A multi-layer vibrating blanket that stimulates blood circulation in the lower extremities of wheelchair users.

January – March 2023

For ENGS021: Introduction to Engineering. This course introduces the student to Engineering through participation, as a member of a team, in a complete design project. The synthesis of many fields involving the laws of nature, mathematics, economics, management, and communication is required in the project. Engineering principles of analysis, experimentation, and design are applied to a real problem, from initial concept to final recommendations.

Promotional Video

Project Summary

After sitting for prolonged periods, wheelchair users experience poor blood circulation in the lower body. With less blood flow, muscles and the immune system weaken, fatigue and chest pressure increase, and organs can fail. We designed a comfortable, effective, and easy-to-use vibration blanket to stimulate blood flow, which will eliminate the risks associated with poor blood circulation.

The CIB uses vibration technology to stimulate blood flow in the lower extremities. On the exterior is a soft polyester fabric that is highly resonant to vibrations. This duvet cover has a zipper that allows you to remove the internal matrix and wash the duvet cover for continued use. On the interior is a multi-layered structure consisting of electronics, fabric, and gel coolant. The first layer is the electronics: 108 vibration motors and amplifiers powered by six Arduinos. The next layer is the polyester-cotton fabric onto which I hand-sewed the electronics. Underneath this layer is the 5-pound coolant ultrasound gel structure, which is then concealed by another layer of polyester cotton fabric. Overall, we have a removable, multi-layered electronic system that is surrounded by a zipper-operated duvet cover.

The Design Process

Our decision to pursue this solution to this problem was based on research and observation, in keeping with the Engineering Design Cycle. My grandmother, while not in a wheelchair, struggles with her circulation and uses compression socks to regulate edema and other risks. Her diminished mobility makes putting on compression socks extremely difficult, time-consuming, and irritating. When we spoke to other elderly people and wheelchair users — our user base — we found that many echoed these frustrations.

We decided to pursue a solution to these frustrations by developing a device to improve blood circulation. We developed specifications with justifications, quantifications, and tests and feasible alternative solutions. We set up a decision matrix to guide our choices. We decided to use vibrations to improve blood circulation.

Why vibrations? Because they are scientifically proven to increase blood circulation! • Increases metabolic rate at site application • Oxygen is required due to process → blood vessels dilate, and blood flow brings oxygen into region [ Fuller, Thomson, R. L., Howe, P. R. C., & Buckley, J. D. (2013). Effect of vibration on muscle perfusion: a systematic review. Clinical Physiology and Functional Imaging, 33(1), 1–10. https://doi.org/10.1111/j.1475-097X.2012.01161.x, and many other sources ]

With our research, problem feedback, state of the art comparisons, specifications, and decisions settled, we began our prototyping: the analyzing and evaluating stage of the Engineering Design Cycle that involves designing, building, testing, experimenting, and surveying.

Throughout this brainstorming/research process and the rest of the project, I spearheaded our executive summaries, presentations, and written report to ensure high-quality work. I delegated work, edited writing and slides, maintained proper formatting, ensured professionality in our work, and assembled everyone’s work together into cohesive final assignments.

We separated into different foci for our first mocks of our final design, thinking about structural and electrical engineering, final construction, and the vibration technology itself.

I sought to create a small, rudimentary structural prototype with detachable, multi-layer components. I wanted to focus on the structural engineering of the blanket, its weight, its cooling mechanism, its detachability, and the user experience.

I found that test users felt a weight difference with the coolant layer, struggled with the velcro, and would prefer a soft fabric for the final prototype. Thus, I advised my team to proceed with non-leakable, coolant layer (like sealed ultrasound gel), to switch the opener to a zipper, and to consider an outer layer (like a duvet cover) that could wrap around an enclosed vibration matrix and gel coolant. Essentially, take my prototype and put it inside a traditional, washable duvet. Because the coolant layer and mock vibration matrix were easy to slide in and out of my multi-layer fabric design, I advised my team to proceed with a washable outer layer and an electrical inner layer. This structure is achievable through a soft duvet that encloses an enclosed vibration matrix and gel coolant layer.

After iterative and experimental prototype design, I returned to my team with structural advice. We should use a zipper for our removable layer, research soft, thin fabrics for the final blanket, work with a weighted coolant that isn’t water (suggested ultrasound gel), prevent the vibration matrix from moving by attaching it to the fabric, and find strong plastic and a strong sealer for the coolant layer — or it will burst.

We regrouped and discussed our specification testing and findings to improve our ultimate design. We developed a game plan for moving forward and met with more medical professionals and electrical engineering experts to further guide our design. Then, we began the assembly of our final prototype.

Our final iteration of the electrical device incorporated the 108 vibration motors, which were connected to amplifiers. The vibration motors were soldered onto stripped wires, allowing the current to flow through a series of six circuits in parallel, ultimately connecting to the Arduino. The Arduinos are coded to deliver vibrations continuously while the CIB is plugged into a power source. Lastly, I hand-sewed all the circuits onto the first interior layer of our blanket.

With electrical matrix assembly underway, we began to assemble the structural components. First, we sealed 2.5 liters of ultrasound gel, which was about 7 pounds, into our tested poly-plastic bags. Research suggests the safe weight for a weighted blanket is within 10% of body weight. Our final weighted layer was within the weighted blanket’s appropriate range of 10–25 pounds, meaning it is safe for most adults. Next, we placed our optimally weighted ultrasound gel layer into the polyester-cotton blend fabric, and we sewed the fabric together, sealing the gel layer inside. Simultaneously, we sewed a soft polyester 23×29 in. duvet cover, as determined earlier, for the vibration matrix to fit snugly inside. Finally, we included a zipper seal so users could easily remove the blanket cover for washing. Our final prototype for the nine-week term was ultimately connected to a power supply, though we aspire to have a battery-operated, wireless product for our future iterations. 

