection (5%) rates, as well as risk of pump assembly perforation (9%) in the short- to intermediate-term follow-up [17].

Zephyr ZSI 375TM (Figure 1c)

The Zephyr ZSI 375 (Mayor Group, Villeurbanne, France) is another one piece, silicone elastomer urinary continence device [18], implanted in limited countries only. Unlike the AMS 800 and FlowSecure devices, it is comprised of two components only, a circular urethral cuff and a pressure-regulating tank placed in the scrotum (Table 1). The cuff consists of moulded curved silicone rubber and is available in different diameters (3.75–5 cm) and pressure ranges (60–70, 70–80 and 90–100 cmH2O). The pressure-regulating tank consists of an activation button, hydraulic circuit and a compensation pouch, and sits in the patient's scrotum. At rest, a piston mechanism, under spring-loaded tension exerts pressure on the fluid in the hydraulic chamber. When the activation button is pressed, the piston descends forcing fluid from the cuff into the hydraulic circuit and compensation chamber, resulting in auto-inflation of the cuff.

The theoretical advantages of Zephyr device over the AMS 800 device are that it is possible to adjust the pressure of the device by injecting or removing fluid from the compensating pouch, and the lack of a third component (to be placed) in the retropubic space thereby decreasing the risk of bladder injury and device migration. Nonetheless the device lacks the ability to provide in situ pressure adjustment to sudden changes in intra-abdominal pressure and the potential risk of infection and damage to the pressure-regulating tank from frequent injections. To date, there has not been any published peer-reviewed study or follow-up data on this new continence device.

Periurethral constrictor (Figure 1d)

The periurethral constrictor continence device (Silimed, Rio de Janeiro, Brazil) was developed by Dr Fabio Vilar specifically to treat paediatric patients with deficient bladder sphincter function and the first clinical paper on this device was published in 2000 [19]. It consists of a constrictor cuff linked by a tube to a hydraulically activated self-sealing valve (Table 1). The cuff is made of a silicone membrane shaped like an open and inflatable ring, with a polyurethane-foam coat on the internal surface and a polyester tissue reinforcement band on the external surface. The external band contains two pairs of buttons and four pairs of holes along its length to allow for adjustment of the device around the bladder neck or the bulbar urethra. The two sections of silicone tubes (200 and 500-mm long) are joined by a plastic connector linking the valve to the constrictor cuff and allow for adjustment of the distance between the valve and the cuff. The system works in a hydraulic fashion through the injection of sterile saline into the self-sealing port. To minimise tissue ischaemia and subsequent cuff erosion, Vilar et al. [20] advocated that the pressure should be relieved for about 2 months each year. The initial report showed satisfactory outcomes in men with post-prostatectomy UI and 73.3% of the patients had functional devices and were socially continent at a mean follow-up of 42.1 months [21]. Nonetheless, the periurethral constrictor device is plagued by high complication rates, e.g. the need for additional fluid in the port to increase the occlusive static pressure of the cuff (seven patients), urethral erosion (four patients), device infection (three patients) and device malfunction from leakage of saline solution (four patients) [21]. It is postulated that the leakage was inadvertently caused by needle perforations at the edge of the valve (where the silicone is thin) during the activation of the device.

Unlike AMS 800 device, this compressive urethral device is relatively inexpensive and the patient avoids the need to manipulate a pump to void. However, patients are required to void against constant resistance created by the device and the long-term effects of this mechanical compression on the urethra and upper urinary tract are unknown. While the preliminary outcomes on this periurethral constrictor device are encouraging, larger patient participation and longer term follow-up need to be conducted to address the long-term effectiveness and safety of this urinary device.

Urinary continence device with partial urethral occlusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Dynamic continence device with circumferential urethral cuff occlusion
  5. Urinary continence device with partial urethral occlusion
  6. Novel and experimental urinary continence devices
  7. Conclusions
  8. Conflict of interest
  9. References

Adjustable continence therapy (Pro-ACTTM) (Figure 1e)

The Pro-ACT device (Uromedia Inc, MN, USA) consists of two silicone balloons on the proximal end and a titanium port in the distal end (Table 1), and was originally conceived and developed for the treatment of female stress UI. The two balloons are placed trans-perineally under fluoroscopy or TRUS-guided to the level of the urethro-vesical junction bilaterally [22, 23]. The balloons can be inflated or deflated to provide mechanical compression and outlet resistance to the urethral lumen. In contrast to the AMS 800 device, the patient is required to void against resistance. The proposed advantages of the Pro-ACT device include: technical ease of insertion, relatively low morbidity, low cost, the lack of circumferential urethral compression and also the ability to adjust the degree of urethral compression.

