April 1, 2008 -- William Brett Johnson has successfully defended his Master's thesis in Biomedical Engineering from Northwestern University. His thesis was entitled “Preliminary Quantitative Gait Analysis of Reciprocating Gait Orthosis (RGO) Users,” and sought to identify potential mechanical causes for the high energy requirements of ambulating with a RGO. This study found that during ambulation with a RGO, a large portion of weight was borne through the arms, which could lead to high energy expenditure. It was hypothesized that the motion and orientation of the trunk encouraged weight bearing through the arms. The results of this study also showed hip extension at the beginning of swing. This motion was counterproductive to the forward advancement of the swing leg and could have been caused in part by the orientation of the subjects’ trunks and compliance within the reciprocal link. Furthermore, small net flexion torques calculated at the hip during swing suggested that the reciprocal link contributed little to the forward advancement of the swing leg. Poor conservation of mechanical energy at the trunk was also observed, which could also contribute to increased energy expenditure. Deceleration of the body center of mass during the later half of swing was suggested as a possible cause for poor energy conservation.

July 10, 2007 -- A. Bolu Ajiboye has been awarded his Doctorate of Philosophy degree in Biomedical Engineering from Northwestern University.  His dissertation was entitled “Investigation of Muscle Synergies as a Control Paradigm for Myoelectric Devices.”  Here is a brief summary of his research:

A need exists to increase the functionality of myoelectric prostheses without increasing the mental requirement of operation. Implantable myoelectric sensors have made it possible to record multiple muscle activities with high fidelity. Given this high dimensionality of inputs, what is the best way of implementing control? Muscle synergies have been proposed for coordinating the many degrees-of-freedom (DOF) of the neuromotor system. This work aimed to investigate synergies as a viable control paradigm for multi-DOF myoelectric devices with regard to the properties of robustness, scalability, and volitional activation.

First, this work investigated if muscle synergies formed a predictive basis set for muscle coordination patterns associated with a variety of hand postures. Subjects mimed hand postures of the American Sign Language alphabet while electromyographic (EMG) activity was recorded from hand muscles. Non-negative matrix factorization (NMF) showed that a small number of hand postures could establish a robust set of synergies for predicting the EMG patterns of a variety of hand postures.

Second, this work investigated the scaling of muscle synergies in hand grasping at sub-maximal force levels. Subjects performed a force-tracking task using different grasps while EMG was recorded. Statistical and NMF analyses showed that the primary synergies of grasping retained their structures and scaled linearly with grasp force.

Third, this work investigated, through a virtual target reaching task, the volitional control of multiple DOFs using muscle synergies versus single-muscle inputs. It was hypothesized that users could more intuitively achieve independent and simultaneous control of myoelectric inputs using muscle synergies over single-muscle activations. The results showed that while users were able to independently and simultaneously modulate synergy activations, this control paradigm was statistically no better than one based upon single-muscle inputs.

From these investigations, it is concluded that while muscle synergies exhibit useful properties for control such as robustness, generalizability, and scaling, their practical benefit in a volitional control task is not significantly greater than a single-muscle control paradigm. Results from these investigations also suggest that the method of control implemented by the neuromotor system is not bound by muscle synergies, but rather by a combination of both synergy and single-muscle activations.

July 10, 2007 -- Todd Farrell has been awarded his Doctorate of Philosophy degree in Biomedical Engineering from Northwestern University.  His dissertation was entitled “Multifunctional Prosthesis Control: The Effects of Targeting Surface vs. Intramuscular Electrodes on Classification Accuracy and the Effect of Controller Delay on Prosthesis Performance.”  Here is a brief summary of his research:

This thesis examined a number of issues related to multifunctional prosthesis control including classification accuracies obtained from different types of electrodes as well as the effects of controller delay on performance.

Intramuscular electromyograms (EMG) are believed to provide several potential advantages over surface EMG for multifunctional myoelectric prosthesis control. One example is the ability to focally record from deep muscles of the forearm. However, intramuscular EMG has rarely been investigated due to the inability to obtain chronic recordings. New technologies are emerging that will make chronic recording of intramuscular EMG clinically feasible. Additionally, while previous investigations of surface systems have either used electrodes targeted to specific muscles or in an untargeted array, no work has compared these two approaches.  Untargeted electrodes are simpler to implement and are preferable for both intramuscular and surface recordings.

