Silvia Bossi

Shape Memory Alloy Microactuation of tf-LIFEs: Preliminary Results

In this paper, a new approach aimed at improving the performance of intraneural longitudinal interfaces (tf-LIFEs) with the peripheral nervous system (PNS) is presented. Our goal is to develop a movable interface by embedding microactuators into the flexible tf-LIFEs structure. In this way, the optimal position of the electrical contacts can be searched inside the PNS and lost connections with neural cells could be replaced. For this purpose a thin film of shape memory alloy (tf-SMA) was selected. A multisegmented SMA was realized and embedded between two polyimide thin films in order to simulate the tf-LIFE structure. Thermal evaluation, fabrication procedure, the first characterization and preliminary experimental results of the new movable interface are described in the manuscript. A total controllable stroke of about 10mum was obtained for the presented prototype

An Implantable Microactuated Intrafascicular Electrode for Peripheral Nerves

Important advancements have been recently achieved in the field of neural interfaces to restore lost sensory and motor functions. The aim of this letter was to develop an innovative approach to increase the selectivity and the lifetime of polyimide-based intrafascicular electrodes. The main idea was to obtain a neural interface that is able to restore a good signal quality by improving the electrical connection between the active sites and the surrounding axons. The high flexibility of polyimide-based neural interfaces allows to embed microactuators in the interface core and achieve desired microdisplacements of the active sites. Nearly equiatomic nickel-titanium alloy was selected as a microactuator because of its shape memory effect. A single TiNi thin film was obtained by dc magnetron sputtering, and was segmented into four distinct sectors. This solution allowed the independent actuation of the different active sites (multiactuation). A corrugated profile was impressed to the new actuated intraneural (ACTIN) interface. The active sites were positioned in correspondence to the peaks of the corrugation, thus maximizing the effects of the single actuations. The technological results, the electrical properties, the thermal behavior, and eventually, the actuation performances of the current ACTIN prototype are shown and discussed. The actuation cycle was thermally compatible for biomedical applications. Promising results were obtained from the current ACTIN prototype with an average controlled movement of 7 mum of the peaks.

A three-dimensional self-opening intraneural peripheral interface (SELINE)

OBJECTIVE In this study we present the development and testing in a rat model of the self-opening neural interface (SELINE), a novel flexible peripheral neural interface. APPROACH This polyimide-based electrode has a three-dimensional structure that provides an anchorage system to the nerve and confers stability after implant. This geometry has been achieved by means of the plastic deformation of polyimide. Mechanical and electrochemical characterizations have been performed to prove the integrity of the electrode with very good results. Functionality of SELINEs for fascicular stimulation has been tested during in vivo acute experiments in the rat. Chronic implants were made to test the biocompatibility of the device. MAIN RESULTS Results showed that SELINEs significantly improve mechanical anchorage to the nerve. Stimulation stability is considerably enhanced compared to common planar transversal electrodes and stimulation selectivity is increased for some motor fascicles. Chronic experimental results showed that SELINEs neither produce changes in the fascicular organization of sciatic nerves nor signs of nerve degeneration. SIGNIFICANCE The presented three-dimensional electrode provides an effective anchorage system to the nervous tissue that can improve the stability of the implant for acute and chronic studies.

Modelization of a self-opening peripheral neural interface: a feasibility study.

In this paper a self-opening intrafascicular neural interface (SELINE) has been modeled using both a theoretical approach and a Finite Element (FE) analysis. This innovative self opening interface has several potential advantages such as: higher selectivity due to its three-dimensional structure and efficient anchorage system. Mechanical, structural and micro-technological issues have been considered to obtain an effective design of the electrode, as a feasibility study of the self-opening approach. A simple framework has been provided to model the insertion and partial retraction into peripheral nerves, resulting in the opening of wings. This integrated approach results in a rational procedure to optimize kinematics, geometry, and structural properties of peripheral interfaces. The design and feasibility study carried out in this work can potentially assure a correct behavior and dimensioning of the neural interface: in this way anomalous breakage should be avoided while mechanical and geometrical biocompatibility should increase.

Activities on PNS neural interfaces for the control of hand prostheses

The development of interfaces linking the human nervous system with artificial devices is an important area of research. Several groups are working on the development of devices able to restore sensory-motor function in subjects affected by neurological disorders, injuries or amputations. Neural electrodes implanted in peripheral nervous system, and in particular intrafascicular electrodes, seem to be a promising approach for the control of hand prosthesis thanks to the possibility to selectively access motor and sensory fibers for decoding motor commands and delivering sensory feedback. In this paper, activities on the use of PNS interfaces for the control of hand prosthesis are presented. In particular, the design and feasibility study of a self-opening neural interface is presented together with the decoding of ENG signals in one amputee to control a dexterous hand prosthesis.

