Community Research and Development Information Service - CORDIS


SocketMaster Report Summary

Project ID: 645239
Funded under: H2020-EU.

Periodic Reporting for period 1 - SocketMaster (Development of a Master Socket for optimised design of prosthetic socket for lower limb amputees)

Reporting period: 2015-02-01 to 2016-07-31

Summary of the context and overall objectives of the project

In developed countries, more than 90% of limb amputees achieve their mobility through the use of prostheses. Nowadays, there is nothing more frustrating to the prosthetic limb users than to be told to stop using their prosthesis because of medical problems. Since the amputees will have to wear a prosthetic limb for the rest of their life, the comfort of a prosthetic limb is the primary consideration for both manufacturer and service providers, as they are keen to help the prosthetic limb users to regain a good quality of life.

In general, the walking energy consumed by an above knee amputee is approximately 80% more than a healthy person. This is because of the movement complexity associated with the human knee and ankle. A significant part of the additional energy is “consumed” between prosthetic socket and stump which exacerbates soft tissue and skin problems.

Pressure sores normally develop on the skin where mechanical pressure is applied locally over a bony prominence. An inappropriately fitted socket creates focal pressure associated with shearing force applied at the amputation site. It initiates irritation and inflammation of the superficial layers of the skin. Continuous weight-bearing degrades the integrity of the skin further. Discomfort will develop when the pressure sore gets into the subcutaneous layers of the fascia. In a worst case, it leads to an infection.

In order to be able to design a proper load bearing characteristic for a specific residual limb, one has to have prolonged training before becoming an experienced prosthetist. Nevertheless, the current design approach of prosthetists is highly subjective, and sockets are made without access to comprehensive information related to the comfort of an amputee such as friction, pressure etc.

The SocketMaster project aims to develop a new technique to address the problems described above. This will be done by integrating micro sensors into a SocketMaster tool which can help prosthetists to achieve fast customised design and manufacturing of prosthetic sockets for lower limb (trans-femoral and trans-tibial) amputees. The project has the following main objectives:

(1) To develop micro sensors able to measure pressure, friction, temperature and other parameters relevant to the comfort of patients within the interface between the residual limb and the socket in both static and dynamic situations. These sensors will be miniaturised such that they can be integrated in a SocketMaster tool.

(2) To develop a SocketMaster framework by assembling the sensor system in a rigid hosting socket in such a way that the sensors' positions can be adjusted to achieve comfortable configuration for the patient. The pressure distributions, friction information and loading etc. during walking tests at will be acquired and processed to achieve optimised socket design. The design process will be completed within 2 hours after activity testing, and the resultant digital 3D data will allow manufacture by a rapid prototyping machine for fast fabrication of tailored sockets for a specific patient.

(3) To perform clinical trials with 50 patients to validate the SocketMaster technique and procedures.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project officially started on February 1st, 2015. During the 18 months of the reporting period from February 1st to July 31st, 2016, work has been carried out mostly according to the original plan. Details of the work and the results are as follows.

Work Package 1: System specification and preparatory research

A further literature review and open discussions have been carried out at the beginning of the project. All partners have provided specifications for the SocketMaster system based on their own experience and expertise associated with prosthetic socket design and manufacturing. This included the work conditions in which the SocketMaster system will operate, the material types and structures of mechanical and electronic framework of the SocketMaster tool, the materials and layout of the pressure, friction and temperature sensors, and the number of patients for clinical validation trial. The result is a specification document that has been agreed by all partners. This specification includes the parameters on the characters of gaits, the geometries, dimensions of the SocketMaster tool that can fit most patients but still maintain sufficient stability, the characters of pressure/friction/etc. between residual limb and socket, and other clinical requirements of the system to be developed.

As the clinical condition of above knee amputees is complex, it is not possible to determine all the parameters in the specification at this stage. Therefore, only recommendations using a range for the parameters were provided, and the functional specification serves as a guide for other tasks of the project. This specification document will be updated when new information is available.

Work package 2: Sensor development

Extensive work on sensor development has been carried out. This started with a comprehensive modelling and analysis of the MEMS piezoresistive force sensors upon mechanical normal and shear forces. During the modelling work, the main physical parameters that will be implemented and optimised in the final design of the sensors were analysed. The first experimental prototype for technological evaluation tests of the system architecture will be based on 5 MEMS force sensors, covered by a polymeric dome (Cover cap) for force distributions. The sensors are mounted on a PCB board with integrated electronics for the sensors read-out and data transmission by I2C bus.

