This document proposes a modified design for the forearm crutch that uses magneto-rheological fluid to variably adjust the grip of the cuff based on the force applied during walking. It describes preparing an MR fluid with iron particles, oil, and grease and using it in the cuff region of a crutch. A pressure sensor would detect the applied force and controller would activate an electromagnet to adjust the fluid viscosity for a comfortable, supportive grip without discomfort. This innovative use of smart materials could improve medical devices for patients.

1. Innovation in Medical Devices:
Using Magneto -Rheological Fluid
in the Forearm Crutch

2. Abstract
Abbreviations
Table of Contents
Market Trends/Challenges
Solution
Best Practices
Conclusion
RReeffeerreennccee
Author Info
3
3
3
4
6
8
9
9
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3. Abstract
Innovation in Medical Devices: Using Magneto-Rheological Fluid in the Forearm Crutch | 3
A forearm crutch is a mobility aid which is used to counter mobility impairment or an injury that limits one’s
walking ability. It has been almost exclusively used by people with permanent or lifelong disabilities. The
forearm crutch used today is obsolete. The cuff, which is used to provide steady grip to the arms of the
patient, actually gives a lot of discomfort.
TThhiiss paper proposes a modified design for the forearm crutch, making the steady grip provided by the cuff
variable, according to the force applied while walking, to actually provide the user with a sense of support
rather than causing discomfort. Magneto Rheological (MR) fluid - a unique fluid that solidifies when a
magnetic field is applied, can come to the aid.
Abbreviations
Sl.No
1
2
3
4
5
6
7
8
9
Acronyms Full Form
MR
g
cP
KHz
kg
V
A
PIC
SCR
Magneto Rheological
Gram
Centipoise
KiloHertz
Kilogram
Voltage
AAmmppeerree
Peripheral Interface Controller
Silicon Control Rectifier
Market Trends/Challenges
Materials and the processes to shape them are developing at a faster pace than at any time before in history.
The challenges and the opportunities are therefore greater than ever before with the evolution of smart
materials. This paper presents a case study to illustrate the use of one such smart material - Magneto Rheo-logical
fluid - in the modification of a medical device – the forearm crutch.
Medical devices and instruments are in a constant state of evolution. Responding to these trends, the need of
the hour is to build effective, accurate and precise devices that ensure the safety of human life. The use of
smart materials provides a convenient solution and compels the industry to adopt such materials by which
the effectiveness and precision of medical devices can be increased manifold. However, there are still
concerns over the desired mechanical and rheological properties of the smart materials that can be used.
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4. Innovation in Medical Devices: Using Magneto-Rheological Fluid in the Forearm Crutch | 4
Forearm crutches are used by slipping the arm into a cuff to get a grip. The cuff, typically made of plastic or
metal, can be a half-circle or a full circle with a V-type opening in the front, allowing the forearm to slip out in
case of a fall. The forearm crutch used today is not too effective as it causes discomfort to the user instead of
providing support with a convenient grip.
Solutions
The proposed modified design of the crutch is to prevent any discomfort to the user and to give a sense of
support for walking as if someone is holding the arms of the user.
This paper elucidates the following aspects of the crutch design:
Preparation of Magneto Rheological fluid to be used in a forearm crutch.
Design of the crutch with the Magneto Rheological fluid in the cuff region with a complete electrical
circuit to actuate the fluid.
Magneto Rheological (MR) fluids are a class of smart materials whose rheological properties can be rapidly
controlled by an external magnetic field. MR fluids are a suspension of micron-sized, magnetically polarizable
particles in oil or other liquids. Under normal conditions, MR fluids are free-flowing liquids having a consis-tency
similar to that of Motor oil.
WWhheenn a magnetic field is applied, the interaction between the magnetically induced dipoles causes the parti-cles
to form a columnar structure which is parallel to the applied field. This results in the restriction of flow of
the fluid thereby increasing its viscosity. The degree of change in a MR fluid depends on the magnitude of the
applied field.
