Healthcare Engineering Innovation Center (HEIC)

Robotic Rehabilitation in Stroke Survivors: A Bio-inspired Modular Compliant System

January 17, 2020

Dr. Kinda Khalaf, Associate Professor and Associate Chair, Biomedical Engineering, is leading a team of researchers at the Healthcare Engineering Innovation Center (HEIC) at Khalifa University to develop innovative methodologies and assistive technologies to assess and rehabilitate patients following a stroke. Dr. Khalaf is focusing on the quantification of disease induced movement impairment in stroke survivors using experimental and computational techniques, while Dr. Dongming Gan, Assistant Professor in the Department of Mechanical Engineering, is supervising a student design project aiming to develop a compliant ankle exoskeleton.

The first step is development of a clinical assessment protocol using gait and other key physiological parameters for the quantification of post stroke movement dysfunction and rehabilitation efficacy. Next, attention turns to rehabilitation techniques. A second HEIC project will design and develop a novel compliant exoskeleton system that can be used towards robotic human lower limb rehabilitation applications, including stroke.

“According to the World Health Organization, every year, 15 million people worldwide suffer a stroke, with five million left permanently disabled,” said Dr. Khalaf. “Instigated by an interruption of blood flow to the brain, resulting in damage to brain cells, stroke is considered the second leading cause of mortality globally for people above 60 years of age, and the second leading cause of disability.”

Stroke is the most common acquired neurological disease in the adult population worldwide with its global prevalence generating a significant burden of illness for healthy life years lost due to disability and premature death. One-third of stroke survivors achieve only a poor functional outcome five years after the onset, and although there has been great progress in managing outcomes, most of the care to reduce dependence among patients depends on rehabilitation.

“While developed countries are reporting an overall decline in the incidence of stroke, it’s increasing in the developing world,” said Dr. Khalaf. “In the UAE, the situation is worrisome, as not only is the incidence rate continuously increasing, but also the average stroke victim in the UAE is 45 years old, which is 20 years younger than the average stroke victim elsewhere in the world. Attributed to higher than global average prevalence of obesity, type 2 diabetes, hypertension and a sedentary lifestyle, statistics reveal that every hour someone in the UAE suffers a stroke. This is quite devastating both socially and economically in a young country.”

Optimal functional recovery is the ultimate goal of neuro-rehabilitation after an acute brain injury—the aim is to get people moving as normally as possible. One of the most common areas affected by stroke is the patient’s motor skills, with survivors experiencing disabilities to different degrees, in different hemispheres, and at different levels. Hemiparesis (muscular weakness or partial paralysis restricted to one side of the body) is seen in 88 percent of stroke victims, commonly affecting the limbs.

“Studies have shown that rehabilitation therapy is most effective if performed soon after stroke and that intensive therapy and task-based exercises may contribute significantly to partial and full motor recovery,” explained Dr. Khalaf.

Most therapists agree that early focused and repetitive exercise is the most impactful aspect of rehabilitation for future recovery. There is also evidence that early treatments involving mechanical structures to bring support and set constraints for movements promote the re-innervation of muscles in the affected limbs.

“Newly emerged robotic rehabilitation has several advantages, including consistency of intensive rehabilitation for a longer duration, irrespective of the skills and endurance of the patient and therapist,” said Dr. Khalaf. “Robot-based systems have the potential to provide programmable movement patterns, control of movement repetitions, and real-time position and force measurement and tracking. Robots can also be programmed to perform a wide variety of motion, including functional movements, allowing the patient to perform autonomous and repetitive training on tasks simulating activities of daily living.”

A senior design project proposed to Dr. Gan seeks to design a compliant ankle exoskeleton for adaptable walking assistance. Students Abdulla Almemari, Sultan Al Ali, Nawwaf Al Nuaimi and Khalifa Aladwan are aiming to assist people with ankle injuries specifically. They have developed a biomimetic exoskeleton that has a soft and safe interface with the human leg and a carefully designed variable stiffness compliant actuator to adapt to the patient’s speed and activity.

“Bio-inspired robotics systems have demonstrated improvement in mimicking natural physiological performance,” explained Dr. Gan. “However, issues such as how to design biological-system-like compliance, the level of the compliance, and how to integrate the compliance into the whole system, remain unsolved. We are prototyping an advanced exoskeleton and integrating it with innovative sensing and control technologies to achieve this compliance.”

The ability to walk independently is a prerequisite for most daily activities. Gait dysfunction is common in individuals with neurological disorders and impairments following stroke usually involve an excessive energy cost during walking. Stroke patients are generally unable to comfortably maintain the most efficient walking speed related to poor motor control, muscle weakness and sensory and balance disturbances. These impediments translate into issues with the proper sequential activation of the muscles in the different stages of gait, causing compensatory strategies that decrease speed and efficacy.

The ankle exoskeleton proposed in the senior design project can be applied to stroke rehabilitation because one of the most common impairments observed in stroke patients is the reduction of ankle dorsiflexion associated with a hyperextension of the knee. Not only does this affect walking speed, but also the ability to walk on irregular surfaces and climb stairs. This is commonly known as drop foot.

Before an exoskeleton can be tailored to a patient, their gait must be analyzed. Dr. Khalaf and her team are devising a comprehensive methodology for the quantification of gait patterns and other physiological parameters of stroke survivors. They plan to develop a patient-specific practical motion analyzer for reliable quantitative post-stroke assessment.

“Gait analysis in general can be of significant importance in identifying and tracking the results of surgical and other therapeutic modalities for the documentation, rectification, and improvement of abnormal gait patterns,” explained Dr. Khalaf. “The application of simplified gait analysis as a tool for assessing patients with stroke will aid in diagnosing and following gait aberrations, and quantifying the effects of therapeutic modalities.”

Identifying the exact ‘settings’ appropriate for each patient depends on accurate and reliable gait analysis. The biomimetic ankle exoskeleton will involve a variable stiffness spring actuator system to retract the ankle from its extended position to its normal position to help patients experiencing drop foot.

Successful rehabilitation strategies include mimicking the physiological joint power and energetics, where joint compliance and stiffness is key. Humans adjust leg stiffness during different locomotion speeds, where controlling ankle stiffness is a primary mechanism that is critical in control during motion.

“To compensate for and augment the human physiological compliance, a compliant joint will be designed and integrated into the lower extremity exoskeleton,” explained Dr. Gan. “The compliant design will ensure smooth motion transformation between the human and the exoskeleton.”

“Currently, health services in the UAE are struggling to provide rehabilitation therapy to victims, meaning many have to travel outside the country following a stroke. This imposes a heavy burden on the local economy and sacrifices the element of family support inherent to the culture here,” explained Dr. Khalaf. “Our multidisciplinary, multinational team with diverse engineering and clinical expertise is designing an innovative strategy for robotic rehabilitation for the UAE and the region, which will provide a more effective and sustainable therapy for patients.”

Jade Sterling
News and Features Writer
9 January 2020