The second version of the system that will be used for the final tests will consist of 5 force sensors integrated on the same silicon chip for functional tests and it will include:
• Optimization of both design/fabrication process (e.g. Circular diaphragms, vertical etching, and backside contacts);
• Optimization of the polymeric dome (Cover cap);
• The board is mounted on a PCB with bus interconnections.

The layout of a piezoresistive MEMS–based sensor prototype has been finalised and the MEMS fabrication process has started. Key features of the sensors include:
• SOI process on 6” Wafer
• 109 DEVICES/wafer
• 256 TEST CHIPS/wafer
• 64 TEST STRIPS/wafer

As an essential part of sensor integration, the first version of the sensors system architecture (chip on board) has also been established. The PCB board has 4 layers with a dimension of28x43 mm. the smallest line width is 100μm. The read-out circuit has 5 independent signals from each Wheatstone bridge, with A/D conversion, I2C data transmission protocol, and 10-bit address space. The bus speed is 100 kbit/s with standard mode.

The prototype sensors were experimentally tested. They were mounted on a first test prototype of PCB board with integrated electronics for the sensors read-out and data transmission by I2C bus. The pressure sensor was tested in the dedicated setup under both pressure gradient and temperature variation. Tests showed that the behaviour of the sensor is linear for all temperatures, and the linear coefficients can be parametrized as a function of temperature obtaining a correction for the pressure values according to the device temperature.

Sensor integration with the Master Socket has also started. Each strut of the Master Socket allows the cabling of the sensors in order to collect data of measured forces and temperature. The sensors use on-board the microprocessor Atmel ATiny1634 which has a native Two-Wire Interface (TWI), i.e. a bi-directional, bus communication interface, which uses only two wires.

As for data collection, two different approaches have been evaluated: the first is using an embedded pc such as Raspberry or Arduino based on ARM architecture; the latter is using a Programmable Interface Controller (PIC) with a development kit. Considering low size, high capabilities and low price, Raspberry model Pi Zero has been assessed as an affordable and quickly programmable choice for this job.

In addition, force piezoelectric sensors based on flexible substrates have been also considered and have been evaluated at experimental level. In this approach the sensor is constituted by a piezoelectric polymeric material (PVDF) sandwiched between two conductive layers (Cu and PEDOT-PSS) deposited on a flexible KATPON printed circuit board. The final structure is a multilayer of KAPTON/Cu/PVDF/PEDOT-PSS. The reason of this choice is to evaluate innovative solutions for implementing the sensors also in parts of the prosthetic socket (e.g. top edge of the prosthetic socket) where the needed conformability of the surfaces could constitute a difficult task for MEMS devices.

Work package 3: Development of a Master Socket

The design of the SocketMaster framework has been carried out. It started with a comprehensive review of the state of the art. The most competitive products, research projects were studied and their weak and strong points identified. Then the core design philosophy of the SocketMaster framework was established, and the required functionality of all the components has been determined. The main components of the mechanical framework include:
• Amputee’s load supporting and stability frame
• Amputee’s volume coverage (stump) features
• Interface with the “comfort” assessment sensors
• Interface with the loading apparatus
• Electronic subsystem

The mechanical frame is expected to conform to this check socket. Its volume adjustment capability will be implemented through two clamping devices and four contact pads with the stump. Figure 10 shows the overview of the initial mechanical frame, “worn” by a human model. It has been updated, where the pad adjustability will be implemented via a fine-tuning small motor on each sensor pad (36 in total). A pilot pad’s actuator unit has been assembled.

The original design of each strut allowed motion of each 3-pad base along its (strut’s) length, facilitating the proper compliance of the socket on the patient’s stump. Each strut comprises two main rigid axis and four 2-DOF (degree of freedom) joints, allowing its movement towards / away from the femur. Two bases interconnect the two shafts, the upper and the lower one. They incorporate features that allow them to move towards / away from the femur and slightly rotate around it. This design is revised by incorporating a new seat component. There are 4 triads at the bottom part, 4 in the middle area and 4 on the upper area. The lower and upper triads, 8 in total, are firmly clamped on the lower and upper rings. Only the middle one’s position is able to be fine-tuned upwards/ downwards.

The electronics of the Master Socket as well as the interfacing of the main control electronics have also been designed. Relevant components have been acquired or ordered.

It should be noted that this mechanical framework will be relatively heavy. As a result, the patient will not be able to wear it to walk directly. Rather, the walking test will be performed in a static manner via a loading apparatus. An initial design of the loading apparatus has also been produced. This design has also been refined and optimised in the final version. The kinematic and static modelling of the system had been carried out to assess the apparatus’ functionality and stability.

