BACKGROUND

A spinal cord injury (SCI) is a critical medical condition that frequently leads to significant morbidity and enduring disability.

C6 and C7 tetraplegics have paralysis of finger and thumb flexor muscles but retain voluntary control of wrist extensor and sometimes wrist flexor and finger extensor muscles.

These individuals typically rely on wheelchairs, and in most cases, both hands are affected, resulting in a loss of sensory abilities in their fingers.

OBJECTIVES

Within the realm of prosthetics and wearables, there are two main categories: remedial and compensatory. Tenodesis splints for spinal cord injuries fall under the compensatory category. While the use of these splints can positively impact the user's life, they do not lead to improvements in finger dexterity.

Standard tenodesis splints allow movement for three fingers: the index, middle, and ring fingers. Although there is potential for accommodating more fingers, any additional fingers should only be included if there is a justified need. It is important to consider that attaching each finger to the splint can be a laborious process for the user, and one of the primary goals is to provide enhanced autonomy. Autonomy begins with the user's ability to independently put on the splint.

Challenges

User‐centric approach becomes indispensable in this project.

Weight Most of the current splints are aluminum.
Ratcheting and grip The splint should be easy to put on and off. It is important to consider that users do not have mobility on their fingers while they are putting them on. Sometimes they use their teeth to adjust straps.
Grip With mechanical devices, the grip works as long as the user is flexing their wrists. This can be tiring and strain the wrists.
Adaptability Every user is different. If some sections of the unit could be standardized, costs would go down.
Looks The appearance is important.

Common tasks that users with disability want to do

Changing their IC bags (Urinary drainage bag / Infection control drainage bag)
Turning pages on books, magazines, or loose sheets of paper.
Putting make up on.
Using a pen, signing papers. The ability to wear it and remove it.
Using food utensils: forks, spoons, etc.
Using a smartphone, stylus. (wheelchair).
Dressing up (infrequent). Not to get entangled.

EXISTING SOLUTIONS

The solutions that are already present in the market are the Flexor Hinge Splint and the Elastic Splint. Both of these devices exploit principles of mechanics to achieve the task of grasping objects.

The Flexor Hinge Splint replaces the tenodesis effect with a contraption. They are powered by wrist extensions and incorporate a ratchet mechanism for pitch adjustment. These splints are typically custom-made to fit the individual's anatomy, making them costly.

The Elastic Splint, instead, enhances the tenodesis effect with a contraption. The activation is provided by the wrist movement and the structure is partially tailor-made. An advantage is given by the possibility to regulate the elastic force changing the thread tension.

Both of these solutions have the main issue of relying on keeping the wrist extended while maintaining the grip thus limiting wrist movement.

THE PROMISE OF SOFT ROBOTS

Soft robots are pliable devices constructed from compliant materials, engineered to exhibit greater adaptability compared to conventional rigid robots. Their organic nature makes them a burgeoning technology in the field of rehabilitation, owing to their inclination toward more natural movements.

CONCEPT AND RESEARCH

The original idea for the device was to create a prototype that seamlessly combined soft robots to complement the grasping motion, employing one inner tube to enable finger bending and a second to provide wrist support.

OUR SOLUTION

We propose a solution that involves a modular orthosis crafted from a blend of plastic and nylon. This orthosis requires only a few molded components to be fitted onto the wearer's limb. To improve comfort and minimize finger strain, our innovative approach incorporates an electronic linear actuator control system connected to the plunger of a 20ml syringe. This system, when activated, controls the inflow and outflow of water within a lightweight silicone chamber (referred to as a "soft robot"). The silicone chamber is strategically positioned at the finger level, while the bulkier components are located on the forearm. The rotational information about wrist position is the input for the driver of the linear actuator, allowing for intuitive control that aligns with users' intentions. Two different thresholds of angle displacement of the hand with respect to the forearm have been selected, one is the limit angle that identifies the wrist extension and triggers the forward movement of the linear actuator, while the second one is the identifier of the wrist flexion and enables the backward movement of the linear actuator.

This device allows the maintainment of a secure grip in a variety of wrist positions, alleviating strain on the forearm muscles that would typically occur when sustaining an extended awkward position.

The orthosis design prioritizes modularity in its construction. The prototype is available as a kit, offering three size variations: XS, S, M, L and XL. The appropriate size should be selected based on the wearer's anthropometric measurements. A professional can easily customize the kit to ensure a perfect fit for the user. The supportive elements are constructed using a thermoplastic material. To secure the orthosis two buckles are fastened one around the hand and the second around the forearm. The buckles can be manipulated either with the mouth or by using the thumb through rings. Velcro is employed to secure the bands at the back. A third velcro band is positioned at the fingers level to provide a stable support, maintaining them in an optimal grip position and facilitating counter leverage.

Both the thumb rest and the c-shaped finger support are also made of thermoplastic material that can be molded to conform to the user's limb.

A significant aspect of this model involves the utilization of soft actuators, composed of silicone and fabric components. When the silicone part inflates, it causes the U-shaped structure to bend inward, with the fabric positioned on the inside. This design employs one single chamber at the fingers, oriented with the fabric in contact to the finger skin. The chambers are constructed using silicone, with a shore hardness of 30.

ELECTRONICS HARDWARE

The hardware setup includes two IMUs, one placed on the hand and the other on the wrist. Wrist extension detection triggers the activation of the linear actuator, which fills and drains the silicone chamber. Once inflated, the chamber will remain so ensuring a sustained grip. To release the grip, the chambers can be deflated bending the wirst.

Here is provided a detailed description of the connections.

It is important to note that the actuator used is powered at 12V (three 18650 batteries in series provide 11.1V), so a big rechargeable battery module is needed. This aspect could be improved selecting a different electronic linear actuator or selecting a stepper motor powered at 5V to reach the same task.

FIRMWARE

To be able to execute the Arduino code, the Arduino_Helpers library must be installed in the Arduino environment together with SparkFun_TB6612FNG_Arduino_Library. To do this, download the .zip folders and add them to the library folder of Arduino, along with the other libraries listed at the beginning of the code. Specifically:

Wire
Adafruit_MPU6050
Adafruit_Sensor
Adafruit_AHRS_Mahony

FUTURE DEVELOPMENTS

Future developments of the project include investigating different controlling systems such as a myoelectric signal (MyoWare) detected by surface electrodes placed on the forearm. The user would then have to learn to activate the muscle in a manner coordinated with his or her movement intention.

The linear actuator could also be replaced with a 5V stepper motor in order to reduce the size and weight of the electronic block as the actual one is powered at 12V. Or investigating bi-directional pump systems.

Miniaturization and reduction of components. The selection of a microcontroller with a larger memory and a smaller size would increase the calculation capacity, making it possible to integrate a calibration stage and reduce the space currently occupied by the present board an example could be the Tactigon ONE board.

Reducing the domension of the battery compartment and consider recharging the battery compartment via a magnetic coupling.

Enhancing the soft robot by optimizing them, specifically evaluating the necessary volume of water to achieve a targeted grip force at the fingertips.

Further optimizing the firmware to improve overall performance and functionality.

Integrating a calibration stage to ensure precise and accurate measurements and adjustments.

It should be incorporated a Bluetooth module to establish a connection for transmitting data to a phone-managed application. This enables us to assess the battery level, communicate potential damages, and identify the need for component replacements.

Project Details