Major Study Project Thesis

MAJOR STUDY PROJECT
THESIS

Ankle Foot Orthosis with integrated smart technology
providing bio-feedback data to improve drop foot
rehabilitation.

Tom Statters (N0564392)
BSc Product Design
School of Architecture, Design and the Built Environment
February 2018

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Tom Statters N0564392
Abstract

This project identified and investigated the causes of drop foot in stroke survivors and the
subsequent effects of prolonged periods of rehabilitation. Utilising a customised user
centred design methodology, the needs of the user and a gap in the market for an Ankle
Foot Orthosis providing bio-feedback on the user’s walking pattern were identified. A final
design solution that fulfilled this clinical need was achieved following the support and
feedback provided by the Nottingham Stroke Association (NSA).

Qualitative and quantitative research methods were used to clearly define the user’s needs.
This subsequently determined the Product Design Specification (PDS), derived from Pugh’s
Total Design Method, which outlines in detail the required features of the product. The
stroke survivors of the NSA proved invaluable throughout the design process, adopting the
role of project clients and giving rich feedback that shaped the design.

The PDS was also influenced by secondary research which looked into existing products and
relevant technologies. User and expert feedback weighted the importance of each element
of the PDS.

Multiple concepts were generated to cover a broad range of possible solutions, these were
subsequently evaluated through the Combinex evaluation method, to determine the most
suitable designs for further development. Recurring user feedback influenced the
developments made to the design.

The final design solution was created using SolidWorks 2017 CAD software, in order to
determine overall form and weight of each of the products components. This data was
subsequently used to define a realistic final costing of the product.

The final outcome of this project successfully delivers a viable user centred design solution
that incorporates bio-feedback and innovative design to reduce the time spent in
rehabilitation for drop foot sufferers.

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Acknowledgments

There are a number of individuals that deserve a great deal of thanks and recognition for
their efforts to aid and assist this project, without them it would not have been possible.

Firstly, I’d like to thank all the member at the Nottingham Stroke Association for their
support and cooperation throughout the project. Their knowledge formed invaluable user
feedback at all stages of the process.

Thanks also to Professor Philip Breedon and Luke Siena for the constructive advice and
guidance throughout all stages of the project.

Finally, I would like to thank my mother, Sian Statters, for her continual advice and support
during this academic year.

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Table of Contents
Chapter 1- Design in Context ............................................................................................. 8
1.1- Introduction ............................................................................................................................ 8
1.2- Background ............................................................................................................................. 8
1.3- The Brief ................................................................................................................................. 8
1.4- Aims and Objectives ............................................................................................................... 9
1.4.1- Project Aim .......................................................................................................................... 9
1.4.2- Product Aim ......................................................................................................................... 9
1.4.3- Project Objectives ................................................................................................................ 9
1.5- Conclusion .............................................................................................................................. 9
Chapter 2 – Research Methodology ................................................................................. 10
2.1- Introduction .......................................................................................................................... 10
2.2- Research Methodology ........................................................................................................ 10
2.3- Designing for Disability ......................................................................................................... 11
2.3.1- Drop Foot ........................................................................................................................... 11
2.3.2- Drop Foot Rehabilitation ................................................................................................... 13
2.4- Interviews-Thematic Analysis ............................................................................................... 14
2.4.1- Evaluation of Interviews .................................................................................................... 14
2.4.2- User Feedback- Nottingham Stroke Association - Focus Group ........................................ 14
2.4.3- Expert Feedback ................................................................................................................ 15
2.4.4- Conclusion of Interviews ................................................................................................... 16
2.5- Existing Products .................................................................................................................. 17
2.5.1 AFO Analysis ....................................................................................................................... 17
2.5.2- Knowledge gained from existing product analysis ............................................................ 18
2.6- Time Management ............................................................................................................... 19
2.6.1- Gantt chart ........................................................................................................................ 19
2.6.2- Critical Path Analysis ......................................................................................................... 20
2.7- Technology Research ............................................................................................................ 22
2.7.1- Force Sensors .................................................................................................................... 22
2.7.2- Initial Test .......................................................................................................................... 23
2.7.3- Foot Force Sensor Test ...................................................................................................... 24
2.7.4- Accelerometers & Gyroscopes .......................................................................................... 26
2.7.5- Arduino Boards .................................................................................................................. 26
2.8- Conclusion ............................................................................................................................ 26
Chapter 3- Design Considerations .................................................................................... 27
3.1- Introduction .......................................................................................................................... 27
3.2- Ergonomics ........................................................................................................................... 27
3.2.1- Gait Abnormalities caused by drop foot ............................................................................ 28
3.3- Anthropometrics .................................................................................................................. 29
3.3.1- Conclusion ......................................................................................................................... 31
3.4- Standards and Regulations ................................................................................................... 31
3.5- Intellectual Property (IP) ...................................................................................................... 32
3.6- Product Design Specification (PDS) ...................................................................................... 33
3.7- Conclusion ............................................................................................................................ 34
Chapter 4- Design Process ............................................................................................... 35
4.1- Introduction .......................................................................................................................... 35
4.2- Design Methodology ............................................................................................................ 35
4.2.1- Chosen Design Method ..................................................................................................... 35
4.2.2- Design and Development Route ........................................................................................ 37

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4.3- Shell & Function Concepts .................................................................................................... 38
4.3.1- Concept 1 .......................................................................................................................... 38
4.3.2- Concept 2 .......................................................................................................................... 39
4.3.3- Concept 3 .......................................................................................................................... 40
4.3.4- Concept 4 .......................................................................................................................... 41
4.3.5- Concept 5 .......................................................................................................................... 42
4.3.6- Concept 6 .......................................................................................................................... 43
4.5- User rated Combinex- Concept Evaluation .......................................................................... 44
4.6- Expert rated Combinex- Concept Evaluation ....................................................................... 45
4.8- Conclusion: User feedback and evaluation of initial concepts ............................................. 45
Chapter 5- Design Development ...................................................................................... 46
5.1- Introduction .......................................................................................................................... 46
5.2- Ankle Hinge Development .................................................................................................... 46
5.3- Ankle stopper & Fastening ................................................................................................... 47
5.3- Pressure Sensor Development ............................................................................................. 48
5.3.1- Force Sensor Testing ......................................................................................................... 48
5.3.2- Electrical Component Housing .......................................................................................... 49
Chapter 6- Materials and Manufacture ............................................................................ 50
6.1- Introduction .......................................................................................................................... 50
6.2- Material Selection Method ................................................................................................... 50
6.2.1- AFO Main Body .................................................................................................................. 50
6.2.2- Sole Cover material selection ............................................................................................ 51
6.2.3- Conclusion ......................................................................................................................... 51
6.3- Method of Manufacture ....................................................................................................... 52
6.3.1- Critical review of methods ................................................................................................. 52
6.3.2- 3D Scanning ....................................................................................................................... 53
6.3.3- CNC Machining .................................................................................................................. 53
6.3.4- Vacuum Forming ............................................................................................................... 53
6.3.5- Set size model .................................................................................................................... 54
6.4- Parts List / Costing ................................................................................................................ 55
6.4.1- Introduction ....................................................................................................................... 55
6.4.2- Materials & Components .................................................................................................. 55
6.5- Conclusion ............................................................................................................................ 55
Chapter 7- Final Design Solution ...................................................................................... 56
7.1- Introduction .......................................................................................................................... 56
7.2 RecuperGAIT™ - Smart Foot Drop Recovery AFO .................................................................. 56
7.3- RecuperGAIT™ - Smart Foot Drop Recovery AFO- Design Features ..................................... 56
7.3.1- Introduction ....................................................................................................................... 56
7.3.2- Smart Technology .............................................................................................................. 57
7.3.4- User Interface .................................................................................................................... 57
7.4- PDS Evaluation ...................................................................................................................... 59
Chapter 8- Conclusion & Further Work ............................................................................ 60
8.1- Further Work ........................................................................................................................ 60
References ...................................................................................................................... 61