The mechanical platform based Master Socket system is expected to only adapt to certain range of amputees with specific dimensions of their residual limbs. Therefore a modified design of the SocketMaster tool is proposed as supplementary solution, i.e., a check socket based approach. This approach is expected to address the need for both accurate in-situ measurement and wider applicability for the SocketMaster technique/system.
The check socket based approach is comprised of the following three main modules:
• 3D reconstruction of the residual limb
• Rapid fabrication of a check socket
• Placement of sensor belts within the check socket

Details of these modules have been formulated. For example, 3D reconstruction of a test sample has been demonstrated by using a demo version of a commercial software package. For patient application, a sequence of images of the residual limb will be captured by a digital camera. By inputting these images to the 3D reconstruction software, a 3D model of the stump will be reconstructed within 10-15 minutes with sufficient accuracy of 1mm. For the fabrication of a check socket, rapid prototyping or 3D printer can be used at moderate cost. This check socket is preferably made of transparent materials

Work package 4: System integration
The following work has been carried out:
• Complete the sensor characterisation of sensor upon the applied normal and shear stresses and parametric testing of the technological parameter at wafer level;
• Refine the electronic circuit enabling the sensor data for the I2C bus;
• Implement and test of the electronic circuit for the I2C data management and wireless transmission;
• Final architecture and prototypes for the integration of the sensors into the Master Socket.

Test of single sensor membranes upon different normal applied forces had been conducted. The final plan for sensor integration with the Master Socket is decided. Tests on a pilot physical integrated pad helped decide the solution for data communication and transmission which will use a Raspberry Pi 3 model B, as Bluetooth has been chosen as standard data wireless transmission between collector and gather. Tests on data communication test with multiple sensors have been performed on a wireless communication test bench.

Work package 5: Stump evaluation

Work on developing a biomechanical model is also in good progress. Originally we planned to use CT/MRI images via digital image processing to extract the density, Young’s modulus and other biomechanical characteristics of the residual limb. This approach has been reported by many other researchers as effective, but has the potential risks of excessive radioactive exposure if additional images are required during clinical applications.

To address this problem, a new approach has been proposed in which the biomechanical properties of the patient’s residual limb will be measured directly via a hand-held device. Finite element simulations have been carried out, which showed the optimal range of indentation and the diameter of the indenter. A draft design of the device is completed, where a force transducer and a displacement transducer will be integrated to measure the response of the residual limb during a indentation test. A prototype device has been developed and is working, it allows measurement of the soft tissue response at any orientation. Only a USB cable is required to connect the device with a laptop, which provides both the power for the stepper motor and the transmission of dynamic data from the force and displacement transducers. No additional external power supply is needed. The control software was also developed, with its user interface shown in Figure 36. Thirteen healthy subjects have been tested using the device. All the information was kept securely as indicated in for ethical application forms. The force-displacement data collected is being analysed, and the results may be published later.

The biomechanical data will be used to help achieve an optimized design of a socket for an individual patient. To this end, comprehensive FEA simulations have been carried out, with a view to establishing a look-up table. This look-up table will be used to adjust the contour of a socket such that the localized relatively high pressure can be alleviated. Both the indentation device and the biomechanical models will be tested extensively in clinical trials in order to demonstrate their effectiveness.

Work package 6: Data processing and software development
It is proposed to develop two principal modules in Software: a patient management module and data analysis module. These modules are complemented with a database to store all relevant information for each patient. To start the Software development and designing of the database, the following software requirements needed to be defined:
• Insert patient;
• Remove patient;
• Update patient;
• List patients;
• Search patient (by name, e-mail, phone number, etc.);
• Start new data acquisition;
• Remove data acquisition;
• Insert patient notes;
• Remove patient notes;
• Visualize model three-dimensional acquired by sensors.
Through the problems to be solved with the development of this application and based on the above requirements, a conceptual data model representing the database and all relations between tables was designed The next step was the analysis of the technology that will be most appropriate to the development of the web platform. This was based on the comparison of the three most popular technologies in web development, analysing the advantages and disadvantages of each one, and justifying the choice made. Taking into account the size of the project and also the choice of working with a flexible and easy tool, PHP was chosen.

