Case Studies

Cardiac Simulator

This case study describes the use of McKibben actuators embedded in a soft elastomeric matrix to mimic heart muscles. 

Soft Prosthetic Hand for Amputees

This case study describes the design and construction of a soft prosthetic hand for amputees designed by a group of students in the Global Immersion Summer Program in India. The thumb is actuated by three pneumatic artificial muscles.

Cardiac Simulator

Clinical need

Existing functional simulators are generally passively driven by flow, the heart walls do not actively contract, and they don’t simulate 3-D twisting motion (with the exception of the Chamberlain surgical trainer) or allow simulation of pathological motion. This limits the clinical relevance of device testing on these test-beds.

Solution

Inspired by biological muscle, where contractile elements are arranged in a soft matrix, soft custom-molded McKibben actuators were fabricated then embedded in a soft elastomeric matrix with material properties close to physiological tissue.

Initial models used simple configurations of actuators in elastomer matrix. Basic geometric properties such as actuator spacing and matrix width/length were varied, and the force and strain behaviors of these models when the actuators are pressurized were observed via image tracking of markers and a tensile test machine.

Once these simple units were characterized, the same principles were applied to the helical arrangement of muscle fibers in an actual heart.

EM trackers were placed on molded alignment features on the simulated ventricle to evaluate its motion. When all actuators were pressurized, apical and basal rotation of the ventricle matching the range of clinical values was observed.  In addition, the effect of deactivating select actuators on the overall motion of the ventricle was observed. This mimics the effect of a section of heart wall losing its function via myocardial infarct or other cardiac diseases and simulates the subsequent pathological motion.

Soft Robotic Prosthetic Hand for Amputees

This case study describes the design and construction of a soft prosthetic hand for amputees designed by a group of students in the Global Immersion Summer Program in India.

 

Clinical Need

Diabetes, peripheral artery disease and trauma cause hundreds of thousands of upper limb amputations worldwide per year. For amputees, restoring the utility of a missing hand is a major factor in being able to do activities of daily living (ADLs) like eating, bathing and dressing themselves. Gaining the ability to do these basic tasks is extremely helpful to the patient achieving a higher quality of life. Current prosthetics including body powered and myoeletric devices give a lot of this function back to the patient, but can be tiring to use, expensive, stiff, or have a limited range of motion.

 

Solution

The team’s solution consists of 4 fiber reinforced bending actuators that mimics the index, middle, ring and little fingers. The thumb is an aluminum mechanism actuated by pneumatic artificial muscles.

The overall goals of the project were to design a soft prosthetic hand that was: cost effective, aesthetic, provided sufficient grip strength for ADLs, low maintenance, and light weight. The design of the hand was broken up into 4 separate modules: Thumb, Palm, Fingers, and Control. These 4 modules were determined to need to come together to into a few potential grip patterns that would be useful to complete ADLs, including pinching, open palm, pointing and a power grip.

The thumb design needed to be rigid and able to transmit forces in multiple different orientations for the different grip patterns. To achieve these grip patterns, the thumb was designed as a hinged aluminum mechanism.

As opposed to the four fingers of the hand, which only need to bend in one plane, the thumb needs multiple degrees of freedom. To achieve this range of motion, the thumb was actuated by three pneumatic artificial muscles in different orientations. These actuators were controlled by a version of the Open Source Control Board described on this site.

The following video shows how the different actuators affect the movement of the thumb:

For more information on the fingers of the hand, visit the case study page in the Fiber Reinforced Actuators section.