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List of Figures:
Figure 2.1- Drop foot diagram
Figure 2.2- Tibialis Anterior Muscles & Peroneal nerve (Inner Body, 2015)
Figure 2.3- Critical Path Analysis flow diagram
Figure 2.4- Heel force test result
Figure 2.5- SingleTact Pc Digital Setup
Figure 2.6- Diagram of parts of foot tested (Author)
Figure 2.7- Foot force sensor test result graph for participant 3 (Author)
Figure 2.8- 450 N Force sensor testing
Figure 3.1- Gait Cycle Diagram
Figure 4.1- Design Methodology (Author)
Figure 4.2- Design and Development Route (Author)
Figure 4.3- Concept 1 initial sketches
Figure 4.9- User rated Combinex graphs
Figure 4.10- Expert rated Combinex graphs
Figure 5.1- Ankle Hinge render (Author)
Figure 5.2- Ankle stopper & fastening render (Author)
Figure 5.3- Pressure sensor matrix render (Author)
Figure 5.4- Electrical Component Housing render (Author)
Figure 6.1- 3D Scanning leg for bespoke AFO
Figure 6.2- Placing PP sheet over mould
Figure 7.1- Final Design Render (Author)
Figure 7.2- User app interface
Figure 7.3- Render of final AFO

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List of Tables:
Table 2.1- Causes of drop foot
Table 2.2- Treatments for Drop Foot
Table 2.3- Symptom of stroke survey- taken at Nottingham Stroke Club
Table 2.4- Weighted importance of AFO features
Table 2.5- Existing product research summary
Table 2.6- Gantt chart
Table 2.7- Critical path analysis breakdown
Table 2.8- Force Sensor Analysis
Table 2.9- Foot force sensor participants
Table 2.10- Arduino Board comparison analysis
Table 3.1- Gait abnormalities caused by drop foot
Table 3.2- Ankle motion abnormalities caused by drop foot
Table 3.3- Anthropometric data for British Adults Aged 19 to 65 Years
Table 3.4- Anthropometric data for British Adults Aged 65 to 80 Years
Table 3.5- Set sizes for AFO
Table 3.6- IP analysis
Table 3.7- PDS List of Headings
Table 3.8- Product Design Specification
Table 4.1- User rated Combinex results for Shell and Function concepts (Author)
Table 4.2- Expert rated Combinex for Shell and Function concepts (Author
Table 6.1- Material analysis of main body
Table 6.2- Sole cover material analysis
Table 6.3- Critical review of manufacturing methods
Table 6.4- Materials & components cost and weight
Table 6.5- Total one off manufacture cost

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Glossary of Terms:

• Bio-feedback: biological signals that are fed back to the patient in order for the
patient to develop techniques of manipulating them
• Dorsiflexion: movement at the ankle joint that points the foot upwards.
• Drop foot: Partial or total inability to dorsiflex the foot, causing toes to drag on the
ground while walking.
• Gait: the manner or style of walking
• Plantar flexion: movement at the ankle joint that points the foot downwards.

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Chapter 1- Design in Context

1.1- Introduction
The aim of this project was to address an issue that millions of individuals have to deal with
worldwide, devise an initial idea and create a fully functioning and commercially viable
product which is ready for market. The following brief was chosen in order to improve the
speed and quality of rehabilitation for people suffering from drop foot, a symptom of
several neurological disorders.

Appendices in this document have been referenced throughout and should be referred to in
order understand the research conducted.

1.2- Background
Drop foot is a relatively simple name for a potentially complex problem. It can be defined as
the inability to lift the front part of the foot, causing the toes to drag along the ground while
walking (Pritchett, 2016). Drop foot can be a consequence of injury to the muscles in the
front of the lower leg, injury to certain nerves, brain injury, stroke and even diabetes
(Douglas, 2005). Stroke is the largest cause of complex disability in the UK, with over half of
all the 1.2 million stroke survivors being left with this drop foot. (Stroke Association, 2016)

In order to prevent toes from dragging, people with drop foot are prone to lifting their knee
higher than normal or they may swing their leg in a wide arc (Retin, 2016). These coping
mechanisms can hinder recovery as a natural gait pattern is not being used. This can lead to
prolonged periods of rehabilitation, and therefore this project will explore the ways in which
the quality of rehabilitation can be improved by providing bio-feedback data to the user.
The design of a novel ankle foot orthosis will provide opportunities for the data to be
monitored and analysed by the user and their physiotherapist in order to adapt their
rehabilitation regime to their specific requirements. This information will increase the speed
of recovery which is a huge benefit to the patient and the overstretched health service. This
identifies a clear and tangible clinical need for this product.

1.3- The Brief
The brief was to design a new ankle foot orthosis that is adaptable to wearers wanting
assisted dorsiflexion and restricted plantarflexion, providing a natural and supported gait
pattern for the wearer. Dorsiflexion is the upwards movement of the front of the foot,
whereas plantarflexion is used to describe the downwards movement of the foot as it
passes 90 degrees. The product designed must also provide live biomechanical feedback
data, through the inclusion of smart technologies, in order to provide the patient and their
physiotherapist with information used to adapt and improve gait pattern during
rehabilitation.

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Essential Design Considerations:
• AFO must gather real time biomechanical data
• Data must be effectively displayed to user and physiotherapist
• Must not encumber user
• Must be affordable
• Offer technologies and features not currently on the market

1.4- Aims and Objectives

1.4.1- Project Aim
The aim of this project is to reduce the time spent by drop foot sufferers in rehabilitation,
through the development of a novel pressure mapping orthosis.

1.4.2- Product Aim
The aim of the product is two-fold, it must:
• Provide the user with biomechanical feedback in the form of a visual pressure map
and gait analysing data.
• Provide adequate support to the user when walking on flat, declining and inclining
ground.

1.4.3- Project Objectives
• Undertake primary and secondary research into symptoms of stroke and the
corresponding rehabilitation to identify a problem.
• Conduct market research on existing products and assess appropriate costing and
implementation factors.
• Identify a range of medical conditions that would benefit from an AFO that
accommodates dorsiflexion and plantarflexion.
• Conduct research alongside rehabilitation specialists and potential users to inform the
design process and product development.
• Undertake concept development and prototyping to demonstrate a practical output.

1.5- Conclusion
Research will be conducted looking to identify a clinical need for an adaptable Ankle
Foot Orthosis that provides biomechanical feedback to the user and the physiotherapist
that can be analysed and used to adapt rehabilitation exercises and targets. The aims
and objectives that were identified used were throughout to ensure the project
remained structured and true to its original goals.

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Chapter 2 – Research Methodology

2.1- Introduction
Chapter 2 will outline the various elements of primary and secondary research undertaken
as throughout the project. As well as detailing research methodologies utilised to create a
suitable design solution.

2.2- Research Methodology
An effectively utilised research methodology can considerably improve the quality of any
project. Appendix C outlines the different methods that were explored and scrutinised.
Primary research in the form of semi-structured and open interviews proved very effective,
when used in conjunction with one another, to provide detailed qualitative data about the
user’s needs.

Whilst qualitative methods of research, including user and expert interviews, were applied
to gain rich data from the user, quantitative methods, such as surveys and user weighted
matrices, were undertaken to gain numerical data that would strengthen the case of this
project further.

In order to ensure that the project’s aims and objectives were met comprehensively, a user
centred research approach was utilised. The use of primary research has proved very
effective when it comes to defining the project brief and aims in the early stages of the
project. Secondary research has provided the theoretical backing to the projects aims and
objectives, offering important information that supported the product design specification
alongside user feedback and evaluation.

Below are the research methods used during the discovery stage of the project:

• Drop Foot Rehabilitation statistics
• Existing product analysis
• Patent searches
• Identify gap in market
• Observe user walking habits
• Gain information from physiotherapist
• Research anatomy and physiology
• Ergonomics and anthropometrics

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2.3- Designing for Disability

Due to the improvements in technology and medical knowledge in the last century,
demographic trends are showing that the number of over-60 group will continue to increase
in Europe, North America, Australia and Japan, this will have significant implications on the
design world (Schrott, 2009).