Other blocks of the software including result visualization and socket contour manipulations are also under development

Work package 7: Clinical studies and tests
The clinical studies and tests are scheduled to be carried out in the second period of the project starting August 2016. Only preparation work relating to ethics approval has been conducted within this review period

Work package 8: Dissemination and exploitation
The project consortium has started to disseminate and promote the project to trade fairs, exhibitions, and conference etc. from late 2015. A number of dissemination and exploitation activities have taken place. Two conference paper have been published, another thee is underway. The project logo has been successfully registered as a trade mark at the EU trademark office on 24 November 2015. So we will use the logo with the 'R' symbol ® on future dissemination and exploitation activities . Project leaflets and promotional goods with the project logo (ball pens, sticky note pads) have also been produced and distributed.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The expected final results are:

1) Multifunctional micro sensor system: With this sensor system, the distribution of pressure, temperature, moisture and friction of the residual limb at a specific point of gait cycle can be quantified.

2) A SocketMaster medical tool: The SocketMaster tool will be able to fit patients with varying sizes of residual limb. The data collected from the SocketMaster tool will be fed into a prosthetic socket design system, so that an optimised prosthetic socket can be designed. The integrated system will help a prosthetist to achieve rapid socket design and manufacturing with optimised comfort for the patient.

3) Residual limb evaluation model: The residual limb of a patient will be evaluated by a hand held device. Comprehensive finite element simulations will be carried out, which will help develop a biomechanical model that can be used to turn the dynamic data collected by the SocketMaster tool during walking tests into an optimised socket for the patient.

4) Data processing software: Various data from the multifunctional sensors will be processed so that an optimal socket design can be achieved.

5) Clinical validation report: This is one of the most important outcomes of the project. It will demonstrate the effectiveness of the SocketMaster system.

6) New socket design procedure: With the novel Master Socket technique, a new clinical procedure for prosthetic socket design will be formulated.

Potential impact and use

Currently, there are three main causes leading to limb loss; (a) trauma, civilian and military (45%), (b) vascular diseases (54%), including diabetes and peripheral arterial disease and (c) cancer (less than 2%). Diabetes is the major cause leading to amputation and according to the International Center for Limb Salvage, patients with diabetes have 70% more probability to develop gangrene and require amputation, compared to normal population. In the US the estimated amputees population is nearly 2 million people and this population is estimated to double by the year 2050 to 3.6 million people. Globally, there are more than one million limb amputations annually –one every 30 seconds- and this number is expected to increase since the International Diabetes Federation predicts that diabetes will burgeon from 336 million in 2011 to 552 million people by 2030.

Existing method for socket design is similar to the process of a tailor making a suit. The first step involves taking the necessary measurements for a good fit; hence it can be understood that the development of the socket significantly depends on the skills of the prosthetist. The socket significantly determines patient’s comfort, as it is responsible for distributing the loads from the residual limb to the prosthetic component. The SocketMaster system targets the development of sockets customised to the residual limb pressure distribution of each individual user while also ensuring an ideal fit to the stump.

The SocketMaster project is expected to contribute to
(1) Secure and reinforce European leadership in the microsystem sector, expanding its share in smart systems for medical applications.
(2) Seize new opportunities in addressing societal challenges in health and well-being.

Firstly, the SocketMaster project targets reinforcement of Europe’s position in the field of medical technology. According to a report published on, orthopedic devices raked in $34.8 billion worldwide in 2014, which is around €30bn. Assuming 10% is for prosthetics, which equates €3bn. Also assuming that the SocketMaster product will capture an overall 1% of the world prosthetics market, this will equate to €30million. This increased market share will allow the European medical technology companies, 95% of which are Small and Medium Sized Enterprises, to strengthen their position in the worldwide market. Assuming that one job is created per €150,000 worth of sales, the SocketMaster product will create approximately 200 new jobs in a period of 5 years after the end of the project. This will give a considerable advantage to the European medical technology sector that currently employs 575,000 people enhancing further the position of the European sector relative to the US medical technology industry that employs around 520,000 people.

Secondly, the SocketMaster project will work towards addressing the “Health and Well-being” societal challenge through the development of a new, safer and more effective solution for designing customised sockets for lower limb amputees. This will lead to a personalised health and care solution for the population of lower-limb amputees (approximately 2.4 million people in the EU), which will not only be developed during the project, but will also be tested through extensive clinical trials that will be performed during the project. Currently, Europe spends nearly 10%GDP on its health and care systems. The sustainability and equity of the European health sector is jeopardised by the ageing European population, the increasing disease burden and the fall-out from the economic crisis. The SocketMaster solution will indirectly minimise the medical expenses related to lower limb amputees as their visits to medical clinics will be reduced from several visits to once.

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