The “nano wrap” that is being developed to be fitted around an amputee’s upper arm nerve bundle is the ambitious other part of the Smarthand’s robotic hand project. Technically speaking, it is called a “cuff electrode”: in practice, it’s a neural interface that will need to be surgically implanted and connected wireless to the hi-tech prosthesis. This nano/invasive/long-term scenario is still being tested. The non-nano/non invasive/short term option, which is featured in this film, has already scored a spectacular success in an experiment that was recently carried out at the University of Lund, in Sweden.
The Smarthand consortium, which gathers 7 partners across Europe and Israel and is funded by the European Commission, has been effectively focusing on two separate options, in order to meet patients’ clinical needs according to the severity of their amputations. Dr Fredrik Sebelius, coordinator of the Smarthand project, says: “In fact, in patients with a lower amputation, half way down the forearm, for instance, you have a lot more muscles remaining, whereas in patients with an above-the-elbow amputation you can work with only a couple of muscle groups in the upper arm, so sensations and movements are much more impaired”.
Smarthand’s current, non-nano option suits patients with a lower amputation best. It is fully portable and it is mechanically attached to the stump via an intelligent bio-interface socket with tactile display, EMG sensors and information processing ability. A sophisticated system of sensors, integrated in the prosthesis, picks up external sensation and triggers a sensory feedback mechanism, that via actuators placed on the forearm creates artificial sensibility. Recordings of muscle activity on remaining limb is used to control the SmartHand, i.e myoelectric control. The socket will in time contain a receiver for the other option, which is the soft neural interface.
This nano device will have to be implanted into the patient’s arm. At the moment, it is still being developed at Tel Aviv University and at the Tyndall Institute in Cork within the project, and another team from the University of Aalborg in Denmark is already testing it. It will raise the mark even further, in that it will make Smarthand ideal even for patients with higher amputations by picking up neural signals and stimulate selected nerves inside the arm. As it is, the project could not be more innovative.
The awesomely impressive cyber hand, which was designed at the ARTS Lab of the Scuola Superiore Sant’Anna in Pisa, can be seen here in its downsized, lighter self, which is almost as big as a natural hand. Dr. Christian Cipriani, who led the hand’s development , says: “The robotic hand has over 40 sensors inside the fingers, regulating position, force and contact. There are also 4 motors inside the palm. The characteristic of these fingers is that with a low number of motors you can hold a high number of objects and perform a lot of daily activities and a few basic gestures, such as pointing. The hand is mainly made of aluminum and steel and has a universal wrist that can be attached to a traditional socket”. The ARTS Lab was recently awarded the Antonio D’Auria Prize by SIRI, the Italian Robotics and Automation Association, for the development of Smarthand’s robotic hand.
The hand is mechanically connected to the arm by way of a carbon-fibre socket shaped like an arm. In its current version, the actuators then press on different points on the stump, giving the sensation of pressure back to the patient in a proportional way. Dr Sebelius explains: “It has been shown that if you push the skin on certain locations of an amputee’s forearm, the amputee feels as if you are pushing on some of the phantom fingers, resulting from a cortical reorganization of the sensory map of the forearm”.
Smarthand’s next step, the longer term nano option, is a superb example of everything the new frontier of ultrathin, highly stretchable, foldable nanoelectronics aims to be. These bendy chips, which are capable of being elastically deformed in diverse configurations as to withstand high levels of strain without breaking, can adapt to highly complex human body shapes and potentially lend themselves to an enormous variety of biomedical applications. Smarthand’s thin films are ideally suited to be wrapped around a selected nerve bundle of the patient’s nervous peripheral system in the upper arm, which would then get connected wireless to the robotic hand.
Flexible circuitry has been around for a little while, but while good at bending like a sheet of paper, these previous chips were not bendable like a rubber band. Until now, that is. Pre-stretching the silicone is doing the trick here for Smarthand. “The electrode is made in Tel Aviv on a very thin layer of polymer, like a film”, Dr. Sebelius adds. “This film is then delivered to Cork, where it is mounted on a silicone sheet. By pre-stretching the silicone before they glue the electrode to it they will get the device to self-curl. You will end up with a tube, which you can open and wrap around a nerve bundle without harming the nerves at all. This is then called a <cuff electrode>.
There are a lot of unresolved issues regarding implantable neural interfaces. The SmartHand team hopes to be able to answer some of the questions. But Smarthand’s nano ambition is clear. It is about restoring the functionality through sensation and control in a natural way for prosthetic hand users.
(31 August 2009)