The conditions that cause drop foot, such as stroke and motor neurone disease, mainly
affects people in their 60s and 70s, however they can affect adults of all ages. This device
will reduce the needless time spent going to the physiotherapist, thus enabling them to
spend their time more effectively on other patients.

There are approximately 152,000 strokes in the UK every year, which equals more than one
every five minutes. There are approximately 1.1 million stroke survivors in the UK, more
than half of all stroke survivors are left with a disability making stoke a leading cause of
adult disability (Stroke Association, 2013).

2.3.1- Drop Foot

Drop foot can be defined as a gait abnormality associated with weakness or paralysis of the
muscle groups involved in in lifting of the foot during walking. Dorsiflexion is the movement
of the toes up towards the front of the shin as a result of the tibialis anterior muscle
shortening. With their weakened muscles the individual is prone to drag their foot along the
floor or swing their whole leg from the hip. These gait abnormalities can increase the
likelihood of falling down and causing further injuries. (Pritchett, 2016). This product will
improve the quality of life for those suffering with drop foot as a more effective
rehabilitation will allow them to become active and not develop other conditions as a result
of a sedentary lifestyle. (Hoyle, B, 2016)

Figure 2.1 - Drop foot diagram

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Figure 2.2- Tibialis Anterior Muscles & Peroneal nerve (Inner Body, 2015)

Drop foot is usually a symptom of a greater problem and not a disease in itself. Thus in
order to solve the problem it is essential to address particular features of the individual
condition that is causing it. (Kerkar, 2015) There are three main causes that lead to foot
drop:

Nerve Injury

Muscle disorder

Brain or Spinal disorders

The peroneal nerve is the
nerve that communicates to
the dorsiflexor muscles that
lift the foot. Damage to the
peroneal nerve is the most
common cause of foot drop
and is caused by sport
injuries, hip or knee
replacements surgery, leg
casts, or child birth.
A condition that causes
muscles to weaken or
slowly deteriorate can also
lead to foot drop. The
disorders may include
muscular dystrophy,
amyotrophic sclerosis and
polio.

Neurological conditions can
also lead to foot drop.
Conditions such as stroke,
cerebral palsy and multiple
sclerosis are common
causes.

Table 2.2- Causes of drop foot
As shown in the table above, drop foot is not merely a symptom of a stroke. Damage to the
peroneal nerve is the most common cause of drop foot, this highlights that the risk of
developing drop foot is not exclusive to sufferers of brain or spinal injuries, increasing the
prevalence of the condition significantly.

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2.3.2- Drop Foot Rehabilitation

A patient’s drop foot rehabilitation regime is dependent on their particular condition that
has caused the symptom of drop foot. Drop foot is treated by dealing with the underlying
condition causing it. In some cases, drop foot is a permanent condition that cannot be
cured, however many people are able to make a full recovery. (Stroke Focus, 2017)

There are four main treatments that can aid drop foot recovery:

Treatments Description
Ankle Foot Orthosis
(AFO)

Wearing an AFO that supports the patient’s foot in a normal
position is a common treatment of foot drop. The device is used to
stabilise your foot and ankle, holding the front part of your foot up
while walking. There are multiple variations of the AFO design,
including rigid and hinged ankle joints, allowing the individual to
choose one suitable to their personal needs.

Physical Therapy

Physiotherapy is the primary treatment for foot drop and if used
correctly will strengthen the foot, ankle and lower leg muscles. This
will be prescribed in addition to the other treatment methods as it is
essential element of rehabilitation.

Functional Electrical
Stimulation (FES)

If your foot drop has been caused by peroneal nerve damage then
FES may be a suitable treatment. It involves a small device that can
be worn or surgically implanted just below the knee that will send
an electrical stimulation to the nerve, causing the anterior tibialis
muscle to contract and lift the foot while walking.

Surgery

If a pinched nerve or herniated disc has caused foot drop then
surgery would be the suitable treatment method in order to repair
tendons or muscles if they were damaged. In severe cases surgery
may be used to fuse ankle and foot bones in order to improve a
patient’s gait.

Table 2.2- Treatments for Drop Foot

Refer to Appendix G for further research into Drop foot

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2.4- Interviews-Thematic Analysis
The interviews were used to provide vital feedback of key problems of the AFOs that were
being used and how best to approach these issues. In order to interpret the qualitative data
provided by interviewing users and medical experts, thematic analysis and coding of the
interviews was undertaken. This provided a means of quantifying and fully analysing the
large amount of information found, highlighting recurrent design themes.

Refer to Appendix B for Interviews and Thematic Analysis

2.4.1- Evaluation of Interviews

2.4.2- User Feedback- Nottingham Stroke Association - Focus Group

Contact was made with the Nottingham Stroke Association (NSA), a social club that provides
a place for stroke survivors to meet other people living with the symptoms of the condition.
The club holds weekly meetings where the members can take part in an exercise class, with
the aim of aiding their rehabilitation. The members had a broad variety of physical
symptoms from their strokes. A survey was conducted in order to establish the most
common symptoms amongst the group. The results are shown below:

Symptom Frequency Rehabilitation
Drop Foot 18 AFO, Surgery,
Physiotherapy
Arm paralysis 15 Physiotherapy
Leg paralysis 13 Physiotherapy
Facial Paralysis 10 Surgery, Physiotherapy
Slurred Speech 3 Speech therapy
Table 2.3- Symptom of stroke survey- taken at Nottingham Stroke Club
Drop Foot was the most frequently suffered condition amongst the group, with 18 of the 25
survivors suffering with the condition. Shown below are some of the key quotes from the
semi-structured interview:

“My AFO makes it very difficult for me to walk uphill. I have to swing my leg round in
an unnatural motion.”
“Getting in to my AFO is very difficult as I have limited mobility in my arms as well as
my legs. I have to get my wife to help me put it on.”

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A small survey was conducted with six of the NSA member regarding the features they
hold in highest regard when choosing an AFO. They were asked to score each features
level of importance, with 1 being not important and 5 being very important. Some
potential features, bio-feedback & aesthetics, were suggested to the partipants.
Name, Age, Severity of Stroke
Sabel,
40, Mild
TBI
James,
31,
Severe
TBI
Glenn,
57,
Severe
Mary,
45,
Mild
TBI
Kerry,
63,
Mild
John,
49,
Severe
Total

Comfort

4 5 4 5 3 3 24
Ease of use

5 3 3 5 4 3 23
Safety 4 4 5 5 3 4 25
Cost 5 2 4 2 1 5 19
Bio-
Feedback
4 5 2 5 5 3 24
Enjoyment 3 1 2 4 5 3 18
Aesthetics 4 3 3 5 5 3 23
Table 2.4- Weighted importance of AFO features
The result displayed that the comfort, safety and bio-feedback were the most important
features that were considered when choosing their AFO. This user feedback proved vital
in defining this project and was used to develop several design features.

2.4.3- Expert Feedback
The main concern from the physiotherapists and doctors was that current products did not
feature any technology that could be used to provide bio-feedback on the patient’s gait
performance. Having live, trackable data could be used by the physiotherapist to alter
rehabilitation regimes or prevent further injury from abnormal gait patterns. This, in turn
will have long term effects on the use’s quality of life, enabling a more active and enjoyable
lifestyle.

‘Having the patient perform relevant exercises for repetitions, setting them goals to
achieve in a set time frame and increasing their workload when they outgrow the
exercises is an excellent means of rehabilitation.’

‘To improve an abnormal gait pattern, the length of the stride, the frequency of the step
and the range of mobility in the affected limbs should all be monitored. If those criteria
are increasing then the patient is responding well to the treatment.’