The effects of surface vs. intramuscular electrodes and electrode targeting on the classification accuracy of pattern recognition based classifiers were investigated by comparing four electrode conditions: targeted surface, targeted intramuscular, untargeted surface and untargeted intramuscular. When additional EMG signal features were extracted, it was found that no statistical differences were observed in the classification accuracies between the electrode conditions across eleven subjects. It was concluded that untargeted surface electrodes provide the simplest and most cost effective method of achieving high classification accuracies and any advantage gained by intramuscular electrodes for pattern recognition based classifiers would result from advantages in clinical implementation (i.e., faithfully providing the same recording site with daily donning and doffing of the prosthesis).

Additionally, a tradeoff exists when considering the delay created by multifunctional prosthesis controllers. Large controller delays will maximize the time used for EMG signal collection and analysis (and thus maximize classification accuracy); however, large delays can decrease responsiveness and degrade prosthesis performance. To elucidate an 'optimal controller delay,' twenty able-bodied subjects performed the Box and Blocks test using PHABS (Prosthetic Hand for Able Bodied Subjects). Tests were conducted with seven different controller delay levels ranging from nearly 0 to 300 ms and with two different artificial hand speeds. Statistical analyses found the optimal controller delay was between 100 and 125 ms for both hand speeds. Finally, equations that related EMG analysis window parameters to the prosthesis controller delay were derived.

June 28, 2007 -- Ryan Williams has been awarded his Master's degree in Biomedical Engineering from Northwestern University.  His thesis was entitled "Prosthetic Foot & Ankle Mechanism Capable of Automatic Adaptation to the Walking Surface."  Here is a brief summary of his research:

This thesis explored the challenges that people using lower-limb prostheses experience when ambulating on sloped surfaces.  A prototype foot and ankle mechanism was designed, developed and tested on three subjects with unilateral transtibial amputations walking on level and ramped surfaces.  The mechanism is capable of automatically adapting to the walking surface by providing variable stiffness throughout the gait cycle.  The mechanism simulates the behavior of the physiologic foot and ankle complex by increasing the stiffness once foot-flat is reached and then reducing the stiffness directly after toe-off.  The “set-point,” at which these changes in stiffness occur, gets reset on every step in order to reach the proper alignment for the walking surface.   The mechanism utilizes the user’s body weight to control the ankle stiffness and does not require any active control.  Several steps would be needed to make the prototype into a commercial product, but the mechanism achieved the design goals and was sufficient for acquiring the necessary data.

June 8, 2007 -- Jonathon Sensinger has been awarded his Doctorate of Philosophy degree in Biomedical Engineering from Northwestern University.  His dissertation was entitled “User-Modulated Impedance Control Using Two-Site Proportional Myoelectric Signals.”  Here is a brief summary of his research:

This thesis explored the usefulness of allowing subjects to modulate the impedance (stiffness, viscosity, and inertia) of a joint using myoelectric signals. The stiffness of the interface between the residual limb and socket was modeled and empirically tested. A prosthetic elbow capable of modulating its impedance was designed, fabricated, and validated. Pilot studies were done to determine foundational questions, such as the appropriate motion paradigm and the ability to decouple preferred impedance from preferred contraction levels. Finally, a pointing and tracking test were done on 15 able bodied subjects and 3 subjects with amputations at or above the transhumeral level. Findings include a transhumeral socket-residual limb stiffness between 25 and 105 Nm/rad, the ability of the elbow to mimic a large range of impedances, the preference of subjects for proportional velocity control, high stiffness, and low inertia, and the inability of subjects to actively modulate their impedance using myoelectric signals while performing tasks, especially in the presence of an additional mental load. Future work should allow subjects more training time and use discrete states of impedance that subjects may select before initiating a movement.

April 25, 2007 -- Regina Konz has been awarded her Doctorate of Philosophy degree in Biomedical Engineering from Northwestern University.  Her dissertation was entitled "The Role of the Spine in Human Walking: Studies of Able-bodied Persons and Individuals with Spine Pathologies."  Here is a brief summary of her research:

The role that spinal motion plays during ambulation is not clearly understood.  Therefore, a kinematic model was developed and validated for the study of regional spinal motion. The model is intended to be used concurrently with the acquisition of conventional gait data.  Application of this model allowed for development of a foundation of able-bodied spinal motion patterns and ranges of motion during gait.  Able-bodied subjects were further studied with and without imposed spinal restriction to gain an understanding of how restricted spinal motion affects kinematics during walking.  To fully appreciate the effects of spinal restriction and surgical spinal fusion on gait, subjects with spine deformity were also studied before and after surgery.