Testing

We tested the final prototype of the CIB extensively after finishing construction through (1) qualitative testing, (2) benchmark testing with exercise and compression socks, and (3) specification testing.

1. For qualitative testing, we surveyed users about our final design. We informally asked 38 people about their first visual impressions of the CIB and had them put it on their laps to feel the vibrations. Overall, they agreed that the CIB is comfortable, soft to the touch, and easy to use—even with the additional weight layer. The zipper was simple to operate and did not catch on any loose clothing or fabric. Many thought the red and blue plaid blanket cover was an attractive choice and would entice them to buy the product. They could all feel the vibrations, some even comparing it to a “purring cat on your lap.” However, recurring avenues for improvement also emerged through conversations with these potential user. We would address these constructive criticisms in future iterations. We also administered a formal survey to 12 of these participants of different ages and sexes.

We asked about the CIB using a balanced, linear Likert scale (1 as “strongly disagree” and 5 as “strongly agree”). I would use the CIB if it were recommended by a doctor; this statement resulted in 90% 5s and 10% 4s. I would say using the CIB was comfortable and easy; this statement resulted in 60% 5s and 40% 4s. Notably, none of our users disagreed with either of these questions; they either strongly agreed with a 5, or agreed with a 4.

2. For benchmark testing, we wanted to assess the performance of the CIB against the state-of-the-art: compression socks and exercise. Initially, we had envisioned using a Doppler ultrasound to quantify the amount of blood flowing through a user’s legs. However, after contacting various members of the Dartmouth-Hitchcock Medical Center (DHMC) vascular team, we determined that an ankle-brachial index (ABI) reading would be a better means of conducting our testing. ABI readings are routinely used to test for peripheral arterial disease and compare the amount of blood flowing in the lower legs to that in the arms. They are an easy, non-invasive way to quantify the amount of blood circulating in the body. 

To take ABI readings, one measures the brachial and dorsal systolic blood pressures using a Doppler probe. To use the Doppler probe, one applies a small quantity of ultrasound gel and gently auscultates for a pulse. The highest blood pressure across both extremities is taken, and various readings are assessed. The ABI is the ratio of the ankle over the brachial blood pressures. ABI readings on a healthy person—“normal” blood circulation—fall between the ranges of 1 and 1.4. We did not perform testing on anyone with vascular disorders; instead, we found a way to calculate the improvement in blood pressure in a healthy user group. DHMC doctors say that after exercise, there is an increased demand for oxygen in the legs, causing an increase in peripheral circulation. As the blood vessels dilate, blood pressure in the lower extremities decreases, leading to a decrease in ABI readings (for instance, from 1.4 to 1.2). Our benchmark testing aimed to mimic the results from our studies for exercise as well as test similar results for compression socks.

For compression sock testing, we took the baseline ABI measurements of six random, healthy participants: three males and three females, ranging from late teens to late sixties (average = 1.218). Our participants then wore compression stockings for 10 minutes; afterwards, we took ABI readings again (average = 1.300). We took the average of these values, which equated to an overall value of 1.206.

For exercise testing, we took the baseline ABI measurements of six random, healthy participants—as done for compression socks (average = 1.2742). Our participants then performed 25 calf raises and light jogging for 5 minutes; afterwards, we took ABI readings again (average = 1.190). We took the average of these values, which equated to an overall value of 1.202.

3. For specification testing, we started with reliability. Our team’s hypothesis was that if our blanket indeed mimicked the circulatory effects of exercise and compression stockings, we would notice a decrease in ABI readings after applying the CIB. We repeated the same procedure on the same 12 random, healthy users on whom we performed benchmark testing (allowing time to see the reversed effects from benchmark testing). We re-took the baseline ABI measurements for each participant, ensuring that their ABI reading returned to normal (equating to seeing revered effects from benchmark testing. Average = 1.246). Our participants then wore the CIB for 7 minutes; afterwards, we took ABI readings again (average = 1.2023).

To quantify whether we had met our safety specification, we measured the amount of time our blanket was able to run without overheating or short-circuiting. The Arduino already has a limitation on current to prevent short-circuiting, but we were also able to determine that our blanket was able to run for 2 full hours continuously without overheating. By letting the CIB run for various times on various days, data suggests that our blanket runs safely for this period of time. Further testing would be needed to determine if the run time is higher, though we predict the safe run time is a few hours higher from observation.

To evaluate whether our blanket met our accessibility requirements, we compared the CIB’s weight to our previously-estimated 10- to 18-pound safety range. The CIB is ~7 lbs, squarely beneath the safety range, and thus safe weight-wise. Additionally, surveyed users gave 4/5 and 5/5 ratings on the balanced Likert scale for ease of use. Our other specifications were demonstrated without extensive testing.

Analysis

For our quantitative analysis, we compared the results of our functional requirement/reliability testing to those of our benchmark testing. We found the percentage by which ABI readings decreased, allowing us to numerically assess how much blood flow increased during our interval of testing. We subtracted the average of the initial ABI readings (without compression socks, exercise, or CIB) from the ABI readings after use of the compression socks, exercise, and CIB. We then took our derived number and divided it by the initial number, from which we were able to find the percentage of average ABI reading decrease. For compression socks, there was an average decrease of 0.09% in readings; for exercise, there was a 5.7% decrease after exercise; for the CIB, there was a 3.51% decrease in readings before and after application. Based on these percentages, we can conclude that CIB, on average, improves blood circulation more than compression socks and is almost as effective as exercise. This conclusion is critical because many wheelchair users are unable to exercise their lower extremities. Our preliminary results suggest that CIB will be a sufficient alternative.

About the Team