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-Dr Cleveland Barnett

‘A pressure map of the stroke sufferer’s foot would enable the physiotherapist to detect
what part of the foot is taking the brunt force during walking, they would then be able to
alter their patient’s rehabilitation methods to make them more suitable to their individual
goals.’
- Pip Logan

(For full interview with Pip Logan see Appendix B.3)

‘A lot of patients dislike coming in to the hospital or rehabilitation centre, it gets in the
way of their day-to-day life, especially if they are in and out regularly. Providing a means
of setting task and accessing their progress remotely would make the process more
enjoyable for a lot of people.’
- James Taylor

(For full interview with James Taylor see Appendix B.7)

2.4.4- Conclusion of Interviews

These interviews and focus groups have proved invaluable to the direction in which the
design developed. The problems addressed above, along with the requirements provided
the relevant information to put the Product Design Specification together.

There are several major concerns for individuals suffering from drop foot. These interviews
highlighted the following key issues that must be addressed in order to benefit the patient
ensure the success of the product:

• Recovery time is too long- patients lose interest when they cannot see results.
• Patients need to see their performance visually- on an app on their phone.
• Getting in to the AFO is difficult for some individuals with affected mobility.
• Walking up hill is compromised by pre-existing AFOs.

These all highlight the clinical need for this particular product.

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2.5- Existing Products

Several existing products were analysed based on criteria and design specifications
identified by the user and experts during the interview phase of the project.

2.5.1 AFO Analysis

From the research conducted on existing products, it was found that no pre-existing AFO
provided bio-feedback data to the patient, it was also discovered that the majority

Features
Reflex AFO

Complete
Care AFO

Extrastrong
Prolite AFO

ToeOff
Dynamic AFO

BraceMasters
AFO

Ergonomic
Adjustability
Weight

Off-shelf sizes
Bespoke to
user
Moisture
abortion
Easy to
disinfect

Chemical
resistance
Number of
parts 3 1 2 4 10
Ease of
cleaning
Accessibility
Strength
Comfort
Bio-Feedback
Table 2.5- Existing product research summary

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2.5.2- Knowledge gained from existing product analysis
In conclusion, after researching the characteristics of existing AFOs, a number of issues
which could be improved have been identified. This project must address these issues in
order to ensure a successful final outcome. The key themes that shaped the final design are
as follows:

• Bio-Feedback: the product must provide useful biomechanical data to the user.
• Accessibility: the product must be easy to put on for those with limited mobility.
• Adaptability: the product must be able to be adapted to multiple terrains.

(Refer to Appendix E for full Existing Product Analysis)

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2.6- Time Management
2.6.1- Gantt chart

In order to ensure that the project was successfully completed on time and in full, a live
Gantt chart was created. This provided an adaptable project time plan which included
milestones and specific goals.

Stages of primary and secondary research were prolonged as the project developed, several
new areas of research were added. Research into force sensors and accelerometers was
added into the ‘technology’ section of Secondary Research. This was added after the
interviews where bio-feedback was identified as a vital feature to this product. Research
conducted into gait analysis and the anatomy of drop foot at the beginning of the project
proved useful as the project progressed and developed.

(Refer to Appendix D.1 for detailed full Gantt chart)

Table 2.6- Gantt chart

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2.6.2- Critical Path Analysis
In order to further ensure that time frames were kept to, a critical path analysis was created
to determine realistic and maximum completion times for the tasks. This provided a clear
guideline for the tasks that needed to be completed in a specific order and timeframe

(Refer to Appendix D.2 for Critical Path Analysis)

Task Activity Order
Duration (in
weeks)
A Initial Research Starting Activity 4
B Primary When A is complete 4
C Secondary When B is complete 4
D Aims & Objectives
When B & C is
complete 1
E PDS When D is complete 2
F Concepts When E is complete 4
G Development of Concepts When F is complete 6
H Thesis When G is complete 6
I Prototyping
When G & H is
complete 6
J Pressure Sensing Testing
When G & H is
complete 2
K Functionality Testing
When G & H is
complete 2
L Final Outcome
When I, J & K is
complete 1
Table 2.7- Critical path analysis breakdown
This planning process provided set deadlines by which each separate task had to be
completed by, allowing the author to structure their time as efficiently as possible. As
shown in tasks B & C and I, J & K some tasks could be completed concurrently. Primary and
secondary research was conducted simultaneously in order to gain a rounded knowledge of
the subject, whereas the prototyping and pressure sensor and functionality testing were
conducted together as finding complimented each other well.

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B
4
1
0 A
2
4
3
8 D
4
9 E
5
11
0 4 4 C 8 1 9 2 11
4
F 4

H 6
6
15
I 15
6
G 6
9
21 J
37 2
8
15 H
7
21
27 6 21
K
2
Figure 2.3- Critical Path Analysis flow diagram
Key:
Activity
Earliest Finish Time
(weeks)
Latest Finish Time
(weeks)

P a g e | 22

2.7- Technology Research
2.7.1- Force Sensors
Capacitive force sensors

Force sensitive
resistors

Force Sensor Matrices

Provider SingleTact (SingleTact
Standard Sensors,2018)
HALJIA (Custom built)
Price £££ ££ £
Range Unknown Specific Customisable
Measuring
unit
Newton’s Grams Customisable
Uses/
Strengths
• Plug and play data
acquisition
software
• Useful for initial
assessment to
prove the concept
• Very thin
• Provides
accurate
measurements
of force
exertion
• Can be made
to cover the
whole sole
plate.
• More cost
effective than
buying
multiple
sensors and
connecting
them

Limitations Extra step of calibration
needed for
measurements
Does not convert
analogue to digital-
requires board add
on.
-Requires further
calibration
-Added manufacturing
steps
Table 2.8- Force Sensor Analysis

From the analysis of different types of force sensors, it was established that creating a
custom force sensor matrix for this product would be the most suitable option. The
following features outline why it is the most feasible choice:

• It is the most cost-effective solution when compared with the other listed options.
• They can be incorporated into fabrics and other materials, making them ideal for
comfort on the sole of the foot.
• With a force sensor matrix, the parameters of the user’s foot will not affect results as
it will be extracting data from the entire sole of the foot and not a set position.

P a g e | 23

2.7.2- Initial Test
This initial assessment determine that a 450 N sensor was required to record useful data on
the range of force exerted by a step.

Figure 2.4 – Heel force test result

Figure 2.5- SingleTact Pc Digital Setup (SingleTact, 2016)
(Refer to Appendix F.1.3 for full initial test results)
161.71875
0
20
40
60
80
100
120
140
160
180
1
13
25
37
49
61
73
85
97
109
121
133
145
157
169
181
193
205
217
229
241
253
265
277
289
301
313
325
337
349
361
373
385
397
409
421
433
Heel Force Test- Participant 2

P a g e | 24

2.7.3- Foot Force Sensor Test

A secondary test was completed looking in to the range of pressure exerted by different
parts of the foot.

Figure 2.6- Diagram of parts of foot tested (Author)

Participant Age
Shoe size Weight
(kg) Height (m) BMI Gender
1 27 11 70 1.81 22.1 Male
2 23 5 60 1.7 20.8 Female
3 21 9 76 1.83 24.4 Male
4 23 7 65 1.65 23.2 Female
5 22 9 74 1.78 24.5 Male
6 22 9 84 1.88 26.3 Male
7 23 10 100 1.82 32.3 Male
8 34 9 78 1.65 27.8 Male
9 25 8 57 1.69 19.8 Male
Table 2.9- Foot force sensor participants

Part of
Foot
A Big toe
B Inner ball
C Outer ball
D Lower ball
E Heel
A
B
C
D
E

P a g e | 25


Figure 2.7- Foot force sensor test result graph for participant 3 (Author)

(Refer to Appendix K.5 for full force sensor test)

Figure 2.8- 450 N Force sensor testing

125.6835938
195.1171875
72.94921875
77.34375
-50
0
50
100
150
200
250 1
32
63
94
125
156
187
218
249
280
311
342
373
404
435
466
497
528
559
590
621
652
683
714
745
776
807
838
869
900
931
962
993
1024
1055
1086
1117
1148
P3
A B C D E

P a g e | 26

2.7.4- Accelerometers & Gyroscopes
Both an accelerometer and a gyroscope have been integrated into this design. The
accelerometer will provide bio-feedback regarding the user’s daily step count. The
gyroscope will assess the user’s gait and be used to display improvements that can be made,
on a smartphone application. Two Arduino boards with integrated accelerometers and
gyroscopes were analysed against the Feather 32u4 Bluefruit LE which does not feature an
accelerometer. (Difference Between, 2016.)