Earlier publications on the Pro-ACT device showed substantial improvement in patient continence rate after an average of three balloon volume adjustments [22]. While the reported initial cure rate was high (67%), more than a third of patients were dissatisfied with the surgical outcome. Similar to male slings, there were lower success rates in irradiated patients and in men with severe UI. Earlier series also reported relatively high complications rates, e.g. urethral or bladder perforation and device failure, migration, infection and erosion [24, 25]. Device explantation rate ranged from 12% to 58% [22-27] but this number decreased with surgical experience. Recent short- to medium-term studies have shown that the Pro-ACT device is effective and safe in a patients with moderate degree of stress UI [23, 26, 27]. The long-term outcome of this device and potential changes to the bladder from voiding against constant outlet resistance is unknown. Therefore the potential risks posed by this device should be weighed against the potential benefit of an adjustable urinary continence system.

Novel and experimental urinary continence devices

  1. Top of page
  2. Abstract
  3. Introduction
  4. Dynamic continence device with circumferential urethral cuff occlusion
  5. Urinary continence device with partial urethral occlusion
  6. Novel and experimental urinary continence devices
  7. Conclusions
  8. Conflict of interest
  9. References

Tape mechanical occlusive deviceTM (TMOD) (Figure 1f)

The TMOD (GT Urological LLC, Minneapolis, MN, USA) is a novel concept using a spring-loaded mechanism to apply circumferential urethral pressure to maintain urinary continence [28]. This one-piece AUS device consists of an occlusive tape and a conduit tape, both made from micro-porous expanding polytetrafluoroethylene (PTFE), as well as a control mechanism that is covered with a flexible silicone boot, to prevent tissue in-growth. The conduit tape originates at the control mechanism while the occlusive tape connects to the conduit tape. The control mechanism houses a nickel-cobalt-chromium alloy spring (ElgiroyTM, Elgiroy Specialty Metals, Elgin, IL, USA) that applies tension to the PTFE-coated conduit and occlusive tapes. The control mechanism has ‘ON’ and ‘OFF’ buttons and the silicone boot has a port for injection of saline into the device that displaces air and creates an isotonic interior. In the ‘ON’ position, the occlusive tape contracts and applies a 50–80 cmH2O radial pressure to compress the urethra. Depression of the ‘OFF’ button removes the occlusive pressure from the urethra and allows patient to void freely. Furthermore, there is a stainless steel locking clip that locks the occlusive tape onto itself to form an annular occlusive ring around the urethra that can be easily unclipped to remove the occlusive tape for repositioning and explantation.

At present the TMOD device has only been tested in a dog model and appeared to meet the current standard for an AUS in terms of function and biocompatibility [28]. There are several perceived advantages of the TMOD device over the AMS 800 device. Firstly, the narrow width of the occlusion tape requires less tissue dissection and minimises the risk of urethral injury. Being a non-hydraulic dependent device, there is no need for a PRB placement. However, there is a concern that a narrow urethral occluding tape might lead to greater compression pressure over a narrow area compared with the wider surface of the AMS 800 inflatable cuff. Whether this ultimately results in higher urethral atrophy and erosion remains to be assessed in longer-term clinical trials.

German artificial sphincter system (GASS) (Figure 1g)

The GASS is an integrative, modular, remote-controlled sphincter prosthesis first designed by Schrag et al. [29] for use in the treatment of faecal incontinence. This continent device uses the principles of piezoelectricity that is a materials shape can be altered when exposed to an electrical field. A piezoelectric ceramic element made from ferroelectric and quartz materials, is polarized by aligning the molecules in a high-voltage electric field. This technology is used to power a bi-directional micro-pump to facilitate the movement of fluid around the sphincter cuff [30]. Activation and deactivation of the sphincter is achieved through a remote control. While the original design was too large and used unsafe voltages to be considered for device implantation [29], the GASS II system has been redesigned with multi-layered actuators to allow for operation at lower voltages and is theoretically safer to operate inside the human body. Furthermore, the standardisation of the connection system, therapy-specific compression units, and application-specific software have allowed for the possibility of this technology to be tested in different scenarios including UI [31]. Indeed, this device provides for the first time an opportunity for remote handling of the urethral sphincteric mechanism and also the potential to alter the occluding cuff pressure to changes in the continence level. However, this technology is far from reality and many issues, such as those relating to external device control and electrical voltage safety, remain to be explored.

Nanotechnology-derived devices

Nanotechnology relates to the production of materials with properties that can be tailored to simulate organ structures including those of healthy natural sphincter. The state-of-art technology has been used in aerospace research and could provide a new dimension to the term artificial urinary-like sphincteric device.

Shape-memory alloys (SMAs) are materials that have the ability to alter their shape with a change in temperature. When cooled they take on a parent shape in what is known as the martensite phase, and when heated, they become more compact (austenite phase) [32]. NanoPowers S.A., a Swiss medtech company has produced advanced AUS prototypes based on SMA wires to occlude the human urethra. This sphincteric device consists of three to four modules placed along the urethra, which exert various and continually changing pressures similar to that of a ‘piano’ mode. This periodic compression along the length of urethra allows for segments of the urethral tissue to recover and should lead to less tissue ischaemia. It is possible that the surgeon can adjust the pressure of each module individually in a patient-specific manner to further reduce the risk of urethral ischaemia. This concept has been tested in a sheep model with the implantation of a modular nickel-titanium AUS [33].