Preparation of MR Fluid
A basic MR fluid consists of three parts: Magnetically Polarizable Particles, Carrier Fluid, and Surfactant. Table
1 enlists the materials that are used to prepare 100 ml of the Magneto Rheological fluid in the laboratory.
Component Used Material Quantity (g)
Magnetically Polarizable
Particles
Ottokemi Electrolytic 99.5%
Iron Powder of 300 mesh
(86.4 microns approx) size
Fork Oil (Teleshocab Oil
from Yamaha)
Pennzoil White Lithium Grease
Table 1. Composition of Magneto Rheological Fluid
Sl.No
1
2
3
150
55
5
Carrier Fluid
Surfactants
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5. Innovation in Medical Devices: Using Magneto-Rheological Fluid in the Forearm Crutch | 5
Procedure for preparation of Magneto Rheological Fluid:
The constituents were weighed using an electronic weighing balance as per the required quantity.
White Lithium Grease and Fork Oil were mixed thoroughly for a period of 30 minutes at 50oC using
a magnetic stirrer to achieve a homogeneous uniform mixture.
Iron powder was added in small amounts while the mixture was being stirred until no dry iron
powder was visible and the mixture appeared uniform without any lumps of iron powder.
The fluid was allowed to mix thoroughly by sonicating it in an ultrasonic bath sonicator ((aatt 3333 KKHHzz))
for 15 minutes to disperse all the particles uniformly.
The sample was placed in between the poles of a magnetometer to check if it displayed the
Magneto Rheological effect.
Figure 1. Magnetic Stirre Figure 2. Sonicator
The MR fluid so obtained was a dark grey, almost black color and highly viscous. Since such a highly viscous
fluid cannot be used in the forearm crutch, we needed a low viscosity MR fluid, the composition of which could
be estimated only by finding out the effect of the particle size, carrier fluid type and the percentage of
magnetic particles on the viscosity. A Magneto Rheological fluid with viscosity comparable to that of conven-tional
fork oil, i.e., close to 60 centipoises (cP) was required. Also, the settling time had to be improved so that
the particulates did not settle down too soon in the forks.
TThhee viscosities of the prepared samples were measured using the Anton Paar Physica Rheometer MCR 301
series at the Indian Institute of Technology, Madras. The settling time for all the nine samples was measured.
The samples were kept in vials and allowed to settle without any external disturbance. The time taken for the
MR particulates to settle down was monitored using a stop clock.
Thus, a sample with 70% concentration of MR fluid, fork oil as the carrier fluid and white lithium grease as the
surfactant was found to be suitable for the fore arm crutch because of its high viscosity and settling time
compared to the other samples.
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6. Innovation in Medical Devices: Using Magneto-Rheological Fluid in the Forearm Crutch | 6
ELECTRO
MAGNET BATTERY
CONTROLLER
MR FLUID
PRESSURE SENSOR
Figure 3. Flowchart to actuate the MR Fluid
MR fluid so obtained can be filled near the cuff region. The force applied to the ground while walking is sensed
by the pressure sensor and a signal is transmitted to the controller which controls the current to be passed to
the electromagnet which is provided in the cuff region in order to produce the magnetic field. MR fluid solidi-fies
according to the magnetic field produced due to this force. Thus, the grip offered to the arm varies accord-ing
to the pressure applied by the user while walking. It clearly provides the sense of someone upholding the
user while walking. The pressure applied is classified into three categories - high, medium and small. The con-ttrroolllleerr
is programmed in a way to provide the corresponding current from the battery to the electro magnet
according to the pressure applied. This actually changes the magnetic field, thereby varying the grip provided
to the arm.