(Refer to Appendix F.3 for Accelerometer and Gyroscope analysis)
2.7.5- Arduino Boards
DFRobot Curie Nano
– Anano
Genuino/Arduino
101 Board

(DFRobot, 2017)
tinyTILE - Intel Curie Dev
Board

(TinyTILE, 2018.)
Feather 32u4 Bluefruit
LE

Features -9 DOF sensor
(accelerometer,
gyroscope, compass)
-Bluetooth Low
Energy (BLE)
-Built in 6 DOF
(accelerometer,
gyroscope)
-BLE
-No accelerometer
-BLE
-Integrated battery
charger & connecter
Processing
speeds
x86 (Quark) – 32MHz
32bit ARC – 32Mhz
x86 (Quark) – 32MHz
32bit ARC – 32Mhz
ATmega32u4 – 8MHz
Dimension
s (mm)
43mm x 23.5mm 35mm x 26mm 51mm x 23mm x 8mm
Weight (g) 6 - 5.7
Price £53.94 £53.89 £29.95
Table 2.10- Arduino Board comparison analysis (Cool Components, 2018)
From analysing these three Arduino boards the most suitable appears to be the Feather
32u4 Bluefruit LE due to it being the least costly and the integrated battery charger feature.
However, further tests will be carried out into these boards with a particular focus on
battery life and processing speed.
2.8- Conclusion
This chapter has provided key issues associated with drop foot and existing AFOs, enabling
the initiation of the ideation stage of the project. This secondary research proved vital in the
subsequent interviews conducted with foot drop sufferers and experts in this condition.
Several design considerations such as the type of sensors to be used and the Arduino board
suitable for the product’s requirements were analysed and chosen during this process.

(Refer to Appendix F.3 for full Arduino board analysis)

P a g e | 27

Chapter 3- Design Considerations

3.1- Introduction
The design considerations will build on the research and knowledge attained through
interviews and existing product analysis, and will focus on ergonomics, anthropometrics,
intellectual property, product standards and the user weighted Product Design
Specification.

3.2- Ergonomics
Analysis into the ergonomic repercussions of designing a smart AFO was undertaken. This
ensured that the final product would work efficiently and comfortably within the user’s daily
schedule.

Figure 3.1 shows the multiple phases of a normal gait cycle. This was then compared with
the gait cycles of those suffering from drop foot.

Figure 3.1- Gait Cycle Diagram (Gait Cycle, 2017)
Further analysis and testing will be done using the normal gait cycle in order determine the
configurations of the gyroscope and accelerometer. This is used as a standard by which the
user’s gait can be compared.

P a g e | 28

3.2.1- Gait Abnormalities caused by drop foot

Listed in the table below are the multiple forms of gait abnormalities caused by drop foot.

Abnormality Steppage gait

Waddling gait

Swing-out gait
Diagram

Description The most common
symptom of foot drop
is characterised by
raising the thigh in an
exaggerated way as if
climbing the stairs, in
order to ensure the
toes do not strike the
ground during the
swing stage of the
gait.

Waddling gait is a gait
abnormality where the
affected patient walks
like a duck. Their trunk
sways from side to side
as they walk causing a
weakness in the
proximal muscles of the
pelvic girdle, leading to
weakening of the
gluteus muscles.

Swing-out gait can be
defined as swinging the
affected leg in an arc in
order to prevent the
toe scraping on the
ground.

Table 3.1- Gait abnormalities caused by drop foot (Study Blue, 2014)

This AFO design will normalise these gait abnormalities and reduce the time spent in
rehabilitation by providing the user with useful bio-feedback regarding their walking
pattern. Challenges and achievements will be set in the application in order to provide the
user with critical feedback when performing an abnormal gait pattern, followed by positive
reinforcement and exercise suggestions that is tailor-made to their case of drop foot. This
data stream can be accessed and analysed by the physiotherapist to design specific
rehabilitation plans that suit the individual’s needs.

The integrated gyroscope and accelerometer will provide bio-feedback to the user regarding
their gait abnormality. This will be presented in an understandable format, both visually and
audibly, on a smartphone application.

P a g e | 29

Shown below are the ankle motion abnormalities that appear in cases of drop foot. The
levels and severity of pronation will be recorded through the force sensors present in the
sole of the AFO and sent to the app via Bluetooth. Here they will display a ‘heat map’ of
which parts of the foot are withstanding the most pressure during periods of activity
throughout the day. Targets and achievements can be set in order to encourage the user to
use a normal ankle motion.

Ankle motion Pronation Supination
Diagram

Description Ankle pronation refers to the
inward roll of the foot during
walking. A moderate amount
of pronation is required for
normal ankle function.
However, damage can occur
during excessive pronation.

Supination is the opposite of
pronation, occurring when the ankle
rolls outwards, and placing excessive
pressure on the outer edge of the foot.

Table 3.2- Ankle motion abnormalities caused by drop foot (Garmaon Health, 2003)
The user will be provided with a heat map displaying what part of their foot is under the
most force during a step. They will then be offered exercises that can help improve their
pronation or supination. Reducing pronation and supination is beneficial as the conditions
can lead to further ankle and foot complications and injuries.

(Refer to Appendix H.1 for ergonomics research)

3.3- Anthropometrics
The utilisation of anthropometric data was particularly vital in this project as it would
dictate the form and size of the product. It was essential to analyse the target demographic
user’s size, range of motion and overall weight in order to determine the size and cost of the
components.

In order to correctly identify the size of the product, foot and leg measurements were taken
from Bodyspace- Stephen Pheasant 1996.

Additional measurements were taken on a sample of target users, in order to aid to
calculate sizes of parts during the development of the product.

P a g e | 30


Men Women
Dimension (mm &
kg)
5th

%ile
50th

%ile
95th

%ile
Standard
Deviation
(SD)
5th

%ile
50th

%ile
95th

%ile
SD
Foot Length

240 265 285 14 215 235 255 12
Foot Breadth 85 95 110 6 80 90 100 6
Popliteal Height

395 440 490 29 355 400 445 27
Body weight 55 75 94 12 44 63 81 11
Table 3.3- Anthropometric data for British Adults Aged 19 to 65 Years (Pheasant, 2005)

Men Women
Dimension
(mm)
5th
%ile 50th

%ile
95th

%ile
SD 5th

%ile
50th

%ile
95th

%ile
SD
Foot
Length
235 255 280 13 210 230 250 12
Foot
Breadth
85 95 105 6 80 85 95 5
Popliteal
Height
385 425 470 27 355 395 440 26
Table 3.4- Anthropometric data for British Adults Aged 65 to 80 Years (Pheasant, 2005)

P a g e | 31

3.3.1- Conclusion
This data indicates that there is a wide range of foot dimensions. Therefore, several sizes
will be required in order to meet the needs of male and female sufferers of drop foot. The
range of dimensions suggested that a small, medium, large and extra-large size would be
required to meet the user’s requirements. Shown below is the set sizes to be used for this
particular AFO.

