Paul Cvancara

Return of the cadaver: Key role of anatomic dissection for plastic surgery resident training

Abstract Successful Plastic Surgery Residency training is subjected to evolving society pressure of lower hourly work weeks imposed by external committees, labor laws, and increased public awareness of patient care quality. Although innovative measures for simulation training of surgery are appearing, there is also the realization that basic anatomy training should be re-enforced and cadaver dissection is of utmost importance for surgical techniques. In the development of new technology for implantable neurostimulatory electrodes for the management of phantom limb pain in amputee patients, a design of a cadaveric model has been developed with detailed steps for innovative transfascicular insertion of electrodes. Overall design for electrode and cable implantation transcutaneous was established and an operating protocol devised. Microsurgery of the nerves of the upper extremities for interfascicular electrode implantation is described for the first time. Design of electrode implantation in cadaver specimens was adapted with a trocar delivery of cables and electrodes transcutaneous and stabilization of the electrode by suturing along the nerve. In addition, the overall operating arena environment with specific positions of the multidisciplinary team necessary for implantable electrodes was elaborated to assure optimal operating conditions and procedures during the organization of a first-in-man implantation study. Overall importance of plastic surgery training for new and highly technical procedures is of importance and particularly there is a real need to continue actual cadaveric training due to patient variability for nerve anatomic structures.

Mechanical deformation of thin film platinum under electrical stimulation.

Thin-film-based electrodes used to interact with nervous tissue often fail quickly if used for electrical stimulation, impairing their translation into long-term clinical applications. We initiated investigations about the mechanical load on thin-film electrodes caused by the fact of electrical stimulation. Platinum electrodes of Ø 300μm on a polyimide carrier were subjected to approximately 50 000 asymmetrical, biphasic stimulation pulses in vitro. The electrodes surface was investigated optically by means of white-light interferometry. The structural expansion for the metallic surface subjected to stimulation was measured to reach roughly 30%. The study points towards a failure mechanism of thin-films being of mechanical nature, inherent to the unavoidable electrochemical processes involved (change in lattice constants) during electrical stimulation at the electrodes surface. Based on further scientific facts, we set 3 hypotheses for the exact mechanisms involved in the failure of thin-films used for electrical stimulation, opening a new door for research and improvement of novel neuroprosthetic devices.

Advanced 56 Channels Stimulation System to Drive Intrafascicular Electrodes

A wearable, 56-channel stimulator was developed and successfully tested to drive multichannel intrafascicular electrodes. It is able to safely elicit sensory afferent signals through the activation of 4 Time-4H intrafascicular electrodes. The STIMEP embeds not only the pulse generator but also a software that ensures: (i) real time control by a hand-prosthesis, (ii) embedded procedures for sensation mapping interfaced with a PC software, (iii) impedance follow-up, (iv) real-time safety management.

On Biocompatibility and Stability of Transversal Intrafascicular Multichannel Electrodes—TIME

Transversal intrafascicular multichannel electrodes (TIME) have been developed to interface with peripheral nerves after upper limb amputation. Intended use is the electrical stimulation of the median and ulnar nerve to deliver sensory feedback during phantom limb pain treatment and artificial hand control. Miniaturized electrode arrays were developed on polyimide substrates with thin film metallization using sputtered iridium oxide as electrode coating. Here, we report on the essential requirements including biocompatibility, mechanical and stimulation stability that have been investigated before permission was granted by the legal authorities to conduct subchronic first-in-man clinical trials. Explants have been investigated to identify possible first failure points and optimize the devices for chronic implantation.

Investigation on the hermeticity of an implantable package with 32 feedthroughs for neural prosthetic applications

This paper presents an implantable package aimed at hosting a bidirectional neural interface for neural prosthetic applications. The package has been conceived to minimize the invasivity for the patient, for this reason a cylindrical container with an outer diameter of 7 mm and a length of 21 mm has been designed. The package, realized in alumina (Al2O3), presents 32 hermetic feedthroughs located at the top and bottom base of the cylinder. The hermetic housing has been assembled using a low-temperature soldering method based on a previous platinum/gold (Pt/Au) metallization of the ceramic parts. The packages hermeticity has been successfully proved by means of in-vitro tests, exhibiting an increase in the inner relative humidity of 20 %RH over 75 days of observation.

Investigations on different epoxies for electrical insulation of microflex structures

The microflex interconnection (MFI) technique is often used to connect electrically and mechanically thin film ribbons or electrodes with a solid substrate like screen printed ceramics. For stabilization reasons epoxy is used to fix the MFI structure. As epoxy tends to form cracks when surrounded by water or electrolytes we are eager to find an epoxy which provides sufficient insulation between the single channels of the MFI structure also in a moist surrounding. Therefore we designed a device to investigate the insulating properties of different epoxies (Uhu Plus Endfest 300, Epo-Tek 353ND and 353ND-T) immersed in saline solution. For comparison reasons we use as well only silicone rubber (Nusil MED-1000) instead of epoxy. We performed the experiment for 23 weeks at 60 °C, which corresponds to 26 months at body temperature. The epoxy of preference is the Epo-Tek 353ND-T as it develops no failures and insulates all channel pairs of the MFI structures electrically over the whole period of experiment.

Decreasing stimulation charge by delaying the discharge phase - comparison of efficacy for various stimulation waveforms

For chronic stimulation of nerve fibers, only charge balanced waveforms should be used. However, if the charge recuperation phase comes right after the stimulation phase, it might abolish activation of the nerve fibers that are close to the threshold level. Delaying the charge recuperation phase may eliminate this abolition effect, and thus reduce the charge required to activate nerve fibers. The objective of this in vivo study, was to determine to which extent the required stimulation charge might be decreased by delaying the discharge phase, depending on the pulse duration and the way the discharge is performed. The results demonstrated that delaying the discharge phase allows to gain more charge for shorter pulses. The difference in the gain between the waveforms with passive and active discharge is less striking. The delayed discharge does not affect much stimulation selectivity.

Investigations on stability of implanted nervous thin-film electrodes

Many micromachined neural implants with multi-channel thin-film electrodes have been presented over the last decades. A transverse intrafascicular multi-channel electrode (TIME) was developed for translational research to treat phantom limb pain (PLP). Four TIME systems (latest electrode version) have been implanted for 30 days into the arm of an amputee. After finishing successfully the clinical trials the TEVIE-3H systems have been explanted. The material composition of the electrode contacts used for stimulation have been investigated with X-ray photoelectron spectroscopy (XPS). System integrity has been examined using focused ion beam (FIB) and pictures were acquired using the integrated scanning electron microscope (SEM). Both methods revealed that the metallization was still intact after explantation and that no delamination occurred. Crack formation without delamination was observed but it could not be determined if it originated while the implant was inside the body or during the explantation or during the cleaning of the implants.