Richard Fechter

A Low-Frequency Versatile Wireless Power Transfer Technology for Biomedical Implants

Implantable biomedical sensors and actuators are highly desired in modern medicine. In many cases, the implants electrical power source profoundly determines its overall size and performance. The inductively coupled coil pair operating at the radio-frequency (RF) has been the primary method for wirelessly delivering electrical power to implants for the last three decades. Recent designs significantly improve the power delivery efficiency by optimizing the operating frequency, coil size and coil distance. However, RF radiation hazard and tissue absorption are the concerns in the RF wireless power transfer technology (RF-WPTT) [4], [5]. Also, it requires an accurate impedance matching network that is sensitive to operating environments between the receiving coil and the load for efficient power delivery. In this paper, a novel low-frequency wireless power transfer technology (LF-WPTT) using rotating rare-earth permanent magnets is demonstrated. The LF-WPTT is able to deliver 2.967 W power at ~ 180 Hz to an 117.1 Ω resistor over 1 cm distance with 50% overall efficiency. Because of the low operating frequency, RF radiation hazard and tissue absorption are largely avoided, and the power delivery efficiency from the receiving coil to the load is independent of the operating environment. Also, there is little power loss observed in the LF-WPTT when the receiving coil is enclosed by non-magnetic implant-grade stainless steel.

Magnamosis II: Magnetic Compression Anastomosis for Minimally Invasive Gastrojejunostomy and Jejunojejunostomy

BACKGROUND Previously we demonstrated the safety and patency of a magnetic compression anastomosis (magnamosis). We present the further development of this technique, with specific focus on optimizing device design for minimally invasive magnamosis. STUDY DESIGN The magnamosis device was designed to incorporate 3 features: 2 convex-concave radially symmetric halves that magnetically self-align, a central channel for immediate patency, and specially engineered radial topography of the mating surfaces to promote gradual remodeling. Each symmetrical half consists of a ring-shaped neodymium-iron-boron magnet encased in polycarbonate casing. Twenty-one young adult pigs underwent either magnetic gastrojejunostomy (n = 13) or jejunojejunostomy (n = 8). Animals were euthanized at 1, 2, 4, and 6 weeks after operation. Anastomoses were studied with contrast radiography, burst pressure, and histology. RESULTS Gastrojejunostomy: In all animals with successful placement of magnets, anastomoses were patent by contrast fluoroscopy, well healed by histologic examination, and showed excellent burst strength. Jejunojejunostomy: All animals had uneventful clinical courses, indicating that the magnamosis with immediate patency functioned properly without device dislodgement. At sacrifice, all magnamoses were patent, well healed by histology, and had burst strengths that equaled or exceeded that of traditional stapled anastomoses. CONCLUSIONS Minimally invasive placement of a custom magnetic device in the stomach and jejunum allows intraluminal self-alignment and subsequent compression anastomosis over 3 to 10 days. The magnamosis is immediately patent and develops strength equal to or greater than that of hand-sewn or stapled anastomoses. Magnamosis is effective in the pig model, and may be a safe, effective, and minimally invasive alternative to current anastomotic strategies in humans.

Magnetic Mini-Mover Procedure for pectus excavatum: II: initial findings of a Food and Drug Administration–sponsored trial

PURPOSE The Magnetic Mini-Mover Procedure (3MP) uses a magnetic implant coupled with an external magnet to generate force sufficient to gradually remodel pectus excavatum deformities. This is an interim report of the evolution of the 3MP during a Food and Drug Administration-approved clinical trial. METHODS After obtaining Institutional Review Board approval, we performed the 3MP on 10 otherwise healthy patients with moderate to severe pectus excavatum deformities (age, 8-14 years; Haller index >3.5). Operative techniques evolved to improve ease of implantation. Patients were evaluated monthly by a pediatric surgeon and orthotist. Electrocardiograms were performed pre- and postoperatively. Sternal position was documented by pre- and postprocedure computed tomographic scan, interval chest x-ray, depth gauge, and interval photographs. RESULTS There was no detectable effect of the static magnetic field on wound healing or cardiopulmonary function. No detectable injuries and minimal skin changes resulted from brace wear. Operative techniques evolved to include a custom sternal punch and a flexible guide wire to guide the posterior plate into position behind the sternum, reducing outpatient operating time to one-half hour. In 9 patients, the procedure was performed as an outpatient basis; and 1 patient was observed overnight. Three patients required evacuation of retained pleural air postoperatively, and 2 required an outpatient revision. A custom-fitted orthotic brace (Magnatract) was extensively modified to increase user friendliness and functionality while incorporating several novel functions: a screw displacement mechanism so patients can easily self-adjust magnetic force, a miniature data logger to measure force and temperature data every 10 minutes, and an interactive online Web portal for remote patient evaluation. All attempts to quantitate sternal position (radiographic, fluid volume, and depth gauge) were inadequate. Visual assessment remains the best indicator. CONCLUSIONS In this interim report, the 3MP appears to be a safe, minimally invasive, outpatient, cost-effective alternative treatment of pectus excavatum. Outcomes will be reported upon the completion of this phase II clinical trial.