Size Foot Length (mm) Foot Breadth (mm) Brace Height (mm)
Small 235 80 265
Medium 250 85 285
Large 270 95 330
X-Large 300 110 390
Table 3.5- Set sizes for AFO

As the size and shape of every individuals foot, ankle and leg is different, having multiple set
sizes provide the most accurate fit. A more suitable method would be to create a cast of the
user’s foot and leg and use that to produce a custom fit AFO. This would be more accurate
and would provide a tailored fit that is comfortable for the user. This would reduce the risk
of further injuries arising due to ill-fitting AFO’s. Custom making the AFO also ensure the
sensors are calibrated to the specific individual’s foot.

(Refer to Appendix H.4 for details of Anthropometric data analysed)

3.4- Standards and Regulations
The design standards for orthotic and prosthetic medical products were examined
thoroughly in order to aid the design process. It is paramount that the product meets or
exceeds the standards set by the British Standards Institution (BSI), International
Organisation for Standardization (ISO). FDA approval standards for drop foot othosis will
also be considered for potential entry into the U.S. market. (FDA, 2011.)

Standards for medical devices were also analysed to ensure the product was fit for market.
(Gov.uk, 2014)

(Refer to Appendix I for full research on Standards and Regulations)

P a g e | 32

3.5- Intellectual Property (IP)
Multiple patent searches were carried out using Google patent search to identify conflicting
IP that may infringe the copyright of a new product design of an AFO featuring pressure
sensor feedback.

The intellectual property search revealed that there were no existing patents for an AFO
with integrated pressure sensors providing bio-feedback data. There were patents found on
pre-existing ankle flexure joints, manufactured by Tamarack Habilitation Technologies that
was considered and analysed for viability during the design process. The final product
features this ankle hinge component as they are the current benchmark of ankle flexure
joints.

Patent No. Image Relevance
US 20130296741 A1
(Wiggin et al, 2013)

Vibrating bio feedback
alerts user of their gait
pattern, no connection
smart phone application.
US 7678067 B1
(Smith, 2010)

Drop foot assisting
mechanism aids normal
gait.
US D385358 S

(Carlson, 1997.)

Benchmark in ankle flexure
hinge joints.

Table 3.6- IP analysis

(Refer to Appendix I for existing patent results and example of patents)

P a g e | 33

3.6- Product Design Specification (PDS)
From the varied and extensive research carried out, a product design specification was
created. The PDS outlines all the necessary requirements and constraints that must be
considered during the design of the final outcome.

PDS Headings
Performance Size
Ergonomics Quality/Reliability
Life in Service Maintenance
Safety Product Cost
Weight Documentation
Customer International Standards
Materials Patents
Testing Environment
Table 3.7- PDS List of Headings
The PDS was developed using Pugh’s model. The requirements in each heading were
identified and evaluated by the user and a physiotherapist.

PDS Heading Description
Performance • The product should improve gait for people with drop foot by
supporting their foot and ankle.
• Must allow dorsiflexion in order to support a natural gait
pattern.
• Must include pressure sensors to detect abnormality in the
wearer’s walking pattern.
• Must include an accelerometer and gyroscope to detect the
movements of the wearer (E.g. Number of steps, gait
pattern).
Ergonomics • Must provide data which can be used by a physiotherapist to
analyse the user’s gait.
• The product must be easy to put on for users with limited
mobility.
• Must be comfortable and supportive, providing adequate
stability for ankle.
Weight • Unit must weigh between 150g - 400g in order for it to be as
unobtrusive to the user’s walking pattern as possible.
Materials • Must have a high impact resistance.
• Existing materials already utilised such as thermoplastic
polymers, polypropylene & polyurethane, and carbon fibre
should be considered in the design.

P a g e | 34

• Lightweight and durable materials will be utilised.
Size • Must be able to manufacture to set sizes for men and women
in small, medium and large.
• Must be able to manufacture a custom fit AFO for user.
Quality/Reliability • 2m drop test should not affect the structural integrity of the
AFO.
• Should last 5 years or until user warrants a new fit or size, or
until medical standards are changed (usually every 3-5 years).
Maintenance • Material must be able to be sterilised to prevent the risk of
infection spreading if an off the shelf unit is resold and worn
by another user.
• Rechargeable batteries power systems electronics
Product Cost • AFO must cost no more than £40 to manufacture.
• Should retail around £250 to £300.
Table 3.8- Product Design Specification
(Refer to Appendix J.2 for full Product Design Specification)

3.7- Conclusion
This chapter identified several considerations in regard to the ergonomics, anthropometrics,
IP and standards that must be adhered to during the design and development stage. This
information will be used as guidelines during the concept ideation and development stage
of the project.

P a g e | 35

Chapter 4- Design Process

4.1- Introduction
In order to develop a functional and useful product it was essential to gain as much
information as possible. The section below outlines the research undertaken into various
areas regarding the product.

4.2- Design Methodology
It was essential that all decisions regarding the development and design of the product were
done with the needs of the user in mind, retrieving feedbacks at regular intervals during the
design process. This ensured the design stayed true to the needs of the user and was not
influenced by the author’s assumptions. In order to select an appropriate design method
that supports the project aims of being user centred, a chart was created to compare and
evaluate the possible design methods. This analysis led to a bespoke design methodology
being created to suit the needs of this individual project.

4.2.1- Chosen Design Method

Below is the custom-made design methodology tailored towards the needs of this project, it
includes user feedback at various stages of the process. This enabled critical user needs to
be established forming vital developmental paths. There were no found methodologies that
met the needs of this product, therefore the Double Diamond process (Design Council), and
French’s model (French, 1985) were combined and adapted to create a specific
methodology.

(Refer to Appendix C.2 for detailed design methodology evaluation)

P a g e | 36


Figure 4.1- Design Methodology (Author)

P a g e | 37

4.2.2- Design and Development Route

Figure 4.2- Design and Development Route (Author)

P a g e | 38


4.3- Shell & Function Concepts

The preceding research and subsequent product design specification has informed the
following range of concepts with regards to function, form and technology.

4.3.1- Concept 1

The design features include:

• A lockable hinge that provides adaptability to the user when walking on transitioning
terrains, providing a rigid support for the foot and ankle when locked and allowing a
limited range of dorsiflexion when unlocked.
• A Velcro strap around shin to provide a close and comfortable fit for the user.


P a g e | 39

4.3.2- Concept 2


• Pressure sensors in the sole of the AFO which provide a force pressure map for user.
• An accelerometer and gyroscope to send bio-feedback to user.
• A low energy Bluetooth connection that sends information from the AFO to the
user’s phone
• Bio-feedback which can be used to make alterations to the patient’s rehabilitation
regime.


P a g e | 40

4.3.3- Concept 3


• An adaptation of a shoe horn that makes it easier for users with limited mobility and
dexterity in their arms and hands to enter the AFO.
• The shoe horn clips in to the side of the AFO when putting it on and easily clips out
when it is on.


P a g e | 41

4.3.4- Concept 4

Concept 4 aims to improve the ease with which the AFO can be fitted by the user. The AFO
sits upright in a dock by the user’s bed. They step into the dock the dock and strap
themselves in to enter the AFO, to remove the AFO the step back into at.


• A docking station in which the AFO sits in.
• A quick release toggle lock which can be pulled to allow the user to exit.


P a g e | 42

4.3.5- Concept 5


• A lockable hinge on the forefoot that will provide enough dorsiflexion for walking
comfortably but also keeps the user’s ankle rigid and secure.
• Suitable for users with severe pronation as it provides rigid ankle support.


P a g e | 43

4.3.6- Concept 6


• An elastomer groove in the forefoot which provides some flexion to the wearer. A
foam inner lining provides comfortability for the user throughout the day.
• Suitable for users with mild cases of foot drop but would provide insufficient support
for those with more severe cases.
• Velcro strapping around shin ensures comfortable fit.


(See Appendix K for full concept analysis)

P a g e | 44

4.5- User rated Combinex- Concept Evaluation
In order to evaluate the initial concepts against a weighted criterion, created using the PDS
and user feedback, in an unbiased and non-subjective way, a Combinex was used. Table 18
shows the Combinex results where Concept 1, the Ankle Hinge – Toggle Lock, came out as
the as the most applicable to develop, followed by concept 3.