The ARTUSTM system (NanoPowers SA, Laussane, Switzerland) is a modular AUR and comprises of two cuffs that operate in a ‘piano’ mode, a control unit, a power unit with replaceable battery, a user remote control and an advanced remote control for the clinician. The device also incorporates a fail-safe mechanism that in times of power failure or lack of operation for a prolonged time, the device will open or deactivate. Unfortunately, repeated use of these modules could result in functional fatigue. As this SMA device requires high energy and better thermal isolation, it may potentially result in a slower response time, posing significant challenge for the device to respond to any sudden increases in intra-abdominal pressure [34].

Another possible future on nanotechnology-derived AUS is in electrically activated polymers (EAP) [33]. The basic function of EAP relates to a capacitor for electrical energy that consists of two electrodes and an intermediate electrically isolating polymer [35]. When a polymer is placed between two electrodes, it expands or decreases in size depending on the electrical voltages. The polymer needs to be elastically deformable, incompressible and able to attain suitable actuation pressures to operate as an AUS device. Silicone, for example, has these features as well as low electrical leakage and >80% efficiency for converting electrical to mechanical energy. As it takes <1 ms for this process to occur, EAPs can attain suitable occlusion pressures rapidly during times of increased abdominal pressure.

The challenge here lies in realisation of stable thin-film nanostructures that allow for reversible switching between two and more states to close and open the human urethra. Furthermore, this low-voltage EAP device requires homogenous and reliable sandwich structures of >1000 alternating nanometre-thin insulating and conducting layers for electrically activated actuators, an extremely time consuming and expensive process [36]. While nanotechnology has the potential to produce such materials with properties that can be tailored to those of the healthy natural sphincter, this is an enormous challenge and it is likely that EAP devices will not be commercially available anytime soon.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Dynamic continence device with circumferential urethral cuff occlusion
  5. Urinary continence device with partial urethral occlusion
  6. Novel and experimental urinary continence devices
  7. Conclusions
  8. Conflict of interest
  9. References

A healthy urinary sphincter is in constant dynamic interplay with the bladder muscle where there is an increase in sphincter tonus during the filling phase of the bladder, and the ability to respond rapidly to changes in the bladder and intra-abdominal pressures to prevent UI. The AMS 800 device is regarded as the standard of care for the treatment of moderate to severe UI [7]. While simplistic in design and being purely mechanically driven, the AMS 800 has a proven long-term record as a safe, durable and effective AUS device [6]. Decades in advances in mechanical design, innovative technologies, and lessons learned from clinical experiments and experience have inspired a new generation of AUS devices. Other continence devices on the market have shown promising outcomes in the short- to intermediate-term follow-up but long-term effectiveness and safety profile are warranted (Table 1).

Conventional AUS devices are constructed specifically for distinct applications and are manual in operation. These AUS-like devices are relatively inflexible and likely to induce atrophy and erosion in the long term. Therefore, this makes it highly desirable to have alternative, more advanced and innovative prototype urinary continent devices that mimic natural sphincteric function. Newer experimental AUS models should be innovative and ambitious with the goal to closely simulate a healthy human sphincter, and is driven by, and respond effectively and rapidly to different external and internal stimuli. However, the developmental costs in prototypes design and production to realisation of an actual working device are often enormous as well as time and effort consuming. The AMS 800 was first conceived as the AS 721 in 1972 [6] and it took at least 10 years of continued development and improvement before the AMS Company arrived at the AMS 800 [37]. During that time, many urinary continence devices were invented and trialled but failed to materialise due to poor clinical outcomes and lack of commercial interest [38-41]. Furthermore, the regulatory issues surrounding human trials and device marketability also place considerable limitations, especially among smaller device companies.

The advent of synthetic slings in the current market offers less invasive surgery and allows for immediate continence and the ability to void without manual operation. While published reports on newer continence devices are promising, it will be awhile before these innovative devices become commercially available and have proven records. Until the emergence of a better engineered AUS device, and/or further achievement in stem cell or tissue engineering, significant challenges remain in the quest for an ideal urinary sphincter device.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Dynamic continence device with circumferential urethral cuff occlusion
  5. Urinary continence device with partial urethral occlusion
  6. Novel and experimental urinary continence devices
  7. Conclusions
  8. Conflict of interest
  9. References
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Abbreviations
AUS

artificial urinary sphincter

EAP

electrically activated polymers

PRB

pressure-regulating balloon

PTFE

polytetrafluoroethylene

SMA

shape-memory alloy

UI

urinary incontinence