Magnetic mini-mover procedure for pectus excavatum III: safety and efficacy in a Food and Drug Administration-sponsored clinical trial

PURPOSE The magnetic mini-mover procedure (3MP) uses magnetic force to gradually remodel pectus excavatum deformity. A magnet is implanted on the sternum and coupled with an external magnetic brace. Under Investigational Device Exemption and Institutional Review Board approval, we performed a pilot study of safety, probable efficacy, and cost-effectiveness of this new treatment of an orphan disease using an implantable pediatric device. METHODS Ten otherwise healthy patients, ages 8 to 14 years, with severe pectus excavatum (pectus severity index [PSI] > 3.5) underwent 3MP treatment (mean, 18.8 ± 2.5 months). Safety was assessed by postimplant and postexplant electrocardiograms and monthly chest x-rays. Efficacy was assessed by change in pectus severity index as measured using pretreatment and posttreatment computed tomographic scan. Cost of 3MP was compared with that of standard procedures. RESULTS The 3MP device had no detectable ill effect. Device weld failure or malpositioning required revision in 5 patients. Average wear time was 16 h/d. Pectus severity index improved in patients in the early or mid puberty but not in patients with noncompliant chest walls. Average cost for 3MP was

Failure Mode Effect Analysis Applied to the Use of Infusion Pumps

46,859, compared with

ROBOImplant II: Development of a Noninvasive Controller/Actuator for Wireless Correction of Orthopedic Structural Deformities

81,206 and

Magnetic Mini-Mover Procedure for pectus excavatum IV: FDA sponsored multicenter trial

81,022 for Nuss and Ravitch, respectively. CONCLUSION The 3MP is a safe, cost-effective, outpatient alternative treatment for pectus excavatum that achieves good results for patients in early and midpuberty stages.

Inductive Sensing to Detect Tissue Thickness Between Magnets for Potential Application in Magnetic Compression Based Anastomosis

Failure Mode Effect Analysis (FMEA) offers a prospective approach to reducing the risk associated with health care delivery. Beginning in February, 2002, an interdisciplinary team of fifteen individuals, including end-users, conducted an FMEA for the use of infusion pumps at UCSF Medical Center. The use of infusion pumps was identified as the area of highest risk, based on incident report data. The team identified sixteen potential failure modes, including their potential effects and causes, and assigned a risk priority number to each based on the potential severity, probability, and detectability of the failure. Notable failure modes included: incorrect programming; improper or inconsistent labeling of solution, tubing, and pump; potential use of malfunctioning or damaged pumps; and incorrect programming by nurses related to device design. The team then broke into smaller work groups and invited more end-users to perform root cause analyses and suggest recommended actions/outcome measures for each failure mode with a risk priority number of 32 or higher (on our scale of 1 to 64). Finally, the FMEA team assembled all of the data, prepared a final report, and assigned responsibility for key recommended actions.

Magnetic Mini-Mover Procedure for pectus excavatum: I. Development, design, and simulations for feasibility and safety

An implantable actuator and its accompanying driver circuit are presented for the purpose of lengthening bones and correcting skeletal deformities without requiring physical contact between the operator and the implanted device. This system utilizes magnetic coupling to form a magnetic gear, allowing an external motor to drive an implantable telescoping rod. The accompanying electronics are able to monitor the progress, in the form of turns delivered, as well as detect procedural errors, such as magnet decoupling. The force applied by the implanted telescoping rod can be accurately measured by monitoring the current necessary for the external controller to drive the extension of the implanted rod. After characterization, the system was shown to reliably deliver extension distances within 34 μm and maintain coupling out to 70 mm. The system is also able to measure torques as low as 0.12 mN m. System variability and accuracy of external monitoring are addressed.

Apparatus and methods for magnetic alteration of deformities

PURPOSE The Magnetic Mini-Mover Procedure (3MP) is a minimally invasive treatment for prepubertal patients with pectus excavatum. This multicenter trial sought to supplement safety and efficacy data from an earlier pilot trial. METHODS Fifteen patients with pectus excavatum had a titanium-enclosed magnet implanted on the sternum. Externally, patients wore a custom-fitted magnetic brace. Patients were monitored closely for safety. Efficacy was determined by the Haller Index (HI) and satisfaction surveys. After 2 years, the implant was removed. RESULTS Mean patient age was 12 years (range 8-14), and mean pretreatment HI was 4.7 (range 3.6-7.4). The device was successfully implanted in all patients. Mean treatment duration was 25 months (range 18-33). Posttreatment chest imaging in 13 patients indicated that HI decreased in 5, remained stable in 2, and increased in 6. Seven out of 15 patients had breakage of the implants titanium cables because of fatigue fracture. Eight out of 13 patients were satisfied with their chest after treatment. CONCLUSION The 3MP is a safe, minimally invasive, outpatient treatment for prepubertal patients with pectus excavatum. However, the magnetic implant design led to frequent device breakage, confounding analysis. The HI indicated mixed efficacy, although surveys indicated most patients perceived a benefit. STUDY TYPE/LEVEL OF EVIDENCE Case series, treatment study. Level IV.