August 7, 2006 -- George Bertos has received his Doctorate of Philosophy degree in Biomedical Engineering from Northwestern University.  His dissertation was entitled "Identification of the Mechanical Impedance of the Human Locomotor System and Quantification of Shock Absorption Characteristics with Applications in Prosthetics."  Here is a brief summary of his research: 

Lower-limb prosthesis users who have commercially available shock absorption components in their prostheses tend to favor them.  However, it is unclear how much shock absorption they provide during walking and what mechanical characteristics they should have.  To determine mechanical characteristics of shock absorbers, this dissertation utilized a 2nd-order vibration model to characterize the mechanical impedance of the locomotor system of able-bodied persons and in persons with lower-limb amputations.  Based on control theory, a prosthesis was proposed that compensates for differences between the shock absorption of able-bodied persons and persons using prostheses with rigid pylons.  Use of the proposed system/prosthesis should result in an overall person-machine system that mimics the able-bodied shock absorption system during gait.  A new prosthetic component was designed and built that may improve the shock absorption ability of lower-limb amputees.

August 7, 2006 -- Angelika Nikole Zissimopoulos received her Master of Science degree in Biomedical Engineering from Northwestern University.  Her thesis was entitled "The Biomechanical and Energetic Effects of a Stance-Control Orthotic Knee Joint."   Here is a brief summary of her research: 

June 12, 2006 -- Devjani Saha received her Master of Science degree in Biomedical Engineering from Northwestern University.  Her thesis was entitled "The Effect of Trunk Flexion on Standing and Walking".  The purpose of her research was to better understand the adaptive mechanisms that may be necessary for balance during trunk-flexed postures.

March 10, 2006 -- Lexyne L. McNealy received her Master of Science degree in Biomedical Engineering from Northwestern University.  Her thesis was titled "The Effect of Prosthetic Ankle Motion on the Gait of Persons with Bilateral Transfemoral Amputations."  Lexyne's research examined and quantified the effect of Seattle LightFoot2 prosthetic feet, multiflex ankle units, and torsion adapters on the gait of four male bilateral transfemoral amputees.  She found that multiflex ankle components allowed the subjects to walk with some gait characteristics that were similar to those of able-bodied individuals.  Additionally, the study participants felt that the multiflex ankles and torsion adapters were beneficial.

November 7, 2005­ -- Sara  R. Koehler received her Master of Science degree in Biomedical Engineering from Northwestern University.  Her thesis was titled "An Investigation of Shock-Absorbing Prosthetic Components for Persons with Transfemoral Amputations."  Sara’s research compared the effect of two different shock-absorbing components­--an Endolite TT Pylon and an Otto Bock 3R60 Knee­--on the gait patterns of ten unilateral, transfemoral amputees walking over a range of self-selected speeds.  The goal of her work was to determine if reducing prosthetic stiffness enhanced the walking performance and comfort for persons with amputations.

June 17, 2005 -- Po-Fu Su and Jonathon Sensinger received Master of Science degrees in Biomedical Engineering from Northwestern University in Evanston, Illinois.  Su's Master's thesis was titled "Bilateral Below Knee (BBK) Amputees with Differential Ankles".  The purpose of his study was to determine if increased prosthetic ankle motion in persons with bilateral transtibial amputations significantly improved their walking performance.  To learn more about his work read the following article:

"The Effect of Increased Prosthetic Ankle Motion on The Gait of Persons with Bilateral Transtibial Amputations"

Sensinger's thesis was titled "Design & Analysis of a Non-backdrivable Series Elastic Actuator for Use in Prostheses".  His work investigated the potential use of non-backdrivable Series Elastic Actuators within upper-limb prosthetics.  To learn more about his work read the following article:

Jonathon W. Sensinger, MS. "May the Force Be with You: Physiologically Appropriate Prostheses," Capabilities, vol. 13, no. 2, Spring 2005. (pdf format)

View a full list of degrees awarded:
Master of Science | Doctor of Philosophy