A (Cost) B (Weight)
C
(Ergonomics)
D
(Complexity)
E (Comfort) F (Ease of use)

Raw
score
Wei
ght
Raw
score
Wei
ght
Raw
score
Wei
ght
Raw
score
Wei
ght
Raw
score
Wei
ght
Raw
score
Wei
ght
TOTAL
RAW
TOTAL
WEIGHTED

Weighting 8.5 3.5 10 0 8 2.5
CONCEPTS
Ankle Hinge-
Toggle Lock
95
807.
5
92 322 93 930 92 0 89 712 71
177.
5
532 2949
Ankle Hinge-
Pressure Sensor
67
569.
5
72 252 90 900 79 0 70 560 62 155 440 2436.5
Shoe Horn 80 680 85
297.
5
95 950 77 0 91 728 79
197.
5
507 2853
Docking Station 60 510 69
241.
5
94 940 73 0 89 712 82 205 467 2608.5
Forefoot Hinge 84 714 95
332.
5
79 790 80 0 55 440 74 185 467 2461.5
Forefoot Flex 83
705.
5
94 329 81 810 79 0 60 480 75
187.
5
472 2512
Table 4.1- User rated Combinex results for Shell and Function concepts (Author)

Figure 4.9- User rated Combinex graphs

P a g e | 45

4.6- Expert rated Combinex- Concept Evaluation
A Combinex was also created in which a physiotherapist who is an expert in treating drop
foot chose and scored the weighting criteria. The results displayed a clear winner which was
Concept 2, the Ankle Hinged Pressure Sensor.

A
(Manufacture
Cost)
B (Weight) C (Bio-
Feedback)
D
(Complexity)
E (Comfort) F (Aiding
Rehabilitation)
Raw
score
Wei
ght
Raw
score
Wei
ght
Raw
score
Wei
ght
Raw
score
Wei
ght
Raw
score
Wei
ght
Raw
score
Wei
ght
TOTAL
RAW
TOTAL
WEIGHTE
D

Weighting 4 3.5 10 3 8 10
CONCEPTS
Ankle Hinge-
Toggle Lock
95 380 95 332
.5
50 500 75 225 81 648 65 650 461 2735.5
Ankle Hinge-
Pressure Sensor
55 220 65 227
.5
94 940 59 177 76 608 92 920 441 3092.5

Shoe Horn 80 320 76 266 50 500 86 258 64 512 61 610 417 2466
Docking Station 85 340 79 276
.5
50 500 81 243 82 656 59 590 436 2605.5
Forefoot Hinge 70 280 84 294 50 500 72 216 57 456 54 540 387 2286
Forefoot Flex 67 268 87 304
.5
50 500 70 210 54 432 54 540 382 2254.5
Table 4.2- Expert rated Combinex for Shell and Function concepts (Author

Figure 4.10- Expert rated Combinex graphs
4.8- Conclusion: User feedback and evaluation of initial concepts
The results from the concept evaluation were then taken back to the user and the expert in
order to get their opinion on their own and each other’s results. From this activity, it was
concluded that combining a system in which the user could lock their ankle hinge as well as
providing bio-feedback data would be beneficial for both the patient and their
physiotherapist.

P a g e | 46

Chapter 5- Design Development

5.1- Introduction
Having completed the initial concepts and evaluated them using user feedback and a non-
subjective Combinex, the selected concepts were developed further. This chapter details
the design choices taken in order to achieve the final design.

5.2- Ankle Hinge Development
The ankle hinge was developed of the AFO with close attention being payed to the required
range of motion, existing patents and the cost implications of designing and manufacturing
the part. It was concluded that buying a Tamarack Dorsiflexion Ankle Hinge would be the
most cost effective method.

Figure 5.1- Ankle Hinge render (Author)

P a g e | 47

5.3- Ankle stopper & Fastening
An ankle stopper was included on the back of the ankle as a means of preventing unwanted
plantarflexion. This feature was included after further client feedback on the design stated it
was a suitable means of preventing the ankle from passing 90 degrees. The protruding
element provides structural support to the heel of the AFO while fitting comfortably just
above the wearers shoe.

The toggle-lock concept was developed into a carbon fibre reinforced polypropylene part
which secures that secures the upper and lower part of the AFO in a fixed position using a
pop rivet. This system provides the adaptable support that was identified as a key design
feature for the user and was outlined in the specification.

Figure 5.2- Ankle stopper & fastening render (Author)

P a g e | 48

5.3- Pressure Sensor Development

Several means of housing the pressure sensors were explored in order to reach the most
viable option. Manufacturing method, cost and user comfort were considered throughout in
order to reach a solution.

The chosen method of securing the pressure sensors to the base of the AFO was to
integrate the sensors into the insole material, via a pressure sensor matrix. This is the most
cost-effective means of including the pressure sensors and does not require any further
production methods, such as injection moulding.

Figure 5.3- Pressure sensor matrix render (Author)
5.3.1- Force Sensor Testing

Pressure sensor testing was undertaken to determine the range of Newton’s required to
record data on each part of the sole of the foot. A sample of 9 participants of varying
weight, shoe size and gender took part in the test to get a comprehensive set of results. The
highest reading taken while waling was 195N, therefore further force testing will be
completed with participants running.

(See Appendix K.5 for full pressure sensor testing)

Pressure
sensor matrix

P a g e | 49


5.3.2- Electrical Component Housing
The means of housing the electrical components were explored by looking into existing
systems of housing batteries and other electrical components.

It was concluded that the most suitable position for the electrical components is in an
internal cavity on the back of the AFO. This position ensures the whole product can be
manufactured using one process, Thermoforming. The wires will use the ankle hinge to
bridge the gap from the lower portion of the AFO to the upper portion.

Figure 5.4-Electrical Component Housing render (Author)

(Refer to K.7, K.8 for further design development)

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Chapter 6- Materials and Manufacture

6.1- Introduction

6.2- Material Selection Method
A detailed material and manufacturing selection method was done for each specific
component of the product using Granta Design CES Edupack 2017 Software, and speaking to
a local orthoptist regarding current and new material choices. (Granta, 2017)

6.2.1- AFO Main Body
The chosen material to manufacture the AFO main body with is the thermoplastic polymer,
Polypropylene, this is due to the following properties:
• low density (weight saving)
• high stiffness
• heat resistance
• chemical inertness
• good impact/rigidity balance
• recyclability
Material Polypropylene Polyethylene Carbon Fibre
Young’s
modulus
(GPa)
0.896 – 1.55 0.621 – 0.896 350 – 450
(very high)
Tensile
Strength
(MPa)
27.6 – 41.4 20.7 – 44.8 4.5 GPa
Yield Stregth
(MPa)
20.7 – 37.2 17.9 - 29 1.83 – 1.84
Strength to
weight ratio

Fracture
toughness
(MPa.am^0.5)
3 - 4.5 1.44 – 1.72
1 - 2
Price (£/kg) 1.29 – 1.34 1.22 – 1.25 101 - 111
Sterilisable

Recyclable

Density
(kg/m^3)
890 - 910 939 - 960 2.05e3 – 2.16e3
Electrical
conductor or
insulator
Good insulator Good insulator

Table 6.1- Material analysis of main body

P a g e | 51

6.2.2- Sole Cover material selection
Material EVA Poron (TPU) Polyurethane Polychloroprene
(Neoprene)

Material
family
Elastomer Thermoplastic Elastomer Elastomer
Young’s
modulus
(GPa)
0.007 –
0.009
3.36 – 3.53 3.3e-4 – 4e-4 0.00165 –
0.0021
Tensile
Strength
(MPa)
9.5 -10 85.4 – 94.1 0.125 – 0.15 12 – 24
Yield
Strength
(MPa)
9.5 -10 68.3 – 75.3 0.025 – 0.03 12 - 24
Price (£/kg) 1.34 -1.38 7.87 – 8.85 5.77 – 6.35 2.75 – 3.4
Recyclable

Density
(kg/m^3)
945 -955 1.32e3 –
1.34e3
75- 85 1.23e3 – 1.3e3
Flexural
Strength
(MPa)
10 - 12 59.1 – 65.2 0.025 – 0.03 23.5 – 41.3
Table 6.2- Sole cover material analysis

6.2.3- Conclusion
From the analysis conducted into the various materials available it was concluded that
Polypropylene would be the most viable choice as it has higher structural properties when
compared with Polyurethane. It is also cost effective material that is abundantly available.
The sole cover will be made from Ethylene vinyl acetate, this will be the material used to
integrate the pressure sensor matrix into the sole of the AFO. This material will provide a
comfortable fit, is lightweight and is the most cost-effective of those analysed.