Fascicular nerve stimulation and recording using a novel double-aisle regenerative electrode

OBJECTIVE As artificial prostheses become more refined, they are most often used as a therapeutic option for hand amputation. By contrast to extra- or intraneural interfaces, regenerative nerve electrodes are designed to enable electrical interfaces with regrowing axonal bundles of injured nerves, aiming to achieve high selectivity for recording and stimulation. However, most of the developed designs pose an obstacle to the regrowth mechanisms due to low transparency and cause impairment to the nerve regeneration. APPROACH Here we present the double-aisle electrode, a new type of highly transparent, non-obstructive regenerative electrode. Using a double-side thin-film polyimide planar multi-contact electrode, two nerve fascicles can regenerate without physical impairment through two electrically isolated aisles. MAIN RESULTS We show that this electrode can be used to selectively record and stimulate fascicles, acutely as well as chronically, and allow regeneration in nerve gaps of several millimeters without impairment. SIGNIFICANCE This multi-aisle regenerative electrode may be suitable for neuroprosthetic applications, such as prostheses, for the restoration of hand function after amputation or severe nerve injuries.

Preliminary investigations on laminin coatings for flexible polyimide/platinum thin films for PNS applications

The aim of this work was to investigate the possibility to obtain stable bioactive coatings for polyimide/platinum neural interfaces based on thin film technology for applications into the peripheral nervous system (PNS). Laminin (LI), a glycoprotein of the extracellular matrix, which guides and promotes differentiation and growth of neurons, was selected to deposit bioactive coatings. Dip-coating was performed on dummy structures at different LI concentrations. Indirect methods allowed to identify and characterize laminin on coated samples. Mechanical stability was also confirmed by indirect evaluations. Pilot experiments with differentiated PC12 cells, by the addition of nerve growth factor (NGF), showed improved neurite outgrowth on the coated probes compared to bare polyimide samples.

Experiments on the development and use of a new generation of intra-neural electrodes to control robotic devices.

The development of interfaces linking the human nervous system with artificial devices is an important area of research and several groups are now addressing it. Interfaces represent the key enabling technology for the development of devices usable for the restoration of motor and sensory function in subjects affected by neurological disorders, injuries or amputations. For example, current hand prostheses use electromyographic (EMG) signals to extract volitional commands but this limits the possibility of controlling several degrees of freedom and of delivering sensory feedback. To achieve these goals, implantable neural interfaces are required. Among the candidate interfaces with the peripheral nervous system intra-neural electrodes seem to be an interesting solution due to their bandwidth and ability to access volition and deliver sensory feedback. However, several drawbacks have to be addressed in order to increase their usability. In this paper, experiments to address many of these issues are presented as part of the development of a new generation of intra-neural electrodes. The results showed seem to confirm that these new interfaces seem to have interesting properties and that they can represent a significant improvement of the state of the art. Extensive experiments will be carried out in the future to validate these results

Neural prosthesis for motor function restoration in upper limb extremity

Restoration of motor function in cases of peripheral nerve injury is a challenging problem. Although peripheral nerves do regenerate, the time required for peripheral nerves to regenerate often causes atrophy to occur in the muscles before they can be re-innervated. This paper presents a solution through proximal recording of nerve signals and distal muscle stimulation. A fully implantable hardware architecture is described that can be operated by means of inductive power and MICS band data transmission schemes. Preliminary experiments and validation studies are reported with non-human primates based on recordings in the median nerve, stimulation of hand muscles, and task decoding and classification. This approach shows promise in creating a neural prosthesis capable of restoring hand movements in patients with upper limb peripheral nerve injuries.

Surface Modification of Polyimide Thin Films for Peripheral Invasive Neural Interfaces

Despite recognized as one key component for establishing a functional electrical connection with nerves, neural invasive peripheral interfaces are still not optimal for long-term applications in humans. An improvement in the field of biocompatible and nontoxic materials is necessary to overcome the issues of interface/tissue mismatch and physiological reactions. The present work aimed to study, implement and characterize a novel approach to modify the surface of neural mi-crolectrodes basedon polyimide thin films. The purpose was to improve biocompatibility and to promote neuronal migration, growth and differentiation by increasing the surface roughness and endowing the surface with structure-reactivity for thiol-containing amino acids or peptides. L-Cysteine-Rhodamine B, used as a model biomolecule, was successfully grafted on samples surface via the introduction of cross-linkable vinyl groups on polyimide foils. Preliminary in vitro biological analysis allowed to evaluate the tendency of PC12 cells to adhere and to proliferate.