The pressure sensor used is the load cell. It is in the form of a wheat stone network. The pressure in the load
cell is used to control the magnetic field by controlling the voltage of the lithium ion battery, using a peripheral
interface controller by means of a SCR (Silicon Control Rectifier) control unit. The voltage of the battery is con-trolled
according to the pressure applied there by varying the magnetic field and changing the viscosity of the
LCD
PIC
CONTROLLER
LOAD CELL
BATTERY
SCR
CONTROL UNIT
ELECTROMAGNET
MR fluid.
Figure 4. Setup to change the magnetic field
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7. Innovation in Medical Devices: Using Magneto-Rheological Fluid in the Forearm Crutch | 7
Finally, the controller setup to actuate the fluid is made and the voltage of the battery is controlled according
to the load applied. The voltage given to the electro magnet actuates the Magneto Rheological fluid, changing
the viscosity to vary the grip provided to the arm.
Electromagnet
Battery
PIC Controller
Load Cell
Figure 5. Prototype of forearm crutch
Load in kg
0-10
10-20
20-30
T
Voltage in V
8
10
12
General Design Prototype
We designed a general design prototype with 12 V 1A batteries, a load cell, PIC controller and electromagnet
in a forearm crutch in solid works software, as shown in Figure 5. Using a single 12 V battery, electromagnets
and the PIC controller increases the weight of the prototype model. The load has to be evenly distributed
along the fore arm crutch to decrease the weight. The problem with this design is that the use of the control-ler,
electromagnet, and battery increases the weight and size of the stick.
Best Practices
Three steps have to be taken to reduce the size and weight of the crutch.
The controller setting has to be done in the chip design, to reduce the size.
The battery must be made small by using batteries of smaller voltages connected in a series to get
12V. It must be distributed along the stick.
The cuff region has to be changed as the electromagnet instead of having a separate magnet
attached to it.
New Design
By following the above three steps to modify the design of the forearm crutch, it can now be considered a for-midable
new product that uses smart materials that increase its effectiveness. The modified prototype is
shown in Figure 6.
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8. Innovation in Medical Devices: Using Magneto-Rheological Fluid in the Forearm Crutch | 8
Electromagnet
Battery
Controller in Chip
Load Cell
Figure 6. Modified Design of Prototype
Conclusion
The new design for the fabrication of the forearm crutch, with the help of Magneto Rheological fluid, seems
to offer great benefits:
A new product, providing the requisite support more effectively to the user.
It provides more comfort to the user and reduces the irritation on the arm.
Using smart materials will draw the attention of a large number of customers.
It provides a feeling of someone actually upholding the user while walking.
This modified design is mainly targeted at the high-end customer who has a higher spending capacity, as this
is an innovative new product using smart materials. Such a breakthrough is sure to attract customers around
the world, mainly in developed economies, such as Europe and North America.
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9. Innovation in Medical Devices: Using Magneto-Rheological Fluid in the Forearm Crutch | 9
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References
1. KetillHeiðarGuðmundssonDesign of a Magneto rheological Fluid for an MR Prosthetic Knee Actuator with an Optimal
Geometry
2. Henry hsu, aliso Viejo Magneto rheological fluid composition and prosthesis knee utilizing same (US) patent in 2004
3. S.Q. Abu-Ein, S.M. Fayyad, WaleedMomani -Experimental Investigation of Using MR Fluids in Automobiles Suspension Systems
.journal publishes in 2011
4. Hugh Herr and Ari WilkenfeldUser-adaptive control of a magneto rheological prosthetic knee
55.. CCaarrllssoonn DDaavviidd JJ..WWhhaatt MMaakkeess aa GGoooodd MMRR FFlluuiidd??,, JJoouurrnnaall ooff IInntteelllliiggeenntt MMaatteerriiaall SSyysstteemmss aanndd SSttrruuccttuurreess,, VVoolluummee 1133,, 22000022,,
Pages 7-8
6. ISO-2631, International Standards Organization, Guide for the Evaluation of Human Exposure to Whole-Body Vibration,
International Standard ISO 2631-1:1997(E)