P a g e | 52

6.3- Method of Manufacture

Several methods of manufacture have been considered for the production of this AFO, each
have been evaluated on the following criteria:
• Repeatability- Can the process be repeated over and over with the same degree of
accuracy?
• Cost- Is the process cost effective?
• Speed- Does the process improve on the current four week lead time of current
methods?
6.3.1- Critical review of methods

Stage Method Advantages Limitations
Mould Traditional
Plaster
Mould
• Low set up cost • Lots of wastage
• Not accurate
3D Scanning
(CNC Mould)
• Minimal wastage
• Very accurate

• High set up
cost

AFO
Injection
Moulding
• Detailed parts
• Low wastage
• High startup
cost
• Longer time
frames
Vacuum
Forming
• Precision
• Fast prototyping
• Ideal for repeat jobs
• Consistent wall
thickness not
achievable
• Intricacy of
parts restricted
Table 6.3- Critical review of manufacturing methods

P a g e | 53

6.3.2- 3D Scanning
The chosen method of manufacture for the custom-fit model will utilise 3D scanning
technology in order to get a detailed and geometrically accurate image of the individual’s
leg and foot. This model will then be used to create a mould of the individual’s legs which
will in turn be used to thermoform the outer shell.

Figure 6.1- 3D Scanning leg for bespoke AFO

6.3.3- CNC Machining
The 3D model will then be used to create a Styrofoam mould using a CNC machine, this is a
cost effective and repeatable method of producing the mould.

6.3.4- Vacuum Forming
The chosen method of manufacturing the AFO components is vacuum forming as it will
provide the quickest and most cost effective means of production.

Figure 6.2- Placing PP sheet over mould

P a g e | 54


6.3.5- Set size model
The set size models will be injection moulded as this method of manufacture would be the
most efficient and cost effective.

(See Appendix P.3 for further details on the method of manufacture)

P a g e | 55

6.4- Parts List / Costing

6.4.1- Introduction
The costing was calculated on the manufacture of one single product by adding the overall
materials & components to the labour cost of each worker.

6.4.2- Materials & Components

Part Qty Material
Weight
(g) Cost(£)
1 Top AFO Shell 1 PP 69.2 £0.10
2 Lower AFO 1 PP 63.1 £0.09
3
Tamarack Flexure
Hinge 2 PP 10.8 £2.00
4 Heel fastening 1
Reinforced
PP 15.4 £0.02
5 Rivets 5 Aluminium 0.1 £0.00
6 Fastening rivet 1 Aluminium 0.1 £0.00
7 EVA sole 1 EVA 5.2 £0.01
8 Velcro Strap 1 - 0.2 £0.06
9 Strap fastening 1 PP 1.1 £0.13
10
Feather 32u4 Bluefruit
LE 1 NA 5.7 £29.95
11
Lithium polymer
Battery 1 NA 2 £7.09
12 Pressure sensor matrix 1 NA 9.7 £16.00
13 Analogue multiplexor 1 NA 0.1 £4.50
14 USB Cable 1 NA NA £0.55
Total 182.70g £60.50
Table 6.4- Materials & components cost and weight
The total weight of the final design fits in the range of between 150-400g, determined in the
PDS.
Materials & Components £ 60.50
Labour £ 249.38
£ 309.88
Overheads (30%) £ 92.96
TOTAL £ 402.84
Table 6.5- Total one off manufacture cost
6.5- Conclusion
The final cost to manufacture the product is over the prescribed cost set out in the PDS,
therefore the RRP price has been altered to factor this in.

(Refer to Appendix P.5. To see the full costing analysis)

P a g e | 56

Chapter 7- Final Design Solution

7.1- Introduction
Following a custom made design process with the inclusion of user feedback loops
throughout the initial design and further development stage of the project, a final design
solution was determined.

7.2 RecuperGAIT™ - Smart Foot Drop Recovery AFO

7.3- RecuperGAIT™ - Smart Foot Drop Recovery AFO- Design Features

7.3.1- Introduction
The RecuperGAIT™ sets a new bench mark for speed and quality of recovery for drop foot
sufferers. Combining maximum comfort, bespoke ergonomics and state-of-the-art smart
technology providing live bio-feedback to the user.

Figure 7.1- Final Design Render (Author)

P a g e | 57

7.3.2- Smart Technology
The RecuperGAIT™ utilises smart technology in order to provide live, real-time feedback to
the user and their physiotherapist.

• Gait pattern- the wearers gait pattern will be assessed using the internal
accelerometer.
• Pressure mapping- the pressure distribution of the users step will be analysed using
internal tactile sensors.
• Step counting- the number of steps the user takes will be counted by accelerometer,
these can be used to set the user daily tasks or goals, allowing them and their
physiotherapist to track their progress.

This gait analysis will be sent to a smartphone application via Low Energy Bluetooth.

7.3.4- User Interface
The product has been designed to be used in conjunction with a smartphone app that will
provide visual and audible cues on improvement that can be made to the user’s gait
pattern.

Figure 7.2- User app interface
• Foot Pressure heat map- a heat map will be displayed on the application showing the

P a g e | 58


Figure 7.3- Render of final AFO

Figure 7.4- Side view final render (Author)

P a g e | 59


Figure 7.5- Hinge render (Author)
7.4- PDS Evaluation
This final design has met the PDS in the following ways:
• It provides Bio-feedback to the patient and physiotherapist to show improvement in
the wearer’s gait.
• It is within the weight range set in order to ensure a comfortable fit.
• It is manufactured in a means that allows for a bespoke and accurate fit.
• Main body of product can be recycled.
• Defies and solves a clinical need for patients with drop foot.

P a g e | 60

Chapter 8- Conclusion & Further Work

This thesis successfully displayed the benefits of a complete user centred design approach,
utilising a unique design methodology custom made for this particular project, to improve
the time spent in rehabilitation for drop foot sufferers.

The final design solution is a result of detailed user research, in both qualitative and
quantitative formats. Throughout the project the Nottingham Stroke Association and
various drop foot experts provided a wealth of knowledge and potential ideas. A substantial
amount of semi-structured interviews were undertaken in order to identify the key themes
and aims of the project.

Relevant secondary research was carried out into the condition of drop foot in order to
create a tailored Product Design Specification (PDS) that solved a clinical need. The user and
relevant experts were also involved in the formulation of the PDS.

From the PDS, Initial sketches were formulated for 6 potential concepts that provided
multiple patient benefits. These were then evaluated using a user and expert weighted
Combinex in order to select the most appropriate designs for further development.

User feedback and the Combinex provided a clear final design solution that fulfilled the
clinical need of reducing time spent in rehabilitation from foot drop. This was achieved by
the integration of smart technologies providing bio-feedback to the user.

Potential materials and manufacturing processes were analysed and evaluated against each
other in order to define the most cost effective method of production.

8.1- Further Work
Further work will be carried out on the structural properties of the AFO using Finite Element
Analysis (FEA). Physical structural tests on prototype models will also be conducted to
assess the comfort and strength of the design.

Further design could be done to develop the pressure sensor system in a sock or insole that
could be used by individuals who do not suffer from drop foot.

P a g e | 61

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